Nanotechnology approaches for the delivery of cytochrome P450 substrates in HIV treatment

Abstract

Introduction:

Antiretroviral therapy (ART) has led to a significant reduction in HIV-1 morbidity and mortality. Many antiretroviral drugs (ARVs) are metabolized by cytochrome P450 (CYP) pathway, and majority of these drugs are also either CYP inhibitors or inducers and few possess both activities. These CYP substrates, when used for HIV treatment in the conventional dosage form, have limitations such as low systemic bioavailability, potential drug-drug interactions, and short half-lives. Thus, an alternative mode of delivery is needed in contrast to conventional ARVs.

Areas covered:

In this review, we summarized the limitations of conventional ARVs in HIV treatment, especially for ARVs which are CYP substrates. We also discussed the preclinical and clinical studies using the nanotechnology strategy to overcome the limitations of these CYP substrates. The preclinical studies and clinical studies published from 2000 to February 2019 were discussed.

Expert opinion:

Since preclinical and clinical studies for prevention and treatment of HIV using nanotechnology approaches have shown considerable promise in recent years, nanotechnology could become an alternative strategy for daily oral therapy as a future treatment.

1. Introduction

While there is no current cure for HIV, antiretroviral therapy (ART) has helped to decrease HIV/AIDS related mortality [1]. There are six different classes of ART: nucleoside reverse transcriptase inhibitors (NRTIs), non-nucleoside reverse transcriptase inhibitors (NNRTIs), protease inhibitors (PIs), integrase strand transfer inhibitors (INSTIs), a fusion inhibitor, and a CCR5 antagonist [2]. Antiretroviral drugs (ARVs) are recommended to use as combination regimens that can attack multiple stages of HIV life cycle, and suppress the virus efficiently [2].There are also some drugs that enhance the pharmacokinetic (PK) profiles of some ART medications, known as pharmacoenhancers or boosters [2]. People living with HIV/AIDS (PLWHA) receive multiple drugs to not only treat their infection but to tackle other comorbidities that they have [3]. In such circumstances, drug-drug interaction(s) (DDI) in PLWHA can result in serious complications ranging from severe systemic toxicities to therapeutic failures [4]. Thus, there is a medical concern for PLWHA who are receiving pharmacoenhancers and multiple ARVs. In fact, many ARVs are substrates of the same cytochrome P450 (CYP) family of enzymes (Table 1), making them susceptible to DDI [3, 5]. Specifically, for those ARVs which can inhibit or induce the CYP enzymes, have higher chance of interfering with the drug metabolism of other coadministered CYP substrates include chemotherapy drugs, antiepileptic drugs, antidepressants, statins, antibiotics, contraceptives, and treatments for opioid and alcohol use disorders, along with many others [4]. Because of the combination of multiple drugs in ART regimens, the CYP-mediated interactions for a specific patient are complex and hard to predict even with the information provided on package inserts [4].

Table 1.

CYP substrates, inhibitors, and inducers, with their half-lives and dosing regimen, used in HIV treatment.

Drug Class	ARVs	Substrate of	Inhibitor of	Inducer of	Half-lives (h)	Dose
INSTIs	Bictegravir [121]	3A4	N/A	N/A	17.3	Oral, once daily
	Dolutegravir [92]	3A4 (minor)	N/A	N/A	14	Oral, once/twice daily
	Elvitegravir [122]	3A4	N/A	2C9	12.9	Oral, once daily
PK Enhancer	Cobicistat [123]	3A4	3A4, 2D6	N/A	3-4	Oral, once daily
	Ritonavir [124]	3A4, 2D6	3A4, 2D6	1A2, 2B6, 2C9	1-2	Oral, once/twice daily
PIs	Atazanavir [125]	3A4	3A4	N/A	6.5	Oral, once daily
	Darunavir [126]	3A4	3A4	2C9	15 (with ritonavir)	Oral, once/twice daily
	Fosamprenavir [127]	3A4	3A4	N/A	7.7	Oral, once/twice daily
	Lopinavir [47]	3A4	3A4	N/A	5-6	Oral, twice daily
	Saquinavir [128]	3A4	3A4	N/A	9-15 (with ritonavir)	Oral, twice daily
	Tipranavir [129]	3A4	2D6	3A4, 1A2, 2C19	6	Oral, twice daily
NNRTIs	Delavirdine [130]	3A4, 2D6	N/A	N/A	5.8	Oral, three times daily
	Doravirine [131]	3A4, 3A5	N/A	N/A	15	Oral, once daily
	Efavirenz [132]	2B6 (3A4 minor)	3A4	3A4, 2B6, 2C19	40-55	Oral, once daily
	Etravirine [133]	3A4, 2C9, 2C19	2C9, 2C19	3A4	41	Oral, twice daily
	Nevirapine [134]	3A4, 2B6	N/A	3A4, 2B6	45	Oral, once/twice daily
	Rilpivirine [135]	3A4	N/A	N/A	50	Oral, once daily
CCR5 Antagonist	Maraviroc [136]	3A4	N/A	N/A	14-18	Oral, twice daily

HIV patients experience adverse effects with long term use of ARVs. Almost all the ARVs ultimately result in hepatotoxicity or even development of drug resistance, which can lead to failed viral suppression [6]. Because of the extensive CYP metabolism and short half-lives, daily dosing is needed with current ARVs (Table 1). However, only approximately 70% adherence rate was found in all groups of treated HIV patients [7]. Moreover, the eradication of virus from the latent HIV reservoirs is impossible unless we develop new approaches for HIV therapy [8]. Moreover, many ARVs belong to biopharmaceutic classification system II, which are hydrophobic and poorly soluble and exhibit low bioavailability when administered orally [9]. The poor oral bioavailability of ARVs is due to either low water solubility and/or extensive first pass metabolism. For example, atazanavir (ATV) suffers poor water solubility and rapid first pass metabolism by CYP3A4 causing reduction in bioavailability by 60% [10]. Darunavir (DRV) has a low water solubility and an extensive drug metabolism via CYP3A4, and exhibits a poor oral bioavailability of approximately 37% [11]. Thus, an alternative mode of delivery is needed for HIV therapy in contrast to conventional ART treatment. One such potential strategy could be nanotechnology because sustained release of ARVs using this technology has shown promising results in the clinical trials [12]. Nanotechnology could be used to improve drug delivery because nanoparticles or nanoformulations are generally taken up by cells more efficiently than traditional formulations due to the small size, large surface area, and superior endocytosis pathway [13]. Nanoformulation of therapeutic molecules has potential to provide targeted delivery of drugs at the site of action, bypass transporters and metabolic enzymes, and cross the blood-brain-barrier (BBB) [14, 15, 16]. In this review, we summarized the limitations of conventional ARVs in HIV treatment, especially for ARVs which are CYP substrates. We also discussed the potential advancements to overcome the limitations of these CYP substrates used in HIV treatment, using the novel nanotechnology strategy. The preclinical studies and clinical studies published from 2000 to February 2019 were discussed.

2. Limitations of CYP substrates in treating HIV using conventional dosage forms

While ART has made considerable strides in combating HIV, there are still, to date, areas where therapy can be improved. These areas include high first pass metabolism of ARVs and low systemic bioavailability, DDI due to CYP induction/inhibition, and short half-lives of ARVs, requiring either pharmacological boosting or regular daily dosing.

2.1. Low systemic bioavailability and first pass metabolism of CYP substrates

As previously noted, many ARVs are substrates of CYP enzymes, which can result in lower systemic exposure of ARVs in people taking these drugs [3]. To overcome the first pass metabolism, in many ART regimens, CYP expression is inhibited by an additional drug, through a process referred to as “pharmacoenhancement” or “boosting” [17]. In previous generations of ARVs, notably boosted protease inhibitors required dosing more often than once daily [18]. More recently, approved drugs which are CYP substrates, notably second-generation PIs and the INSTI EVG, can be administered daily to have high efficacy over the course of the day. However, pharmacoenhancement is necessary to achieve the required efficacy [19, 20]. For example, DRV oral bioavailability increases from 37% to 82% in the presence of RTV [19]. Similarly, boosting increases EVG availability in plasma by up to 20-fold (measured through area under the curve, AUC) as compared to non-boosted EVG therapy, due almost entirely to a decrease in first pass metabolism [20]. The requirement for boosting, however, greatly increases the potential of DDI with drugs for other concomitant diseases.

2.2. Drug-drug interactions and CYP enzyme

The requirement for boosting ARV concentrations by inhibiting CYP3A activity can be associated with negative outcomes in other comorbid conditions. For example, the concentrations of many antipsychotics, including quetiapine and risperidone can be increased with coadministration with RTV, and can result in negative outcomes [7, 21, 22, 23]. These interactions can necessitate decreasing concentrations of the antipsychotic medications, a lengthy and difficult process. Also of note, coadministration of boosted PIs and the antimycobacterial rifabutin can result in significant increases in plasma concentrations and the AUC of rifabutin, commonly requiring therapeutic drug monitoring of rifabutin to avoid potential toxicities [7, 23, 24]. Additionally, pharmacoenhancers and many of the drugs used to treat hepatitis C can interact, resulting in greatly increased concentrations of the hepatitis C drugs, to the point where the two drugs are not recommended to be coadministered [7]. This decreases the therapeutic options for individuals with HIV, which can be associated with worsened outcomes. Because of these and other DDI between pharmacoenhancers and other drugs, care must be taken when prescribing these and other drugs. ARVs from PIs and NNRTIs are expected to have a high chance of potential DDI via CYP metabolism even without coadministration of pharmacoenhancers. CYP-mediated DDIs are found with all PIs and NNRTIs, efavirenz (EFV) and etravirine (ETR) when coadministered with statins, anti-TB drugs, antifungals, and anticonvulsants [25]. It is thus of high importance to develop novel ARV combinations and delivery systems, which can bypass drug efflux transporter and metabolism and show reduced DDI.

2.3. Short half-lives and need for extended release

In addition to the low bioavailability of ARVs that are CYP substrates, there is also a concern of rapid metabolism from the body, resulting in subtherapeutic concentrations before the administration of the next dose or a requirement of twice daily dosing in the absence of pharmacoenhancers. In the absence of coadministration with either RTV or cobicistat (COBI), atazanavir (ATV) has a half-life of approximately 6.5 hour [26]. Boosting with RTV can increase the half-life to approximately 10 hours [27]. EVG has an un-boosted half-life of 3.83 hours, but in the presence of RTV it has a half-life of 8.62 hours [28]. As previously noted, however, pharmacoenhancement is not without a cost in terms of the risk of DDI. Even with pharmacoenhancement, there is a need for once daily administration of these and other medications. Thus, there is a considerable interest in extended release for ARVs, primarily as a method to increase patient adherence to their ART regimens. The long-acting intramuscular cabotegravir (CAB) and rilpivirine (RPV) in adults with HIV infection (LATTE-2) 92-week Phase 2b trial demonstrated that CAB and RPV could be administered intramuscularly every 4-8 weeks with high efficacy. As expected, this formulation/dosage also showed higher patient satisfaction than the oral administration of ARVs every day [12]. Based on these and other trials, there is considerable interest, and a significant unmet need to develop long-acting ART formulations, of which nanoformulation may represent a strategy to achieve this need.

3. Nanotechnology approaches for the delivery of CYP substrates in HIV treatment

Recently, nanoformulation(s) of ARVs was developed to overcome the limitations and adverse effects of current HIV treatment [29]. Although the development of nanotechnology for HIV treatment is still at an earlier stage, preclinical and clinical studies for prevention and treatment of HIV have shown considerable promise [29]. In general, the preferential size of nanoparticles used as drug delivery vehicles is <200 [30]. The effectiveness of using nanotechnology for therapeutics is attributed to their small size, targeted delivery, enhanced bioavailability, reduced toxicity, and controlled release of drug(s) [13]. The use of nanotechnology for ARVs could show similar advantages. For example, ARVs can be formulated into control release nanoparticles, which will enhance their half-lives. This control release profile could help improve the adherence to the ARVs, which is one of the main limitations for the current lifelong ART treatment [7]. Moreover, the use of nanotechnology could enhance bioavailability, bypass CYP metabolism, and bypass transporters of ARVs [31]. This could also help to avoid the potential DDI and minimize the complexity of ART regimens by eliminating the need for pharmacoenhancers [32]. In addition, ARVs can be formulated into nanoparticles to show the targeted delivery profile to the latent viral reservoirs, such as CD4+ T cells and macrophages [33]. Furthermore, literatures have also demonstrated that nanoparticle loaded with ARVs can cross the blood-brain barrier (BBB), which may help to address the issue of HIV-associated neurocognitive disorders (HAND) [34].

In general, the most commonly used nanomaterials for HIV treatment are liposomes, dendrimers, micelles, solid lipid nanoparticles (SLN), nanosuspensions, and polymeric nanoparticles that are made from natural or synthetic polymers or inorganic materials [29]. In this section, we summarized the nanotechnology approaches for delivery of CYP substrates in HIV treatment. We also discussed the potential advancements in bypassing CYP metabolism and improving efficacy of these CYP substrates, using nanotechnology. The use of nanotechnology of the CYP substrates in HIV treatment is still at an early stage, less than 2% peer-reviewed articles studied nanoformulation of CYP substrates used in HIV treatment (Fig. 1 (a)). The most commonly used nanoformulation of CYP substrates used in HIV treatment are polymeric nanoparticles, SLN, and polymer micelles (Fig. 2 (b)). In this review, we summarized the most recently published nanoformulations of CYP substrates in HIV treatment. Table 2 summarized size, zeta potential, and entrapment efficiency of these nanoformulations, the outcome of each nanoformulation was discussed in the following section in detail.

Figure 1.

(a) Peer-reviewed articles studying native CYP substrates/nanoformulation of CYP substrates used in HIV treatment published in PubMed until February 15, 2019. *indicates the percentage (%) of nanoformulation studies of total studies. (b) Structure of the commonly used nanoformulation of CYP substrates in HIV treatment.

Table 2.

Summary of nanoformulations of CYP substrates that are used in HIV treatment. The table describes the polymer types, size and zeta potential of the nanoparticles, and their entrapment efficiency for a particular drug.

Nanomaterial		ARVs	Size (nm)	Zeta potential (mV)	Entrapment efficiency (%)	Ref
Polymeric nanoparticles	PLGA	LPV	331.2	−13.8	45	[54]
	PLGA	LPV	142.1	−27.2	93.03	[55]
	PLGA	LPV, EFV, RTV	262	−11.4	45	[56]
	PLGA	NFV	185	28.7	72	[69]
	PLGA	EFV	200	−25	-	[72]
	PLGA	ETR	371.4	−21.0	91.0	[79]
	PLGA	MVC	331.6	−26.5	12.0	[79]
	PLGA	NVP	93-186	-	20–75	[83]
	PLGA	RPV	200	-	-	[90]
	PLGA	EVG	47	−6.47	-	[99]
	PLGA	EVG	190.2	−19.2	44.6	[101]
	CAP	EFV	96.9	−17.08	98.1	[73]
	CAP	DTG	212	−25	70	[97]
	PCL	LPV	195.3	−19.74	93.9	[52]
	PEO-PCL	SQV	271.0	−26.2	-	[60]
	PACA, HP-β-CD	SQV	250-350	−36.9	-	[61]
	PBCA	SQV, DLV	184	-	70.5 - 98.1	[66]
	MMA-SPM	SQV, DLV	68	-	25-90.4	[66]
	Eudragit RL 100	ATV	390-487	21.63-26.47	41.3-51.9	[38]
	PLA	EVG				[100]
SLNs	Stearic acid	ATV	167	−18.43	98.9	[37]
	Stearic acid	LPV	180.6	−13.4	91.5	[50]
	Stearic acid	LPV	223	−21.23	83	[51]
	Stearic acid	SQV	215	−30.21	79.24	[64]
	Tripalmitin, cocoa butter	SQV, DLV	-	-	-	[66]
	Soya lecithin	DRV	181-276	−22	2-60	[42]
	Hydrogenated castor oil	DRV	200	−35.45	90	[43] [44]
	Glyceryl behenate	LPV	214.5	−12.7	81.6	[49]
Polymer micelles	Poloxamer 188	ATV	281	−15.31	-	[39, 137]
	Polysaccharide consisting of maltotriose units	LPV	197	−3	75	[57]
	Poloxamer 407	DTG	234	−21.6	82.2	[95]
Nanoemulsions	Soya bean oil, egg lecithin	DRV	109.5	−41.1	93	[45]
	Maisine, Transcutol HP	LPV	53.16	−21.56	-	[58]
	Polyunsaturated fatty acids, deoxycholic acid	SQV	100-200	−49.55	-	[63]
Nanosuspensions	Lutrol F 127, poloxamer 407, HPMC	NVP	298.8-827.6	-	-	[82]
	Serum albumin, polysaccharide, polyethylene glycol	NVP	457.6	−33	-	[84]
Nanocrystals	-	SQV	205.93	−53.5	-	[62]
Solid drug nanoparticles	PVA, AOT	MVC	728	−25.3	-	[104]

PCL- poly (ε-caprolactone), PLGA- poly (DL-lactide-co-glycolide), PBCA- polybutylcyanoacrylate, MMA-SPM- methyl methacrylate–sulfopropyl methacrylate, PEO- poly(ethylene oxide), CAP- cellulose acetate phthalate polymer, PACA- poly(alkyl-cyanoacrylate), PLA- poly(lactic acid), HP-β–CD- hydroxypropyl-β-cyclodextrin, AOT- 1,4-bis(2-ethylhexoxy)-1,4-diox- obutane-2-sulfonate, PVA- polyvinyl alcohol, HPMC- hydroxylpropyl methyl cellulose, ATV- Atazanavir, DRV- Darunavir, DTG- Dolutegravir, DLV- Delavirdine, EFV- Efavirenz, ETR- Etravirinel, EVG- Elvitegravir, LPV- Lopinavir, MVC- Maraviroc, NVP- Nevirapine, NVP- Nevirapine, RTV- Ritonavir, RPV- Rilpivirine, SQV- Saquinavir. – Data not available.

3.1. Nanotechnology approaches for delivery of CYP substrates from the PIs

PIs act against HIV by inhibiting viral protease enzyme [35]. By inhibiting protease, PIs interrupt viral lifecycle. The new virus formed stops multiplying and remains immature, which is unable to infect new cells [35]. All PIs are CYP substrates, and all PIs are either CYP inhibitors or CYP inducers. Thus, PI-based regimen is often involved in CYP-mediated DDI [3]. Because of the rapid first-pass metabolism of PIs by CYP enzymes, pharmacoenhancers RTV or COBI are required to achieve therapeutic concentrations of PIs. Therefore, different nanotechnology approaches have been developed to overcome the limitations of current PI regimens. Nanoformulations of atazanavir (ATV), darunavir (DRV), lopinavir (LPV), saquinavir (SQV), and nelfinavir (NFV) are discussed in this subsection. Other drugs from PIs are not discussed here because no nanoformulation is available for those drugs.

3.1.1. Atazanavir

ATV is a highly selective and potent inhibitor of HIV protease and possesses superior clinical profiles [36]. However, high lipophilicity and rapid first-pass metabolism in liver by CYP3A4 results in low ATV bioavailability. To overcome this limitation, stearic acid based SLN was developed by the Bendayan group using microemulsion method that utilizes Pluronic F68 as an emulsifier [37]. In vitro studies on human brain microvessel endothelial cell line (hCMEC/D3) demonstrates significantly higher uptake of the nanoformulation than the native drug. Their findings suggest that SLN formulated ATV could bypass efflux transporters resulting in higher accumulation in the brain [37]. In another study, the authors have utilized Eudragit RL 100-based formulation to stabilize the nanoparticles of ATV. A relatively increased oral bioavailability (3-fold) in comparison to the native drug was achieved in healthy male Wistar rats, suggesting the potential of polymer based nanoparticles such as Eudragit RL 100 polymer in achieving maximal oral bioavailability [38].

The Poluektova group also developed a nanosuspension of ATV and RTV using poloxamer 188 as a stabilizer [39]. The authors demonstrate a significantly longer release of drugs from the nanosuspension and higher uptake by human monocyte-derived macrophages than the native drugs. These results further confirm the potential of nanoformulations to reach therapeutic levels even in difficult HIV reservoirs, which makes the delivery of therapeutics at these regions an arduous task for HIV treatment management [39].

3.1.2. Darunavir

DRV represents the most-prescribed PI for treating HIV individuals [11]. However, it has a poor oral bioavailability of approximately 37% due to its low hydrophilicity and its first pass metabolism by intestinal and hepatic CYP3A enzymes [11]. DRV is administered in combination with RTV, however this combination may lead to DDI , causing adverse effects such as liver disorders and hypersensitivity reactions [40, 41]. Based on these findings, the Madgulkar group developed SLN of DRV, taking advantage of the properties associated with lipid nanoparticles of enhancing drug solubility and forming stable dispersion [42]. The authors demonstrate significant enhancement in the ex vivo permeability through the rat intestinal epithelium due to the endocytic uptake and enhanced lymphatic transport, owing to the ability of DRV to be entrapped in the lipid matrix of the nanoparticles. This eventually enhance the bioavailability by decreasing both hepatic and intestinal CYP metabolism and also reduces drug efflux [42].

Similar finding was in concordance with the findings from the Thakkar group, SLN of DRV enhanced the oral bioavailability by ~4-fold in comparison to native DRV suspension obtained from the healthy male Wistar rats pharmacokinetics data [43]. They showed that the enhancement in oral bioavailability could indeed be attributed to DRV entrapping in the lipid matrix causing enhancement in the lymphatic uptake of nanoparticles, as well as, resulting in enhanced absorption over native drug [43]. The same group also utilized their developed nanoparticles loaded with DRV and grafted the surface with a peptide sequence (CARRPKFYRAPYVKNHPNVWG) that has affinity for CD4 receptors on the HIV host cells [44]. The authors reported an enhancement in permeability of SLN loaded DRV in Caco-2 cells (mimics gastrointestinal membrane) by 4-fold in contrast to native DRV suspension, due to increased endocytosis. Further, the confocal imaging showed significantly higher uptake in HIV host cells (Molt-4 cells which have CD4 receptors) than non-CD4 receptor bearing Caco-2 cells, due to the peptide grafting causing SLM-mediated target specificity. The in vitro bioavailability of DRV from SLN was also enhanced by 5-fold relative to native drug suspension. These SLN were able to penetrate the BBB and have 3-fold increased accumulation in the brain in comparison to native DRV suspension. Thus the authors have clearly demonstrated both advantages of solid lipid nanoparticles as well as active targeting of the drugs to reach the HIV reservoir [44].

A Nanoemulsion prepared by high pressure homogenization using soya bean oil, egg lecithin and tween 80 is also improved oral bioavailability of DRV in Wistar rats [45]. In contrast to native drug suspension, the nanoemulsion of DRV showed 223% improvement in the oral bioavailability and ~2-fold increase in the brain from the male Wistar rats pharmacokinetics data. The usage of Tween 80, which is a known inhibitor of P-gp and CYP, could be attributed to the improved activity. Also, the presence of lipids prevents the drug from getting cleared resulting in enhanced lymphatic transport [45]. Further, the Sosnik group developed novel Nanoparticle-in-Microparticle Delivery System (NiMDS) to deliver DRV and RTV combination and achieved 2-fold increase in DRV oral bioavailability in comparison to the un-formulated drug combination from the Sprague Dawley rats pharmacokinetics study [46].

3.1.3. Lopinavir

LPV is coformulated with RTV as part of a tablet branded in the US as Kaletra and was recommended to use in pregnant women with HIV infection [47]. LPV is another PI that undergoes extensive CYP3A4 mediated hepatic first pass metabolism and efflux through the P-gp transporters, leading to poor oral bioavailability [48]. LPV is used in combination with RTV due to LPV’s inhibitory effect on CYP3A4 activity. However, this approach is not suited due to adverse effects of DDI such as glucose intolerance, gastrointestinal intolerance, lipid elevations, and perioral paresthesia [48]. To overcome these limitations, scientists started developing nanoparticle formulation for LPV. For example, the Ram group developed SLNs using lipids of glyceryl behenate (GB), poloxamers 407, and poly ethylene glycol 4000 (PEG4000) as co-surfactant to increase the high lymphatic drug transport [49]. Oral bioavailability of the SLN loaded LPV in Wistar rats was 3-fold higher than LPV solution, suggesting the ability of the nanoparticles to bypass the P-gp efflux transport and CYP3A mediated hepatic metabolism. The enhancement in oral bioavailability could be attributed to the presence of poloxamer, which is known inhibitor for both the transporters. In addition, the presence of long chain fatty acid of GB entraps the drug in the lipid matrix [49]. Further, the same group also developed SLN using long chain fatty acid stearic acid (SA) with poloxamer 407 and PEG and achieved 2-fold increase of oral bioavailability in Wistar rats compared to LPV solution [50].

A stearic acid based SLN was developed for a combination of LPV and RTV by Ravi et al. and achieved 5-fold increment of oral bioavailability in Wistar rats of LPV and ~3-fold for LPV/RTV combination in comparison to free LPV [51]. The same authors developed polymeric nanoparticles of LPV using poly(ε-caprolactone) (PCL) that increased the oral bioavailability of the LPV by 4-fold as seen from PK study conducted on male Wistar rats [52]. An increase in the apparent permeability from nanoparticles was also observed over free drug, suggesting that LPV can cross the intestinal barriers by active endocytosis via M-cells and also prevent P-gp efflux [53].

Another polymer-based nanoparticle is a water-in-oil-in-water emulsion of poly (DL-lactide-co-glycolide) (PLGA) nanoparticles [54]. This PLGA nanoparticle demonstrated an 8-fold increase in the serum concentration of LPV in contrast to native drug solution in non-infected Balb/c mice. Also, a 30-day prolonged release of LPV in Balb/c mice was observed even after a single 20 mg/kg dose. This PLGA nanoparticles could also suppress HIV in viral reservoir monocytes-derived macrophages in a sustained inhibition manner. Higher biodistribution of LPV from nanoparticles was also found in liver, kidney, spleen, and even brain of the Balb/c mice [54]. Another PLGA nanoparticle of LPV was generated by the Sawant group to improve its oral bioavailability [55]. The PLGA nanoparticle demonstrates a 3-fold enhanced permeability in Caco-2 cells and ~14-fold increase in oral bioavailability of male Wistar rats compared to that of free drug. The authors demonstrate an increased LPV concentration to reach the lymphatic viral reservoir sites, by inhibiting the P-gp efflux and bypassing the CYP3A4 first pass metabolism [55]. Moreover, the Destache group developed PLGA nanoparticles for LPV and found peak concentration of LPV in 4 days and continue to show intracellular concentration for 28 days in peripheral blood mononuclear cells (PBMCs), in contrast to free drug that was eliminated in 2 days signifying potential to suppress replication of HIV in the reticuloendothelial system (RES) where macrophages migrate [56].

Other than SLN and PLGA nanoparticles, a biodegradable polymer called pullulan (polysaccharide polymer consisting of maltotriose units) was modified to pullulan acetate (PA) by acetylation process in the presence of pyridine and was utilized to form self-aggregating mono-dispersed nanoparticles of LPV [57]. Relative bioavailability of the nanoparticle in male Wistar rats was increased by ~2-fold in comparison to free drug and demonstrated high biodistribution in viral reservoirs such as liver, spleen, and lymph nodes, attributed to the reduced metabolism and inhibition of P-gp efflux [57]. Additionally, solid self-nanoemulsifying oily formulations was developed to circumvent these effects of LPV [58], and this improved the oral bioavailability of the nanoformulation by ~4-fold in comparison to native drug in male Wistar rats.

3.1.4. Saquinavir

SQV was the first PI approved by Food and Drug Administration (FDA) and has been in clinical use since 1995 [59]. SQV is rarely used in current HIV therapy. However, nanoformulations of SQV may be used to repurpose SQV for HIV therapy as well as it may serve as an example for nanoformulation of other PIs. However, SQV suffers from poor oral bioavailability of only 4%, primarily because of poor solubility, metabolism by CYP3A4, and efflux by P-gp transporters. Polymer based nanoparticle were formulated by the Shah group using PCL, which is a synthetic, biocompatible polymer that is highly permeable [60]. The surface of the nanoparticle was modified using poly (ethylene oxide) to prevent aggregation of the nanoparticle. Intracellular drug concentration of the nanoparticle was increased by 10-fold compared to the aqueous SQV solution consistently for 12 hours in HIV reservoir monocytes/macrophages. These nanoparticles also demonstrated prolonged residence time in vivo in contrast to free drug solution, as the drug is entrapped in the polymer matrix [60].

Another polymer nanoparticle of SQV was fabricated using poly(alkyl-cyanoacrylate) and hydroxypropyl-β-cyclodextrin, that increased the apparent solubility of the nanoparticle by 400-fold due to the presence of cyclodextrin complexes subsequently improving its absorption by 20 folds due to enhanced drug loading [61]. Additionally, nanocrystals were engineered to increase SQV loading by an anti-solvent precipitation-high pressure homogenization method that showed ~2-fold increase in oral bioavailability as in contrast to coarse crystalline SQV suspension in male Wistar rats [62]. This improved effect was probably due to increased drug dissolution rate and intracellular endothelial uptake as a result of P-gp inhibition and inhibition of intestinal and hepatic metabolisms [62]. Moreover, nano-emulsion of SQV was developed using essential polyunsaturated fatty acids as internal oil and Lipoid®-80 and deoxycholic acid as surfactants [63]. This nano-emulasion increased the SQV concentration by 3-fold in the systemic circulation as well as in the brain in the male Balb/c mice model. The improved PK parameter attributes to the presence of deoxycholic acid, which is known to have a P-gp inhibitory effect, and also its potential to bypass the barriers of gastrointestinal tract [63]. Similar findings were also demonstrated by Dodiya et al. [64] using SLNs in contrast to nanosuspension and microsuspension. LPV in SLN showed a 66% improvement in relative bioavailability, and LPV in nanosuspension and microsuspension showed 37% and 19% improvement in relative bioavailability, respectively, compared with the native drug. This suggests the usage of wide range of nanoparticle systems for improving bioavailability of poorly soluble drugs. In addition, Beloqui et al. [65] engineered nanostructured lipid carriers (NLCs) with lipids Precirol ATO and Miglyol 812 and Tween 80, which increased the apparent permeability of SQV across Caco-2 monolayers by 3.5-fold in contrast to native drug. The authors confirmed the improved activity of NLCs were due to the P-gp inhibition as demonstrated by an increase in permeability of NLCs in Caco-2 cells by 2-fold [65]. Further, Kuo et al. [66] demonstrated improved permeability across the in vitro BBB for stavudine, delavirdine, and saquinavir using polymeric (polybutylcyanoacrylate [PBCA]) nanoparticles, methyl methacrylate–sulfopropyl methacrylate (MMA-SPM) nanoparticles, and SLNs of tripalmitin and cocoa butter. Permeability for all the three drugs increased 12– to 16-fold with PBCA, 3– to 7-fold with MMA-SPM, and 4– to 11-fold with SLNs. The best entrapment efficiency was noticed with SLNs for lipophilic SQV due to the presence of the lipid matrix, indicating the better suitability of SLNs for lipophilic drugs. The authors further displayed electromagnetic field transports of ARVs across in vitro BBB due to larger frequency or modulation with electromagnetic field, resulting in enhanced permeability [67]. Another similar strategy to enhance delivery of SQV is a polymeric nanoparticles conjugated with RMP-7, which promotes penetration through in vitro BBB [68]. This strategy enhanced in vitro BBB penetration of SQV and two other ARVs stavudine and delavirdine (DLV) by 1.4-, 1.4-, and 2.1-fold, respectively, compared to the non-grafted nanoparticles. This nanoformulation is also discussed in detail under the section with DLV.

3.1.5. Nelfinavir

NFV is a potent PI and used in combination with other ARVs in the HIV therapy for both adult and child. NFV is a non-peptidic HIV protease inhibitor that belongs to the biopharmaceutics classification system class IV drug and is characterized by a short half-life of 3.5–5 hours that require frequent dosing. In this regard, the Goti group [69] formulated PLGA nanoparticles and demonstrated a sustain release of NFV up to 24 hours. An enhancement of 4.94-fold was achieved with PLGA-NFV versus NFV suspension after oral administration in male New Zealand rabbits.

3.2. Nanotechnology approaches for delivery of CYP substrates from the nonnucleoside reverse trasncriptase inhibitors

In general, non-nucleoside reverse transcriptase inhibitors (NNRTIs) inhibit viral reverse transcriptase enzyme and prohibit the conversion of RNA to DNA [3]. As such, the virus fails to incorporate itself within host cell genome, thereby, cells stop producing new virus. All NNRTIs are metabolized by CYP3A4, while EFV and nevirapine (NVP) are also substrates of CYP2B6, and ETR is also metabolized by CYP2C9 and CYP2C19 [3]. Additionally, EFV is a CYP3A4 inhibitor, but a CYP3A4, CYP2B6, and CYP2C19 inducer. Similar to EFV, ETR can induce CYP3A4, but inhibit CYP2C9 and CYP2C19 [3]. Nanoformulations of EFV, ETR, NVP, delavirdine (DLV), and rilpivirine (RPV) are discussed in this subsection. Nanoformulation of doravirine (DOR) has not been studied.

3.2.1. Efavirenz

EFV is a preferential choice of patients infected who have coinfection with both tuberculosis and HIV [70]. CYP2B6 was found to metabolize EFV and inactivate the drug [71]. The Destache group developed a PLGA-based nanoparticles containing RTV, LPV, and EFV using a multiple emulsion-solvent evaporation procedure [56]. The PLGA nanoparticles containing all three ARVs showed an enhanced drug levels in PBMCs until 4^th week without cytotoxicity. Another PLGA nanoparticle was developed by the Woodrow group [72]. Biodegradable PLGA-NP-EFV exhibited effective protection against HIV infection in vitro (HIV-1_BaL) and found effective to a 50-fold reduction in the 50% inhibitory concentration compared to free drug.

EFV has also been formulated in a cellulose acetate phthalate polymer (CAP-EFV-NPs) using nanoprecipitation method [73]. CAP is a pH sensitive polymer that dissolves at a pH higher than 6 [74]. CAP also has potential activity against HIV virus, and a potential topical microbicide. The CAP-EFV-NPs showed a higher prevention activity to TZM-bl cells when challenged with HIV infection as compared to EFV free drug solution [73]. Also, in order to achieve long-term HIV prophylaxis, CAP-EFV-NPs were formulated into a thermosensitive gel (CAP-EFV-NP-Gel). The CAP-EFV-NP-Gel showed a lower toxicity to HeLa cells, compared to the EFV solution [73].

3.2.2. Etravirine

ETR is a second-generation NNRTI [75]. It has a unique characteristic with higher genetic barrier to viral resistance and is prescribed for treatment of patients developing mutations that possess resistance to NNRTIs [76, 77]. Studies show that CYP2C19 is the primary metabolizing enzyme for the formation of major monohydroxylated and dihydroxylated metabolites of ETR [78]. The Woodrow group formulated ETR into PLGA-based nanoparticles using a single emulsion/solvent evaporation method [79]. The ETR nanoparticles showed higher antiretroviral potency for cell-free and cell-associated HIV infection. The ETR nanoparticles also showed a higher intracellular drug level compared to the free drug solution. Moreover, the ETR nanoparticles can also be used with a reduced dose against both cell-free and cell-associated HIV infection in the TZM-bl cell line [79].

3.2.3. Nevirapine

NVP is the first NNRTI approved drug by FDA for use in combination against HIV [80]. NVP is recommended for the use of HIV treatment in pregnant women. NVP is metabolized by CYP3A34, which is also an inducer of CYP3A4 [81]. NVP has low solubility, which causes a large fraction of variability in oral bioavailability. The Jithan group prepared nanosuspensions with different polymers using nanoprecipitation method, followed by a homogenization [82]. Nanosuspensions of NVP can improve oral bioavailability of healthy male Wistar rats with great effectiveness using surfactant polymers Lutrol F 127, or Poloxamer 407 and hydroxylpropyl methyl cellulose.

Studies also showed the potential of using NVP nanoformulation to target viral reservoirs including the CNS and macrophage [83, 84]. To enhance the transmigration efficacy of NVP, PLGA nanoparticles were conjugated with transferrin to target human brain microvascular endothelial cells (HBMECs) [83]. PLGA was found to be a valuable carrier across HBMECs in-vitro for delivery of NVP to the CNS. Additionally, the Singh group developed a surface modified nanosuspension of NVP with serum albumin, polysaccharide, and polyethylene glycol [84]. Compared with the free drug solution, this surface modified NVP nanosuspension was able to improve drug level in macrophages, and drug accumulation in the brain, liver, and spleen of healthy Wister rats. This NVP nanosuspension can enter the brain and accumulate in the brain for more than 24 hours.

3.2.4. Delavirdine

DLV is not as potent as other NNRTIs, and therefore, three times dosage a day of DLV is recommended [85]. In addition, DLV undergoes substantial metabolism by CYP3A4 enzyme with little urinary excretion. DLV is also an inhibitor of CYP3A4, leading to increased systemic exposure to PIs. DLV also inhibits CYP1A2 and CYP2D6 [86], thus affecting other coadministered drugs, which are CYP1A2 and CYP2D6 substrates. Because of these factors, DLV is not recommended as part of initial ART [3]. Polymeric nanoparticles of DLV showed an improved delivery of the drug across the in vitro BBB [66, 68]. The Kuo group has demonstrated the transport of DLV and SQV across the in vitro BBB by using PBCA nanoparticles, MMA-SPM nanoparticles, and SLNs [66]. Compared with the free DLV, the permeability of DLV nanoparticles across HBMECs can be improved by 3- to 16-fold. The same group further modified the surface of the MMA-SPM nanoparticle for targeting delivery of stavudine, DLV, and SQV across the in vitro BBB [68]. They found that the RMP-7 conjugated nanoparticles were able to open the tight junction and enhance endocytosis of the BBB, improving the permeability of these three ARVs into the brain.

3.2.5. Rilpivirine

RPV is a first-generation NNRTI and has been approved for oral administration to treat HIV in combination with other ARVs [87]. RPV is predominately metabolized by CYP3A4 [88]. Coadministration of CYP3A inhibitors or inducers with RPV may cause either adverse effects or virological failure. The Destache group encapsulated RPV in PLGA nanoparticles, and delivered them using a thermosensitive gel, which is highly viscous at body temperature and liquid at room temperature. They showed that this PLGA-gel can provide significant protection from HIV vaginal infection from a high-dose HIV challenges in the CD34+ NOD.Cg-Prkdc^scid Il2rg^tm1Wjl/SzJ (NSG) mice[89]. Additionally, poloxamer 338, a hydrophilic, nonionic surfactant was used to formulate a 200-nm nanosuspension formulation of RPV [90]. This RPV nanosuspension showed a sustained release profile, slowly releasing RPV for 2 months in Sprague-Dawley rats and for 6 months in healthy male beagle dogs. Moreover, this RPV nanosuspension was mainly uptaken by macrophages. Over 100-fold increase of plasma concentration was observed after 1 month, while the concentrations in the lymphoid tissues decreased. This long-acting RPV nanosuspension was further evaluated in the clinical trials. We will discuss the clinical trials of long-acting RPV in the next section in detail.

3.3. Nanotechnology approaches for delivery of CYP substrates from the INSTIs

As the name suggests, drugs under INSTIs inhibit integrase protein, which is essential for viral replication. Due to this inhibition, HIV DNA is unable to integrate within host genome, blocking HIV pro virus formation as well as further replication [91]. Bictegravir (BIC), dolutegravir (DTG), and elvitegravir (EVG) from INSTIs are metabolized by CYP3A4, however, only EVG has the ability to induce CYP2C9 [3]. We discuss nanoformulations of DTG and EVG in this subsection, while BIC has no nanoformulation available.

3.3.1. Dolutegravir

DTG is used not only together with other ARVs as an HIV treatment but also used as part of post exposure prophylaxis [92]. DTG is primarily metabolized by UGT1A1 and to a lesser extent by CYP3A4 [93]. The terminal plasma half-life (t_1/2) of DTG is 11-12 h in HIV-infected individuals, which determines that DTG needs to be used as a once- or twice-daily regimen to maintain its therapeutic drug levels [94]. Recently, the Gendelman group developed a poloxamer 407-based nanoformulation of a modified DTG prodrug using high-pressure homogenization process [95]. The chemical structure of DTG was altered to a water-insoluble prodrug, subsequently packed into poloxamer nanoparticles. The nanoformulation of DTG was able to maintain therapeutic concentration in balb/c mice plasma and tissues for 56 and 28 days, respectively. This DTG nanoformulation also improved the antiretroviral potency of DTG, protecting CD34+ NSG mice from HIV challenge for two weeks [95]. The same group also performed a PK study of this nanoformulated DTG prodrug in rhesus macaques. The plasma DTG was detectable until day 91, and the drug level was above the 90% inhibitory concentration until day 35 [96].

DTG has also been formulated with a pH sensitive polymer CAP to achieve a higher pre-exposure prophylaxis efficacy [97]. The DTG–loaded CAP nanoparticle was prepared using water-oil-in-water homogenization. This DTG nanoparticle showed a smooth and spherical morphology with 200 nm of size, and were able to retain in vaginal cell lines over seven days [97].

3.3.2. Elvitegravir

EVG was first approved by FDA in 2012 and only available as part of a combination regimen [98]. Since EVG is primarily metabolized by CYP3A4, coadministration with a CYP3A4 inhibitor is required to achieve the therapeutic concentration and extended half-life of EVG [3]. Since COBI is a potent CYP3A4 inhibitor, unexpected DDI may occur when boosting EVG with COBI [99]. Recently, Kumar and Yallapu groups developed a PLGA-based nanoparticle of EVG [99]. EVG was encapsulated into a PLGA-based nanoparticle with an outer layer of the mixture of PLGA, polyvinyl alcohol (PVA), and poly-L-lysine. Poloxamer 188 was added to this EVG formulation to maintain a stable suspension for therapeutic application. This PLGA-EVG nanoformulation showed improved intracellular uptake of EVG in monocytic cells and enhanced viral suppression in HIV-infected primary macrophages, compared with the free EVG. This improved delivery method of EVG may help to eliminate the use of COBI upon bypassing CYP metabolism. Thus, the cost of COBI and the potential CYP-mediated DDI may be reduced.

EVG has also been formulated into nanoparticles for protection against HIV. The Saltzman group developed a poly(lactic acid)-based nanoparticle (PLA NPs), with the hyperbranched polyglycerols (HPG) forming a corona on the NP surface [100]. They further modified the surface of this PLA-HPG NP, created bioadhesive PLA-HPG NPs loaded with EVG. Prolonged retention of EVG in C57BL/6 mice vaginal lumen was observed using this bioadhesive PLA-HPG NP compared with either free drug or nonadhesive NP. This NP was distributed widely throughout the reproductive tract, suggesting that prolonged intravaginal delivery of EVG may be achieved by using this bioadhesive PLA-HPG NP. The Destache group developed a PLGA-based nanoparticle containing EVG and tenofovir alafenamide (TFV) for subcutaneous delivery as a prevention strategy against HIV [101]. They used an oil-in-water emulsion methodology, emulsified organic phase containing PLGA, and poloxamer 407 with aqueous phase containing PVA. EVG and TFV were encapsulated into the PLGA core and showed detectable drug level for 14 days, while the free drug solution had detectable drug level for 72 h. This nanoformulation injection was able to protect the mice with 100% and 60% of uninfected rate on day 4 and day 14, respectively, after HIV challenge. In the PK study, the t_1/2 of TFV was improved from 14 h to 5 days, and the t_1/2 of EVG was improved from 11 h to 3.3 days in humanized CD34+ NSG mice [102].

3.4. Nanotechnology approaches for delivery of CYP substrate from the CCR5 antagonist class

Marviroc (MVC) is a CCR5 antagonist, which blocks HIV entry into the host cell. MVC is extensively metabolized by CYP3A4, and thus only 33% oral bioavailability can be achieved by the conventional dosage form [103]. The concentration of MVC can be altered by the activity of CYP3A4, and therefore, dose adjustment is necessary when co-administrated with inhibitors or inducers of CYP3A4. Thus, a twice-daily dose is required to maintain therapeutic range of MVC over the dosing interval [103]. To overcome the low bioavailability, Rannard and Owen groups screened a series of MVC solid drug nanoparticles (SDN) to select the suitable excipients for manufacturing purpose [104]. They prepared a series of SDNs using the emulsion templated freeze-drying strategy. The SDNs prepared using PVA and 1,4-bis(2-ethylhexoxy)-1,4-diox- obutane-2-sulfonate (AOT) were considered as the lead formulation and showed increased apparent permeability of MVC, compared to a conventional MVC preparation. A 2.5-fold increase in AUC of MVC was observed using the PVA-AOT nanoformulation, compared with the conventional regimen in a Wistar rat model. The PK study in Wistar rats demonstrated a 3.4-fold increase in AUC and a 2.6-fold increase in t_1/2 by this PVA-AOT nanoformulation, and the concentration of MVC is detectable until day 10. The CYP-mediated DDI may also reduce due to the decrease in t_1/2 [104].

Moreover, MVC has been formulated into a PLGA nanoparticle using emulsion-solvent evaporation techniques [79]. Three ARVs including MVC, ETR, and RAL were incorporated in a PLGA and emulsified with PVA solution. This triple-drug nanoparticle showed higher viral suppression potency in both cell-free and cell-associated HIV infection, compared with free drugs in vitro. Moreover, it demonstrated a more efficient control of HIV-1 transmission in ex vivo macaque cervicovaginal tissue, compared with free-drug combinations [79].

4. Nano-formulated CYP substrates for HIV treatment in clinical trials

CYP substrates have been developed in the form of numerous nanoformulations for HIV treatment, but very few of them reached to the clinical trials. In clinical trial database (https://clinicaltrials.gov), there were less than 10 studies documented under subsection of nanoformulated ARVs, so far. The nano-drug systems belonging to ART family have been made to various stages of clinical trials that includes phase I/II/III [105]. The nanoformulations of ARVs such as EFV, LPV, CAB, and RPV were predominantly implicated in HIV treatment [105]. A clinical trial ( NCT02631473) was conducted by St Stephens Aids Trust and University of Liverpool confirmed a 50% dose reduction can be used for nano-drugs (LPV and EFV) compared to native drug regimens in HIV negative patients. Further, this study has demonstrated the tolerability and safety profiles of nanoformulated EFV and nanoformulated LPV at varying doses ranging from 50-400 mg [97, 106]. However, the results of this study remain undisclosed.

The PATH pharmaceutical company has formulated the long acting forms of RPV (RPV LA) through nanosuspension using poloxamer 338 and PEG 1000 succinate, and successfully evaluated its efficacy in pre-clinical models [107]. Further, this RPV-LA formulation has been investigated for safety and acceptability profiles for pre-exposure prophylaxis by phase II clinical trial study ( NCT02165202) [14]. In this study, one patient died and 4 patients encountered with severe side effects among the 91 patients[108]. Moreover, another phase I clinical trial ( NCT02547870) demonstrated the PK effects of RPV-LA nanosuspension at different storage conditions. Though this study was completed, the results were not disclosed[109]. In randomized clinical trial ( NCT02076178), HIV integrase inhibitor-CAB LA (GSK1265744 LA) was evaluated for safety, tolerability, and acceptability profiles in HIV patients. There was only one among the 124 patients recruited for this study has encountered with serious adverse events (appendicitis) and no mortalities were observed during CAB LA therapy[110]. In another study the combinatorial treatment of CAB LA and RPV-LA was effective for 4-8 weeks in comparison to daily oral therapy. This combinational dose is effective, tolerated, and substantially inhibited HIV replication till 96 weeks [12]. Additionally, Spreen et al demonstrated the safety and tolerability profiles of CAB LA and RPV LA nanosuspension, and were evaluated in healthy individuals [111]. The results of this resoundingly state potential clinical implication of CAB LA and PRV LA with no adverse effects.

Since only few ART nano-therapies are available under clinical trials, it would be highly encouraged to convert the translational potential of ART nanoformulations from preclinical to clinical perspective. Overall, preclinical research evidences on nano-ARVs are much stronger and larger in number. However, the rationale of these therapeutic regimens must be evaluated at clinical level.

5. Expert opinion

Currently there is no definite cure for the treatment of HIV patients, but just preventive measures that are used to prevent the infection from getting transmitted. However, once the virus is transmitted, the infection still remains irreversible [112]. Although ART has made significant advances in improving quality of life among PLWHA, ART does not result in cure and needs to be taken lifelong with frequent dosing [113]. Nanotechnology has already begun to show promising results in overcoming the limitations of CYP substrates in HIV treatment (Figure 2). Nanoformulation can be designed based on the need to show the controlled release profile, high permeability, biodegradation, and targeting capability [114]. According to this review, the most commonly used nanoformulation of CYP substrates used in HIV treatment are polymeric nanoparticles, SLN, and polymer micelles. Common limitations for CYP substrates used in HIV treatment including rapid first-pass metabolism, low systemic bioavailability, short half-lives, and potential DDI may be addressed by using these nanoformulation.

Figure 2.

A comparison of CYP substrates used in HIV treatment between conventional drug delivery and nano-based drug delivery. The comparisons of first pass metabolism, drug-drug interactions, the use of pharmacoenhancers and long-acting profile are included.

Although only a few of nanotechnology has reached to the clinical trials for HIV treatment, nanotechnology may provide a new approach for delivery of safe and efficient ARVs for long-term therapy [29]. Developing long-acting injectable ARVs, which can offer reduced frequency of dosing, may be the future goal for CYP substrates in HIV treatment. Researchers are engaged in both preclinical and clinical studies to develop a long-acting ART nanoformulation, which could improve patients’ adherence and decrease adverse effects of current ART [14]. Ideally, long-acting ARVs will exhibit a longer half-life and a sustained systemic exposure. Currently, there is no sufficient PK/PD data to study the potential DDIs between the long-acting ART and other drugs. However, the potential DDIs using long-acting ARVs are expected for patient who are on prevalent-use of concomitant medications, including hepatitis C drugs, chemotherapy, anti-TB drugs, statins, contraceptives, and other CYP substrates. A potential DDI between a long-acting ARV and other drugs may increase the level or extend the exposure time of long-acting ARV, leading to an unexpected side effect or an inappropriate dose period for an HIV individual. A potential DDI may also reduce the level of long-acting ARV, leading to treatment failure and increase of viral replication. Drug levels of other drugs may be affect by long-acting ARVs, leading to side effect or treatment failure. Other than DDIs, drug resistant may also develop on individuals who are on ARVs for a long time period. A close monitoring of drug resistance could be required for long-acting ARVs. Overall, potential DDIs, development of drug resistance, close monitoring, and patient preference of long-acting ARV need to be considered for researchers before moving forward to the clinical use.

Another major impediment for the success of current ART seems to be the lack of a specific target where the viral reservoir can be completely exterminated [29]. HIV persistently exist in the latent reservoir including T cells and macrophages despite of patients continuously receiving ARVs [8]. The eradication of virus from the latent HIV reservoirs is impossible unless we develop new approaches for HIV therapy. Thus, an alternative mode of delivery is needed for targeting HIV infection in infected cells in contrast to conventional ART treatment. Targeted nanoparticles have shown promise in improvement in cancer therapy associated with the conventional chemotherapy [115]. Based on the studies in cancer therapy, using targeted nanoparticles to deliver ARVs to the viral reservoirs such as T-cells, monocytes/macrophages, microglia, and brain may offer advantages including increased viral suppression, and minimize off-target toxicity [116]. Receptors CD4 and CD8 for T cells, CD52 and CD14 for monocytes/macrophages, Iba1and TMEM119 for microglia, and transferrin for BBB can be used as target to deliver ARVs to the viral reservoirs [117, 118].

Since nanotechnology is a novel delivery method, in order to move forward to the clinical use, comprehensive toxicity and safety assessments of nanoformulation need to be addressed. Another important consideration in investigating nanotechnology for HIV treatment is the stability and their capability for large-scale production. Nanotechnology may increase the overall cost of treatment, which may not be afforded in underdeveloped countries. Another important aspect to consider is the route of administration. Most of the long-acting nanoformulation for HIV treatment are designed for parenteral administration. A survey was done with 400 adult HIV patients who were prescribed with ART revealed that majority of the patients (73%) were willing to try injectable long-acting nanoformulated ARVs, but 35% of patients were very concerned about needle use [119].

The alternative nanotechnology approach for delivery of ARVs could be using caged protein as a nanocarrier to overcome limitations of other nanoparticles. Using biological protein may achieve a better stability, ideal sizes, no/low-toxic profile, and less immunoreaction[120]. Although caged protein delivery has not been studied for HIV treatment, recent studies have shown early applications of using virus-like particles in gene therapy and cancer research. Overall, nanotechnology is likely to provide a new approach for delivery of CYP substrates for a long-term HIV therapy. In order to move to the clinical use, further research is required including long-term adverse reactions, systemic toxicities, accumulation of nanomaterials, and their interactions with plasma proteins.

Article highlights.

• Most of the antiretroviral drugs (ARVs) are metabolized by cytochrome P450 (CYP) pathway and majority of these drugs are also either CYP inhibitors or inducers and few possesses both activities.

• These CYP substrates, inhibitors, and inducers, when used for HIV treatment in conventional dosage forms, have limitations including low systemic bioavailability, potential drug-drug interactions, and short half-lives. Thus, current ARVs require either pharmacological boosting or regular daily dosing.

• Nanoformulation can be designed based on the need to show the controlled release profile, high permeability, biodegradation, or targeting capability. Although only a few of nanoformulations has reached to the clinical trials for HIV treatment, nanotechnology may provide a new approach for a safe and efficient delivery of ARVs for long-term therapy.

• We reviewed the most commonly used nanoformulation of CYP substrates in HIV treatment including polymeric nanoparticles, solid lipid nanoparticles, and polymer micelles in this article.