Evaluating the safety, pharmacokinetics, and antiparasitic activity of DSM265, a novel antimalarial plasmodium dihydroorotate dehydrogenase inhibitor: a systematic review and meta-analysis of early clinical trials

Abstract

Background

The growing resistance to current antimalarial drugs has stalled the eradication of malaria in endemic countries. DSM265 has recently been studied in phase I and II clinical trials.

Aim

This meta-analysis aims to evaluate the safety, pharmacokinetics (PK), and antiparasitic activity of DSM265 based on available early-phase clinical trials.

Methods

This systematic review (PROSPERO: CRD42024499167) was conducted to identify any relevant clinical trials reporting DSM265 safety and PK data. Five databases were searched, i.e., PubMed, Cochrane CENTRAL, EBSCOhost, Clinicaltrials.gov, and ScienceDirect. Eligible clinical trials on DSM265 that reported safety outcomes and PK parameters were included. The risk of bias was assessed by Cochrane’s Collaboration tool. Meta-analysis was conducted to present the pooled adverse events (AEs) and summary estimates for PK parameters, including maximum drug concentration (C_max [μg/mL]), time to maximum drug concentration (T_max [hours (h)]), elimination half-lives (T_1/2 [h]), and area under the concentration–time curves (AUCs [h·μg/mL]). Subgroup analysis and meta-regression analyses were conducted among various doses and drug formulations.

Results

Seven trials were eligible for systematic review. Overall, DSM265 was associated with increased risks of AEs (relative risk [RR] [95% CI] = 1.46 [1.15, 1.84]); subgroup analysis showed significant risks only among the low-dose (25–250 mg) (RR [95% CI] = 1.86 CI [1.36, 2.54]) and high-dose (600–1200 mg) (RR [95% CI] = 1.67 CI [1.03, 2.72]) subgroups. When given as oral suspension at 400 mg dose, DSM265 achieved C_max: 9.3 μg/mL (95% CI = 7.5, 11.2), T_max: 5.4 h (95% CI = 2.7, 8.2), T_1/2: 112.1 h (95% CI = 91.3, 132.9), and AUC_0-∞h: 1,601.9 h·μg/mL (95% CI = 1,233.5, 1970.3). A substantial heterogeneity in PK parameters was evident and justified in meta-regression, which showed linear dose-PK parameter relationships. DSM265 has been shown to target Plasmodium falciparum DHODH with greater selectivity compared to Plasmodium vivax. Furthermore, the drug did not exhibit anti-gametocyte activity which was consistent with preclinical studies.

Conclusion

In this meta-analysis, DSM265 demonstrated a favorable safety profile after a single 400 mg dose. While preclinical signals of teratogenicity and testicular toxicity have halted further development, these effects were not reported in the included clinical trials. Substantial variability in PK parameters was noted, driven primarily by administered doses.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12936-026-05826-y.

Introduction

DSM265 has emerged as a potential candidate for antimalarial treatment and chemoprophylaxis, with the added advantage of improved convenience and medication adherence [1, 2]. This is also considering that the progress toward malaria eradication has stalled globally. According to the World Health Organization’s (WHO) World Malaria Report 2025 annual report, malaria incidence in 2024 reached 64 cases per 1000 people at risk, which is more than threefold higher than the Global Technical Strategy (GTS) target level of 18 cases per 1000. Overall, incidence has risen by 8.5% between 2015 and 2024 [3], 4. Furthermore, across 80 malaria endemic countries, there were approximately 282 million malaria cases reported in 2024, which was an increased of 9 million cases (3%) compared to 2023 [3], 5, 6. Considering the WHO’s ambitious goals of the overall reduction of morbidity and mortality of malaria over the next 15 years by 90%, the current trends do not seem encouraging.

Part of the challenges in eradicating malaria infection in recent years were largely attributed to the growing rate of resistance, particularly in endemic countries [7, 8]. This includes the spread of P. falciparum Kelch13 (PfKelch13) in western Cambodia, the Lao People’s Democratic Republic, and Papua New Guinea, among others [8–11] resulting in high failure of artemisinin-combination therapy (ACT) (13.5 to 22.6%) [4, 9]. The increase in ACT therapeutic failure has also been reported in sub-Saharan Africa, from 0.4% in 2016 to as high as 4.6% in 2019 [11].

DSM265 belongs to a triazolopyrimidine compound that selectively antagonizes the plasmodium dihydroorotate dehydrogenase (pDHODH) enzyme that catalyzes de novo DNA polymerization and pyrimidine synthesis [12]. The structural variations in the ubiquinone-binding site, and the more hydrophobic and larger active site pocket of pDHODH compared to human DHODH (hDHODH) enables the selective inhibition by DSM265 [1]. In addition, unlike human who can synthesize pyrimidines via both the de novo and salvage pathways, Plasmodium lacks a salvage pathway for pyrimidine synthesis and depends entirely on DHODH [13], with absolute reliance to pDHODH for parasite survival [14, 15].

In-vitro and animal studies have demonstrated selectivity for pDHODH and good antiparasitic activities in blood-stage (erythrocytic) and liver-stage (pre-erythrocytic) parasites [15–17]. Furthermore, early clinical trials have demonstrated good pharmacokinetic (PK) profiles, safety, and potential efficacy of single-dose DSM265 in patients with malaria [18–21]. McCarthy et al. [19] was the first phase 1 randomized controlled trial (RCT), which suggested the tolerability of a single ≤ 1200 mg dose of DSM265 and good PK profiles. The study also found that the dose of 340 mg for patients weighing 60 kg is efficacious for Plasmodium (P.) falciparum cure [19]. Furthermore, chemoprophylaxis efficacy was evaluated by Sulyok et al. [18], who found that a single dose of 400 mg confers effective prophylaxis properties when administered one day before a controlled human malaria infection (CHMI). However, the prophylaxis was not as effective when given 1 week before the P. falciparum CHMI [18]. DSM265 also confers more convenience compared to the standard ACT recommendation by the WHO considering that it was hypothesized that a DSM265-based combination treatment might be a single dose cure.

Despite the encouraging prospect, the currently available data on DSM265 safety and PK profiles are derived from relatively small cohorts of patients [18–22]. The available data are also largely inconsistent, with variability in the reported PK parameters and the tolerability of DSM265. For that reason, this meta-analysis aims to summarize the available early human clinical trials on DSM265, focusing on evaluating drug safety, efficacy, and its PK properties.

Methodology

Protocol and registration

This meta-analysis was performed in compliance with the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) reporting guideline and is registered in the International Prospective Register of Systematic Reviews (PROSPERO) under the identification number CRD42024499167.

Literature search strategy

Five electronic databases, i.e., PubMed/MEDLINE, Cochrane CENTRAL, EBSCOHost, Clinicaltrials.gov, and ScienceDirect, were systematically searched using specific keywords to identify all available and relevant prospective clinical trials. All available studies from inception up to January 2024 were retrieved. The original plan of inclusion of studies within the past 10 years was not implemented as the earliest clinical trials were published in 2017. The search keywords were constructed as: ((DSM265[Title/Abstract]) OR (triazolopyrimidine[Title/Abstract]) OR (dihydroorotate dehydrogenase[Title/Abstract]) OR (dihydroorotate dehydrogenase inhibitor[Title/Abstract])) AND ((malaria[Title/Abstract]) OR (plasmodium[Title/Abstract])) and were modified according to the search language of each electronic database. This process was done by two coauthors (MCJ and IS). Furthermore, the references of the retrieved studies were thoroughly reviewed to identify and retrieve any potentially relevant trials. Following the retrieval of available records, the screening process was conducted initially with duplicate screening, followed by screening for the eligibility criteria through title/abstract screening and full-text screening. Eligible studies were included in the meta-analysis.

Eligibility criteria

Studies that met all the following criteria were included in this review: (1) being prospective clinical trials; (2) using the DSM265 drug in the study; and (3) reporting safety outcomes and PK parameters. Dihydroorotate dehydrogenase (DHODH) inhibitors that evaluated conditions other than Plasmodium infection were excluded. Three reviewers (IS, IA, and TK) independently assessed the retrieved records for duplication and compliance with the eligibility criteria. Any dispute between the three reviewers was resolved by discussion with the fourth coauthor (MJ).

Quality assessment

Two reviewers (IA and MG) independently assessed the quality of included trials using Cochrane’s Collaboration tool to assess the risk of biases. This tool evaluates seven key domains: (1) random sequence generation, (2) allocation concealment, (3) blinding of participants and personnel, (4) blinding of outcome assessment, (5) incomplete outcome data, (6) selective reporting, and (7) other potential sources of bias. Each domain is assessed as having a low, high, or unclear risk of bias according to the fulfillment of the criteria. The final evaluation of each trials classifies the study as having a low, high, or unclear overall risk of bias based on the assessment of these seven domains [23, 24].

Data extraction

A standardized extraction form was developed by MJ. Data extraction was performed independently by two authors and a third author served as a tie breaker (MJ, IA, and IS). The data extraction form consisted of following variables: the name of the principal author, year of publication, trial registry, country of the study, design and phase of the clinical trials, blinding status, total sample size, sample size of each arm, sex distribution, mean age, DSM265 dose, DSM265 formulation of DSM265 (i.e., oral suspension, liquid emulsion, spray dry dispersion [SDD]), duration of follow-up, and Plasmodium species being inoculated. Data on PK parameters, namely DSM265 C_max (μg/mL), C_168h (μg/mL), t_max (hours), t_1/2 (hours), AUC_0–∞h (h·μg/mL), and AUC_0–168 h (h·μg/mL), AUC_480h (h·μg/mL), were also recorded on the same form. The reported adverse events were also collected. Any data expressed as median, range, or interquartile range (IQR) were converted into mean and standard deviation via a standardized method [25].

Outcome measures

Early studies on DSM265 showed large variability in administered dose ranges and formulations, ranging from 25 mg to 1200 mg. Most studies use 400 mg dosing regimen. Thus, we categorized the dose as follows: common dose (400 mg), low dose (less than 400 mg) and high dose (more than 400 mg). The primary endpoints of this study were safety and PK parameters across different DSM265 dosing categories and oral formulations. PK outcomes were later adopted in our study to better understand the impact of increasing dose on PK properties as included clinical trials had a broad range of diverse dosing. Efficacy analysis was not feasible given limited number of trials and early trials mostly reported on safety outcomes rather than efficacy analyses. We defined safety outcome as the pooled risk of adverse events (AEs). PK measures encompass DSM265 C_max (i.e., maximum plasma concentration [μg/mL]), C_168h (concentration at 168 h [μg/mL]), t_max (time to maximum concentration [hours]), t_1/2 (elimination half-life [hours]), AUC_0–∞h (area under the curve from zero to infinite hours [hours·μg/mL]), and AUC_0–168 h (area under the curve from zero to 168 h [hours·μg/mL]), and AUC_480h (area under the curve from zero to 480 h [hours·μg/mL]). Furthermore, secondary efficacy outcomes are described qualitatively, which include parasite reduction ratio (PRR), parasite clearance half-life (t½), recrudescence of malarial infection, and prophylactic efficacy of DSM265.

Statistical analysis

The safety endpoint was reported as the pooled relative risk (RR) of AEs. The pooled study-level PK data were regarded as continuous variables and were reported as the overall mean. The forest plots were synthesized using the random-effects/DerSimonian-Laird method to generate summary mean estimates of DSM265 pharmacokinetic parameters owing to considerable heterogeneity between studies. We determined the risk of heterogeneity using the I² statistics. In addition, subgroup analysis was performed based on different dose categories, i.e., common dose (400 mg), low dose (25–250 mg), and high dose (600–1200 mg). The cutoff was determined because all included trials employed a 400 mg dosing regimen alongside the alternative dosing regimens. Subset subgroup analysis was also carried out among the common dose subgroups based on oral drug formulations, i.e., SDD, oral suspension, and liquid emulsion. Meta-regression analysis was conducted to demonstrate the linearity of dose-pharmacokinetic relationships across study endpoints. All statistical analyses were carried out using OpenMeta [Analyst] software v.10.12. Prediction intervals (95% PI) were calculated to indicate the expected range of true effects in future similar settings, using the Higgins-Thompson-Spiegelhalter formula: PI = μ̂ ± t(k − 2) × √(τ² + SE²)."

Result

Literature search results

The PRISMA flow chart of the study is depicted in Fig. 1. A total of 291 studies were identified from five different databases, namely PubMed/MEDLINE (n = 185), Cochrane CENTRAL (n = 17), EBSCOHost (n = 38), Clinicaltrials.gov (n = 6), and ScienceDirect (n = 45). Following the exclusion of duplicate records (n = 59), titles/abstracts screening excluded 222 records due to the following reasons: book chapter (n = 2); review (n = 25), non-human study (n = 43), irrelevant studies (n = 136), and non-clinical trial study (n = 16). Full-text review of the remaining 10 records excluded non-clinical trial studies (n = 2) and a non-human trial (n = 1). A total of seven trials were subsequently considered eligible for qualitative and quantitative analysis.

Fig. 1.

PRISMA flow chart of the study. PICO, population/intervention/control/outcome

Characteristics of included studies

A summary of the key baseline characteristics of the seven included studies in this review is shown in Table 1. The total pooled sample size was 238 patients, with most of them were males (79%). All clinical trials were phase 1 except for Llanos-Cuentas et al. [20], which was phase 2. The studies were published between 2017 and 2020 in four different countries: Australia, the United States, Peru, and Germany. Participants in the treatment arms of all studies received a single dose of DMS265 apart from McCarthy et al. [22], in which they received the combination of DMS265 plus artefenomel [22]. The DSM265 formulation included oral suspension, solution, emulsion, and SDD with doses ranging from 25 mg to 1,200 mg. The common dose of DSM265 across all studies was 400 mg once. The follow-up duration ranged from 3 to 6 weeks. Targeted plasmodium species were either P. falciparum only [18, 19, 22, 26] or P. falciparum and P. vivax in different study phases [20, 21]. Two studies [19, 27] included healthy, non-infected subjects. The diagnosis and follow-up of malaria in the included studies were principally made through thick blood smear [18, 20, 21] and/or the quantitative reverse-transcriptase polymerase chain reaction (qRT-PCR) which targeted 18S ribosomal DNA [18, 20–22, 26]. Gametocytemia was assessed through microscopic examination by Llanos Cuentas et al. [20], while three blood-stage volunteer infection trials, i.e. McCarthy et al. [19]; McCarthy, et al. [22]; and Collins et al. 26 evaluated gametocytes using PCR study [19, 20, 22, 26]. PCR adjustment was performed in one study to distinguish between true treatment failure, i.e. recrudescence, and a new infection (reinfection) acquired after treatment [20].

Table 1.

Baseline characteristics of the included studies

Author, year, registry	Country	Study design, phase, blinding	Arms	Sample size				Age ± SD	Intervention	Dose (mg)	RoA	FU (w)	Duration of Tx	Plasmodium species
				Σ	Each arm	M	F
McCarthy et al. [19], ACTRN12613000522718 and ACTRN12613000527763	Australia	RCT, 1a, double-blind	Tx 1A	73	6	6	0	26.1 ± 6.8	DSM265	25	oral suspension	3	single dose	NA (healthy subjects)
			Tx 1B		6	6	0		DMS265	75	oral suspension		single dose
			Tx 1C		6	6	0		DSM265	150	oral suspension		single dose
			Tx 1D		8	8	0		DSM265	250	oral suspension		single dose
			Tx 1E		8	8	0		DMS265	250	oral suspension		single dose
			Tx 1F		11	11	0		DSM265	400	oral suspension		single dose
			Tx 1G		6	6	0		DMS265	600	oral suspension		single dose
			Tx 1H		6	6	0		DSM265	800	oral suspension		single dose
			Tx 1I		6	6	0		DMS265	1200	oral suspension		single dose
			Con		18	18	0	27.9 ± 8.9	Placebo	NA	oral solution		single dose
		RCT, 1b, open-label	Tx	9	7	7	0	24.1 ± 2.0	DSM265	150	oral suspension	3	single dose	P. falciparum
			Con		2	2	0	27.0 ± 5.7	Mefloquine	10/kg	oral tablet		single dose
Sulyok et al. [18], NCT02450578	Germany	RCT, 1, double-blind	Tx 1A	8	6	4	2	25.0 (22–28)	DMS265	400	liquid emulsion	4	single dose	P. falciparum
			Con 1A		2	1	1	27.0 (25–29)	Placebo	NA	liquid emulsion		single dose
			Tx 1B	8	6	4	2	25.5 ± 2.05	DSM265	400	liquid emulsion		single dose
			Con 1B		2	1	1	25.0 ± 1.5	Placebo	NA	liquid emulsion		single dose
Llanos-Cuentas et al. [20], NCT02123290	Peru	NRCT, 2a, open-label	Tx 1A	24	13	10	3	36.2 ± 12.1	DSM265	400	oral suspension	4–5	single dose	P. falciparum
			Tx 2A		11	8	3	43.9 ± 17.25	DMS265	250	oral suspension		single dose
		NRCT, 2a, open-label	Tx 1B*	21	5	3	2	35.0 ± 4.9	DSM265	400	oral suspension		single dose	P. vivax
			Tx 2B*		9	5	4	41.9 ± 15.1	DMS265	600	oral suspension		single dose
			Tx 3B*		7	4	3	38.3 ± 15.2	DSM265	800	oral suspension		single dose
Murphy et al. [21], NCT02562872	USA	RCT, 1, double-blind	Tx	24	18	12	12	NA	DSM265	400	oral suspension	6	single dose	P. falciparum (phase 1-2a), P. falciparum and P. vivax (phase 2b)
			Con		6			NA	Placebo	NA	oral suspension		single dose
Collins et al. [26], NCT02573857	Australia	NRCT, 1b, open-label	Tx	16	8	5	3	24.8 ± 4.0	DSM265	400	oral suspension	4	single dose	P. falciparum
			Con		8	8	0	24.9 ± 4.6	OZ439	200	oral suspension		single dose
McCarthy, [22], NCT02389348	Australia	NRCT, 1b, open-label	Tx	13	8	5	3	27.8 ± 12.4	DSM265 + Artefenomel	100	oral suspension	5	single dose	P. falciparum
			Con		5	3	2	23.4 ± 2.3	DSM265 + Artefenomel	50	oral suspension		single dose
Chalon et al., [27], NCT03637517	USA	RCT, 1, open-label	Tx 1A	42	14	11	3	37.9 + 10.78	DSM265	400	SDD	3	single dose	NA (healthy subjects)
			Tx 1B		14	11	3	36.1 + 9.23	DSM265	400	SDD		single dose
			Tx 1C		14	11	3	38.6 + 10.58	DSM265	400	SDD		single dose

ACTRN, Australian New Zealand Clinical Trials Registry; Con, control arm; F (female); FU (follow-up); M (male); NA (Not Applicable); NRCT: non-randomized controlled trial; RCT, randomized controlled trial; RoA (Route of Administration); SD, standard deviation; SDD, spray dry diversion; Tx, treatment arm; w, weeks

Quality of studies

Cochrane risk of bias assessment tool was developed to evaluate the risk of bias in included clinical trials (Table 2). Among the seven included studies, three were regarded as low risk of bias and were deemed to be of good quality [18, 19, 21]; three were considered to be of poor quality [20, 22, 26], and one study by Chalon et al. [27] could not be assessed for methodological quality due to unavailable details on their methodology [27].

Table 2.

Cochrane collaboration tool assessment of the quality of studies

Study	Cochrane collaboration questionnaires1
	Q1	Q2	Q3	Q4	Q5	Q6	Q7	Overall
McCarthy et al. [19]	Low	Low	Low	Low	Low	Low	Low	Good quality
Sulyok et al. [18]	Low	Low	Low	Low	Low	Low	Low	Good quality
Llanos-Cuentas [20]	High	High	Low	Uncertain	High	Uncertain	Low	Poor quality
Murphy et al. [21]	Low	Low	Low	Low	Low	Low	Low	Good quality
Collins et al. [26]	High	High	Low	Uncertain	High	Uncertain	Low	Poor quality
McCarthy, [22]	High	High	Low	Uncertain	High	Uncertain	Low	Poor quality
Chalon et al., [27]	NA	NA	NA	NA	NA	NA	NA	NA

1 Questions included: Q1, Random sequence generation; Q2, Allocation concealment; Q3, Selective reporting; Q4, Other Bias; Q5, Blinding of participants and personnel; Q6, Blinding of outcome assessment; Q7, Incomplete outcome data. NA, not assessed

Overall risks of adverse events

As illustrated in Fig. 2A, there was a significant pooled risk of AEs in the oral suspension DSM265 arm (RR [95% CI] = 1.46 [1.15, 1.84], I² = 54.48%). However, a significant increase in the AE risk was only reported among the low- (25–250 mg) (RR [95% CI] = 1.86 CI [1.36, 2.54], I² = 29.14%) and high-dose subgroup (600–1200 mg) (RR [95% CI] = 1.67 CI [1.03, 2.72] I² = 0.00%) compared to the control arms. No difference was demonstrated among various DSM265 formulations of 400 mg dose. The summary of AEs is provided in the Supplementary materials, Appendix 1, Table 1. The most frequently reported side effects among those receiving DSM265 (n = 140) were mild, the most common of which were headache (n = 42/140), pyrexia (n = 29/140), fatigue (n = 22/140), myalgia (n = 16/140), and nausea (n = 11/140).

Fig. 2.

Rate of overall adverse events with subgroup analysis based on the dose of oral formulation (A) and subset group analysis of 400 mg dose based on oral formulation (B)

There were no serious AEs (SAEs) reported across all included trials which were attributed to the drug. McCarthy et al. [19] reported 1 (for unclear reason) and 2 SAEs (one participant with multiple injuries due to accident and another participant with Bell’s palsy) in patient in part 1 and 2 of the study, respectively, all of which was unrelated to studied drug [19]. Llanos Cuentas et al. [20] reported one event of bacteremia occurred in P. falciparum patient receiving 250 mg of DSM265 [20]. In Sulyok et al. [18] trial, one patient in cohort 1 developed bilateral pulmonary embolism, which was mostly attributed to the participant’s long flight and oral contraceptives use; whereas in cohort 2, two participants had asymptomatic hyperkalemia which was categorized as severe but deemed attributed to sampling error [18]. Meanwhile, McCarthy et al. [19] study showed one subject that developed elevated aspartate transaminase of > 10 times the upper limit of normal (ULN) with concurrent elevated creatine kinase of > 170 times ULN. This was not considered to be related to study interventions and was attributed to resumption of weightlifting program after periods of inactivity [18–22]. It should be noted that no mortality occurred in any of included trials (Table 3).

Table 3.

Efficacy outcomes reported by included studies

Study	Arms	DSM265 dose	Malaria species	Efficacy parameters
				PRR48 (log10)	Parasite clearance t½ (hours)	Gametocytemia	Recrudescence
McCarthy et al. [19]	Cohort 2	DSM265 150 mg (n = 6)	P. falciparum	1.55 (1.42—1.67)	9.4 (8.7—10.2)	Detection of pfs25, which indicates gametocytemia, was demonstrated 5 days following DSM265 administration	All participants receiving DSM265 developed recrudescence between 10–22 days
Llanos Cuentas et al. [20]	Cohort 2A	DSM265 250 mg (n = 7)	P. falciparum	3.1 (1.6–5.6)	4.7 (2.6—9.3)	62.5% of patients infected with P. falciparum had microscopically negative gametocytemia at the start of therapy, which became positive for gametocytes on day 28. Two patients with initial positive results had persistently positive gametocytes after day 28	4 patients (26.7%) with P. falciparum infection developed recrudescence
	Cohort 1A	DSM265 400 mg (n = 8)	P. falciparum	2.9 (1.8 – 9.6)	5.0 (1.5—8.0)
	Cohort 1B	DSM265 400 mg (n = 4)	P. vivax	0.77 (0.63 – 1.5)	19 (9.9—23)	33% of patients infected with P. vivax who had no gametocytemia at baseline developed gametocytemia at day 28. No positive gametocytemia after day 5 among those with baseline-positive gametocytemia (n = 3)	Recrudescence could not be reliably assessed As DSM265 was not sufficiently effective. Only one participant with cleared parasites by day 7 without recrudescing by day 14
	Cohort 2B	DSM265 600 mg (n = 9)	P. vivax	1.5 (0.57 – 2.6)	9.4 (5.6—25)
	Cohort 3B	DSM265 800 mg (n = 6)	P. vivax	1.2 (0.45 – 2.5)	12 (5.7—32)
McCarthy, et al. [22]	Cohort 1*	DSM265 100 mg (n = 8)	P. falciparum	2.80 (2.56—3.04)	5.17 (4.76—5.65)	Presence of low-level gametocytemia (1—330 female gametocytes/ml) in all subjects 7 days following therapy	Recrudescence reported in 62.5% of subjects between days 19 – 28
		DSM265 50 mg (n = 8)	P. falciparum	2.71 (2.57—2.85)	5.33 (5.07—5.62)		Recrudescence reported in all subjects between days 15 – 22
Collins et al. [26]	Tx	DSM265 400 mg (n = 8)	P. falciparum	2.78 (2.61—2.95)	5.20 (4.90—5.53)	Low-level gametocytemia (15 to 937 gametocytes/mL) starting from day 9 of therapy, predominantly female gametocytes. No decrease in gametocytes following second dose of DSM265	No recrudescent asexual parasitemia developed in any participant

*Both arms received Artefenomel 200 mg in addition to DSM265. P. falciparum. Plasmodium falciparum; P. vivax, Plasmodium vivax; PRR₄₈, parasite reduction ratio at 48 h; t½, half-life

Pharmacokinetics analysis

Details on the differences of the pharmacokinetics parameters among different formulations are displayed in Table 4. All forest plots and meta-regression plot analyses of DSM265 PK parameters are displayed in Supplementary materials, Appendix 2.

Table 4.

Differences in pharmacokinetics of 400 mg doses in different formulations

Study, year, registry	Formulation	DSM265 dose	Cmax (μg/mL)		tmax (h)		t1/2 (h)		C168h (μg/mL)		AUC480 (h·μg/mL)		AUC0–∞ (h·μg/mL)		AUC0–168 (h·μg/mL)
			Mean	SD or range	Mean	SD or range	Mean	SD or range	Mean	SD	Mean	SD	Mean	SD or range	Mean	SD
McCarthy, et al. [19], ACTRN12613000522718	Oral suspension	400 mg	11.5	3.22	4	(2–4)	96	26.88	2.5	0.9	1160	371.2	1210	435.6	NA	NA
Sulyok et al. [18], NCT02450578	Liquid emulsion	400 mg	7.06	1.04	8.08	6.58	118	36.9	NA	NA	NA	NA	967	272	579	75.7
	Liquid emulsion	400 mg	11.3	2.03	8.08	6.58	119	37.2	NA	NA	NA	NA	1630	452	968	135
Llanos-Cuentas et al., [20], NCT02123290	Oral suspension	400 mg	7.03	2.11	8.1	(2.0–24)	96.7	35.78	NA	NA	NA	NA	NA	NA	638	153.12
	Oral suspension	400 mg	7.88	2.84	5	(2.0–24)	115	41.4	NA	NA	NA	NA	NA	NA	657	183.96
Murphy et al. [21], NCT02562872	Oral suspension	400 mg	11.2	5.9	14.3	(1–72)	108.60	30.7	NA	NA	NA	NA	1706	939	NA	NA
Collins et al. [26], NCT02573857	Oral suspension	400 mg	9.99	7.8–14.5	2	1–24	140	106–164	NA	NA	NA	NA	1807.6	1598.2 – 2049.8	NA	NA
Chalon et al., [27], NCT03637517	SDD	400 mg	15.3	4.13	2.4	1.4	NA	NA	4.09	1.02	NA	NA	1960	568.4	1100	154
	SDD	400 mg	14.2	3.98	2.1	0.9	NA	NA	3.54	0.89	NA	NA	1760	457.6	987	167.8
	SDD	400 mg	11.2	3.02	11.4	8.4	NA	NA	4.2	1.01	NA	NA	2040	469.2	1160	255.2

NA not available; SD standard deviation; SDD spray dried dispersion;

C_max

The overall pooled mean of oral suspension DSM265 C_max (μg/mL) was 9.0 μg/mL (95% CI = 7.4, 10.7; 95% PI = 0.4, 17.6). The mean C_max (μg/mL) across oral formulation dose subgroups were as follows: (a) common dose: 9.3 μg/mL (95% CI = 7.5, 11.2); (b) low dose: 5.2 μg/mL (95% CI = 3.3, 7.0); high dose: 16.5 μg/mL (95% CI = 11.1, 22.0). High heterogeneity was observed among different formulations in the 400 mg dose (I² = 91.95%), with liquid emulsion DSM265 C_max of 9.1 μg/mL (95% CI = 5.0, 13.3) in oral suspension and 13.5 μg/mL (95% CI = 10.9, 16.0) in SDD. Meta-regression demonstrated a linear dose-C_max relationship (coefficient = 0.018, p = 0.001; Fig. 1.C. Appendix 2, Supplementary materials).

C_168h

Overall, the pooled mean of oral suspension DSM265 C_168h (μg/mL) was 2.8 μg/mL (95% CI = 2.0, 3.5; 95% PI = 0.1, 5.4), with subgroup analysis based on dose categories as follows: (a) common dose: 2.5 μg/mL (95% CI = 1.7, 3.3); (b) low dose: 1.1 μg/mL (95% CI = 0.4, 1.7); (c) high dose: 6.4 μg/mL (95% CI = 3.0, 9.8). Among the 400 mg dose, the SDD subgroup had a mean C_168h (μg/mL) of 3.9 μg/mL (95% CI = 3.5, 4.3). Meta-regression demonstrated a linear dose- C_168h relationship (coefficient = 0.008, p = 0.001; Fig. 3.C. Appendix 2, Supplementary materials).

Fig. 3.

Funnel plot for assessment of publication bias

t_max

The pooled mean of t_max (hours) was 2.7 h (95% CI = 2.2, 3.3; 95% PI = 0.7, 4.6). Furthermore, the t_max (hours) of the subgroups were: (a) common dose: 5.4 h (95% CI = 2.7, 8.2), (b) low dose: 2.0 h (95% CI = 1.9, 2.1), and (c) high dose: 3.2 h (95% CI = 1.9, 4.6). High variability was observed among various formulations in 400 mg dose (I² = 86.6%); the t_max (hours) of SDD was 3.2 h (95% CI = 1.6, 4.9), whereas that of liquid emulsion was 8.1 (95% CI = 4.4, 11.8). Meta-regression did not demonstrate a linear dose- t_max relationship (coefficient = 0.001, p = 0.364; Fig. 4.C. Appendix 2, Supplementary materials).

t_1/2

The pooled analysis of oral suspension DSM265 t_1/2 (hours) across subgroups demonstrated the following: (a) overall: 102.6 h (95% CI = 93.6, 111.6; 95% PI = 89.5, 115.7); (b) common dose: 112.1 h (95% CI = 91.3, 132.9), (c) low dose: 96.6 h (95% CI = 90.4, 102.8); and (d) high dose: 103.6 h (95% CI = 89.3, 117.9). The liquid emulsion formulation revealed a higher mean t_1/2 (hours) compared to oral suspension (t_1/2 [hours] = 118.5 [95% CI = 97.5, 139.5]). Meta-regression did not demonstrate a linear dose- t_1/2 relationship (coefficient = 0.021, p = 0.121; Fig. 2.C. Appendix 2, Supplementary materials).

AUC_0-∞h, AUC_0-168 h, and AUC_0-480 h

The pooled AUC_0-∞h (h·μg/mL) mean among oral suspension DSM265 was 1372.5 h·μg/mL (95% CI = 1065.8, 1679.1; 95% PI = 195.7, 2549.3); the AUC_0-∞h (h·μg/mL) for different dose categories were as follows: (a) common dose: 1601.9 h·μg/mL (95% CI = 1233.5, 1970.3); (b) low dose: 465.5 h·μg/mL (95% CI = 326.1, 604.8); and (c) high dose: 3013.7 h·μg/mL (95% CI = 1471.4, 4556,0). Meta-regression demonstrated a linear dose- AUC_0-∞h relationship (coefficient = 3.535, p = 0.001; Fig. 5.C. Appendix 2, Supplementary materials). Furthermore, subset subgroup analysis of the common dose revealed a higher AUC_0-∞h (h·μg/mL) h·μg/mL with SDD formulation (AUC_0-∞h = 1914.3 [95% CI = 1741.0, 2087.5 h·μg/mL]) compared to other formulations.

Furthermore, the overall AUC (h·μg/mL) was 669.3 h·μg/mL (95% CI = 456.2, 882.4; 95% PI = 20.7, 1317.9) and high dose (AUC_0-168 h = 901.1 h·μg/mL [95% CI = 572.5, 1229.7]). Meta-regression demonstrated a linear dose- AUC_0-∞h relationship (coefficient = 1.49, p = 0.001; Fig. 6.C. Appendix 2, Supplementary materials). Among the 400 mg dose subgroup, the SDD subgroup demonstrated a higher AUC_0-168 h of 1074.6 h·μg/mL (95% CI = 979.1, 1170.1). Similar patterns with a greater amplitude were also observed in the AUC_0-480 h (h·μg/mL). There was a linear dose-AUC demonstrated in the meta-regression analysis. Meta-regression demonstrated a linear dose- AUC_0-480 h relationship (coefficient = 3.273, p = 0.001; Fig. 7. Appendix 2, Supplementary materials). AUC_0-480 h was 1228.9 h·μg/mL (95% CI = 935.0, 1522.7; 95% PI = 73.8, 2384.0).

Efficacy outcomes

The majority of early safety trials reported some insights into DSM265 efficacy outcomes. The logarithmic parasite reduction ratio at 48 h (PRR₄₈log₁₀) was reported in 4 studies (Table 3). McCarthy et al. [19] found a median PRR₄₈log₁₀ of 1.55 (1.42 – 1.62) following DSM265 150 mg administration, corresponding to a parasite clearance t½ of 9.4 h [19].

As in pre-clinical studies, DSM265 did not exhibit anti-gametocyte activity. Four included studies reported the persistence of gametocytes, although in low concentrations, following DSM265 administration. McCarthy, et al. [22] reported a low-level gametocytemia in all subjects, ranging from 1–330 gametocytes/mL 7 days following therapy [22]. Collins et al. [26] demonstrated no decrease in gametocyte levels following the administration of second-dose DSM265 [26]; rescue treatment with artemether-lumefantrine and primaquine was given to all participants (n = 8). The gametocytes were predominantly female [22, 26].

Recrudescence was variably reported across studies; only one study reported no recrudescence following the DSM265 administration [26], which may be explained by the administration of rescue therapies for persistent gametocytemia. The > 50% recrudescence rate of P. falciparum infection was reported in two studies [19, 22], whereas one study reported a rate of 26.7% [20].

Two studies assessed the potential use of DSM265 for malarial prophylaxis. Sulyok, et al. [18] suggested that a single-dose DSM265 of 400 mg demonstrated a causal prophylactic role when given 1 day before infection [18]. However, Murphy et al. [21] found that only one-third of participants were protected against the infection following CHMI with direct venous inoculation of sporozoites and mosquito bites [21].

Overall heterogeneity

Our analysis suggests a high between-study heterogeneity among DSM265 PK parameters (I² =  > 75%) (Supplementary Materials, Appendix 2). Such heterogeneity findings were partly attributed to different dosing regimens; but did not appear to be related to different drug formulations. The linear dose-PK relationships also supported the assumption of the influence of dosing regimens as the source of heterogeneity.

Publication bias assessment

The risk of publication bias in this study was regarded as low, as demonstrated by the symmetrical funnel plot (Fig. 3) and the non-statistically significant Egger’s regression test for publication bias (p-value = 0.40).

Discussion

Resistance to current antimalarial drugs is a serious global concern. To date, there is a wide variety of available antimalarial medications, e.g., chloroquine, sulfadoxine-pyrimethamine, mefloquine, atovaquone, and artemisinin derivatives; the current guidelines suggest artemisinin-based combination therapy (ACT) as the most potent and should be considered as the first-line antimalarial choice. Nevertheless, there have been increasing reports of the growing resistance of malaria parasites to these treatment regimens [3, 4, 28]. Thus, the development of new drugs to treat malaria is an essential step to address this concern, and DSM265 holds promising potential. Our meta-analysis suggests that the commonly used 400 mg dose appeared safe and did not contribute to significant AEs. On the other hand, both lower and higher doses were found to be associated with a higher risk of AEs compared to the control arms. The main AE reported in most participants receiving DSM265 was headache (25%); others included pyrexia, myalgia, fatigue, and nausea. No SAEs reported that were attributed to DSM265. Pharmacokinetic parameters were heterogeneous across studies and were observed to have a linear dose-PK relationship.

We assume that the pharmacokinetic properties of DSM265, particularly the long plasma elimination t½, support the single 400 mg regimen as an effective regimen against mainly plasmodial asexual and pre-erythrocytic agents. It was demonstrated that the 400 mg dose possesses the ability to maintain plasma concentrations above the minimum inhibitory concentration (MIC) for an extended period of time. A phase-1 RCT found that the single-dose regimen demonstrates the capability to sustain plasma concentrations at or above MIC levels for over 8 days [19]. This prolonged duration of therapeutic levels in the bloodstream likely plays a crucial role in the overall effectiveness of the 400 mg regimen. The clearance rate of P. falciparum following 400 mg of DSM265 administration was also comparable to other antimalarial agents, including ferroquine (PRR₄₈log₁₀ = 2.21, parasite clearance t½ = 6.5 h) and mefloquine (PRR₄₈log₁₀ = 2.34, parasite clearance t½ = 6.2 h) [19, 22]. However, Llanos Cuentas et al. [20] study had not been able to demonstrate a similar degree of parasite clearance against P. vivax [20]. It is therefore understood that DSM265 falls into the category of relatively slow acting anti-malarial agents, akin to agents such as atovaquone, sulfadoxine-pyrimethamine, and proguanil, due to its mechanism of selectively inhibiting Plasmodium dihydroorotate dehydrogenase (DHODH), which gradually depletes pyrimidine pools and slows parasite replication. This contrasts with other drugs such as artesunate, cipargamin, artefenomel, and ganaplacide act rapidly by directly targeting multiple parasite stages or essential cellular processes, resulting in markedly faster parasite clearance [15].

Furthermore, it was demonstrated across clinical trials that DSM265 does not inhibit gametocytogenesis and eliminate mature gametocytes [22, 26]; this was consistent with in-vitro studies that indicated no activity of DSM265 against gametocytes [15]. Furthermore, the synthesis of pyrimidine nucleotides, the process blocked by DSM265, is downregulated in nonreplicating gametocytes [29]. Thus, it is important to consider the addition of gametocidal antimalarial agents to the DSM265 regimen to inhibit both early- and late-stage (mature) gametocytes. Furthermore, it is important to note that different formulations have different properties. Among the three different formulations used in across studies (i.e. oral suspension, liquid emulsion and spray dried dispersion) spray dried dispersion appears to achieve greater pharmacokinetic properties at therapeutic dose of 400 mg which might reflect to better efficacy [27]. However, as it was only reported in one trial, the evidence is substantially lacking to support the benefits.

Strengths and limitations

DSM265 is regarded as a promising novel antimalarial candidate for malaria treatment. The prospect of a single-dose regimen with DSM265 based on the early data represents a notable advancement in achieving malaria eradication and combating the resistant strains. To our knowledge, this is the first meta-analysis that attempts to understand the risks, benefits, efficacy and PK profiles of DSM265 based on early clinical trial data. Hence, our analysis allows a better understanding of DSM265 clinical safety in humans and its PK profiles after single-dose administration. Furthermore, subgroup analysis and meta-regression analysis determined the impacts of how different doses affected the study outcomes. Similarly, the subset analysis of the 400 mg drug formulations also showcased the impacts of various drug formulations of the same dosing regimen on the study outcomes.

However, some limitations exist in our study. First, the individual patient data (IPD) meta-analysis could not be performed. Our initial request to the corresponding authors was declined due to ethical issues pertaining to participants’ consent. No pregnant women and children were included any included study. The data were also mostly derived from male participants. The exclusion of women was partly influenced by the contraceptive requirements, which posed challenges to recruiting female participants. The analysis of these specific populations is pertinent since many recommended antimalarial drugs are contraindicated or should be used with caution when treating malaria. Similarly, quantitative analysis of the efficacy outcomes, i.e., PRR₄₈log₁₀ and parasite clearance t½ was not performed due to inadequate data. Another difference that contributed to the heterogeneity of the results (especially the safety) were the differences across the studies in the doses used, types of the parasite, differences in the follow up and time of assessment of the outcomes. Furthermore, the studies by McCarthy et al. [19], Sulyok et al. [18], and Murphy et al. [21], were CHMI with small parasite inoculum and parasitemia whilst Llanos Cuentas et al. [20] was a field study with naturally infected patients and higher parasite densities [18–21]. It is noteworthy, however, that the development of DSM265 has been suspended due to off-target toxicities observed in some preclinical studies, including teratogenicity and testicular toxicity [30]. Both concerns were not reported as no pregnant women were included (or unknown pregnancy status) and no investigations into sperm count were conducted to identify risk of teratogenicity and testicular toxicity, respectively, in any of included trials. Including pregnant women is completely unethical given the teratogenic signal. As a result, as of now, further clinical trials are currently unrealistic to bridge the gaps in understanding DSM265. Prediction intervals were calculated in order to provide estimates of the expected ranges of PK parameters in future similar populations. Given the small number of studies and substantial heterogeneity, these prediction intervals are wide and should be interpreted with caution.

Conclusion

This meta-analysis suggests that DSM265 is safe when given at a standard single dose of 400 mg. The elimination t½ of oral DSM265 was long and showed an increase in the t½ with increased dose. Similarly, dose-PK relationships, (i.e. C_max, T_max, AUC, among others.) were proportional to the increasing dose across other PK parameters. DSM265 is mainly effective against plasmodial asexual stages. The efficacy against P. vivax was also limited. The status of DMS265 clinical trials is currently suspended due to concerns on teratogenicity and testicular toxicity derived from preclinical studies, concerns of which was not investigated in included trials.

Author contributions

Conceptualization, MJ. and IS.; methodology, MJ and IS.; software, MJ and IS.; validation, LCM and MMA.; database searching, MJ and ID.; reports screening, MJ, IS, IA, and TK.; quality, MG and IA.; data extraction and analysis, MJ and ID,: writing—original draft preparation, TK, MG, IA, MJ, and IS; writing—review and editing, MMA and LCM.; visualization, MJ.; supervision, LCM.; project administration, MJ;. All authors have read and agreed to the published version of the manuscript.

Funding

Open access funding provided by Datta Meghe Institute of Higher Education and Research. This research received no internal or external funding.

Data availability

The data presented in this study are available on request from the corresponding author.

Declarations

Conflicts of interest

The authors declare no competing interests.