Topical pravibismane as adjunctive therapy for moderate or severe diabetic foot infections: A phase 1b randomized, multicenter, double‐blind, placebo‐controlled trial

Abstract

This Phase 1b study was designed to evaluate the safety and efficacy of pravibismane, a novel broad‐spectrum topical anti‐infective, in managing moderate or severe chronic diabetic foot ulcer (DFU) infections. This randomized, double‐blind, placebo‐controlled, multicenter study consisted of 39 individuals undergoing pravibismane treatment and 13 individuals in the placebo group. Assessment of safety parameters included clinical observations of tolerability and pharmacokinetics from whole blood samples. Pravibismane was well‐tolerated and exhibited minimal systemic absorption, as confirmed by blood concentrations that were below the lower limit of quantitation (0.5 ng/mL) or in the low nanomolar range, which is orders of magnitude below the threshold of pharmacological relevance for pravibismane. Pravibismane treated subjects showed approximately 3‐fold decrease in ulcer size compared to the placebo group (85% vs. 30%, p = 0.27). Furthermore, the incidence of ulcer‐related lower limb amputations was approximately 6‐fold lower (2.6%) in the pooled pravibismane group versus 15.4% in the placebo group (p = 0.15). There were no treatment emergent or serious adverse events related to study drug. The initial findings indicate that topical pravibismane was safe and potentially effective treatment for improving recovery from infected chronic ulcers by reducing ulcer size and facilitating wound healing in infected DFUs (ClinicalTrials.gov Identifier NCT02723539).

1. INTRODUCTION

Diabetic foot ulcers (DFUs), which are typically related to suboptimal glycaemic control, peripheral neuropathy, and poor foot care, occur in up to 34% of persons with diabetes mellitus. ¹ , ² DFUs are typically colonized with a mixture of microbial flora, usually including aerobic gram‐negative and gram‐positive bacteria, as well as obligate anaerobes. ³ Unless adequately treated, at least half of DFUs will become infected. Such infections result in inflammatory changes, which may delay wound healing, ⁴ and can lead to sepsis. Approximately 20% of people with DFU will require some form of lower extremity amputation, ¹ usually to deal with progressive infection. Many microorganisms can be isolated from DFU, but the most common pathogens in clinically infected wounds are Staphylococcus aureus, followed by beta‐haemolytic streptococci, coagulase‐negative staphylococci and Pseudomonas aeruginosa. ³

Accumulating evidence suggests that bacterial pathogens in diabetic foot infections (DFI) exist at least in part as biofilms, which are structured, self‐organized communities of adherent bacteria that can typically withstand most host defenses and antimicrobial therapy. ⁵ These biofilm infections are more resistant to currently available systemic antimicrobial therapy, leading to poor outcomes, such as amputations and poor quality of life. ⁶ , ⁷ Most DFIs are treated with systemic antibiotics, but topical agents may have a beneficial role in properly selected cases. ⁸ Topical agents have the potential advantage over systemic therapy of requiring small doses only directly on the infected wound, which achieve high local levels, all without the risk of systemic adverse effects. Eradicating pathogens in the wound should help resolve the infection and may also improve wound healing. The recognition of the increasing prevalence of antibiotic‐resistant biofilm organisms in DFI has led to efforts to develop new broad‐spectrum anti‐biofilm agents. Of particular interest are agents that can be administered topically, specifically at the site of infection, at a small dose, as these can potentially reduce time to wound healing while avoiding systemic adverse events and the development of antibiotic resistance.

One such new agent is pravibismane, the first drug in a new class of therapeutics with a novel mechanism of action and broad‐spectrum anti‐infective and anti‐biofilm activity, including against antibiotic‐resistant organisms ⁹ that are commonly associated with DFI. Pravibismane disrupts bacterial bioenergetics by reducing bacterial concentrations of adenosine triphosphate in both planktonic and biofilm phenotypes and exhibits potent anti‐biofilm activity against DFI‐relevant pathogens, such as S. aureus and P. aeruginosa. ⁹ , ¹⁰ Prior to clinical testing, pravibismane was extensively evaluated for safety both in vitro and in vivo. In vivo topical GLP toxicology studies (90 days of repeat dosing and 28 days of repeat dosing), both resulting in systemic exposure, demonstrated no systemic toxicity and no observed cardiac effects via electrocardiogram testing in any of the pravibismane dose groups. It is important to note that systemic levels of pravibismane have been in the nanomolar range in all in vivo and clinical testing to date, reducing the likelihood of systemic toxicity and helping to establish pravibismane's safety margin.

The primary objective of this Phase 1b randomized, double‐blind, placebo‐controlled, multicenter trial was to evaluate the safety and tolerability of topical pravibismane (MBN‐101) used as an adjunct to standard of care in subjects with a moderate or severe DFI. Secondary objectives of the study were to evaluate the effect of adjunctive treatment with topical pravibismane on reducing ulcer size, preventing lower extremity amputation and resolution of infection.

2. MATERIALS AND METHODS

This was a randomized, double‐blind, placebo‐controlled, multicenter study in subjects with diabetes mellitus and a foot ulcer that was present for ≥28 days that had an infection classified as moderate or severe according to the Infectious Disease Society of America (IDSA) infection severity rating ¹¹ scheme. This was a multiple ascending dose study performed at five study sites in the United States where subjects were enrolled into cohorts (N = 12–15 per cohort) receiving either pravibismane at concentrations of 150, 375 or 750 μg/mL (resulting in doses of 3, 7.5 and 15 μg/cm²) or placebo, at a ratio of 3:1 (pravibismane to placebo). Pravibismane dose volume was administered based on ulcer area, with a minimum of 0.2 mL administered for ulcers ≤10 cm² up to a maximum of 4 mL for ulcers 200 cm² in size (maximum ulcer area allowed to be included in the study). A member of the study team explained to each subject the study rationale and investigational goals. Prior to the initiation of any study procedures, each subject signed and dated an informed consent form. The study plan and protocol were reviewed by the Sterling Institutional Review Board and received approval on January 27, 2017.

During a visit by each enrolled patient to the clinic, investigators topically applied either pravibismane or placebo to the ulcer three times per week, for 2–3 weeks. The wound was covered with a non‐antimicrobial dressing after application of either pravibismane or placebo. Based on the characteristics of the wound, particularly the amount of exudate, one of the following three wound dressings were selected: Optilock (Medline), Enluxtra (OSNovative systems) or Comfeel Plus (Coloplast). The decision to stop pravibismane treatment after a minimum of 2 weeks was at the discretion of the Principal Investigator and based on the resolution of clinical findings of infection. This treatment of infected DFU was provided as an adjunct to standard of care, which included sharp debridement of necrotic and infected material from the ulcer and systemic (administered orally or parenterally) antibiotic therapy selected based on the recommendations of the IDSA guidelines. ¹¹ Subjects could be included in the study if they had received antibiotic therapy for no more than 36 h immediately prior to presentation, or if they had evidence of failure of whatever antibiotic therapy they had received prior to enrolment. Subjects could only be enrolled if they had adequate arterial perfusion in the affected limb, defined as having at least one of the following: palpable dorsalis pedis or posterior tibial pulses; normal Doppler wave forms; a toe brachial index [TBI] ≥ 0.75; or an ankle brachial index [ABI] of >0.9. When needed, all subjects were prescribed, and required to adhere to, proper pressure off‐loading of the foot ulcer, as directed by the treating physician. Subjects were evaluated at end of treatment (EOT; 3 days after the last dose), at test of cure (TOC; 2 weeks after EOT) and end of study (EOS; 4 weeks after EOT) (Figure 1).

FIGURE 1.

Schematic representation of the study design.

Assessments of each subject included: documentation of adverse events; measurement of ulcer area by three‐dimensional digital photography (Quantificare Inc. [Alpharetta, GA]); documentation of any lower‐extremity amputations, bacterial reinfection or relapse; and measurement of serum levels for systemic exposure to pravibismane. After cleaning and debriding the ulcer, tissue samples were obtained from non‐epithelialized regions using a dermal curette or scalpel and sent for aerobic and anaerobic microbial culture and antibiotic susceptibility testing to International Health Management Associates (Schaumburg, IL) at baseline and again at EOS. Culture results, in conjunction with clinical examination, were used at EOS to assess for microbial reinfection (with a pathogen different from the index infection) or relapse (with the same pathogen). We defined reinfection as isolation of a new organism from a clinically infected ulcer that was not present on the initial (baseline) culture, and relapse as isolation of the same organism (by genus and species) that was present on the initial culture. Such determinations (reinfection or relapse) were made only after the ulcer was initially confirmed as having eradicated the index infection by the presence of either a sterile culture or a presumed eradication (no material to culture). Because of limitations in the methods used to determine biofilm activity and irregularities in the methods of assessment (imaging using epifluorescence microscope or confocal scanning laser microscope), pravibismane's effect on biofilm eradication could not be reliably assessed. Adverse events occurring after the initiation of the study were coded to system organ class and preferred term using the Medical Dictionary for Regulatory Activities (MedDRA) Version 19.1. A treatment emergent adverse event (TEAE) was defined as one starting after administration of the first dose of study drug. If the adverse event occurred before the first dose, but increased in severity, it was also considered a TEAE. A serious adverse event (SAE) was defined by any of the following outcomes: death; life‐threatening AE; hospitalization, or prolongation of existing hospitalization; a persistent or significant disability/incapacity; or, a congenital anomaly/birth defect. The study data were reviewed by an independent data monitoring committee on an ongoing basis to ensure the safety of all subjects enrolled.

3. RESULTS

A total of 53 subjects were randomized into the study, of which 52 subjects were enrolled in the modified intention to treat (MITT) population, which consisted of all subjects who were randomized and underwent protocol‐defined treatment (1 subject was almost immediately discontinued due to a disqualifying protocol deviation). The safety population, defined as all subjects who received any amount of the study drug (active or placebo), included all 52 subjects. The efficacy results were based on the MITT population. Among the enrolled subjects with a clinically documented non‐responsive DFU (69.2% on the plantar surface and 78.8% in the forefoot) of ≥28 days duration, 49 (92.5%) were <65 years of age, 50 (94.3%) were white, 45 (84.9%) were male, and the mean body mass index was 32.64 kg/m². The mean documented duration of DFU at presentation in the study subjects was 186.4 days. The mean baseline ulcer size, calculated from digital photographs (multiplying the greatest length and width of the ulcer) was: 0.752 cm² in the 3 μg/cm² dose group; 4.354 cm² in the 7.5 μg/cm² dose group; 3.937 cm² in the 15 μg/cm² dose group and 2.731 cm² in the placebo group (Table 1). The mean baseline ulcer depth was: 0.166 mm in the 3 μg/cm² dose group; 0.118 mm in the 7.5 μg/cm² dose group; 0.339 in the 15 μg/cm² dose group and 0.312 mm in the placebo group.

TABLE 1.

Summary of demographic and baseline characteristics for enrolled subjects.

Demographics/characteristics Category/statistic	3 μg/cm2 (N = 12) n (%)	7.5 μg/cm2 (N = 13) n (%)	15 μg/cm2 (N = 15) n (%)	Placebo (N = 13) n (%)	Total (N = 53) n (%)
Age (years)
n	12	13	15	13	53
Mean (SD)	55.4 (10.00)	51.7 (7.99)	50.8 (10.27)	53.6 (7.72)	52.8 (9.01)
Age group
<65 years	10 (83.3)	13 (100.0)	13 (86.7)	13 (100.0)	49 (92.5)
≥65 years	2 (16.7)	0 (0.0)	2 (13.3)	0 (0.0)	4 (7.5)
Gender
Male	11 (91.7)	11 (84.6)	11 (73.3)	12 (92.3)	45 (84.9)
Female	1 (8.3)	2 (15.4)	4 (26.7)	1 (7.7)	8 (15.1)
Race
American Indian or Alaska Native	0 (0.0)	0 (0.0)	1 (6.7)	0 (0.0)	1 (1.9)
Black or African American	0 (0.0)	1 (7.7)	1 (6.7)	0 (0.0)	2 (3.8)
White	12 (100.0)	12 (92.3)	13 (86.7)	13 (100.0)	50 (94.3)
BMI (kg/m2)
n	12	12	15	13	52
Mean (SD)	30.07 (7.110)	30.45 (6.732)	34.10 (5.630)	35.35 (7.024)	32.64 (6.794)
Documented DFU duration (days) a
n	12	12	15	13	52
Mean (SD)	243.9 (287.29)	169.3 (169.58)	86.3 (61.59)	264.4 (354.68)	186.4 (244.92)
Baseline ulcer wound size (cm2) based on digital photographs
n	12	12	15	13	52
Mean (SD)	0.752 (1.1488)	4.354 (11.9367)	3.937 (6.7401)	2.731 (3.5205)	2.997 (6.9498)

Note: Percentage was calculated using the number of subjects in the column heading as the denominator. Baseline was defined as the last measurement or assessment prior to the first dose of study drug.

Abbreviations: BMI, body mass index; DFU, diabetic foot ulcer; SD, standard deviation.

^a Documented DFU duration (days) = date of first dose of study drug − documented start date of DFU.

The severity of DFI was classified as moderate in 50 (96.2%) subjects and severe in 1 (1.9%) subject. The most commonly selected concomitant systemic antibiotic as part of standard of care by the clinical investigators was levofloxacin (49 [94.2%] subjects). Other concomitant medications frequently taken by enrolled subjects included insulin (glargine and others), lisinopril and metformin.

3.1. Ulcer size

The change in ulcer size was based on the percent change from baseline at each subsequent visit in the MITT population. Overall, subjects in all four treatment groups (three pravibismane + SOC groups, one placebo + SOC group) exhibited reduced ulcer size at the EOS visit. Given the small number of subjects enrolled in each dosage group, we elected to pool the results from the three pravibismane treated groups and compare that to the placebo group. The median ulcer size in the pooled pravibismane group was 0.732 cm² and in the placebo group it was 0.888 cm² at baseline. The median percent reduction in ulcer size from baseline at the EOT, TOC and EOS visits were 41.5%, 78.2% and 85.2%, respectively, in the pooled pravibismane groups, and 6.1%, 26.5% and 29.7%, respectively, in the placebo group (Figure 2).

FIGURE 2.

Ulcer size reduction in pooled pravibismane groups compared to that in the placebo group. EOS, end of study (4 weeks after end of treatment); EOT, end of treatment; TOC, test of cure (2 weeks after end of treatment).

Subjects in the pooled pravibismane group (black bars in Figure 2) exhibited a nearly 3‐fold greater reduction in ulcer size compared to the placebo group (grey bars in Figure 2) at EOS. This study was not powered to demonstrate statistically significant differences.

Representative images of the ulcers taken at baseline (day 1), TOC and EOS, in three of the study subjects treated with pravibismane (Figure 3A–C) and one placebo subject (Figure 3D) are shown in Figure 3.

FIGURE 3.

Before and after photographs of ulcers in enrolled subjects treated with pravibismane or placebo. Representative ulcer photographs from three subjects randomized to three different pravibismane dose groups (subjects A–C) demonstrate gradual reduction in ulcer size (2 and 4 weeks after end of treatment) compared to baseline ulcer size. No change in ulcer size was recorded in the subject randomized to the placebo group (subject D). For the purposes of this study, any ulcer located on or distal to the malleolus was considered a diabetic foot ulcer.

3.2. Lower‐extremity amputations

When pooling all subjects randomized to the three pravibismane dose groups, 1 of 39 (2.6%) had a lower extremity amputation related to the target infected ulcer, compared to 2 of 13 (15.4%) subjects in the placebo group, representing an approximately a 6‐fold lower amputation rate in subjects treated with pravibismane.

3.3. Microbiological response and susceptibility of isolated pathogens to pravibismane

At the EOS visit, four (12.5%) of the subjects in the pooled pravibismane dose groups experienced a reinfection or relapse, compared to four (33.3%) subjects in the placebo group. The microbiologically evaluable (ME) population consisted of 44 (83%) subjects. The most common pathogens isolated at baseline in the total ME population were as follows: methicillin‐susceptible S. aureus (MSSA) in 11 (25.0%); methicillin‐resistant S. aureus (MRSA) in eight (18.2%); Enterococcus faecalis in six (13.6%) and P. aeruginosa in five (11.4%) (data in Table S1). Pravibismane demonstrated in vitro efficacy, with low mean minimum inhibitory concentration (MIC) values (0.06–6 μg/mL), against all the aerobic and obligately anaerobic species isolated from DFIs in this study. Mean pravibismane MICs for the most common pathogens isolated at baseline were low: for MSSA 0.21 μg/mL; for MRSA 0.17 μg/mL; for E. faecalis 2.53 μg/mL; and, for P. aeruginosa 1.43 μg/mL. Pravibismane mean MICs for 12 of the 13 anaerobic bacterial species isolated at baseline were ≤1 μg/mL (data in Tables S2–S4).

3.4. Adverse events

In total, 27 (51.9%) of the enrolled subjects experienced a TEAE, but none were considered related to the study drug. The majority of TEAEs were considered mild or moderate in severity; one subject in the placebo group experienced osteomyelitis that was considered severe. TEAEs that occurred in ≥5% of the total study population were as follows: new or worsening/reinfection of target DFI (21.2%); DFU (defined as occurrence of new non‐target ulcer) (17.3%); cellulitis (5.8%); osteomyelitis (5.8%); musculoskeletal and/or connective tissue disorder (7.7%).

In total, 2 (3.8%) subjects, both in the 7.5 μg/cm² pravibismane dose group, experienced a TEAE that led to discontinuation of study drug. One subject had a new infection of a non‐target ulcer, and the other had new osteomyelitis develop under the study ulcer.

A total of 6 (11.5%) subjects experienced at least one SAE, including two subjects in the placebo group. None of the SAEs were considered related to study drug and there were no deaths in the study. The most commonly reported SAEs were as follows: osteomyelitis (3.8%); cardiac disorders (1.9%); gastrointestinal disorders (1.9%) and, infections including DFI (3.8%). Among pravibismane treated subjects, one had new infection of a non‐target ulcer and one had worsening of a target ulcer after completion of study drug treatment. All SAEs that occurred during the study resolved after treatment.

3.5. Clinical evaluations and pharmacokinetics

There were no clinically meaningful mean changes during the study from baseline for values of serum chemistries (e.g., albumin, calcium, bicarbonate, glucose) or haematological parameters (e.g., erythrocytes, leukocytes, lymphocytes, monocytes) in any of the study groups. Vital signs, physical examination findings, and 12‐lead electrocardiogram findings were normal for the majority of assessments, and most findings classified as abnormal were not clinically significant. Additionally, the pharmacokinetics (PK) concentration data collected from a small number of subjects (n = 12) did not indicate any relevant systemic exposure with pravibismane in those treated with the drug.

4. DISCUSSION

The results of this randomized, double‐blind, placebo‐controlled, multicenter, Phase 1b study demonstrated that treatment with topical pravibismane in persons with DFI was safe and well‐tolerated at all doses tested. None of the TEAEs and SAEs occurring in the study were related to study drug. The study results also suggest that treatment with pravibismane was associated with a progressive reduction in DFU size. While this trial was not powered to demonstrate statistical differences for efficacy endpoints between study groups, there was an approximately three‐fold greater reduction in ulcer size in subjects receiving adjunctive pravibismane compared to those receiving placebo. Similarly, the very limited data in this study suggest a possible trend towards a reduction in lower extremity amputation rates and a reduction in infection relapse and reinfection rates in pravibismane, compared to placebo treated DFIs. These preliminary findings suggest that further investigation of these endpoints in future larger clinical studies is warranted.

Pravibismane exhibited broad‐spectrum activity against both aerobic gram‐positive and gram‐negative bacteria, as well as obligately anaerobic bacteria isolated from the DFIs in this study. By MIC testing, bacterial strains cultured from the infected tissue, which were similar to those commonly associated with DFIs, were susceptible to pravibismane at concentrations equal to, or lower than, a panel of comparator antibiotics commonly used to manage such infections (data in Tables S2–S4). In addition, evidence from previous work demonstrating the ability of pravibismane to eradicate bacterial biofilms, ⁹ suggests that it may play a significant role in managing the types of chronic infections common in DFIs, which are frequently complicated by biofilm‐forming bacteria. Based on data reported in a recent abstract, pravibismane exhibited superior antibiofilm activity against P. aeruginosa compared to tobramycin, amikacin, meropenem and ceftazidime. ⁹ Similarly, pravibismane exhibited higher efficacy in eradicating S. aureus MRSA biofilms compared to linezolid and clindamycin. Together, these results suggest that pravibismane is safe for topical administration to DFUs and may be able to eradicate infecting organisms, even in biofilms, which may lead to more rapid wound healing. These possible benefits must, of course, be confirmed by larger, well‐designed clinical trials.

While the results of this study are encouraging, there are limitations in the study design. Because the primary objective of the study was to evaluate the safety of topical pravibismane, the number of subjects enrolled was small, precluding statistical analysis of efficacy. In addition, a dose–response curve could not be established for pravibismane because a minimum volume of drug (0.2 mL) needed to be delivered (due to the accuracy of syringe delivery) for ulcers ≤10 cm² in size (mean ulcer size for all pravibismane dosing groups in this study was <10 cm²). This effectively made the planned dose escalation strategy on a dose per surface area basis for topical pravibismane impractical.

This study demonstrates that treatment with topical administration of pravibismane was safe and well‐tolerated at all doses tested, and the data suggest that its use adjunctive to standard of care for DFI is associated with improved wound healing and patient outcomes. This study thus provides support for further studies of this new anti‐infective agent. While the study was primarily geared to evaluate safety, the results suggest that topically applied pravibismane has the potential to address the unmet need of a new DFI treatment that can simultaneously treat bacterial biofilm‐related infections and accelerate ulcer size reduction, potentially leading to complete re‐epithelialization along with reduction of reinfection and amputation risks.

FUNDING INFORMATION

Funding for this study was provided by Microbion Corporation.

CONFLICT OF INTEREST STATEMENT

Benjamin A. Lipsky, Paul J. Kim and David G. Armstrong have served as paid consultants for Microbion Corporation but have no financial or patent‐related conflicts of interest, and no equity interests in Microbion Corporation. Brian Murphy is employed by Medpace, Inc. the clinical research organization that conducted this study. The following authors have financial conflicts of interest: Patricia A. McKernan serves as a consultant for Microbion Corporation and holds equity interest. Brett H. J. Baker is employed as the President and Chief Innovation Officer of Microbion Corporation and holds equity interest. Brett H. J. Baker has assigned all patent rights to Microbion Corporation. Brett H. J. Baker also serves as a member of the Board of Directors of Microbion Corporation.

ETHICS STATEMENT

The protocol and informed consent form were submitted to and approved by the duly constituted Institutional Review Board. The study was conducted in accordance with the Declaration of Helsinki and with all applicable laws and regulations of the United States and the locale where the study was conducted, and in compliance with Good Clinical Practice Guidelines.

CONSENT TO PARTICIPATE

The rationale of the study, procedural details and investigational goals were explained to each subject, along with potential risks and benefits. Each subject was assured of his/her right to withdraw from the study at any time.

Supporting information

Data S1: Supporting information.

Lipsky BA, Kim PJ, Murphy B, McKernan PA, Armstrong DG, Baker BHJ. Topical pravibismane as adjunctive therapy for moderate or severe diabetic foot infections: A phase 1b randomized, multicenter, double‐blind, placebo‐controlled trial. Int Wound J. 2024;21(4):e14817. doi: 10.1111/iwj.14817

DATA AVAILABILITY STATEMENT

Data available on request from the authors.