Azelaic Acid

The non-prostaglandin hair active category has grown rapidly over the past several years, driven partly by genuine scientific interest in alternative follicular mechanisms and partly by regulatory pressure on prostaglandin analogs in cosmetic applications. The EU Scientific Committee on Consumer Safety has concluded that several prostaglandin analogs — including MDN, isopropyl cloprostenate, and DDDE — cannot be considered safe for cosmetic use in lash and brow growth products. Health Canada already prohibits prostaglandins in cosmetics outright. In the United States, the FDA has issued warning letters and secured a $2.3 million settlement against companies marketing prostaglandin-containing products with drug-like claims. Against this regulatory backdrop, ingredients from the 2,4-diaminopyrimidine N-oxide class have attracted renewed attention. Three molecules in particular — PDPO (pyrrolidinyl diaminopyrimidine oxide), DPO (diaminopyrimidine oxide, commonly known as aminexil), and OTZ (L-2-oxothiazolidine-4-carboxylic acid, known as procysteine) — form the basis of a multi-target formulation strategy. But attention is not evidence, and the temptation to flatten complex pharmacology into simple marketing claims has created real problems in this space. This article separates what is established in the peer-reviewed literature from what remains inferential, and examines what that distinction means for product development teams working in this category. PDPO (CAS 55921-65-8, MW 195.22) differs from minoxidil (CAS 38304-91-5, MW 209.25) by a single structural modification: a pyrrolidine ring at the C6 position where minoxidil carries a piperidine ring. Both compounds share the identical 2,4-diaminopyrimidine-3-oxide pharmacophore — the structural motif associated with potassium channel opening activity. The biology of that pharmacophore is well established. Shorter et al. (2008, FASEB Journal) mapped ATP-sensitive potassium channel subunits across human hair follicle compartments, identifying Kir6.1/SUR2B channels in dermal papilla cells and connective tissue sheath, and Kir6.2/SUR1 channels in epithelial matrix keratinocytes. Minoxidil sulfate is selective for SUR2-containing channels, acting primarily on dermal papilla. The genetic validation is striking: Cantú syndrome, caused by gain-of-function mutations in ABCC9 (encoding SUR2), produces congenital hypertrichosis — direct proof that constitutive SUR2 activation promotes hair growth in humans. Downstream, minoxidil's follicular effects are multi-modal. Lachgar et al. (1998, British Journal of Dermatology) demonstrated dose-dependent VEGF mRNA upregulation — up to approximately six-fold at 24 µM in dermal papilla cells. Kwack et al. (2011, Journal of Dermatological Science) showed that minoxidil activates β-catenin signaling in human dermal papilla cells via GSK3β phosphorylation. Marubayashi et al. (2001, Journal of Investigative Dermatology) identified SUR2B expression in dermal papilla cells and proposed adenosine-mediated signaling as an intermediary mechanism. At the proliferative level, minoxidil at 0.1–1.0 µM increases dermal papilla cell proliferation by 60–108% and activates ERK phosphorylation by 287–351%. The problem is that none of this has been demonstrated for PDPO specifically. No published peer-reviewed study reports PDPO's EC₅₀ for K_ATP channel opening, its SUR subtype selectivity, whether it requires sulfotransferase activation (as minoxidil does via SULT1A1), or its effects on any isolated cell type or follicular tissue. The sole clinical evidence comes from multi-ingredient formulations — primarily the Spectral DNC-N study (Draelos et al., 2019, Skin Appendage Disorders), an open-label trial of 49 women using a product containing PDPO alongside azelaic acid, lysophosphatidic acid, copper tripeptide-1, adenosine, retinol, and caffeine. Attribution to PDPO is impossible. Structure-activity relationship data from Murad et al. (1992, Archives of Biochemistry and Biophysics) adds an important constraint: replacement of minoxidil's piperidine ring with pyrrolidine abolished lysyl hydroxylase inhibitory activity. This means PDPO likely does not share DPO's collagen-maturation mechanism. Whether K_ATP channel activity is similarly affected by the pyrrolidine substitution remains untested. Additionally, approximately 40% of minoxidil users are non-responders, linked to low SULT1A1 sulfotransferase activity (Goren et al., 2014, Dermatologic Therapy). Whether PDPO requires analogous metabolic activation is completely unknown. The honest framing is this: PDPO is a structurally plausible K_ATP channel opener. Its membership in the pharmacologically active class remains a hypothesis, not an established fact. Product teams should position it as a contributor within combination systems, not as a standalone proven mechanism. DPO (2,4-diaminopyrimidine-3-oxide, CAS 74638-76-9) is the compound more commonly known as aminexil, developed and commercialized by L'Oréal beginning in the late 1980s. Its mechanism has been more directly studied than PDPO's, but it suffers from a different problem: widespread misidentification of its molecular target. The foundational paper by Mahé et al. (1996, Skin Pharmacology) demonstrated that DPO retains strong inhibition of lysyl hydroxylase mRNA expression in vitro, even without the C6 substituent present in minoxidil. The mechanism is transcriptional — DPO reduces lysyl hydroxylase mRNA levels rather than directly inhibiting enzyme catalysis. No Ki or IC₅₀ values have been published. The original work by Murad and Pinnell (1987, Journal of Biological Chemistry) established that minoxidil suppresses lysyl hydroxylase activity in cultured fibroblasts at 25–500 µM, with recovery blocked by actinomycin D, confirming the transcriptional nature of the effect. Lysyl hydroxylase (encoded by PLOD genes) is an Fe²⁺/2-oxoglutarate-dependent dioxygenase that hydroxylates lysine residues in collagen, enabling subsequent cross-link formation. Lysyl oxidase (LOX) is a completely different enzyme — a copper-dependent amine oxidase that catalyzes a later step in cross-linking via allysine formation. These are distinct proteins with distinct substrates, distinct cofactors, and distinct genomic locations. The conflation of "lysyl hydroxylase" with "lysyl oxidase" in marketing materials is not a semantic quibble; it represents a genuine scientific error that undermines credibility with the technical audience these products are being sold to. DPO is listed in EU Annex III (Entry 93) at a maximum concentration of 1.5% in hair care products, based on the SCCNFP opinion of 3 May 2000. The largest published study is Reygagne et al. (2021, Dermatologic Therapy), an international multicenter observational study of 527 subjects using Aminexil Clinical 5 — a multi-ingredient product. Results included an 82% reduction in pull test at day 90 in men (p < 0.01). However, the study was open-label, uncontrolled, and used a multi-ingredient formula, making attribution to DPO alone impossible. Multiple authors were L'Oréal employees. In a mouse model, Jalilzadeh et al. (2024, BioImpacts) reported that 5% kopexil showed significantly higher hair weight, follicle count, anagen percentage, and VEGF/HGF expression compared to 5% minoxidil over 28 days. This is encouraging preclinical data, but animal model results do not automatically translate to human scalp outcomes. No independent, placebo-controlled, DPO-monotherapy human trial with phototrichogram endpoints has been published. OTZ (L-2-oxothiazolidine-4-carboxylic acid, CAS 19771-63-2, MW 147.15) is the best-characterized molecule in this trio from a biochemical standpoint, yet paradoxically the one with the least hair-specific evidence. Williamson and Meister (1981, Proceedings of the National Academy of Sciences) established OTZ as a substrate for 5-oxoprolinase (EC 3.5.2.9), demonstrating that OTZ administration to glutathione-depleted mice restored normal hepatic glutathione levels. They described OTZ as "an intracellular delivery system for cysteine." The mechanism is clean: 5-oxoprolinase cleaves OTZ in an ATP-dependent reaction, yielding an unstable S-carboxycysteine intermediate that spontaneously decarboxylates to L-cysteine and CO₂. Cysteine then enters the two-step glutathione biosynthesis pathway as the rate-limiting substrate. The head-to-head ARDS trial by Bernard et al. (1997, Chest, n=46, randomized, double-blind, placebo-controlled) showed a 49% increase in red blood cell glutathione with intravenous OTZ — comparable to the 47% increase seen with NAC. Oral dosing up to 9 g/day for two years was safe with no significant clinical pathology changes. OTZ has been studied in HIV, ALS, coronary artery disease, and peritoneal dialysis contexts (Moberly et al., 1998, Journal of the American Society of Nephrology). Key advantages over NAC include superior chemical stability, neutral taste and odor, purely intracellular activation (no extracellular thiol reactivity), and better bioavailability. In neonatal toxicity studies, OTZ showed dramatically lower toxicity than equimolar free cysteine — 10% versus 80% mortality at equivalent cysteine-delivering doses. Despite this robust systemic pharmacology, no published peer-reviewed study has examined topical OTZ on human scalp or hair follicle tissue. The mechanistic rationale — cysteine supports keratin synthesis via disulfide cross-links, glutathione provides antioxidant defense against ROS-mediated follicular damage — is sound but unvalidated in the specific tissue context. Jacques et al. (2021, International Journal of Cosmetic Science) demonstrated that OTZ formulated in a sunscreen emulsion was rapidly absorbed through reconstructed human epidermis, providing the most directly relevant evidence for topical OTZ penetration and antioxidant activity in a cosmetic context. This is encouraging for delivery feasibility, but it is not a scalp-specific study. The connection to AGA pathology is indirect but coherent: Shin et al. (2013, BMB Reports) showed that reactive oxygen species mediate androgen-induced TGF-β1 expression in dermal papilla cells. If OTZ can deliver cysteine to follicular tissue and support local glutathione levels, it could theoretically dampen the ROS-TGF-β1 axis. But "theoretically" is the operative word. Responsible product development in this category requires acknowledging specific evidence boundaries: PDPO-specific pharmacological data does not exist in published literature. No electrophysiology, no EC₅₀, no SUR selectivity, no monotherapy clinical trials. DPO's molecular target is lysyl hydroxylase, not lysyl oxidase. Marketing materials that use "LOX inhibitor" language are citing an enzyme that has not been shown to be the target in published peer-reviewed studies. DPO clinical evidence is entirely from multi-ingredient formulations. No independent, controlled, DPO-monotherapy human RCT has been published. OTZ scalp-specific data is absent. The biochemistry is robust; the tissue-specific translation is an open question. Dual-active salt bioavailability has not been directly demonstrated. Whether both the active base and the OTZ counterion reach effective intracellular concentrations from topical application is an evidence gap for both Kopyrrol Aqua and Kopexil Aqua. The three mechanisms map to distinct pathological axes in androgenetic alopecia. K_ATP channel opening (PDPO) addresses the vascular and proliferative axis — vasodilation, VEGF signaling, dermal papilla proliferation. Lysyl hydroxylase inhibition (DPO) addresses the structural and fibrotic axis — reducing collagen cross-linking maturation in the perifollicular environment. Cysteine and glutathione support (OTZ) addresses the oxidative and metabolic axis — ROS scavenging and keratin substrate delivery. This multi-target framing is mechanistically rational. Liu et al. (2025, Nature Reviews Disease Primers) characterize AGA as multifactorial, involving androgen signaling, genetic susceptibility, Wnt pathway modulation, and inflammatory-fibrotic remodeling. A single-mechanism approach is unlikely to address this complexity adequately. However, complementarity between these specific ingredients at cosmetically relevant concentrations and in topical delivery formats has not been experimentally demonstrated. The synergy narrative is a hypothesis, not established fact. Formulators who build programs around this rationale should design studies capable of testing it rather than assuming it. The strongest non-prostaglandin programs being built today share a common characteristic: they separate evidence tiers explicitly in their technical communication. They frame PDPO as a structurally plausible K_ATP-class ingredient with a promising but unvalidated pharmacological profile. They describe DPO's mechanism accurately — as lysyl hydroxylase transcriptional modulation, not LOX inhibition. They present OTZ as a well-characterized cysteine prodrug with systemic proof of concept and plausible topical relevance. This approach is not merely conservative branding. In a regulatory environment where the FDA defines classification by intended use and the EU is actively restricting prostaglandin analogs based on safety evidence gaps, the capacity to make precise, evidence-bounded claims is a structural advantage. It reduces legal risk, accelerates regulatory review, builds trust with sophisticated B2B buyers, and — perhaps most importantly — creates a foundation for genuine clinical substantiation programs that can strengthen claims over time rather than defending overclaims retroactively. The data gaps identified here are not reasons to avoid these ingredients. They are reasons to invest in the specific studies — K_ATP electrophysiology for PDPO, salt-form bioavailability and skin delivery profiling, controlled monotherapy clinical trials — that would move the evidence base from plausible to proven. The market opportunity created by prostaglandin regulatory pressure is real. The question is whether teams will pursue it with the scientific discipline it deserves.

Repibresib gel (VYN201) Phase 2b vitiligo top-line results expected in mid-2025 VYN202 Phase 1b psoriasis trial initiated with results anticipated by year-end 2025 Expected cash runway into 2H 2026 BRIDGEWATER, N.J., March 06, 2025 (GLOBE NEWSWIRE) -- VYNE Therapeutics Inc. (Nasdaq: VYNE) (“VYNE” or the “Company”), a clinical-stage biopharmaceutical company focused on developing differentiated therapies to treat chronic inflammatory and immune-mediated conditions with high unmet need, today announced financial results as of and for the fourth quarter and year ended December 31, 2024, and provided a business update. “Based on our significant progress in 2024, we are now positioned to announce two key data readouts for repibresib gel and VYN202 in 2025,” said David Domzalski, President and Chief Executive Officer of VYNE. “We are off to a strong start in 2025. In January, we announced the completion of enrollment in the Phase 2b trial of our locally administered pan-BD BET inhibitor, repibresib, in nonsegmental vitiligo, and we expect to report topline results in mid-2025. We also recently initiated the Phase 1b trial of our oral BD2-selective BET inhibitor, VYN202, in subjects with moderate-to-severe plaque psoriasis, and we anticipate reporting topline results from this trial by the end of this year.” Recent Pipeline Updates Repibresib gel (VYN201), a locally-administered small molecule pan-BD BET inhibitor (Phase 2b, nonsegmental vitiligo): Top-line results from the Phase 2b trial are expected in mid-2025. The fully enrolled, Phase 2b trial (NCT06493578) is a randomized, double-blind, vehicle-controlled trial evaluating the efficacy, safety and pharmacokinetics of once-daily repibresib gel in three dose cohorts (1%, 2% or 3% concentrations) compared to vehicle for 24 weeks in subjects with active or stable nonsegmental vitiligo. Subjects have been randomized equally (1:1:1:1 ratio) across the active drug cohorts or vehicle (approximately 45 subjects in each arm). Top-line results from the 24-week double-blind, vehicle-controlled portion of the trial are expected mid-year. Following the 24-week treatment period, subjects who have been randomized in the three active dose cohorts will continue treatment with their respective dose concentrations for an additional 28-week active treatment extension. Subjects who have been randomized in the vehicle group during the initial 24-week treatment period will be equally re-randomized into one of the three active dose cohorts for an additional 28 weeks. VYN202, an oral small molecule BD2-selective inhibitor: Top-line results from the Phase 1b trial are expected by year-end 2025. In February 2025, the Company announced the initiation of patient enrollment in the Phase 1b trial which is a randomized, double-blind, placebo-controlled trial evaluating the safety, tolerability and pharmacokinetics of once-daily VYN202 in three dosing cohorts (0.25 mg, 0.5 mg, 1 mg doses) compared to placebo, for 12 weeks in subjects with moderate-to-severe plaque psoriasis. Exploratory efficacy of VYN202 will also be evaluated, including measures of psoriasis area and severity index, Static Physician Global Assessment, scalp disease, quality of life, and biomarker analyses. Subjects will be randomized equally (1:1:1:1, approximately 20 subjects per arm) across the active drug cohorts or placebo. Following the 12-week treatment period, all subjects will be followed for a 4-week safety period. Upcoming Conference Participation Investor Conferences. VYNE will be participating in the upcoming Leerink Partners Global Healthcare Conference, taking place in Miami from March 10-12, 2025, as well as the H.C. Wainwright 3rd Annual Autoimmune & Inflammatory Disease Virtual Conference being held on March 27, 2025. Financial Results as of and for the Year Ended December 31, 2024 Cash position. As of December 31, 2024, VYNE had $61.5 million of cash, cash equivalents and marketable securities. Based on current operating assumptions, VYNE believes its cash, cash equivalents and marketable securities as of December 31, 2024 will be sufficient to fund its operations into the second half of 2026. Share count. As of December 31, 2024, VYNE had 14,830,013 common shares issued and outstanding, and outstanding pre-funded warrants to purchase 27,842,740 shares of common stock at an exercise price of $0.0001 per share. Revenues. Revenues totaled $0.5 million and $0.4 million for the years ended December 31, 2024 and 2023, respectively, consisting of royalty revenue from the Company's royalty agreement with LEO Pharma A/S, to whom VYNE previously licensed the rights to Finacea® foam. Research and development expenses. VYNE’s research and development expenses for the years ended December 31, 2024 and 2023 were $30.9 million and $16.3 million, respectively. The increase was primarily due to an increase of $11.7 million in expenses for repibresib, an increase of $2.5 million in expenses for VYN202 and an increase of $0.8 million of employee-related expenses following the hiring of additional research and development personnel. The $11.7 million increase in expenses for repibresib primarily relates to preparatory activity and clinical trial costs incurred for VYNE's ongoing Phase 2b trial of repibresib in subjects with nonsegmental vitiligo. The $2.5 million increase in expenses for VYN202 is primarily associated with costs incurred for our Phase 1a SAD/MAD trial which was completed in the fourth quarter of 2024. Both trials were initiated in June 2024. These increases were partially offset by lower consulting expenses of $0.4 million. General and administrative expenses. VYNE’s general and administrative expenses for the years ended December 31, 2024 and 2023 were approximately $13.2 million and $13.4 million, respectively. The decrease was primarily driven by a reduction in employee related expenses of $0.9 million, partially offset by increased consulting and professional fees of $0.8 million. Net loss. Net loss and net loss per share for the year ended December 31, 2024 was $39.8 million and $0.93, respectively, compared to a net loss and net loss per share of $28.5 million and $2.78, for the comparable period in 2023. About VYNE Therapeutics Inc. VYNE is a clinical-stage biopharmaceutical company focused on developing differentiated therapies to treat chronic inflammatory and immune-mediated conditions with high unmet need. VYNE's unique and proprietary BET inhibitors, which comprise its InhiBET™ platform, are designed to overcome limitations of early generation BET inhibitors by leveraging alternative routes of administration and enhanced selectivity. For more information about VYNE Therapeutics Inc. or its product candidates, visit www.vynetherapeutics.com. VYNE may use its website to comply with its disclosure obligations under Regulation FD. Therefore, investors should monitor VYNE’s website in addition to following its press releases, filings with the U.S. Securities and Exchange Commission, public conference calls, and webcasts. Investor Relations:John FrauncesLifeSci Advisors, LLC917-355-2395jfraunces@lifesciadvisors.com Tyler ZerondaVYNE Therapeutics Inc.908-458-9106Tyler.Zeronda@VYNEtx.com Media Relations: Mike BeyerSam Brown Inc.312-961-2502mikebeyer@sambrown.com Cautionary Statement Regarding Forward-Looking Statements This release includes forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995, including, but not limited to, statements regarding the clinical development of, and timing for reporting top-line results from trials of, repibresib and VYN202, the impact of the reported top-line results from trials on clinical development, VYNE's participation in upcoming conferences, VYNE’s projected cash runway, and other statements regarding the future expectations, plans and prospects of VYNE. All statements in this press release which are not historical facts are forward-looking statements. Any forward-looking statements are based on VYNE’s current knowledge and its present beliefs and expectations regarding possible future events and are subject to risks, uncertainties and assumptions that could cause actual results to differ materially and adversely from those set forth or implied by such forward-looking statements. These risks and uncertainties include, but are not limited to: VYNE’s ability to successfully develop its product candidates; the timing of commencement of future preclinical studies and clinical trials; VYNE’s ability to complete and receive favorable results from clinical trials of its product candidates; VYNE’s ability to obtain additional funding, either through equity or debt financing transactions or collaboration arrangements; and VYNE’s ability to comply with various regulations applicable to its business. For a discussion of other risks and uncertainties, and other important factors, any of which could cause VYNE’s actual results to differ from those contained in the forward-looking statements, see the section titled “Risk Factors” in VYNE’s Annual Report on Form 10-K for the year ended December 31, 2024, and VYNE’s other filings from time to time with the U.S. Securities and Exchange Commission. Although VYNE believes these forward-looking statements are reasonable, they speak only as of the date of this announcement and VYNE undertakes no obligation to update publicly such forward-looking statements to reflect subsequent events or circumstances, except as otherwise required by law. Given these risks and uncertainties, you should not rely upon forward-looking statements as predictions of future events. Third-party products and company names mentioned herein may be the trademarks of their respective owners.