KDC-MN-281 – Kodiac biolabs

Plain-language summaryIntrigue 55 / 100

RU58841 is a topical androgen receptor blocker developed by Roussel-Uclaf in the 1990s as a hair-loss treatment. The idea was elegant: rather than systemically lowering DHT (and risking sexual side effects), apply an AR blocker directly to the scalp where it competes with DHT at the hair follicle, with minimal absorption into the rest of the body. Phase 1 and 2 trials showed efficacy in slowing or reversing male-pattern baldness, but the compound was abandoned commercially (the reasons remain unclear and the compound was simply shelved). It is now used in DIY scalp solutions sourced as a research chemical, with minimal long-term safety data and no manufacturer accountability. Not stocked by Kodiac. This monograph is provided for research and educational reference.

Intrigue 0–100 blends mechanism novelty, evidence strength, and translational potential. Kodiac editorial, not peer-reviewed.

Our opinion on this compoundEstablished workhorse

41/100

A 1990s topical AR antagonist with real phase 2 data, now largely eclipsed by clascoterone

Look, RU58841 is a compound that almost made it. Roussel-Uclaf synthesized this hydantoin in the early 1990s with a genuinely smart idea behind it: get an AR antagonist into the scalp follicle without the systemic exposure that makes drugs like flutamide a liability. The structure binds the AR with enough affinity to compete with DHT locally, and if you keep it topical, you theoretically sidestep the sexual side effects that plagued oral antiandrogen use. Phase 1 and phase 2 trials were run, hair retention signals were real, and then the corporate machinery of a Sanofi merger ground the program to a halt. Not because it failed. Because priorities shifted.

That history matters for how we score it. We’ve got actual human data, which puts RU58841 ahead of a lot of compounds in this library that are still swimming in rodent studies. Phase 2 efficacy is real evidence. But the data is also thirty years old, never advanced to phase 3 confirmation, and hasnt been meaningfully replicated by independent groups in modern trial formats. What we have is a snapshot of mid-90s clinical pharmacology, not a living literature.

The bigger issue for differentiation is clascoterone. Cassiopea got Winlevi approved by the FDA in 2020, first as a topical AR antagonist for acne, and its been investigated for androgenetic alopecia since. That approval changes the landscape. RU58841 was the only reference topical AR antagonist for about two decades; now there’s a regulatory-approved alternative with a cleaner development history and ongoing Phase 2/3 AGA work. RU58841 doesn’t disappear from the toolbox, but it stops being the only option.

Where it still earns its keep is as a bench probe. If you’re studying follicular androgen biology, mapping AR occupancy in explant models, or trying to isolate DHT-mediated effects in scalp tissue, RU58841 is a well-characterized reference with published pharmacokinetics and selectivity data. Thats real utility for a narrow but serious research program. We dont dismiss that. But it’s probe value, not frontier value.

Honestly, the compound sits in a frustrating middle ground: too much evidence to call it speculative, not enough development to call it mature, and now partially overshadowed by a compound that finished what it started. A serious AGA researcher in 2025 would probably reach for clascoterone first and keep RU58841 as a backup reference tool. That’s the honest picture.

Novelty: 20
Mechanism promise: 35
In-category differentiation: 45
Evidence quality: 50
Translational signal: 50
Research bench value: 58

Rationale RU58841 scores low on novelty because it is a three-decade-old hydantoin developed at Roussel-Uclaf using straightforward single-receptor AR antagonism; its phase 2 human data lifts evidence and translational scores above most research peptides, but those gains are offset by commercial abandonment and the subsequent approval of clascoterone (Winlevi) as a topical AR antagonist, which erodes its differentiation. Bench value survives as a reference compound for follicular AR pharmacology, preventing a lower overall.

Topical androgen receptor antagonist

A topical non-steroidal AR antagonist developed for androgenetic alopecia; never advanced to commercial development but widely used as a research compound.

Abstract

RU58841 (PSK3841; CAS 154992-24-2; molecular formula C17H18F3N3O3; molecular weight 369.34) is a non-steroidal androgen receptor antagonist developed at Roussel-Uclaf (now Sanofi) in the 1990s as a topical treatment for androgenetic alopecia. The compound is structurally a hydantoin and binds the AR with sufficient affinity to compete with DHT in scalp tissue. Topical application allows local AR antagonism in hair follicles with minimal systemic absorption, theoretically avoiding the sexual side effects of systemic 5AR inhibitors. Phase 1 and 2 trials demonstrated efficacy in slowing or reversing scalp hair loss. Development was discontinued at Roussel-Uclaf (subsequent corporate merger and prioritization). The compound entered the research-grade and DIY hair loss community via the published patents and has remained in informal use without regulatory approval. Used as a reference topical AR antagonist in dermatologic and androgen pharmacology research.

Read the full monograph

The full reference document covers compound identification, discovery and developmental history, mechanism of action, pharmacokinetics, sourcing and quality verification, and a curated reference list. Embedded inline below; download for offline reading.

KDC-MN-281Open in new tab →

Download PDF →

FOR RESEARCH USE ONLY. Not for medical, diagnostic, or therapeutic purposes. Not for human consumption. All information is provided for research and educational purposes only.

Tag: KDC-MN-281

RU58841

Abstract

Read the full monograph