ENDO-205: A Non-Hormonal Endometriosis Peptide
A peptide its developer says is designed to trigger cell death only inside endometriosis lesions. In March 2026 the company announced FDA clearance of its IND for first-in-human trials. Here is what the peer-reviewed evidence supports today, and what remains unproven.
How It Works
Endometriotic lesions resist apoptosis (programmed cell death), which lets them persist and spread; survival pathways such as PI3K/Akt are implicated. Its developer says ENDO-205 is designed to force apoptosis selectively inside lesion tissue (not yet shown in published data).
Current treatments are limited to surgery, hormonal treatments and pain relievers, which carry adverse effects and rarely provide long-term relief; reviews call for non-hormonal options acceptable to women who wish to conceive. ENDO-205 is developed to avoid hormonal manipulation.
Ectopic lesions survive in a hostile, hypoxic peritoneal microenvironment distinct from healthy tissue. EndoCyclic Therapeutics reports ENDO-205 senses a microenvironmental difference (a pH trigger) so it acts only in diseased tissue (a company claim not yet in the peer-reviewed literature).
In March 2026 EndoCyclic announced FDA clearance of ENDO-205’s IND and said it plans a first-in-human study in healthy pre-menopausal women. Phase 1 tests safety and dosing, not whether it treats endometriosis.
What the Data Shows
Key Takeaways
- ENDO-205 is an investigational, non-hormonal peptide for endometriosis; its developer announced FDA clearance of its Investigational New Drug application in March 2026 and plans a first-in-human Phase 1 study.
- Endometriosis affects an estimated 5–10% of reproductive-age women, about 176 million worldwide.
- Resistance to apoptosis is an established driver of lesion survival and growth in endometriosis.
- Current therapies are largely hormonal or surgical, have limited long-term efficacy and notable side effects, and are associated with high recurrence, so the unmet need is real.
- About a third of women do not respond to first-line progestins or oral contraceptives.
- Whether ENDO-205 actually reduces endometriosis symptoms or lesions in humans: the Phase 1 trial enrolls healthy volunteers and tests safety, not efficacy.
- Its preclinical "lesion elimination" results are company-reported and not yet published in the peer-reviewed literature.
- Long-term safety, the effect on fertility, dosing, and durability of any benefit are all unknown.
- Whether ENDO-205 really acts only in diseased tissue: lesion-selective apoptosis is the developer's design claim, and how its reported pH/microenvironment trigger performs in the human peritoneal environment is untested.
- When (or whether) it reaches market; first-in-human clearance is years from any approval.
- It is not available to buy or prescribe anywhere; anything sold as "ENDO-205" is not the investigational drug.
Frequently Asked Questions
What is ENDO-205?
ENDO-205 is an investigational, non-hormonal peptide therapeutic for endometriosis that its developer, EndoCyclic Therapeutics, calls first-in-class. In March 2026 the company announced FDA clearance of its Investigational New Drug application and said it plans a first-in-human Phase 1 study. The company says it is designed to trigger apoptosis (programmed cell death) selectively in endometriosis lesions; that selectivity has not yet been shown in peer-reviewed data.
How does ENDO-205 work?
According to its developer, it is designed to induce programmed cell death only inside endometriotic lesions rather than suppressing hormones; no peer-reviewed data on ENDO-205 itself is published yet. The developer describes a mechanism that senses a difference in the lesion microenvironment (a pH trigger). This targets established biology: endometriotic lesions resist apoptosis and survive in a hostile, hypoxic peritoneal microenvironment.
Is ENDO-205 FDA-approved or available to buy?
No. In March 2026 EndoCyclic announced that the FDA cleared ENDO-205’s IND, allowing Phase 1 human trials to begin — that is not the same as approval. It is investigational, not marketed, and not available for purchase or prescription anywhere.
Is ENDO-205 hormonal like most endometriosis drugs?
No — it is non-hormonal, which is what makes it notable. About a third of women fail first-line hormonal therapy, and hormonal options limit fertility and long-term use, so a non-hormonal, lesion-targeted approach addresses a real unmet need.
When will ENDO-205 be available?
Unknown. Phase 1 is the first of several trial stages; efficacy in patients has not yet been tested. If it succeeds through Phase 2 and 3 and is approved, availability would still be years away.
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ENDO-205 is an investigational drug that is not approved by the FDA and not available for purchase or prescription. Consult a qualified clinician about endometriosis care.