Greywolf Reports Early Responses with Oral ERAP1 Inhibitor in Solid Tumours

Why It Matters

The data suggest that ERAP1 inhibition can sensitize tumors that have failed checkpoint therapy, potentially expanding immunotherapy to resistant indications such as MSS colorectal cancer. If confirmed, this oral agent could become a valuable partner for existing PD‑1 inhibitors, reshaping combination strategies in oncology.

Key Takeaways

• GRWD5769 + cemiplimab shows 13‑36% ORR across six tumor types
• Highest response observed in urothelial carcinoma (36% ORR)
• Durable clinical benefit reached 55% with median PFS 33 weeks
• Early data lack cemiplimab‑only control, limiting attribution
• Oral ERAP1 inhibition may overcome PD‑1 resistance in MSS colorectal cancer

Pulse Analysis

The emergence of ERAP1 as a drug target reflects a deeper understanding of antigen processing and presentation. By trimming peptides within the endoplasmic reticulum, ERAP1 shapes the repertoire displayed on MHC‑I molecules, influencing T‑cell recognition. Inhibiting this enzyme can broaden the peptide pool, potentially exposing tumor cells that were previously invisible to the immune system. Greywolf’s oral inhibitor, GRWD5769, leverages this mechanism to augment the activity of cemiplimab, an established anti‑PD‑1 antibody, offering a novel way to overcome adaptive resistance that limits checkpoint efficacy.

Greywolf’s Phase 1b EMITT‑1 data, presented at ASCO, reveal encouraging signals despite the trial’s small, non‑randomised design. Objective response rates varied by tumor type, peaking at 36% in urothelial carcinoma, while a durable clinical benefit was reported in more than half of the participants. Notably, the cohort of microsatellite‑stable colorectal cancer without liver metastases—a population traditionally refractory to immunotherapy—showed partial responses and a 33‑week median progression‑free survival. The safety profile was favorable, with only Grade 1 adverse events, underscoring the practicality of an oral agent paired with intravenous checkpoint inhibitors.

Looking ahead, Greywolf plans to expand EMITT‑1 into Stage 2 cohorts and launch a randomised Phase 2 study that will include a cemiplimab‑only arm to isolate the contribution of ERAP1 inhibition. Success could catalyze a wave of combination regimens that pair oral immunomodulators with existing checkpoint blockers, potentially unlocking new revenue streams for biotech firms and offering clinicians more flexible treatment options. Investors will watch the upcoming data closely, as validation could position GRWD5769 as a first‑in‑class therapy that broadens the reach of cancer immunotherapy.