WILMINGTON, DE — Prelude Therapeutics Inc. (Nasdaq: PRLD) has entered a clinical trial collaboration with Eli Lilly and Co. to evaluate an experimental breast cancer treatment alongside two Lilly drugs, expanding the development strategy for a therapy designed to overcome resistance to existing treatments.
The Wilmington-based biotechnology company will test its oral drug candidate PRT13722 in combination with Lilly’s CDK4/6 inhibitor abemaciclib and estrogen receptor antagonist imlunestrant in patients with hormone receptor-positive, HER2-negative (HR+/HER2-) breast cancer.
Under the agreement, Lilly will supply both medicines for the combination studies. Prelude retains full global development and commercialization rights to PRT13722.
The U.S. Food and Drug Administration recently cleared Prelude’s investigational new drug application, allowing the company to proceed with a Phase 1 clinical trial.
Prelude expects to begin enrolling patients during the fourth quarter of 2026, initially evaluating PRT13722 alone through dose escalation before advancing to combination treatment groups.
PRT13722 is designed to selectively degrade KAT6A, a protein involved in regulating gene expression and a therapeutic target in hormone receptor-positive breast cancer.
Prelude’s approach differs from treatments that inhibit both KAT6A and the related protein KAT6B. The company believes selectively targeting KAT6A could improve treatment effectiveness and reduce blood-related toxicity, potentially allowing the drug to be combined with established breast cancer therapies.
“Our preclinical data demonstrate that selectively degrading KAT6A has the potential to improve upon the efficacy and hematologic toxicity seen with dual KAT6A/B inhibitors,” said Sean Brusky, Prelude’s chief business and strategy officer.
The collaboration follows preclinical findings presented at the American Association for Cancer Research’s annual meeting in April 2026.
In laboratory and animal models of HR+/HER2- breast cancer, PRT13722 produced sustained complete tumor regressions when administered alone, according to the company.
Prelude also reported enhanced antitumor activity when the experimental drug was combined with endocrine therapies, CDK4/6 inhibitors and PI3K inhibitors.
Those findings included models involving ESR1 mutations and cancer cells that had developed resistance to previous treatments.
The company further reported a more favorable blood-related safety profile in preclinical testing compared with prifetrastat, a dual KAT6A/B inhibitor.
The results remain preclinical, and the upcoming Phase 1 trial will begin evaluating PRT13722’s safety, tolerability and dosing in patients.
For Prelude, the Lilly agreement provides access to established breast cancer treatments as it investigates whether selective KAT6A degradation can support combination regimens for patients with HR+/HER2- disease.
The clinical program could eventually inform development in earlier treatment settings, although the initial study is focused on establishing the investigational drug’s clinical profile.
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