South San Francisco-based Circle Pharma, Inc. has raised USD 92.5 million in an oversubscribed Series E financing to advance its lead cyclin D1 inhibitor into clinical trials, with a Phase I study in estrogen receptor-positive (ER+) breast cancer targeted for Q1 2027.
The Column Group led the round, with participation from Nextech Invest, RA Capital Management, and Euclidean Capital. Eli Lilly and Company contributed a strategic investment. Circle has an existing relationship with Lilly, signing up in September 2025 to enhance its artificial intelligence and machine learning capabilities leveraging Lilly TuneLab. The Series E follows a USD 90 million Series D closed in 2024, bringing total financing to more than USD 212 million, according to Circle Pharma.
Proceeds will fund early clinical development of CID-165, an oral macrocyclic cyclin D1 RxL inhibitor, alongside continued pipeline work on the company's broader cyclin-targeted program. CID-165 is designed to disrupt the interaction between cyclin D1 and the retinoblastoma protein, keeping the tumor suppressor active and suppressing cancer cell proliferation. In preclinical models, the company said CID-165 demonstrated anti-tumor activity both as a monotherapy and in combination with CDK4/6-dual inhibitors, CDK4-selective inhibitors, and endocrine therapies. Circle Pharma nominated CID-165 as a development candidate in late 2025.
The company's lead clinical asset, CID-078, a dual cyclin A/B RxL inhibitor, is already in Phase I trials for solid tumors. Circle Pharma presented clinical and preclinical data from that program at the American Association for Cancer Research (AACR) annual meeting in 2026.