SOUTH SAN FRANCISCO, Calif. — September 16, 2026
Circle Pharma, Inc. announced an oversubscribed $92.5 million Series E financing led by The Column Group, with participation from Nextech Invest, RA Capital Management, Euclidean Capital and strategic investor Eli Lilly and Company. The financing provides capital to advance CID-165, Circle Pharma’s first-in-class oral macrocyclic cyclin D1 RxL inhibitor, into clinical development and support the company’s broader pipeline of cyclin-targeted macrocycles. CID-165 is expected to enter clinical development in the first quarter of 2027, initially targeting patients with ER-positive breast cancer. The financing represents a significant expansion of resources for Circle Pharma as the company transitions its lead cyclin D1 program from preclinical development toward human clinical evaluation.
CID-165 Directly Targets Cyclin D1-Rb Interaction
CID-165 is designed to selectively disrupt the interaction between cyclin D1 and retinoblastoma protein (Rb), a mechanism intended to preserve Rb tumor-suppressor activity and limit uncontrolled cancer-cell proliferation. Cyclin D1 is a key regulator of cell-cycle progression and is dysregulated in several malignancies, including ER-positive breast cancer and certain lymphomas. Directly targeting cyclin D1 has historically presented challenges because of the characteristics of the target, but Circle Pharma is using a macrocyclic approach designed to achieve cell permeability and oral bioavailability. In preclinical studies, CID-165 demonstrated robust anti-tumor activity in cyclin D1-driven cancer models, including activity as a monotherapy and in combination with CDK4/6-dual inhibitors, CDK4-selective inhibitors and endocrine therapies. These findings are supporting the company’s decision to advance the program toward clinical testing.
Circle Advances Macrocycle Approach in Breast Cancer
Lilly TuneLab was established to give participating biotechnology companies access to AI/ML drug discovery models trained using decades of Lilly’s proprietary research data. The platform is intended to help companies apply predictive capabilities to their own discovery programs while contributing to a broader collaborative innovation ecosystem. The Twist agreement adds specialized antibody characterization and developability data to this model-driven environment, creating an additional pathway for experimental datasets to support AI-enabled research. TuneLab forms part of Lilly Catalyze360, alongside Lilly Ventures, Lilly Gateway Labs and Lilly ExploR&D, which collectively provide biotechnology companies with access to strategic capital, laboratory infrastructure, technology and research capabilities. The expanding network illustrates how large pharmaceutical companies and specialized technology providers are building connected discovery ecosystems to support external innovation and potentially shorten early drug-development timelines.
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Circle Pharma Prepares for First Clinical Data
The Series E financing gives Circle Pharma the resources to execute the transition of CID-165 into the clinic while continuing development of additional cyclin-targeted programs. The company expects clinical development of CID-165 to begin in Q1 2027, providing an opportunity to generate the first human data for its cyclin D1 program and evaluate whether the preclinical activity translates into patients with ER-positive breast cancer. Circle’s broader strategy is built around using macrocycles to develop targeted therapies against cancer-driving proteins that have been difficult to address with traditional small molecules. With support from a syndicate that includes specialist biotechnology investors and Eli Lilly, the company is positioning CID-165 as the lead clinical program while maintaining investment in its wider cyclin portfolio. The move into clinical development marks an important transition for Circle Pharma’s macrocycle platform and its strategy to develop therapies against previously challenging cancer targets.
Source:Circle Pharma,, press release
