Circle Pharma, a South San Francisco-based clinical-stage biopharmaceutical company pioneering next-generation targeted macrocycle therapeutics for cancer, has announced an oversubscribed $92.5 million Series E financing round. The financing was led by The Column Group and included participation from Nextech Invest, RA Capital Management, Euclidean Capital, and Eli Lilly and Company. The new capital will support the advancement of CID-165, a first-in-class oral macrocyclic cyclin D1 RxL inhibitor, into clinical development for patients with ER-positive breast cancer.
Financing Details and Investor Support
The Series E round attracted both existing and new investors, reflecting strong confidence in Circle Pharma's cyclin-targeted pipeline. Proceeds will primarily advance CID-165 through early clinical development while also supporting the company's broader portfolio of cyclin-targeted macrocycles. The strategic investment from Eli Lilly and Company adds significant industry validation to the syndicate.
CID-165 Clinical Development Plans
Circle Pharma expects CID-165 to enter clinical development in the first quarter of 2027 for patients with ER-positive breast cancer. The company plans to use the financing to generate meaningful clinical data that can validate the drug candidate's therapeutic potential. This timeline positions CID-165 as an important near-term value driver for Circle Pharma's pipeline.
Preclinical Evidence and Combination Potential
Preclinical studies have shown that CID-165 potently and selectively disrupts the interaction between cyclin D1 and the retinoblastoma protein. The compound has demonstrated robust anti-tumor activity in cyclin D1-driven cancer models, both as a monotherapy and in combination with other treatments. Those combinations include CDK4/6-dual inhibitors, CDK4-selective inhibitors and endocrine therapies.
Mechanism and Scientific Rationale
Cyclin D1 is a regulatory protein that plays a crucial role in cell cycle progression and is dysregulated in several malignancies, including ER-positive breast cancer and certain lymphomas. In these cancers, dysregulated cyclin D1 drives abnormal cell proliferation by inactivating the tumor suppressor retinoblastoma protein, leading to uncontrolled cell division. By preserving retinoblastoma protein activity, CID-165 offers a novel approach to directly target this fundamental driver of tumor growth.
Leadership Perspectives
David J. Earp, president and chief executive officer of Circle Pharma, described the financing as a significant milestone and noted that CID-165 could become a new backbone therapy for ER-positive breast cancer. Marie Evangelista, chief scientific officer, added that cyclin D1 is a well-established cancer driver and a lineage dependency in ER-positive breast cancer. She also noted that robust preclinical activity provides strong conviction as CID-165 moves toward the clinic.
Company Platform and Future Outlook
Circle Pharma is leveraging its proprietary MXMO platform to overcome key challenges in macrocycle drug development and create orally bioavailable therapies for historically undruggable targets. The company's pipeline focuses on cyclins, which are master regulators of the cell cycle that drive many cancers. Based in South San Francisco, California, Circle Pharma is positioned to continue advancing next-generation targeted therapies.
The $92.5 million Series E financing provides Circle Pharma with the resources to validate CID-165 in clinical studies and potentially address a critical unmet need in ER-positive breast cancer treatment. By advancing a first-in-class oral cyclin D1 inhibitor, the company is targeting a fundamental mechanism that has long evaded direct therapeutic intervention. With clinical entry planned for early 2027, Circle Pharma is moving closer to expanding treatment options for patients with cyclin-driven cancers.