Circle Pharma Closes $92.5 Million Series E to Advance Oral Macrocyclic Peptide Cyclin D1 RxL Inhibitor CID-165 into Early Clinical Development for ER-Positive Breast Cancer
Circle Pharma announced Wednesday September 16, 2026 an oversubscribed $92.5 million Series E financing led by The Column Group with participation from Nextech Invest, RA Capital Management, Euclidean Capital, and Eli Lilly and Company. Founded in 2012, the South San Francisco biotech develops orally bioavailable macrocyclic peptides against cancer-driving intracellular protein-protein interactions historically considered undruggable by conventional small molecules. Lead asset CID-165 is an oral macrocyclic peptide cyclin D1 RxL inhibitor designed to block the interaction between cyclin D1 and its downstream substrates in ER-positive breast cancer. Proceeds advance CID-165 into early clinical development plus expansion of the broader Circle discovery pipeline. Lilly's investor participation adds to a growing Lilly obesity-and-oncology-adjacent equity portfolio that already includes Moonwalk Biosciences (adipose RNAi, $70M Series B September 8), Superluminal Medicines (MC4R agonist, $60M Series B September 3), and Verve Therapeutics (base editing, acquired July 2025). The macrocyclic peptide category has attracted substantial VC and pharma investment throughout 2026, with Syneron Bio, Parabilis Medicines (formerly FogPharma), Bicycle Therapeutics, Unnatural Products, and Circle Pharma all closing major funding rounds or strategic collaborations.