Circle Pharma builds macrocyclic peptide drugs for intracellular protein–protein interaction targets — the 'undruggable' space where small molecules struggle and antibodies cannot reach. The lead clinical candidate is CID-078, a cyclin-targeted bicyclic peptide for RB1-deficient tumors.
CID-078 readouts have appeared at AACR 2026 and adjacent venues, with Phase 1 dose-escalation and biomarker work covered on this site. The company's broader pipeline targets cyclin family members and other cell-cycle regulators that have eluded conventional drug discovery.
Stories here cover trial readouts, AACR presentations, and partnership announcements. See #cid-078, #cyclin, #rb1, and #macrocyclic-peptide for adjacent threads.
Circle Pharma announced on 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. The South San Francisco company said the money will take CID-165, which it describes as a first-in-class oral macrocyclic cyclin D1 RxL inhibitor, through early clinical development in ER-positive breast cancer and support its broader pipeline of cyclin-targeted macrocycles. Circle expects CID-165 to enter clinical development in the first quarter of 2027.
Circle Pharma presents early clinical data for CID-078 in the AACR 2026 Clinical Trials Plenary (Sunday, April 19, 1:00-3:00 PT). CID-078 is a first-in-class orally bioavailable macrocyclic peptide cyclin A/B RxL inhibitor evaluated in a Phase 1 multicenter trial (NCT06577987) for advanced solid tumors with RB1 alterations. The plenary slot — a coveted showcase for private biotechs — tests whether macrocyclic peptides can establish themselves as a third modality alongside small molecules and biologics.
Circle Pharma presents "Orally Bioavailable Peptide Macrocycles Disrupting Intracellular Protein-Protein Interactions: Selective Inhibitors of the RxL-binding Site of Cyclin Family Proteins" at AACR's Chemistry to the Clinic Part 3 session on Saturday, April 18, 12:30-2:00 p.m. PST. The presentation covers CID-078, an orally bioavailable macrocycle with dual activity blocking cyclin A/B protein-protein interactions, selectively targeting tumor cells with RB1 alterations.
ApexOnco analysis frames AACR 2026 as a breakout moment for private peptide-based biotechs. Circle Pharma (macrocyclic peptides), Bicycle Therapeutics (bicyclic peptide drug conjugates), and SignaBlok (TREM-1 peptide) all landed prominent slots. Antibody-drug and peptide-drug conjugates remain the dominant theme, with conjugate-related abstracts outpacing any other modality in the clinical late-breaker sessions.
Circle Pharma secured a coveted oral plenary slot at AACR 2026 to present early Phase 1 clinical activity data for CID-078, a first-in-class orally bioavailable macrocyclic peptide cyclin A/B RxL inhibitor for patients with advanced solid tumors harboring RB1 alterations. The plenary (Sunday, April 19) validates macrocyclic peptides as viable oral oncology drugs — a major milestone for the modality.