RB1 (retinoblastoma 1) loss is a defining mutation across multiple tumor types — small-cell lung cancer, retinoblastoma, and subsets of breast and ovarian cancer. RB1 deficiency disrupts cell-cycle control and creates synthetic-lethality opportunities that traditional small-molecule chemistry has struggled to reach.
The lead peptide approach: Circle Pharma's CID-078, a first-in-class oral macrocyclic peptide cyclin A/B RxL inhibitor in Phase 1 for RB1-deficient solid tumors. The AACR 2026 Clinical Trials Plenary covered early clinical activity data.
Stories here cover the RB1-deficient tumor work and the synthetic-lethality peptide approaches. See #cid-078, #circle-pharma, #cyclin, and #macrocyclic-peptide.
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.
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.