Targeting G1–S-checkpoint-compromised cancers with cyclin A/B RxL inhibitors

Cancer cell proliferation requires precise control of E2F1 activity; excess activity promotes apoptosis. We developed cell-permeable and bioavailable macrocycles that selectively kill small cell lung cancer (SCLC) cells with inherent high E2F1 activity by blocking RxL-mediated interactions of cyclin A and cyclin B with select substrates. This work uncovers gain-of-function mechanisms by which cyclin A/Bi induce apoptosis in cancers with high E2F activity, and suggests cyclin A/Bi as a therapeutic strategy for SCLC and other cancers driven by high E2F activity. Comparative gene expression profiling analysis of RNA-seq data in a human SCLC patient-derived xenograft (PDX) tumor model treated with a cyclin A/B RxL inhibitor (CIRc-014) or vehicle, and a human SCLC cell line NCI-H1048 after treatment with DMSO (vehicle), cyclin A/B RxL inhibitor (CIRc-004 or CIRc-014), inactive enantiomer (CIRc-005) or a Cdk2 inhibitor (PF-07104091). The SCLC PDX model DFCI393 was grown in NSG mice and established tumors were treated with the orally bioavailable cyclin A/B RxL inhibitor CIRc-014 at 100 mg/kg PO TID or vehicle (30% PEG400, 20% Solutol HS15, 50% Phosal 53 MCT) three times a day for 4 days and tumors were collected 8 hours after the morning dose on the last day of treatment and snap frozen for RNA-seq. 6 independent tumors from 6 independent mice were used for CIRc-014 and 5 independent tumors from 5 independent mice were used for vehicle. For cell line experiments, NCI-H1048 cells were plated at 500,000 cells/mL density in presence of DMSO (vehicle), cyclin A/B RxL inhibitor (CIRc-004 or CIRc-014, 200nM), inactive enantiomer (CIRc-005, 200nM) or a Cdk2 inhibitor (PF-07104091, 500nM). 24 hours after treatment with drugs, cells were harvested for RNA. The NCI-H1048 cell line experiments were done in 2 biological replicates.