Fovinaciclib

Cyclin-dependent kinase 4 and 6 inhibitors (CDK4/6i) plays a major role in breast cancer therapeutics acting through preventing the cell cycle from G1 to the S phase. Recently, Endocrine therapy combined with CDK4/6i represented a major milestone in hormone receptor (HR)-positive and human epidermal growth factor receptor 2 (HER2)-negative breast cancer treatment. However, the resistance of CDK4/6i is clinically common, and the mechanism remains to be clarified. Retinoblastoma (Rb) is a negative regulator of cell cycle. It inhibits cell cycle transition by binding to E2F transcription factors, and prevent cells division in this way. Rb is regulated by phosphorylation. The CDK4/6i have been shown to affect cancer by blocking phosphorylation of Rb. In addition, decreasing estrogen signal has been confirmed to reduce cyclin D-CDK4/6 complexing. Currently, FCN-437c is a new CDK4/6i that is in clinical trials. Here, we present the case of an HR-positive and HER2-negative patient whose disease continued to rapidly progress after receiving FCN-437c. To determine why, we did a series of examinations and found that her Rb1 had mutated after using CDK4/6i. To our surprise, the Rb1 mutations recovered after treatment with eribulin, and CDK4/6i was shown to exert a renewed effect. In this way, a hypothesis was made that eribulin may influence the pathway of cyclin D- CDK4/6- Rb- E2F by effecting in Rb. This case provides new insights into strategies for CDK4/6i therapy resistance options and shows the significance of next-generation sequencing in the clinic.

Summary Purpose This phase 1a, first-in-human study assessed the safety, maximum tolerated dose (MTD), pharmacokinetics (PK), and antitumor activity of FCN-437c, a cyclin-dependent kinase 4 and 6 (CDK4/6) inhibitor. Methods The study enrolled female patients with HR + /HER2- advanced breast cancer (BC) who failed standard of care therapy. A 3 + 3 dose-escalation design was utilized with a starting dose of 50 mg daily for 3 weeks on and 1 week off treatment in 28-day cycles. Patients received escalating doses of FCN-437c monotherapy (50, 100, 200, 300, and 450 mg). Results Seventeen patients received FCN-437c 50 mg (n = 3), 100 mg (n = 3), 200 mg (n = 3), 300 mg (n = 6), and 450 mg (n = 2). Two patients who received the 450-mg dose experienced dose-limiting toxicities (DLTs; grade 4 thrombocytopenia and neutropenia); no DLT was observed at any other dose level. Frequently reported treatment-emergent adverse events (TEAEs) of any grade were hematological: leukopenia (94.1%), neutropenia (88.2%), anemia (64.7%), and thrombocytopenia (47.1%). Grade 3–4 TEAEs included neutropenia (64.7%) and leukopenia (47.1%). Exposure of FCN-437c increased almost proportionally to doses ranging from 50 to 200 mg. At doses from 200 to 450 mg, there appeared to be a trend of saturation. The MTD was determined to be 300 mg. Of 15 patients with measurable disease, nine (60.0%) patients experienced stable disease; no complete or partial responses were observed. Conclusions These results established an acceptable safety profile for FCN-437c in patients with advanced BC, and there were no unexpected signals relative to other CDK4/6 inhibitors. (NCT04488107; July 13, 2020)