Abstract
PURPOSE: Trilaciclib is a first-in-class CDK4/6 inhibitor that transiently arrests hematopoietic stem and progenitor cells (HSPCs) in the G1 phase of the cell cycle to preserve them from chemotherapy-induced damage (myelopreservation). We report integrated analyses of preclinical and clinical data that informed selection of the recommended Phase II dose (RP2D) used in trilaciclib trials in extensive-stage small cell lung cancer (ES-SCLC). METHODS: A semi-mechanistic pharmacokinetic/pharmacodynamic (PK/PD) model developed from preclinical data guided selection of an optimal dose for G1 bone marrow arrest in a first-in-human Phase I study (G1T28-1-01). PK, PD, safety, and efficacy data from G1T28-1-01 and two Phase Ib/IIa studies (G1T28-02/-03) in ES-SCLC were analyzed to support RP2D selection. RESULTS: Model simulation of bone marrow arrest based on preclinical data predicted that a ≥ 192 mg/m(2) dose would induce a 40-50% decrease in total bone marrow proliferation in humans and almost 100% cell cycle arrest of cycling HSPCs. Consistent with this model, analysis of bone marrow aspirates in healthy volunteers after trilaciclib 192 mg/m(2) administration demonstrated almost 100% G1 arrest in HSPCs and 40% decrease in total bone marrow proliferation, with minimal toxicity. G1T28-02/-03 reported similar PK parameters with trilaciclib 200 mg/m(2) but slightly lower exposures than expected compared with healthy volunteers; consequently, 240 and 280 mg/m(2) doses were also tested to match healthy volunteer exposures. Based on PK and relevant safety data, 240 mg/m(2) was selected as the RP2D, which was also favored by myelopreservation endpoints in G1T28-02/-03. CONCLUSION: Integrated PK/PD, safety, and efficacy data support 240 mg/m(2) as the RP2D for trilaciclib. CLINICALTRIALS. GOV IDENTIFIERS: NCT02243150; NCT02499770; NCT02514447.