Phase I study of PD 0332991, a cyclin-dependent kinase inhibitor, administered in 3-week cycles (Schedule 2/1).

Background: This phase I, open-label, first-in-human study determined dose-limiting toxicities (DLTs) and maximum tolerated dose (MTD) of PD 0332991, an oral cyclin-dependent kinase 4/6 inhibitor with potent anti-proliferative activity in vitro/vivo.
Methods: A total of 33 patients with retinoblastoma protein-positive advanced solid tumours or non-Hodgkin's lymphoma refractory to standard therapy or for which no therapy was available received PD 0332991 once daily (QD) for 14 days followed by 7 days off treatment (21-day cycles; Schedule 2/1).
Results: Six patients had DLTs (18%; four receiving 200 mg QD; two receiving 225 mg QD); the MTD was 200 mg QD. Treatment-related, non-haematological adverse events occurred in 29 patients (88%) during cycle 1 and 27 patients (82%) thereafter. Adverse events were generally mild-moderate. Of 31 evaluable patients, one with testicular cancer achieved a partial response; nine had stable disease (≥10 cycles in three cases). PD 0332991 was slowly absorbed (mean T(max) 4.2 h) and eliminated (mean half-life 26.7 h). Volume of distribution was large (mean 3241 l) with dose-proportional exposure. Using a maximum effective concentration model, neutropenia was proportional to exposure.
Conclusion: PD 0332991 was generally well tolerated, with DLTs related mainly to myelosuppression. The MTD, 200 mg QD, is recommended for phase II study.