Supplementary Table S1-2. Table S1 - Clinical exposure for palbociclib, fulvestrant and chemotherapeutic agents used in this study. Table S2 - Cell cycle analysis in human bone marrow mononuclear cells treated with palbociclib for 4 days. Supplementary Figure S1-4. Figure S1 - Microscopic images of bone marrow sternum taken from A) a female dog treated with vehicle control and B) a female dog treated with palbociclib at 3 mg/kg/day for 274 days. Figure S2 - Assessment of lineage-specific effects of palbociclib treatment in human bone marrow CD34+ hematopoietic stem cells. Figure S3 - Assessment of effect of palbociclib treatment in human peripheral blood mononuclear cells (hPBMCs). Figure S4 - Assessment of relative estrogen receptor alpha (ERα) and retinoblastoma 1 (Rb1) expression in hBMNCs and MCF-7 cells using qRT-PCR.
ARTICLE ABSTRACT
Purpose: Palbociclib (PD-0332991) is the first selective cyclin-dependent kinase (CDK) 4/6 inhibitor approved for metastatic breast cancer. Hematologic effects, especially neutropenia, are dose-limiting adverse events for palbociclib in humans.Experimental Design: Reversible hematologic effects and bone marrow hypocellularity have been identified in toxicology studies in rats and dogs after palbociclib treatment. To understand the mechanism by which the hematologic toxicity occurs, and to further differentiate it from the myelotoxicity caused by cytotoxic chemotherapeutic agents, an in vitro assay using human bone marrow mononuclear cells (hBMNC) was utilized.Results: This work demonstrated that palbociclib-induced bone marrow suppression occurred through cell-cycle arrest, with no apoptosis at clinically relevant concentrations, was not lineage-specific, and was reversible upon palbociclib withdrawal. In contrast, treatment with chemotherapeutic agents (paclitaxel and doxorubicin) resulted in DNA damage and apoptotic cell death in hBMNCs. In the presence or absence of the antiestrogen, palbociclib-treated hBMNCs did not become senescent and resumed proliferation following palbociclib withdrawal, consistent with pharmacologic quiescence. The breast cancer cells, MCF-7, conversely, became senescent following palbociclib or antiestrogen treatment with additive effects in combination and remained arrested in the presence of antiestrogen.Conclusions: Palbociclib causes reversible bone marrow suppression, clearly differentiating it from apoptotic cell death caused by cytotoxic chemotherapeutic agents. This study also distinguished the cell-cycle arresting action of palbociclib on normal bone marrow cells from the senescent effects observed in breast cancer cells. These results shed light on the mechanism and support risk management of palbociclib-induced bone marrow toxicity in the clinic. Clin Cancer Res; 22(8); 2000–8. ©2015 AACR.
