Phase 1/2 study of cyclin-dependent kinase (CDK)4/6 inhibitor palbociclib (PD-0332991) with bortezomib and dexamethasone in relapsed/refractory multiple myeloma.

This phase 1/2 study was the first to evaluate the safety and efficacy of the cyclin-dependent kinase (CDK) 4/6-specific inhibitor palbociclib (PD-0332991) in sequential combination with bortezomib and dexamethasone in relapsed/refractory multiple myeloma. The recommended phase 2 dose was palbociclib 100 mg orally once daily on days 1-12 of a 21-day cycle with bortezomib 1.0 mg/m2 (intravenous) and dexamethasone 20 mg (orally 30 min pre-bortezomib dosing) on days 8 and 11 (early G1 arrest) and days 15 and 18 (cell cycle resumed). Dose-limiting toxicities were primarily cytopenias; most other treatment-related adverse events were grade≤3. At a bortezomib dose lower than that in other combination therapy studies, antitumor activity was observed (phase 1). In phase 2, objective responses were achieved in 5 (20%) patients; 11 (44%) achieved stable disease. Biomarker and pharmacodynamic assessments demonstrated that palbociclib inhibited CDK4/6 and the cell cycle initially in most patients.

Myeloma is characterized by stage-specific alterations in DNA methylation that occur early during myelomagenesis.

Epigenetic changes play important roles in carcinogenesis and influence initial steps in neoplastic transformation by altering genome stability and regulating gene expression. To characterize epigenomic changes during the transformation of normal plasma cells to myeloma, we modified the HpaII tiny fragment enrichment by ligation-mediated PCR assay to work with small numbers of purified primary marrow plasma cells. The nano-HpaII tiny fragment enrichment by ligation-mediated PCR assay was used to analyze the methylome of CD138(+) cells from 56 subjects representing premalignant (monoclonal gammopathy of uncertain significance), early, and advanced stages of myeloma, as well as healthy controls. Plasma cells from premalignant and early stages of myeloma were characterized by striking, widespread hypomethylation. Gene-specific hypermethylation was seen to occur in the advanced stages, and cell lines representative of relapsed cases were found to be sensitive to decitabine. Aberrant demethylation in monoclonal gammopathy of uncertain significance occurred primarily in CpG islands, whereas differentially methylated loci in cases of myeloma occurred predominantly outside of CpG islands and affected distinct sets of gene pathways, demonstrating qualitative epigenetic differences between premalignant and malignant stages. Examination of the methylation machinery revealed that the methyltransferase, DNMT3A, was aberrantly hypermethylated and underexpressed, but not mutated in myeloma. DNMT3A underexpression was also associated with adverse overall survival in a large cohort of patients, providing insights into genesis of hypomethylation in myeloma. These results demonstrate widespread, stage-specific epigenetic changes during myelomagenesis and suggest that early demethylation can be a potential contributor to genome instability seen in myeloma. We also identify DNMT3A expression as a novel prognostic biomarker and suggest that relapsed cases can be therapeutically targeted by hypomethylating agents.