Flavopiridol in patients with relapsed or refractory multiple myeloma: a phase 2 trial with clinical and pharmacodynamic end-points.

Flavopiridol downregulates anti-apoptotic regulators including Mcl-1, upregulates p53, globally attenuates transcription through inhibition of P-TEFb, binds to DNA, and inhibits angiogenesis. Eighteen myeloma patients were treated with 1-hour flavopiridol infusions for 3 consecutive days every 21 days. Immunoblotting for Mcl-1, Bcl-2, p53, cyclin D, phosphoRNA polymerase II and phosphoSTAT 3 was conducted on myeloma cells. Ex vivo flavopiridol treatment of cells resulted in cytotoxicity, but only after longer exposure times at higher flavopiridol concentrations than were anticipated to be achieved in vivo. No anti-myeloma activity was observed in vivo. As administered, flavopiridol has disappointing activity as a single agent in advanced myeloma.