The pre clinical data demonstrated that P276-00 is a selective Cdk4-D1 and Cdk1-B inhibitor with potent cytotoxic effects against MM cells including sensitive (MM1.S, RPMI 8226, OPM1, OPM2) and resistant (MM1.R, Dox-40, LR5) to conventional chemotherapy as well as in mouse xenograft models. The IC50 for this effect is between 300-1000 nM in vitro, and potential doses to be evaluated in the clinical study can achieve these concentrations. This evidence supports a rationale for evaluating the effects of P276-000 in patients with relapsed/refractory MM in order to determine safety and tolerability as well as pharmacokinetics and potential efficacy. The current study design allows for adequate assessment of patient safety in terms of the potential adverse effects of P276-00.