Flavopiridol inhibits soft tissue sarcoma growth with preferential sensitivity in a CDK4 gene amplified subtype

Abstract Introduction: Current chemotherapy for advanced soft tissue sarcoma (STS) has low overall response rates. It has been shown that the CDK4 gene is frequently amplified in some STS subtypes. Here we tested flavopiridol, a pan cyclin dependent kinase inhibitor, with STS subtypes that have amplified (dedifferentiated liposarcoma, DDLS) or non-amplified (malignant peripheral nerve sheath tumor, MPNST) CDK4. Methods: DDLS and MPNST cell lines were evaluated for cellular proliferation using CyQuant fluorescence assay, cell cycle distribution by FACS analysis and apoptosis using AnnexinV/7-AAD staining following 24h of treatment with flavopiridol. CDK4 amplification was confirmed via FISH analysis. Results: Flavopiridol inhibited proliferation of DDLS and MPNST cells with IC50s of 100 and 150nM, respectively. DDLS cells, which possess amplified CDK4, demonstrated a dose dependent increase in apoptosis with 15% and 27% cells undergoing apoptosis at 150 and 300nM flavopiridol respectively, after 24h of treatment. In contrast, the MPNST cells demonstrated a 3-fold lower apoptotic percentage compared to DDLS cells at these concentrations of flavopiridol. Lastly, the DDLS cells underwent G1 cell cycle arrest with as little as 150nM flavopiridol whereas the cell cycle distribution of the MPNST cells remained unchanged with up to 300nM flavopiridol. Conclusions: Flavopiridol has antiproliferative activity in STS cell lines. CDK4 gene amplification in dedifferentiated liposarcoma renders these cells more sensitive to flavopiridol mediated G1 cell cycle arrest and apoptosis. Our findings suggest flavopiridol to be a novel therapeutic agent for the treatment of STS, preferentially with amplified CDK4.