Sensitive detection of gamma-H2AX induction as a pharmacodynamic marker for profiling patients with cancer treated with topotecan.

3093 Background: Chemotherapies for cancer patients are often designed to inhibit growth or induce apoptosis in malignant cells. Several genotoxic agents have proved effective in inducing significant DNA damage, such that apoptosis is triggered in the cell. Topotecan is a chemical inhibitor of DNA topisomerases. The inhibition of topisomerases blocks the ligation of the phosphate backbone of DNA and leads to the generation of strand breaks. In this study we evaluated gamma-H2AX as marker for drug efficacy, using antibodies that recognize the phosphorylated S139 epitope. Results: We present an automated blood-based assay for detecting phosphorylated gamma-H2AX before and after drug treatment. We first screened subpopulations of the blood for cell types that exhibit the great response in gamma-H2AX induction after drug treatment. Using this sub-phenotype, we then developed two approaches for isolating these cell types: immunomagentic enrichment of the top responding cell types, and immunophenotyping of the ...