Abstract C226: Clinical evidence of mechanism-based activity in voreloxin-treated AML patients

Voreloxin is a first‐in‐class anticancer quinolone derivative that intercalates DNA and poisons topoisomerase II (Stockett et al. and Hawtin et al., AACR 2008). This leads to replication‐dependent, site‐selective DNA double strand breaks (DSB) targeting G/C‐rich sequences that are characteristic sites of quinolone‐induced DNA cleavage (Noble et al, 2003, Richter et al 2007, Stockett et al, AACR 2008). A consequence of this DNA damage is G2 arrest and cell death by apoptosis. Voreloxin is under clinical investigation in acute myeloid leukemia (AML) and ovarian cancer. Clinical responses have been observed in these indications (Lancet et al., ASCO 2009; Maris et al., ASCO 2009; McGuire et al., SGO 2008), as well as in NSCLC and SCLC (Burris et al., ECCO 2007). The current analysis was performed in support of the ongoing phase 1b/2 study clinical study (SPO‐0012) of voreloxin in combination with cytarabine in relapsed or refractory AML. The purposes were to; (1) characterize voreloxin‐induced biomarkers of mechanism‐based pharmacodynamic (PD) activity in cell lines and peripheral blood mononuclear cells (PBMC) from AML patients; (2) differentiate between the cellular PD DNA damage responses to voreloxin and cytarabine; (3) profile patient PBMC before and following the combination treatment with voreloxin and cytarabine in SPO‐0012, to evaluate PD markers of cellular response; (4) investigate potential correlations between cellular PD markers of DNA damage and clinical outcome. Based on our understanding of voreloxin9s mechanism of action, pharmacodynamic (PD) markers of S phase delay, G2 arrest and DNA damage following treatment with voreloxin were profiled in cell lines and then evaluated in primary AML cells. These included markers of stalled replication forks (pRPA‐32, pCHK1) and DNA DSB (DNA‐PKcs, p53, and pCHK2). Cellular response to cytarabine was also characterized in these in vitro model systems. Cytarabine is a mainstay of treatment in AML, administered for 7 days per treatment cycle in combination with daunorubicin on days 1–3 (the “7+3” treatment schedule). Cytarabine is incorporated into DNA and causes inhibition of DNA polymerase resulting in decreased DNA synthesis and repair. DNA damage responses were observed with cytarabine, but these occurred later than with voreloxin treatment. Voreloxin induction of pDNA‐PKcs and pCHK2 were chosen for PD assessments in the ongoing phase 1b/2 study of voreloxin in combination with cytarabine in relapsed or refractory AML. PBMC were purified from blood samples collected from patients at time points pre‐ and post‐dosing. Upregulation of pDNA‐PKcs and pCHK2 was detected within 2 hours post‐dose, providing evidence of mechanism‐based PD responses to voreloxin. Inconsistent quality of PBMC preparation at individual sites precluded correlation of PD response with clinical outcome. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C226.