Abstract C222: Voreloxin is synergistic in in vitro combination with cytarabine and additive in combination with azacitidine, decitabine, and clofarabine

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 a Phase 1b/2 clinical study (SPO‐0012) of voreloxin in combination with cytarabine in relapsed or refractory AML, and to investigate the feasibility for combining voreloxin with other agents currently in clinical use for the treatment of AML. The cytotoxicity of of voreloxin in combination with cytarabine was evaluated in 3 acute leukemic cell lines (HL‐60 acute promyelocytic (APL), MV4‐11 Flt‐3 ITD positive AML and CCRF‐CEM acute lymphoblastic leukemia (ALL)). The cytotoxicity of voreloxin in combination with the nucleoside analog hypomethylating agents azacitidine, decitabine (pyrimidine analogs), and clofarabine (purine analog) was also studied in the HL‐60 APL cell line. Cytotoxicity was assessed by proliferation inhibition. The combined activity of voreloxin and cytarabine was evaluated using the combination index (CI) analysis method, in which each drug is serially diluted based on either 10X or 1X single agent IC 50 values. The combination was synergistic in the AML cell lines MV4‐11 and HL‐60, as demonstrated by a leftward shift in the voreloxin IC 50 curves and calculated CI less than 0.85. In the ALL cell line CCRF‐CEM, an additive increase in cytotoxicity was observed with CI of ≤ 0.99. Voreloxin in combination with azacitidine, decitabine or clofarabine was evaluated after simultaneous or sequential addition of the drugs. The combinations were analyzed by: 1) serial‐dilution of voreloxin combined with a fixed dose (IC 10 ) of the second compound, and 2) fixed dose (IC 10 ) of voreloxin combined with a serial dilution of the second compound. No significant change in activity was observed when compared with the single‐agent activity of each compound. Sequential dosing of the agents did not alter the cytotoxicity of the reagents in combination. These data support the ongoing phase 1b/2 clinical study of voreloxin in combination with cytarabine in relapsed or refractory AML and demonstrate the feasibility for combining voreloxin with other DNA damaging agents currently in clinical use for the treatment of AML. Citation Information: Mol Cancer Ther 2009;8(12 Suppl):C222.