Abstract 287: CPX-351 cytotoxicity against fresh AML blasts is increased for FLT3-ITD+ cells and correlates with drug uptake and clinical outcomes
Authors: Gordon Max , Tardi Paul , Mayer Lawrence D. , Tyner Jeffrey 
Published: July 2016

Background: CPX-351, a synergistic ratio of cytarabine (Cyt) and daunorubicin (Daun) co-encapsulated in a nano-scale carrier, has demonstrated improved complete remission and overall survival rates compared to conventional Cyt + anthracycline treatments in two randomized clinical trials and is currently being evaluated in a Phase 3 trial vs 7+3 Cyt:Daun. To determine whether these effects are attributable to liposome-mediated altered drug PK or specific AML blast genotypes/phenotypes, we investigated the ex vivo cytotoxic potency of CPX-351 against fresh AML blast samples. Cytotoxicity results were correlated with patient characteristics as well as CPX-351 cellular uptake and molecular phenotype status including FLT3-ITD, NPM1 and CEBPα. Methods: Peripheral blood was obtained at diagnosis from patients with AML. White blood cells were isolated on Ficoll gradients. Cells were incubated over graded concentrations of CPX-351 for 72 hr at which time cell viability was assessed by MTS assay. Cell viability values were normalized to patient-matched untreated cells. Patient-specific IC50 values were calculated and correlated with clinically-relevant disease features. Uptake of intact CPX-351 liposomes by AML cells was determined by monitoring cells for daunorubicin fluorescence by flow cytometry. Results: CPX-351 cytotoxicity was evaluated in 53 AML patient specimens. CPX-351 IC50 values ranged from 0.03:0.006 uM to 10:2 uM (Cyt:Daun), and all values were significantly lower than the 72 hour plasma drug concentration of 60:12 uM Cyt:Daun observed in patients receiving CPX-351. Sensitivity to CPX-351 was similar regardless of cytogentic risk, NPM1 and CEBPα status as well as whether the patients went on to achieve a CR or PD upon receiving standard 7+3 Cyt:Daun after blast samples were taken. Surprisingly, AML blasts exhibiting the FLT3-ITD phenotype exhibited some of the lowest IC50 values and as a group were 5-fold more sensitive to CPX-351 than those with wild type FLT3. Flow cytometric analysis revealed a correlation between uptake of CPX-351 into AML blasts and its cytotoxic potency. Taken together, the data are consistent with clinical observations where CPX-351 retains significant anti-leukemic activity in AML patients exhibiting high-risk characteristics that are typically associated with poor outcomes when treated with conventional regimens. Conclusions: The profile of ex vivo AML blast sensitivity to CPX-351 mirrors the efficacy profile observed clinically and may provide a means to identify specific AML patient genotypes/phenotypes that could benefit most from CPX-351 treatment. The increased sensitivity of FLT3-ITD+ blasts to CPX-351 is an example of how such analyses may identify additional AML patient populations warranting further clinical investigation.

Citation Format: Max Gordon, Paul Tardi, Lawrence D. Mayer, Jeffrey Tyner. CPX-351 cytotoxicity against fresh AML blasts is increased for FLT3-ITD+ cells and correlates with drug uptake and clinical outcomes. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 287.