Drug Sensitivity Across Acute Myeloid Leukemia Subtypes Using an in Vitro Assay

Introduction:

Acute myeloid leukemia (AML) remains a challenging malignancy to treat, with high mortality despite recent advances in cancer care. The mainstay of therapy is intensive chemotherapy including anthracyclines and antimetabolites, with or without allogeneic bone marrow transplant. The standard of care has not changed significantly in decades, and treatment options are limited for patients who do not respond to induction, or who relapse. Although the genetic and molecular diversity of AML is well recognized, the effective integration of targeted therapies into treatment regimens has been difficult. The current study evaluates the in vitro activity of an array of antineoplastic agents in AML, with the goal of identifying drug sensitivity patterns that may help guide therapies based on mutational and cytogenetic profiling.

Methods:

51 patients with AML were enrolled in the study from September 2013 to July 2016 under an IRB approved consenting process at Scripps Health. Samples were collected at both diagnosis and relapse if available. Both bone marrow and peripheral blood were accepted, with a requirement of significant circulating blasts if peripheral blood was used. Samples were tested for common biomarkers and cytogenetic abnormalities. 2,500 cells per well were transferred onto tissue culture treated plates. Drugs with potential antileukemic activity were added to each well in concentrations of 0.1, 1.0, and 10.0 μM. The cells were incubated with the drugs for 96 hours at 37^oC. Cell viability was measured and reported as a percentage of plate-specific controls incubated with dimethylsulfoxide alone.

Results:

Drugs were grouped by therapeutic class. In vitro responses to anthracyclines and antimetabolites were noted across all mutational subtypes of AML. BCL-2 inhibitors and the histone deacetylase inhibitor romidepsin showed significant in vitro antileukemic activity across all subtypes. Proteasome inhibitors almost universally showed robust in vitro activity, even at the lowest drug concentration.

The drug pevonedistat, a selective small-molecule inhibitor of NEDD8-activating enzyme, had significant differential activity depending on mutational status. FLT3-ITD mutations conferred sensitivity to the molecule, while mutations in NPM1 appeared to confer resistance. For the 10.0 μM concentration of pevonedistat, the average cell viability was 149.8% vs 37.3% (P=0.02) for the NPM1 mutated samples vs the FLT3-ITD mutated samples respectively.

Conclusion:

This in vitro assay demonstrates the ability to rapidly determine sensitivity of human AML cells to a wide variety of antileukemic drugs. Limitations include the fixed concentrations used across all medications which allowed comparisons between patients, but limits comparison of drug efficacy for an individual patient. The mechanism of some medications, such as hypomethylating agents and tretinoin, may require longer duration of exposure, thus confounding interpretation of the 96-hour viability results. Despite these limitations, we were able to find interesting patterns of responses across a wide spectrum of AML types. Anticipated applications of the assay include experimentation with novel drug combinations, directing in vivo clinical studies, and informing individualized treatment decisions in AML.