Towards the Treatment of Secondarily Mutated Leukemia

  Acute myeloid leukemia (AML) is a devastating cancer with an overall 5-year survival rate of approximately 30%, despite efforts to develop therapeutics to combat this disease. AML is caused by various mutations, and frequent genetic errors found in 30% of AML patients are mutations in the FMS-like tyrosine kinase 3 (FLT3). Recently two FLT3 drugs for AML, Midostaurin and Gilteritinib, have been approved by the FDA, but resistance to these drugs, such as FLT3D835Y/V and F691L, mutations have limited the efficacies of both of these drugs. Thus, there is a need for newer generation FLT3 inhibitors that cover mutations encountered in the clinic. The Sintim laboratory has developed a FLT3 inhibitor, HSN748, which has shown remarkable efficacies against the majority of the FLT3 mutants. Pre-IND studies are now ongoing to support a potential clinical trial of HSN748 for AML treatment that is resistant to the approved therapeutics midostaurin and gilteritinib. The characterization of HSN748 on the proteome and phosphoproteome level was undertaken to provide a more granular view on how this potential AML therapeutic affects key cellular processes. Global proteomic and phosphoproteomic analysis revealed that HSN748 may play a role in cell cycle regulation, spindle formation, leukemic stem cell maintenance, and transcription and confirmed previous in vitro studies that showed inhibition of other kinases relevant to AML treatment, such as AURKB and Raf-1.

Recently, there have been efforts to improve the timespan of therapeutic efficiency of FLT3 inhibitors by combining FLT3 inhibitors with other drugs that target other processes essential to AML. Clinical trials (e.g. NCT03735875) are ongoing to evaluate FLT3 inhibitors combined with venetoclax against AML. The second part of this thesis project evaluated the combination of HSN748 analogs with venetoclax and discovered that the combinations synergize to increase apoptotic activity in AML cells harboring FLT3-ITD with secondary mutations D835Y or F691L, which are two clinically important genetic alterations that lead to drug resistance against current FLT3 inhibitors. We determined that the nicotinamide analog, HSL468, synergized with venetoclax with a coefficient of inhibition of 0.23 for the combination with HSL468 at 1.25 nM and venetoclax at 80 nM against an AML cell line that has both the FLT3-ITD and F691L mutations, which are responsible for resistance to most current FLT3-targeted AML therapeutics, including the combination therapy of gilterinitib and venetoclax.