Targeting MCL-1 and MAPK overcomes venetoclax resistance in FLT3-ITD-positive AML cells harbouring activating PTPN11...

Venetoclax (VEN)-based therapies have improved the treatment of acute myeloid leukaemia (AML); however, the emergence of resistance remains a major limitation. Mutations in protein tyrosine phosphatase (PTP) non-receptor type 11 (PTPN11) and FMS like tyrosine kinase 3 with internal tandem duplication (FLT3-ITD) are common in resistant patients and are linked to activation of mitogen-activated protein kinase (MAPK) signalling and increased expression of anti-apoptotic proteins such as myeloid cell leukaemia 1 (MCL-1) and b-cell lymphoma-extra large (BCL(x)L). Murine Ba/F3 cells with different FLT3-ITD variants were lentiviral transduced to express either wild-type PTPN11 (Src-homology 2 containing PTP) or the activating PTPN11-E76K mutation. Cells were treated with VEN, the MCL-1 inhibitor S63845 and the mitogen-activated protein kinase (MEK) inhibitor trametinib (TRA), alone or in combination. Additionally, primary AML samples were examined for drug sensitivity and protein expression profiles. Cells expressing PTPN11-E76K showed marked resistance to VEN, coinciding with sustained extracellular signal-regulated kinase activation and elevated MCL-1 and BCL(x)L levels. Combining VEN with MCL-1 inhibition significantly increased apoptosis. Co-treatment with TRA provided substantial synergistic benefits while yielding a more modest benefit in PTPN11-E76K-mutant cells. Both PTPN11 and FLT3 mutations confer resistance in AML, making them key factors in identifying high-risk patients. The presented results highlight the role of MAPK-driven MCL-1 and BCL(x)L expression, which mediates VEN resistance. While dual inhibition of B-cell lymphoma 2 and MCL-1 is already effective, additional MEK inhibition may further improve outcomes in PTPN11-mutated AML.