# Targeting MCL‐1 and MAPK overcomes venetoclax resistance in FLT3‐ITD‐positive AML cells harbouring activating PTPN11 (SHP‐2) mutations

## TL;DR

This study shows that combining venetoclax with MCL-1 and MEK inhibitors can overcome resistance in AML cells with specific mutations.

## Contribution

The study identifies a novel therapeutic strategy for overcoming venetoclax resistance in AML with PTPN11 and FLT3-ITD mutations.

## Key findings

- PTPN11-E76K mutation causes resistance to venetoclax by increasing MCL-1 and BCL(x)L levels.
- Combining venetoclax with MCL-1 and MEK inhibitors significantly enhances apoptosis in resistant cells.
- PTPN11 and FLT3 mutations are key factors in venetoclax resistance and patient risk stratification.

## Abstract

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.