Combination of a mitogen-activated protein kinase inhibitor with the tyrosine kinase inhibitor pacritinib combats cell adhesion-based residual disease and prevents re-expansion of FLT3-ITD acute myeloid leukaemia.

Minimal residual disease (MRD) in acute myeloid leukaemia (AML) poses a major challenge due to drug insensitivity and high risk of relapse. Intensification of chemotherapy and stem cell transplantation are often pivoted on MRD status. Relapse rates are high even with the integration of first-generation FMS-like tyrosine kinase 3 (FLT3) inhibitors in pre- and post-transplant regimes and as maintenance in FLT3-mutated AML. Pre-clinical progress is hampered by the lack of suitable modelling of residual disease and post-therapy relapse. In the present study, we investigated the nature of pro-survival signalling in primary residual tyrosine kinase inhibitor (TKI)-treated AML cells adherent to stroma and further determined their drug sensitivity in order to inform rational future therapy combinations. Using a primary human leukaemia-human stroma model to mimic the cell-cell interactions occurring in patients, the ability of several TKIs in clinical use, to abrogate stroma-driven leukaemic signalling was determined, and a synergistic combination with a mitogen-activated protein kinase (MEK) inhibitor identified for potential therapeutic application in the MRD setting. The findings reveal a common mechanism of stroma-mediated resistance that may be independent of mutational status but can be targeted through rational drug design, to eradicate MRD and reduce treatment-related toxicity.