Exploiting PP2A dependent and independent effects of forskolin for therapeutic targeting of KMT2A (MLL)-rearranged acute leukaemia.

Background and purpose: Activation of Protein Phosphatase 2A (PP2A), via genetic and pharmacologic modulation of SET, has recently being identified as a promising strategy to therapeutically target acute myeloid leukaemia (AML) carrying KMT2A (MLL) chromosomal translocations (KMT2A-r AML).

Experimental approach: In this study, we investigated the expression of PP2A subunits and the therapeutic potential of forskolin, a cyclic adenosine monophosphate (cAMP) elevating natural compound that has been reported as a PP2A activator.

Key results: Our data show that PPP2CA encoding protein phosphatase 2 catalytic subunit α is abundantly expressed in KMT2A-r AML cells. Treatment with forskolin arrests proliferation; induces cell death; represses the expression of MYC, HOXA9 and HOXA10; stimulates PP2A activity; and attenuates the activity of ERK1/2 in KMT2A-r AML cells. Forskolin increases sensitivity to standard-of-care daunorubicin in KMT2A-AML cell lines and PDX. Silencing PPP2CA partially rescues the cytotoxic effect of forskolin, stimulates ERK1/2, inhibits GSK3β, and abolishes the forskolin-mediated repression of c-MYC and HOXA10, but it did not affect the potentiation of response to daunorubicin. This effect was also not dependent on increase of cAMP, but it was because of increase in the intracellular accumulation of daunorubicin, through inhibition of drug efflux pump P-glycoprotein 1 (multidrug resistance protein).

Conclusions and implications: In conclusion, our findings highlight a novel mechanism of action for forskolin and support a potential role of this natural compound in combination with current conventional agent daunorubicin in the treatment of KMT2A-r AML.