Pharmacologic co-inhibition of Mnks and mTORC1 synergistically suppresses proliferation and perturbs cell cycle progression in blast crisis-chronic myeloid leukemia cells.

The Ras/Raf/MAPK and PI3K/Akt/mTORC1 cascades are two most aberrantly regulated pathways in cancers. As MAPK-interacting kinases (Mnks) are part of the convergent node of these two pathways, and play a pivotal role in cellular transformation, targeting Mnks has emerged as a potential therapeutic strategy. Herein, a dual-specific Mnk1/2 inhibitor MNKI-57 and a potent Mnk2-specific inhibitor MNKI-4 were selected for a panel screen against 28 human cancer cell lines. The study reveals that MNKI-57 and MNKI-4 are most potent against leukemia cells KYO-1 (i.e. BC-CML) and KG-1 (i.e. AML). Interestingly, we found that sensitivity of selected leukemia cells to Mnk inhibitors is correlated with the level of phosphorylated 4E-BP1 at Thr70. The anti-proliferative effects of Mnk inhibitors are cytostatic in the sensitive KYO-1 cells, inducing significant G1 arrest via down-regulation of cyclin D1 expression. In KYO-1 cells where Akt is not constitutively active, Mnk inhibitors increase the sensitivity of cells to rapamycin, resulting in a more pronounced anti-proliferative activity. Remarkably, the synergistic anti-proliferative effects are associated with a marked de-phosphorylation of 4E-BP1 at Thr70. Collectively, these data highlight the importance of 4E-BP1 as a key integrator in the MAPK and mTORC1 cascades, and suggest that a combined pharmacologic inhibition of mTORC1 and Mnk kinases offers an innovative therapeutic opportunity in BC-CML.