mTOR Inhibitors Alone and in Combination with JAK2 Inhibitors Effectively Inhibit Cells of Myeloproliferative Neoplasms

Abstract

BackgroundDysregulated signaling of the JAK/STAT pathway is a common feature of chronic myeloproliferative neoplasms (MPN), usually associated with JAK2V617F mutation. Recent clinical trials with JAK2 inhibitors showed significant improvements in splenomegaly and constitutional symptoms in patients with myelofibrosis but meaningful molecular responses were not documented. Accordingly, there remains a need for exploring new treatment strategies of MPN. A potential additional target for treatment is represented by the PI3K/AKT/mammalian target of rapamycin (mTOR) pathway that has been found constitutively activated in MPN cells; proof-of-evidence of efficacy of the mTOR inhibitor RAD001 has been obtained recently in a Phase I/II trial in patients with myelofibrosis. The aim of the study was to characterize the effects in vitro of mTOR inhibitors, used alone and in combination with JAK2 inhibitors, against MPN cells.FindingsMouse and human JAK2V617F mutated cell lines and primary hematopoietic progenitors from MPN patients were challenged with an allosteric (RAD001) and an ATP-competitive (PP242) mTOR inhibitor and two JAK2 inhibitors (AZD1480 and ruxolitinib). mTOR inhibitors effectively reduced proliferation and colony formation of cell lines through a slowed cell division mediated by changes in cell cycle transition to the S-phase. mTOR inhibitors also impaired the proliferation and prevented colony formation from MPN hematopoietic progenitors at doses significantly lower than healthy controls. JAK2 inhibitors produced similar antiproliferative effects in MPN cell lines and primary cells but were more potent inducers of apoptosis, as also supported by differential effects on cyclinD1, PIM1 and BcLxL expression levels. Co-treatment of mTOR inhibitor with JAK2 inhibitor resulted in synergistic activity against the proliferation of JAK2V617F mutated cell lines and significantly reduced erythropoietin-independent colony growth in patients with polycythemia vera.Conclusions/SignificanceThese findings support mTOR inhibitors as novel potential drugs for the treatment of MPN and advocate for clinical trials exploiting the combination of mTOR and JAK2 inhibitor.

Pro-Apoptotic Activity of Ruxolitinib Alone and in Combination with Hydroxyurea, Busulphan, and PI3K/mTOR Inhibitors in JAK2-Positive Human Cell Lines

“…Thus, our data showed that LY294002 is a more potent inducer of apoptosis of SET2 and HEL cells than RAPA, which may be related to differences in the inhibition target (Akt1 vs mTORC1), as similar differences were observed on JAK2V617F mutated human and murine leukemia cell lines between the ATP mimetic inhibitor PP242 (inhibitor of both mTORC complexes) and the allosteric inhibitor RAD001 (everolimus, inhibitor of mTORC1) [12,19]. The authors conclude that inhibition of JAK2V617F positive cells by RAD001 was more likely due to a cytostatic than an apoptotic effect and suggested that inhibition of both TORC1 and TORC2 complexes is essential for induction of apoptosis.…”

“…For example, beside the abnormal JAK/STAT pathway, constitutive activation of the phosphoinositide 3-kinase (PI3K)/protein kinase B (Akt)/mammalian target of rapamycin (mTOR) pathway was discovered [10,11]. Recently, it has been shown in preclinical studies that a combination of everolimus (rapamycin analogue) and RX demonstrated strong synergism in inhibiting different MPNs cells [12,13]. Moreover, everolimus was efficient (phase I/II trial) in reducing splenomegaly and systemic symptoms in patients with myelofibrosis.…”

Emerging treatments for classical myeloproliferative neoplasms

“…Everolimus (RAD-001), an mTORC1 inhibitor used in prevention of organ rejection, effectively inhibited proliferation of JAK2V617F-mutated cell lines, alone and synergistically with JAK1/JAK2i. 82 In a phase 1/2 study in patients with MF, the response rate was 23%. 85 At present, there is no ongoing trial in MF.…”

JAK kinase targeting in hematologic malignancies: a sinuous pathway from identification of genetic alterations towards clinical indications

“…149,150 A similar synergistic action was also observed between mTOR and JAK2 inhibitors. 151 A translational phase I clinical study is currently evaluating the safety and maximal tolerated doses of the combination of ruxolitinib and BKM120, a PI3K inhibitor, in MF patients (NCT01730248). In addition to further clinical benefit, simultaneous blockade of oncogenic signaling at multiple levels by combined therapy approaches (such as ruxolinitib with PI3K inhibitors or HSP90 inhibitors) might avoid the emergence of resistance by distributing the selective pressure between distinct targets.…”