Momelotinib inhibition of JAK/STAT in a mouse JAKV617F myelofibrosis model showed concurrent activation of p-ERK and p-AKT which was reversed by combination therapy using LP-182, a novel MEK/PI3K/mTOR inhibitor Free

Introduction: Most cases of myelofibrosis (MF) arise from constitutive activation of the JAK/STAT signaling pathway in hematopoietic stem cells (HSCs) with resultant activation of bone marrow stromal cells driving fibrosis. Treatment options are limited to approved Janus kinase (JAK) inhibitors that produce minimal reductions in fibrosis or malignant HSCs, the primary drivers of disease. Overall five-year survival remains ~40%, underscoring the dismal plight of patients with MF. Aberrant JAK/STAT signaling activates downstream PI3K/AKT/mTOR pathway and MAPK/ERK pathways with interconnections between these pathways regulating outputs such as gene expression, proliferation, and survival. Due to considerable signaling crosstalk, we posited that combined targeting of both upstream (JAK/STAT) along with downstream (MEK and PI3K/mTOR) signaling effectors would increase treatment efficiency compared to current, single agent JAKi's.

Methods & Results: Treatment of in vitro SET-2 cells revealed IC₅₀ for proliferation of LP-182, MMB and LP-182+MMB was 14.4, 0.13 and 0.07mm, respectively. MRI was used to quantify changes in spleen volumes over time in a mouse JAK2-mutant MF mouse model. Treatment cohorts consisted of vehicle (n=11), LP-182 (400 mg/kg, PO, n=5), momelotinib (MMB, 50 mg/kg, PO, n=7) and combination (LP-182+MMB, n=4) OD for 28 days. Mean spleen volume/body weight (mm³/BW) were assessed over time at T0/T28 (mean(+/-sem)) days for vehicle (23.5(2.1)/25.8(2.1)), MMB (24.0(3.0)/19.8(2.5)), LP-182 (26.5(2.73)/22.6(3.2)) and combination group (22.0(1.9)/16.1(2.8). Measurements of spleen volumes in LP-182 and MMB treatment groups generally declined over the treatment period but to a lesser extent than the combination treatment group. Harvested spleens at the end of study were evaluated for signaling modulation which revealed for the MMB treated cohort, no significant reduction of pATK or pERK1/2 levels, however, MMB treatment resulted in significantly reduced pSTAT5 levels (p<0.001) compared to vehicles. LP-182 treatment alone or in combination with MMB revealed normalization of pAKT and pERK was achieved.

Clinical Implications: Jaki's such as MMB and ruxolitinib are unable to down modulate oncogenic driver signals such as PI3K/mTOR and MAPK necessitating development of an improved therapeutic strategy. LP-182 was demonstrated to have potency as single agent and in combination with MMB for down-modulating proliferative and survival signals. As LP-182 was demonstrated to provide therapeutic potency in combination with MMB, clinical evaluation of this combination strategy appears warranted. LP-182 has been demonstrated to be absorbed through the lymphatic system which provides a unique opportunity to establish an efficacious, less toxic combination approach towards development of an efficacious MF treatment strategy for ultimately improving patient outcomes.