RMC-4550, an Allosteric Inhibitor of SHP2, Displays Therapeutic Efficacy in Pre-Clinical Models of Myeloproliferative Neoplasms
Authors: Pandey Garima , Horvat Nathan , Amin Narmin E. , Akuffo Afua A. , Colin Christelle , Epling-Burnette Pearlie K. , Reuther Gary W. 
Published: November 2019

Philadelphia chromosome negative myeloproliferative neoplasms (MPNs) are JAK2-driven disorders resulting from mutations in JAK2, MPL, or CALR. Ruxolitinib, the only FDA-approved JAK2 inhibitor for MPNs, alleviates patient symptomology and improves quality of life, but has little effect on reducing mutant allele burden. This persistent survival of MPN cells in the face of ruxolitinib, as well as other JAK2 inhibitors that have been clinically tested, is a major clinical bottleneck to the development of an effective targeted therapy for MPN patients. Identifying new therapeutic targets which play critical roles in MPN cells and/or in JAK2 inhibitor persistence may lead to improved MPN therapies. SHP2 is an oncogenic tyrosine phosphatase that is an effector of growth factor and cytokine receptor signaling. SHP2 plays a critical role in the activation of the RAS-ERK pathway and regulates JAK-STAT signaling via numerous phosphatase-dependent mechanisms. Activating mutations of SHP2(PTPN11) have been identified in leukemia, including 8% of MPN patients whose disease progressed to acute myeloid leukemia (AML). In addition, SHP2 has been shown to mediate adaptive resistance to targeted therapies in several cancers.
Given the role of SHP2 in cytokine and JAK-STAT signaling, we envisaged a potential role of SHP2 in MPN cell growth and/or survival and ruxolitinib persistence. Treatment of JAK2-V617F-driven MPN model cell lines (UKE1, SET2, and BaF3-JAK2-V617F) with ruxolitinib blocked constitutive tyrosine phosphorylation of SHP2, including phosphorylation of Y542, a marker for activated SHP2. This phosphorylation, however, was restored in ruxolitinib persistent cells. Combination treatment of the allosteric SHP2 inhibitor RMC-4550 (Revolution Medicines) with ruxolitinib prevented the development of ruxolitinib persistent cells and pre-established persistent cells remained sensitive to SHP2 inhibition. RMC-4550 treatment led to significantly reduced levels of pERK consistent with the role of SHP2 in RAS signaling. Interestingly, pERK levels in persistent cells were more sensitive to SHP2 inhibition compared to drug naïve cells suggesting pERK was more dependent on SHP2 in ruxolitinib persistent cells. SHP2 inhibitor treatment increased pSTAT5(Y694) in drug naïve cells but this increase was not observed in similarly treated persistent cells. Furthermore, while ruxolitinib inhibited pERK levels in UKE1 and SET2 cells, pERK levels recovered within 24 hrs of treatment. SHP2 inhibition prevented the recovery of pERK in the presence of ruxolitinib. Collectively, these data suggest that signaling pathways in MPN cells treated with ruxolitinib can become rewired, gaining greater dependence on SHP2, concomitant with sustained pERK and cell survival/growth. Interestingly, we identified a known activating SHP2 mutation (F71L) in UKE1 cells obtained from two independent sources - consistent with the presence of PTPN11 mutations in post-MPN AML. The persistent survival of UKE1 cells in ruxolitinib was antagonized by CRISPR-mediated reduction of SHP2 expression, providing further evidence that SHP2 contributes to ruxolitinib persistence.
To assess the effects of a SHP2 inhibitor on MPN progression in vivo, we employed the MPLW515Lbone marrow transplant mouse model of MPN. Initial assessment of therapeutic treatment of mice with an established MPN phenotype indicated that once daily treatment of RMC-4550 (10 or 30 mg/kg) antagonized the MPN phenotype. Complete blood counts indicated a significant reduction in white blood cells, monocytes, and neutrophils compared to vehicle treated mice, while flow cytometry analysis indicated RMC-4550 diminished CD11b+ cell numbers to near that observed in mice transplanted with MPLWT-transduced bone marrow. RMC-4550 improved the overall health of diseased mice, as indicated by increased weight, and significantly reduced organomegaly of the spleen and liver compared to vehicle treated MPN mice. Finally, erythropoietin independent erythroid colony formation of JAK2V617F-positive MPN patient cells was suppressed following SHP2 inhibition, which synergized or enhanced the inhibition induced by ruxolitinib in this assay.
In summary, our results suggest that SHP2 inhibition may represent a potential MPN therapy in both ruxolitinib naïve and resistant patients and is an attractive therapeutic target for future clinical investigation.

Disclosures
Epling-Burnette: Incyte Corporation: Research Funding; Forma Therapeutics: Research Funding; Celgene Corporation: Patents & Royalties, Research Funding. Reuther:Incyte Corporation: Research Funding.