Small Molecule Kinase Inhibitor Sunitinib Specifically Targets Juvenile Myelomonocytic Leukemia Cells with SHP2(PTPN11) Mutation

Juvenile myelomonocytic leukemia (JMML) is a highly fatal malignant disease in early childhood. It is still unknown of the specific pathogenesis, and there is shortage of effective targeted therapeutic approaches. Gain of function SHP2 mutation encoded by PTPN11 gene is found in approximately 35% of JMML patients, which maybe contributed to its pathogenesis. JMML patients with SHP2 mutation have lower survival rate and higher recurrence rate. All of the above make development of new therapies imperative. Currently, there is no stable cell line that can accurately reflect the characteristics of JMML abnormal cells for research on JMML. In this study, we established two leukemia cell lines that depend on mutated SHP2 for survival, and discovered promising drugs that targeted mutated-SHP2-dependent oncogenic signaling pathway through drug screening method.

HCD-57 cells are murine erythroleukemia cells that solely depend on exogenic erythropoietin (EPO) for survival. We constructed SHP2-D61Y and SHP2-E76K transformed HCD-57 cell lines through retroviral vectors, the survival of which dependent on mutated SHP2 mediated signaling pathway. Based on these cells, we established a drug screening platform and screened small molecule compound library containing 2862 FDA-approved drugs and 1707 kinase inhibitors. We performed cell viability, flow cytometry, Wright-Giemsa staining, and western blot to evaluate cells after drug treatment. To further assess therapeutic potential, we established in-vivo transplantation model that SHP2-D61Y transformed HCD-57 cells were implanted into immunodeficient NCG mice, and verified the effectiveness of the in-vitro screened drugs.

We found that the survival and proliferation of HCD-57 cells transduced by SHP2-D61Y and SHP2-E76K no longer required EPO, but completely relied on the abnormal activation of signaling pathway mediated by mutated SHP2. Western blot results showed that the phosphorylation status of ERK1/2 and AKT of HCD-57 cells expressing SHP2 mutation were abnormally increased, consistent with SHP2-mutated JMML. Thus, we have obtained the leukemia cell lines that can represent the characteristics of activated signaling pathway in JMML with SHP2 mutation. Through drug screening, we observed that drug sunitinib (Sutent ^®) selectively inhibits SHP2-mutated HCD-57 cell lines. CCK-8-based cell viability assay demonstrated a dose-dependent inhibition of SHP2-D61Y and SHP2-E76K transformed HCD-57 cell and no effects on the parental HCD-57 cells. Live cell counting with trypan blue revealed that the proliferation of SHP2-mutated HCD-57 cells was totally halted after one day upon treatment with 250 nM sunitinib, whereas the HCD-57 cells were unaffected. Wright-Giemsa staining demonstrated that SHP2-mutated HCD-57 cells showed no normal morphology change and no mitotic activity under sunitinib treatment, otherwise parental HCD-57 cells showed normal mitotic activity. Sunitinib induced apoptosis and cell cycle arrest at G1 phase in SHP2-mutated HCD-57 cells by flow cytometry, but had little effect on the parental HCD-57 cells. Sunitinib effectively downregulates the phosphorylation of ERK and AKT in SHP2-mutated cells, revealing the mechanism of sunitinib targeting SHP2-mutated cells. In addition, after transplantation of SHP2-D61Y transformed HCD-57 cells for 3 weeks, the spleen of NCG mice increased from an average of 45 mg to more than 300 mg; flow cytometry analysis showed that the implanted cells accounted for over 75% of the total nucleated cells in the bone marrow and spleen. Compared with the vehicle control, the number of monocytes in these mice was reduced to the normal range by treatment with sunitinib, and the spleen weights were reduced by about 50%. Histochemical staining showed disappearance of the myeloid infiltration in the spleen, liver and bone marrow. The above results all indicate that sunitinib has strong in-vivo anti-leukemia activity. Furthermore, western blot analysis showed that the administration of sunitinib significantly inhibited the phosphorylation expression level of AKT and ERK, indicating the effectivity of sunitinib in vivo.

In conclusion, our data demonstrated that HCD-57 cell line is an effective tool for studying oncogenic signaling pathway and screening drugs that targeted JMML with SHP2 mutation. Sunitinib can be an effective drug for the targeted treatment of JMML in the future.