Mutated Ptpn11 alters leukemic stem cell frequency and reduces the sensitivity of acute myeloid leukemia cells to Mcl1 inhibition

Abstract

PTPN11 encodes the Shp2 non-receptor protein-tyrosine phosphatase implicated in several signaling pathways. Activating mutations in Shp2 are commonly associated with juvenile myelomonocytic leukemia (JMML) but are not as well defined in other neoplasms. Here we report that Shp2 mutations occur in human acute myeloid leukemia (AML) at a rate of 6.6% (6/91) in the ECOG E1900 dataset. We examined the role of mutated Shp2 in leukemias harboring MLL translocations which co-occur in human AML. The hyperactive Shp2E76K mutant, commonly observed in leukemia patients, significantly accelerated MLL-AF9 mediated leukemogenesis in vivo. Shp2E76K increased leukemic stem cell frequency and affords MLL-AF9 leukemic cells IL3 cytokine hypersensitivity. As Shp2 is reported to regulate anti-apoptotic genes, we investigated Bcl2, Bcl-xL and Mcl1 expression in MLL-AF9 leukemic cells with and without Shp2E76K. While the Bcl2 family of genes was upregulated in Shp2E76K cells, Mcl1 showed the highest upregulation in MLL-AF9 cells in response to Shp2E76K. Indeed, expression of Mcl1 in MLL-AF9 cells phenocopies expression of Shp2E76K suggesting Shp2 mutations cooperate through activation of anti-apoptotic genes. Finally, we show Shp2E76K mutations reduce sensitivity of AML cells to small molecule mediated Mcl1 inhibition suggesting reduced efficacy of drugs targeting MCL1 in patients with hyperactive Shp2.

Genetic biomarkers of sensitivity and resistance to venetoclax monotherapy in patients with relapsed acute myeloid leukemia

“…We note that FLT3‐ITD or PTPN11 mutations may confer primary and secondary resistance to venetoclax. Consistent with this, previous studies have shown that FLT3‐ITD or PTPN11 mutations can enhance the expression of anti‐apoptotic BCL‐2 relatives like BCL‐X L and MCL‐1 7, 8. When combined with venetoclax, the FLT3 inhibitor quizartinib induced more durable responses in FLT3‐ITD+ tumor‐bearing mice than either agent alone (Figure 1D).…”

Role of SHP2 in hematopoiesis and leukemogenesis

“…In a mouse model co-expression of MLL-AF10 and PTPN11 G503A resulted in accelerated disease development as compared to MLL-AF10 alone [23**]. Increase in leukemia stem cell frequency along with rapid AML development is also seen when Ptpn11 E76K is co-expressed with MLL-AF9 fusion oncogene [24]. In presence of mutant PTPN11, the leukemic cells show increase in the transcription of colony stimulating factor 1 (Csf1) and secretion of macrophage colony stimulating factor (M-CSF) resulting in enhanced differentiation of HSCs into myeloid lineage cells [23**].…”

“…In presence of mutant PTPN11, the leukemic cells show increase in the transcription of colony stimulating factor 1 (Csf1) and secretion of macrophage colony stimulating factor (M-CSF) resulting in enhanced differentiation of HSCs into myeloid lineage cells [23**]. Although co-expression of MLL-AF9 with constitutively active SHP2 does not alter the expression of Meis1 or HoxA9 [24], it can reverse cytokine induced tyrosine phosphorylation of HoxA9 and HoxA10 leading to sustained expression of CDX4, a homeodomain transcription factor (Figure 2) [25]. During normal myelopoiesis CDX4 is downregulated as HSCs differentiate into myeloid cells.…”

“…Thus its sustained high expression would inhibit differentiation and contribute to more stem cell like phenotype of leukemic cells. AML cells co-expressing mutant Ptpn11 with MLL fusion oncogenes are also more resistant to Mcl-1 inhibitor and daunorubicin [23**,24]. These studies provide insights into how co-existence of PTPN11 mutations can alter disease progression and drug resistance.…”

Venetoclax for AML: changing the treatment paradigm

“…It is important to note that previous studies had shown that FLT3-ITD or PTPN11 mutations could enhance the expression of other members of the BCL-2 family, including BCL-XL and MCL-1, providing a potential explanation for the resistance to venetoclax. 72,73 Chan et al performed a large-scale RNA interference screen to identify genes that were synthetic lethal to IDH1/2 mutations in AML. 74 Interestingly, IDH1/2-mutant primary human AML cells were more sensitive to venetoclax than IDH1/2 wild-type cells, both ex vivo and in xenograft mouse models.…”