Reactive stromal cells are an integral part of tumor microenvironment (TME) and interact with cancer cells to regulate their growth. Although targeting stromal cells could be a viable therapy to regulate the communication between TME and cancer cells, identification of stromal targets that make cancer cells vulnerable has remained challenging and elusive. Here, we identify a previously unrecognized mechanism whereby metabolism of reactive stromal cells is reprogrammed through an upregulated glutamine anabolic pathway. This dysfunctional stromal metabolism confers atypical metabolic flexibility and adaptive mechanisms in stromal cells, allowing them to harness carbon and nitrogen from noncanonical sources to synthesize glutamine in nutrient-deprived conditions existing in TME. Using an orthotopic mouse model for ovarian carcinoma, we find that co-targeting glutamine synthetase in stroma and glutaminase in cancer cells reduces tumor weight, nodules, and metastasis. We present a synthetic lethal approach to target tumor stroma and cancer cells simultaneously for desirable therapeutic outcomes.

SUMMARY While recombinant human erythropoietin (rhEpo) has been widely used to treat anemia in cancer patients, concerns about its adverse effects on patient survival have emerged. A lack of correlation between expression of the canonical EpoR and rhEpo’s effects on cancer cells prompted us to consider the existence of an alternative Epo receptor. Here, we identified EphB4 as an Epo receptor that triggers downstream signaling via STAT3 and promotes rhEpo induced tumor growth and progression. In human ovarian and breast cancer samples, expression of EphB4 rather than the canonical EpoR correlated with decreased disease-specific survival in rhEpo-treated patients. These results identify EphB4 as a critical mediator of erythropoietin-induced tumor progression and further provide clinically significant dimension to the biology of erythropoietin.

We have previously shown that complement component 3 (C3) is secreted by malignant epithelial cells. To understand the mechanism of upregulation of C3 expression in tumor cells we studied the C3 promoter; and identified that TWIST1 binds to the C3 promoter and enhances its expression. Because TWIST1 mediates epithelial-mesenchymal transition (EMT), we studied the effect of C3 on EMT and found that C3 decreased E-cadherin expression on cancer cells and promoted EMT. We showed that C3-induced reduction in E-cadherin expression in ovarian cancer cells was mediated by C3a and is Krüppel-like factor 5 (KLF5)-dependent. We investigated the association between TWIST1 and C3 in malignant tumors and in murine embryos. TWIST1 and C3 co-localized at the invasive tumor edges, and in the neural crest and limb buds of mouse embryos. Our results identified TWIST1 as a transcription factor that regulates C3 expression during pathologic and physiologic EMT.

We investigated the effect of platelets on ovarian cancer and the role of adenosine diphosphate (ADP) receptors (P2Y12 and P2Y1) on platelets in the growth of primary ovarian cancer tumors. We showed that in murine models of ovarian cancer, a P2Y12 inhibitor (ticagrelor) reduced tumor growth by 60% compared with aspirin and by 75% compared with placebo. In P2Y12 mice, the growth of syngeneic ovarian cancer tumors was reduced by >85% compared with wild-type (WT) mice. In contrast, there was no difference in tumor growth between P2Y1 and WT mice. Reconstitution of hematopoiesis in irradiated P2Y12 mice by hematopoietic progenitor cells from WT mice (WT→P2Y12) restored tumor growth in P2Y12 mice. Finally, knockdown of ecto-apyrase (CD39) on ovarian cancer cells increased tumor growth in tumor-bearing mice. Although in the absence of platelets, ADP, the P2Y12 inhibitor, recombinant apyrase, or knockdown of CD39 did not affect cancer cell proliferation, in the presence of platelets, the P2Y12 inhibitor and recombinant apyrase reduced and knockdown of CD39 increased platelet-enhanced cancer cell proliferation. These results suggest that P2Y12 on platelets and ADP concentration at the interface between cancer cells and platelets affect the growth of primary ovarian cancer tumors in mice. If additional studies in mice and in pilot human trials confirm our results, inhibition of P2Y12 might be a new therapeutic option that can be used in adjuvant to the traditional surgery and chemotherapy in patients with ovarian cancer.