Abstract 2519: Targeting glucose metabolism in HER2+breast cancer

Primary and metastatic breast cancers are driven by oncogenic mutations to rely on glucose metabolism to support their rapid proliferation. Of these genetic changes, the increased activity of the human epidermal growth factor receptor 2 (HER2/ErbB2) is observed in a third of all breast tumors. HER2 has been shown to activate downstream effectors (e.g. Ras, HIF-1α) that stimulate glycolysis - in part by activation of the 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase family of enzymes (PFKFB1-4). The PFKFBs produce fructose-2,6-bisphosphate (F26BP) which activates a key rate-limiting glycolytic enzyme, 6-phosphofructo-1-kinase (PFK1). In preliminary studies, we found that the PFKFB4 family member was highly expressed in a series of patient-derived HER2+ breast tumors relative to normal breast with markedly higher expression in their matched metastatic lymph nodes. We next determined that silencing PFKFB4 markedly reduced F26BP, glycolysis and cell survival in HER2+ breast cancer cells and inhibited tumor growth in vivo. Through virtual screening, we have discovered a first-in-class small molecule inhibitor of PFKFB4, termed 5MPN, that selectively inhibits PFKFB4 activity with a resultant decrease in F26BP, glycolysis and cancer cell growth. 5MPN also caused a significant decrease in the invasion and migration of HER2+ breast cancer cells in vitro, importantly at concentrations well below levels that affect cell viability and marked suppression in the growth of established tumors, without systemic toxicity. In additional studies, we have found that the related PFKFB3 isoform is also expressed in HER+ breast tumors. Our previous work found that the PFKFB4 enzyme localizes to the cytoplasm (where PFK1 and the glycolytic pathway function) indicating a possible dominant role for PFKFB4 in glycolytic regulation. PFKFB3 however largely localized to the nucleus where it serves an important function in proliferation via activation of cyclin-dependent kinases. Based on the different roles played by these enzymes in cancer cells, we next evaluated the effects of simultaneous administration of 5MPN ± a clinical candidate PFKFB3 inhibitor on survival and proliferation in HER2+ breast cancer and found that the combination synergistically and significantly decreased viability and growth in several examined HER2+ breast cancer cell lines. Our data indicate that targeting PFKFB4 may be a viable therapeutic option against breast cancer and strongly support the further