Abstract 907: Targeting glycolysis enzyme, PFKFB3, in endocrine therapy resistant breast cancers

Reprogrammed glucose metabolism is recognized as one of the hallmarks of cancer. High energy demand in cancer cells leads to increased glycolysis to maintain anabolic processes that may be driven by altered enzyme levels. The second committed step in the glycolysis pathway is catalyzed by phosphofructokinase1 (PFK1), which converts fructose-6 phosphate (F6P) to fructose 1,6-bisphosphate (F1,6BP). Another enzyme, 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3), converts F6P to fructose 2,6-bisphosphate (F2,6BP) that then functions as an allosteric activator of PFK1 and drives glycolysis. PFKFB3 enzyme is upregulated in many cancers including breast cancers. PFKFB3 is regulated by estrogen in ER-positive breast cancer cells but its role in endocrine-therapy resistant breast cancer cells is largely unknown. We investigated the expression of PFKFB3 mRNA and protein in estrogen-responsive MCF7 cells and compared it with LCC9 cells that are estrogen-independent and resistant to 4-hydroxytamoxifen (4OHT) and fulvestrant (Fulv). Twofold higher PFKFB3 mRNA and protein levels were expressed in LCC9 cells compared to MCF7 cells. In addition, the estrogen-mediated stimulation of PFKFB3 that was evident in MCF7 cells was not observed in LCC9 cells. We further studied the effect of pharmacological inhibition of PFKFB3, on the growth of therapy-resistant breast cancer cells using a compound PFK158, a potent inhibitor of the PFKFB3 enzyme. Treatment with PFK158 inhibited the growth of LCC9 cells as well as another cell line, MCF7:5C that is also resistant to 4OHT and partially resistant to Fulv. PFK158 alone was effective in suppressing the growth of both the cell lines at a concentration of 5 µM or higher. Notably, combining PFK158 with either 4OHT or Fulv significantly potentiated the effect of PFK158 treatment in blocking the growth of the cells. In MCF7:5C cells the combination treatment of 2.5 µM PFK158 and Fulv (500nM) or 4OHT(500nM) inhibited cell growth by ~70% as compared to ~30% inhibition in the presence of PFK 158 alone. In LCC9 cells >70% of growth was inhibited in the combination treatment as compared to no inhibition when PFK158, 2.5 µM or 4OHT or Fulv alone was used. In publicly available datasets of ER+, node-negative breast cancer patients, high expression of PFKFB3 was associated with adverse recurrence-free survival (hazard ratio = 4.12 and p= 5.5x10-5). Our study shows an increased basal expression of PFKFB3 mRNA and protein in estrogen