One distinguishing hallmark of cancer cells includes a deregulated cellular metabolism that can be reprogrammed to preferentially exhibit dependence on glycolysis over oxidative phosphorylation (OXPHOS) even in the presence of oxygen (Warburg Effect). The bi-directional conversion of glucose to lactate is mainly driven by the lactate-dehydrogenase (LDH) enzyme, of which, its A isoform is overexpressed in various tumors types. In the present study, we characterized two novel LDH inhibitors (NCI-006 and NCI-737) in combination with ionizing radiation (IR) for their anti-cancer and radio-sensitization effects across cell lines of pancreatic (MiaPaca, Hs766T, Panc-1), lung (H460, A549), head and neck (FaDU, UMSCC-1), and prostate (DU145, PC3) origin. Our preliminary results indicated that targeting LDH in conjunction with IR can enhance radiosensitivity under both hypoxic and normoxic conditions across glycolytic tumor cell lines while not affecting non-glycolytic/normal cells (1522, skin fibroblast) in vitro. Further, we established that this enhanced radiosensitivity could be attributed to reduced DNA repair as seen by enhanced expression of y-H2AX and reduced ATP generation. Our results also indicated that increased expression of lactate and glucose transporters, combined with cellular bioenergetics changes, leads to a reprogramming of cells to OXPHOS. Lastly, we found that inhibition of OXPHOS and NAD+ in conjunction with these novel LDH inhibitors promotes metabolic synthetic lethality in vitro. As cancer patients continue to receive radiation for local tumor control, we believe that future studies targeting cancer metabolic vulnerabilities in combination with IR in vivo will enhance the therapeutic ratio of radiotherapy.