There is a critical public health need for the development of anti-cancer chemotherapeutics which selectively target cancerous vs. non-cancerous tissues. The glycolysis enzyme lactate dehydrogenase A (LDH-A) represents a novel and selective anti-cancer target since it is crucial in allowing cancers to maintain their highly-glycolytic metabolism (the Warburg effect), survive in hypoxic conditions, and maintain an acidic tumor microenvironment to help evade immune response. Interestingly, congenital absence or inhibition of LDH-A has minimal side effects in humans and other mammals, suggesting that therapeutic inhibition of LDH-A would have little or no on-target side effects. LDH-A overexpression has been correlated with poor prognosis and survival in an array of human cancers, and emerging research presents compelling evidence for LDH-A inhibition as a tractable anti-cancer strategy. This proposal aims to biologically characterize a class of recently discovered N-hydroxyindole (NHI) class LDH-A inhibitors. The long-term goals of this research project are to advance these inhibitors into animal studies and eventually into the clinic and, in doing so, to contribute valuable knowledge to the field of cancer biology and metabolism. The objective of the Research Training Plan is to perform further biological characterization on three promising NHI-class LDH-A inhibitors - 1j, 4j, and glucose-4j - using an established sequence of in vitro and cell culture tests. The central hypotheses of the proposed research, which have been formulated based on a strong body of preliminary results, are 1) that 1j, with its free carboxylic acid, is a potent LDH-A inhibitor; 2) that while both 1j and 4j inhibit LDH-A in cancer cells, 4j is a more cell-permeable, methyl ester pro-drug that is cleaved to 1j intracellularly; 3) that glucose-4j is acting as a pro-drug cleaved to 1j by intracellular glucosidases; 4) that glucose-4j is entering cells through GLUT transporters; 5) that glucose-4j's enhanced cancer cell toxicity over 4j is due to its ability to be more readily imported into cancer cells; and 6) tat expression levels of various GLUT transporters and glucosidases will be predictive of the toxicity of glucose-4j to various cancer cell lines. This proposal has two specific aims: 1) to further assess and characterize 1j and 4j as LDH-A inhibitors using a battery of in vitro and cell culture studies, and 2) to assess the cellular entry, cleavage, and cancer cell toxicity profile of glucose-4j.
These aims will detail how this proposal's hypotheses will be addressed using an array of techniques and assays in which the applicant is trained using equipment and resources readily available at the sponsoring institution. The proposed research is significant because it will greatly advance the development of this novel and drug-like class of LDH-A inhibitors, which have strong potential as drug candidates in the targeted and selective treatment of a wide array of cancers.
The proposed research supports the NIH and NCI's core missions to advance knowledge and improve public health through the development of novel anti-cancer therapeutics. Through the biological development of these N-hydroxyindole class lactate dehydrogenase A (LDH-A) inhibitors, this project will help push a promising, targeted and selective anti-cancer agent into the clinics.
