Colon cancer is the fourth most common cancer in this country. A wide variety of strategies are currently used for treatment of colon cancer, but none of them offers a permanent cure for the disease. New drug targets are sorely needed to succeed in the fight against this deadly disease. The current proposal focuses on one such drug target. It is a nutrient transporter, known as ATB0,+ encoded by the gene SLC6A14, which transports all essential amino acids as well as glutamine. This transporter is expressed only at low levels in normal tissues, but is induced several-fold in colon cancer. We hypothesize that tumor cells up-regulate ATB0,+ to meet their increasing demand for essential amino acids and glutamine. Since ATB0,+ transports all essential amino acids as well as glutamine, it is sufficient for the tumor cells to turn on a single gene to satisfy their amino acid needs. Since tumor cells rely on ATB0,+ as the primary source of essential amino acids and glutamine, blocking the transporter function may offer a logical strategy for cancer treatment. To validate this strategy, we propose three specific aims.
Aim 1 is to evaluate the effects of shRNA-based silencing of ATB0,+ on the growth and progression of tumor with colon cancer cell lines in the nude mouse xenograft model. Here we will silence the transporter in colon cancer cell lines using a molecular biological approach and then examine the effects of the knockdown of the transporter on the growth and progression of tumor when these cells are xenografted into nude mice.
Aim 2 is to evaluate the effects of ATB0,+ deletion on colon cancer by comparing the formation/progression of tumors induced by a carcinogen. Azoxymethane is used to induce colon cancer in mice. This is a genetic approach to delete the gene coding for the transporter. We predict that the transporter knockout mouse will be resistant to azoxymethane-induced colon cancer.
Aim 3 is to evaluate the effects of pharmacological blockade of ATB0,+ with 1-methyl-L- tryptophan (1-MLT) on tumor growth in two different mouse models of colon cancer: a xenograft mouse model with human colon cancer cell lines and a carcinogen-induced colon carcinoma mouse model. This is a pharmacological approach to block the function of the transporter. We will use 1-MLT as a blocker of ATB0,+ to evaluate its ability to prevent colon cancer in these animal models. 1-MLT is also a potent inhibitor of indoleamine dioxygenase (IDO). Inhibition of IDO is known to potentiate the activity of immune system against tumors. Therefore, we predict that 1-MLT will function as an anti-cancer agent in vivo by acting through two different mechanisms: by blocking the tumor-specific nutrient transporter ATB0,+ thereby starving the tumor cells of essential amino acids, and also by inhibiting IDO thereby enhancing the activity of the immune system against the tumor. These studies will generate important information regarding the therapeutic potential of the cancer-specific amino acid transporter ATB0,+ for the treatment of colon cancer.
The goal of this project is to evaluate the therapeutic potential of a cancer-specific amino acid transporter, known as SLC6A14 or ATB0,+ in the treatment of colon cancer. Studies will involve the use of a xenograft mouse model with human colon cancer cell lines and a carcinogen- induced mouse model of colon cancer. The potential of the transporter as a drug target for treatment of colon cancer will be evaluated in these models with two approaches: a genetic approach with the deletion of ATB0,+ (Slc6a14-/- mouse) and a pharmacological approach with the use of a chemical blocker of ATB0,+
|Singh, Nagendra; Gurav, Ashish; Sivaprakasam, Sathish et al. (2014) Activation of Gpr109a, receptor for niacin and the commensal metabolite butyrate, suppresses colonic inflammation and carcinogenesis. Immunity 40:128-39|
|Coothankandaswamy, Veena; Elangovan, Selvakumar; Singh, Nagendra et al. (2013) The plasma membrane transporter SLC5A8 suppresses tumour progression through depletion of survivin without involving its transport function. Biochem J 450:169-78|
|Karunakaran, Senthil; Ramachandran, Sabarish; Coothankandaswamy, Veena et al. (2011) SLC6A14 (ATB0,+) protein, a highly concentrative and broad specific amino acid transporter, is a novel and effective drug target for treatment of estrogen receptor-positive breast cancer. J Biol Chem 286:31830-8|
|Thangaraju, Muthusamy; Cresci, Gail A; Liu, Kebin et al. (2009) GPR109A is a G-protein-coupled receptor for the bacterial fermentation product butyrate and functions as a tumor suppressor in colon. Cancer Res 69:2826-32|