"Starve the Tumor Cells to Death": SLC6A14 as a Drug Target for Colon Cancer

描述（由申请人提供）：结肠癌是该国第四大常见癌症。目前有各种各样的策略用于治疗结肠癌，但没有一种能永久治愈这种疾病。迫切需要新的药物靶点，以成功地对抗这种致命的疾病。目前的建议集中在一个这样的药物靶点。它是一种营养转运蛋白，称为ATB 0+，由基因SLC 6A 14编码，可转运所有必需氨基酸和谷氨酰胺。这种转运蛋白在正常组织中仅以低水平表达，但在结肠癌中被诱导数倍。我们假设肿瘤细胞上调ATB 0，+以满足其对必需氨基酸和谷氨酰胺日益增加的需求。由于ATB 0，+转运所有必需氨基酸以及谷氨酰胺，因此肿瘤细胞只需打开单个基因即可满足其氨基酸需求。由于肿瘤细胞依赖于ATB 0，+作为必需氨基酸和谷氨酰胺的主要来源，因此阻断转运蛋白功能可能为癌症治疗提供合理的策略。为了验证这一战略，我们提出了三个具体目标。目的1：利用大肠癌细胞株裸鼠移植瘤模型，研究ATB 0，+基因沉默对肿瘤生长和进展的影响。在此，我们将使用分子生物学方法沉默结肠癌细胞系中的转运蛋白，然后检查当这些细胞异种移植到裸鼠体内时，转运蛋白的敲低对肿瘤生长和进展的影响。目的2是通过比较致癌物诱导的肿瘤形成/进展来评价ATB 0，+缺失对结肠癌的影响。氧化偶氮甲烷被用于诱发小鼠结肠癌。这是一种遗传学方法来删除编码转运蛋白的基因。我们预测，转运蛋白基因敲除小鼠将对氧化偶氮甲烷诱导的结肠癌具有抗性。目的3是在两种不同的结肠癌小鼠模型（人结肠癌细胞系异种移植小鼠模型和致癌物诱导的结肠癌小鼠模型）中评价ATB 0，+与1-甲基-L-色氨酸（1-MLT）的药理学阻断对肿瘤生长的影响。这是一种阻断转运蛋白功能的药理学方法。我们将使用1-MLT作为ATB 0，+的阻断剂，以评价其在这些动物模型中预防结肠癌的能力。1-MLT也是吲哚胺双加氧酶（IDO）的有效抑制剂。已知IDO的抑制增强免疫系统对抗肿瘤的活性。因此，我们预测1-MLT将通过两种不同的机制发挥体内抗癌剂的作用：通过阻断肿瘤特异性营养转运蛋白ATB 0+，从而使肿瘤细胞缺乏必需氨基酸，以及通过抑制IDO，从而增强免疫系统对肿瘤的活性。这些研究将产生关于癌症特异性氨基酸转运蛋白ATB 0，+治疗结肠癌的治疗潜力的重要信息。 公共卫生相关性： 该项目的目标是评估癌症特异性氨基酸转运蛋白（称为SLC 6A 14或ATB 0+）在结肠癌治疗中的治疗潜力。研究将涉及使用具有人结肠癌细胞系的异种移植小鼠模型和致癌物诱导的结肠癌小鼠模型。将在这些模型中采用两种方法评价转运蛋白作为结肠癌治疗药物靶标的潜力：缺失ATB 0，+的遗传方法（Slc 6a 14-/-小鼠）和使用ATB 0，+化学阻断剂的药理学方法

DESCRIPTION (provided by applicant): 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. PUBLIC HEALTH RELEVANCE: 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,+