Abstract 1506: Prodrug targeted gene therapy for colorectal cancer

Abstract

Abstract In the US colorectal cancer is the second and third most common cause of cancer death in men and women, respectively. The drawback of conventional therapy is its non-specificity and a median survival of only 10-15 months with the present combinations. Our studies with human colorectal cancer cell lines demonstrate a relationship between human nicotinamide mononucleotide adenylyltransferase-2 (hNMNAT-2) expression and cell kill with tiazofurin (TR) and benzamide riboside (BR). Thus, the purpose of the present study is to examine whether over-expressing hNMNAT-2 selectively confers sensitivity to TR and BR in human colorectal cancer cells that show resistance to TR and BR therapy. TR and BR are pro-drugs that are metabolized by the action of NMNAT to its active form, TAD (thiazole-4-carboxamide adenine dinucleotide) and BAD (Benzamide adenine dinucleotide), respectively. TAD/BAD potently inhibit inosine-5’-monophosphate dehydrogenase (IMPDH) causing reduced guanylate synthesis resulting in cancer cell death. We achieved 2- to 5-fold increase in expression of hNMNAT-2 by transfecting colorectal cancer cells (Caco-2 and HT-29) with pTracerNMNAT-2 as demonstrated by Western blot and FACS. hNMNAT-2 transfected colorectal cancer cells exhibited a 3- to 7-fold increase in tumor-cell kill with TR and BR. hNMNAT-2 transfected cells did not exhibit modulation of either NAD levels or IMPDH expression. Folate receptor alpha (FR-α) is overexpressed on the colorectal cancer cell surface to sequester available folate to promote cancer cell proliferation. Primary colorectal carcinomas which exhibit high FR-α overexpression also correlated with decreased 5-year survival. We demonstrated an upregulation of FR-α expression in human colorectal cancer cells (up to 10-fold) by adaptation to growth in physiological low folate medium resulting in 2- to 5-fold increase in colorectal cancer cell-kill with TR or BR encapsulated in folate-tethered liposomes. To translate in vitro studies to in vivo applicability, we are utilizing adeno-associated virus (AAV-2) to transduce hNMNAT-2 gene into colorectal cancers implanted in athymic mice. To achieve this goal, we engineered hNMNAT-2 gene into AAV-2 vector to increase efficiency of gene transfer, and encapsulated in folate-tethered liposomes to target colorectal cancer cells. The potential significance of these new proof-of principle studies is that they will set the stage for the next level of studies that could culminate in a new form of pro-drug targeted gene therapy for colorectal cancer with enhanced tumor cell-kill with little toxicity. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1506.