Abstract 1506: Prodrug targeted gene therapy for colorectal cancer

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC 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.