ONX 0801 is designed to work by combining two proven approaches to improving outcomes for cancer patients. These include receptor-mediated targeting of tumor cells and inhibition of thymidylate synthase, a key enzyme involved in cell growth and division.  ONX 0801 targets malignant cells that overexpress the alpha-folate receptor, which is located on the cell's surface. Once ONX 0801 enters the cell via this receptor, the compound inhibits, or switches off, thymidylate synthase (TS).  ONX 0801 is distinct from currently marketed TS inhibitors, such as pemetrexed, 5 fluorouracil, and raltitrexed, due to its selective tumor cell-specific uptake by the alpha-folate receptor. The alpha-folate receptor is overexpressed in a number of tumor types with significant unmet needs, including ovarian cancer, lung cancer, breast cancer, and colorectal cancer.