I. To determine the maximum tolerated dose (MTD) of CPI-613 (6,8-bis[benzylthio]octanoic acid), when used in combination with 5-FU (fluorouracil), in patients with non-resectable metastatic colorectal cancer who have failed FOLFOX (leucovorin calcium, fluorouracil and oxaliplatin), FOLFIRI (leucovorin calcium, fluorouracil, and irinotecan hydrochloride) and, if Kirsten rat sarcoma viral oncogene homolog (KRAS) wild type, then a epidermal growth factor receptor (EGFR) inhibitor-based regimen.