Abstract 2086 Preliminary pharmacokinetic study of OXi8007, an effective vascular disrupting agent, in an orthotopic RENCA tumor-bearing BALB/c mouse model

OXi8007 is a phosphate prodrug of the indole-based compound OXi8006. After dephosphorylation by non-specific phosphatase(s) such as alkaline phosphatase, OXi8007 is converted to the active agent OXi8006, which binds to the colchicine site located on the tubulin heterodimer causing inhibition of tubulin polymerization. The net result is rapid microtubule disruption, cell rounding and detachment. OXi8006 has a dual mechanism of action. As an antimitotic agent it results in cell cycle arrest at the G2/M phase and apoptosis. As a vascular disrupting agent (VDA), it causes selective tumor vascular collapse, ischemia, hypoxia, cell death and necrosis. As part of a study of OXi8007 for the treatment of RENCA tumor-bearing BALB/c mice as a model for renal cell carcinoma (RCC), preliminary pharmacokinetics were conducted. Plasma and tissue samples were collected at varying times (20 min and 1, 2, 4, 8 and 16 h) from orthotopic (right kidney) RENCA tumor-bearing BALB/c mice treated IP with 250 mg/kg or 325 mg/kg OXi8007 (20 min, and 1, 2, and 4 h). After extraction, LC-MS was used to analyze OXi8007 (prodrug), OXi8006 (active agent) and metabolites. The LC-MS method was optimized for separation and detection of OXi8007, OXi8006, phase I and II metabolites including OXi8006-glucuronide, desmethyl-OXi8006, desmethyl-OXi8006-glucuronide, and N-acetyl-OXi8006-glucuronide, and as internal standards (ISs) the well-established VDA combretastatin A-4 (CA4) and 13C-trilabeled OXi8006. Analytes including 13C-trilabeled OXi8006 and 13C-trilabeled OXi8007 were analyzed by retention time and exact mass ([M+H] +) with LC/MS. The extraction protocol was optimized for recovery of analytes and standard curves were obtained for OXi8007 and OXi8006 with each tissue type and plasma from untreated tumor-bearing BALB/c (control) mice. OXi8007 and OXi8006 were most abundant in the plasma samples at the earliest time point (20 min), then started to decrease. Similar trends were observed in other tissues except for the right kidney with associated tumor tissue, in which the highest concentrations of both OXi8006 and OXi8007 were observed at 1 h post treatment. In addition, the concentration of OXi8006 was higher than OXi8007 in liver, left kidney, heart, lung, spleen, and brain tissues. The most abundant phase II metabolite was OXi8006-glucuronide, which peaked at 1 h post treatment in the plasma and tissue samples; whereas, in the right kidney with associated tumor tissue the amount of OXi8006-glucuronide remained steady for 4 h after treatment, then started to decrease. In conclusion, OXi8007 administered IP appeared rapidly in blood plasma along with its dephosphorylated parent agent OXi8006. The right kidney with associated tumor tissue contained the largest amount of OXi8007 and OXi8006 among all tissues, whereas brain tissue was observed to have the least amount of OXi8007 and OXi8006 likely due to the blood-brain barrier, indicating that OXi8007 mainly targets tumor tissue and tumor vasculature. As expected, liver as the main detoxification organ contained a significant amount of OXi8006. Research reported in this publication was supported by the National Cancer Institute of the National Institutes of Health under Award Number R01CA244579. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.