Exploring vitamin D metabolism and function in cancer

Vitamin D, traditionally known as an essential nutrient, is a precursor of a potent steroid hormone that regulates a broad spectrum of physiological processes. In addition to its classical roles in bone metabolism, epidemiological, preclinical, and cellular research during the last decades, it revealed that vitamin D may play a key role in the prevention and treatment of many extra-skeletal diseases such as cancer. Vitamin D, as a prohormone, undergoes two-step metabolism in liver and kidney to produce a biologically active metabolite, calcitriol, which binds to the vitamin D receptor (VDR) for the regulation of expression of diverse genes. In addition, recent studies have revealed that vitamin D can also be metabolized and activated through a CYP11A1-driven non-canonical metabolic pathway. Numerous anticancer properties of vitamin D have been proposed, with diverse effects on cancer development and progression. However, accumulating data suggest that the metabolism and functions of vitamin D are dysregulated in many types of cancer, conferring resistance to the antitumorigenic effects of vitamin D and thereby contributing to the development and progression of cancer. Thus, understanding dysregulated vitamin D metabolism and function in cancer will be critical for the development of promising new strategies for successful vitamin D-based cancer therapy.

Plasma and cerebrospinal fluid pharmacokinetics of intravenously administered ABT-751 in non-human primates

PURPOSE

ABT-751 is an orally bioavailable sulfonamide that binds to the colchicine binding site on beta-tubulin and inhibits microtubule polymerization. The plasma and cerebrospinal fluid (CSF) pharmacokinetics of ABT-751, after a short intravenous infusion, were evaluated in a non-human primate (Macaca mulatta) model that is highly predictive of the CSF penetration of drugs in humans.

MATERIALS AND METHODS

Plasma and CSF samples were collected over 24 h after 7.5 mg/kg (150 mg/m2) ABT-751 infused over 0.25-0.70 h, and ABT-751 concentrations in plasma and CSF were quantified using a validated HPLC-MS/MS assay. Pharmacokinetic parameters in plasma and CSF were derived using non-compartmental methods.

RESULTS AND CONCLUSION

Plasma disappearance was bi-exponential with a terminal half-life of 13 h. The mean +/- SD clearance was 100 +/- 18 ml/min m2, the mean +/- SD volume of distribution at steady state was 1.3 +/- 0.5 l/kg, and the mean +/- SD mean residence time was 4.6 +/- 1.8 h. The mean +/- SD peak ABT-751 concentration in CSF was 0.26 +/- 0.08 microM, and the mean +/- SD CSF half-life of 1.3 +/- 0.3 h. CSF penetration was limited (mean +/- SD AUC(CSF):AUC(plasma), 1.1 +/- 0.3%) relative to total (protein-bound + free) plasma drug concentrations, but the CSF concentrations approximated the estimated free drug concentrations in plasma.