Bioavailability and interactions of schisandrin B with 5-fluorouracil in a xenograft mouse model of colorectal cancer

Schisandrin B (Sch B) is a predominant bioactive lignan from the fruit of a Chinese medicine food homology plant, Schisandra chinensis. Previously, we observed potent anti-tumor effect of Sch-B in colorectal cancer (CRC) and enhanced chemotherapy efficacy with fluorouracil (5-FU). However, their bioavailability and reciprocal interactions under CRC conditions are unclear. In this study, we first compared the bioavailability, metabolism and tissue distribution of Sch-B between non-tumor-bearing and xenograft CRC tumor-bearing mice. Next, we examined SchB-5-FU interactions via investigating alterations in drug metabolism and multidrug resistance. Using a validated targeted metabolomics approach, five active metabolites, including Sch-B and fluorodeoxyuridine triphosphate, were found tumor-accumulative. Co-treatment resulted in higher levels of Sch-B and 5-FU metabolites, showing improved phytochemical and drug bioavailability. Multidrug resistance gene (MDR1) was significantly downregulated upon co-treatment. Overall, we demonstrated the potential of Sch-B to serve as a promising chemotherapy adjuvant via improving drug bioavailability and metabolism, and attenuating MDR.