Reversal of P-glycoprotein-mediated multidrug resistance of cancer cells by five schizandrins isolated from the Chinese herb Fructus Schizandrae.
OBJECTIVE
Fructus Schizandrae (FS) is commonly used as a tonic in traditional Chinese medicine. Recently, FS was found to significantly improve liver dysfunction in chronic hepatitis patients. The present study was to assess the reversal effect of five schizandrins and crude extract from FS (named LCC) on multidrug resistance (MDR) of cancer cells, both in vitro and in vivo. Chemically, the five schizandins are derivatives of dibenzo-(a, c)-cyclooctene lignan with distinct structures differing from any known MDR reversal agents.


METHODS
A panel of sensitive and resistant cancer cell lines were treated with various concentrations of LCC and schizandrins. Drug sensitivity, accumulation of Doxorubicin (Dox), expression of P-glycoprotein and protein kinase C (PKC), and apoptosis were determined in vitro. The in vivo effect was tested in nude mice grafted with sensitive and resistant human epidermal cancer cell line to vincristine (VCR) (KB, KBv200).


RESULTS
The tested five compounds at 25 muM showed various levels of MDR reversal activity, of which, schizandrin A (Sin A) was the most potent one. Sin A reversed VCR resistance in KBv200 cells, MCF-7/Dox cells and Bel7402 cells by 309-, 38-, and 84-folds, respectively. Also, Sin A reversed the resistance of Dox in the above cancer cell lines. LCC at 25 mug/ml reversed VCR resistance by 619-folds in KBv200, 181-folds in MCF-7/Dox cell line, and 1,563-folds in innate resistance of human hepatic cellular carcinoma Bel7402 cells to VCR. Furthermore, LCC and its active component Sin A potently reversed the cross-resistance to paclitaxel in those cell lines. Both Sin A and LCC markedly increased intracellular Dox accumulation and enhanced apoptosis, down-regulated Pgp protein and mRNA and total PKC expression in MDR cells. Coadministration of LCC (p.o.) significantly potentiated the inhibitory effect of VCR (i.p.) on tumor growth in nude mice bearing KBv200 xenograft.


CONCLUSIONS
The LCC and its active component Sin A have remarkable reversal effect on MDR in cancer cells by inhibition of both the function and expression of Pgp and total PKC.
Huang
Min
M
Division of Oncology, Department of Internal Medicine, Stanford University, Stanford, CA 94301, USA.
Jin
Jing
J
Sun
Hua
H
Liu
Geng Tao
GT
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D045744:Cell Line, Tumor / Q000187:drug effects; D034242:Cyclooctanes / Q000494:pharmacology* / Q000627:therapeutic use; D004149:Dioxoles / Q000494:pharmacology; D004317:Doxorubicin / Q000378:metabolism / Q000627:therapeutic use; D004353:Drug Evaluation, Preclinical; D018432:Drug Resistance, Multiple / Q000187:drug effects* / Q000235:genetics; D019008:Drug Resistance, Neoplasm / Q000187:drug effects* / Q000235:genetics; D004365:Drugs, Chinese Herbal / Q000494:pharmacology* / Q000627:therapeutic use; D005638:Fruit / Q000737:chemistry; D019450:Genes, MDR / Q000187:drug effects; D006801:Humans; D017705:Lignans / Q000494:pharmacology* / Q000627:therapeutic use; D051379:Mice; D008819:Mice, Nude; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors* / Q000096:biosynthesis; D008517:Phytotherapy; D028321:Plant Preparations / Q000494:pharmacology* / Q000627:therapeutic use; D011083:Polycyclic Compounds / Q000494:pharmacology* / Q000627:therapeutic use; D011493:Protein Kinase C / Q000096:biosynthesis / Q000235:genetics; D032141:Schisandra / Q000737:chemistry; D023041:Xenograft Model Antitumor Assays
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D034242:Cyclooctanes; D004149:Dioxoles; D004365:Drugs, Chinese Herbal; D017705:Lignans; D009363:Neoplasm Proteins; D028321:Plant Preparations; D011083:Polycyclic Compounds; C015499:schizandrin B; C033585:schizandrol B; C034734:schizandrin A; D004317:Doxorubicin; C031409:schizandrin C; D011493:Protein Kinase C; C011105:schizandrin