P-glycoprotein (P-gp) is known to contribute to chemotherapy resistance. Tetrandrine (TET) has been reported to inhibit P-gp function. Sinomenine (SIN) may have a similar efficacy, while its effect on P-gp have little been clarified. Cepharanthine (CEP), a structural TET analog, has little been investigated for its anti-cancer efficacy. 3-Dimensionally (3D) cultured spheroids reflect in vivo environment closer than 2-dimensionally (2D) cultured cells. Then, we aimed to investigate the suppressive efficacy of these herbal ingredients on the growth of 2D and 3D cultured triple negative breast cancer cells.
MDA-MB-231 cells were cultured in a well of normal flat bottom plate or DSeA-3D Plate filled with TGP. After incubating in 5% CO2 for one night, cells or spheroids were treated by alone/combination of doxorubicin (DOX), docetaxel (DOC), SIN, CEP, or TET and then further cultured for 48 or 72hs. After incubating, the cell viability in each well was evaluated by WST-8 assay. Likewise, cells or spheroids were treated by DOC and/or a P-gp inhibitor verapamil (Vera) and evaluated the cell viability.
DOX or DOC alone suppressed 2D cultured MDA-MB-231 cells dose-dependently, and significant effects were observed by > 5 × 10−7M DOX or > 2 × 10−8M DOC (p < 0.05). However, 3D spheroids showed resistance, and 2 × 10−4M of DOC showed no effect. Combination of DOC and Vera did not significantly alter the cell viability compared with DOC alone in both 2D and 3D. For 2D, 0.03 to 100μg/mL of SIN had no effect on the cell viability, while 300μg/mL of SIN inhibited significantly (p < 0.05). Otherwise, CEP and TET showed similar effect on 2D cells and decreased the cell viability dose-dependently. Significant inhibitory effects were observed when >30μg/mL of these compounds alone were used (p < 0.05).
3D cultured TNBC cells showed chemotherapy resistance compared with 2D cultured cells, and it may not be because of P-gp. TET, SIN and CEP suppress the 2D cultured TNBC cells, and thus further studies are encouraging for their combined use with anti-cancer drugs.
Tokyo University of Pharmacy & Life Sciences
Tokyo University of Pharmacy & Life Sciences
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All authors have declared no conflicts of interest.