Thaliblastine, a plant alkaloid, circumvents multidrug resistance by direct binding to P-glycoprotein
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G Chen1, C Ramachandran, A Krishan
1Department of Radiation Oncology, University of Miami Medical School, Florida 33136.
Abstract:
The effect of thaliblastine (TBL, NSC-68075), a plant alkaloid, in over-coming multidrug resistance was investigated in doxorubicin (ADR)-resistant murine leukemic P388/R-84 cells. In the soft agar clonogenic assay, a nontoxic concentration of TBL (2 microM) reduced the 50% inhibitory dose of ADR (1-h exposure) from 10.8 to 1.4 microM with a dose modification factor of 7.7. Continuous treatment of P388/R-84 cells with ADR and TBL for 24 h further lowered the 50% inhibitory dose from 3.5 to 0.07 microM, the resistance level being decreased from 233-fold in the absence of TBL to 4.7-fold in the presence of TBL as compared to the parental P388 cells. Although ADR or TBL individually had no detectable effects on cell cycle traverse, the combination of the two drugs caused a significant G2 block. Flow cytometric analysis showed that TBL enhanced ADR retention in P388/R-84 cells in a dose- and time-dependent manner. TBL partially blocked the photolabeling of P-glycoprotein with [3H]azidopine, and this blocking effect was further enhanced in combination with ADR. Our results indicate that TBL can reverse multidrug resistance by direct interaction with P-glycoprotein, thereby increasing cellular ADR retention.
Insights
Thaliblastine (TBL) effectively overcomes multidrug resistance in cancer cells. This plant alkaloid enhances doxorubicin (ADR) retention and reverses resistance by interacting with P-glycoprotein.
Area of Science:
- Pharmacology
- Cancer Biology
- Drug Resistance
Background:
- Multidrug resistance (MDR) is a major challenge in cancer chemotherapy.
- P-glycoprotein (P-gp) is a key efflux pump responsible for MDR.
- Doxorubicin (ADR) resistance in leukemic cells limits treatment efficacy.
Purpose of the Study:
- To investigate the potential of thaliblastine (TBL) in overcoming multidrug resistance.
- To elucidate the mechanism by which TBL affects drug retention and P-gp activity.
Main Methods:
- Soft agar clonogenic assay to assess drug sensitivity.
- Cell cycle analysis using flow cytometry.
- Drug retention studies using flow cytometry.
- P-glycoprotein photolabeling assay with [3H]azidopine.
Main Results:
- TBL significantly reduced the IC50 of ADR in resistant P388/R-84 cells, decreasing the resistance level.
- Combined ADR and TBL treatment induced a G2 cell cycle block.
- TBL enhanced ADR retention in a dose- and time-dependent manner.
- TBL inhibited P-gp photolabeling, an effect potentiated by ADR.
Conclusions:
- Thaliblastine reverses multidrug resistance in doxorubicin-resistant leukemic cells.
- TBL acts by directly interacting with P-glycoprotein, increasing intracellular ADR levels.
- TBL holds promise as an adjuvant therapy to overcome MDR in cancer treatment.