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Characterisation of a mouse tumour cell line with in vitro derived resistance to verapamil
P R Twentyman1, K A Wright, N E Fox
1MRC Clinical Oncology and Radiotherapeutics Unit, Cambridge, UK.
Abstract:
We have established a subline (EMT6/VRP) of the mouse tumour cell line EMT6/P with acquired resistance to the calcium transport blocker verapamil (VRP). The subline was 4-fold resistant to the cytoxicity of VRP alone compared with the parent line but of similar sensitivity to adriamycin, vincristine or colchicine. EMT6/VRP cells growing in 75 micrograms ml-1 VRP were morphologically different from and larger in diameter than EMT6/P cells, but these two parameters reverted almost to normal within 3 days of VRP removal, although resistance was retained. Expression of an mRNA coding for P-glycoprotein was similar in EMT6/VRP and the parent cell line, although considerable hyperexpression was seen in a multidrug resistant subline, EMT6/AR1.0. Cellular accumulation of both 3H-daunorubicin and 3H-VRP were greater in EMT6/VRP than in the parent line. Sensitisation to adriamycin by 3.3 micrograms ml-1 VRP was, however, somewhat reduced in EMT6/VRP (i.e. to 6.1-fold) compared with the 11-fold sensitisation seen in the parent line. It is clear that resistance to VRP seen in this cell line occurs via a different mechanism from the resistance to drugs such as adriamycin, vincristine and colchicine seen in multidrug resistant cell lines.
Insights
Researchers developed a mouse tumor cell line (EMT6/VRP) resistant to verapamil (VRP). This resistance differs from multidrug resistance, impacting VRP
Area of Science:
- Pharmacology
- Cancer Biology
- Cell Biology
Background:
- Acquired resistance to chemotherapy agents is a major challenge in cancer treatment.
- Verapamil (VRP), a calcium channel blocker, has shown potential in overcoming certain drug resistance mechanisms.
Purpose of the Study:
- To establish and characterize a new cell line (EMT6/VRP) with acquired resistance to verapamil (VRP).
- To investigate the mechanism of VRP resistance in this new cell line and compare it to multidrug resistance.
Main Methods:
- Development of a verapamil-resistant subline (EMT6/VRP) from the parent EMT6/P mouse tumor cell line.
- Assessment of cytotoxicity to VRP and other chemotherapeutic agents (adriamycin, vincristine, colchicine).
- Morphological analysis and measurement of cellular drug accumulation (3H-daunorubicin, 3H-VRP).
- Analysis of P-glycoprotein mRNA expression.
Main Results:
- EMT6/VRP cells exhibited 4-fold resistance to VRP cytotoxicity compared to EMT6/P cells.
- VRP resistance was retained after drug removal, though morphological changes reverted.
- Cellular accumulation of daunorubicin and VRP was higher in EMT6/VRP cells.
- VRP-mediated sensitization to adriamycin was reduced in EMT6/VRP cells compared to the parent line.
- P-glycoprotein mRNA expression was similar in EMT6/VRP and EMT6/P cells, unlike in a multidrug-resistant line.
Conclusions:
- The mechanism of verapamil (VRP) resistance in the EMT6/VRP cell line is distinct from the P-glycoprotein-mediated multidrug resistance.
- This finding suggests novel therapeutic strategies may be needed to overcome VRP resistance in specific cancer contexts.