Related Experiment Videos
Circumvention of confluence-dependent resistance in a human multi-drug-resistant colon-cancer cell line
C Garrido1, B Chauffert, D Pinard
1CJF INSERM 94/08, Faculty of Medicine, Dijon, France.
Abstract:
Colorectal adenocarcinomas are inherently resistant to anthracyclines and other topoisomerase-II inhibitors. Resistance to doxorubicin of colon cancer cells (Caco2) depends on 2 main mechanisms. The first is typical multi-drug resistance, characterized by the mdr1 gene and its product the P170 membrane glycoprotein. P170 effluxes anthracyclines out of cancer cells and is antagonized in vitro by verapamil. The second mechanism, which develops when cell-culture density increases, we have designated confluence-dependent resistance. Confluence-dependent resistance depends on the reduced topoisomerase II content of the G0/G1-phase cells which accumulate in the confluent population. We show here that short treatments of confluent Caco2 cells with slightly toxic concentrations of DNA-damaging agents (cisplatin, melphalan or mitomycin C) produced a transient accumulation of cells in S- and G2/M-phases of the cell cycle. Concomitantly with the increase in the S-phase population, the topoisomerase II cellular level and the sensitivity of cells to doxorubicin were greatly enhanced. Overcoming confluence-dependent resistance through S-phase accumulation and inhibition of multi-drug resistance by verapamil were fully additive, and a nearly complete reversal of confluent Caco2 cells' resistance to doxorubicin was obtained when both strategies were combined.
Insights
Colorectal cancer cells resist doxorubicin through P170 efflux and reduced topoisomerase II. DNA-damaging agents and verapamil synergistically overcome this resistance by enhancing topoisomerase II and blocking efflux.
Area of Science:
- Oncology
- Molecular Biology
- Cancer Cell Biology
Background:
- Colorectal adenocarcinomas exhibit inherent resistance to anthracyclines and topoisomerase-II inhibitors.
- Doxorubicin resistance in colon cancer cells (Caco2) involves multi-drug resistance (P170 glycoprotein) and confluence-dependent resistance (reduced topoisomerase II in G0/G1 cells).
Purpose of the Study:
- To investigate methods for overcoming doxorubicin resistance in confluent Caco2 cells.
- To evaluate the combined efficacy of strategies targeting both multi-drug resistance and confluence-dependent resistance.
Main Methods:
- Confluent Caco2 cells were treated with DNA-damaging agents (cisplatin, melphalan, mitomycin C) to induce cell cycle changes.
- Cellular topoisomerase II levels and sensitivity to doxorubicin were assessed.
- The effects of verapamil (P170 inhibitor) and DNA-damaging agents were evaluated individually and in combination.
Main Results:
- Short treatments with DNA-damaging agents transiently increased S- and G2/M-phase cell populations.
- This cell cycle shift led to enhanced topoisomerase II levels and increased sensitivity to doxorubicin.
- Combining DNA-damaging agents with verapamil resulted in additive effects, nearly completely reversing doxorubicin resistance in confluent Caco2 cells.
Conclusions:
- Confluence-dependent resistance in colorectal cancer cells can be overcome by inducing S-phase accumulation using DNA-damaging agents.
- Combined treatment strategies targeting both P170-mediated efflux and topoisomerase II levels offer a potent approach to reversing doxorubicin resistance.