Development of drug resistance in a murine mammary tumour
Abstract:
The development of resistance to melphalan, cis-platinum and cyclophosphamide has been examined in the MT murine mammary carcinoma. A gradual decrease in therapeutic response was detected using growth delay and clonogenic cell survival during repeated drug treatment. A slow rate of resistance development, a gradual change in the slope of the dose-survival curves and the inability of 180 mg kg-1 cyclophosphamide to bring about a reduction in tumour response at a faster rate than 60 mg kg-1 cyclophosphamide suggest that resistance development was not due to the selection of a pre-existing highly drug resistant sub-population of tumour cells. Partial drug-resistance is proposed as one possible reason for the apparent inconsistency between these data and existing models of drug-resistance development. The drug-resistant lines were characterized for karyotype, DNA content and cell volume, but only the cyclophosphamide-resistant line showed any significant difference from the wild-type tumour. Cross-resistance studies revealed some inconsistencies with previous reports. Also, resistance to cyclophosphamide developed more quickly in the line which was resistant to melphalan, than in the wild-type tumour, despite the initial appearance of little cross-resistance. This increased rate of resistance development may be important in salvage chemotherapy.
Insights
This study investigated drug resistance in murine mammary carcinoma, finding that gradual development, not pre-existing cells, drives resistance to melphalan, cis-platinum, and cyclophosphamide, impacting chemotherapy strategies.
Area of Science:
- Oncology
- Pharmacology
- Cancer Research
Background:
- Acquired resistance to chemotherapy agents like melphalan, cis-platinum, and cyclophosphamide is a major challenge in cancer treatment.
- Understanding the mechanisms of drug resistance is crucial for developing more effective therapeutic strategies.
Purpose of the Study:
- To investigate the development of resistance to melphalan, cis-platinum, and cyclophosphamide in the MT murine mammary carcinoma model.
- To characterize the mechanisms underlying acquired drug resistance and explore potential cross-resistance patterns.
Main Methods:
- Repeated administration of melphalan, cis-platinum, and cyclophosphamide to MT murine mammary carcinoma.
- Assessment of therapeutic response using tumor growth delay and clonogenic cell survival assays.
- Characterization of drug-resistant cell lines for karyotype, DNA content, and cell volume.
- Cross-resistance studies to evaluate resistance patterns between different chemotherapeutic agents.
Main Results:
- A gradual decrease in therapeutic response was observed during repeated drug treatment, suggesting a slow development of resistance.
- Evidence suggests resistance development is not due to selection of pre-existing resistant cells, with partial drug resistance proposed as a mechanism.
- The cyclophosphamide-resistant line showed significant differences in karyotype, DNA content, and cell volume compared to the wild-type tumor.
- Cross-resistance studies revealed inconsistencies with previous reports, and resistance to cyclophosphamide accelerated in melphalan-resistant lines.
Conclusions:
- Drug resistance in MT murine mammary carcinoma develops gradually, likely through mechanisms other than selection of pre-existing resistant subpopulations.
- Partial drug resistance may explain observed inconsistencies with current models of resistance.
- Accelerated resistance development in cross-resistant lines has implications for salvage chemotherapy strategies.
