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Pharmacological determinants of the antitumour activity of mitomycin C
V J Spanswick1, J Cummings, A A Ritchie
1Imperial Cancer Research Fund, Medical Oncology Unit, Western General Hospital, Edinburgh, UK.
Abstract:
Recent investigations into bioreductive anticancer drugs have focused on profiling reductase enzymes and relating their expression to therapeutic activity in an approach referred to as enzyme directed drug development. However, few studies have attempted to validate this approach in vivo and even less is known about how the expression of reductases relates quantitatively and qualitatively to metabolic activation. In the present study, the antitumour activity, pharmacokinetics and metabolism of mitomycin C (MMC) has been determined in vivo in two murine adenocarcinomas of the colon, MAC 16 (high DT-diaphorase activity) and MAC 26 (low DT-diaphorase activity) after intra-tumoural injection of drug. Over a broad range of drug concentrations (50-250 microg), MAC 16 proved to be consistently the more sensitive tumour (e.g. 75 microg of MMC, T/C 11% for MAC 16 and 31% for MAC 26). Higher levels of parent drug (peak concentration 103 microg/tumour compared to 58 microg/tumour) were maintained over 45 min in MAC 16 after which time clearance was rapid from both tumours. Four metabolites were detected in both tumours characteristic of different pathways of metabolism. However, by far the major metabolite was 2,7-diaminomitosene (2,7-DM), an accurate indicator of metabolic activation of MMC. Despite higher reductase levels and greater sensitivity to the drug, there was 4-fold less production of 2,7-DM in MAC 16. These results indicate a lack of a simple relationship in vivo between reductase expression and metabolic activation and suggest factors other than pharmacological determinants being responsible for the chemosensitivity of the MAC tumours to MMC.
Insights
Enzyme-directed drug development for bioreductive anticancer drugs like mitomycin C (MMC) shows that high reductase levels do not always correlate with increased drug activation in vivo. Tumor sensitivity to MMC is complex and not solely determined by reductase expression.
Area of Science:
- Pharmacology
- Oncology
- Biochemistry
Background:
- Enzyme-directed drug development for bioreductive anticancer agents relies on linking enzyme expression to therapeutic efficacy.
- In vivo validation of this approach and the quantitative relationship between reductase expression and metabolic activation remain underexplored.
Purpose of the Study:
- To investigate the in vivo antitumour activity, pharmacokinetics, and metabolism of mitomycin C (MMC) in two murine colon adenocarcinomas with differing DT-diaphorase activities (MAC 16 high, MAC 26 low).
- To determine the relationship between reductase expression, metabolic activation, and chemosensitivity to MMC.
Main Methods:
- Intra-tumoural injection of mitomycin C (MMC) into MAC 16 and MAC 26 murine colon adenocarcinoma models.
- Assessment of antitumour activity (T/C values), pharmacokinetics (drug concentration over time), and metabolite analysis (identifying 2,7-diaminomitosene as a key indicator of activation).
Main Results:
- MAC 16 (high DT-diaphorase) demonstrated significantly greater sensitivity to MMC compared to MAC 26 (low DT-diaphorase).
- Higher concentrations of parent MMC were maintained in MAC 16, but a major metabolite (2,7-diaminomitosene), indicating metabolic activation, was 4-fold lower in MAC 16 than in MAC 26.
- Despite higher reductase levels and sensitivity, MAC 16 showed reduced metabolic activation of MMC.
Conclusions:
- A direct, simple correlation between in vivo reductase expression and metabolic activation of mitomycin C was not observed.
- Tumor chemosensitivity to MMC appears to be influenced by factors beyond reductase levels and metabolic activation, suggesting a complex interplay of determinants.