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Metabolic stability of experimental chemotherapeutic agents in hepatocyte:tumor cell co-cultures
Abstract:
A U.S. National Cancer Institute screening program for new anticancer drugs, based on the growth of primary human tumor cells in an in vitro soft agar colony formation assay, has resulted in the identification of a number of compounds that have cytotoxic activity against primary human tumor cells in vitro but are inactive in the conventional in vivo murine P388 leukemia animal model pre-screen. To investigate whether metabolic inactivation ov the compounds might be a factor in the lack of in vivo cytotoxicity we have co-cultured rat hepatocytes with A204 rhabdomyosarcoma and murine P388 leukemia cell lines in the soft agarose colony formation assay for 24 h during exposure to the compounds. Twenty compounds with a range of in vitro activities were studied. Thirteen compounds exhibited cytotoxicity against A204 cells in culture; nine of them were less active when co-cultured with hepatocytes, two were activated by hepatocyte co-culture, and two showed no effect of hepatocyte co-culture. P388 cells were more sensitive to the antiproliferative effects of the compounds than A204 cells. Two compounds that were not active against A204 cells exhibited cytotoxicity against P388 cells. One compound was inactivated by hepatocyte co-culture and one showed no effect. Five compounds showed no cytotoxicity toward either A204 cells or P388 cells. Two of the compounds showing hepatocyte inactivation in vitro possess activity in one or more in vivo tumor models. Thus, evidence for metabolic inactivation in hepatocyte co-culture is not always an indication for lack of in vivo antitumor activity. Hepatocyte co-culture methodology provides a simple and objective means, amenable to large-scale screening, of distinguishing metabolic activation or inactivation of a given compound from other pharmacokinetic and pharmacodynamic factors with a minimum of material.
Insights
Drug screening identified compounds cytotoxic to human tumors but not in animal models. Hepatocyte co-culture revealed metabolic inactivation, but this doesn't always mean lack of in vivo antitumor activity.
Area of Science:
- Drug Discovery and Development
- Cancer Research
- Pharmacology
Background:
- A National Cancer Institute screening program uses in vitro soft agar colony formation assays for anticancer drug discovery.
- Some compounds show in vitro cytotoxicity against human tumor cells but are inactive in the in vivo murine P388 leukemia model.
- Metabolic inactivation by the body could explain the lack of in vivo efficacy.
Purpose of the Study:
- To investigate the role of metabolic inactivation in the lack of in vivo anticancer activity.
- To assess the utility of rat hepatocyte co-culture in predicting drug metabolism for anticancer compounds.
Main Methods:
- Co-culturing rat hepatocytes with A204 rhabdomyosarcoma and murine P388 leukemia cell lines in a soft agar colony formation assay.
- Exposing co-cultures to 20 anticancer compounds for 24 hours to evaluate cytotoxicity and metabolic effects.
- Comparing in vitro cytotoxicity with and without hepatocyte co-culture.
Main Results:
- Thirteen of 20 compounds were cytotoxic to A204 cells; 9 showed reduced activity with hepatocytes, 2 were activated, and 2 had no change.
- P388 cells were more sensitive; 2 compounds inactive against A204 cells showed cytotoxicity against P388 cells.
- Two compounds inactivated by hepatocytes in vitro demonstrated in vivo antitumor activity, suggesting metabolic inactivation doesn't preclude in vivo efficacy.
Conclusions:
- Hepatocyte co-culture can distinguish metabolic activation/inactivation from other pharmacokinetic factors.
- Metabolic inactivation observed in vitro does not always predict a lack of in vivo antitumor activity.
- This methodology is a simple, scalable tool for assessing drug metabolism in early drug screening.