Camptothecin derivatives induce regression of human ovarian carcinomas grown in nude mice and distinguish between non‐tumorigenic and tumorigenic cells in vitro

We have recently shown that the plant alkaloid 20(S)‐camptothecin and its derivatives 9‐nitro‐20(S)‐camptothecin(9NC) and 9‐amino‐2O(S)‐camptothecin(9AC) inhibit the growth of a variety of human tumors xenografted in nude mice. In this report, we demonstrate that 9NC and 9AC effectively inhibit growth, and subsequently induce regression, of human ovarian tumors grown in nude mice. Tumor regression is accompanied by degenerative changes in the tumor cells as assessed by microscopic observations of histological sections prepared from the tumors. Parallel experiments in vitro show that 9NC inhibits in a similar manner the growth of human ovarian carcinoma cells, regardless of their ability to induce tumors when xenografted in nude mice, and induces similar morphological changes in both non‐tumorigenic and tumorigenic cells, as assessed by microscopic observation. Flow cytometry studies show that 9NC‐induced growth inhibition of the non‐tumorigenic cells is associated with accumulation of these cells in G 2 . In contrast, 9NC‐induced growth inhibition of the tumorigenic cells is associated with the generation of cells containing a reduced DNA content, that is, cells programmed to die. In conclusion, camptothecins appear to be cytostatic for non‐tumorigenic, but cytotoxic for tumorigenic cells, an important finding from viewpoints of cell biology, pharmacology and cancer chemotherapy.