Conversion of 9‐nitro‐camptothecin to 9‐amino‐camptothecin by human blood cells in vitro

To the Editor: In recent reports, we have shown that the compound 9-nitro-camptothecin (9NC) is cytostatic or cytotoxic for human cells in vitro, depending on the ability of these cells to induce tumors when xenografted into nude mice (1-5). Specifically, cells that are not tumorigenic in nude mice accumulate at late-S/G2 phase of the cell cycle, in presence of 9NC, and remain arrested for a prolonged period of time or re-enter cell cycling upon cessation of exposure to 9NC. In contrast, tumorigenic cells die by apoptosis while they traverse the S phase in the presence of 9NC, and cell death continues regardless of discontinuation of exposure to the drug. Also, we have shown that 9NC suppresses growth of and induces regression of human tumors established in nude mice

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