Combination Chemotherapy of Cancer: Potentiation of Carcinostatic Activity of 8-Azaguanine by 6-Formylpteridine.

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Abstract
2-amino-4-hydroxy-6-formylpteridine (6-formylpteridine), although non-carcinostatic, augmented the carcinostatic action of 8-azaguanine against a mammary adenocarcinoma. This effect was found to be dependent upon a time interval between the injn. of 6-formylpteridine and 8-azaguanine. 6-Formylpteri-dine inhibited the in vitro deamination of 8-azaguanine by tumor extracts. Pre-incubation of enzyme with inhibitor was found to be essential for max. inhibition. It was postulated that the enhanced carcinostatic effect observed in vivo could be due to inhibition of 8-azaguanine deamination by 6-formylpteridine, since the deaminated product (8-azaxanthine) is non-carcinostatic.