Device for intracellular increase of oxygen free radicals and inhibition of MethA tumour cell proliferation: in vitro and in vivo studies.

We investigated the efficacy of chemical agents aimed at increasing and accumulating oxygen free radicals inside tumour cells to act as inhibitors of the proliferation of these cells. Using MethA tumour cells derived from Balb/c mice, diethyldithiocarbamate (DDC), a copper chelator which is known to inactivate superoxide dismutase, and ascorbic acid (AsA) which mediates catalase inhibition, were employed to accumulate oxygen free radicals inside the tumour cells. It was found that inhibition of the tumour-cell proliferation in vitro, along with greater than 95% reduction of tritiated thymidine uptake by these cells, was attained only when both DDC (5 x 10(-7) M) and AsA (2 x 10(-5) M approximately 2 x 10(-4) M) were added simultaneously and cultured for 48 h. A similar inhibitory effect was observed when the MethA tumour cells were pretreated simultaneously or separately with both DDC and AsA at 37 degrees C for 1 h and cultured for 48 h. The augmented inhibitory effect was completely inhibited by the addition of catalase (2000 U/ml). In vivo, two million MethA tumour cells were inoculated s.c. into the mice, and DDC and/or AsA were injected i.v. or i.t. 7 days later when the diameter of each tumour had reached about 8 mm. An early development of tumour necrosis, and a significant inhibition of the tumour growth, occurred when both agents were used together. Thus a marked augmentation of the inhibitory effect was observed when DDC and AsA were used in combination.(ABSTRACT TRUNCATED AT 250 WORDS)