Calcium pterin as an antitumor agent.

A series of in vivo studies are reported that provide evidence for an immunologically mediated mechanism for the antitumor response from a calcium pterin (CaPterin) suspension. Strong antitumor efficacy was demonstrated in fully immunocompetent female C3H/HeN-MTV+ mice (retired breeders) presenting spontaneous mammary gland adenocarcinomas. Comparison of results obtained by testing CaPterin in either nude or SCID mice (severely compromised immunodeficient) implanted with MDA-MB-231 human cancer cells showed a significant antitumor response in the nudes and no response in the SCIDs. This comparison argues for B-cell immunological involvement in the mechanism of CaPterin antitumor activity since nude mice possess B-cell capability while SCID mice do not. This comparison also indicates that there is no measurable direct cancer cell toxicity from the CaPterin. Results showing no CaPterin antitumor efficacy against EMT6 tumor cells implanted in Balb/c mice also suggest an antitumor mechanism involving B-cells, since transforming growth factor beta (TGF-beta), produced by EMT6 cells, is known to cause B-cell apoptosis. Taken together, these results, along with those of other researchers, indicate that CaPterin's antitumor mechanism involves antibody-dependent cellular cytotoxicity (ADCC) mediated, for example, by natural killer (NK) cells, interlukin-2, and CaPterin.