Failure of 6-thioGMP to inhibit guanylate kinase in intact cells

Inhibitory effect of 8-oxo-7,8-dihydro-2'-deoxyguanosine on the growth of KG-1 myelosarcoma in Balb/c nude mice

We previously found that 8-oxo-7,8-dihydro-2'-deoxyguanosine (oh(8)dG) kills KG-1, a human myelocytic leukemic cell line with mutational loss of 8-oxoguanine glycosylase (OGG1) activity in vitro. This observation prompted us to investigate the cytotoxicity of oh(8)dG on KG-1 in vivo. This cytotoxicity was observed by administrating oh(8)dG (3.3-330mg/kgb.w./day) for 14 days into nude mice bearing a KG-1 myelosarcoma. The results were as follows; oh(8)dG inhibited the growth of KG-1 myelosarcoma dose-dependently in terms of tumor size and weight, but had no effect on the growth of myelosarcoma of U937, a human monocytic leukemic cell line possessing wild-type OGG1. 6-Thioguanine (6-TG), an anticancer drug inhibited the growths of KG-1 and U937 tumors. 2'-Deoxyguanosine (dG) had a statistically insignificant anti-growth effect on both tumors. The oh(8)dG-treated KG-1 tumor showed the increased expression of apoptosis-processing caspases 8, 9 and 3 together with DNA fragmentation, the increased expression of cell cycle inhibitors, p16 and p27, and the decreased expression of cell cycle accelerator, cyclins and cdks, indicating the nature of cytotoxicity is cell cycle arrest and apoptosis. The genomic DNA of oh(8)dG-treated KG-1 tumors showed an increase in OGG1 sensitive sites, which is consistent with an increase in the 8-oxo-7,8-dihydroguanine (oh(8)Gua) level in the DNA of KG-1 treated with oh(8)dG in vitro. Presumably an increased level of oh(8)Gua in DNA may trigger the cytotoxicity. These findings suggest that oh(8)dG is selectively cytotoxic to KG-1 or tumors that are OGG1-deficient.

9-Deazaadenosine--a new potent antitumor agent

-Deazaadenosine (9-DAA), a novel purine analog, was found to be a potent inhibitor of the growth of nine different human solid tumor cell lines in vitro and of pancreatic carcinoma (DAN) in antithymocyte serum (ATS)-immunosuppressed mice. In culture, IC50 values ranged from 1.1 to 8.5 X 10(-8)M. Ovarian carcinoma (MR) was the only cell line in which the activity of 9-DAA was potentiated (about 10-fold) by pretreatment with the adenosine deaminase inhibitor 2'-deoxycoformycin (dCF). After incubation of cultured pancreatic DAN cells with 9-DAA (10(-5)M) for 2 hr, a peak appeared in the triphosphate region of HPLC nucleotide profiles that was identified tentatively as 9-deazaATP. Under the same incubation conditions, the incorporation of [3H]uridine into RNA and of [3H]thymidine into DNA was inhibited by 34 and 80% respectively. In vivo studies using ATS-immunosuppressed mice showed that 9-DAA at 0.4 mg/kg/day for 3 consecutive days reduced pancreatic carcinoma (DAN) tumor weights to approximately 50% of untreated controls. The nucleoside transport inhibitor p-nitrobenzyl-6-thioinosine (NBMPR) was shown to selectively protect host tissues from 9-DAA toxicity and, thereby, potentiated the antitumor activity of 9-DAA in vivo at optimal dosages.

Biochemical pharmacology and toxicology of 8-azaadenosine alone and in combination with 2'-deoxycoformycin (pentostatin)

The toxicology and metabolism of 8-azaadenosine (8-azaAdo) were examined both as a single agent and in combination with the adenosine deaminase inhibitor, 2'-deoxycoformycin (dCF). The LD10 (mice) for 8-azaAdo alone on a once daily for 5 days (q.d. x 5) schedule was 30 mg . kg-1 . day-1. When the animals were pretreated with 0.1 mg . kg-1 . day-1 of dCF, the LD10 dose was reduced to 10 mg . kg-1 . day-1 x 5. The major organ toxicity seen was hepatic. Bone marrow cellularity was only slightly altered at the LD10 dose. 8-AzaAdo nucleotides were detected in the livers of treated mice as determined by high performance liquid chromatography. Further, after 2 hr of incubation, isolated rat hepatocytes accumulated 8-azaATP to levels of 2.2 mumoles/g of cells with 8-azaAdo (1 mM) alone and to 4.3 mumoles/g of cells when 8-azaAdo was used in combination with dCF (1 microgram/ml). ATP levels decreased to below the limits of detection after 2 hr in cells treated with the combination. The replacement of cellular ATP by 8-azaATP may provide an explanation for the hepatotoxicity observed in the murine toxicology studies.