Pharmacokinetics of guanosine in rats following intravenous or intramuscular administration of a 1:1 mixture of guanosine and acriflavine, a potential antitumor agent.

A 1:1 mixture of acriflavine (ACF; CAS 8063-24-9) and guanosine is under evaluation in preclinical studies as a possible antitumor agent. Guanosine is known to potentiate the anti-cancer activity of ACF. We therefore investigated the pharmacokinetics of guanosine following administration of the ACF/guanosine mixture in rats. Rats were given guanosine (1 or 5 mg/kg) or ACF/guanosine (2 or 10 mg/kg) by i.v. bolus; or guanosine (3 or 15 mg/kg) or ACF/guanosine (6 or 30 mg/kg) by i.m. injection. We found that guanosine was rapidly cleared from the blood and transferred to tissues after i.m. administration of ACF/guanosine. The mean plasma half-lives (t(1/2)) at the alpha and beta phases were 0.091 and 6.86 h, or 0.09 and 7.51 h at a dose of 1 or 5 mg/kg guanosine, respectively. ACF had no effect on the plasma disappearance of guanosine following either i.v. bolus or i.m. administration of the combination mixture. Moreover, the ACF combination with guanosine did not significantly alter the values of MRT, V(dss), and CL(t) of guanosine. Guanosine exhibited linear pharmacokinetics over the dose range from 1 to 5 mg/kg for i.v. doses and 3 to 15 mg/kg for i.m. doses. The bioavailability of guanosine after i.m. administration was 84% for 3 mg/kg dose and 88% for 15 mg/kg dose. ACF had no effects on biliary and urinary excretion of guanosine after i.m. administration. The cumulative amount of guanosine in urine after i.m. administration was about 5-fold larger than that in bile, indicating that guanosine is mostly excreted into the urine. Guanosine was widely distributed in all tissues examined in this study, but was most highly concentrated in the kidney after i.m. administration, followed by slow excretion to bile or urine. ACF had no effect on the tissue distribution of guanosine following i.m. administration. These characterizations of the pharmacokinetics of guanosine after administration of the ACF/guanosine combination will be useful in providing preclinical and clinical bases for the potential application of this combination to the treatment of cancer.

Extensive intracellular accumulation of ID-6105, a novel anthracycline, in SK-OV-3 ovarian cancer cells.

We investigated the anticancer activity of 11-hydroxyaclacinomycin X (ID-6105), a novel anthracycline, on weakly doxorubicin (Dox)-resistant SK-OV-3 ovarian cancer cells, and elucidated the relationship between its anticancer activity and accumulation in cells compared with those of Dox. Accumulation of ID-6105 in the cells was time-and concentration-dependent, a result of drug-induced cytotoxicity in the cells. SK-OV-3 cells were preloaded with ID-6105 or Dox for 12 h at concentrations ranging from 100 to 2000 nM and then incubated with drug-free medium for 0-48 h. Cell viability was measured using a proliferation-based assay (XTT assay). The inhibitory effects of ID-6105 on cell viability were more pronounced than those of Dox. The IC(50) values of ID-6105 after 24-and 48-h incubation with drug-free medium were 1.58 and 0.084 microM, while those of Dox were 2 and 0.334 microM, respectively. To investigate the relationship between the intracellular levels and the cytotoxic effects of the drugs, we preloaded SKOV-3 cells with ID-6105 or Dox (100-2000 nM) for 12 h and then measured the intracellular levels of drugs by HPLC in drug-free medium for 0-48 h. After preloading the drugs, the intracellular concentrations of ID-6105 at time 0 were 1.3-, 1.8-, and 1.4-fold larger than those of Dox at initial concentrations of 500, 1000, and 2000 nM, respectively. The extent of ID-6105 accumulation in the cells was more pronounced than that of Dox. These findings suggest that ID-6105 effluxed less from the cells than Dox, resulting in its extensive cytotoxicity compared with that of Dox. These results show that accumulation of ID-6105 within tumor cells may be important for the inhibitory effects of this drug in cancer cells. ID-6105 has an antiproliferative effect on SK-OV-3 cells that is due to its cytotoxicity. This effect is more pronounced than that of Dox, and may be attributed to extensive accumulation of ID-6105 in the cells.