Potential Anticancer Agents.1 LXII. The Relationship of Chemical Structure to Antileukem'c Activity with Analogs of 1-Methyl-3-nitro-1-nitrosoguanidine (NSC-9369). II

Formation of DNA adducts and tumor growth delay following intratumoral administration of DTI-015

Intratumoral (IT) administration of DTI-015 (BCNU in 100% ethanol) utilizes solvent facilitated perfusion for the treatment of tumors. RIF-1 tumors were treated by IT injection of either ethanol alone or 0.05-1.0 mg of DTI-015 or by i.v. injection of 0.5 mg of BCNU. Treatment with ethanol alone or i.v. injection of 0.5 mg of BCNU did not produce a significant growth delay. In contrast, IT administration of DTI-015 produced a significant growth delay at each of the treatment doses (p < 0.05 to p < 0.001). We have quantified the levels of N7-(2-hydroxyethyl) guanine (N7-HOEtG) in RIF-1 tumors 24h following either IT treatment with 0.5 mg DTI-015 or i.p. administration of 0.5 mg BCNU. Levels of N7-HOEtG (micromol/mol DNA) were < or = 0.08 for both untreated controls and following i.p. treatment with BCNU and 13.1 +/- 5.6 following IT administration of DTI-015. The levels of N7-HOEtG detected in RIF-1 tumors following IT administration of DTI-015 were 164-fold higher than the level(s) of N7-HOEtG in the i.p. BCNU treated tumor samples. These studies demonstrate that IT administration of DTI-015 produces high levels of DNA adducts in the tumor which correspond to a significant increase in tumor growth delay compared to the same dose of BCNU administered systemically.

Inhibitors of N-nitroso compounds-induced mutagenicity

N-Nitroso compounds are environmental mutagens that are present in the air, water, soil etc. or can be formed by nitrosation of various nitrosatable compounds. The present paper gives a survey of inhibitors of N-nitroso compounds-induced mutagenicity. Inhibitors covered include: thiols, metals, vitamins, phenolic acids, complex mixtures of plant, animal and human origin, organic solvents, inhibitors of mixed-function oxidases etc. Data on inhibitors that prevent the formation of N-nitroso compounds are not covered in this review.

Detoxification of nitrosamides and nitrosocarbamates in blood plasma and tissue homogenates

Nitrosamides and nitrosocarbamates exhibit relatively high mutagenic activity in Salmonella when compared with nitrosoureas. This high activity can be accounted for by activation of nitrosamides and nitrosocarbamates by cellular thiols, predominantly reduced glutathione, that are present intracellularly at concentrations in the millimolar range. In striking contrast to the in vitro mutagenicity tests, a number of studies have indicated that nitrosamides and nitrosocarbamates are less potent than nitrosoureas when tested in vivo in model systems such as the mouse. We extend here previous studies [Aukerman et al, 1983] that demonstrate striking chemical decomposition and inactivation of mutagenic activity of nitrosamides and nitrosocarbamates during exposure to murine blood plasma. Plasma glutathione concentrations are inadequate to account for the rapid inactivations noted. Furthermore, the predominant inactivating species is heat-sensitive, nondialyzable, and is greater than 25,000 daltons in size as judged by ultrafiltration experiments. Serum albumin has some inactivating capacity at the concentration found in undiluted plasma and could account for the very low but significant inactivating capacity of human plasma. On the other hand, serum albumin lacks the potency necessary to account for the extremely high levels of inactivating activity observed in rodent and rabbit plasma. Elsewhere we present evidence that carboxylesterase activity is the predominant inactivating species in mouse plasma [Aukerman et al, 1983; Aukerman, 1983; Brundrett and Aukerman, 1984]. Mouse liver, large intestine, kidney, and stomach have more activity per milligram protein under the assay conditions used than plasma itself. Rat liver S9 is also active at enhancing the decomposition of nitrosamides and nitrosocarbamates; most of this inactivating capacity resides in the microsomal fraction. The relatively rapid detoxification of these N-nitroso compounds by plasma and other tissues of rodents has important implications regarding the utility of rodents in assessment of tumorigenicity and/or antitumor activity of these classes of drugs in other animal species. Tests with Salmonella may be of use in estimating relative levels of protection that vary widely among mammalian species.

Preclinical and clinical studies on chlorozotocin, a new nitrosourea with decreased bone marrow toxicity

Chlorozotocin is a glucose-substituted chloroethyl nitrosourea with pharmacologic properties suggesting it is a relatively nonmyelosuppressive cancer chemotherapy drug. Preclinical studies have shown that this drug possesses approximately twice the in vitro alkylating activity of the chloroethyl nitrosoureas BCNU and CCNU. In the L1210 leukemia system, chlorozotocin has curative activity at doses that result in minimal bone marrow toxicity. In vitro studies of human bond marrow stem cells have shown that chlorozotocin is relatively sparing of these cells compared to BCNU. Phase I and phase II trials in man have been performed that show that chlorozotocin's dose-limiting toxicity is thrombocytopenia at doses greater than 120 mg/m2. In the phase II trial, 16% of patients with colon cancer and 20% of patients with malignant melanoma evidenced objective regression of disease. Chlorozotocin is now undergoing phase II evaluation in combination chemotherapy trials in colon and stomach cancer.