Richard H. Adamson

Toxicity of antineoplastic agents in man, chromosomal aberrations antifertility effects, congenital malformations, and carcinogenic potential.

Publisher Summary This chapter consolidates and quantitates some deleterious effects of cancer chemotherapeutic agents in humans—namely, their ability to induce chromosomal aberrations, their antifertility effects, their ability to produce congenital malformations under certain conditions, and their carcinogenic potential when used to treat neoplastic and nonneoplastic diseases. It discusses the three classes of antitumor compounds: alkylating agents, antimetabolites, and antitumor antibiotics. These compounds have been extensively studied in vitro and in vivo and they induce chromosomal aberrations; these abnormalities vary according to the agent and the test system used. Combinations of agents or agents plus irradiation also produce cytogenetic damage in human cells. It also provides information on the possible adverse effects of the antimetabolites, antitumor antibiotics, and miscellaneous synthetic agents on spermatogenesis. The current evidence indicates that these effects are related to the dose and duration of chemotherapy, both for single alkylating agents and for combination chemotherapy in which the alkylating agent is one of the components. Anticancer drugs other than the alkylating agents should be more thoroughly studied for possible effects on the fertility in the human female.

The effect of isomers of DDD on the ACTH-induced steroid output, histology and ultrastructure of the dog adrenal cortex.

The effect of 3 geometric isomers of DDD on ACTH-induced steroid production, histology, and ultrastructure of the dog adrenal cortex were examined. When administered iv, equal doses of all 3 compounds eventually inhibited ACTH-induced steroid production. The order of onset of inhibition was m,p′-DDD > o,p′-DDD > p,p′-DDD with the inhibition reaching 50% of control values at 27 min, 87 min and between 4–18 hr, respectively. Histologic examination of the various zones of the adrenal cortex showed minimal effects, from any of the isomers, on the zona glomerulosa at times when the internal structure and spacial arrangement of the cells of the zona fasciculata and reticularis were markedly disrupted. Electron micrographs revealed that these DDD isomers exhibited very minimal effects on the mitochondria of the zona glomerulosa. On the other hand, the mitochondria of the zonas fasciculata-reticularis underwent progressive swelling, dissolution, and eventual rupture following DDD treatment. The order of onset of histologic and ultrastructural effects was m,p′-DDD > o,p′-DDD > p,p′-DDD. However, for each isomer the ultrastructural damage was detected prior to the observation of histologic lesions. Thus, there was a marked temporal correlation between the percentage inhibition of ACTH-induced steroid production, the disruption of normal cellular structure and arrangement in the innermost zones of the adrenal cortex, and the severity of the DDD-induced mitochondria damage in the cells of the zonas fasciculata-reticularis by each of the 3 isomers of DDD.

The clinical pharmacology of the adenosine deaminase inhibitor 2'-deoxycoformycin.

Summary2′-deoxycoformycin (2′-dCF; Pentostatin), a stoichiometric inhibitor of mammalian adenosine deaminase (ado deaminase), exhibits immunosuppressive and antilymphocytic activity in animal test systems. A clinical pharmacology/phase I study of 2′-dCF administered as a single agent has been completed (18 patients). Dose levels ranged from 0.1 mg/kgx1 to 0.25 mg/kg/dayx5; ado deaminase and 2′-dCF were measured spectrophotometrically. Plasma decay curves were bi-exponential (α and βt1/2 values about 1 and 10 h respectively). Recovery of unchanged 2′-dCF from urine (48 h) was 32%–48% of the administered drug. Major toxic manifestations were lymphocytopenia (all patients) and urate nephropathy (1 patient, with subsequent patients in the series receiving allopurinol, 300 mg/day). Three partial responses were seen in seven patients with acute lymphocytic leukaemia receiving 0.25 mg 2′-dCF/kg/dayx5.

Stoichiometric inhibition of mammalian dihydrofolate reductase by the γ-glutamyl metabolite of methotrexate, 4-amino-4-deoxy-N10-methylpteroylglutamyl-γ-glutamate

Summary 4-Amino-4-deoxy-N 10 -methylpteroylglutamyl-γ-glutamate, a recently identified metabolite of methotrexate, was found to be equal in activity to methotrexate as an inhibitor of dihydrofolate reductase from murine L1210 leukemia cells, and as an inhibitor of the replication of L1210 cells in vitro and in vivo . The enzyme-inhibitory and cytotoxic activity of the metabolite was some 11-fold greater than anticipated from earlier studies utilizing microbiological assay systems. The results indicate that 4-amino-4-deoxy-N 10 -methylpteroylglutamyl-γ-glutamate formed in vivo may contribute significantly to the pharmacological activity of the parent drug.

Metabolism of food-derived heterocyclic amines in nonhuman primates.

During the cooking of meats, several highly mutagenic heterocyclic amines (HCAs) are produced. Three HCAs, IQ, MeIQx, and PhIP have been under study for carcinogenicity in cynomolgus monkeys, and to date, IQ has been shown to be a potent hepatocarcinogen. Concomitantly, the metabolic processing of these HCAs has been examined. Metabolism studies show that the potent hepatocarcinogenicity of IQ is associated with the in vivo metabolic activation of IQ via N-hydroxylation and the formation of DNA adducts. In monkeys undergoing carcinogen bioassay with IQ, N-hydroxylation was confirmed by the presence of the N-hydroxy-N-glucuronide conjugate of IQ in urine. The N-hydroxylation of IQ appears to be carried out largely by hepatic CYP3A4 and/or CYP2C9/10, and not by CYP1A2, an isoform not expressed in liver of this species. Notably MeIQx is poorly activated in cynomolgus monkeys and lacks the potency of IQ to induce hepatocellular carcinoma after a 5-year dosing period. The poor activation of MeIQx appears to be due to the lack of constitutive expression of CYP1A2 and an inability of other cytochromes P450, such as CYP3A4 and CYP2C9/10, to N-hydroxylate the quinoxalines. MeIQx is detoxified in monkeys largely by conjugation with glucuronide at the N-1 position. Although the carcinogenicity of PhIP is not yet known, the metabolic data suggest that PhIP will be carcinogenic in this species. PhIP is metabolically activated in vivo in monkeys by N-hydroxylation, as discerned by the presence of the N-hydroxy-N-glucuronide conjugate in urine, bile, and plasma. PhIP also produces DNA adducts that are widely distributed in tissues. The results from these studies support the importance of N-hydroxylation in the carcinogenicity of HCAs in nonhuman primates and by analogy, the importance of this metabolic activation step in the possible carcinogenicity of dietary HCAs in humans.

Extrapolation of Heterocyclic Amine Carcinogenesis Data from Rodents and Nonhuman Primates to Humans

Twenty different heterocyclic amines have been isolated and identified from cooked foods especially beef, fish, pork and fowl. Other HCAs have also been isolated but their structure remains to be elucidated and new HCAs are likely to be identified in the future. The HCAs are highly mutagenic and all ten HCAs that have been tested for carcinogenic activity, produce tumors in mice and rats. For humans the average daily intake of HCAs is in quantities of 10-20 mg/person/day. The HCAs are procarcinogens and are activated by the cytochrome P450 system especially CYP 1A2. Rodents, monkeys and humans have the capacity to activate HCAs. Studies using hepatic microsomes demonstrated that humans have a greater capacity to activate the majority of HCAs tested than rodents or cynomolgus monkeys. Three HCAs are currently under evaluation in nonhuman primates for carcinogenic activity and one, IQ, is highly carcinogenic inducing primary hepatocellular carcinomas in the majority of cynomolgus monkeys treated. Epidemiological studies, although not definitive, are supportive of an association of HCAs intake to the etiology of human cancer. Risk assessments from animal data show a risk of HCAs to humans in the range of 10(-3) to 10(-4) which is an order of magnitude greater than compounds currently regulated by the U.S. Food and Drug Administration or the Environmental Protection Agency. Taken together evidence from mutagenicity data, activation by various species including humans, carcinogenicity in animals, human consumption data, epidemiological studies and risk assessment, supports the conclusion that HCAs are probable human carcinogens.

Serum Sialic Acid Levels in Lung Cancer Patients

The levels of N-acetyl neuraminic acid (sialic acid) in normal men and pre-and post-menopausal women were determined. Smoking post-menopausal estrogen therapy, oral contraceptives, and refreezing had no effects on sialic acid levels. Pre-treatment values from patients with lung carcinoma showed markedly elevated levels of sialic acid (0.697 +/- 0.149 muM/ml) as compared to those from normal controls (0.432 +/- 0.067 muM/ml). The potential usefulness of sialic acid as a biological marker is discussed.

Enzyme inhibition titration assay for 2′-deoxycoformycin and its application to the study of the relationship between drug concentration and tissue adenosine deaminase in dogs and rats

Abstract An assay has been developed for 2′-deoxycoformycin (2′-dCF), utilizing the inhibition by the drug of the enzyme adenosine deaminase. This assay is suitable for the detection of 2′-dCF in tissue extracts and biological fluids with a maximal sensitivity of 2 nM. The assay has been used to study the disposition of the drug in foxhounds and to examine the relationship between tissue drug levels and residual tissue adenosine deaminase activity. 2′-dCF was administered intravenously to foxhounds at doses of 0.1, 0.25 and 1.0 mg/kg. The drug disappeared from plasma with α- and β-half times of 12–15 min and 90–120 min respectively. It was cleared into urine at a rate of 2.24 to 3.12 ml/min/kg. Of the administered drug, 54–83 per cent was recovered in the urine and another 10–15 per cent in the tissues at the time of death. Drug accumulation in tissues correlated with the adenosine deaminase content of the tissues. Residual adenosine deaminase activity was under 50 per cent of control activity in all tissues examined after 0.1 mg/kg of 2′-dCF and under 20 per cent of control activity in all tissues after 1.0 mg/kg of 2′-dCF. Rats given 2′-dCF showed initial inhibition of adenosine deaminase with recovery over time in tissues capable of new enzyme synthesis. The variable rates of recovery from enzyme inhibition may be determinants of tissue specific toxicity of 2′-dCF alone or 2′-dCF in combination with adenosine analogs. Dosage schedules are suggested for different clinical objectives.

Studies on Poly I:C toxicity in experimental animals☆☆☆

Abstract Polyinosinic:polycytidylic acid copolymer (Poly I:C), a synthetic double stranded RNA, has been proposed as a candidate for clinical introduction as an antitumor agent. In preclinical toxicologic evaluation, acute lethality studies were undertaken in 3 mouse strains, anaphylaxis studies in guinea pigs, and acute and subchronic toxicities were evaluated in rhesus monkeys and beagle dogs following daily parenteral dosing for up to 28 days. Poly I:C is more lethal to mice following iv administration than ip, and there appear to be differences in mouse strain susceptibility. No evidence of anaphylaxis was seen in guinea pigs. Signs of toxicity in dogs and monkeys were dose related, were qualitatively similar in the 2 species, and included hypoactivity, anorexia, emesis, diarrhea, ataxia and weight loss. Clinical changes included anemia, elevations of transaminases, lactic dehydrogenase, and alkaline phosphatase, decreased clotting rate and increased prothrombin time. Pathologic changes consisted of focal hemorrhages, infarction or congestion of a variety of organs, vasculitis and decreased erythroid hematopoiesis. The effects were more severe in dogs than in monkeys for equivalent mg/kg doses. In the monkey iv administration produced greater toxicity than im or ip administration. Signs of toxicity and pathologic changes appeared to be reversible in both dogs and monkeys after cessation of dosing.

Effects of long-term oral administration of DDT on nonhuman primates

Abstract Because of reports on tumorigenic activity in different animal species exposed to DDT a decision was made in 1969 to evaluate the long-term effects of DDT on 24 cynomolgus and rhesus monkeys. DDT (20 mg/kg) was given in the diet for 130 months, followed by an observation period that ended in 1994. The two cases of malignant tumor detected in the DDT group included a metastatic hepatocellular carcinoma in a 233-month-old male and a well-differentiated adenocarcinoma of the prostate in a 212-month-old monkey. Benign tumors detected in the DDT group included three cases of leiomyoma, two of which were uterine and one, esophageal. No tumor was detected in the control group of 17 monkeys. Fatty changes in the liver were observed in 52.9% of the DDT group and 29.4% of the control group. More specific signs of hepatotoxicity were documented microscopically in seven DDT monkeys. Severe tremors and histological evidence of CNS and spinal cord abnormalities were observed in six DDT monkeys. The present findings show clear evidence of hepatic and CNS toxicity following long-term DDT administration to cynomolgus and rhesus monkeys. However, the two cases involving malignant tumors of different types are inconclusive with respect to a carcinogenic effect of DDT in nonhuman primates.