Cancer weight of evidence for three lower acrylates: Conclusions and recommendations from an expert panel.

An international panel of experts was engaged to assess the cancer weight of evidence (WOE) for three lower acrylates: methyl acrylate, ethyl acrylate, and 2-ethylhexyl acrylate. The review was structured as a three-round, modified Delphi format, a systematic process for collecting independent and deliberative input from panel members, and it included procedural elements to reduce bias and groupthink. Based upon the available science, the panel concluded: (1) The MOA for point of contact tumors observed in rodent cancer bioassays that is best supported by available data involves increased cell replication by cytotoxicity and regenerative proliferation; (2) The WOE supports a cancer classification of "Not likely to be carcinogenic to humans" a conclusion that is more in line with an IARC classification of Group 3 rather than Group 2 B; (3) Quantitative cancer potency values based on rodent tumor data are not required for these chemicals; and (4) Human health risk assessment for these chemicals should instead rely on non-cancer, precursor endpoints observed at the point of contact (e.g., hyperplasia). The degree of consensus (consensus scores of 0.84-0.91 out of a maximum score of 1) and degree of confidence (7.7-8.7 out of a maximum score of 10) in the WOE conclusions is considered high.

Subchronic dermal toxicity study of triethanolamine in C3H/HeJ mice.

Triethanolamine (TEA) was applied to the skin of male and female C3H mice (15 per sex per dose group) three times weekly for 95 days (37 applications). TEA was administered at concentrations of 0 (acetone vehicle), 10, 33 and 100% (undiluted) in a volume of 50 microliters. The approximate daily doses of TEA were 0.14, 0.46 or 2.0 g/kg per male and 0.16, 0.54 or 2.3 g/kg per female, respectively. The animals were weighted weekly and observed for clinical signs including skin irritation. 10 mice per sex per dose group were designated for clinical chemistry and haematology at terminal killing. Complete autopsies were performed, and the liver, kidneys, brain, heart, spleen, thymus and testes were weighted. Histopathology was performed on tissues from control and high-dose mice and on target organs. Treatment-related effects were limited to a slight epidermal hyperplasia at the site of application at all TEA concentrations. The results indicate that TEA caused a mild local reaction at all concentrations tested, but did not cause systemic toxicity under these conditions.

Comparison of ketorolac tromethamine with other injectable nonsteroidal anti-inflammatory drugs for pain-on-injection and muscle damage in the rat.

The local tolerance of ketorolac tromethamine (Toradol, Syntex) was compared with that of four other injectable nonsteroidal anti-inflammatory drugs (NSAIDs) (diclofenac sodium, piroxicam, ketoprofen, and metamizol magnesium) in the rat paw-lick/muscle irritation assay as described previously. All drugs were tested at concentrations approved for clinical use. After subplantar (footpad) injection, ketorolac produced virtually no pain-on-injection as assessed by the number of paw-lick/lift responses during a 15 min observation period. The other NSAIDs produced slight to moderate paw-lick/lift responses. Redness and swelling at the injection site were less severe for ketorolac than for the other NSAIDs. After intramuscular (i.m.) injection, all of the NSAIDs produced some degree of muscle damage, as assessed histopathologically 24 h after injection. The lesions, consisting primarily of muscle degeneration, were less severe for ketorolac than for the other NSAIDs. Ketorolac and metamizol produced the smallest elevations in serum creatine kinase, as measured 2 h after i.m. dosing, not significantly different from isotonic saline. Overall, ketorolac was better tolerated in the assay than the other injectable NSAIDs, thereby suggesting the possibility of improved local tolerance on clinical use.

Acute and subchronic toxicity studies with detirelix, a luteinizing hormone-releasing hormone antagonist, in the rat and monkey.

Acute (single dose), 2-week, and 3-month toxicology studies were conducted with detirelix, a luteinizing hormone-releasing hormone (LHRH) antagonist, in rats and cynomolgus monkeys. Acute studies were conducted by intravenous and subcutaneous injection. Subchronic studies were conducted by daily subcutaneous injection. Clinical signs after a single intravenous dose included lethargy, edema, cyanosis, pallor, and red ears in rats at greater than or equal to 0.3 mg/kg and lethargy and facial flushing in monkeys at greater than or equal to 0.5 mg/kg. In subchronic studies, detirelix at greater than or equal to 0.4 mg/kg/day (rats) and at greater than or equal to 0.2 mg/kg/day (monkeys) produced atrophy of the reproductive organs, inhibition of ovulation and spermatogenesis, decreased body weight gain in male rats and monkeys, and increased body weight gain in female rats. In the rat, morbidity and/or mortality occurred throughout the treatment phase at a subcutaneous dose of greater than or equal to 2.0 mg/kg/day. In both species, the time to recovery of normal reproductive organ morphology and function was directly related to dose. Exogenous testosterone decreased the severity of reproductive and body weight effects in male rats. In conclusion, the acute effects of detirelix were consistent with peripheral vasodilation. Subchronic effects were associated with inhibition of pituitary gonadotropic and gonadal hormone secretion.

False positive result for a peptide drug in the gene conversion assay with Saccharomyces cerevisiae strain D7.

A battery of mutagenicity tests was performed with nafarelin, an agonist analogue of luteinizing hormone releasing hormone (LHRH) containing tryptophan (Trp) and histidine (His). Included were the Ames assay and the gene conversion assay with yeast strain D7. Both tests were negative without S9 activation, and the Ames test was negative with S9, but the yeast test was positive with S9 activation. Since the yeast test is based on conversion of cells to Trp independence, release of Trp by metabolism of the drug could account for the positive result. The test was repeated using Trp instead of the drug. The result was positive even at the lowest Trp concentration. In another experiment with the drug, amino acid analysis of the incubation mixture revealed the presence of Trp but no detectable His. Since the Ames test is based on mutation to His-independent cells, these data are completely consistent with the negative result in the Ames test and the false positive result in the yeast test. These data suggest the need for caution in interpreting the results from mutagenicity assays with peptide drugs.

Alternative approaches in median lethality (LD50) and acute toxicity testing.

The LD50 test was introduced by Trevan in 1927 for biological standardization of dangerous drugs. Since then, the LD50 has gained wide acceptance as a measure of acute toxicity of all types of substances. Recently, however, the LD50 test has been criticized as an unnecessary waste of resources. Therefore, efforts have been made to reduce the number of animals used in such tests and to avoid using this test unless required by regulations. A review of the literature has shown that a relatively small number of animals per dose level (5) and a small number of dose levels (2 or 3) are usually sufficient to calculate an LD50 and slope using moving average methods. In addition, one sex should suffice since large sex differences are seldom encountered. When a formal LD50 is not required, one of several approximate methods may be used to estimate the lethal dose. Future approaches include in vitro cytotoxicity methods and computer-based structure-activity models. The in vitro methods are still in an early stage of development and will require extensive validation before they are accepted by the toxicology community. In conclusion, when LD50 tests are required, the most economical approach should be used, without undue concern for statistical precision.

Dermal oncogenicity studies on two methoxysilanes and two ethoxysilanes in male C3H mice.

The dermal oncogenic potential of beta-(3,4-epoxycyclohexyl)ethyltrimethoxysilane (EEMS), gamma-glycidoxypropyltrimethoxysilane (GPMS), beta-(3,4-epoxycyclohexyl)ethyltriethoxysilane (EEES), and gamma-glycidoxypropyltriethoxysilane (GPES) was assessed by applying 25-microliters aliquots of acetone solutions to the skin of 40 male C3H/HeJ mice. The concentrations applied were 100, 25, 10, and 10% by volume for EEMS, GPMS, EEES, and GPES, respectively. Applications were made thrice weekly until the death of the animals. A negative control group received acetone (solvent) only. No treatment-related skin tumors were observed, nor was there evidence of increased incidence of any internal tumor in the groups that received GPMS, EEES, or GPES. In the group treated with EEMS, four mice were observed with squamous cell carcinomas of the treated skin and two mice had subcutaneous sarcomas outside of the treated area. No skin tumors were observed in the group treated with acetone, but two mice had subcutaneous sarcomas outside of the treated area. The mean survival times were 529, 482, 545, 492, and 502 days for the EEMS, GPMS, EEES, GPES, and acetone control groups, respectively. In no case was the mortality rate significantly different from that of the controls. The results indicate that only EEMS was oncogenic under the conditions of these studies.

Dermal carcinogenic activity of petroleum-derived middle distillate fuels.

In general, the carcinogenic potential of petroleum-derived materials is related to the polycyclic aromatic hydrocarbon (PAH) content. Thus it has been assumed that liquids which boil below the PAH distillation range (i.e., below approx. 370 degrees C (700 degrees F) would not be carcinogenic. Several early studies supported this conclusion but were of relatively short duration. Several recent and more rigorous studies have shown that repeated application of certain petroleum-derived materials boiling between approximately 177-370 degrees C (350-700 degrees F) (i.e., middle distillate fuels) can produce tumors in mouse skin. The current studies assessed the tumorigenic potential of a series of middle distillates which varied with respect to boiling range, composition, and source of blending stocks. All of the samples produced evidence of weak tumorigenic activity which was characterized by low tumor yields and long median latencies. However, the majority of the tumor yields were significantly different from the control. There were no apparent differences in response among the samples. Thus the various parameters examined did not substantially influence tumor outcome. In particular, there was no association of tumorigenic activity with aromatic carbon content; this finding, coupled with evidence that PAH levels were low, suggested that the tumorigenic responses were not PAH-dependent. In addition to the tumors, there was evidence of non-neoplastic dermal changes including hyperplasia. These may have contributed to the tumorigenic responses; however, the actual mechanism of tumor induction is unknown.

Dermal oncogenicity studies on various ethyleneamines in male C3H mice.

The dermal oncogenic potential of diethylenetriamine, high purity and commercial grades (DETA-HP and DE-TA-C), triethylenetetramine (TETA), tetraethylenepentamine (TEPA), and polyamine HPA No. 2 was assessed by applying 25-microliter aliquots of aqueous solutions to the skin of groups of 50 male C3H/HeJ mice. The concentrations applied were 5.0, 5.0, 5.0, 25.0, and 10.0% by volume for DETA-HP, DETA-C, TETA, TEPA, and HPA No. 2, respectively. Applications were made thrice weekly until the death of the animals. A negative control group received deionized water (solvent) only. All animals were individually housed. No treatment-related skin tumors were observed, nor was there evidence of increased incidence of any internal tumor. Twenty TEPA-treated mice had hyperkeratosis and 13 had necrosis of the epidermis, both indicative of skin irritation. Such lesions were absent or occurred very infrequently in the other groups of mice. The mean survival times were 587, 662, 627, 591, 601, and 626 days for the DETA-HP, DETA-C, TETA, TEPA, HPA No. 2, and water control groups, respectively. In no case was the mortality rate significantly different from that of the controls. The results indicate that none of these compounds was oncogenic under the conditions of these studies.