Study of the ability of phenacetin, acetaminophen, and aspirin to induce cytotoxicity, mutation, and morphological transformation in C3H/10T1/2 clone 8 mouse embryo cells.

Use of the analgesic compounds acetylsalicylic acid (aspirin), phenacetin, and acetaminophen has been correlated with increased risk of renal cancer in humans. Hence, we studied these compounds for ability to induce cytotoxicity, mutation to ouabain resistance, and morphological transformation in cultured C3H/10T1/2 clone 8 (10T1/2) mouse embryo cells. All three compounds were cytotoxic from 0.5-mg/ml to 2-mg/ml concentrations as evidenced by decreased plating efficiency. None of the compounds induced detectable base substitution mutations to ouabain resistance even at cytotoxic concentrations. Aspirin did not induce morphological transformation. Both phenacetin and acetaminophen induced low but concentration-dependent numbers of atypical, weak type II morphologically transformed foci; at equimolar concentrations, phenacetin was 1.1- to 3.0-fold more active in inducing these foci. Neither phenacetin nor acetaminophen was cotransforming with 3-methylcholanthrene, and neither compound promoted cell transformation when added to 3-methylcholanthrene-initiated 10T1/2 cells. The focus-inducing potency of both compounds was increased by addition of an Arochlor-induced hamster liver S9 fraction as an exogenous metabolizing system. However, seven putative metabolites of phenacetin and acetaminophen that were tested--N-hydroxyphenacetin, p-phenetidine, p-aminophenol, p-nitrosophenol, benzoquinone, acetamide, and N-acetyl-p-benzoquinoneimine--were inactive in transformation assays at the concentrations reducing plating efficiency of treated cells to 50% of the plating efficiency of nontreated (control) cells. Several acetaminophen- and phenacetin-induced foci were cloned, expanded into cell lines, and characterized. These cell lines stably formed type II foci when maintained at confluence for 2 to 4 wk in reconstruction experiments with nontransformed 10T1/2 cells; however, they did not exhibit significantly increased saturation density compared to 10T1/2 cells, and they did not grow in soft agarose. These results suggest that metabolic intermediates of high concentrations of phenacetin and acetaminophen induce a low frequency of nonneoplastic morphological transformation of 10T1/2 mouse embryo cells.

Duke Scholars

Author Steven Patierno Medicine, Medical Oncology