Short-term in vitro and in vivo analyses for assessing the tumor-promoting Potentials of cigarette smoke condensates

Previous studies found that repeated application of smoke condensate from tobacco-burning reference cigarettes to chemically initiated SENCAR mouse skin promoted the development of tumors in a statistically significant and dose-dependent manner, while condensate from prototype cigarettes that primarily heat tobacco promoted statistically fewer tumors. Based on the recognized correlation between sustained, potentiated epidermal hyperplasia and tumor promotion, we conducted tests to examine the utility of selected short-term analyses for discriminating between condensates exhibiting significantly different promotion activities. In vitro analyses assessing the potential for inducing cytotoxicity (ATP bioluminescence) or free radical production (cytochrome c reduction, salicylate trapping) demonstrated significant reductions when comparing condensate collected from prototype cigarettes to reference condensate. Short-term in vivo analyses conducted within the context of a mouse skin, tumor-promotion protocol (i.e., comparative measures of epidermal thickness, proliferative index, myeloperoxidase activity, leukocyte invasion, mutation of Ha-ras, and formation of modified DNA bases) provided similar results. Reference condensate induced statistically significant and dose-dependent increases (relative to vehicle control) for nearly all indices examined, while prototype condensate possessed a significantly reduced potential for inducing changes that we regarded as consistent with sustained epidermal hyperplasia and/or inflammation. Collectively, these data support the contention that selected short-term analyses associated with sustained hyperplasia and/or inflammation are capable of discriminating between smoke condensates with dissimilar tumor-promotion potentials. Moreover, our results suggest that comparative measures of proliferative index and myeloperoxidase activity, both possessing favorable correlation coefficients relative to tumor formation (i.e.,greater than or equal to0.95 after 8 or 12 weeks of promotion), may constitute reasonable end points for further investigation.