Abstract
Discussion and Summary
It is interesting that the data from our in vitro studies corroborate the in vivo results obtained by Bock, Swain and Stedman (16). Bock, Swain and Stedman (16) reported that the weak acid (phenol) fraction (No. 8) and two neutral fractions (Nos. 13 and 14) had statistically significant tumor inducing activity. In addition, the third neutral fraction, 12, gave results suggesting activity, and the ether-soluble base fraction (No. 5) exhibited possible activity. We found cell transforming activity with four fractions (Nos. 3, 8, 13 and 14) of CSC. Fractions 8 and 14 exhibited early transformation in infected mouse and rat cells and also subsequently in uninfected hamster cells suggesting that they were most active. Fraction 13 showed transformation in infected mouse cells and uninfected hamster cells. In addition, fraction 3 demonstrated changes in infected mouse and rat cells. However, none of the fractions exhibited cell alteration in uninfected mouse and rat cells. These findings are consistent with previous reports that rat and mouse cells were readily transformed by chemical carcinogens (6–12) and smog extract (13, 14) when these cells were preinfected with C-type RNA viruses, whereas cells treated with chemical or virus alone were not transformed.
A number of bioassays of major fractions of CSC have been reported (16, 20, 21). However, the in vivo assay systems are time consuming. Bock, Swain and Stedman (16) detected the positive fractions by their in vivo accelerated technique after 40 wk. These and previous findings suggest that in vitro transformation systems such as described herein have certain distinct advantages, particularly for rapid quantitative assays of putative carcinogens in tobacco smoke as well as in other suspect environmental materials.
In a preliminary study Freeman et al. (15) reported transforming activity in hamster cells by three fractions, Nos. 9, 6, and 13.
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