Enhancement of Viral Transformation for Evaluation of the Carcinogenic or Mutagenic Potential of Inorganic Metal Salts¹

Thirty-eight metal salts were tested for their capacity to enhance transformation of Syrian hamster embryo cells by a simian adenovirus, SA7. All of the metal salts with known carcinogenic potential in animals or mutagenic activity in microbial or mammalian cells increased the SA7 transformation frequency. Metals were classified into three groups according to the concentration necessary to produce significant enhancement. Those showing highest activity (positive at less than 0.05 mm) were the salts of antimony, arsenic, cadmium, chromium, and platinum. The second group (positive from 0.05 to 0.6 mm) included beryllium, cobalt, copper, lead, manganese, mercury, nickel, silver, thallium, and zinc. Iron salts were placed in a third group (only positive at concentrations greater than 0.9 mm). With the exception of ZnCl₂ and ZnSO₄, enhancement was demonstrated by both a relative increase in the viral transformation frequency and an absolute increase in the number of transformed foci among treated cells. The latter observation and the demonstration of enhancement in the absence of overt cell killing negate the possibility that enhancement resulted from the selection of transformation-sensitive cells.