Biological Activation of Virus-Like Particles from Chemically Induced Guinea Pig Sarcomas 1

Virus-like particles have been observed in oogonia and oocytes of fetal, neonatal, and adult albino guinea pigs (1). Moreover, reports from many laboratories indicate that virus-like particles have been activated from cultured cells of leukemic and normal guinea pigs by chemical treatments (2-6). Such particles have also been described in cells of 3-methyl-cholanthrene (MCA)-in-duced guinea pig tumor cells after induction by 5-bromodeoxyuridine (5).

We recently observed particles resembling viruses in three different types of MCA-induced guinea pig sarcomas that had morphological, biochemical, and biophysical properties similar to each other and to the virus-like particles found in tumors induced by known oncornaviruses (7).

We report the induction of similar particles by biological activation of the guinea pig sarcoma cells with adenovirus and chemical treatments. We report the biochemical, biophysical, and immunovirological properties of the particles found in both non-activated and activated cultures.

Materials and Methods. Guinea pigs. Adult Sewall Wright, strain 2 female guinea pigs were used in this study. This strain has been maintained by continuous single line brother-sister mating. First- and second-set skin grafts between members of this strain are permanently accepted (8).

Tumors. Tumors investigated in this study were of three distinct histologic types: MCA-25, an osteogenic sarcoma; MCA-A, a liposarcoma; and MCA-1, a fibrosarcoma. Each was induced by subcutaneous injections of MCA, in female strain 2 guinea pigs. The histopathology, immunogenicity, and in vivo growth characteristics of MCA-induced guinea pig sarcoma tumors have been previously described (9-11). Tumors were maintained by dorsal subcutaneous injection of 1 ml of a 30 % suspension (v/v) of minced tumor in Eagle's minimal essential medium (MEM) unsupplemented. Earlier tumor transplant generations were preserved by slow freezing in 10% dimethyl-sulfoxide in RPMI 1640 with 40% fetal bovine serum (FBS) and storage at —190°. Sera. Serum specimens were collected by standard methods and stored at —70° in 1-ml quantities. Serum blood specimens were obtained from breeder animals, from animals with growing tumors, from animals in which the growing tumors had been excised, from animals prior to tumor inoculation, and from animals immunized by temporary tumor growth after subsequent tumor challenge.