Inducible mutagenesis in TEPC 2372, a mouse plasmacytoma cell line that harbors the transgenic shuttle vector lambdaLIZ

The plasmacytoma cell line, TEPC 2372, was derived from a malignant plasma cell tumor that developed in the peritoneal cavity of a BALB/c mouse that harbored the transgenic shuttle vector for the assessment of mutagenesis in vivo, lambdaLIZ. TEPC 2372 was found to display the typical features of a BALB/c plasmacytoma. It consisted of pleomorphic plasma cells that secreted a monoclonal immunoglobulin (IgG2b/lambda), was initially dependent on the presence of IL-6 to grow in cell culture, contained a hyperdiploid chromosome complement with a tendency to undergo tetraploidization, and harbored a constitutively active c-myc gene by virtue of a T(6;15) chromosomal translocation. TEPC 2372 was further characterized by the ability to respond to in vitro exposure with 4-NQO (4-nitroquinoline-1-oxide), an oxidative model mutagen, with a vigorous dose-dependent increase in mutagenesis that peaked at a 7.85-fold elevation of mutant rates in lambdaLIZ when compared to background mutant rates in untreated controls. Cotreatment with 4-NQO and BSO (buthionine sulfoximine), a glutathione-depleting compound that causes endogenous oxidative stress, resulted in a 9.03-fold increase in the mutant frequency in lambdaLIZ. These results demonstrated that TEPC 2372, the malignant plasma cell counterpart of the lambdaLIZ-based in vivo mutagenesis assay, may be useful as an in vitro reference point for the further elucidation of oxidative mutagenesis in lymphoid tissues.

Elevated mutant frequencies in lymphoid tissues persist throughout plasmacytoma development in BALB/c.lambdaLIZ mice

Using the phage lambdaLIZ-based transgenic in vivo mutagenesis assay, the mean mutant frequencies in the target gene, lacI, were found to be significantly increased in lymphoid tissues of congenic BALB/c.lambdaLIZ N5 mice in the terminal stage of a plasmacytoma induction experiment, 213-280 days after the first i.p. injection of the plasmacytomagenic agent pristane (2,6,10,14-tetramethylpentadecane). In plasmacytoma-bearing mice (n = 7), mutant frequencies in the spleens and mesenteric lymph nodes were elevated 2.46-fold and 5.35-fold, respectively, when compared with age-matched controls. In plasmacytoma-negative mice (n = 11), mutant frequencies were increased 2.30-fold (spleens) and 3.48-fold (mesenteric nodes). These results, interpreted in conjunction with our previous findings (K. Felix et al., Cancer Res., 58: 1616-1619, 1998) of approximately 3-fold elevations in pristane-induced splenic mutagenesis on day 42 postpristane, indicate that increased mutant levels in lymphoid tissues persist throughout plasmacytomagenesis in genetically susceptible BALB/c mice.