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The myeloma proteins produced by 44 plasmacytomas (PCTs) recently induced by pristane in BALB/cAnPt and closely related PCT susceptible congenic strains of mice were isolated chromatographically and screened against a panel of 10 protein, nucleic acid and lipid antigens. This sample was highly unusual because 82% of the proteins had IgG isotopes. Nine of the proteins bound to Hsp65 (GroEL), and all of these were polyreactative. Twenty-one of the myeloma proteins were polyreactive and bound two or more antigens in the panel, and five were monoreactive. Thus, an antigen binding activity was determined for 59% of these myeloma proteins.

While the mechanism of how Indo inhibits PCTGEN is not established, Several hypothetical explanations provide new potential experimental approaches. Indo may block production of cytokines such as Il-6 in accessory cells that are critical for B-cell growth, viability and maturation, or it may directly target B cells via PPAR-gamma receptors. The latter mode of action is described in other cell types but not yet defined in B cells.

Injection of silicone gel or silicone oil intraperitoneally into BALB/c mice induced the formation of antibodies that reacted by ELISA with highly purified crystalline cholesterol and, to a much lesser extent, antibodies that reacted with a phospholipid (dimyristoyl phosphatidylglycerol). Although IgM and IgG antibodies to cholesterol were detected, the titers of IgG antibodies were low when compared with IgM. The titers of IgM antibodies to cholesterol in certain sera exhibited activities that reached baseline values at dilutions as high as 1:5000, thus making them equivalent to titers that have been previously published for ascites fluid containing murine monoclonal antibodies to cholesterol. The antibodies to cholesterol induced by silicone compounds are indistinguishable in their binding to crystalline cholesterol from naturally-occurring antibodies to cholesterol in normal human serum. They are also indistinguishable from antibodies induced by a proposed vaccine to cholesterol that is currently in late preclinical development for prevention of hypercholesterolemia in humans. The anti-cholesterol vaccine, which consists of liposomes heavily laden with cholesterol as an antigen and lipid A as an adjuvant, induces antibodies that react with low density lipoproteins (LDL) and opsonize them for removal by liver macrophages. It appears that silicone gel or silicone oil causes recruitment and adsorption of cholesterol at the injection site, and also serves as an adjuvant that may have immunostimulant properties similar to lipid A for inducing antibodies to lipids. Antibodies to lipids such as cholesterol or phospholipids are not harmful to intact cell membranes because of steric hindrance from surrounding lipids and larger macromolecules that block binding of the antibodies.

Inclusion complexes of gamma-cyclodextrin and octamethylcyclotetrasiloxane (D4), decamethyltetrasiloxane (M10TS), and 1,3,5,7-tetramethyltetravinylcyclotetra - siloxane (TMTV-D4) were prepared to compare the cytotoxic effects of siloxanes in vitro. In these preparations, the hydrophobic siloxanes are surrounded by a hydrophilic shell of eight circularly linked D-glucose molecules (gamma-cyclodextrin), and upon contact with plasma membranes the siloxane molecule can intercalate into the lipid bilayer of the cell membrane. XRPC24, 2-11 plasmacytoma, CH12.LX lymphoma and P388D1 macrophage-like cells were used as indicator cells in toxicity assays. Using an MTT tetrazolium reduction to formazan test, a colorimetric method to determine the number of viable cells, the 50% minimal lethal doses (CD50) for the siloxane compounds were found to range from 30 to 50 microM. Sublethal doses (e.g., 15 microM and lower) resulted in the loss of lactate dehydrogenase (LDH) and glutathione (GSH) from the cytosolic compartment of the target cells and thus indicated cytotoxicity. Treatment of macrophages with siloxanes resulted in a higher production of interleukin-6 (IL-6) than was exhibited by untreated macrophages. The B9 cell bioassay of these treated cells showed as much as a 10 fold higher production (500 U/ml) of IL-6 than did the untreated cells. The degree of increase was dependent on the compound and concentration used. The results of this study show that low molecular weight siloxanes produce lethal effects on B-lymphocyte derived target cells in vitro and permeabilize the plasma membranes at lower sublethal concentrations.

Silicone gels derived from commercially obtained implants induce plasmacytomas in 60-70% of highly susceptible BALB/cAn.DBA/2-Idh1-Pep3 congenic mice. In contrast, dimethylpolysiloxane (DMPS) silicone oils with viscosities of 5, 1000 and 12,500 cs fail to elicit these tumors. 1000 cs vinylmethylpolysiloxane is also inactive. Silicone gels, in contrast to the oils, induce a highly inflammatory silicone granuloma. Silicone gels contain chemical components not found in the oils. The chemical component responsible for inducing the permissive environment for plasmacytoma formation has not yet been identified. Silicone gels are well tolerated for long periods of time in mice without adverse effects other than plasmacytoma formation. The response to different gel preparations varies; some are associated with relatively rapid formation of plasmacytomas resembling that seen with pristane, while in others the plasmacytoma formation is extended nearly over a two year period.

Silicone gels injected intraperitoneally into strains of mice related to BALB/c develop plasmacytomas in approximately the same numbers and with similar phenotypes as previously obtained with pristane. Silicone gels produce few side effects and are well tolerated for long periods. Silicone gels contain several components that are potentially biologically active: residual vinyl groups and platinum. Microscopic and histological evidence suggests the silicone gel is degraded over a long period of time. Preliminary studies with long chain liquid dimethylpolysiloxanes with viscosities of 1000 cSt and 12,500 cSt have not produced plasmacytomas as yet. The plasmacytomagenic action of the gel appears to be due to the release of liquids from the gel matrix.

Genetic rearrangements activating the proto-oncogene c-myc comprise a mandatory oncogenic step in plasma cell tumor development in BALB/cAnPt mice. In the majority of plasmacytomas, c-myc activating rearrangements take the form of reciprocal chromosomal translocations t(12;15) that juxtapose c-myc to the immunoglobulin heavy chain alpha locus (IgH alpha) in particular the switch alpha region (S alpha). The genetic basis for the prevalence of S alpha/c-myc recombinations in BALB/cAnPt plasmacytomas is not known but may be related to a hypothetical regional genomic instability of the c-myc and IgH alpha loci in BALB/cAnPt mice. We wished to test whether the genomic instability of both loci might be revealed by the diversity of genetic recombinations that can be observed in IgH alpha and c-myc. We employed PCR methods to detect new recombinations of c-myc and IgH alpha in the preneoplastic stage of plasma cell tumor development and found that c-myc can be joined to more genes or genomic regions than known before. This is indicative but does not formally prove a particular genomic instability of c-myc and IgH alpha in BALB/cAnPt B cells. Since defective DNA repair provides a mechanistic explanation for genomic instability, we measured the efficiency of repair in IgH alpha and c-myc using an assay that quantitates the removal of UV-induced pyrimidine dimers within specific genomic regions. We used plasmacytoma XRPC 24 as a model system and found that both IgH alpha and c-myc were poorly repaired, whereas c-abl, a proto-oncogene not related to conventional pristane-induced plasmacytoma-genesis, was efficiently repaired.

Recombinations between c-myc and immunoglobulin loci are a hallmark of Burkitt's lymphomas and mouse plasmacytomas. Analyzing the fine structure of these illegitimate rearrangements has revealed differences between the recombinations in these two tumors. Recombinations are nearly reciprocal in Burkitt's lymphomas, whereas in most BALB/c plasmacytomas large stretches of c-myc sequences have been deleted. The recombinations detected during preneoplastic development of plasmacytomas, in contrast, have most of the c-myc sequences retained on either one of the translocated chromosomes. We conclude that initial recombination structures are subjected to secondary changes in mouse plasmacytomas. In Burkitt's lymphomas the primary recombination sequence is preserved in tumor cells.

We have studied DNA repair after UV damage in the murine c-myc locus. It appears that a region in B cells upstream of the murine c-myc gene is repaired with a different efficiency in plasmacytoma-resistant DBA/2N mice than in plasmacytoma-susceptible BALB/cAn mice. The region just upstream of c-myc is inefficiently repaired in B lymphoblasts derived from BALB/cAn mice. In contrast, this same region of c-myc is efficiently repaired in B lymphoblasts derived from DBA/2N mice. DNA fragments located in the coding region of c-myc and in another gene, dihydrofolate reductase (DHFR), are repaired with equal efficiency in cells from these two strains of mice. It is possible that repair efficiency of the 5' flank of c-myc may be involved in tumor susceptibility of the mouse strain.