Flavonol-stimulated efflux of 7,12-dimethylbenz(a)anthracene in multidrug-resistant breast cancer cells.

We used a series of P-glycoprotein (P-gp) expressing multidrug-resistant (MDR) cells, developed from human breast cancer MCF-7 cells by exposure to Adriamycin, to investigate the effects of flavonoids on P-gp-mediated efflux mechanisms for chemical carcinogens. We previously showed that MDR cells derived from exposure to Adriamycin are cross-resistant to a chemical carcinogen, benzo(a)pyrene, due to its cellular efflux by the P-gp-mediated putative drug efflux pump. Our current studies extended this observation to another polycyclic aromatic hydrocarbon, 7,12-dimethylbenz(a)anthracene, known to induce mammary tumors in animals. In our attempt to find naturally occurring dietary compounds which may stimulate the P-gp-mediated efflux of carcinogens, we found that certain flavonols, kaempferol, quercetin, and galangin, are potent stimulators of the P-gp-mediated efflux of 7,12-dimethylbenz(a)-anthracene. The increased efflux decreased the cellular burden of 7,12-dimethylbenz(a)anthracene. Since these flavonol compounds are widely distributed in fruits and vegetables, their stimulatory effect on P-gp may be a mechanism relevant to carcinogenesis and the observed lowered cancer risk in humans with higher dietary intake of fruits and vegetables.

A new functional role for P-glycoprotein: efflux pump for benzo(alpha)pyrene in human breast cancer MCF-7 cells.

We propose that the cellular burden of certain carcinogens may be mitigated by P-glycoprotein (P-gp), the putative drug efflux pump. In a series of multidrug resistant human breast cancer MCF-7 cells with increasing P-gp expression we examined this hypothesis using benzo(alpha)pyrene, a widely distributed environmental and dietary carcinogen. We found that multidrug resistant cells were cross-resistant to benzo(alpha)pyrene and the rates of efflux for benzo(alpha)pyrene were higher in multidrug resistant cells than in wild type cells. Evidence supporting the involvement of P-gp included the inhibition of azidopine binding to P-gp benzo(alpha)pyrene and the inhibition of benzo(alpha)pyrene efflux by Adriamycin and verapamil. Our findings suggest that P-gp may play a role in the cellular defense to carcinogens. The expression of P-gp and the modulation of its function may affect the susceptibility of normal tissues to transformation by carcinogens.

Rapid assessment of relationships among HIV isolates by oligopeptide analyses of external envelope glycoproteins.

The most variable proteins, the gp120's, of the many isolates of HIV-I can be readily compared by two-dimensional oligopeptide maps. The gp120 in a given cell line is completely stable, but the cell line defines the actual gp120 size and may induce minor peptide changes. HTLV-IIIB and LAV differ slightly from each other even when grown in the same cell line, while LAV grown in a B cell line is less related. Molecularly distant isolates have unique patterns. While anti-HTLV-IIIB gp120 antibody neutralized both HTLV-IIIB and LAV, it recognizes only the homologous HTLV-IIIB infected cells in cytotoxicity assays. Structural analysis of isolates should be helpful in defining the range of immunological reactivities among variants as a contribution to a rational approach to a vaccine against AIDS.

Prevention of experimental allergic encephalomyelitis by ganglioside GM4. A follow-up study.

The myelin-specific ganglioside GM4, when incubated with myelin basic protein prior to inoculation, prevents experimental allergic encephalomyelitis in the guinea pig. The monosialoganglioside GM1, the predominant ganglioside of mammalian myelin, also prevents experimental allergic encephalomyelitis, whereas a mixture of neural gangliosides rich in polysialogangliosides causes enhanced disease. Guinea pigs inoculated with both myelin basic protein and GM4 develop serum IgG antibodies against basic protein, but not against GM4.

Thymotropic envelope gene recombinants of Moloney leukemia virus have highly conserved envelope structures.

Envelope gp70s were isolated from the thymotropic recombinant viruses related to Moloney murine leukemia virus (RM-M-MuLVs) which were generated by the inoculation of two strains of ecotropic M-MuLV (strain 1869 and temperature-sensitive mutant-1) into BALB/c or CFW/D mice. Chymotrypsin oligopeptide maps of parental ecotropic MuLV, RM-M-MuLV, and inducible xenotropic MuLV showed each of the above virus types had a distinctly characteristic peptide map. The majority of RM-M-MuLV gp70 molecules examined showed a high degree of peptide homology. Data from restriction endonuclease mapping demonstrated that the newly acquired sequences in each of the RM-M-MuLVs were very related and encompassed both the polymerase and the envelope genes. The source of the sequences acquired by the RM-M-MuLV was from endogenous nonecotropic and nonxenotropic proviruses. This suggested that the family of endogenous proviruses which combined with the parental ecotropic virus was either specifically selected or was much more available than other endogenous proviruses. Although slight variations of envelope-specific sequences and peptides existed among various RM-M-MuLV isolates; within a single thymoma, individual clones of tumor cells yielded RM-M-MuLV gp70s which were identical to each other. These findings are discussed within the context of the leukemogenic potential of RM-MuLVs.

Prevention of experimental allergic encephalomyelitis by ganglioside GM4.

Guinea pigs inoculated with a mixture of myelin basic protein and the myelin-specific ganglioside, sialosylgalactosylceramide (GM4), do not develop the signs or neuropathology of experimental allergic encephalomyelitis. The results indicate that GM4 cloaks the basic protein molecule so that it is no longer immunopathogenic in these animals. The interaction of basic protein with GM4, previously shown in vitro, appears to be relevant to the pathogenesis of experimental allergic encephalomyelitis in guinea pigs.

Generation of recombinant murine leukemia viruses de novo: an alternative model for leukemogenesis.

Evidence for the viral etiology of murine lymphoma is very complex. Although ecotropic viruses were considered in the past to be the causative agents, envelope gene recombinant (RM) types of murine leukemia virus (MuLV) seem to be the best candidates at present. The following factors are relevant in the murine model: Pure ecotropic MuLV causes disease but induces RM-MuLV de novo in every case. RM-MuLV can cause disease in pure form. However, the mere presence of RM-MuLV may not be sufficient to cause disease in some cases. Ecotropic MuLV is needed under natural conditions for inducing T-cell blastogenesis, donating its coat to recombinant MuLV, and to become a partial parent for RM-MuLV. Early elimination of ecotropic MuLV can prevent disease. In a number of virus-free mouse lymphomas, the only indicator of virus involvement was on RM-MuLV glycoprotein on cell surface. Based on the above, a signal hypothesis model is proposed which attempts to integrate the above observations.