Studies on the chemopreventive potentials of vegetable oils and unsaturated fatty acids against breast cancer carcinogenesis at initiation.

The effect of dietary fat on breast cancer is a longstanding and an unresolved issue. We found that 17beta-estradiol (E2) could be activated by the epoxide-forming oxidant dimethyldioxirane (DMDO) to bind DNA-forming DNA adducts both in vitro and in vivo, and to inhibit nuclear RNA synthesis. We proposed that E2 epoxidation is the underlying mechanism for the initiation of breast cancer carcinogenesis (Carcinogenesis 17, 1957-61, 1996). This report is on the transcriptional and DNA-binding properties of vegetable oils and fatty acids, and on the potentials of these compounds to prevent the formation of E2 epoxide. The results show that vegetable oils, having no effect on nuclear RNA synthesis either before or after DMDO treatment, were all able to prevent the formation of E2 epoxide independent of their mono- or polyunsaturated fatty acid content. Similarly, unsaturated fatty acids, regardless of chain length and number of double bonds, were all able to prevent the formation of E2 epoxide as reflected by the loss of the ability of [3H]E2 to bind DNA. In contrast to vegetable oils, the results indicated that the unsaturated fatty acids palmitoleic, oleic, linoleic, linolenic and arachidonic acid could be activated by DMDO to inhibit nuclear RNA synthesis, and that the mono-unsaturated fatty acids (i.e. palmitoleic and oleic acid) were stronger inhibitors than fatty acids with more than one double bond (e.g. linoleic, linolenic and arachidonic acid). [32P]Post-labeling analysis revealed that under identical DMDO activation, the DNA adducts formed for oleic acid were 17098 adducts/10(8) nucleotides, which was 20-fold more than palmitoleic acid (815), and 120-fold more than alpha-linolenic acid (142). This result strongly suggests that oleic acid could be a potential initiating carcinogen after epoxidation.

Changes in telomerase activity and telomere length during human T lymphocyte senescence.

It has been proposed that telomeres shorten with every cell cycle because the normal mechanism of DNA replication cannot replicate the end sequences of the lagging DNA strand. Telomerase, a ribonucleoprotein enzyme that synthesizes telomeric DNA repeats at the DNA 3' ends of eukaryotic chromosomes, can compensate for such shortening, by extending the template of the lagging strand. Telomerase activity has been identified in human germline cells and in neoplastic immortal somatic cells, but not in most normal somatic cells, which senesce after a certain number of cell divisions. We and others have found that telomerase activity is present in normal human lymphocytes and is upregulated when the cells are activated. But, unlike the immortal cell lines, presence of telomerase activity is not sufficient to make T cells immortal and telomeres from these cells shorten continuously during in vitro culture. After senescence, telomerase activity, as detected by the TRAP technique, was downregulated. A cytotoxic T lymphocyte (CTL) cell line that was established in the laboratory has very short terminal restriction fragments (TRFs). Telomerase activity in this cell line is induced during activation and this activity is tightly correlated with cell proliferation. The level of telomerase activity in activated peripheral blood T cells, the CTL cell line, and two leukemia cell lines does not correlate with the average TRF length, suggesting that other factors besides telomerase activity are involved in the regulation of telomere length.

Induction of human cytotoxic T lymphocytes specific for prostate-specific antigen.

Prostate-specific antigen (PSA), a tissue-specific protein expressed by most adenocarcinomas of the prostate, might be a useful target for T-cell-mediated immunotherapy of prostate cancers. The current study examined whether it is possible to elicit human cytotoxic T lymphocytes (CTL) with specificity for PSA. A synthetic nonamer peptide, corresponding to residues 146-154 of PSA and containing a canonical HLA-A2-binding motif, was shown to stabilize the expression of HLA-A2 on the T2 antigen-processing mutant cell line. Repeated in vitro stimulation of peripheral blood lymphocytes from a normal HLA-A2+ donor induced CTL with specificity for the PSA 146-154 peptide. The peptide-induced CTL expressed the CD4- CD8+ cell surface phenotype and were restricted by HLA-A2. A large portion of patients with prostate cancer express the HLA-A2 phenotype, implying that many prostate cancers might be targeted by HLA-A2-restricted CTL with specificity for the PSA 146-154 epitope.

Differentiation arrest by autologously replicating DNA loops formed along differentiation pathway: an hypothesis of carcinogenesis.

The current hypothesis attempts to explain tumor development from the perspective of deoxyribonucleic acid structural changes rather than mutational alterations of single or multiple genes. The hypothesis postulates that stable deoxyribonucleic acid loops capable of autologous replication, translation and expression cause cell-differentiation arrest and contribute to the carcinogenesis and various abnormal biological behaviors of tumor. The formation of deoxyribonucleic acid loops at particular steps along the differentiation pathway determines tumor phenotype, grade and behavior. The outcome of deoxyribonucleic acid loop-formation in a cell is highly affected by the differentiation signals imposed by the cell's differentiation microenvironment which is considered as a very important regulatory factor during tumor development in this hypothesis. The incompatibility of adhesion molecules between tumor cells and surrounding normal cells is proposed in this hypothesis as a major reason for separation of tumor cells from primary lesions and thus metastasis. This hypothesis also postulates that tumor invasion is caused by the expression of proteins related to the transient invasive phenotype of normal cells in physiologic process that is controlled by the genes within autologous deoxyribonucleic acid loops.