The effect of 17beta-estradiol-DNA adducts on the replication of exon # 5 of the human suppressor gene p53

Detection of human papillomavirus infection in oral cancers reported at dental facility: assessing the utility of FFPE tissues

Incidence of human papillomavirus (HPV)-associated oral cancers is on the rise. However, epidemiological data of this subset of cancers are limited. Dental hospital poses a unique advantage in detection of HPV-positive oral malignancies. We assessed the utility of formalin-fixed paraffin-embedded (FFPE) tissues, which are readily available, for evaluation of high-risk HPV infection in oral cancer. For protocol standardization, we used 20 prospectively collected paired FFPE and fresh tissues of histopathologically confirmed oral cancer cases reported in Oral Medicine department of a dental hospital for comparative study. Only short PCRs (~ 200 bp) of DNA isolated using a modified xylene-free method displayed a concordant HPV result. For HPV analysis, we used additional 30 retrospectively collected FFPE tissues. DNA isolated from these specimens showed an overall 23.4% (11/47) HPV positivity with detection of HPV18. Comparison of HPV positivity from dental hospital FFPE specimens with overall HPV positivity of freshly collected oral cancer specimens (n = 55) from three cancer care hospitals of the same region showed notable difference (12.7%; 7/55). Further, cancer hospital specimens showed HPV16 positivity and displayed a characteristic difference in reported sub-sites and patient spectrum. Overall, using a xylene-free FFPE DNA isolation method clubbed with short amplicon PCR, we showed detection of HPV-positive oral cancer in dental hospitals.

Evidence for the preventive effect of the polyunsaturated phytol side chain in tocotrienols on 17beta-estradiol epoxidation

BACKGROUND

We found that 17beta-estradiol (E2) could be activated by epoxidation to bind DNA and to inhibit nuclear RNA synthesis. Vitamin E compounds are powerful antioxidants and chain-breaking free radical scavengers. The chromanol ring in Vitamin E is believed to be involved in these reactions.

METHODS

Here, we examined the preventive effect of alpha-tocopherol, alpha-, gamma- and delta-tocotrienols on E2 activation.

RESULTS

We found that when any one of these Vitamin E compounds was mixed with E2 for epoxidation by the epoxide-forming oxidant dimethyldioxirane (DMDO), alpha-tocopherol was the least effective as compared with the tocotrienols against the formation of E2 epoxide as reflected by the loss of the ability of E2 to inhibit nuclear RNA synthesis. This conclusion was further confirmed by the binding studies of [3H] labeled E2 to DNA using either DMDO or liver microsomes activation system.

CONCLUSIONS

Since the chromanol ring is shared by both tocopherols and tocotrienols and the only difference between these two subgroups of Vitamin E is the phytol side chain, we conclude that the polyunsaturated phytol group in tocotrienols plays a key preventive role in E2 epoxidation. This is the first report showing that the polyunsaturated phytol side chain in tocotrienols is involved in an antioxidative activity and it may also have a preventive effect against the E2 epoxide induced breast cancer carcinogenesis at the initiation.

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.

17Beta-estradiol epoxidation as the molecular basis for breast cancer initiation and prevention

Epidemiological and animal studies have indicated that 17beta-estradiol (E2) is involved in breast cancer; however, the mechanism is unclear. We found that E2 could be activated by epoxidation, resulting in its ability to inhibit nuclear DNA-dependent RNA synthesis, and to bind DNA, forming DNA adducts both in vitro and in vivo. Because epoxidation is required for the activation of many chemical carcinogens, including benzo(a)pyrene, 7,12-dimethylbenz(a)anthracene and aflatoxins, we proposed previously that E2 epoxidation is the underlying mechanism for the initiation of breast cancer. The first part of this review is to present the experimental evidence obtained from this laboratory in support of this hypothesis. Based on these newly discovered insights on E2 epoxidation and its initiation role in breast cancer carcinogenesis, a method to screen chemopreventive agents against breast cancer has been developed. This constitutes the second part of the review. Two examples will be used to illustrate the utility of this screening technique. The effect of fat on breast cancer has been a longstanding but unresolved issue. Epidemiological studies provide conflicting results regarding the association of dietary fat and breast cancer. Because vegetable oils contain various amount of mono- and polyunsaturated fatty acids, they are potential antioxidants. Data are presented to show that commercial vegetable oils, independent of their mono- or polyunsaturated fatty acid content, are all able to prevent the formation of E2 epoxide, as measured by the loss of the ability of E2 to inhibit nuclear RNA synthesis in vitro. Tamoxifen (TAM), an anti-estrogen used for breast cancer treatment, has recently been found to have a strong breast cancer preventive effect. The mechanism for this is unknown. Using the same screening technique, we found that when incubated together with E2 for epoxidation, TAM was able to prevent the formation of E2 epoxide, as evidenced by both the loss of the ability of E2 to inhibit nuclear RNA synthesis and the reduced binding of [3H]-labelled E2 to nuclear DNA in a dose-dependent manner. These experimental results suggest that the breast cancer preventive effect of TAM is to prevent the formation of E2 epoxide through a competitive epoxidation mechanism with E2.

A proposed mechanism of tamoxifen in breast cancer prevention

Recent clinical trials suggest that tamoxifen (TAM) is a preventive agent for breast cancer, however, the mechanism is unknown. Previously, we found that both 17beta-estradiol (E2) and estrone (E1) could be activated by epoxidation resulting in their ability to bind to DNA, forming DNA adducts both in vitro and in vivo, and to inhibit nuclear DNA-dependent RNA synthesis. Since epoxidation is required for the activation of many well-known chemical carcinogens including benzo(a)pyrene, 7,12-dimethylbenz(a)anthracene, aflatoxins, etc., we proposed that estrogen epoxidation is the underlying mechanism for the initiation of breast cancer (Carcinogenesis 17 (1996) 1957). Here, we report that TAM is able to dramatically inhibit the formation of E2 and E1 epoxides as measured by both the loss of their ability to inhibit nuclear DNA-dependent RNA synthesis and to bind to nuclear DNA. These findings suggest that the breast cancer preventive effect of TAM may be through a competitive epoxidation inhibition mechanism that prevents the formation of E2 and E1 epoxides and consequently, the initiation of breast cancer.

Prevention of chemical carcinogen DNA binding and inhibition of nuclear RNA polymerase activity by organosulfur compounds as the possible mechanisms for their anticancer initiation and proliferation effects

This report examines the transcriptional roles and DNA binding properties of the three major organosulfur compounds (OSCs) from garlic, diallyl sulfide (DAS), diallyl disulfide (DADS) and diallyl trisulfide (DATS). We found DADS and DATS, but not DAS, could be activated by the versatile epoxide-forming oxidant dimethyldioxirane (DMDO) and could strongly inhibit nuclear RNA synthesis in vitro. We also found that when incubated together with [3H]-labeled 17beta-estradiol (E(2)) for activation by DMDO, DADS and DATS, but not DAS, were able to prevent the binding of [3H]E(2) to DNA. This preventive effect of DADS and DATS was confirmed when liver microsomes were used, and further verified by 32P post-labeling analysis. Additionally, we discovered that the DMDO treated DADS and DATS, but not DAS, were able to directly inhibit the enzyme RNA polymerase per se. These novel findings provide new insights into the potential mechanisms of the preventive effects of OSCs on tumor initiation and promotion.