| 1. |
- Gao, Li, et al.
(author)
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A mechanistic hypothesis for the cytochrome P450-catalyzed cis-trans isomerization of 4-hydroxytamoxifen : an unusual redox reaction
- 2011
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In: Journal of Chemical Information and Modeling. - : American Chemical Society (ACS). - 1549-9596 .- 1549-960X. ; 51:9, s. 2293-2301
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Journal article (peer-reviewed)abstract
- We provide a detailed description of the cis-trans isomerization of 4-hydroxytamoxifen/endoxifen catalyzed by several isoforms from the cytochrome P450 (CYP) superfamily, including CYP1B1, CYP2B6, and CYP2C19. We show that the reactions mainly involve redox processes catalyzed by CYP, DFT calculation results strongly suggest that the isomerization occurs via a cationic intermediate. The cationic cis-isomer is more than 3 kcal/mol more stable than the trans form, resulting in an easier conversion from trans-to-cis than cis-to-trans. The cis-trans isomerization is a rarely reported CYP reaction and is ascribed to the lack of a second abstractable proton on the ethenyl group of the triarylvinyl class of substrates. The cationic intermediates thus formed instead of the stable dehydrogenation products allow for isomerization to occur. As a comparison, the reactions for the tamoxifen derivatives are compared to those of other substrates, 4-hydroxyacetanilide and raloxifene, for which the stable dehydrogenation products are formed.
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| 2. |
- Gao, Li, et al.
(author)
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Conformational enantiomerization and estrogen receptor alpha binding of anti-cancer drug tamoxifen and its derivatives
- 2011
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In: Journal of Chemical Information and Modeling. - : American Chemical Society (ACS). - 1549-9596 .- 1549-960X. ; 51:2, s. 306-314
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Journal article (peer-reviewed)abstract
- The anticancer drug tamoxifen (TAM) displays two chiral vinyl propeller structures, which interconvert so rapidly that the process is undetectable on the NMR time scale. In the present work, the enantiomerization processes were investigated with molecular modeling techniques. The threshold mechanisms probed at the different rings were shown to be identical, i.e., involving a synchronous three-ring flip, with a correlated rotation of the rings. In order to reveal the pharmacological profiles of the two chiral forms, we performed structural studies on the ligand binding domain of estrogen receptor alpha. (ER alpha LBD) and associated ligands. The enantiomers, with opposite torsional twist, were found to be discriminated by ER alpha. For TAM and its main metabolites, the effects of the stereoselectivity of ER alpha are overcome by the low energy cost for helical inversion between the two torsional enantiomers, estimated to be similar to 3 kcal/mol.
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| 3. |
- Licznerska, Barbara E., et al.
(author)
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In situ levels of oestrogen producing enzymes and its prognostic significance in postmenopausal breast cancer patients
- 2008
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In: Breast Cancer Research and Treatment. - Berlin : Springer. - 0167-6806 .- 1573-7217. ; 112:1, s. 15-23
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Journal article (peer-reviewed)abstract
- Background The risk of developing breast cancer is strongly correlated with the overall exposure to oestrogen and most tumours are more or less dependent on oestrogen for their growth. A great majority of breast cancers occur after menopause when the ovaries have ceased to be functional, yet breast tumours in postmenopausal women maintain high intratumoural oestrogen concentrations, primarily through enzymatic conversion of androgenic precursors. Patients with a hormone dependent tumour generally receive the anti-oestrogen tamoxifen that mediate its anti-tumour effect by competing with oestrogen for binding to the oestrogen-receptor (ER). We therefore propose that the levels of oestrogen producing enzymes may affect the prognosis in postmenopausal breast cancer patients treated with tamoxifen. Methods We measured the mRNA and protein levels of aromatase and sulfatase by real-time PCR (n = 161) and immunohistochemistry (n = 131) in postmenopausal women with breast cancer. Results A significant better recurrence-free survival was detected in patients with weak or high protein expression of stromal aromatase (P = 0.0008), as also demonstrated by a decreased relative risk (RR = 0.50, CI = 0.33–0.76, P = 0.003). When we combined patients with weak and high stromal aromatase and selected only ER-positive patients, the improved prognosis was even more evident (P = 0.0000) and was shown to be a significant prognostic factor in a multivariate Cox-model (HR = 0.15, CI = 0.06–0.39, P = 0.000). The mRNA expression of aromatase and sulfatase, as well as the protein expression of sulfatase revealed no prognostic significance. Conclusion Protein expression of stromal aromatase may serve as a significant prognostic marker in ER-positive patients.
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| 4. |
- Wegman [Palmebäck-Wegman], Pia, et al.
(author)
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Genetic alterations in the K-ras gene influence the prognosis in patients with cervical cancer treated by radiotherapy
- 2011
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In: International Journal of Gynecological Cancer. - : Lippincott Williams & Wilkins. - 1048-891X .- 1525-1438. ; 21:1, s. 86-91
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Journal article (peer-reviewed)abstract
- Introduction: A high incidence of K-Ras mutations has been identified in a variety of human cancers, especially in codon 12, 13, and 61. Nevertheless, the presence of K-Ras mutations in cervical cancer remains controversial. The aim of this study was to investigate possible mutations in exon 1 and 2 of the K-Ras gene and to assess whether K-Ras mutation status had prognostic and predictive significance and were linked to clinicopathological parameters. Methods: Genomic DNA from 107 patients with cervical cancer, treated with radio-chemotherapy, were examined for mutations in the coding exons 1 and 2, including exon/intron borders of the K-Ras gene using single-stranded conformation polymorphism and sequence analyses. Results: K-Ras mutations were detected in 11 patients (10%). Seven tumors showed a mutation in codon 59, 3 tumors in codon 38, and 1 tumor in codon 13. In 6 of the cases with a mutation in codon 59, an additional alteration located in codon 65 was found. Patients with K-Ras mutations had significantly worse recurrence-free survival (P = 0.03), and an association between K-Ras status and distant metastases was also seen (P = 0.04). Conclusions: The present data indicate that K-Ras mutations are relatively uncommon in cervical cancer but associates with poorer prognosis, especially in the subset of squamous cell carcinomas. There is a need for new markers in cervical cancer to improve individual treatment, but whether K-Ras mutation status is a potential biomarker in this situation needs further investigations in larger tumor series and in more regions of the K-Ras gene.
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| 5. |
- Bergman, Malin, 1967-, et al.
(author)
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Polymorphism in the manganese superoxide dismutase (MnSOD) gene and risk of breast cancer in young women
- 2005
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In: Journal of Cancer Research and Clinical Oncology. - : Springer Science and Business Media LLC. - 0171-5216 .- 1432-1335. ; 131:7, s. 439-444
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Journal article (peer-reviewed)abstract
- Purpose: Manganese superoxide dismutase (MnSOD) is one of the major enzymes implicated in the cellular defence against reactive oxygen species. Low expression of MnSOD has been observed in different cancer tissues and several reports have shown that overexpression of MnSOD inhibits growth in various human cancer cells. These observations suggest that MnSOD is involved in carcinogenesis. A polymorphism (Ala-9Val) in the mitochondrial targeting sequence (MTS) of the MnSOD gene has been proposed to affect protein localization and thereby influence cellular defence against superoxide radicals.Methods: In the present case-control study, including 118 early onset breast cancer patients (≤36 years) and 174 age-matched controls, the MTS polymorphism and loss of heterozygosity (LOH) in the locus of MnSOD were analysed.Results: We found that individuals with MnSODVal/Val and MnSODVal/Ala genotypes showed an increased risk of breast cancer (OR, 2.7; 95% CI, 2.2–5.5, p=0.01, OR, 3.0; 95%CI, 1.4–6.5, p=0.002). Moreover, 45% of the informative cases expressed allelic loss at the chromosomal locus of the MnSOD gene. No correlation was found between LOH and the genotype.Conclusion: The present study suggests that MnSOD may be implicated in breast carcinogenesis in young women.
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| 6. |
- Lang, Anna, et al.
(author)
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The significance of MDM2 SNP309 and p53 Arg72Pro in young women with breast cancer
- 2009
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In: ONCOLOGY REPORTS. - Athens, Greece : Spandidos Publications. - 1021-335X .- 1791-2431. ; 22:3, s. 575-579
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Journal article (peer-reviewed)abstract
- The p53 protein and its regulator MDM2 is central to tumorigenesis by directing cells to undergo cell cycle arrest and/or apoptosis in response to DNA damage or other stress signals. The genes encoding these proteins contain nucleotide variation (p53 codon 72, MDM2 SNP309) that influences cellular response. We examined the p53 codon 72 and MDM2 SNP309 to determine their implication with age of disease onset and risk of breast cancer in young women (andlt;= 36 years). No risk of breast cancer was observed for the genotypes of p53 and MDM2, however, a tendency (P=0.15) towards increased risk of early onset breast cancer was observed in carriers of two or more Pro and/or G alleles. We further calculated the influence on age at diagnosis. Cases were grouped according to the number of G and Pro alleles (0, 1, 2 or 3-4) and age at diagnosis. A significant trend towards decreased age at diagnosis with increased number of risk alleles was found (P=0.013). Our results suggest that p53 codon 72 and MDM2 SNP309 may be implicated in early onset breast cancer.
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| 7. |
- Palmebäck Wegman, Pia, et al.
(author)
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Biological significance of allele specific loss of the p53 gene in breast carcinomas
- 2009
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In: BREAST CANCER RESEARCH AND TREATMENT. - Berlin : Springer Science and Business Media LLC. - 0167-6806 .- 1573-7217. ; 118:1, s. 15-20
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Journal article (peer-reviewed)abstract
- The p53 tumor suppressor gene has a central role in the defense against cancer, including breast cancer, and contains a polymorphic variant (Arg/Pro) at codon 72 that has been shown to have different biological properties regarding apoptosis and cell cycle arrest. Earlier studies have shown allele specific loss of heterozygosity (LOH) at this particular site and we aimed to investigate its biological relevance in codon 72 heterozygous breast cancer patients (i.e., survival and age of disease onset). 199 postmenopausal cases were analyzed for LOH using MegaBACE(1000) and statistics was performed using Statistical Package for Social Sciences. LOH was found in totally 124 (62.3%) patients and the Pro allele (n = 103) was significantly more often deleted compared to the Arg allele (n = 21) (P = 0.001). Patients with LOH of the Arg allele were diagnosed at an earlier age (mean age 62.5 years) than those with loss of the Pro allele (mean age 69.2 years) (P = 0.011). LOH of the Arg allele was also associated with worse survival (P = 0.05). LOH in comparison to ROH correlated significantly with increased S-phase fraction. Tumor size, stage or number of positive lymph nodes was not related to LOH. Our results and earlier findings suggest a selective loss of the Pro allele during carcinogenesis that might confer a growth advantage for cancer cells. On the other hand, it appears to be more harmful for patients to loose the Arg allele since we found that loss of this allele was associated with earlier onset and worse prognosis.
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| 8. |
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| 9. |
- Palmebäck Wegman, Pia, 1964-
(author)
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Studies of tamoxifen resistance in breast cancer
- 2007
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Doctoral thesis (other academic/artistic)abstract
- Oestrogen is one of the most important hormonal regulators and is known to play a key role in the development and growth of breast cancer. The majority of tumours have a hormone dependent growth, and this is indicated by the presence of oestrogen receptors (ERs). About two thirds of breast cancers occur after the menopause when the ovaries have ceased to produce oestrogen and despite the low levels of circulating oestrogen’s the tumour concentrations of oestrone, oestradiol and their sulfates have been shown to be significant. Patients with hormone dependent tumours are candidates for treatment with the anti-oestrogen tamoxifen, which acts by competing with oestrogen for binding to the ER thereby, diminish the transcription of oestrogen regulated genes. The drug is mainly metabolised by cytochrome P450 enzymes in the liver and to a lesser extent locally in the breast, where upon several produced metabolites have higher affinity for the ER than the mother substance. Patients treated with tamoxifen have in general a prolonged disease-free survival. Even if most patients respond well to tamoxifen about 30-50 % either fail to respond or become resistant by incompletely understood mechanisms. Therefore, the aim of this thesis was to investigate possible mechanisms responsible for tamoxifen resistance. In paper I and II we studied genetic variants of enzymes participating in the metabolism of tamoxifen and assessed whether these variants correlated to breast cancer prognosis and/or to the benefit of tamoxifen. The results indicate an influence of CYP2D6, CYP3A5, and SULT1A1 genotypes in tamoxifen response. Further, tamoxifen has shown to compete with oestrogen for the binding to ER. In paper III we measured the expression levels of enzymes involved in the local synthesis of oestrogens in order to see if they correlated to clinical outcome. The protein expression of stromal aromatase was shown to have a prognostic significance, especially in ER-positive patients. Finally, tamoxifen and its ER-active metabolites have shown to induce both cell cycle arrest and apoptosis and one central mediator in these processes is the tumour suppressor protein p53. The proapoptotic activity of p53 is dependent on a proline rich domain containing a common Pro-to-Arg polymorphism. In paper IV we examined the value of this genetic variant as a predictive marker for anti-cancer therapy and found that patients carrying the Pro-allele might be good responders of tamoxifen therapy. The present thesis further indicates the complexity of the mechanisms underlying tamoxifen resistance. In summary, genetic variants of metabolic enzymes, genetic variants in p53, as well as expression levels of enzymes involved in local oestrogen synthesis, may have influence on breast cancer prognosis and may be useful markers in the prediction of tamoxifen response.
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| 10. |
- Wegman Palmebäck, Pia, et al.
(author)
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Genetic variants of CYP3A5, CYP2D6, SULT1A1, UGT2B15 and tamoxifen response in postmenopausal breast cancer patients
- 2007
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In: Breast Cancer Research. - : Springer Science and Business Media LLC. - 1465-5411 .- 1465-542X. ; 9:1, s. R7-
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Journal article (peer-reviewed)abstract
- IntroductionTamoxifen therapy reduces the risk of recurrence and prolongs the survival of oestrogen-receptor-positive patients with breast cancer. Even if most patients benefit from tamoxifen, many breast tumours either fail to respond or become resistant. Because tamoxifen is extensively metabolised by polymorphic enzymes, one proposed mechanism underlying the resistance is altered metabolism. In the present study we investigated the prognostic and/or predictive value of functional polymorphisms in cytochrome P450 3A5 CYP3A5 (*3), CYP2D6 (*4), sulphotransferase 1A1 (SULT1A1; *2) and UDP-glucuronosyltransferase 2B15 (UGT2B15; *2) in tamoxifen-treated patients with breast cancer.MethodsIn all, 677 tamoxifen-treated postmenopausal patients with breast cancer, of whom 238 were randomised to either 2 or 5 years of tamoxifen, were genotyped by using PCR with restriction fragment length polymorphism or PCR with denaturing high-performance liquid chromatography.ResultsThe prognostic evaluation performed in the total population revealed a significantly better disease-free survival in patients homozygous for CYP2D6*4. For CYP3A5, SULT1A1 and UGT2B15 no prognostic significance was observed. In the randomised group we found that for CYP3A5, homozygous carriers of the *3 allele tended to have an increased risk of recurrence when treated for 2 years with tamoxifen, although this was not statistically significant (hazard ratio (HR) = 2.84, 95% confidence interval (CI) = 0.68 to 11.99, P = 0.15). In the group randomised to 5 years' tamoxifen the survival pattern shifted towards a significantly improved recurrence-free survival (RFS) among CYP3A5*3-homozygous patients (HR = 0.20, 95% CI = 0.07 to 0.55, P = 0.002). No reliable differences could be seen between treatment duration and the genotypes of CYP2D6, SULT1A1 or UGT2B15. The significantly improved RFS with prolonged tamoxifen treatment in CYP3A5*3 homozygotes was also seen in a multivariate Cox model (HR = 0.13, CI = 0.02 to 0.86, P = 0.03), whereas no differences could be seen for CYP2D6, SULT1A1 and UGT2B15.ConclusionThe metabolism of tamoxifen is complex and the mechanisms responsible for the resistance are unlikely to be explained by a single polymorphism; instead it is a combination of several mechanisms. However, the present data suggest that genetic variation in CYP3A5 may predict response to tamoxifen therapy.
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