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Central to intrinsic apoptosis signaling is the release of cytochrome c from mitochondria, which depends on the pro-apoptotic effector proteins Bax, Bak or Bok. These pore-forming effector proteins share four Bcl-2 homology (BH) domains, a functionally essential and conserved sequence of hydrophobic amino acids in their BH3-domain and a C-terminal transmembrane-domain whose specific function remains rather unknown. To elucidate the molecular basis of Bok-mediated apoptosis we analyzed apoptosis induction by transmembrane-domain deficient BokΔTM compared to the respective Bax and Bak proteins and proteins in which the first leucine in the BH3-stretch was mutated to glutamic acid. We show that deletion of the C-terminal transmembrane-domain reduces the pro-apoptotic function of each protein. Mutation of the first leucine in the BH3-domain (L78E) blocks activity of Bak, while mutation of the homologue residues in Bax or Bok (L63E and L70E respectively) does not affect apoptosis induction. Unexpectedly, combined mutation of the BH3-domain and deletion of the transmembrane-domain enhances the pro-apoptotic activity of Bok(L70E)ΔTM by abolishing the interaction with anti-apoptotic proteins, especially the primary Bok-inhibitory protein Mcl-1. These results therefore suggest a specific contribution of the transmembrane-domain to the pro-apoptotic function and interaction of Bok.

Tamoxifen, a standard therapy for breast cancer, is metabolized to compounds with anti-estrogenic as well as estrogen-like action at the estrogen receptor. Little is known about the formation of estrogen-like metabolites and their biological impact. Thus, we characterized the estrogen-like metabolites tamoxifen bisphenol and metabolite E for their metabolic pathway and their influence on cytochrome P450 activity and ADME gene expression. The formation of tamoxifen bisphenol and metabolite E was studied in human liver microsomes and Supersomes™. Cellular metabolism and impact on CYP enzymes was analyzed in upcyte® hepatocytes. The influence of 5 µM of tamoxifen, anti-estrogenic and estrogen-like metabolites on CYP activity was measured by HPLC MS/MS and on ADME gene expression using RT-PCR analyses. Metabolite E was formed from tamoxifen by CYP2C19, 3A and 1A2 and from desmethyltamoxifen by CYP2D6, 1A2 and 3A. Tamoxifen bisphenol was mainly formed from (E)- and (Z)-metabolite E by CYP2B6 and CYP2C19, respectively. Regarding phase II metabolism, UGT2B7, 1A8 and 1A3 showed highest activity in glucuronidation of tamoxifen bisphenol and metabolite E. Anti-estrogenic metabolites (Z)-4-hydroxytamoxifen, (Z)-endoxifen and (Z)-norendoxifen inhibited the activity of CYP2C enzymes while tamoxifen bisphenol consistently induced CYPs similar to rifampicin and phenobarbital. On the transcript level, highest induction up to 5.6-fold was observed for CYP3A4 by tamoxifen, (Z)-4-hydroxytamoxifen, tamoxifen bisphenol and (E)-metabolite E. Estrogen-like tamoxifen metabolites are formed in CYP-dependent reactions and are further metabolized by glucuronidation. The induction of CYP activity by tamoxifen bisphenol and the inhibition of CYP2C enzymes by anti-estrogenic metabolites may lead to drug–drug-interactions. Electronic supplementary material The online version of this article (10.1007/s00204-017-2147-y) contains supplementary material, which is available to authorized users.

Tamoxifen is a mainstay in the treatment of estrogen receptor-positive breast cancer and is metabolized to more than 30 different compounds. Little is known about in vivo concentrations of estrogenic metabolites E-metabolite E, Z-metabolite E, and bisphenol and their relevance for tamoxifen efficacy. Therefore, we developed a highly sensitive HPLC-ESI-MS/MS quantification method for tamoxifen metabolites bisphenol, E-metabolite E, and Z-metabolite E as well as for the sex steroid hormones estradiol, estrone, testosterone, androstenedione, and progesterone. Plasma samples were subjected to protein precipitation followed by solid phase extraction. Upon derivatization with 3-[(N-succinimide-1-yl)oxycarbonyl]-1-methylpyridinium iodide, all analytes were separated on a sub-2-μm column with a gradient of acetonitrile in water with 0.1 % of formic acid. Analytes were detected on a triple-quadrupole mass spectrometer with positive electrospray ionization in the multiple reaction monitoring mode. Our method demonstrated high sensitivity, accuracy, and precision. The lower limits of quantification were 12, 8, and 25 pM for bisphenol, E-metabolite E, and Z-metabolite E, respectively, and 4 pM for estradiol and estrogen, 50 pM for testosterone and androstenedione, and 25 pM for progesterone. The method was applied to plasma samples of postmenopausal patients taken at baseline and under tamoxifen therapy. Graphical Abstract Sample preparation and derivatization for highly sensitive quantification of estrogenic tamoxifen metabolites and steroid hormones by HPLC-MS/MS.

The Hedgehog signaling pathway is known to be involved in embryogenesis, tissue remodeling, and carcinogenesis. Because of its involvement in carcinogenesis, it seems an interesting target for cancer therapy. Indeed, Sonidegib, an approved inhibitor of the Hedgehog receptor Smoothened (Smo), is highly active against diverse carcinomas, but its use is also reported to be associated with several systemic side effects. Our former work in adult mice demonstrated hepatic Hedgehog signaling to play a key role in the insulin-like growth factor axis and lipid metabolism. The current work using mice with an embryonic and hepatocyte-specific Smo deletion describes an adverse impact of the hepatic Hedgehog pathway on female fertility. In female SAC-KO mice, we detected androgenization characterized by a 3.3-fold increase in testosterone at 12 weeks of age based on an impressive induction of steroidogenic gene expression in hepatocytes, but not in the classic steroidogenic organs (ovary and adrenal gland). Along with the elevated level of testosterone, the female SAC-KO mice showed infertility characterized by juvenile reproductive organs and acyclicity. The endocrine and reproductive alterations resembled polycystic ovarian syndrome and could be confirmed in a second mouse model with conditional deletion of Smo at 8 weeks of age after an extended period of 8 months. We conclude that the down-regulation of hepatic Hedgehog signaling leads to an impaired hormonal balance by the induction of steroidogenesis in the liver. These effects of Hedgehog signaling inhibition should be considered when using Hedgehog inhibitors as anti-cancer drugs.

The pro-apoptotic multidomain Bcl-2 proteins Bax and Bak (also known as BAK1) are considered the gatekeepers of the intrinsic pathway of apoptosis by triggering the mitochondrial release of cytochrome c The role of the third Bax- and Bak-homologous multidomain protein Bok, however, is still unresolved. As cells doubly deficient for Bax and Bak are largely resistant to various apoptotic stimuli, it has been proposed that Bok is either dispensable for apoptosis or that its role is dependent on Bax and Bak. Here, we demonstrate, in several cell systems, that Bok efficiently induces cytochrome c release and apoptosis even in the complete absence of both Bak and Bax. Moreover, modulation of endogenous Bok levels affects the apoptosis response. By RNA interference and targeted deletion of the Bok gene, we demonstrate that Bok can significantly influence the apoptotic response to chemotherapeutic drugs in ovarian carcinoma cells. Hence, our results not only establish Bok as a Bak- and Bax-independent apoptosis inducer, but also suggest a potential impact of Bok expression in ovarian cancer therapy.

Enzymatic conversion of most xenobiotic compounds is accomplished by hepatocytes in the liver, which are also an important target for the manifestation of the toxic effects of foreign compounds. Most cell lines derived from hepatocytes lack important toxifying or detoxifying enzymes or are defective in signaling pathways that regulate expression and activity of these enzymes. On the other hand, the use of primary human hepatocytes is complicated by scarce availability of cells and high interdonor variability. Thus, analyses of drug metabolism and hepatotoxicity in vitro are a difficult task. The cell line HC-AFW1 was isolated from a pediatric hepatocellular carcinoma and so far has been used for tumorigenicity and chemotherapy resistance studies. Here, a comprehensive characterization of xenobiotic metabolism in HC-AFW1 cells is presented along with studies on the functionality of the most important transcriptional regulators of drug-metabolizing enzymes. Results from HC-AFW1 cells were compared with commercially available HepaRG cells and cultured primary human hepatocytes. Data show that the nuclear receptors and xenosensors AHR (aryl hydrocarbon receptor), CAR (constitutive androstane receptor), PXR (pregnane-X-receptor), NRF2 [nuclear factor (erythroid-derived 2)-like 2], and PPARα (peroxisome proliferator-activated receptor α) are functional in HC-AFW1 cells, comparable to HepaRG and primary cells. HC-AFW1 cells possess considerable activities of different cytochrome P450 enzymes, which, however, are lower than corresponding enzyme activities in HepaRG cells or primary hepatocytes. In summary, HC-AFW1 are a new promising tool for studying the mechanisms of the regulation of drug metabolism in human liver cells in vitro.

Tamoxifen (Tam), a standard therapy for estrogen receptor (ER)-positive breast cancer, is excessively metabolized mainly by enzymes of the CYP450 family to anti-estrogenic and estrogenic compounds. Whereas in breast cancer cells the anti-estrogenic metabolites endoxifen and 4-hydroxy-Tam inhibit the ER, Tam bisphenol (Bis) and both isomers (E)- and (Z)- of metabolite E (Met E) show full estrogenic properties, with (E)-Met E being the most potent ER agonist. Contrary to known clinical effects of ER antagonists, the influence of Tam Bis, (E)-, and (Z)-Met E on treatment outcome is not thoroughly explored. Therefore we analyzed whether interindividual differences in plasma levels of estrogenic Tam metabolites interact with Tam therapy in vivo. Plasma concentrations of estrogenic metabolites Bis, (E)-, and (Z)-Met E and their metabolic ratios (MR) to Tam were quantified in 306 premenopausal breast cancer patients mainly of European origin who were treated with 20 mg/day of Tam (Eccles D, et al. BMC Cancer 2007; 7: 160) using recently published LC-MS/MS methods (Johänning et al. Anal Bioanal Chem 2015; Mürdter et al. Clin Pharmacol Ther 2011). The endpoints recurrence-free interval (RFI) and event-free survival (EFS) were analyzed in hormone-receptor positive patients (N = 296) by Kaplan-Meyer and multivariate Cox regression adjusted for age, nodal status, tumor size, grade and plasma concentrations of endoxifen (as MR of desmethyl-Tam to endoxifen). Plasma concentrations were as follows: Bis 13-832 pM (median 187 pM), (E)-Met E 15-1029 pM (median 213 pM), (Z)-Met E 128-2484 pM (median 889 pM), and Tam 47-1061 nM (median 360 nM). Patients with higher (E)-Met E to Tam ratios showed a higher risk of breast cancer recurrence when classified into quartiles: compared to patients of the lower quartile, patients had shorter RFI when they grouped to the interquartile (P = 0.037) and the upper quartile (P = 0.005). There was a trend of higher recurrence risk for patients belonging to the upper quartile compared to the interquartile (P = 0.063). These findings were confirmed in multivariate Cox analyses: patients belonging to the upper quartile had a significantly increased hazard ratio (HR) of 2.77 (95% confidence interval (CI) 1.34-5.71; P = 0.006) and patients belonging to the interquartile showed a trend for increased HR of 1.75 (CI = 0.88-3.46; P = 0.1). For EFS, a linearly increased HR was confirmed for patients with higher (E)-Met E to Tam ratios (HR = 1.44, CI = 1.06-1.97; P = 0.021). Bis, (Z)-Met E and their MRs to Tam showed no significantly altered risk of cancer recurrence or death. These findings suggest that higher formation rates of the most potent estrogenic Tam metabolite (E)-Met E influence Tam outcome in breast cancer patients and may be linked to therapeutic failure. Citation Format: Janina Johänning, Diana M. Eccles, Bryony Eccles, Michel Eichelbaum, Matthias Schwab, Hiltrud Brauch, Thomas Mürdter, Werner Schroth. A high ratio of tamoxifen metabolite E to tamoxifen is associated with an increased risk of breast cancer recurrences in premenopausal women. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2029.