CYP2D6 Genotyping for Personalized Therapy of Tamoxifen in Indonesian Women with ER+ Breast Cancer

PurposeTamoxifen, common adjuvant therapy prescribed in estrogen receptor positive (ER+) breast cancer, is metabolized by CYP2D6 enzyme into endoxifen. The phenotypes of CYP2D6, a highly polymorphic gene, vary from ultrarapid (UM), normal (NM), intermediate (IM), and poor metabolizers (PM). Studies showed that reduced CYP2D6 activity in IMs and PMs resulted in lower endoxifen level, thereby reducing therapy efficacy. This study aims to observe the distribution of CYP2D6 profiles and their corresponding endoxifen levels in Indonesian ER+ breast cancer patients.Methods151 patients who have received tamoxifen therapy for ≥8 weeks were recruited prospectively. DNA and blood samples were collected with buccal swab and finger-prick methods, respectively. Genotyping was performed using the qPCR method while metabolites measurement was performed using HPLC-tandem MS. Patients with IM/PM CYP2D6 profile were advised to increase their tamoxifen dose or switch to aromatase inhibitor, while patients with UM or NM CYP2D6 profile remained on 20 mg daily dose. Tamoxifen metabolites levels of those given 40 mg/day of tamoxifen were measured eight weeks post dose adjustment.ResultsWe found that 40.7% of patients recruited were IM. CYP2D6*10 was the most abundant allele (28.8%) and *10/*36 was the most frequently observed diplotype (23.6%). Endoxifen levels between the NM-PM, NM-IM, and IM-PM were statistically significant, and dose increase of tamoxifen successfully increased endoxifen levels in IMs to a similar level with NMs at baseline.ConclusionIndonesian women have a relatively high proportion of IMs. The correlation between CYP2D6 genotype and phenotype was shown in the significant difference in endoxifen levels among NMs, IMs, and PMs. Dose adjustment of tamoxifen to 40 mg daily positively increased endoxifen levels in IMs to a similar level as NMs. Implementing pharmacogenomics testing of CYP2D6 on ER+ breast cancer women taking tamoxifen can potentially increase the likelihood of achieving better treatment efficacy.Trial RegistrationThe trial was retrospectively registered at ClinicalTrials.gov on 18 March 2020 with identifier NCT04312347 (accessible at: https://clinicaltrials.gov/ct2/show/NCT04312347).

Repurposing of the Tamoxifen Metabolites to Treat Methicillin-Resistant Staphylococcus epidermidis and Vancomycin-Resistant Enterococcus faecalis Infections

The development of new antimicrobial therapeutic strategies requires immediate attention to avoid the tens of millions of deaths predicted to occur by 2050 as a result of MDR bacterial infections. In this study, we assessed the antibacterial activity of three major tamoxifen metabolites, N -desmethyltamoxifen (DTAM), 4-hydroxytamoxifen (HTAM), and endoxifen (ENDX), against methicillin-resistant Staphylococcus epidermidis (MRSE) and Enterococcus spp. ( E. faecalis and E. faecium ).

Repurposing of the tamoxifen metabolites to treat methicillin-resistant Staphylococcus epidermidis and vancomycin-resistant Enterococcus faecalis infections

Repurposing drugs provides a new approach to the fight against multidrug-resistant (MDR) bacteria. We have reported that three major tamoxifen metabolites, N-desmethyltamoxifen (DTAM), 4-hydroxytamoxifen (HTAM) and endoxifen (ENDX), presented bactericidal activity against Acinetobacter baumannii and Escherichia coli. Here, we aimed to analyse the activity of a mixture of the three tamoxifen metabolites against methicillin-resistant Staphylococcus epidermidis (MRSE) and Enterococcus spp. MRSE (n=17) and Enterococcus spp. (E. faecalis n=8, and E. faecium n=10) strains were used. MIC of the mixture of DTAM, HTAM and ENDX, and vancomycin were determined by microdilution assay. The bactericidal activity of the three metabolites together and vancomycin against MRSE (SE385 and SE742) and vancomycin-resistant E. faecalis (EVR1 and EVR2) strains was determined by time-kill curve assays. Finally, changes in membrane permeability of SE742 and EVR1 strains were analyzed using fluorescence assays. MIC50 and MIC90 of tamoxifen metabolites were 1 mg/L for MRSE strains and 2 mg/L for Enterococcus spp. strains. In the time-killing assays, tamoxifen metabolites mixture showed bactericidal activity at 2x and 4xMIC for MRSE (SE385 and SE742) and E. faecalis (EVR1 and EVR2) strains. This antimicrobial activity of tamoxifen metabolites paralleled an increased membrane permeability of SE385 and EVR2 strains. Altogether, these results showed that tamoxifen metabolites presented antibacterial activity against MRSE and vancomycin-resistant E. faecalis, suggesting that tamoxifen metabolites might increase the arsenal of drugs treatment against these bacterial pathogens.

Association of CYP2D6 genotype and tamoxifen metabolites with breast cancer recurrence in a low-dose trial

Low-dose tamoxifen halves recurrence in non-invasive breast cancer without significant adverse events. Some adjuvant trials with tamoxifen 20 mg/day had shown an association between low endoxifen levels (9–16 nM) and recurrence, but no association with CYP2D6 was shown in the NSABP P1 and P2 prevention trials. We studied the association of CYP2D6 genotype and tamoxifen metabolites with tumor biomarkers and recurrence in a randomized phase III trial of low-dose tamoxifen. Median (IQR) endoxifen levels at year 1 were 8.4 (5.3–11.4) in patients who recurred vs 7.5 (5.1–10.2) in those who did not recur (p = 0.60). Tamoxifen and metabolites significantly decreased C-reactive protein (CRP, p < 0.05), and a CRP increase after 3 years was associated with higher risk of recurrence (HR = 4.37, 95% CI, 1.14–16.73, P = 0.03). In conclusion, endoxifen is below 9 nM in most subjects treated with 5 mg/day despite strong efficacy and there is no association with recurrence, suggesting that the reason for tamoxifen failure is not poor drug metabolism. Trial registration: ClinicalTrials.gov, Identifier: NCT01357772.

Repurposing of the Tamoxifen Metabolites to Combat Infections by Multidrug-Resistant Gram-Negative Bacilli

The development of new strategic antimicrobial therapeutic approaches, such as drug repurposing, has become an urgent need. Previously, we reported that tamoxifen presents therapeutic efficacy against multidrug-resistant (MDR) Acinetobacter baumannii, Pseudomonas aeruginosa, and Escherichia coli in experimental infection models by modulating innate immune system cell traffic. The main objective of this study was to analyze the activity of N-desmethyltamoxifen, 4-hydroxytamoxifen, and endoxifen, three major metabolites of tamoxifen, against these pathogens. We showed that immunosuppressed mice infected with A. baumannii, P. aeruginosa, or E. coli in peritoneal sepsis models and treated with tamoxifen at 80 mg/kg/d for three days still reduced the bacterial load in tissues and blood. Moreover, it increased mice survival to 66.7% (for A. baumannii and E. coli) and 16.7% (for P. aeruginosa) when compared with immunocompetent mice. Further, susceptibility and time-kill assays showed that N-desmethyltamoxifen, 4-hydroxytamoxifen, and endoxifen exhibited minimum inhibitory concentration of the 90% of the isolates (MIC90) values of 16 mg/L, and were bactericidal against clinical isolates of A. baumannii and E. coli. This antimicrobial activity of tamoxifen metabolites paralleled an increased membrane permeability of A. baumannii and E. coli without affecting their outer membrane proteins profiles. Together, these data showed that tamoxifen metabolites presented antibacterial activity against MDR A. baumannii and E. coli, and may be a potential alternative for the treatment of infections caused by these two pathogens.

New opportunities of pharmacogenetics approach to personalized tamoxifen therapy (updated systematic review)

Tamoxifen is the selective modulator of estrogen receptors. Nowadays, it is widely used in the treatment of ER(+) breast cancer and substantially decreases the risks of recurrence and disease progression. However, high interindividual variability in response is observed, calling for a personalized approach to tamoxifen treatment. Tamoxifen is metabolized by cytochrome P450, resulting in the formation of active metabolites, including 4-hydroxy-tamoxifen and endoxifen. The effectiveness and success of treatment depends largely on concentrations of the active tamoxifen metabolites in blood plasma. Polymorphisms in the genes encoding these enzymes are proposed to influence on pharmacokinetics and pharmacodynamics of tamoxifen. Therefore, pharmacogenetic approach may form the basis of personalized treatment of breast cancer. In the updated systematic review, we analyze all current data about the potential use of genotyping of CYP2D6, CYP2С19, CYP3A4/5, CYP2B6 to predict an individual response on tamoxifen treatment.

Perspectives of pharmacogenetics approach to personalized tamoxifen therapy

Tamoxifen is the selective modulator of estrogen receptors. Nowadays, it is widely used in the treatment of ER(+) breast cancer and substantially decreases the risks of recurrence and disease progression. However, high interindividual variability in response is observed, calling for a personalized approach to tamoxifen treatment. Tamoxifen is metabolized by cytochrome P450, resulting in the formation of active metabolites, including 4-hydroxy-tamoxifen and endoxifen. The effectiveness and success of treatment depends largely on concentrations of the active tamoxifen metabolites in blood plasma. Polymorphisms in the genes encoding these enzymes are proposed to influence on pharmacokinetics and pharmacodynamics of tamoxifen. Therefore, pharmacogenetic approach may form the basis of personalized treatment of breast cancer. In this systematic review, we analyze all current data about the potential use of genotyping of CYP2D6, CYP3A4/5, CYP2B6 to predict an individual response on tamoxifen treatment.