Functional characterization of 22 novel CYP2D6 variants for the metabolism of Tamoxifen

Specificity and efficiency of tamoxifen-mediated Cre induction is equivalent regardless of age

Temporally controlling Cre recombination through tamoxifen (Tam) induction has many advantages for biomedical research. Most studies report early post-natal/juvenile (<2 m.o.) Tam induction, but age-related neurodegeneration and aging studies can require Cre induction in older mice (>12 m.o.). While anecdotally reported as problematic, there are no published comparisons of Tam-mediated Cre induction at early and late ages. Here, microglial-specific Cx3cr1creERT2 mice were crossed to a floxed NuTRAP reporter to compare Cre induction at early (3-6 m.o.) and late (20 m.o.) ages. Specificity and efficiency of microglial labeling at 21-22 m.o. were identical in mice induced with Tam at early and late ages. Age-related microglial translatomic changes were also similar regardless of Tam induction age. Each Cre and flox mouse line should be independently validated, however, these findings demonstrate that Tam-mediated Cre induction can be performed even into older mouse ages and should be generalizable to other inducible Cre models.

Consistent specificity and efficiency of tamoxifen-mediated cre induction across ages

Temporally controlling cre recombination through tamoxifen (Tam) induction has many advantages for biomedical research. Most studies report Tam induction at early post-natal/juvenile (<2 m.o.) mouse ages, but age-related neurodegeneration and aging studies can require cre induction in older mice (>12 m.o.). While anecdotally reported as problematic, there are no published comparisons of Tam mediated cre induction at early and late ages. Here, microglial-specific Cx3cr1 creERT 2 mice were crossed to a floxed NuTRAP reporter to compare cre induction at early (3-6 m.o.) and late (20 m.o.) ages. Specificity and efficiency of microglial labeling at 21-22 m.o. were identical in mice induced with Tam at 3-6 m.o. or 20 m.o. of age. Age-related microglial translatomic changes were also similar regardless of Tam induction age. Each cre and flox mouse line should be validated independently, however, these findings demonstrate that Tam-mediated cre induction can be performed even into older mouse ages.

A functional variant near XCL1 gene improves breast cancer survival via promoting cancer immunity

Most genome-wide association studies (GWASs) identify genetic variants for breast cancer occurrence. In contrast, few are for recurrence and mortality. We conducted a GWAS on breast cancer survival after diagnosis in estrogen receptor-positive patients, including 953 Taiwanese patients with 159 events. Through Cox proportional hazard models estimation, we identified 24 risk SNPs with p < 1 × 10^-5 . Based on imputation and integrated analysis, one SNP, rs1024176 (located in 1q24.2, p = 2.43 × 10^-5 ) was found to be a functional variant associated with breast cancer survival and XCL1 gene expression. A series of experimental approaches, including cell-based analyses and CRISPR/Cas9 genome-editing system, were then used and identified the transcription factor MYBL2 was able to discriminately bind to the A allele of rs1024176, the protective variant for breast cancer survival, which promoted XCL1 expression, but not to the G allele of rs1024176. The chemokine XCL1 attracts type 1 dendritic cells (DC1s) to the tumor microenvironment. In breast cancer tissues, we applied a two-step Mendelian randomization analysis, using expression quantitative trait loci as instrumental variables, to confirm higher XCL1 expression was correlated with higher DC1 signatures and favorable disease progression, through the causal effect of rs1024176-A allele. Our study supports the genetic effect on preventing breast cancer survival through XCL1-induced DC1 recruitment in tumor microenvironment.

Tamoxifen and CYP2D6: A Controversy in Pharmacogenetics

Tamoxifen reduces the rate of breast cancer recurrence by about one-half. It is converted to more active metabolites by enzymes encoded by polymorphic genes, including cytochrome P450 2D6 (CYP2D6) and transported by ATP-binding cassette transporters. Genetic polymorphisms that confer reduced CYP2D6 activity or concurrent use of CYP2D6-inhibiting drugs may reduce the clinical efficacy of tamoxifen. The issue of the clinical utility of CYP2D6 genotype testing is subject to considerable and ongoing academic and clinical controversy. In this chapter, we outline tamoxifen's clinical pharmacology and give an overview of the research to date on the association between CYP2D6 inhibition and tamoxifen effectiveness. Based on the evidence to date, the impact of drug-induced and/or gene-induced inhibition of CYP2D6 activity is likely to be null or small, or at most moderate in subjects carrying two reduced function alleles. Future research should examine the effect of polymorphisms in genes encoding enzymes in tamoxifen's complete metabolic pathway, should comprehensively evaluate other biomarkers that affect tamoxifen effectiveness, such as the transport enzymes, and focus on subgroups of patients, such as premenopausal breast cancer patients, for whom tamoxifen is the only guideline approved endocrine therapy.

The effect of rs5758550 on CYP2D6*2 phenotype and formation of endoxifen in breast cancer patients using tamoxifen

Aim: CYP2D6*2 is considered fully active, but it has been suggested that it only happens in the presence of rs5758550. This study aims to elucidate the impact of this enhancer. Materials & methods: DNA and blood samples from women enrolled in the CYPTAM study (NTR1509) were analyzed. Fourteen CYP2D6*2 carriers without the enhancer were reclassified. The relationship of CYP2D6 phenotypes and drug levels was studied. Results: After correction for the absence of the enhancer, the correlation between CYP2D6 phenotypes and endoxifen did not improve (R2: 0.290 vs 0.279). No difference was observed in mean concentrations between CYP2D6*2 individuals with and without the enhancer. Conclusion: The rs5758550 enhancer does not lead to improved prediction of endoxifen levels in breast cancer patients.