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Endoxifen

Endoxifen is an active metabolite of Tamoxifen, a widely used breast cancer drug. Treatment of breast cancer directly with Endoxifen may eliminate Tamoxifen metabolism associated variability and avoid a potential serious drug-drug interaction. Upon oral administration, tamoxifen (TAM) is extensively metabolized by cytochrome P450(CYP) enzymes into active metabolites including 4-hydroxy tamoxifen and endoxifen (4-hydroxy N-desmethyl Tamoxifen)

Endoxifen is one hundred times more potent than TAM and is generated via CYP3A4/5-mediated N-demethylation and CYP2D6-mediated hydroxylation (Figure 1). Due to genetic polymorphism of CYP2D6, there are large variations among patients in both the therapeutic efficacy and side effects. Furthermore, CYP2D6 interacts with specific selective serotonin reuptake inhibitors (SSRIs), frequently used to prevent the hot flushes experienced by up to 45% of patients taking TAM. As a consequence, significant numbers of women might not receive optimal benefit from TAM treatment. Our pre-clinical studies have validated the concept of using Endoxifen for the treatment of breast cancer (Ahmad et al. 2010). Treatment of breast cancer directly with Endoxifen may eliminate TAM metabolism associated variability and avoid a potential serious drug-drug interaction.

WhyEndoxifen Treatment may have better therapeutic outcome

  • Endoxifen may overcome the unpredictable therapeutic outcome due to pharmacogenomic variation of Tamoxifen and Aromatase inhibitors
  • Endoxifen would help women taking anti-depressants who have problems metabolizing Tamoxifen
  • Endoxifen acts directly at the target
  • Tamoxifen have been shown to be more effective than Aromatase inhibitors in patients with wild type CYP2D6
  • Showed enhanced therapeutic efficacy against established human tumor model in mice
  • Only potential drug for ER positive premenopausal women with CYP2D6 deficiency