Endocrine Abstracts

Introduction: The efficacy and exceptionally good tolerance of estrogen blockade in the treatment of breast cancer is well recognized. Acolbifene (ACOL) is a novel and unique completely free of estrogen-like activity in both the mammary gland and uterus. In theory, this new antiestrogen represents a unique opportunity for a highly potent and specific blockade of estrogen action in the mammary gland and uterus while exerting estrogen-like beneficial effects in other tissues (selective estrogen receptor modulator or SERM activity).

Description of methods/design: In order to better understand the specificity of action of acolbifene, we have used Affymetrix GeneChips containing 45,000 probe sets to analyze 34,000 genes to determine the specificity of this compound compared to the pure antiestrogen fulvestrant, as well as the mixed antagonists/agonists tamoxifen and raloxifene, in their ability to block the effect of estradiol (E2) and to induce effects of their own on gene expression in the mouse mammary gland. The genes modulated by E2 were those identified in two separate experiments and validated by quantitative real-time PCR (Q_RT-PCR).

Results: Three hours after the single subcutaneous injection of E2 (0.05 μg), the simultaneous administration of acolbifene, fulvestrant, tamoxifen and raloxifene blocked by 98%, 62%, 43% and 92% the number of E2 upregulated genes, respectively. On the other hand, 70%, 10%, 25% and 55% of the genes down-regulated by E2 were blocked by the same compounds. Acolbifene was also the compound which, when used alone, modulated the smallest number of genes also influenced by E2, namely 4%.

Conclusion: The present data offer a possible explanation for the potent tumoricidal action of acolbifene in human breast cancer xenografts where 61% of tumors disappeared, thus bringing a new paradigm in the hormonal therapy of breast cancer.

Declaration of interest: The authors declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Funding: This work was supported, however funding details unavailable.