3rd meeting of young researchers at UP 1 - IJUP - Universidade do ...

Two new aromatase inhibitors: Biological evaluation and effects in
an estrogen-dependent breast cancer cell line
A.M. Azevedo Dias 1 , G. Correia da Silva 1,2 , C. Amaral 1,2 , M. Borges 1,2 , M. Cepa 1 , C.
Varela 3 , E. Tavares da Silva 3 , F. M. Roleira 3 and N. Teixeira 1,2
1 Laboratory of Biochemistry, Faculty of Pharmacy, University of Porto, Portugal. 2 Institute for
Molecular and Cell Biology (IBMC), University of Porto, Portugal. 3 Center of Pharmaceutical Studies,
Pharmaceutical Chemistry Laboratory, Faculty of Pharmacy, University of Coimbra, Portugal.
Estrogens are required for normal growth and development of various tissues; however, they
are also responsible for promoting tumors, like breast tumors. As the enzyme aromatase
catalyzes the last step in estrogens biosynthesis, the discovery of aromatase inhibitors (AIs)
have shown to be an effective alternative to the classical tamoxifen for the treatment of
postmenopausal patients with estrogen receptor-positive breast cancer [1].
In a previous work, we have designed and prepared new steroids with several chemical features
that proved to be potent AIs in different breast cancer cell lines, reducing cell proliferation and
inducing cell death [2,3]. In this work we present the results for the biological evaluation of
two new steroidal AIs, 18 and 20, resulting from modifications in the A-ring of the natural
substrate of aromatase, androstenedione. Inhibition of aromatase activity was evaluated in
human placental microssomes by a radiometric assay. Both compounds revealed to be effective
inhibitors of aromatase in a dose dependent manner being compound 20 the most potent AI.
This aromatase inhibition was also demonstrated in MCF-7aro cells, an estrogen-dependent
human breast cancer cell line stably transfected with the aromatase gene. MCF7-aro cells were
also used to study the effect of these compounds on proliferation and cell viability, using
thymidine incorporation assays and 7AAD-staining flow cytometry, respectively. Nuclear and
cell morphology was studied by Hoechst and Giemsa staining. The results showed that the new
AIs inhibit proliferation of MCF-7aro cells in a time and dose-dependent manner. Cell viability
decrease was accompanied by morphologic alterations such as membrane blebbing and
chromatin condensation. Although compound 20 revealed to be the strongest inhibitor of
aromatase activity, compound 18 was more effective in inducing cell death. These in vitro
studies showed that the two steroidal AIs are potent inhibitors of aromatase activity and of
MCF-7aro cell proliferation. These results are important for the elucidation of the cellular
effects of steroidal AIs in breast cancer.
[1] Blackwell K.L., (2008), Are all the aromatase inhibitors alike? Breast Cancer Res.
Treat.Med.Chem., 112 (1), 35-43.
[2] Cepa M., Correia-da-Silva G., Tavares da Silva E.J., Roleira F.M. HongY., Chen S., and Teixeira,
N. A. (2008), Molecular mechanisms of aromatase inhibition by new A, D-ring modified steroids, Biol.
Chem.,389 (9), 1183-91.
[3] Cepa M., Correia-da-Silva G., da Silva E.J., Roleira F.M., Borges M., and Teixeira N. A. (2008),
New steroidal aromatase inhibitors:supression of estrogen-dependent breast cancer cell proliferation
and induction of cell death. BMC Cell Biology,24 (9), 41-45.
3 rd meeting of young researchers at UP 59