Dear Guillermo:

The standard aromatase expressing model suitable for studying acquired resistance is derived from MCF-7aro (which are estrogen receptor–positive MCF-7 cells stably transfected with the aromatase gene, developed at the Beckman Research Institute of the City of Hope (Duarte, CA) [1-7]. From the parent MCF-7aro cells, cell lines resistant to letrozole (T+LET R), anastrozole (T+ANA R), exemestane (T+EXE R) and tamoxifen (T+TAM R) were generated, and the three AI-resistant cell lines T+LET R, T+ANA R, and T+EXE R can be used for AI-specific resistance (without tamoxifen), or T+TAM R can be included as a control or contrastive cell if desired.

Collectively therefore the T+LET R, T+ANA R, and T+EXE R breast cancer cell lines constitute the richest and most sophisticated cell culture model system for AI-resistance.

You can contact Shiuan Chen in the Department of Surgical Research at Beckman Research Institute of the City of Hope, at:

[email protected]

for additional information

References

1. Masri S, Phung S, Wang X, Chen S. Molecular characterization of aromatase inhibitor-resistant, tamoxifen-resistant and LTEDaro cell lines. J Steroid Biochem Mol Biol 2010 Feb 28; 118(4-5):277-82.

2. Masri S, Phung S, Wang X, Wu X, Yuan YC, Wagman L, Chen S. Genome-wide analysis of aromatase inhibitor-resistant, tamoxifen-resistant, and long-term estrogen-deprived cells reveals a role for estrogen receptor. Cancer Res. 2008;68 (12):4910–4918.

3. Chen S, Masri S, Wang X, Phung S, Yuan YC, Wu X. What do we know about the mechanisms of aromatase inhibitor resistance? J Steroid Biochem Mol Biol. 2006;102(1–5):232–240.

4. Chen S, Masri S, Hong Y, et al. New experimental models for aromatase inhibitor resistance. J Steroid Biochem Mol Biol 2007 Aug-Sep; 106(1-5):8-15

5. Sun XZ, Zhou D, Chen S. Autocrine and paracrine actions of breast tumor aromatase. A three-dimensional cell culture study involving aromatase transfected MCF-7 and T-47D cells. J Steroid Biochem Mol Biol 1997; 63: 29–36.

6. Masri S, Phung S, Wang X, et al. Genome-wide analysis of aromatase inhibitor-resistant, tamoxifen-resistant, and long-term estrogen-deprived cells reveals a role for estrogen receptor. Cancer Res 2008 Jun 15; 68(12):4910-8.

7. Itoh T, Karlsberg K, Kijima I, et al. Letrozole-, anastrozole-, and tamoxifen-responsive genes in MCF-7aro cells: a microarray approach. Mol Cancer Res 2005; 3(4):203-18.

Constantine Kaniklidis

Director of Medical Research,

No Surrender Breast Cancer Foundation (NSBCF)

European Association for Cancer Research (EACR)

Why the transfection with aro? Is it common for BC cells to make their own estrogen? I would assume that simple long term estrogen deprivation should be a more conservative approach. Is the MCF-7aro model the gold standard?

AI-sensitive (Aro) cells are invariably generated by stably transfecting MCF-7 cells with the aromatase gene, CYP19. As to standards,, I am unaware of any other cell culture model system for AI-resistance that has any significant traction in this field, so it remains the de facto standard until a rival with comparable currency and molecular and genomic validation is developed, and I see no such activity at present.

So you would recommend the MCF-7aro model over this alternative one?

Breast Cancer Res Treat. 2011 Jul;128(1):109-17. doi: 10.1007/s10549-010-1072-z. Epub 2010 Aug 4

Correct, I would, and by a large margin of preference: the cited Berstein study, which I reviewed, uses the AI-generic MCF7-LTED model, that is, long-term estradiol-deprived (LTED) MCF-7 cells, while the refined parent MCF7-aro model recapitulates not only general aromatase inhibitory activity, but also AI-specific activity via the generated T+LET R, T+ANA R, and T+EXE R agent-particular resistance cell lines.

Furthermore given that the aggregated data to date suggests that there is important agent-specificity between the AI inhibitors, namely that all AIs are not created equal, hence that exemestane, letrozole and anastrozole inhibit aromatase through different mechanisms - take for example that the irreversible steroidal AI exemestane can destabilize the aromatase protein and induce its degradation by the proteosome after its irreversible inactivation, which has not been observed in letrozole and anastrozole [1] - we can capture the potential for different AIs to exhibit unique resistance mechanisms, namely the concept of differential resistance pathways, a potential absent from the generic MCF7-LTED model. Similarly, both exemestane and 17-hydroexemestane (its principal metabolite) exhibit androgenic effects, allowing for high-affinity binding to the androgen receptor, absent from the other AIs, among still other differences.

Given these considerations, I view it that the MCF7-aro model with its T+LET R, T+ANA R, and T+EXE R agent-particular resistance cell lines continues to be the most sophisticated recapitulation of AI resistance and remains the de facto model of preference in preclinical research.

1. Wang X, Chen S. Aromatase destabilizer: novel action of exemestane, a food and drug administration-approved aromatase inhibitor. Cancer Res 2006 66: 10281–10286.

2. Miller WR, Bartlett J, Brodie AM, Brueggemeier RW, di Salle E, et al. Aromatase inhibitors: are there differences between steroidal and nonsteroidal aromatase inhibitors and do they matter? Oncologist 2008 13: 829–837.

3. Gluck S. Exemestane as first-line therapy in postmenopausal women with recurrent or metastatic breast cancer. Am J Clin Oncol 2010 33: 314–319.

4. Deeks ED, Scott LJ. Exemestane: a review of its use in postmenopausal women with breast cancer. Drugs 2009 69: 889–918.

Thank you vey much for your detailed response!!

Dear Guillermo;

Glad to help - it was a great question!

Regards

Constantine

Dear Guillermo,

I totally agree with Constantine. My previous lab has been focusing on the AI and aromatase resistance in the past 10 years.

1. I also agree with Constantine that exemestane works differently from letrozole and anastrozole. More interestingly, exemestane has weak estrogenic effect.

Masri S, Lui K, Phung S, Ye J, Zhou D, Wang X, Chen S. (2009) Characterization of the weak estrogen receptor alpha agonistic activity of exemestane. Breast Cancer Res Treat. 116:461-70.

2. To add more comment, parental MCF7 cells do NOT express (or very low level) aromatase by itself. That's why we stably overexpress aromatase into MCF7 cells, so named MCF7aro. One of the important reasons we use MCF7 cells is that it expresses high level of ER and its growth depends on estrogen. We usually do assay using C/D stripped serum that all hormones are removed. Then, we treat cells with testosterone which will subsequently be converted to estrogen to support its growth.

Best,

Ki

Update: I have emailed Dr. Chen several times requesting his aro cells, but received no response. Can you guys suggest an alternative source for these cells?

Guillermo:

Dr. Shiuan Chen is currently the Chair of Department of Cancer Biology at the Beckman Research Institute of City of Hope (Duarte, CA), and his laboratory phone contact number at the position is 626-256-4673, so you might give it one more try and either speak to him or someone in his laboratory ("Laboratory of Shiuan Chen") who may be able to direct you. Good luck.