OK, let’s talk about a breast cancer target, estrogen receptor-beta. It’s been the subject of a great deal of research over the years, but its exact actions have proven difficult to work out. One of the problems has been that there are a number of different antibodies available to locate it in tissue, but they don’t give mutually consistent results. Overall, though, the consensus has been that it’s found in a large proportion of breast cancer types, and that it’s a potentially valuable drug target for that indication. Clinical trials have been run on this hypothesis, and companies have invested time and money into the idea.
Well, there’s a reason that this area has been a disappointing sink of effort. Those doubts about the antibodies were, as it happens, very well founded. This new paper has the verdict:
The discovery of oestrogen receptor β (ERβ/ESR2) was a landmark discovery. Its reported expression and homology with breast cancer pharmacological target ERα (ESR1) raised hopes for improved endocrine therapies. After 20 years of intense research, this has not materialized. We here perform a rigorous validation of 13 anti-ERβ antibodies, using well-characterized controls and a panel of validation methods. We conclude that only one antibody, the rarely used monoclonal PPZ0506, specifically targets ERβ in immunohistochemistry. Applying this antibody for protein expression profiling in 44 normal and 21 malignant human tissues, we detect ERβ protein in testis, ovary, lymphoid cells, granulosa cell tumours, and a subset of malignant melanoma and thyroid cancers. We do not find evidence of expression in normal or cancerous human breast. This expression pattern aligns well with RNA-seq data, but contradicts a multitude of studies. Our study highlights how inadequately validated antibodies can lead an exciting field astray.
Whoops. Bad antibodies have been a problem for a long time, but validation is a tedious business that’s too often glossed over. But this study shows how important it really is. The entire ER-beta field is going to have to be re-evaluated in light of this (unless, of course, you’d already concluded that there was something squirrely about it). But the authors want to make sure that the lesson is broader:
While our study focuses on ERβ, we do not think that antibodies towards ERβ are significantly poorer than those targeting other proteins, and it is not unlikely that this problem generates similar obstacles in many other fields. Our study illustrates the consequences of using antibodies not specific for the intended targets. We wish to argue for the need of a more thorough validation from the vendors, and a higher level of consciousness among buyers, about the fact that each antibody must be validated for its intended application using proper controls.
This is one of those statements that everyone agrees with, but not enough people apparently act on. The twenty-year history of ER-beta should – one hopes – add a bit of urgency to it, but we’ll see if that happens.