[Rich66]

From the abstract:

antagonistic function of EGCG was evident only with boronic acid-based proteasome inhibitors (BZM, MG-262, PS-IX), but not with several non-boronic acid proteasome inhibitors (MG-132, PS-I, nelfinavir).

From the paper:

The severe antagonistic effect of EGCG appeared to require the presence of the boronic acid moiety in BZM. Among the 6 proteasome inhibitors tested, the boronic acid–containing ones (BZM, MG-262, PS-IX) were similarly incapacitated by EGCG, whereas none of those without this functional group (NFV, MG-132, PS-I) were affected by EGCG. In this context, it is noteworthy that the chemical structures of MG-262 (effective inhibition by EGCG) and MG-132 (no inhibition by EGCG) differ only in the presence/absence of the boronic acid moiety (Figure 4A), indicating that the decisive mechanism of EGCG's antagonism resides with the chemical structure of the target molecule (ie, the boronic acid moiety), not its function (ie, proteasome inhibition).

Seems like a potential issue for a class within a class of chemo...demonstrated in two cancers other than BC.

But along the dietary line, those in this narrow category may have a number of things to avoid:
http://bloodjournal.hematologylibrar...ll/113/24/6262

In addition, since this appears to be a class effect (ie, boronic acid–based drugs will likely bind polyphenols with similar structures), we suggest that other food products that contain high concentrations of polyphenols, such as berries, red wine, walnuts, peanuts, and pomegranates, should also be avoided by patients who are receiving bortezomib