The anti-proliferative properties of 4-benzylphenoxy ethanamine derivatives are mediated by the anti-estrogen binding site (ABS), whereas the anti-estrogenic effects of trifluopromazine are not.

We compared the anti-proliferative properties of 4-benzylphenoxy-N ethyl morpholine (morpho-BPE) and trifluopromazine (TFP) on both the human breast cancer cell lines, MCF7, and its tamoxifen-resistant variant RTx6. We found that the calmodulin antagonist trifluopromazine (TFP) which bound ABS weakly, inhibited MCF7 cell growth but did not follow the relationship observed for diphenylmethane derivatives between MCF7-inhibitory potencies and their Ki. Regarding the tamoxifen-resistant RTx6 cells, TFP but not morpho-BPE induced inhibition of the proliferation. Using a tritiated derivative of morpho-BPE, two distinct binding sites could be demonstrated. Indeed, a low affinity binding site was present in both cell lines whereas a high affinity binding site was mainly found in MCF7 cells although being in lower concentration (less than 10%) in RTx6 cells. Both tamoxifen and TFP displaced morpho-BPE from the two binding sites. The uptake and efflux of the tritiated drug were similar in the two cell lines. The drug did not appear to be metabolized. We concluded that TFP and morpho-BPE belong to distinct classes of molecules and that ABS mediates the anti-proliferative action of diphenylmethane derivatives but not the inhibitory effect of the calmodulin antagonist TFP.