A small inhibitor of the interaction between Bax and Bcl-X(L) can synergize with methylprednisolone to induce apoptosis in Bcl-X(L)-overexpressing breast-cancer cells.
OBJECTIVE
To identify inhibitors of the interaction between Bax and Bcl-X(L).


METHODS
Using an assay based on biosensor technology, we screened a chemical library of 10,000 compounds for inhibitors of the interaction between Bax and Bcl-X(L). Using cell-culture systems we tested active compounds for their ability to induce apoptosis in Bcl-X(L)-overexpressing MCF7 cells and increase the sensitivities of the cells to apoptosis-inducing drugs [vincristine sulphate, dexamethasone, cycloheximide and 6alpha-methylprednisolone (MP)].


RESULTS
A single compound, 2',4',5',7'-tetrabromofluorescein (A5), from the library was found to inhibit this interaction efficiently. Several structural analogues of A5 were tested and two of these [4',5'-dibromofluorescein (A9) and 3,4,5,6-tetrabromofluorescein (A11)] were found to be active, and their activities were confirmed by an independent in vitro pull-down assay. These active compounds were observed to induce apoptosis in Bcl-X(L)-overexpressing MCF7 cells. Moreover, two of the compounds (A5 and A11) appeared to increase the sensitivities of the cells to MP. A more rigorous test using the isobologram technique showed that there is a synergistic cytotoxic effect between A11 and MP.


CONCLUSIONS
We have identified a small inhibitor of the interaction between Bax and Bcl-X(L) that can synergize with methylprednisolone to induce apoptosis in Bcl-X(L)-overexpressing breast-cancer cells.
Tan
Yee-Joo
YJ
Institute of Molecular and Cell Biology, 30 Medical Drive, 117609, Singapore, Republic of Singapore. mcbtanyj@imcb.nus.edu.sg
Teng
Eileen
E
Ting
Anthony E
AE
D018931:Antineoplastic Agents, Hormonal / Q000494:pharmacology*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000378:metabolism*; D004357:Drug Synergism; D004801:Eosine Yellowish-(YS) / Q000494:pharmacology*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D008775:Methylprednisolone / Q000494:pharmacology*; D011518:Proto-Oncogene Proteins / Q000037:antagonists & inhibitors* / Q000187:drug effects / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors* / Q000187:drug effects / Q000378:metabolism; D014162:Transfection; D014407:Tumor Cells, Cultured; D015854:Up-Regulation / Q000187:drug effects; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein
D018931:Antineoplastic Agents, Hormonal; C494826:BAX protein, human; C494811:BCL2L1 protein, human; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D004801:Eosine Yellowish-(YS); D008775:Methylprednisolone