Clarithromycin enhances bortezomib-induced cytotoxicity via endoplasmic             reticulum stress-mediated CHOP (GADD153) induction and autophagy in breast cancer             cells.
The specific 26S proteasome inhibitor, bortezomib (BZ) potently induces             apoptosis as well as autophagy in metastatic breast cancer cell lines such as             MDA-MB-231 and MDA-MB-468. The combined treatment of clarithromycin (CAM) and             BZ significantly enhances cytotoxicity in these cell lines. Although treatment             with up to 100 µg/ml CAM alone had little effect on cell growth inhibition, the             accumulation of autophagosomes and p62 was observed after treatment with 25 µg/ml             CAM. This result indicated that CAM blocked autophagy flux. However, the combined             treatment of BZ and CAM resulted in more pronounced autophagy induction, as assessed             by increased expression ratios of LC3B-II to LC3B-I and clearance of intracellular             p62, than treatment with BZ alone. This combination further enhanced induction             of the pro-apoptotic transcription factor CHOP (CADD153) and the chaperone protein             GRP78. Knockdown of CHOP by siRNA attenuated the death-promoting effect of BZ             in MDA-MB-231 cells. A wild-type murine embryonic fibroblast (MEF) cell line also             exhibited enhanced BZ-induced cytotoxicity with the addition of CAM, whereas a             Chop knockout MEF cell line completely abolished this enhancement and exhibited             resistance to BZ treatment. These data suggest that endoplasmic reticulum (ER)-stress             mediated CHOP induction is involved in pronounced cytotoxicity by combining these             reagents. Simultaneously targeting two major intracellular protein degradation             pathways such as the ubiquitin-proteasome system by BZ and the autophagy-lysosome             pathway by CAM may improve the therapeutic outcome in breast cancer patients via             ER-stress mediated apoptosis.
Department of Breast Oncology, Tokyo Medical University, Tokyo                     160-8402, Japan.
Seiichiro
S
Komatsu
Keisuke
K
Miyazawa
Shota
S
Moriya
Akiko
A
Takase
Munekazu
M
Naito
Masato
M
Inazu
Norio
N
Kohno
Masahiro
M
Itoh
Akio
A
Tomoda
D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001343:Autophagy / Q000187:drug effects; D001897:Boronic Acids / Q000494:pharmacology*; D000069286:Bortezomib; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D017291:Clarithromycin / Q000494:pharmacology*; D003602:Cytotoxicity, Immunologic; D004357:Drug Synergism; D004721:Endoplasmic Reticulum / Q000187:drug effects* / Q000378:metabolism; D000091342:Endoplasmic Reticulum Chaperone BiP; D005260:Female; D015870:Gene Expression; D006801:Humans; D011719:Pyrazines / Q000494:pharmacology*; D051742:Transcription Factor CHOP / Q000096:biosynthesis*
D001897:Boronic Acids; C497249:DDIT3 protein, human; D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D011719:Pyrazines; D051742:Transcription Factor CHOP; D000069286:Bortezomib; D017291:Clarithromycin