Peripheral benzodiazepine receptor ligands induce apoptosis and cell cycle arrest in human hepatocellular carcinoma cells and enhance chemosensitivity to paclitaxel, docetaxel, doxorubicin and the Bcl-2 inhibitor HA14-1.
OBJECTIVE
Hepatocellular carcinoma (HCC) is one of the most common causes of cancer deaths worldwide. Thus, novel therapies are urgently needed. A promising approach is the use of peripheral benzodiazepine receptor (PBR) ligands which inhibit the proliferation of various tumors.


METHODS
PBR expression both in human HCC cell lines and in tumor specimens of HCC patients was analyzed by RT-PCR and immunostaining. To evaluate PBR ligands for the treatment of HCC, we tested their effects on human HCC cells.


RESULTS
PBR was localized to the mitochondria both of HCC cell lines and tumor tissues of HCC patients. In contrast, normal liver did not express PBR. PBR ligands inhibited the proliferation of HCC cell lines by inducing apoptosis and cell cycle arrest. Apoptosis was characterized by a breakdown of the mitochondrial membrane potential, caspase-3 activation and nuclear degradation. Furthermore, pro-apoptotic Bax was overexpressed while anti-apoptotic Bcl-2 and Bcl-X(L) were suppressed. Cell cycle was arrested both at the G1/S- and G2/M-checkpoints. Synergistic anti-neoplastic effects were obtained by a combination of PBR ligands with cytostatic drugs (paclitaxel, docetaxel, doxorubicin), or with an experimental Bcl-2 inhibitor.


CONCLUSIONS
This is the first report on the induction of apoptosis and cell cycle arrest by PBR ligands in HCC cells. Moreover, PBR ligands sensitized HCC cells to taxans and doxorubicin.
Sutter
Andreas P
AP
Medical Clinic I, Charité-Universitätsmedizin Berlin, Campus Benjamin Franklin, Hindenburgdamm 30, 12200 Berlin, Germany.
Maaser
Kerstin
K
Grabowski
Patricia
P
Bradacs
Gesine
G
Vormbrock
Kirsten
K
Höpfner
Michael
M
Krahn
Antje
A
Heine
Bernhard
B
Stein
Harald
H
Somasundaram
Rajan
R
Schuppan
Detlef
D
Zeitz
Martin
M
Scherübl
Hans
H
D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000378:metabolism / Q000494:pharmacology; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D001578:Benzopyrans / Q000494:pharmacology; D006528:Carcinoma, Hepatocellular; D002453:Cell Cycle / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D045744:Cell Line, Tumor; D000077143:Docetaxel; D004317:Doxorubicin / Q000494:pharmacology; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D007546:Isoquinolines / Q000378:metabolism / Q000494:pharmacology; D008024:Ligands; D008113:Liver Neoplasms; D009570:Nitriles / Q000494:pharmacology; D017239:Paclitaxel / Q000494:pharmacology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000037:antagonists & inhibitors / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis; D011963:Receptors, GABA-A / Q000235:genetics / Q000378:metabolism*; D043823:Taxoids / Q000494:pharmacology; D014316:Tritium; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein
D000903:Antibiotics, Antineoplastic; D000970:Antineoplastic Agents; D000972:Antineoplastic Agents, Phytogenic; C494826:BAX protein, human; C494811:BCL2L1 protein, human; D001578:Benzopyrans; D004791:Enzyme Inhibitors; D007546:Isoquinolines; D008024:Ligands; D009570:Nitriles; D019253:Proto-Oncogene Proteins c-bcl-2; D012333:RNA, Messenger; D011963:Receptors, GABA-A; D043823:Taxoids; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; C456800:ethyl 2-amino-6-bromo-4-(1-cyano-2-ethoxy-2-oxoethyl)-4H-chromene-3-carboxylate; D014316:Tritium; D000077143:Docetaxel; D004317:Doxorubicin; D017239:Paclitaxel; C037850:PK 11195