Inhibition of radiation-induced DNA repair and prosurvival pathways contributes to vorinostat-mediated radiosensitization of pancreatic cancer cells.
OBJECTIVE
The intrinsic radioresistance of pancreatic cancer (PaCa) is caused by multiple oncogenic signaling pathways. In contrast to combining radiation therapy (RT) with targeted therapeutic agent(s) whose blockade can be circumvented by redundant signaling pathways, we evaluated the combination of RT with a broad-spectrum histone deacetylase inhibitor, vorinostat.


METHODS
Radiosensitization by vorinostat was analyzed using clonogenic survival assays. Apoptosis was evaluated using flow cytometry and immunoblotting. DNA repair was evaluated using immunofluorescence assessment of histone 2AX phosphorylation and immunoblotting for DNA repair proteins. Prosurvival pathway proteins were measured by immunoblotting and electrophoretic mobility shift assays.


RESULTS
Vorinostat significantly sensitized PaCa cells to radiation, but vorinostat-induced apoptosis did not contribute significantly to the observed radiosensitization. However, vorinostat inhibited DNA damage repair by targeting key DNA repair proteins and also abrogated prosurvival pathways responsible for PaCa aggressiveness and radioresistance. Specifically, the constitutively overexpressed epidermal growth factor receptor and nuclear factor κB pathways were shown to be induced by radiation and inhibited by vorinostat.


CONCLUSIONS
Vorinostat augments the antitumor effects of RT by abrogating radioresistance responses of PaCa cells mediated by prosurvival and DNA repair pathways and promises to be a clinically relevant adjunct to RT for treatment of PaCa.
Department of Experimental Radiation Oncology, The University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA.
Amit
A
Deorukhkar
Shujun
S
Shentu
Hee Chul
HC
Park
Parmeswaran
P
Diagaradjane
Vinay
V
Puduvalli
Bharat
B
Aggarwal
Sushovan
S
Guha
Sunil
S
Krishnan
D017209:Apoptosis / Q000187:drug effects* / Q000528:radiation effects; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects / Q000528:radiation effects; D004260:DNA Repair / Q000187:drug effects* / Q000528:radiation effects; D004305:Dose-Response Relationship, Drug; D004307:Dose-Response Relationship, Radiation; D024202:Electrophoretic Mobility Shift Assay; D066246:ErbB Receptors / Q000378:metabolism; D056572:Histone Deacetylase Inhibitors / Q000494:pharmacology; D006657:Histones / Q000378:metabolism; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology*; D015151:Immunoblotting; D016328:NF-kappa B / Q000378:metabolism; D010190:Pancreatic Neoplasms / Q000378:metabolism / Q000473:pathology; D010766:Phosphorylation / Q000187:drug effects / Q000528:radiation effects; D011485:Protein Binding; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects* / Q000528:radiation effects; D000077337:Vorinostat
C468783:H2AX protein, human; D056572:Histone Deacetylase Inhibitors; D006657:Histones; D006877:Hydroxamic Acids; D016328:NF-kappa B; D011838:Radiation-Sensitizing Agents; D000077337:Vorinostat; D066246:ErbB Receptors