HIV Protease Inhibitors Sensitize Human Head and Neck Squamous Carcinoma Cells to Radiation by Activating Endoplasmic Reticulum Stress.
BACKGROUND
Human head and neck squamous cell carcinoma (HNSCC) is the sixth most malignant cancer worldwide. Despite significant advances in the delivery of treatment and surgical reconstruction, there is no significant improvement of mortality rates for this disease in the past decades. Radiotherapy is the core component of the clinical combinational therapies for HNSCC. However, the tumor cells have a tendency to develop radiation resistance, which is a major barrier to effective treatment. HIV protease inhibitors (HIV PIs) have been reported with radiosensitizing activities in HNSCC cells, but the underlying cellular/molecular mechanisms remain unclear. Our previous study has shown that HIV PIs induce cell apoptosis via activation of endoplasmic reticulum (ER) stress. The aim of this study was to examine the role of ER stress in HIV PI-induced radiosensitivity in human HNSCC.


RESULTS
HNSCC cell lines, SQ20B and FaDu, and the most commonly used HIV PIs, lopinavir and ritonavir (L/R), were used in this study. Clonogenic assay was used to assess the radiosensitivity. Cell viability, apoptosis and cell cycle were analyzed using Cellometer Vision CBA. The mRNA and protein levels of ER stress-related genes (eIF2α, CHOP, ATF-4, and XBP-1), as well as cell cycle related protein, cyclin D1, were detected by real time RT-PCR and Western blot analysis, respectively. The results demonstrated that L/R dose-dependently sensitized HNSCC cells to irradiation and inhibited cell growth. L/R-induced activation of ER stress was correlated to down-regulation of cyclin D1 expression and cell cycle arrest under G0/G1 phase.


CONCLUSIONS
HIV PIs sensitize HNSCC cells to radiotherapy by activation of ER stress and induction of cell cycle arrest. Our results provided evidence that HIV PIs can be potentially used in combination with radiation in the treatment of HNSCC.
Jiangsu Center for Drug Screening, China Pharmaceutical University, Nanjing, 210009, China; Department of Microbiology & Immunology, Virginia Commonwealth University, Richmond, VA, 23298, United States of America.
Runping
R
Liu
Jiangsu Center for Drug Screening, China Pharmaceutical University, Nanjing, 210009, China.
Luyong
L
Zhang
Jiangsu Center for Drug Screening, China Pharmaceutical University, Nanjing, 210009, China; Department of Microbiology & Immunology, Virginia Commonwealth University, Richmond, VA, 23298, United States of America.
Jing
J
Yang
Jiangsu Center for Drug Screening, China Pharmaceutical University, Nanjing, 210009, China; Department of Microbiology & Immunology, Virginia Commonwealth University, Richmond, VA, 23298, United States of America.
Xiaoxuan
X
Zhang
Department of Radiation Oncology, Virginia Commonwealth University, Richmond, VA, 23298, United States of America.
Ross
R
Mikkelsen
Department of Radiation Oncology, Virginia Commonwealth University, Richmond, VA, 23298, United States of America.
Shiyu
S
Song
Department of Microbiology & Immunology, Virginia Commonwealth University, Richmond, VA, 23298, United States of America; McGuire Veterans Affairs Medical Center, Richmond, VA, 23298, United States of America.
Huiping
H
Zhou
D017209:Apoptosis / Q000187:drug effects; D002294:Carcinoma, Squamous Cell / Q000188:drug therapy* / Q000235:genetics / Q000473:pathology / Q000532:radiotherapy*; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D002465:Cell Movement / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D019938:Cyclin D1 / Q000378:metabolism; D059865:Endoplasmic Reticulum Stress / Q000187:drug effects*; D015852:Eukaryotic Initiation Factor-2 / Q000378:metabolism; D017320:HIV Protease Inhibitors / Q000494:pharmacology / Q000627:therapeutic use*; D006258:Head and Neck Neoplasms / Q000188:drug therapy* / Q000235:genetics / Q000473:pathology / Q000532:radiotherapy*; D006801:Humans; D008954:Models, Biological; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D011836:Radiation Tolerance / Q000187:drug effects; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology / Q000627:therapeutic use*; D000077195:Squamous Cell Carcinoma of Head and Neck; D056811:Unfolded Protein Response / Q000187:drug effects
D015852:Eukaryotic Initiation Factor-2; D017320:HIV Protease Inhibitors; D012333:RNA, Messenger; D011838:Radiation-Sensitizing Agents; D019938:Cyclin D1