Proliferation Inhibition Effects Of A Novel NF-κB Inhibitor, Dehydroxymethylepoxyquinimicin (DHMEQ) On Head And Neck Squamous Carcinoma Cell Lines

BACKDROUND: Head and neck squamous cell carcinoma (HNSCC) is themost common malignancy of the upper aerodigestive tract, accounting for morethan 90% of the malignancies in this site. Despite recent advancements in treatmentmodalities, the survival of patients with HNSCC has not been improved because oflocal recurrence and distant metastasis. Recent studies provide evidence thatconstitutive activation of NF-κB plays critical roles in several types ofmalignancies including HNSCC. It is associated with cacinogenesis, progressionand metastasis, and NF-κB becomes a molecular target in anti-cancer treatment.Dehydroxymethylepoxyquinomicin (DHMEQ) is a novel NF-κB inhibitor,synthesized from the structure of natural antibiotics epoxyquinomicin C. Its effectson HNSCC cells need to be determined.OBJECTIVE: To investigate the effects of DHMEQ on growth, induction ofapoptosis, gene expression, invasion and chemosensitivity in HNSCC cell lines.METHOD: Three HNSCC cell lines (KB, YCU-N861 and YCU-H891)were usedin this study. Western blot was used to detect nuclear NF-κB protein expression andexpression changes of nuclear NF-κB, Bcl-xL, cyclinD1, MMP-9 protein after theuse of DHMEQ in three cell lines. The change of VEGF mRNA expression afterDHMEQ administration was detected by RT-PCR method. The sensitivity of threecell lines to DHMEQ alone and in combination with cisplatin (CDDP) wasdetermined by WST-1 assay. Apoptotic cell death was assessed and quantifiedusing the Cell Death Detection ELISA kit. Transcriptional activity of NF-κB,VEGF and cyclinD1 was determined using luciferase reporter gene assay. Cellinvasion was evaluated using BD BioCoat^TM Matrigel^TM Invasion Chamber kit.RESULTS: YCU-H891 and KB cells strongly expressed nuclear NF-κB protein,while YCU-N cells weakly. DHMEQ showed similar growth inhibitory effects on three cell lines, with an IC₅₀ of about 20μg/ml. These growth inhibitory effectswere associated with inhibition of the NF-κB activity. Treatment with DHMEQinduced apoptosis in a dose-dependent manner accounting, at least in part, for thegrowth inhibition by DHMEQ. DHMEQ strongly inhibited cyclinD1 promoteractivity and decreased the levels of cyclinD1 protein in YCU-N 861 and KB cells.DHMEQ also inhibited VEGF promoter activity and caused a decrease in the levelof VEGF mRNA in KB cells. DHMEQ also inhibited the invasion of YCU-H891and YCU-N861 cells. In addition, low concentrations of DHMEQ (1.0 or 5.0μg/ml) synergistically enhanced the cellular sensitivity of YCU-H891 and KB cells tocisplatin, which is a key chemotherapeutic agent in the treatment of HNSCC.CONCLUSION: These results demonstrate that in HNSCC, NF-κB isconstitutively activated and is associated with cacinogenesis, progression andadvanced malignancy. DHMEQ can inhibit the nuclear translocation of NF-κBthereby inhibit NF-κB activity in HNSCC cells. By inhibiting NF-κB, DHMEQ caninhibit the proliferation of HNSCC cells in vitro through increased apoptosis; downregulate genes that related to cacinogenesis, progression and metastasis; enhancecellular sensitivity to chemotherapeutic agents. NF-κB is a molecular target inHNSCC treatment and its inhibitor DHMEQ, may be effective when used alone orin combination with other agent.