bafilomycin-a and Carcinoma--Squamous-Cell

Honokiol, an active natural product derived from Magnolia officinalis, exerted anticancer effects through a variety of mechanisms on multiple types of cancers. In this study, the molecular mechanisms of honokiol in suppressing the human oral squamous cell carcinoma (OSCC) cells were evaluated. Treatment of two OSCC cell lines with honokiol resulted in reducing the cell proliferation and arresting the cell cycle at G1 stage which was correlated with the down-regulation of Cdk2 and Cdk4 and the up-regulation of cell cycle suppressors, p21 and p27. In addition, the caspase-dependent programmed cell death was substantially detected, and the autophagy was induced as the autophagosome formation and autophagic flux proceeded. Modulation of autophagy by autophagic inducer, rapamycin or inhibitors, 3-MA or bafilomycin, potentiated the honokiol-mediated anti-OSCC effects where honokiol exerted multiple actions in suppression of MAPK pathway and regulation of Akt/mTOR or AMPK pathways. As compared to clinical therapeutic agent, 5-FU, honokiol exhibited more potent activity against OSCC cells and synergistically enhanced the cytotoxic effect of 5-FU. Furthermore, orally administrated honokiol exerted effective antitumour activity in vivo in OSCC-xenografted mice. Thus, this study revealed that honokiol could be a promising candidate in preventing human OSCCs.

Topics: Adenine; Animals; Antineoplastic Agents, Phytogenic; Apoptosis; Autophagy; Biphenyl Compounds; Carcinoma, Squamous Cell; Cell Line, Tumor; Cell Proliferation; Cyclin-Dependent Kinase 2; Cyclin-Dependent Kinase 4; Cyclin-Dependent Kinase Inhibitor p21; Cyclin-Dependent Kinase Inhibitor p27; Fluorouracil; G1 Phase Cell Cycle Checkpoints; Gene Expression Regulation, Neoplastic; Humans; Lignans; Macrolides; Male; Mice; Mice, Inbred BALB C; Mice, Nude; Mouth Neoplasms; Proto-Oncogene Proteins c-akt; Signal Transduction; Sirolimus; TOR Serine-Threonine Kinases; Tumor Burden; Xenograft Model Antitumor Assays

Photodynamic therapy (PDT) is a promising approach to treat head and neck cancer cells. Here, we investigated whether mitochondrial iron uptake through mitoferrin-2 (Mfrn2) enhanced PDT-induced cell killing. Three human head and neck squamous carcinoma cell lines (UMSCC1, UMSCC14A, and UMSCC22A) were exposed to light and Pc 4, a mitochondria-targeted photosensitizer. The three cell lines responded differently: UMSCC1 and UMSCC14A cells were more resistant, whereas UMSCC22A cells were more sensitive to Pc 4-PDT-induced cell death. In non-erythroid cells, Mfrn2 is an iron transporter in the mitochondrial inner membrane. PDT-sensitive cells expressed higher Mfrn2 mRNA and protein levels compared with PDT-resistant cells. High Mfrn2-expressing cells showed higher rates of mitochondrial Fe(2+) uptake compared with low Mfrn2-expressing cells. Bafilomycin, an inhibitor of the vacuolar proton pump of lysosomes and endosomes that causes lysosomal iron release to the cytosol, enhanced PDT-induced cell killing of both resistant and sensitive cells. Iron chelators and the inhibitor of the mitochondrial Ca(2+) (and Fe(2+)) uniporter, Ru360, protected against PDT plus bafilomycin toxicity. Knockdown of Mfrn2 in UMSCC22A cells decreased the rate of mitochondrial Fe(2+) uptake and delayed PDT plus bafilomycin-induced mitochondrial depolarization and cell killing. Taken together, the data suggest that lysosomal iron release and Mfrn2-dependent mitochondrial iron uptake act synergistically to induce PDT-mediated and iron-dependent mitochondrial dysfunction and subsequent cell killing. Furthermore, Mfrn2 represents a possible biomarker of sensitivity of head and neck cancers to cell killing after PDT.

Topics: Carcinoma, Squamous Cell; Cation Transport Proteins; Cell Line, Tumor; Chelating Agents; Gene Expression Regulation, Neoplastic; Head and Neck Neoplasms; Humans; Iron; Lysosomes; Macrolides; Microscopy, Confocal; Mitochondria; Models, Biological; Photochemotherapy; Reactive Oxygen Species; Time Factors