Live imaging observation of elevation of the anterior palatal shelf in mouse embryos.

The mammalian secondary palate develops through complex processes including palatal shelf growth, elevation, and fusion. Palatal shelf elevation is a process accompanied by large-scale morphological changes over a short period. The elevation pattern changes along the anterior-posterior axis; the anterior region elevates by the "flip-up" model, and the middle and posterior regions reorient through the "flow" model. However, the mechanisms of both models are unclear because of the rapid progression of the elevation in utero. To observe palatal elevation in real time in detail, we aimed to establish a live imaging method using explants of the anterior region of the palatal shelf in mouse embryos before the beginning of elevation. Changes in the degree of shelf orientation were measured, which showed that the palatal shelf continuously changed shape toward the lingual side. The changes in the angle between the lingual and buccal bases of the palatal shelf were different; the morphological change at the lingual side resulted in a more acute angle, and the change at the buccal side resulted in a more obtuse angle. The morphological changes of the lingual and buccal sides occurred nearly simultaneously, suggesting that the anterior region of the palatal shelf in vitro elevated according to the "flip-up" model. This live imaging method enables the continuous observation of palatal shelf elevation and provides new insights into palatogenesis.

Spatial and chronological localization of septoclasts in the mouse Meckel's cartilage.

Meckel's cartilage (MC) in the first branchial arch of mammals is a transient structure that disappears before birth, except for the most anterior and posterior portions. Recent studies reported that some congenital abnormalities in craniofacial regions are linked with the persistence or dysplasia of MC. However, the mechanisms underlying the resorption of MC have not been elucidated. Cartilage resorption in endochondral ossification is performed by multinuclear osteoclasts/chondroclasts as well as mononuclear septoclasts, which were newly added to the list of cartilage phagocytes. Septoclasts located exclusively at the chondro-osseous junction of the growth plate resorb the uncalcified cartilage matrix. We hypothesized that septoclasts participate in the resorption of MC and attempted to clarify the localization and roles of septoclasts in MC of mouse using a specific immunohistochemistry marker, epidermal type-fatty acid-binding protein (E-FABP/FABP5). E-FABP-immunopositive septoclasts were detected for the first time at the beginning of MC resorption and localized along the resorption surface. Septoclasts of MC in embryonic mice possessed several processes that elongated toward the uncalcified cartilage matrix, expressed cathepsin B, and exhibited characteristic pericapillary localization. Additionally, they localized between hypertrophied cartilage and osteoclasts/chondroclasts in the resorption surface. Confocal laser-scanning microscopy revealed a decrease in the numbers of septoclasts and their processes with the progression of MC disappearance before birth. The present study showed that E-FABP-immunopositive septoclasts participated in the disappearance of MC through the resorption of the uncalcified cartilage matrix and that they have different roles from osteoclasts/chondroclasts.

Spatiotemporal Gene Expression Regions along the Anterior-Posterior Axis in Mouse Embryos before and after Palatal Elevation.

The mammalian secondary palate is formed through complex developmental processes: growth, elevation, and fusion. Although it is known that the palatal elevation pattern changes along the anterior-posterior axis, it is unclear what molecules are expressed and whether their locations change before and after elevation. We examined the expression regions of molecules associated with palatal shelf elevation (Pax9, Osr2, and Tgfß3) and tissue deformation (F-actin, E-cadherin, and Ki67) using immunohistochemistry and RT-PCR in mouse embryos at E13.5 (before elevation) and E14.5 (after elevation). Pax9 was expressed at significantly higher levels in the lingual/nasal region in the anterior and middle parts, as well as in the buccal/oral region in the posterior part at E13.5. At E14.5, Pax9 was expressed at significantly higher levels in both the lingual/nasal and buccal/oral regions in the anterior and middle parts and the buccal/oral regions in the posterior part. Osr2 was expressed at significantly higher levels in the buccal/oral region in all parts at E13.5 and was more strongly expressed at E13.5 than at E14.5 in all regions. No spatiotemporal changes were found in the other molecules. These results suggested that Pax9 and Osr2 are critical molecules leading to differences in the elevation pattern in palatogenesis.

Origin of the torus mandibularis: an embryological hypothesis.

Torus mandibularis, a well-known protuberance in the dental field, has been defined as a hyperostosis in the lingual aspect of the body of the mandible above the mylohyoid line. However, the origin of the torus mandibularis has not yet been clarified. The aim of this study was to provide a better understanding on the origin of the torus in view of the specific development of Meckel's cartilage at the site corresponding to the adult torus. A total of 40 mid-term human fetuses at 7-16 weeks of gestation were examined. The 10-13 weeks stage corresponded to the critical period in which Meckel's cartilage with endochondral ossification underwent a bending at the beginning of the intramandibular course. At the level of mental foramen, which was located between the deciduous canine and the first deciduous molar germs, the medial lamina of the mandible protruded medially to reach Meckel's cartilage. Thus, the medial lamina covered the posterior and superior aspect of the bending Meckel's cartilage just above the attachment of the developing mylohyoid muscle (i.e., in the oral cavity). We considered a bony prominence, which composed the protruding medial lamina and the bending Meckel's cartilage as the fetal origin of the torus mandibularis. A new theory is proposed for the origin of the torus mandibularis based on the existence of an anlage formed during the development of the mandible, variable in morphology and size, but always constant.

Localization of heat shock protein 27 (hsp27) in the rat gingiva and its changes with tooth eruption.

Heat shock protein 27 kDa (Hsp27) functions as a molecular chaperon to prevent apoptosis as well as to contribute to the regulation of cell proliferation and differentiation during development. In the present study, the localization of Hsp27 in the oral epithelium of rats and its expression change during formation of the gingiva with the tooth eruption were examined immunohistochemically to elucidate the roles of Hsp27 in the oral mucosa.In adult rats, Hsp27-immunoreactivity was localized in the prickle and granular layers but absent in the basal and horny layers of the oral epithelium. On the other hand, in the outer and sulcular epithelia of the free gingival, Hsp27-immunoreactivity was detected in the whole layers, while it was not found in the proliferation zone of the junctional epithelium immunoreactive for Ki67. In immature rats on 10th postnatal day, Hsp27-immunoreactivity was intense in the prickle and granular layers of the oral epithelium, but was not detected in its basal layer. In rats at the eruptive phase on 15th postnatal day, Hsp27-immunoreactivity was detected in sites of the basal layer adjacent to where the dental cusps penetrated through the oral epithelium. Although the immunoreactivity for Ki67 was found in the basal layer of the oral epithelium, it was not localized in the Hsp27-immunopositive sites of tooth-penetration in the basal layer. Just after the tooth-eruption on 20th postnatal day, Hsp27-immunoreactivity was not found in the stratified squamous epithelium at the dentogingival junction, whereas it was intense in a single layer of cuboidal epithelial cells attached to the tooth neck. Ki67-positive cells were scattered in the stratified squamous epithelium at the dentogingival junction, whereas no positive cells were found in the portion of a single layer of cuboidal epithelial cells.These findings suggest that the outer and sulcular epithelia of the free gingiva have a relatively slower rate of proliferation than other gingival and oral epithelia, and that Hsp27 might inhibit the proliferation of the basal cells. Such specific phenomenon in the free gingiva occurred immediately after the dental cusps were exposed to the oral cavity.

Biological Properties of the Aggregated Form of Chitosan Magnetic Nanoparticle.

BACKGROUND/AIM: Chitosan-coated iron oxide nanoparticles (Chi-NP) have gained attention because of their biocompatibility, biodegradability, low toxicity and targetability under magnetic field. In this study, we investigated various biological properties of Chi-NP. MATERIALS AND METHODS: Chi-NP was prepared by mixing magnetic NP with chitosan FL-80. Particle size was determined by scanning and transmission electron microscopes, cell viability by MTT assay, cell cycle distribution by cell sorter, synergism with anticancer drugs by combination index, PGE2 production in human gingival fibroblast was assayed by ELISA. RESULTS: The synthetic process of Chi-NP from FL-80 and magnetic NP increased the affinity to cells, up to the level attained by nanofibers. Upon contact with the culture medium, Chi-NP instantly formed aggregates and interfered with intracellular uptake. Aggregated Chi-NP did not show cytotoxicity, synergism with anticancer drugs, induce apoptosis (accumulation of subG1 cell population), protect the cells from X-ray-induced damage, nor affected both basal and IL-1ß-induced PGE2 production. CONCLUSION: Chi-NP is biologically inert and shows high affinity to cells, further confirming its superiority as a scaffold for drug delivery.

Tumor-specific cytotoxicity and type of cell death induced by sodium 5,6-benzylidene-L-ascorbate.

The cytotoxic activity of sodium 5,6-benzylidene-L-ascorbate (SBA) against eight human cancer cell lines and three human normal cells was investigated, SBA showed slightly higher cytotoxicity against human tumor cell lines, as compared with normal cells, with a tumor-specificity index of 2.0. The human myelogenous leukemia cell lines (HL-60, ML-1, KG-1) were the most sensitive to SBA, followed by human oral squamous cell carcinoma (HSC-2, HSC-3, HSC-4) and human glioblastoma (T98G, U87MG). Human oral normal cells (gingival fibroblast, pulp cell, periodontal ligament fibroblast) were the most resistant. In contrast to actinomycin D, SBA induced little or no activation of caspase-3, caspase-8 and caspase-9 in the HSC-2, HSC-4, T98G and HL-60 cells, regardless of incubation time (either 6 or 24 h). SBA induced little or no internucleosomal DNA fragmentation after 6 h in all of these cells. However, prolonged treatment with SBA (24 h) induced a smear pattern of DNA fragmentation in the HSC-2, HSC-4 and T98G cells and a low level of internucleosomal DNA fragmentation in the HL-60 cells. Electron microscopy demonstrated the destruction of mitochondrial structure and autophagocytosis of broken organelles by SBA in the HSC-2, HSC-4 and HL-60 cells. At higher concentrations of SBA, necrotic cell death was observed in the HSC-2 cells, but not in the T98G cells, where the production of acidic organelles (detected by acridine orange staining) was much lower than that attained by nutritional starvation, a well-defined method of inducing autophagy. The present study suggests that SBA induces various degrees of autophagic cell death, followed by either necrosis or apoptosis at laters stage, depending on the cell type.

Tumor-specific cytotoxicity and type of cell death induced by beta-cyclodextrin benzaldehyde inclusion compound.

The cytotoxicity of beta-cyclodextrin benzaldehyde inclusion compound (CDBA) against human normal and cancer cell lines was investigated. CDBA showed slightly higher cytotoxicity against human tumor cell lines, as compared to normal cells, with a tumor-specificity index of 2.2. Human myelogenous leukemia cell lines (HL-60, ML-1, KG-1) were the most sensitive to CDBA, followed by human oral squamous cell carcinoma (HSC-2, HSC-3, HSC-4) and human glioblastoma (T98G, U87MG). Human normal cells (gingival fibroblasts, pulp cells, periodontal ligament fibroblasts) were the most resistant. CDBA induced internucleosomal DNA fragmentation in HL-60 cells and caspase-3, -8, -9 activation, but to a much lesser extent than that attained by UV irradiation or actinomycin D. On the other hand, CDBA did not induce DNA fragmentation, nor caspase activation in HSC-2, HSC-4 or T98G cells. Electron microscopy demonstrated that CDBA induced the destruction of mitochondrial structure and digestion of broken organelles by secondary lysosomes in all of these cells. CDBA also increased the number of acidic organelles as judged by acridine orange staining. The present study suggests that CDBA induces autophagic cell death in cancer cell lines.

Tumor-specific cytotoxicity and type of cell death induced by benzocycloheptoxazines in human tumor cell lines.

Twenty-six benzocycloheptoxazine derivatives were investigated for their tumor-specific cytotoxicity and apoptosis-inducing activity against three human normal cells (gingival fibroblast HGF, pulp cell HPC, periodontal ligament fibroblast HPLF) and four human tumor cell lines (squamous cell carcinoma HSC-2, HSC-3, HSC-4, promyelocytic leukemia HL-60). Benzo[b]cyclohepta[e][1,4]thiazine [1] exhibited very weak cytotoxicity, whereas its 6,8,10-tribromo derivative [3] exhibited higher cytotoxicity and tumor specificity (TS = 5.6). 6H-Benzo[b]cyclohepta[e][1,4]diazine [4] and its cation [5] exhibited no tumor specificity. Among eighteen benzo[b]cyclohepta[e][1,4]oxazine derivatives [6-23], 6,8,10-triboromo- [9], 6-bromo-2-methyl- [20], and 6-bromo-2-chloro- [21] derivatives showed the highest tumor-specific cytotoxicity (TS = 12.5, 9.1 and 11.5, respectively). 14H-[1,4]Benzoxazino[3',2':3,4]cyclohepta[1, 2-b][1,4]benzoxazine [24] and its 7-bromo- [25] and 7-isopropyl- [26] derivatives had much lower cytotoxicity and tumor-specificity. Compounds [9, 20, 21] at 50% cytotoxic concentration (CC50) induced internucleosomal DNA fragmentation and caspase activation in HL-60 cells. On the other hand, these compounds induced apoptosis only at concentrations higher than CC50 in HSC-2 cells and failed to induce apoptosis in HSC-4 cells. Compounds [9, 20, 21] induced the formation of acidic organelles as measured by acridine orange staining. Transmission electron microscopy demonstrated the induction of moderate enlargement of mitochondria, the endoplasmic reticulum and nuclear membrane, and the vacuolation of the endoplasmic reticulum and the presence of a number of lamellar body-like organelles. These results indicate the diversity of the type of cell death induced by benzocycloheptoxazine derivatives in human tumor cell lines.

Tumor-specific cytotoxicity and type of cell death induced by peplomycin in oral squamous cell carcinoma cell lines.

The antitumor antibiotic peplomycin showed higher cytostatic antiproliferative effect on five cultured human oral squamous cell carcinoma (OSCC) cell lines (HSC-2, HSC-3, HSC-4, Ca9-22 and NA), as compared with three human oral normal cells (gingival fibroblast HGF, pulp cell HPC and periodontal ligament fibroblast HPLF). Although the antiproliferative activity of peplomycin declined with increasing cell density, peplomycin showed tumor-specific cytotoxicity at any cell density. The five OSCC cell lines showed considerable differences in sensitivity against peplomycin; the HSC-2 cells were the most sensitive, followed by the NA, HSC-3, Ca9-22 and HSC-4 cells. Peplomycin did not induce internucleosomal DNA fragmentation in any of the five OSCC cell lines, and only slightly modified caspase-3, -8 and -9 activities in the HSC-2, Ca9-22 and NA cell lines. Electron microscopy revealed that peplomycin induced the vacuolation of mitochondria accompanying electron lucent matrices lacking cristae and the enlargement of the endoplasmic reticulum in the HSC-2 cells. These data suggest that the anti-proliferative effect of peplomycin is time-dependent, and therefore prolonged treatment with peplomycin in combination with cytotoxic chemotherapeutic agents may induce greater cytotoxic action.

Changes in Metabolic Profiles of Human Oral Cells by Benzylidene Ascorbates and Eugenol.

Sodium-5,6-benzylidene-L-ascorbate (SBA), and its component units, benzaldehyde (BA) and sodium ascorbate (SA), are known to exert antitumor activity, while eugenol exerts anti-inflammatory activity. To narrow down their intracellular targets, metabolomic analysis was performed. Viable cell number was determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. Fine cell structures were observed under transmission electron microscope. Cellular metabolites were extracted with methanol and subjected to capillary electrophoresis-mass spectrometry (CE-MS) for quantification of intracellular metabolites. Results showed that SBA was cleaved into BA and SA under acidic condition. Among these three compounds, BA showed the highest-tumor specificity in vitro against human oral squamous cell carcinoma (OSCC) cell line. BA did not induce the vacuolization in HSC-2 OSCC cells, and its cytotoxicity was not inhibited by catalase, in contrast to SBA and SA. Only BA suppressed the tricarboxylic acid (TCA) cycle at early stage of cytotoxicity induction. Eugenol more rapidly induced the vacuolization and suppressed the TCA cycle in three human normal oral cells (gingival fibroblast, periodontal ligament fibroblast, pulp cell). Neither BA nor eugenol affected the ATP utilization, further supporting that they do not induce apoptosis. The present study demonstrated for the first time that both BA and eugenol suppressed the TCA cycle in tumor cells and normal cells, respectively. It is crucial to design methodology that enhances the antitumor potential of BA and reduces the cytotoxicity of eugenol to allow for safe clinical application.

Tumor-specific cytotoxic activity and type of cell death induced by 4-trifluoromethylimidazoles in human oral squamous cell carcinoma cell lines.

Fourteen 4-trifluoromethylimidazole derivatives were investigated for their cytotoxicity against three human normal cells (gingival fibroblast HGF, pulp cell HPC and periodontal ligament fibroblast HPLF) and four human tumor cell lines (oral squamous cell carcinoma HSC-2, HSC-3, HSC-4 and promyelocytic leukemia HL-60). Among these compounds, 4-trifluoromethyl-1,2-diphenylimidazole (IM5), 1-benzyl-4-trifluoromethyl-2-phenylimidazole (IM7) and 5-[1-ethoxy-2,2,2-trifluoro-1-(trifluoromethyl) ethyl]-1-methyl-2-phenyl-1H-imidazole (IM12) showed much higher cytotoxicity and tumor-specificity than the other compounds. IM5, the most potent compound, induced different types of cell death depending on the target cells. IM5 induced DNA fragmentation of oligonucleosomal units (a biochemical hallmark of apoptosis) in the HL-60 cells, but not in such a clear-cut laddering pattern in the HSC-2 cells. On the other hand, IM5 produced secondary lysosomes digesting broken organelles, without induction of internucleosomal DNA fragmentation and disappearance of cell surface microvilli in the HSC-4 cells, even though the HSC-2 and HSC-4 cells showed comparable sensitivity to IM5. These data suggest that the type of cell death is determined by the type of target cells, but not by the drug-sensitivity of the cells.

Induction of Apoptosis in Human Oral Keratinocyte by Doxorubicin.

BACKGROUND/AIM: We have previously reported that doxorubicin (DXR) showed much higher cytotoxicity against human oral squamous cell carcinoma cell lines compared to normal human mesenchymal normal oral cells (gingival fibroblast, periodontal ligament fibroblast, pulp cell), yielding high tumor-specificity. However, we unexpectedly found that doxorubicin showed potent cytotoxicity against human normal oral keratinocytes and primary gingival epithelial cells. In the present study, we investigated the reproducibility, underlining mechanisms and generality of this unexpected finding. MATERIALS AND METHODS: Viable cell number was determined by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide method, fine cell structure by transmission electron microscopy and apoptosis induction by western blot analysis. RESULTS: Doxorubicin induced keratinocyte toxicity, regardless of cell density and concentration of FBS in the culture medium. Doxorubicin induced apoptosis (characterized by the loss of cell surface microvilli, chromatin condensation, nuclear fragmentation and caspase-3 activation) in keratinocytes. A total of 11 anticancer drugs showed similar keratinocyte toxicity. Alkaline extract of the leaves of Sasa senanensis Rehder partially alleviated the DXR-induced keratinocyte cytotoxicity by promoting cell growth. CONCLUSION: The present study suggested that oral keratinocyte toxicity is a novel adverse effect of most anticancer agents.

Effects of 3-styrylchromones on metabolic profiles and cell death in oral squamous cell carcinoma cells.

4H-1-benzopyran-4-ones (chromones) are important naturally-distributing compounds. As compared with flavones, isoflavones and 2-styrylchromones, there are only few papers of 3-styrylchromones that have been published. We have previously reported that among fifteen 3-styrylchromone derivatives, three new synthetic compounds that have OCH3 group at the C-6 position of chromone ring, (E)-3-(4-hydroxystyryl)-6-methoxy-4H-chromen-4-one (compound 11), (E)-6-methoxy-3-(4-methoxystyryl)-4H-chromen-4-one (compound 4), (E)-6-methoxy-3-(3,4,5-trimethoxystyryl)-4H-chromen-4-one (compound 6) showed much higher cytotoxicities against four epithelial human oral squamous cell carcinoma (OSCC) lines than human normal oral mesenchymal cells. In order to further confirm the tumor specificities of these compounds, we compared their cytotoxicities against both human epithelial malignant and non-malignant cells, and then investigated their effects on fine cell structures and metabolic profiles and cell death in human OSCC cell line HSC-2. Cytotoxicities of compounds 4, 6, 11 were assayed with MTT method. Fine cell structures were observed under transmission electron microscope. Cellular metabolites were extracted with methanol and subjected to CE-TOFMS analysis. Compounds 4, 6, 11 showed much weaker cytotoxicity against human oral keratinocyte and primary human gingival epithelial cells, as compared with HSC-2, confirming their tumor-specificity, whereas doxorubicin and 5-FU were highly cytotoxic to these normal epithelial cells, giving unexpectedly lower tumor-specificity. The most cytotoxic compound 11, induced the mitochondrial vacuolization, autophagy suppression followed by apoptosis induction, and changes in the metabolites involved in amino acid and glycerophospholipid metabolisms. Chemical modification of lead compound 11 may be a potential choice for designing new type of anticancer drugs.

Induction of apoptosis by beta-diketones in human tumor cells.

A variety of beta-diketones were evaluated for their cytotoxic profiles against oral human normal and tumor cells. Among 22 compounds (BD1-22) tested, the cytotoxicity of 3-formylchromone (BD17) (CC50=7.8 microg/mL) against human oral squamous cell carcinoma (HSC-2) cells was higher than that of curcumin (CC50=23.6 microg/mL). Tumor cell-specific cytotoxicity was also detected in BD17 which exhibited little cytotoxic activity against a normal human cell, gingival fibroblast (HGF). (-)-3- (BD13) (CC50=21.7 microg/mL) and (+)-3-(Trifluoroacetyl)camphor (BD12) (CC50=29.7 microg/mL) are enantiomers and showed cytotoxicity comparable to curcumin and dibenzoylmethane (BD2) (CC50=22.5 microg/mL). BD13 did not induce DNA fragmentation in HL-60 cells nor activate caspase 3, 8 and 9 in both HL-60 and HSC-2 cells, regardless of the presence or absence of FeCl3. On the other hand, BD17 was found to induce apoptosis in HSC-2 and HL-60 cells, as judged by internucleosomal DNA fragmentation, caspase 3, 8 and 9 activation and dysfunction of mitochondrial membrane potential. The cytotoxic activity of BD13, BD17 and curcumin was significantly reduced by chelation with FeCl3. The tumor-specific cytotoxicity and apoptosis-inducing activity of BD17 against human tumor cells undoubtedly warrant further studies of its efficacy as a cancer chemotherapeutic agent.

Different expression of 25-kDa heat-shock protein (Hsp25) in Meckel's cartilage compared with other cartilages in the mouse.

The 25-kDa heat-shock protein (Hsp25) is expressed in the cartilage of the growth plate and suggested to function in chondrocyte differentiation and degeneration. Using immunohistochemistry, we examined the temporal and spatial occurrence of Hsp25 in Meckel's cartilage in embryonic mice mandibles, and in other types of cartilage in both embryonic and adult mice. In adults, Hsp25 immunoreactivity was detected in the hypertrophic chondrocytes located in growth plates of long bones and in non-osteogenic laryngeal and tracheal cartilages. No chondrocytes in the resting or proliferating phase exhibited Hsp25 immunoreactivity. In the embryonic mandibles, resting and proliferating chondrocytes in the anterior and intermediate portions of Meckel's cartilage showed Hsp25 immunoreactivity from the 12th day of gestation (E12) through E15, whereas those in the posterior portion showed little or no immunoreactivity. After E16, the overall Hsp25 immunoreactivity in Meckel's cartilage substantially reduced in intensity, and little or no immunoreactivity was detected in the hypertrophic chondrocytes located in the degenerating portions of Meckel's cartilage. The antisense oligonucleotide for Hsp25 mRNA applied to the culture media of the mandibular explants from E10 embryos caused significant inhibition of the development of the anterior and middle portions of Meckel's cartilage. These results suggested that Hsp25 is essential for the development of Meckel's cartilage and plays different roles in Meckel's cartilage from those in the permanent cartilages and the cartilages undergoing endochondral ossification.

Quantitative structure-activity relationship analysis of cytotoxicity and anti-UV activity of 2-aminotropones.

BACKGROUND: We newly synthesized twenty 2-aminotropones with different lengths of methylene units, with or without introduction of isopropyl group at C-4 position of the cycloheptatriene ring, which were then subjected to quantitative structure-activity relationship (QSAR) analysis. MATERIALS AND METHODS: Viable cell number was evaluated by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) method. The tumor specificity was determined by the ratio of the mean CC50 (50% cytotoxic concentration) for the normal cells (human gingival fibroblast, HGF) to that of the human oral squamous cell carcinoma (OSCC) cell line (Ca9-22) derived from gingival tissue. Anti-UV activity (SI) was determined by the ratio of CC50 to EC50 (the concentration that increased the viability of UV-irradiated cells to 50%) using HSC-2 OSCC cells. Physico-chemical, structural, and quantum-chemical parameters were calculated based on conformations optimized by the LowModeMD method followed by the Discrete Fourier Transform (DFT) method. Fine-cell structure was observed by transmission electron microscopy. RESULTS: 2-Aminotropones induced cytotoxicity, accompanied by the production of many rough endoplasmic reticula with enlarged lacuna and vacuolated mitochondria. Their cytotoxicity was a positive function of the number of methylene units and hydrophobicity. Anti-UV activity showed a good correlation with lowest unoccupied molecular orbital (LUMO) energy, but not with the length of methylene units. All twenty 2-aminotropones induced a very low level of hormetic growth stimulation at lower concentrations. CONCLUSION: Different types of chemical descriptors may be applicable to estimating the cytotoxicity and anti-UV activity of 2-aminotropones.

Analysis of type of cell death induced by topoisomerase inhibitor SN-38 in human oral squamous cell carcinoma cell lines.

Despite frequent use of topoisomerase inhibitors (TIs) as antitumor agents, their application to oral squamous cell carcinoma (OSCC) has not been reported. We investigated three inhibitors of topoisomerase I [camptothecin, irinotecan, SN-38 (active metabolite of irinotecan)] and two inhibitors of topoisomerase II (etoposide, teniposide) for their cytotoxicity towards a total of 15 human tumor cell lines and normal cultured cells. All TIs exhibited higher cytotoxicity towards tumor cell lines (OSCC, glioblastoma, myelogenous leukemia) as compared with normal mesenchymal (gingival fibroblast, pulp cell, periodontal ligament fibroblast) and epithelial cells (skin keratinocytes). Among TIs, SN-38 had the highest cytotoxicity towards OSCC cell lines, with a tumor specificity index of 1321 compared to mesenchymal cells and 22 compared with epithelial cells. SN-38 induced different types of cell death in two OSCC cell lines: apoptosis (caspase-3 activation and internucleosomal DNA fragmentation) in HSC-2 cells and autophagy (formation of autophagosome and secondary lysosome) in HSC-4 cells. The cell death of HSC-2 and HSC-4 cells was significantly inhibited by pre-treatment with caspase inhibitor (Z-VAD-FMK) and autophagy inhibitors (3-methyladenine, bafilomycin A1), respectively. The present study demonstrated that SN-38 is highly cytotoxic to OSCC cell lines, regardless of the type of induced cell death, suggesting its future application for chemotherapy of OSCC.

Tumor-specific cytotoxicity and type of cell death induced by benzaldehyde.

We have previously reported that sodium 5,6-benzylidene-L-ascorbate (SBA) induced dramatic antitumor activity in inoperable cancer patients, but induced only marginal tumor specificity in vitro. Here the tumor specificity and type of cell death induced by benzaldehyde (BA), a degradation product of SBA, was investigated, using human tumor cell lines (oral squamous cell carcinoma [OSCC], glioblastoma, myelogenous leukemia) and human normal oral cells (gingival fibroblast, pulp cell, periodontal ligament fibroblast). BA showed much higher tumor-specific cytotoxicity than SBA. BA induced the formation of autophagosomes, the destruction of mitochondrial structure and digestion of broken organelles, without any apparent induction of internucleosomal DNA fragmentation and caspase activation in an OSCC cell line HSC-2, in a similar manner to SBA. However, pretreatment with 3-methyladenine or bafilomycin A(1), autophagy inhibitors, did not completely rescue the cells from the cytotoxicity induced by BA. The study suggests that BA may play an important role in the induction of antitumor activity of SBA in vivo, although the autophagic phenotypes induced by BA may be involved in both cell death and survival.

Tumor-specific cytotoxicity and type of cell death induced by gefitinib in oral squamous cell carcinoma cell lines.

Gefitinib is an orally active, selective epidermal growth factor receptor-tyrosine kinase inhibitor. The present study was aimed at evaluating the antitumor activity of gefitinib alone or in combination with other antitumor agents. Gefitinib showed higher cytotoxicity against five human tumor cell lines (HSC-2, HSC-3, HSC-4, T98G and U87MG) than against three human normal oral cells (gingival fibroblast HGF, pulp cell HPC and periodontal ligament fibroblast HPLF). Gefitinib showed little or no growth stimulation effects at lower concentrations (so-called hormetic effect). Non-cytotoxic concentration of gefitinib effectively enhanced the cytotoxicity of docetaxel against HSC-2 and T98G cell, but failed to enhance the cytotoxicity of other antitumor agents (mitoxantrone, doxorubicin, methotrexate, cisplatin, sodium ascorbate, sodium fluoride) or herbal extracts (Drynaria baronii, Angelica sinensis and Cornus officinalis Sieb. et Zucc). Gefitinib alone and combined with docetaxel induced internucleosomal DNA fragmentation and caspase-3 activation in human promyelocytic leukemia HL-60 cells, but not in HSC-2 or T98G cells. Combination treatment with gefitinib and docetaxel induced the formation of acidic organelles (stained with acridine orange) and mitochondrial shrinkage, vacuolization and production of autophagosome and the loss of cell surface microvilli, without destruction of cell surface and nuclear membranes in HSC-2 and T98G cells (demonstrated by transmission electron microscopy), suggesting the induction of autophagy in HSC-2 and T98G cells.