Background: Oral squamous cell carcinoma (OSCC), with high mortality rates, is one of the most diagnosed head and neck cancers. Epithelial-to-mesenchymal transition (EMT) and the generation of cancer stem cells (CSCs) are two keys for therapy-resistance, relapse, and distant metastasis. Accumulating evidence indicates that aberrantly expressed cluster of differentiation (CD)47 is associated with cell-death evasion and metastasis; however, the role of CD47 in the generation of CSCs in OSCC is not clear. Methods: We investigated the functional roles of CD47 in OSCC cell lines SAS, TW2.6, HSC-3, and FaDu using the bioinformatics approach, immunoblotting, immunofluorescence staining, and assays for cellular migration, invasion, colony, and orosphere formation, as well as radiosensitivity. Results: We demonstrated increased expression of CD47 in OSCC patients was associated with an estimated poorly survival disadvantage (p = 0.0391) and positively correlated with the expression of pluripotency factors. Silencing CD47 significantly suppressed cell viability and orosphere formation, accompanied by a downregulated expression of CD133, SRY-Box transcription factor 2 (SOX2), octamer-binding transcription factor 4 (OCT4), and c-Myc. In addition, CD47-silenced OSCC cells showed reduced EMT, migration, and clonogenicity reflected by increased E-cadherin and decreased vimentin, Slug, Snail, and N-cadherin expression. Conclusion: Of therapeutic relevance, CD47 knockdown enhanced the anti-OSCC effect of radiotherapy. Collectively, we showed an increased CD47 expression promoted the generation of CSCs and malignant OSCC phenotypes. Silencing CD47, in combination with radiation, could provide an alternative and improved therapeutic efficacy for OSCC patients.

Background: Oral squamous cell carcinoma (OSCC) has a high prevalence and predicted global mortality rate of 67.1%, necessitating better therapeutic strategies. Moreover, the recurrence and resistance of OSCC after chemo/radioresistance remains a major bottleneck for its effective treatment. Molecular targeting is one of the new therapeutic approaches to target cancer. Among a plethora of targetable signaling molecules, PDK1 is currently rising as a potential target for cancer therapy. Its aberrant expression in many malignancies is observed associated with glycolytic re-programming and chemo/radioresistance. Methods: Furthermore, to better understand the role of PDK1 in OSCC, we analyzed tissue samples from 62 patients with OSCC for PDK1 expression. Combining in silico and in vitro analysis approaches, we determined the important association between PDK1/CD47/LDHA expression in OSCC. Next, we analyzed the effect of PDK1 expression and its connection with OSCC orosphere generation and maintenance, as well as the effect of the combination of the PDK1 inhibitor BX795, cisplatin and radiotherapy in targeting it. Results: Immunohistochemical analysis revealed that higher PDK1 expression is associated with a poor prognosis in OSCC. The immunoprecipitation assay indicated PDK1/CD47 binding. PDK1 ligation significantly impaired OSCC orosphere formation and downregulated Sox2, Oct4, and CD133 expression. The combination of BX795 and cisplatin markedly reduced in OSCC cell’s epithelial-mesenchymal transition, implying its synergistic effect. p-PDK1, CD47, Akt, PFKP, PDK3 and LDHA protein expression were significantly reduced, with the strongest inhibition in the combination group. Chemo/radiotherapy together with abrogation of PDK1 inhibits the oncogenic (Akt/CD47) and glycolytic (LDHA/PFKP/PDK3) signaling and, enhanced or sensitizes OSCC to the anticancer drug effect through inducing apoptosis and DNA damage together with metabolic reprogramming. Conclusions: Therefore, the results from our current study may serve as a basis for developing new therapeutic strategies against chemo/radioresistant OSCC.

Primary cultures of rat tracheal epithelial cells were treated with the chemical carcinogen N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) to quantitatively study the early events during neoplastic transformation. Epithelial cells were dissociated from tracheas of specific-pathogen-free Fischer-344 rats and were plated on collagen-coated tissue culture dishes. To determine cytotoxicity, cells were exposed on day 1 to various concentrations of MNNG for 3 h and colony forming efficiency (CFE) was determined on day 7. MNNG at a concentration of 0.1 microgram/ml did not decrease CFE as compared to the control cultures, whereas 1 microgram/ml reduced the CEF by 75%. For transformation studies, primary cell cultures received single exposures to MNNG (0.1-0.6 microgram/ml) or multiple exposures to 0.1 microgram/ml of MNNG for 3 h between days 1 and 17. In carcinogen-exposed cultures, morphologically altered foci appeared on day 18, recognizable by high cell density. Transformation frequencies between 1 and 8% were observed depending on MNNG concentration. Cultures containing altered foci continued to grow during the third and fourth week when control cultures had ceased to proliferate and exfoliated from the dish. Over 40% of the cultures which received multiple exposures to MNNG acquired cell line status and could be subcultured greater than or equal to 20 times. None of the 30 control cultures became cell lines. Seventy per cent of MNNG-exposed cell lines showed the anchorage independent growth phenotype at passage 20 as judged by growth in agarose. Four of 10 cultures exposed either 6 or 8 times to MNNG formed invasive squamous cell carcinomas at passage 20 upon inoculation into nude mice. Based on these and previous studies, we feel that unrestricted cell replication is an early key event in carcinogen-exposed epithelial cell populations, preceding neoplastic transformation.