CD4+CD25+ regulatory T cells (Treg), an essential subset for preventing autoimmune diseases, is implicated as a negative regulator in anti-tumor immunity. We found that metformin (Met) reduced tumor-infiltrating Treg (Ti-Treg), particularly the terminally-differentiated CD103+KLRG1+ population, and also decreased effector molecules such as CTLA4 and IL-10. Met inhibits the differentiation of naïve CD4+ T cells into inducible Treg (iTreg) by reducing forkhead box P3 (Foxp3) protein, caused by mTORC1 activation that was determined by the elevation of phosphorylated S6 (pS6), a downstream molecule of mTORC1. Rapamycin and compound C, an inhibitor of AMP-activated protein kinase (AMPK) restored the iTreg generation, further indicating the involvement of mTORC1 and AMPK. The metabolic profile of iTreg, increased Glut1-expression, and reduced mitochondrial membrane-potential and ROS production of Ti-Treg aided in identifying enhanced glycolysis upon Met-treatment. The negative impact of Met on Ti-Treg may help generation of the sustained antitumor immunity.

CD11b⁺ myeloid subpopulations, including myeloid-derived suppressor cells (MDSCs) and tumor-associated macrophages (TAMs), play crucial roles in the suppression of T-cell-mediated anti-tumor immunity. Regulation of these cell types is a primary goal for achieving efficient cancer immunotherapy. We found that metformin (Met) induces CD11b⁺-cell-mediated growth inhibition of a K7M2neo osteosarcoma independent of T cells, as growth inhibition of K7M2neo was still observed in wild-type (WT) mice depleted of T cells by antibodies and in SCID; this contrasted with the effect of Met on Meth A fibrosarcoma, which was entirely T-cell-dependent. Moreover, the inhibitory effect seen in SCID was abrogated by anti-CD11b antibody injection. PMN-MDSCs were significantly reduced in both spleens and tumors following Met treatment. In TAMs, production of IL-12 and TNF-α, but not IL-10, became apparent, and elevation of MHC class II with reduction of CD206 was observed, indicating a shift from an M2- to M1-like phenotype via Met administration. Metabolically, Met treatment decreased basal respiration and the oxygen consumption rate (OCR)/extracellular acidification rate (ECAR) ratio of CD11b⁺ cells in tumors, but not in the spleen. In addition, decreased reactive oxygen species (ROS) production and proton leakage in MDSCs and TAMs were consistently observed in tumors. Uptake of both 2-deoxy-2-d-glucose (2-NBDG) and BODIPY® decreased in MDSCs, but only BODIPY® incorporation was decreased in TAMs. Overall, our results suggest that Met redirects the metabolism of CD11b⁺ cells to lower oxidative phosphorylation (OXPHOS) while elevating glycolysis, thereby pushing the microenvironment to a state that inhibits the growth of certain tumors.

Platinum‑based antitumor agents have been widely used to treat head and neck squamous cell carcinoma (HNSCC) and numerous other malignancies. Cisplatin is the most frequently used platinum‑based antitumor agent, however drug resistance and numerous undesirable side effects limit its clinical efficacy for cancer patients. Cancer cells discharge cisplatin into the extracellular space via copper transporters such as ATPase copper transporting beta (ATP7B) in order to escape from cisplatin‑induced cell death. In the present study, it was demonstrated for the first time that the copper chelator ammonium tetrathiomolybdate (TM) has several promising effects on cisplatin and HNSCC. First, TM suppressed the ATP7B expression in HNSCC cell lines in vitro, thereby enhancing the accumulation and apoptotic effect of cisplatin in the cancer cells. Next, it was revealed that TM enhanced the antitumor effect of cisplatin in HNSCC cell tumor progression in a mouse model of bone invasion, which is important since HNSCC cells frequently invade to facial bone. Finally, it was demonstrated that TM was able to overcome the cisplatin resistance of a human cancer cell line, A431, via ATP7B depression in vitro.

The process of fracture healing consists of an inflammatory reaction and cartilage and bone tissue reconstruction. The inflammatory cytokine interleukin-1β (IL-1β) signal is an important major factor in fracture healing, whereas its relevance to retinoid receptor (an RAR inverse agonist, which promotes endochondral bone formation) remains unclear. Herein, we investigated the expressions of IL-1β and retinoic acid receptor gamma (RARγ) in a rat fracture model and the effects of IL-1β in the presence of one of several RAR inverse agonists on chondrocytes. An immunohistochemical analysis revealed that IL-1β and RARγ were expressed in chondrocytes at the fracture site in the rat ribs on day 7 post-fracture. In chondrogenic ATDC5 cells, IL-1β decreases the levels of aggrecan and type II collagen but significantly increased the metalloproteinase-13 (Mmp13) mRNA by real-time reverse transcription-polymerase chain reaction (RT-PCR) analysis. An RAR inverse agonist (AGN194310) inhibited IL-1β-stimulated Mmp13 and Ccn2 mRNA in a dose-dependent manner. Phosphorylated extracellular signal regulated-kinases (pERK1/2) and p-p38 mitogen-activated protein kinase (MAPK) were increased time-dependently by IL-1β treatment, and the IL-1β-induced p-p38 MAPK was inhibited by AGN194310. Experimental p38 inhibition led to a drop in the IL-1β-stimulated expressions of Mmp13 and Ccn2 mRNA. MMP13, CCN2, and p-p38 MAPK were expressed in hypertrophic chondrocytes near the invaded vascular endothelial cells. As a whole, these results point to role of the IL-1β via p38 MAPK as important signaling in the regulation of the endochondral bone formation in fracture healing, and to the actions of RAR inverse agonists as potentially relevant modulators of this process.

Bone destruction of maxillary and mandibular bone by invasive oral squamous cell cancer (OSCC) raises various problems in the management of patients, resulting in poor outcomes and survival. However, the mechanism behind bone destruction by OSCC remains unclear. High-mobility group box 1 (HMGB1), a highly conserved ubiquitous nuclear non-histone DNA-binding protein, has been demonstrated to be secreted by aggressive cancers and regulate osteoclastogenesis, a central player during bone destruction. We therefore reasoned that HMGB1 secreted by OSCCs contributes to bone destruction. Our results showed that HMGB1 is produced by human cell lines of OSCC and promotes osteoclastogenesis via up-regulation of the expression of receptor activator of nuclear factor kappa-Β ligand in osteoblasts and osteocytes, and consequently osteoclastic bone destruction in mice. Further, we found that these actions of HMGB1 are mediated via the receptor for advanced glycation end products and toll-like receptors. These findings suggest that HMGB1 of OSCC and its down-stream signal pathways are potential targets for the treatment of bone destruction associated with advanced OSCC.

It is generally accepted that the greater palatine nerve and artery supply the palatal mucosa, gingiva, and glands, but not the bone or tooth adjacent to those tissues. When the bony palate is observed closely, multiple small foramina are seen on the palatal surface of the alveolar process. The authors hypothesized that the greater palatine nerve and artery might supply the maxillary teeth via the foramina on the palatal surface of the alveolar process and the superior alveolar nerve and artery. The authors aimed to investigate the palatal innervation and blood supply of the maxillary teeth. Eight cadaveric maxillae containing most teeth or alveolar sockets were selected. The mean age at the time of death was 82.4 years. The samples were examined with colored water injection, latex injection, microcomputed tomography with contrast dye, gross anatomic dissection, and histologic observation. Through both injection studies and microcomputed tomographic analysis, the authors found that the small foramina on and around the greater palatine groove connected to the alveolar process and tooth sockets. The small foramina in the greater palatine and incisive canal also continued inside the alveolar process and the tooth sockets. The alveolar branches of the greater palatine nerve and artery as well as the nasopalatine nerve and sphenopalatine artery supply maxillary teeth, alveolar bone, and periodontal tissue via the palatal alveolar foramina with superior alveolar nerves and arteries. This knowledge is essential for dentists when administering local anesthetic to the maxillary teeth and performing an osteotomy. Anatomic and dental textbooks should be updated with this new knowledge for better patient care.