Osteosarcoma, the most common primary bone malignancy, occurs most frequently in adolescents with a peak of incidence at 11–15 years. Melatonin, an indole amine hormone, shows a wide range of anticancer activities. The decrease in melatonin levels simultaneously concurs with the increase in bone growth and the peak age distribution of osteosarcoma during puberty, so melatonin has been utilized as an adjunct to chemotherapy to improve the quality of life and clinical outcomes. While a large amount of research has been conducted to understand the complex pleiotropic functions and the molecular and cellular actions elicited by melatonin in various types of cancers, a few review reports have focused on osteosarcoma. Herein, we summarized the anti-osteosarcoma effects of melatonin and its underlying molecular mechanisms to illustrate the known significance of melatonin in osteosarcoma and to address cellular signaling pathways of melatonin in vitro and in animal models. Even in the same kind of osteosarcoma, melatonin has been sparingly investigated to counteract tumor growth, apoptosis, and metastasis through different mechanisms, depending on different cell lines. We highlighted the underlying mechanism of anti-osteosarcoma properties evoked by melatonin, including antioxidant activity, anti-proliferation, induction of apoptosis, and the inhibition of invasion and metastasis. Moreover, we discussed the drug synergy effects of the role of melatonin involved and the method to fortify the anti-cancer effects on osteosarcoma. As a potential therapeutic agent, melatonin is safe for children and adolescents and is a promising candidate for an adjuvant by reinforcing the therapeutic effects and abolishing the unwanted consequences of chemotherapies.

Osteosarcoma, the most prevalent malignant bone tumor in the pediatric age group, is responsible for the great majority of cancer-associated deaths owing to its highly metastatic potential. The anti-metastatic effects of the new curcumin analogue L48H37 in human osteosarcoma are still unknown; hence, we investigated whether L48H37 represses human osteosarcoma cells’ biological behavior of migratory potential and invasive activities and attempted to delve into its underlying mechanisms. L48H37 up to 5 μM inhibited, without cytotoxicity, the motility, migration, and invasion of human osteosarcoma U2OS and MG-63 cells. In U2OS cells, the human protease array revealed an obvious decrease in urokinase plasminogen activator (uPA) expression after L48H37 treatment, and L48H37 actually reduced the level, protein and mRNA expression, and promoter activity of uPA dose-dependently. L48H37 decreased the phosphorylation of STAT3, JAK1, JAK2, and JAK3 in U2OS cells, but did not affect the phosphorylation of ERK, JNK, p38, and Akt. Using colivelin, an activator of STAT3, the L48H37-induced decrease in uPA and migratory potential could be countered as expected. Collectively, L48H37 represses the invasion and migration capabilities of U2OS and MG-63 cells by the suppression of uPA expression and the inhibition of JAK/STAT signaling. These results suggest that L48H37 may be a potential candidate for anti-metastatic treatment of human osteosarcoma.

Osteosarcoma is the most common primary bone malignancy in teenagers and continues to confer a generally poor prognosis due to its highly metastatic potential. Poor solubility in water and instability of curcumin limits its bioavailability for use in the adjuvant situation to improve the prognosis and the long-term survival of patients with osteosarcoma. To further obtain information regarding the apoptosis induced by a new curcumin analog, GO-Y078, in human osteosarcoma cells, flow cytometric analysis, annexin V-FITC/PI apoptosis staining assay, human apoptosis array, and Western blotting were employed. GO-Y078 dose-dependently decreased viabilities of human osteosarcoma U2OS, MG-63, 143B, and Saos-2 cells and induced sub-G1 fraction arrest and apoptosis in U2OS and 143B cells. In addition to the effector caspase 3 and poly adenosine diphosphate-ribose polymerase, GO-Y078 significantly activated both initiators of extrinsic caspase 8 and intrinsic caspase 9, whereas cellular inhibitors of apoptosis 1 (cIAP-1) and X-chromosome-linked IAP (XIAP) in U2OS and 143B cells were significantly repressed. Moreover, GO-Y078 increased phosphorylation of extracellular signal-regulated protein kinases (ERK)1/2, c-Jun N-terminal kinases (JNK)1/2, and p38 in U2OS and 143B cells. Using inhibitors of JNK (JNK-in-8) and p38 (SB203580), GO-Y078′s increases in cleaved caspases 8, 9, and 3 could be expectedly suppressed, but they could not be affected by co-treatment with the ERK inhibitor (U0126). Altogether, GO-Y078 simultaneously induces both apoptotic pathways and cell arrest in U2OS and 143B cells through activating JNK and p38 signaling and repressing IAPs. These findings contribute to a better understanding of the mechanisms responsible for GO-Y078′s apoptotic effects on human osteosarcoma cells.

Due to the poor prognosis of metastatic osteosarcoma, chemotherapy is usually employed in the adjuvant situation to improve the prognosis and the chances of long-term survival. 4-[3,5-Bis(2-chlorobenzylidene)-4-oxo-piperidine-1-yl]-4-oxo-2-butenoic acid (CLEFMA) is a synthetic analog of curcumin and possesses anti-inflammatory and anticancer properties. To further obtain information regarding the apoptotic pathway induced by CLEFMA in osteosarcoma cells, microculture tetrazolium assay, annexin V-FITC/PI apoptosis staining assay, human apoptosis array, and Western blotting were employed. CLEFMA dose-dependently decreased the cell viabilities of human osteosarcoma U2OS and HOS cells and significantly induced apoptosis in human osteosarcoma cells. In addition to the effector caspase 3, CLEFMA significantly activated both extrinsic caspase 8 and intrinsic caspase 9 initiators. Moreover, CLEFMA increased the phosphorylation of extracellular signal-regulated protein kinases (ERK)1/2, c-Jun N-terminal kinases (JNK)1/2 and p38. Using inhibitors of JNK (JNK-in-8) and p38 (SB203580), CLEFMA’s increases of cleaved caspases 3, 8, and 9 could be expectedly suppressed, but they could not be affected by co-treatment with the ERK inhibitor (U0126). Conclusively, CLEFMA activates both extrinsic and intrinsic apoptotic pathways in human osteosarcoma cells through JNK and p38 signaling. These findings contribute to a better understanding of the mechanisms responsible for CLEFMA’s apoptotic effects on human osteosarcoma cells.

Osteosarcoma, which is the most prevalent malignant bone tumor, is responsible for the great majority of bone cancer-associated deaths because of its highly metastatic potential. Although tomatidine is suggested to serve as a chemosensitizer in multidrug-resistant tumors, the anti-metastatic effect of tomatidine in osteosarcoma is still unknown. Here, we tested the hypothesis that tomatidine suppresses migration and invasion, features that are associated with metastatic process in human osteosarcoma cells and also investigate its underlying pathway. Tomatidine, up to 100 μM, without cytotoxicity, inhibited the invasion and migration capabilities of human osteosarcoma U2OS and HOS cells and repressed presenilin 1 (PS-1) expression of U2OS cells. After the knockdown of PS-1, U2OS and HOS cells’ biological behaviors of cellular invasion and migratory potential were significantly reduced. While tomatidine significantly decreased the phosphorylation of c-Raf, mitogen/extracellular signal-regulated kinase (MEK), and extracellular signal-regulated protein kinase (ERK)1/2 in U2OS cells, no obvious influences on p-Jun N-terminal kinase, p38, and Akt, including their phosphorylation, were observed. In ERK 1 silencing U2 OS cells, tomatidine further enhanced the decrease of their migratory potential and invasive activities. We conclude that both PS-1 derived from U2OS and HOS cells and the c-Raf–MEK–ERK pathway contribute to cellular invasion and migration and tomatidine could inhibit the phenomenons. These findings indicate that tomatidine might be a potential candidate for anti-metastasis treatment of human osteosarcoma.

Timosaponin AIII (TSAIII) is a steroidal saponin which demonstrates anti-tumour activities. However, the effect of TSAIII on human osteosarcoma cells remains largely unknown. In this study, we demonstrated that TSAIII exerted a significant inhibitory effect on the distribution of cytoskeletal F-actin and cytoskeletal-related proteins, which contributed to the suppression of cell migration and invasion, without inhibiting cell growth or apoptosis. In the synergistic inhibitory analysis, cotreatment of TSAIII with αVβ3 integrin inhibitor [Cyclo(RGDyK)] or focal adhesion kinase (FAK) inhibitor (PF-573228) exerted greater synergistic inhibitory effects on the expression of Intergin αVβ3/FAK/cofilin axis, thus inhibiting the migration and invasion capacities of human osteosarcoma cells. TSAIII was demonstrated to significantly inhibit the pulmonary metastasis formation of human osteosarcoma cells in vivo in metastasis animal models. These findings reveal the inhibitory effects of TSAIII on the metastasis progression of human osteosarcoma cells and the regulation of integrin-αVβ3-FAK-Src and TESK1/p-cofilin mediated cytoskeletal F-actin pathway. Therefore, TSAIII might represent a novel strategy for the auxiliary treatment of human osteosarcoma cells.