MEK inhibition preferentially suppresses anchorage‐independent growth in osteosarcoma cells and decreases tumors in vivo

Abstract

Osteosarcoma is the most common high‐grade malignancy of bone, and novel therapeutic options are urgently required. Previously, we developed mouse osteosarcoma AXT cells that can proliferate both under adherent and nonadherent conditions. Based on metabolite levels, nonadherent conditions were more similar to the in vivo environment than adherent conditions. A drug screen identified MEK inhibitors, including trametinib, that preferentially decreased the viability of nonadherent AXT cells. Trametinib inhibited the cell cycle and induced apoptosis in AXT cells, and both effects were stronger under nonadherent conditions. Trametinib also potently decreased viability in U2OS cells, but its effects were less prominent in MG63 or Saos2 cells. By contrast, MG63 and Saos2 cells were more sensitive to PI3K inhibition than AXT or U2OS cells. Notably, the combination of MAPK/ERK kinase (MEK) and PI3K inhibition synergistically decreased viability in U2OS and AXT cells, but this effect was less pronounced in MG63 or Saos2 cells. Therefore, signal dependence for cell survival and crosstalk between MEK–ERK and PI3K–AKT pathways in osteosarcoma are cell context‐dependent. The activation status of other kinases including CREB varied in a cell context‐dependent manner, which might determine the response to MEK inhibition. A single dose of trametinib was sufficient to decrease the size of the primary tumor and circulating tumor cells in vivo. Moreover, combined administration of trametinib and rapamycin or conventional anticancer drugs further increased antitumor activity. Thus, given optimal biomarkers for predicting its effects, trametinib holds therapeutic potential for the treatment of osteosarcoma.

FKBP11 improves the malignant property of osteosarcoma cells and acts as a prognostic factor of osteosarcoma

“…It has also been reported that MEK inhibition can inhibit osteosarcoma cell growth and thus reduce tumor growth in vivo. According to the study, the growth of osteosarcoma cells was diminished when MEK was inhibited, thus reducing tumor growth in the body [20]. These studies all suggest that the MAPK pathway exerts a weighty influence on the process of osteosarcoma development.…”

Depletion of R270C Mutant p53 in Osteosarcoma Attenuates Cell Growth but Does Not Prevent Invasion and Metastasis In Vivo

“…In addition, tumors derived from AX cells or the p53-knockout cells exhibited the same histological findings, including osteoid and bone formation (data not shown). Given that AX cells express GFP, GFP expression using total RNA extracted from blood or tissues can be used to quantify circulating tumor cells or metastatic lesions, respectively [ 41 ]. Although there were quantitative variations, knockout of p53 did not significantly affect the amount of circulating tumor cells or lung metastasis ( Figure 3 e,f) These findings suggest that the simultaneous presence of the wild-type p53 allele and the R270C mutation did not alter tumor initiation or the progression of osteosarcoma in vivo.…”

“…AXT cells are highly tumorigenic in syngeneic C57BL/6 mice [ 6 , 7 , 8 , 9 , 10 , 41 ]. We examined the role of mutant p53 in tumorigenesis and tumor progression and investigated whether mutant p53 could be a potential target for osteosarcoma.…”

“…Notably, R270C mutant p53 bound in the vicinity of the transcription start sites of Cdkn1a and Mdm2 ( Figure 6 b,c). In addition, the R270C mutant bound to the transcription start sites of Ccnd1 and Trp53 ( Figure 6 d,e), both of which are highly expressed in AXT cells [ 41 ] ( Figure 4 a,b). However, unlike the findings in the AX cells (which contain wild-type p53), treatment of AXT cells with doxorubicin did not increase the expression of Cdkn1a or Mdm2 ( Figure 6 f,g).…”

Chemoresistance-Related Stem Cell Signaling in Osteosarcoma and Its Plausible Contribution to Poor Therapeutic Response: A Discussion That Still Matters

“…Recently, Shimizu et al reported that MEK inhibition with trametinib inhibited the cell cycle and induced apoptosis in non-adherent-growing U2OS cells. Moreover, trametinib decreased the size of primary tumors and circulating tumor cells in an in vivo mouse model [ 124 ].…”