In Situ Analysis of mTORC1/C2 and Metabolism-Related Proteins in Pediatric Osteosarcoma

Abstract

Activation of the mTOR pathway has been observed in osteosarcoma, however the inhibition of mammalian target of rapamycin (mTOR) complex 1 has had limited results in osteosarcoma treatment. Certain metabolic pathways can be altered by mTOR activation, which can affect survival. Our aim was to characterize the mTOR profile and certain metabolic alterations in pediatric osteosarcoma to determine the interactions between the mTOR pathway and metabolic pathways. We performed immunohistochemistry on 28 samples to analyze the expression of mTOR complexes such as phospho-mTOR (pmTOR), phosphorylated ribosomal S6 (pS6), and rapamycin-insensitive companion of mTOR (rictor). To characterize metabolic pathway markers, we investigated the expression of phosphofructokinase (PFK), lactate dehydrogenase-A (LDHA), β-F1-ATPase (ATPB), glucose-6-phosphate dehydrogenase (G6PDH), glutaminase (GLS), fatty acid synthetase (FASN), and carnitin-O-palmitoyltransferase-1 (CPT1A). In total, 61% of the cases showed low mTOR activity, but higher pmTOR expression was associated with poor histological response to chemotherapy and osteoblastic subtype. Rictor expression was higher in metastatic disease and older age at the time of diagnosis. Our findings suggest the importance of the Warburg-effect, pentose-phosphate pathway, glutamine demand, and fatty-acid beta oxidation in osteosarcoma cells. mTOR activation is linked to several metabolic pathways. We suggest performing a detailed investigation of the mTOR profile before considering mTORC1 inhibitor therapy. Our findings highlight that targeting certain metabolic pathways could be an alternative therapeutic approach.

Metabolic reprogramming in osteosarcoma

“…The improvement of the fatty acid synthesis pathway and the MVA metabolism favor rapid growth and metastasis in OS. Expression of rate‐limiting enzymes in β ‐oxidation of fatty acid is positive in approximately 90% of OS cases 68 . The PPP is a primary source of NADPH, and SSP, glutamine metabolism, FAO, and the TCA cycle can also directly or indirectly provide NADPH for anabolic reactions and redox homeostasis offering reducing capacity 139 .…”

“…Upregulation of G6PD is present in various tumors, and increased G6PD expression leads to increased biosynthesis of nucleotides and lipids necessary for cell division and proliferation, favoring tumor cell proliferation 66,67 . One study found that approximately 70% of OS samples showed high G6PD expression 68 . Wang et al.…”

“…GS and GLS are therapeutic targets for cancer 84 . The growth of OS cells depends on glutamine 68,85–87 . Anso and his colleagues found that MYC‐induced glutamine metabolism was essential for MYC‐dependent proliferation and survival in OS cells 86 .…”

“…66,67 One study found that approximately 70% of OS samples showed high G6PD expression. 68 Wang et al found that LncR-OR3A4 affected the proliferation of OS cells by regulating the miR-1207-5p/G6PD axis. 69 The PPP is a major source of Amino acids are involved in biosynthesis and energy supply and help maintain redox homeostasis.…”

“…84 The growth of OS cells depends on glutamine. 68,[85][86][87] Anso and his colleagues found that MYC-induced glutamine metabolism was essential for MYC-dependent proliferation and survival in OS cells. 86 The amino acid transporter protein ASCT2 is considered the major glutamine transporter protein, and ASCT2 is expressed overly in various cancers and is strongly associated with poor prognosis.…”