Efficacy of an anti-cancer strategy targeting SET in canine osteosarcoma

Abstract

Osteosarcoma (OSA) is the most common bone tumor in dogs. Protein phosphatase 2A (PP2A), an evolutionary conserved serine/threonine protein phosphatase, is a crucial tumor suppressor. SET is a PP2A inhibitory protein that directly interacts with PP2A and suppresses its phosphatase activity. SET has been reported as a contributor of wide range of human and dog tumor malignancies. However, the role of SET in canine OSA (cOSA) remains unknown. In this study, we investigated the role of SET in cOSA by using 2 cOSA cell lines: POS (primary origin) and HM-POS (metastatic origin). Knockdown (KD) of SET expression was noted to slightly suppress POS cell proliferation only. Furthermore, SET KD effectively suppressed colony formation ability of both POS and HM-POS cells. SET KD was observed to repress ERK1/2, mTOR, E2F1, and NF-κB signaling in HM-POS cells, whereas it inhibited only ERK1/2 signaling in POS. Further, it was observed that SET-targeting drug, FTY720, exerted anti-cancer effects in both POS and HM-POS cells. Moreover, the drug also enhanced the anti-cancer effect of cisplatin. The data suggested that a combination therapy, based on SET targeting drugs and cisplatin, could be a potent strategy for cOSA.KEY WORDS: canine, osteosarcoma, protein phosphatase 2A (PP2A), SET Osteosarcoma (OSA) is a predominant bone tumor diagnosis in dogs. Although, any dog could potentially develop OSA, but dog breeds with body weight above 40 kg are at an increased risk of developing OSA [16,23]. Surgery, limb amputation and limb salvage/sparing, constitutes the first choice of treatment, however, more than 90% of the patients possess micro-metastasis [16,23]. Therefore, adjuvant and non-adjuvant chemotherapy is important to improve the survival rate. In canine OSA (cOSA), adjuvant chemotherapy with cisplatin, carboplatin, or doxorubicin have been associated with increased survival rates over amputation alone [1,20]. OSA is a rare cancer in humans, whereas its incidence rate in dogs is 27-times higher [22], suggesting cOSA as a good model for human disease. The standard adjuvant chemotherapeutic approach in human OSA comprises of a combination of cisplatin, methotrexate, and doxorubicin, and has remained relatively unaltered for years [25,26]. Prognosis in both the species is poor and the survival rate has not improved in decades. Therefore, establishment of novel anti-cancer drugs is urgently required.Protein phosphatase 2A (PP2A) is an evolutionally conserved serine/threonine phosphatase that suppresses the activity of multiple intracellular signals such as Akt, ERK1/2, and mTOR signaling which regulates cancer cell growth, stemness, and survival [12,18,19]. PP2A is reported to negatively regulate the activity of transcription factors such as c-Myc, E2F1, and NF-κB, that mediates tumor cell stemness and the cell cycle [9,12,19]. Inhibition of PP2A activity is required for tumor transformation and increased expression of endogenous PP2A inhibitory proteins (such as SET, CIP2A, and PME-1) contributes to lower PP2A activity in cance...

Review: NF-kB activation in canine cancer

“…99,100 As previously stated, increased SET protein levels in canine osteosarcoma positively regulate NF-kB signaling secondary to decreased PP2A activity. 38,86…”

Epigenetic Mechanisms in Canine Cancer

“…Inhibition of SET methyltransferase by shRNA and FTY720, reported to directly interact with SET proteins, suppressed cell proliferation, colony formation, and in vivo tumor growth of canine mammary and osteosarcoma cell lines. Furthermore, SET knockdown repressed mTOR and NF-kB signaling in both types of canine cancer (223,224). Using BB-Cl-Amidine (BB-CLA) to inhibit protein-arginine deiminases (PADs) resulted in the decrease of viability and tumorigenicity of FIGURE 3 | Effects of some alternative epigenetic inhibitors in canine mammary cancer cells.…”

Characterizing the metabolic role of STAT3 in canine osteosarcoma

“…Macroscopic metastases are extremely refractory to treatment, including chemotherapy and kinase inhibitors (i.e., toceranib) necessitating the identification of novel targets for therapeutic intervention 1,2 . Consequently, increased emphasis has been placed on targeting recently defined aberrant signalling pathways in canine OS, such as those involving MAPK and PI3K/mTOR, among others 3–9 …”

“…1,2 Consequently, increased emphasis has been placed on targeting recently defined aberrant signalling pathways in canine OS, such as those involving MAPK and PI3K/mTOR, among others. [3][4][5][6][7][8][9] Signal transducer and activator of transcription 3 (STAT3) is a transcription factor that mediates a number of critical biologic processes, including cellular differentiation and proliferation, cell cycle progression, inflammation and apoptosis by transmitting cytokine signals through gp130. 10,11 These activities are traditionally associated with STAT3 phosphorylation on conserved tyrosine 705 (Y705) residues, with subsequent homodimerization and nuclear translocation.…”

“…1 , 2 Consequently, increased emphasis has been placed on targeting recently defined aberrant signalling pathways in canine OS, such as those involving MAPK and PI3K/mTOR, among others. 3 , 4 , 5 , 6 , 7 , 8 , 9 …”