Investigation of anticancer activities of STA-9090 (ganetespib) as a second generation HSP90 inhibitor in Saos-2 osteosarcoma cells

Aykut Özgür

To cite this article: Aykut Özgür (2021): Investigation of anticancer activities of STA-9090 (ganetespib) as a second generation HSP90 inhibitor in Saos-2 osteosarcoma cells, Journal of Chemotherapy, DOI: 10.1080/1120009X.2021.1908650
To link to this article: https://doi.org/10.1080/1120009X.2021.1908650

Anticancer Original Research Paper
Investigation of anticancer activities of STA-9090 (ganetespib) as a second generation HSP90 inhibitor in Saos-2 osteosarcoma cells
Aykut O€ zgu€r
Artova Vocational School, Department of Veterinary Medicine, Laboratory and Veterinary Health Program, Tokat Gaziosmanpas¸a University, Tokat, Turkey

Osteosarcoma is common childhood tumour type of the bone. Chemotherapy is the most important step in treatment of osteosarcoma. Despite advanced diagnosis methods and target specific cancer therapeutics, osteosarcoma has still a high mortality rate and a tendency to metastasize. Therefore, new therapeutic strat- egies are evaluated in osteosarcoma treatment in pre-clinical and clinical studies. In the last ten years, heat shock protein 90 (HSP90) has been important biological target to design target specific cancer drugs. HSP90 play vital roles in proper folding, stabilization and maintenance of oncogenic client proteins in tumorigenesis. Therefore, inhibition of HSP90 has been significant therapeutic aspects in cancer drug design. STA-9090 (ganetespib) is a second generation small molecule HSP90 inhibitor which blocks tumurogenesis in cancer cells. STA-9090 inhibited ATP hydrolysis and protein folding process of HSP90. In this study, STA-9090 decreased Saos-2 cell proliferation and IC50 dose of STA-9090 was found out as 18.71 mM and 10.25 mM at 24 h and 48 h, respectively. STA-9090 inhibited HSP90 ATPase function and disrupted oncogenic client pro- tein folding activity. Also, STA-9090 decreased protein level of the HSP90 in osteosarcoma cells. Expression analysis of osteosarcoma and bone metabolism related genes was performed by RT2 Profiler PCR Array. This study has found the down-regulation of the expression levels of oncogenic genes: DKK1, TWIST1, WNT10B, WNT3A, RANK, RANKL, PTH, FGFR1, FGFR2, LTBP2, IL6, TGFb1, MMP2 and SPARC genes, in
STA-9090 treated Saso-2 cells. Furthermore, expression levels of osteosarcoma related genes, OPG, ERa, ERb, IL15, BMP2 and BMP7, were found to have increased significantly. Biological activities of STA-9090 on Saos-2 cell line show its potential as a target specific drug to inhibit osteosarcoma and its metastasis.
Keywords: Osteosarcoma, Saos-2, HSP90, STA-9090, ganetespib, chemotherapy

1.Introduction
Osteosarcoma (osteogenic sarcoma) is the most common bone cancer type of children and young people. In the world, osteosarcoma is the third common cancer type among children and teens after lymphomas and brain cancer cases. This neo- plasm develops either in femur and tibia bone, and humerus bone in the upper arm. Especially, radi- ation and genetic factors cause formation of osteo- sarcoma, but its molecular mechanisms of the disease are not fully understood yet.1–4 Surgery, chemotherapy and radiotherapy are applied for treatment of patients with osteosarcoma, however; long-term survival rate is not at the desired level.
Correspondence to: Aykut O€ zgu€r Tokat Gaziosmanpas¸a University, Artova Vocational School, Department of Veterinary Medicine, Laboratory and Veterinary Health Program, Tokat, Turkey. Email: [email protected]

Approximately twenty percent of osteosarcoma has ability to spread over lung, brain, and other bones. Survival ratio of osteosarcoma patients are estimated around 60–70% and 20-30% in the non-metastatic and metastatic conditions, respectively. Chemotherapy is still the most effective treatment method for early and advanced stage of osteosarcoma and its metastases.5–7 Therefore, for alternative treatment options, research- ers have been focussed on the development of next generation drugs for treatment of osteosarcoma and its metastases.
Heat shock proteins (HSPs) are highly conserved
protein family which is expressed from prokaryotes to eukaryotic organisms and play crucial roles in folding of nascent proteins, prevention of protein aggregation, protein stabilization and elimination of misfolded proteins. Small HSPs, HSP60, HSP70,

© 2021 Edizioni Scientifi che per l’Informazione su Farmaci e Terapia
DOI 10.1080/1120009X.2021.1908650 Journal of Chemotherapy 2021 1

Figure 1. Structure of STA-9090 and HSP90 NTD. (Structure of HSP90 NTD was extracted from protein data bank (pdb code: 3T0Z)).

HSP90 and HSP100 are identified as five main members of the HSPs according to their molecular weights. Each of HSP members consists of different isoforms which are located in different part of cells.8,9 HSPs perform cellular functions in intracel- lular or extracellular location. Intracellular HSPs exhibit cyto-protective functions for survival of cell, whereas extracellular HSPs modulate immuno- logical and signalling function.10,11 HSPs are up- regulated under cellular and environmental stress conditions (infections, oxidative stress, tumorigen- esis, fever, heavy metals, radiation, heavy metals, etc.) to promote protein homeostasis and block cell death pathways in cells. Especially in cancer cells, these protective mechanisms of the HSPs are associ- ated with either poor prognosis or resistance to chemotherapy for survival of cancer cells. Numerous studies have shown that HSPs are highly expressed in a wide range of human cancer types and involved in almost of all steps of the tumorigenesis. Therefore, understanding signalling pathways of the HSPs are vital to develop next generation diagnosis and treat- ment methods of cancer.8,12–15
HSP90 is an important member of the HSPs pro- tein family and plays essential roles in tumorigenesis. HSP90 is evolutionary conserved protein which is one of the most abundant expressed proteins in nor- mal eukaryotic cells (1-2% of total cellular proteins) and expression level of HSP90 increases up to 4-6% in cancer cells. HSP90 participates in proper folding and stabilization of oncogenic client proteins into their functional conformation in cancer cells.

Therefore, HSP90 has been significant biological tar- get for development of target specific cancer drugs. HSP90 provides sustainability of tumorigenesis and inhibition of HSP90 chaperone activity has been good idea to blocks multiple oncogenic pathways in cancer cells. In this regard, numerous compounds were designed but there are no FDA approved HSP90 inhibitors are available in cancer treat- ment.8,12,16 However, more effective HSP90 inhibitors will get approval from FDA and they will routinely apply to treat various types of cancer in the near future.
STA-9090 (also known as ganetespib) is a potent second generation small-molecule inhibitor of HSP90. Being structurally unrelated to geldanamy- cin and its analogs; STA-9090 selectively binds to HSP90 NTD domain and inhibits ATPase function of HSP90 (Figure 1). STA-9090 has anticancer activities in a wide variety of hematological and solid tumour cell lines. Compared with geldanamy- cin and its derivatives, STA-9090 exhibits more anti-proliferative feature including less hepatotox- icity and favourable safety profile in different can- cer subtypes. In pre-clinical study, STA-9090 significantly disrupted oncogenic cellular processes resulted in inhibition of receptor tyrosine kinases signalling pathways and differential regulation of Cyclins/CDKs, and modulation of apoptotic and cell cycle arrest processes in cancer cells.12,17,18 Clinical phase studies evaluating STA-9090 as a front-line chemotherapeutic for a range of cancer patients including lung, pancreas, squamous,

leukaemia, ovarian, breast, cervical and esophagus have been proceeded (www.clinicaltrials.gov).
The main objective of this study was to investi- gate the HSP90 inhibitory potential of STA-9090 against human osteosarcoma cells. The experimen- tal results indicate that STA-9090 offers consider- able promise as a potent therapeutic candidate to target osteosarcoma.

2.Materials and methods
2.1.Materials
Saos-2 cell lines were supplied from ATCC (American Type Culture Collection, USA). McCoy’s 5 A medium (modified), trypsin–EDTA, phosphate buffer saline (PBS), heat-inactivated foe- tal bovine serum (FBS), penicillin-streptomycin solution, L-glutamine and XTT cell proliferation kit were purchased from Biological Industries Ltd. STA-9090 was from Adooq (A11402). Total RNA isolation kit was from Favorgen Biotech Corp. cDNA synthesis kit obtained from Bioline. Human HSP90 ELISA kit was obtained from YL Biont Ltd. RT2 Profiler PCR Array (PAHS-170ZA) and SYBR Green mastermix (330500) were purchased from Qiagen. Recombinant HSP90 protein was from Sigma Aldrich (385898). RIPA lysis buffer was obtained from Serva. All other chemical reagents were supplied from Merck and Sigma Aldrich.

2.2.Cell culture
Saos-2 cells were cultured in McCoy’s 5 A medium supplemented with 10% FBS and 1% penicillin/strepto- mycin. Cells were cultured in a 75 cm2 flask and incu- bated at 37 ○C in a 5% CO2 humidified atmosphere until cells reached approximately 90% confluence.

2.3.Measurement of cytotoxicity
Cellular viability was determined using the colorimet- ric XTT (2,3-bis-(2-methoxy-4-nitro-5-sulfophenyl)- 2H-tetrazolium-5-carboxanilide) assay according to the manufacturer’s protocol. Saos-2 cells were seeded in 96-well plates (5 × 103 cells/well) and cells were dosed with graded concentrations of STA-9090 for 48 h. STA-9090 was dissolved in dimethyl sulfoxide (DMSO) and diluted with McCoy’s 5 A medium (DMSO concentration was under 0.1%). At the end of the incubation time, STA-9090 containing medium were removed and the cells were washed with PBS solution. Then, 50 ml XTT reagents (in 100 ml medium) was added to each well and cells were incu- bated in an incubator for 4 h. Colour intensity of the wells were measured using microplate ELISA reader at 450 nm. The cell viability was expressed in percent- age related to control and IC50 value of STA-9090 was calculated with GrapPad Prism v7.0 software.
2.4.
ATPase assay
ATPase activity of HSP90 was measured by coupled enzyme assay (pyruvate kinase/lactate dehydrogenase).19,20 This assay is based on meas- urement of the consumption of NADH. Basically, pyruvate and ATP are generated from phosphoe- nolpyruvate (PEP) by pyruvate kinase (PK). Pyruvate is converted to lactate by lactate dehydro- genase (LDH) and NADH is oxidized to NADþ. In this assay, 10 mg/ml pure nucleotide free HSP90 was incubated at 37 ○C for 5 min in 500 ml, pH 7.4 reaction mixture (50 mM HEPES, 50 mM NaCl, 4 mM MgCl2, 0.2 mM NADH, 0.5 mM PEP, 18
unit LDH, 24 unit PK/mL). The IC50 dose of STA- 9090 (10.25 mM) and 0.5 mM ATP were added in the reaction mixture and optical density was meas- ured at 340 nm. The ATPase activity of HSP90 in the absence of STA-9090 assumed 100% ATPase activity and inhibitory effect of STA-9090 were determined proportionally.

2.5.Luciferase aggregation assay
Luciferase aggregation assay was optimized in pre- vious published study.19 In this assay, luciferase was denatured with urea and diluted in pH:7.4 25 mM HEPES, 50 mM KCl, 5 mM MgCl2, 2 mM
ATP, and 5 mM dithiothreitol solution. Then, Saos-2 cell lysate and the IC50 dose of STA-9090 (10.25 mM) were added to the reaction mixture. This assay was applied in the presence of non- hydrolysable ATP (PMP-AMP) and recombinant HSP90. The level of aggregation prevention was calculated spectrometrically at 320 nm.

2.6.Determination of HSP90 protein levels To investigate protein expression level of the HSP90 with STA-9090, commercial sandwich ELISA kit was used according to the manufac- turers’ instructions. After 48 h incubation, STA- 9090 containing medium was removed and Saos-2 cells were washed twice with sterile ice-cold PBS. Cold RIPA lysis buffer was added and incubated during 15 min on ice. Then, cell lysate was trans- ferred to a microcentrifuge tubes with using sterile cell scrapers. The total protein concentrations of the cell lysates were determined by Bradford method. Cell lysates were then collected and stored at —80 ○C to perform ELISA assays.
2.7.Determination of gene expression changes
The gene expression changes produced by the IC50 dose of STA-9090 were determined in Saos-2 cells with RT-PCR. In this experiment, 1 106 cells were seeded into 25 cm2 flask and the cells were

Figure 2. XTT cell proliferation result of STA-9090 on Saos-2 cell line. STA-9090 have significant anticancer activity against Saos-2 cells in time- and dose-dependent manner for 48 h. A) IC50 dose of STA-9090 was calculated as 18.71 mM in the 24 h on Saos-2 cell line. B) IC50 dose of STA-9090 was determined as 10.25 mM in the 24 h on Saos-2 cell line. Vertical bars indi- cate the standard deviation. Values are expressed mean ± SEM (n 5 3).

treated with the IC50 dose of STA-9090 (10.25 mM) for 48 h. After incubation time, total RNA was extracted and cDNA synthesis was performed with commercial kits. Expression changing of the genes associated with osteosarcoma and bone metabolism was examined using human Osteoporosis RT2 Profiler PCR Array. Experiments were performed in Roche Light Cycler 480 RT-PCR and used SYBR green detection with following cycling condition: 1 cycle: 95 ○C for 10 min, 45 cycles: 95 ○C for 15 s. and 60 ○C for 1 min. Relative expression level of tar- get genes was determined using the 2—DDCt method.
2.8.Statistical analysis
Statistical analysis and comparable data groups were assessed using GraphPad Prism 7.0 software by Student’s t-test and one-way ANOVA test. Probability values of p < 0.05 were considered to be statistically significant.

3.Results
3.1.Cell proliferation assay
Antiproliferative activity of STA-9090 was eval- uated on human osteosarcoma cell line (Saos-2) with using colorimetric XTT cell proliferation assay. XTT (2,3-bis-(2-methoxy-4-nitro-5-sulfo- phenyl)-2H-tetrazolium-5-carboxanilide) is a yel- low-colored tetrazolium salt which is cleaved to water soluble and orange-colored formazan salt by mitochondrial dehydrogenase enzymes. The amount of formazan formed is detected at 450 nm wavelength and the formazan product closely cor- relates to the number of metabolically viable cells. To determine the STA-9090 IC50 value, STA-9090 dilutions in range from 100 mM to 1.56 mM were treated for 48 h in Saos-2 cells. STA-9090 exhibited anticancer potential against Saos-2 cells in a time and dose-dependent manner. IC50 values of STA- 9090 on Saos-2 cell line were calculated as

18.71 mM and 10.25 mM at 24 h and 48 h, respect- ively (Figure 2).

3.2.ATPase assay
To detect HSP90 inhibition potential of STA-9090, spectrophotometric ATP hydrolysis experiment was performed. The IC50 dose of STA-9090 (10.25 mM) was incubated with recombinant HSP90 during 48 h. The results indicated that STA-9090 was ser- iously decreased ATP hydrolysis activity of HSP90 (Figure 3). HSP90 requires hydrolysis energy of ATP in order to perform proper folding of onco- genic client proteins. Therefore, measuring of ATPase activity of HSP90 is important parameter for efficiency of the HSP90 inhibitors. The set of experiments demonstrate effectiveness of STA-9090 for HSP90 inhibition.

3.3.Luciferase aggregation assay
Inhibitory effect of STA-9090 on protein folding activity of HSP90 was determined by luciferase aggregation assay. Refolding of luciferase by HSP90 was determined at IC50 dose of STA-9090 (10.25 mM) in osteosarcoma cells at 48 h. In this assay, cell lysate (CL) and non-hydrolysable ATP (nhATP) were used as negative control. The results demonstrated that STA-9090 inhibited luciferase refolding activity in the presence of ATP (Figure 4). This assay supports that STA-9090 is a potent HSP90 inhibitor by inhibiting its ATP hydroly- sis function.

3.4.Determination of HSP90 protein levels To determine alteration of protein level of HSP90, commercial ELISA kit was used in STA-9090- treated Saos-2 cells. ELISA results demonstrated that, STA-9090 decreased protein level of HSP90 compare to control in Saos-2 cells (Figure 5). Protein levels were determined as 41.17 ± 4.25 ng/ml

Figure 3. ATPase activity is vital biological process for chaperone functions of HSP90. ATP hydrolysis assay in the presence of STA-9090 significantly decreased ATP hydrolysis of HSP90. Values are expressed mean ± SEM (n 5 3). m p < 0.05 compared to control.

Figure 4. Luciferase aggregation assay in the presence of STA-9090. In this assay, STA-9090 effectively inhibited refolding of luciferase in the presence of ATP. Values are expressed mean ± SEM (n 5 3). m p < 0.05, mm p < 0.01, mmm p < 0.001 compared to control. ns: not-significant.

Figure 5. Protein levels of HSP90 in STA-9090 treated Saos-2 cells compared with control by ELISA assay. IC50 value of STA-9090 significantly reduced cellular HSP90 level in Saos-2 cell line. Values are expressed mean ± SEM
(n 5 3). m p < 0.05 compared to control.
and 25.95 ± 3.22 ng/ml in STA-9090 treated and control group of Saos-2 cells respectively. STA-

9090 was significantly reduced protein level of HSP90 in osteosarcoma cells.

3.5.PCR array experiment
The alteration of osteosarcoma related gene expres- sions with STA-9090 were determined with human Osteoporosis RT2 Profiler PCR Array in Saos-2 cell line and altered expression profile is shown in Figures 6 and 7. Expression level of genes associ- ated with RANK/RANKL/OPG pathway, WNT/ b-Catenin pathway, cytokines growth factors & receptors, calciotropic hormones & receptors and bone remodelling & BMP signalling were examined in STA-9090-treated Saos-2 cells. When the 48 h gene changes of Saos-2 cells exposed to the IC50 dose of STA-9090 (10.25 mM) were compared with the control group (Figure 6). Particularly, DKK1, TWIST1, WNT10B, WNT3A, RANK, RANKL, PTH, FGFR1, FGFR2, LTBP2, IL6, TGFb1,
MMP2 and SPARC genes are down-regulated and

Figure 6. The summary of gene expression changes in the presence of STA-9090 in Saos-2 cells according to the PCR-array experiment (green boxes: down-regulated genes, red boxes: up-regulated genes).

OPG, ERa, ERb, IL15, BMP2 and BMP7 genes are up-regulated in effect of STA-9090 in osteosar- coma cells. These genes play essential roles in almost all steps of the tumourigenesis of osteosarcoma.

4.Discussion
Osteosarcoma is the most common bone cancer and often occurs in teenagers and young adults. Chemotherapy is the most important step in treatment of osteosarcoma, but patient survival rates are not at the desired levels. Therefore, developments in the determination of molecular mechanisms of osteosar- coma focus on designing next generation molecular targeted treatments for the patients with osteosar- coma.1–3 Cancer cells have high metabolic rate and signalling traffic compared to normal cells, thereby need more HSPs for survival and maintenance of can- cer cells. According to biochemical and pharmaco- logical studies, HSP90 has become key target chaperone protein in cancer drug design. HSP90 are ATP-depended chaperone protein which is ubiqui- tously expressed in healthy cells and its expression level increases up to 2-3 times in tumorigenesis. HSP90 supports tumorigenesis with increased activa- tion of anti-apoptotic and metastatic pathways, and

resistance to chemotherapy in cancer cells. To partici- pate in these cancer-causing signalling pathways, HSP90 assists proper folding and stabilization of oncogenic client proteins (transcriptional factors, ser- ine/threonine kinases, hormone receptors and cell cycle regulators) in cancer cells. HSP90 consists of three conserved domains: 25 kDa N-terminal ATP binding domain (NTD), 55 kDa middle domain (MD), and 10 kDa C-terminal dimerization domain (CTD). NTD contains ATP binding sites and hydrolysis of ATP is essential in protein folding processes. Therefore, designing of new compounds to inhibit of ATPase activity of the HSP90 is intensely investigated in devel- opment target specific cancer drugs.8,12–16
STA-9090 is a new generation HSP90 inhibitor which selectively blocks ATPase activity of HSP90.17 STA-9090 exhibits strong anti-proliferative activity and it is being evaluated in clinical trials against vari- ous cancer types (www.clinicaltrials.gov). To evaluate antiproliferative activity of STA-9090, Saos-2 was selected as in-vitro osteosarcoma model. In this study, STA-9090 effectively decreased proliferation at mM level in Saos-2 osteosarcoma cell line. Cell prolifer- ation assay demonstrated that STA-9090 have signifi- cant anti-proliferative activity against Saos-2 cells in a time and dose-dependent manner.

Figure 7. PCR-array results of STA-9090 in Saos-2 cell line. These genes play key roles in bone metabolism and tumorigen- esis of osteosarcoma. Major osteosarcoma gene expressions show significant difference in effect of STA-9090 compared to
control. Values are expressed mean ± SEM (n 5 3). mp < 0.05, mmp < 0.01, mmmp < 0.001, mmmmp < 0.0001 compared to control. ns:
not-significant.

ELISA assay demonstrated that, STA-9090 decreased cellular protein level of the HSP90 (1.59- fold) in Saos-2 cells. Decreased HSP90 protein expression supports anti-cancer activities of the STA-9090 in this study. Briefly, STA-9090 is prom- ising candidate as target specific HsSP90 inhibitor in treatment of osteosarcoma.
In current study, IC50 dose of STA-9090 decreases ATP hydrolysis and this causes a decrease in chaperone function of HSP90 since ATP hydrolysis is essential process for HSP90

substrate protein folding function. HSP90 ATPse function perturbation by inhibitors may be employed to disrupt cancer causing signalling path- ways by preventing folding of oncogenic client pro- teins in osteosarcoma cells.12 To support ATPase assay, luciferase aggregation assay was performed in osteosarcoma cells. CL served exhibited low luci- ferase refolding activity and the addition of nhATP and recombinant HSP90 to CL did not signifi- cantly increase refolding of luciferase. Nevertheless, the addition of ATP and recombinant HSP90

improved luciferase re-folding activity. The IC50 dose of STA-9090 inhibited luciferase refolding activity in the presence of ATP. Obtained results demonstrated that, STA-9090 exhibited significant anti-proliferative activity in osteosarcoma cells and inhibited ATPase function of HSP90 and perturbs luciferase refolding activity in osteosarcoma cells. HSP90 involves in almost all steps of the tumuro- genesis and inhibition of HSP90 chaperone activity changes gene expression profiles of cancer cells.
According to the cell proliferation, ATPase, luci- ferase activity and ELISA results, STA-9090 exhib- ited effective anti-proliferative activity and inhibited HSP90 chaperone function in Saos-2 cell line. Inhibitory effects of the STA-9090 altered osteosarcoma related gene expressions in Saos-2 cell line. RANKL/RANK/OPG is the key pathway for bone formation and to develop osteosarcoma. RANKL (receptor activator of nuclear factor-jB
ligand, also known as TNFSF11) is expressed by
osteoblasts and stromal stem cells and binds its sig- nalling receptor RANK (receptor activator of nuclear factor-jB, also known as TNFRSF11A). In normal cellular conditions, RANKL mediates osteoclastogenesis and RANK play vital roles in activation and differentiation of osteoclasts. OPG (osteoprotegerin, also known as TNFRSF11B) is expressed by osteoblasts and osteogenic stromal stem cells, and blocks RANK-RANKL interactions. OPG has higher approximately 500-fold affinity than RANK for interaction with RANKL and it inhibits differentiation and formation of osteoclasts and
excessive bone resorption. Hence, the RANKL/OPG ratio is crucial for bone homeostasis.21–23 RANKL and RANK are over-expressed in osteosarcoma cells and RANK/RANKL/OPG signalling pathway is involved in cancer cell proliferation, migration and metastases processes. Up-regulation of RANKL/OPG ratio leads to pathological bone remodelling and tumour growth in osteosarcoma. Aberrant expression of RANKL causes uncontrolled bone destruction mediated by osteoclasts in osteosarcoma cells. Therefore, inhibition of RANKL activity and the decrease in the RANKL/OPG expression ratio have been an important strategy to design target specific drugs for patients with osteosarcoma.24,25 PCR array results indicated that, STA-9090 decreased RANKL and RANK gene expression level while increased OPG level. Furthermore, the ratio of RANKL/OPG was significantly decreased after treatment with STA- 9090 in Saos-2 cells.
Wnt/b-catenin signalling pathway plays signifi- cant roles in pathogenesis of osteosarcoma.26–28 It was found that, STA-9090 decreased expression level of the DKK1, TWIST1, WNT10B and
WNT3A genes in osteosarcoma cells. In the

literature, overexpression of DKK1 and TWIST1 promotes the proliferation, migration, invasion and tumorigenicity of osteosarcoma cells.29,30
Calciotropic hormones and receptors are involved in pathogenesis of osteosarcoma.31,32 According to the results of our study, the significant increase in ERa and ERb in Saos-2 cells that exposed to STA- 9090 indicates that it could be used in the treatment of osteosarcoma. It is stated that ERa and ERb are generally related to inhibition of osteosarcoma growth and metastases in the literature. Unlike nor- mal osteoblast cells, osteosarcoma cells do not express ERa. Osuna and coworkers reported that decitabine (5-Aza-20-deoxycytidine) stimulated expres- sion of ERa and induced inhibition of cell prolifer- ation, metastases and differentiation of osteoblast in 143B osteosarcoma cells.31 Yang et al reported that ERb inhibited cell viability, migration and invasion ability by regulating integrin, IAP, NF-kB/BCL-2 and PI3K/Akt signal pathway in U2-OS osteosar- coma cell line.32 Several studies have shown associ- ation between hyperparathyroidism and bone malignancy.33,34 A high level of parathyroid hormone (PTH) regulates osteosarcoma cells and induces the migration of osteosarcoma cells via hyaluronan metabolism. To prevent overexpression of PTH is an important target to treat patients with osteosar- coma.35 In our study, the significant decrease in PTH gene expression in Saos-2 cells that were exposed to STA-9090 indicates that this compound could be used in the remedy of osteosarcoma.
Numerous experimental studies showed that, cytokines and growth factors are involved in almost all parts of the tumurogenesis.36–38 IL15 plays vital roles in immunotherapy of cancer and activates natural killer (NK) cells in cancer cells. In chemotherapy-resistant and chemotherapy-sensitive osteosarcoma cells, IL15 induces NK cells and cells are eliminated with NK cell–mediated cytolysis.39 STA-9090 was increased IL15 gene expression and the data support the exploitation of NK cells or NK cell–activating agents in patients with high- grade osteosarcoma. Fibroblast growth factor fam- ily of growth factors is essential in a number of biological processes in various types of cancer cells.40,41 Up-regulation of fibroblast growth factor 1 (FGFR1) and fibroblast growth factor 2 (FGFR2) play crucial roles in formation of osteosarcoma and regulation of the development of lung metastases.42,43 Consistent with the literature, the down-regulation of FGFR1 and FGFR2 in the osteosarcoma cells exposed to STA-9090 came out as a positive result in this study. Pre-clinical studies demonstrated that latent transforming growth factor b-binding protein 2 (LTBP2) exhibited an obvious up-regulation and has been consistently connected with poor prognosis in

various cancer cells.44,45 Liang and coworkers reported that, LTBP2 gene expression was regulated negatively by miR-421 that induced apoptosis and inhibited metastasis via targeting LTBP2 in osteosar- coma cells.46 In this study, LTBP2 gene expression was found to be decreased in Saos-2 cells treated with STA-9090. Osteosarcoma cells produce cyto-

Funding
This work was supported by Tokat Gaziosmanpas¸a University, Foundation of Scientific Researches Projects. (Project number: 2019/76).

Note on contributor

kines and growth factor, including interleukin-6 (IL-

Aykut

O€ zgu€r is an assistant professor at Tokat

6) and transforming growth factor-b1 (TGF-b1), which stimulate osteoclastogenesis and tumour growth.47,48 In agreement with the literature, this study consider that the decline in the expression level of the IL-6 and TGF-b1 genes in Saos-2 cells treated with STA-9090 may be inhibit tumurogenesis in osteosarcoma cells.
Bone remodelling and bone morphogenetic pro- teins (BMPs) related signalling pathways are essential to understand pathogenesis of osteosarcoma.49,50 BMPs are identified as the main source of ectopic bone formation but their molecular mechanisms in osteosarcoma is not fully understood yet. Pre-clinical and clinical studies reported that BMP2 and BMP7 exhibit inhibitory effect in proliferation and metasta- ses processes of osteosarcoma cells. BMP7 inhibits telomerase activity in cancer cells.51 In addition, BMP2 increases the tendency for osteosarcoma to undergo apoptosis.52 PCR array results indicated that expression levels of the BMP2 and BMP7 genes were increased in STA-9090 treated Saos-2 cells. Matrix metalloproteinase 2 (MMP2) is an important member of the zinc-dependent endopeptidases which is confirmed to be related with the invasion and metastasis of many cancer types. Therefore, MMP2 has been significant target to develop new generation drugs in cancer treatment.53–55 In this study, MMP2 gene expression was found to be decreased in osteo- sarcoma cells treated with STA-9090. SPARC is iden- tified as bone remodelling related gene which is closely related with pathogenesis of osteosarcoma. SPARC gene is over-expressed in osteosarcoma cells and lung metastasis tends to be induction with SPARC expression.56,57 In this study, SPARC gene showed significant loss of expression in STA-9090 treated osteosarcoma cells.

5.Conclusion
In conclusion, STA-9090 inhibited HSP90 chaper- one activity and significantly decreased osteosar- coma cell proliferation. Moreover, meaningful results have been obtained for osteosarcoma and bone metabolism associated gene expression levels. Obtained in-vitro results can be supported by
advanced in-vivo studies and contribute to treat-
ment approaches.

GaziosmanpaÅY€ a University, Artova Vocational
School, Department of Veterinary Medicine, Laboratory and Veterinary Health Program, Turkey. His primary research field is molecular drug design and protein engineering.

Funding
This work was supported by Tokat Gaziosmanpas¸a University, Foundation of Scientific Researches Projects. (Project number: 2019/76).

ORCID
Aykut O€ zg€ur http://orcid.org/0000-0002-4457-1249

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