Expression of c-kit Protein and Mutational Status of the c-kit Gene in Osteosarcoma and Their Clinicopathological Significance

Tyrosine kinase inhibitors in osteosarcoma: Adapting treatment strategiesa

Osteosarcoma (OS) is an aggressive primary bone malignancy that metastasizes rapidly. The standard of care has changed little over the previous four decades, and survival rates have plateaued. In this context, tyrosine kinase inhibitors (TKIs) emerge as potential treatments. A literature search was conducted to collect data related to receptor tyrosine kinase genetic alterations and expression in OS specimens. Gene amplification and protein expression of these receptors were linked to prognosis and tumor behavior. Relevant TKIs were evaluated as monotherapies and as parts of combination therapies. Certain TKIs, such as apatinib, regorafenib, and cabozantinib, present a potential therapeutic avenue for OS patients, especially when combined with chemotherapy. Producing long-lasting responses and enhancing quality of life remain key goals in OS treatment. To this effect, optimizing the use of TKIs by identifying biomarkers predictive of response and assessing promising TKIs in larger-scale trials to validate the efficacy and safety outcomes relative to these drugs reported in phase II clinical trials. To this effect, it is necessary to identify biomarkers predictive of response to TKIs in larger-scale trials and to validate the efficacy and safety of these drugs reported in phase II clinical trials.

New challenges in integrated diagnosis by imaging and osteo-immunology in bone lesions

INTRODUCTION

High-resolution imaging is the gold standard to measure the functional and biological features of bone lesions. Imaging markers have allowed the characterization both of tumour heterogeneity and metabolic data. Besides, ongoing studies are evaluating a combined use of 'imaging markers', such as SUVs, MATV, TLG, ADC from PET and MRI techniques respectively, and several 'biomarkers' spanning from chemokine immune-modulators, such as PD-1, RANK/RANKL, CXCR4/CXCL12 to transcription factors, such as TP53, RB1, MDM2, RUNX family, EZH2, YY1, MAD2. Osteoimmunology may improve diagnosis and prognosis leading to precision medicine in bone lesion treatment. Areas covered: We investigated modalities (molecular and imaging approach) useful to identify bone lesions deriving both from primary bone tumours and from osteotropic tumours, which have a higher incidence, prevalence and prognosis. Here, we summarized the recent advances in imaging techniques and osteoimmunology biomarkers which could play a pivotal role in personalized treatment. Expert commentary: Although imaging and molecular integration could allow both early diagnosis and stratification of cancer prognosis, large scale clinical trials will be necessary to translate pilot studies in the current clinical setting.

ABBREVIATIONS

ADC: apparent diffusion coefficient; ALCAM: Activated Leukocyte Cell Adhesion Molecule; ALP: Alkaline phosphatases; BC: Breast cancer; BSAP: B-Cell Lineage Specific Activator; BSAP: bone-specific alkaline phosphatase; BSP: bone sialoprotein; CRIP1: cysteine-rich intestinal protein 1; CD44: cluster of differentiation 44; CT: computed tomography; CXCL12: C-X-C motif ligand 12; CXCR4: C-X-C C-X-C chemokine receptor type 4; CTLA-4: Cytotoxic T-lymphocyte antigen 4; CTX-1: C-terminal end of the telopeptide of type I collagen; DC: dendritic cell; DWI: Diffusion-weighted MR image; EMT: mesenchymal transition; ET-1: endothelin-1; FDA: Food and Drug Administration; FDG: ¹⁸F-2-fluoro-2-deoxy-D-glucose; FGF: fibroblast growth factor; FOXC2: forkhead box protein C2: HK-2: hexokinase-2; ICTP: carboxyterminal cross-linked telopeptide of type I collagen; IGF-1R: Insulin Like Growth Factor 1 Receptor; ILC: innate lymphocytes cells; LC: lung cancer; IL-1: interleukin-1; LYVE1: lymphatic vessel endothelial hyaluronic acid receptor 1; MAD2: mitotic arrest deficient 2; MATV: metabolically active tumour volume; M-CSF: macrophage colony stimulating factor; MM: multiple myeloma; MIP1a: macrophage inflammatory protein 1a; MSC: mesenchymal stem cell; MRI: magnetic resonance imaging; PC: prostate cancer; NRP2: neuropilin 2; OPG: osteoprotogerin; PDGF: platelet-derived growth factor; PD-1: Programmed Cell Death 1; PET: positron emission tomography; PINP: procollagen type I N propeptide; PROX1: prospero homeobox protein 1; PSA: Prostate-specific antigen; PTH: parathyroid hormone; RANK: Receptor activator of NF-kB ligand; RECK: Reversion-inducing-cysteine-rich protein; SEMAs: semaphorins; SPECT: single photon computed tomography; SUV: standard uptake value; TLG: total lesion glycolysis; TP53: tumour protein 53; VCAM-1: vascular endothelial molecule-1; VOI: volume of interest; YY1: Yin Yang 1.

Biomarkers of Osteosarcoma, Chondrosarcoma, and Ewing Sarcoma

Osteosarcoma is the most frequent malignant bone neoplasm, followed by chondrosarcoma and Ewing sarcoma. The diagnosis of bone neoplasms is generally made through histological evaluation of a biopsy. Clinical and radiological features are also important in aiding diagnosis and to complete the staging of bone cancer. In addition to these, there are several non-specific serological or specific molecular markers for bone neoplasms. In bone tumors, molecular markers increase the accuracy of the diagnosis and assist in subtyping bone tumors. Here, we review these markers and discuss their role in the diagnosis and prognosis of the three most frequent malignant bone neoplasms, namely osteosarcoma, chondrosarcoma, and Ewing sarcoma.

Stem cell growth factor receptor in canine vs. feline osteosarcomas

Osteosarcoma is considered the most common bone cancer in cats and dogs, with cats having a much better prognosis than dogs, since the great majority of dogs with osteosarcoma develop distant metastases. In search of a factor possibly contributing to this disparity, the stem cell growth factor receptor KIT was targeted, and the messenger (m)RNA and protein expression levels of KIT were compared in canine vs. feline osteosarcomas, as well as in normal bone. The mRNA expression of KIT was quantified by reverse transcription-quantitative polymerase chain reaction, and was observed to be significantly higher in canine (n=14) than in feline (n=5) osteosarcoma samples (P<0.001). KIT protein expression was evaluated by immunohistochemistry, which revealed that 21% of canine osteosarcoma samples did not exhibit KIT staining in their neoplastic cells, while in 14% of samples, a score of 1 (<10% positive tumour cells) was observed, and in 50% and 14% of samples, a score of 2 (10–50% positivity) and 3 (>50% positivity), respectively, was observed. By contrast, the cancer cells of all the feline bone tumour samples analysed were entirely negative for KIT. Notably, canine and feline osteocytes of healthy bone tissue lacked any KIT expression. These results could be the first evidence that KIT may be involved in the higher aggressiveness of canine osteosarcoma compared with feline osteosarcoma.

Cisplatin-resistant osteosarcoma cells possess cancer stem cell properties in a mouse model

Osteosarcoma is the most common malignancy of the bones, and although advances in chemotherapy and surgery had been achieved in recent years, the long-term survival rate has reached a plateau. The main reason for this is the aggressive malignant potential and poor response of the disease to chemotherapy. However, several studies have found that tumor resistance is associated with cancer stem cells (CSCs). To address this issue, in the present study, osteosarcoma cells were treated with specially designated concentrations of cisplatin (CDDP) in a mouse model. Hematoxylin and eosin staining analyses were performed to assess tissue structure, in vivo passaging and CDDP treatment. Drug resistance genes and well-established stemness genes were detected by quantitative polymerase chain reaction. A serum-starved sphere formation assay was adopted to evaluate the ability to generate spherical clones and flow cytometry as used to test the expression of the cluster of differentiation 117 and Stro-1 surface markers, known as markers of CSCs. It was found that CDDP could induce an effect of resistance in the osteosarcoma cells, which possessed cancer stem CSC properties, as shown by the elevated expression of CSC marker genes and the higher expression of the cluster of differentiation 117 and Stro-1 surface markers. Moreover, the cells that dissociated from the tumor tissues exhibited an increased ability to form sarcospheres. The results of this study provided a significant correlation between resistance and CSCs, and revealed a clue indicating that osteosarcoma recurrence is likely to be associated with CSCs.

Targeting receptor tyrosine kinases in osteosarcoma and Ewing sarcoma: current hurdles and future perspectives

Osteosarcoma (OS) and Ewing sarcoma (ES) are the two most common types of primary bone cancer, which mainly affect children and young adults. Despite intensive multi-modal treatment, the survival of both OS and ES has not improved much during the last decades and new therapeutic options are awaited. One promising approach is the specific targeting of transmembrane receptor tyrosine kinases (RTKs) implicated in these types of bone cancer. However, despite encouraging in vitro and in vivo results, apart from intriguing results of Insulin-like Growth Factor-1 Receptor (IGF-1R) antibodies in ES, clinical studies are limited or disappointing. Primary resistance to RTK inhibitors is frequently observed in OS and ES patients, and even patients that initially respond well eventually develop acquired resistance. There are, however, a few remarks to make concerning the current set-up of clinical trials and about strategies to improve RTK-based treatments in OS and ES. This review provides an overview concerning current RTK-mediated therapies in OS and ES and discusses the problems observed in the clinic. More importantly, we describe several strategies to overcome resistance to RTK inhibitors which may significantly improve outcome of OS and ES patients.

CD117 and Stro-1 identify osteosarcoma tumor-initiating cells associated with metastasis and drug resistance

Emerging evidence indicates the presence of tumor-initiating cells (TIC) or cancer stem cells in osteosarcoma. However, no study has shown specific markers to identify osteosarcoma TICs with in vivo tumor formation ability. Additionally, there has been a lack of investigations gauging the contribution of osteosarcoma TICs to metastatic and drug-resistant properties. In this study, we have identified mouse and human osteosarcoma TICs using mesenchymal stem cell markers CD117 and Stro-1. These markers were preferentially expressed in spheres and doxorubicin-resistant cells. Both mouse and human cells expressing these markers were sorted and analyzed for their abilities of tumor formation with as few as 200 cells, self-renewability, multipotency, drug resistance, metastatic potential, and enrichment of a metastasis-associated marker (CXCR4) and a drug resistance marker (ABCG2). CD117(+)Stro-1(+) cells efficiently formed serially transplantable tumors, whereas CD117(-)Stro-1(-) cells rarely initiated tumors. On orthotopic injections, CD117(+)Stro-1(+ )cell-derived tumors metastasized at a high frequency. Further, CD117(+)Stro-1(+) cells showed high invasive and drug-resistant properties and were efficiently enriched for CXCR4 (20-90%) and ABCG2 (60-90%). These results suggest possible mechanisms for the high metastatic and drug-resistant properties of osteosarcoma TICs. In summary, CD117 and Stro-1 identify osteosarcoma TICs associated with the most lethal characteristics of the disease-metastasis and drug resistance-and these markers offer candidates for TIC-targeted drug delivery aimed at eradicating osteosarcoma.

Prognostic markers in osteosarcoma

Osteosarcoma is the most common bone tumor seen in the pediatric and adolescent age group. Survival rates in osteosarcoma have improved considerably from 20 to 65% since the 1980s with the advent of multiagent chemotherapy. Further improvement in survival has not been achieved owing to lack of well-validated prognostic markers and better therapeutic agents. Markers involved with angiogenesis, cell adhesion, apoptosis and cell cycle have been shown recently to play an important role in osteosarcoma growth, differentiation and metastasis. Over the coming years, the new molecular markers may be able not only to prognosticate osteosarcoma patients at baseline but also to serve as therapeutic targets and thereby improve survival rates further. Noninvasive imaging methods in osteosarcoma such as PET-CT and dynamic contrast enhanced and diffusion-weighted MRI hold a lot of promise as surrogate methods for prognostication and response assessment.

c-kit (CD117) expression in human tumors and its prognostic value: an immunohistochemical analysis

c-kit functions as a tyrosine kinase receptor and represents a target for small molecule kinase inhibitors. The expression pattern for c-kit was studied in different human tumor types to their correlation with prognosis. Paraffin-embedded tumor tissues from 282 patients were analyzed immunohistochemically for c-kit expression. Survival and follow-up data were available from 192/282 (68%) patients. c-kit immunopositivity was found in 62/282 (22%) cases. c-kit expression was found in 14/83 (17%) colorectal cancers, in 13/62 (21%) breast cancers, in 7/20 sarcomas (35%), in 5/14 (36%) renal cell carcinomas, in 2/12 ovarian cancers (17%) and in 2/12 (17%) hepatocellular carcinomas. We found no significant correlation between c-kit expression and prognosis although a trend to a worse prognosis in patients with c-kit positive tumors could be observed. Expression of c-kit was found in tumor samples with varying intensities and infrequently.