Expression of platelet-derived growth factor and its receptors in spontaneous canine hemangiosarcoma and cutaneous hemangioma

Immunohistochemical Expression of Platelet-Derived Growth Factor Receptor β (PDGFR-β) in Canine Cutaneous Peripheral Nerve Sheath Tumors: A Preliminary Study

Simple Summary

The peripheral nerve sheath tumors are relatively common neoplasms, belong to the soft tissue sarcomas group, and are poorly investigated in veterinary medicine; the diagnosis is complex, and therapeutic options are limited. The platelet-derived growth factor receptors, namely the β subunit, are an important class of tyrosine kinase receptors that can be activated by genetic alterations and contribute to the process of carcinogenesis, so the inhibition of this receptor is an important therapeutic target. Using the immunohistochemical technique, this study aims to evaluate the expression of this receptor in 19 samples, 10 malignant and 9 benign tumors. The results showed that the majority of benign tumors, about 67% of cases, expressed the receptor in less than 25% of neoplastic cells and, in 80% cases of malignant tumors, the receptor was expressed in more than 25% of neoplastic cells. It was also found that, in the larger tumors, the expression of this receptor was significantly higher. With these findings it seems reasonable to speculate that the drugs able to inhibit this receptor, such as toceranib, may be considered in the therapeutic approach of these tumors.

Abstract

As in humans, the prevalence of tumors in companion animals is increasing dramatically and there is a strong need for research on new pharmacological agents particularly for the treatment of those tumors that are resistant to conventional chemotherapy agents such as soft tissue sarcomas (STS). Because malignant (MPNST) and benign peripheral nerve sheath tumors (BPNST) are relatively common STS in dogs, the aim of this retrospective study was to evaluate the immunohistochemical (IHC) expression of PDGFR-β, contributing to its characterization as a potential target for their treatment. A total of 19 samples were included, 9 histologically classified as benign and the other 10 as malignant. The results showed diffuse immunoexpression in the cytoplasm of neoplastic cells. Six (66.7%) BPNST expressed the receptor in less than 25% of neoplastic cells and only three (33.3%) exhibited labelling in more than 25% of neoplastic cells. In contrast, all MPNST expressed PDGFR-β, and in 8 (80%) of these samples, the receptor was expressed in more than 25% of neoplastic cells, and only 2 (20%) cases expressed the receptor in less than 25% of neoplastic cells. PDGFR-β expression was significantly higher in MPNST and larger tumors, suggesting that drugs able to inhibit the activity of this tyrosine kinase receptor, such as toceranib, may be considered in the approach of unresectable tumors and/or in the context of adjuvant or neoadjuvant therapies.

An Update on Molecular Pathways Regulating Vasculogenic Mimicry in Human Osteosarcoma and Their Role in Canine Oncology

Canine tumors are valuable comparative models for human counterparts, especially to explore novel biomarkers and to understand pathways and processes involved in metastasis. Vasculogenic mimicry (VM) is a unique property of malignant cancer cells which promote metastasis. Thus, it represents an opportunity to investigate both the molecular mechanisms and the therapeutic targets of a crucial phenotypic malignant switch. Although this biological process has been largely investigated in different human cancer types, including osteosarcoma, it is still largely unknown in veterinary pathology, where it has been mainly explored in canine mammary tumors. The presence of VM in human osteosarcoma is associated with poor clinical outcome, reduced patient survival, and increased risk of metastasis and it shares the main pathways involved in other type of human tumors. This review illustrates the main findings concerning the VM process in human osteosarcoma, search for the related current knowledge in canine pathology and oncology, and potential involvement of multiple pathways in VM formation, in order to provide a basis for future investigations on VM in canine tumors.

Antiproliferative effects of masitinib and imatinib against canine oral fibrosarcoma in vitro

Background

Canine oral fibrosarcoma (COF) is one of the most common oral tumors in dogs and carries a guarded prognosis due to a lack of effective systemic therapeutic options. Mastinib and imatinib are two commonly used tyrosine kinase inhibitors (TKIs) in veterinary oncology but their potential efficacy against COF is uncharacterized. To begin investigating the rationale for use of these TKIs against COF, the present study tested for the presence TKI targets PDGFR-α, PDGFR-β, Kit, and VEGFR-2 and examined the in vitro effects on cell viability after TKI treatment alone or with doxorubicin.

Immunohistochemistry for PDGFR-α, PDGFR-β, Kit, and VEGFR-2 was performed in 6 COF tumor biopsies. Presence of these same receptors within 2 COF cell lines was probed by reverse transcription-polymerase chain reaction and, for those with mRNA detected, confirmed via western blot. Effects on cell viability were assessed using an MTS assay after masitinib or imatinib treatment alone (0-100 μM), or in combination with doxorubicin (0-3000 nM doxorubicin). Anti-PDGFRB siRNA knockdown was performed and the effect on cell viability quantified.

Results

Expression of the TKI targets evaluated was similar between the 2 COF cell lines and the 6 COF tumor biopsies: PDGFR-α and PDGFR-β were detected in neoplastic cells from most COF tumor biopsies (5/6 and 6/6, respectively) and were present in both COF cell lines; KIT and KDR were not detected in any sample. Masitinib and imatinib IC50 values ranged from 7.9–33.4 μM, depending on the specific TKI and cell line tested. The addition of doxorubicin resulted in synergistic cytotoxicity with both TKIs. Anti-PDGFRB siRNA transfection reduced PDGFR-β protein expression by 77 % and 67 % and reduced cell viability by 24 % (p < 0.0001) and 28 % (0 = 0.0003) in the two cell lines, respectively.

Conclusions

These results provide rationale for further investigation into the use of TKIs, possibly in combination with doxorubicin, as treatment options for COF.

Targeting the PDGF signaling pathway in tumor treatment

Platelet-derived growth factor (PDGF) isoforms and PDGF receptors have important functions in the regulation of growth and survival of certain cell types during embryonal development and e.g. tissue repair in the adult. Overactivity of PDGF receptor signaling, by overexpression or mutational events, may drive tumor cell growth. In addition, pericytes of the vasculature and fibroblasts and myofibroblasts of the stroma of solid tumors express PDGF receptors, and PDGF stimulation of such cells promotes tumorigenesis. Inhibition of PDGF receptor signaling has proven to useful for the treatment of patients with certain rare tumors. Whether treatment with PDGF/PDGF receptor antagonists will be beneficial for more common malignancies is the subject for ongoing studies.