Evaluation of expression and function of vascular endothelial growth factor receptor 2, platelet derived growth factor receptors-alpha and -beta, KIT, and RET in canine apocrine gland anal sac adenocarcinoma and thyroid carcinoma

Radiotherapy for Canine Apocrine Gland Anal Sac Adenocarcinoma: Survival Outcomes and Side Effects of a Palliative Treatment Protocol of 20 Gy in Five Consecutive Fractions

This research aims to evaluate the outcomes of a radiotherapy protocol, consisting of five fractions of 4 Gy each, resulting in a total dose of 20 Gy for apocrine gland anal sac tumors and local lymph nodes in canines. This protocol was assessed as a palliative treatment for macroscopic tumors alone, or in combination with additional therapies under different scenarios. Medical records from fifty canine patients met the inclusion criteria and were divided into different treatment groups: radiotherapy alone (n = 22, 44%), radiotherapy with chemotherapy or targeted therapy with toceranib (n = 18, 36%), surgery with radiotherapy (n = 5, 10%), and surgery with radiotherapy and chemotherapy or targeted therapy with toceranib (n = 5, 10%). Patients who received radiotherapy alone had a median survival time of 384 days (95% CI 198-569) and 628 days (95% CI 579-676) for RT + additional therapies. The median time to progression for patients with radiotherapy alone was 337 days (95% CI 282-391 days), and 402 days (95% CI 286-517 days) for radiotherapy plus additional treatments. Acute side effects were mild, with the majority having diarrhea (61%), and only one patient developed grade III late effects VRTOG v2 classification; however, this happened 22 months after the first radiotherapy protocol after re-irradiation. The results demonstrate that radiotherapy alone under this protocol provided a comparable median time to progression vs. radiotherapy plus additional treatments while maintaining acceptable side effects. The combination of this protocol with other treatment modalities offers attractive results for local disease control and survival while maintaining acceptable toxicities. Overall, these findings contribute to the growing evidence supporting the role of radiotherapy in managing apocrine gland anal sac adenocarcinoma in dogs.

Retrospective evaluation of toceranib phosphate (Palladia) use in the treatment of feline pancreatic carcinoma

Objective

To retrospectively assess the biological response in cats with pancreatic carcinoma treated with toceranib phosphate.

Animals

Twenty-six client-owned cats.

Procedure

Patient information from multiple institutions was solicited via an emailed REDCap survey. For inclusion, cats were required to have a confirmed diagnosis of exocrine pancreatic carcinoma either by histopathology, cytology, or both; to have received treatment with toceranib phosphate; and to have adequate follow-up data for analysis.

Results

Twenty cats were treated for gross disease and 6 for microscopic disease/incomplete margins. Clinical benefit (complete response, partial response, or stable disease ≥ 10 wk) was observed in 9/20 cats treated in the gross disease setting (45%; complete response: n = 1, stable disease: n = 8). The remaining 11 cats with gross disease did not respond to toceranib phosphate. In the cats with microscopic disease, response was mixed. The median survival time for all cats was 97 d (range: 1 to 1666 d).

Conclusion

Toceranib phosphate was well-tolerated and provided modest clinical benefit to a subset of cats treated.

Clinical relevance

Although feline exocrine pancreatic carcinoma continues to be a challenging disease to treat, toceranib phosphate appeared to provide potential clinical benefit.

A Scoping Review on Tyrosine Kinase Inhibitors in Cats: Current Evidence and Future Directions

Tyrosine kinase inhibitors (TKIs) have become invaluable in the treatment of human and canine malignancies, but their role in feline oncology is less defined. While toceranib phosphate and masitinib mesylate are licensed for use in dogs, no TKI is yet approved for cats. This review systematically maps the research conducted on the expression of tyrosine kinases in neoplastic and non-neoplastic domestic feline tissues, as well as the in vitro/in vivo use of TKIs in domestic cats. We identify and discuss knowledge gaps and speculate on the further research and potential indications for TKI use in cats. A comprehensive search of three electronic databases and relevant paper reference lists identified 139 studies meeting the inclusion criteria. The most commonly identified tumors were mast cell tumors (MCTs), mammary and squamous cell carcinomas and injection-site sarcomas. Based on the current literature, toceranib phosphate appears to be the most efficacious TKI in cats, especially against MCTs. Exploring the clinical use of TKIs in mammary carcinomas holds promise. Despite the progress, currently, the evidence falls short, underscoring the need for further research to discover new indications in feline oncology and to bridge the knowledge gaps between human and feline medicine.

Immunolabelling of c-KIT and CAM5.2 in Canine Anal Sac Gland Adenocarcinoma

The role of c-KIT receptor in anal sac gland adenocarcinoma (ASGAC) is unclear despite its importance in the development of tumours. In this preliminary study, the expression of c-KIT was investigated in rarely observed canine ASGAC. The potential use of CAM5.2 in distinguishing ASGAC from perianal gland tumours was also evaluated. ASGAC was diagnosed in five out of 25 examined perianal tumours. By immunohistochemistry, cytosolic (abnormal) c-KIT expression was seen in four of the five cases. CAM5.2 immunoreactivity was detected in neoplastic cells of all ASGAC cases examined, whereas it was not evident in any case of perianal gland tumour. The findings suggest that c-KIT expression and its cellular localization may be important in the oncogenesis of ASGAC and CAM5.2 can be used to distinguish between ASGAC and perianal gland tumours.

Pilot study evaluating the tolerability of a 3 Gy × 10 daily fraction 3D-conformal palliative radiation therapy protocol plus toceranib for the treatment of measurable carcinomas in the dog

The use of radiation therapy in conjunction with small molecule inhibitors is an appealing treatment combination for non-resectable carcinomas, which tend to be locally invasive with variable risk of locoregional metastasis. This prospective, pilot study aimed to evaluate the tolerability and adverse event profile of concurrent toceranib and palliative-intent radiation therapy (PRT) in dogs with measurable carcinoma and to secondarily evaluate short-term measurable tumor response. Fifteen dogs with measurable carcinoma received toceranib and 3D-conformal PRT in 3 Gy/fraction for 10 daily fractions. Adverse events were graded using standard schemes and tolerability was followed via quality-of-life questionnaires during the 12-week treatment period. Thirteen dogs (87%) experienced acute radiation toxicity, graded as severe in three dogs. All dogs experienced toceranib toxicity, graded as severe in one dog. Seven dogs (47%) completed the 12-week study protocol; four were withdrawn due to toxicity and/or associated poor quality of life and four developed progressive disease. Based on these preliminary results, this 3D-conformal chemoradiation protocol should be considered with caution and only with proper owner education on potential toxicity. More conformal treatment planning techniques or alternative protocols should be investigated for improved tolerability.

Canine Apocrine Gland Anal Sac Adenocarcinoma: A Review

Apocrine gland anal sac adenocarcinoma (AGASAC) is a relatively uncommon tumor in the dog and comprises approximately 17% of perianal malignancies; however, it is one of the most common causes of paraneoplastic hypercalcemia. Clinical signs in affected dogs most commonly are associated with mechanical obstruction caused by the primary tumor or enlarged regional metastatic lymph nodes and the effects of paraneoplastic hypercalcemia when present. Surgical excision of the primary tumor and metastasectomy of affected locoregional lymph nodes is the preferred initial treatment option for most dogs, although radiation therapy and adjuvant chemotherapy are commonly incorporated into multi-modality treatment plans. A significant role for the use of adjuvant chemotherapy has not been clearly demonstrated. Prolonged survival times are possible, especially for dogs with smaller primary tumors and for dogs that undergo further treatments for recurrent disease. In this article, we review the clinical signs, diagnosis, staging, treatment, and prognosis of AGASAC in the dog.

Hypofractionated radiation therapy of a thyroid tumor in a pet raccoon (Procyon lotor)

Thyroid neoplasia has been documented in raccoons; however, successful management and treatment has not been well-described. A 15-year-old, intact female pet raccoon (Procyon lotor) was examined for evaluation of a right-sided ventral cervical mass and a cough of 4 to 5 mo duration. Cytology and computed tomography (CT) findings of the mass were most consistent with a thyroid tumor. The raccoon was treated with a hypofractionated external beam radiation protocol (8 Gy/fraction for 4 once/wk fractions). Treatments were well-tolerated and no radiation-induced side effects were detected. This is the first report of radiation treatment of thyroid neoplasia in a raccoon, presenting the challenges of animals that are difficult to handle or medicate.

The role of toceranib phosphate in dogs with non-mast cell neoplasia: A systematic review

The use of tyrosine kinase inhibitors (TKI) has gained significant importance in veterinary cancer patients over the last decade. Toceranib phosphate has been licensed for the treatment of dogs with mast cell tumours. Its molecular similarity to sunitinib, a TKI used in human medicine, has led many veterinary oncologists to use this agent for multiple neoplastic diseases. The aim of the current study was to perform a systematic review of the evidence for the use of toceranib in dogs with non-mast cell neoplasia. Two electronic databases were searched. Publications were included if toceranib was used as a treatment option in canine patients. Studies and case reports were excluded if toceranib was used as part of a multi-modal treatment plan and response or outcome data related to toceranib therapy were not described. A total of 28 studies were included from 122 references. The most common types of neoplasias identified were neuroendocrine tumours, anal gland sac adenocarcinoma, and osteosarcoma. Multiple other neoplasias had one or two studies identified to describe the use of toceranib. Results of the study support that toceranib phosphate may have efficacy against certain types of neoplasia under certain conditions, such as neuroendocrine tumours, gastrointestinal stromal tumours and anal sac adenocarcinomas, while it is probably not effective for the management of metastatic osteosarcoma based on the findings of the review.

A Retrospective Study of Clinical and Histopathological Features of 81 Cases of Canine Apocrine Gland Adenocarcinoma of the Anal Sac: Independent Clinical and Histopathological Risk Factors Associated with Outcome

Canine apocrine gland anal sac adenocarcinoma (AGASAC) is a malignant tumour with variable clinical progression. The objective of this study was to use robust multivariate models, based on models employed in human medical oncology, to establish clinical and histopathological risk factors of poor survival. Clinical data and imaging of 81 cases with AGASAC were reviewed. Tissue was available for histological review and immunohistochemistry in 49 cases. Tumour and lymph node size were determined using the response evaluation criteria in the solid tumours system (RECIST). Modelling revealed tumour size over 2 cm, lymph node size grouped in three tiers by the two thresholds 1.6 cm and 5 cm, surgical management, and radiotherapy were independent clinical variables associated with survival, irrespective of tumour stage. Tumour size over 1.3 cm and presence of distant metastasis were independent clinical variables associated with the first progression-free interval. The presence of the histopathological variables of tumour necrosis, a solid histological pattern, and vascular invasion in the primary tumour were independent risk factors of poor survival. Based upon these independent risk factors, scoring algorithms to predict survival in AGASAC patients are presented.

Long-term survival in a dog with primary hepatic neuroendocrine tumor treated with toceranib phosphate

Primary hepatic neuroendocrine tumors (PHNETs) are rare in dogs, and limited information exists about the treatment of these tumors. A 12-year-old castrated male French bulldog was presented to our clinic with gastrointestinal signs. Diagnostic tests revealed increased hepatic enzyme levels, a mass in the hepatic quadrate lobe, multiple intrahepatic nodules, and enlarged hepatic hilar lymph nodes. The liver mass was diagnosed cytologically as a malignant epithelial tumor suspected to be of neuroendocrine origin. The dog was treated with single-agent toceranib phosphate (TOC) and survived 25.1 months after the initial presentation. On necropsy, a liver mass was found and was subsequently diagnosed as a PHNET on histopathology. To the best of our knowledge, this is the first report of long-term survival in a dog with PHNET treated with TOC.

Characterization of receptor tyrosine kinase activation and biological activity of toceranib phosphate in canine urothelial carcinoma cell lines

Background

Urothelial carcinoma (UC) accounts for > 90% of canine tumors occurring in the urinary bladder. Toceranib phosphate (TOC) is a multi-target receptor tyrosine kinase (RTK) inhibitor that exhibits activity against members of the split kinase family of RTKs. The purpose of this study was to evaluate primary UC tumors and UC cell lines for the expression and activation of VEGFR2, PDGFRα, PDGFRβ, and KIT to assess whether dysregulation of these RTKs may contribute to the observed biological activity of TOC.

Results

Transcript for VEGFR2, PDGFRα, PDGFRβ, and KIT was detected in all UC tissue samples and UC cell lines. The Proteome Profiler™ Human Phospho-RTK Array Kit (R & D Systems) provided a platform to assess phosphorylation of 42 different RTKs in primary UC tumors and UC cell lines. Evidence of PDGFRα and PDGFRβ phosphorylation was present in only 11% or 33% of UC tumors, respectively, and 25% of UC cell lines. Treatment of UC cell lines with TOC had no significant impact on cell proliferation, including UC cell lines with evidence of PDGFRβ phosphorylation.

Conclusions

Phosphorylation of several key RTKs targeted by TOC is present in a small subset of primary UC tumors and UC cell lines, suggesting that these RTKs do not exist in a state of continuous activation. These data suggest that activation of RTKs targeted by TOC is present in a small subset of UC tumors and UC cell lines and that treatment with TOC at physiologically relevant concentrations has no direct anti-proliferative effect on UC cells.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-021-03027-0.

C-kit, flt-3, PDGFR-β, and VEGFR2 expression in canine adrenal tumors and correlation with outcome following adrenalectomy

The objective of this retrospective study was to evaluate the expression of receptor tyrosine kinases (RTKs) in canine adrenal tumors and correlate this expression with features of tumor aggressiveness and survival in dogs undergoing adrenalectomy. Forty-three canine adrenal tumors were evaluated for expression of c-kit, fms-like tyrosine kinase 3 (flt-3), platelet-derived growth factor receptor-β (PDGFR-β), and vascular endothelial growth factor receptor 2 (VEGFR2) using immunohistochemistry. Tumor RTK staining characteristics were compared to normal adrenals. Medical records were reviewed for data regarding patient outcome and tumor characteristics. Expression of c-kit, flt-3, PDGFR-β, and VEGFR2 was detected in 26.9%, 92.3%, 96.2%, and 61.5% of cortical tumors and 0%, 63.2%, 47.4%, and 15.8% of pheochromocytomas, respectively. Expression of RTKs was not significantly increased when compared to normal adrenals and did not correlate with survival after adrenalectomy. Receptor tyrosine kinases are not overexpressed in canine adrenal tumors compared to normal adrenal tissue. Therapeutic inhibition of these receptors may still represent an effective approach in cases where receptor activation is present.

Toceranib phosphate (Palladia) for the treatment of canine exocrine pancreatic adenocarcinoma

Background

Canine pancreatic carcinoma is a rare, aggressive tumour that is often diagnosed late in the course of disease. Effective treatment strategies have been elusive, and overall survival time is short. In humans, treatment with tyrosine kinase inhibitors alone, or in combination with IV gemcitabine, have been moderately effective. As canine and human pancreatic carcinomas share many clinical aspects, strategies that mimic human treatment regimens may confer a better outcome in canine patients. The aim of this study was to assess the role of the veterinary tyrosine kinase inhibitor, toceranib phosphate, in the treatment of cytologically or histologically confirmed canine pancreatic carcinomas.

Results

Retrospectively, medical records of dogs with confirmed pancreatic carcinoma treated with toceranib were reviewed. Eight dogs were identified that fit the inclusion criteria. Toceranib was well-tolerated by all patients. Six were treated in the gross disease setting. Four had image-based evaluation of clinical benefit (complete response, partial response, or stable disease of > 10 weeks). Of those patients, 1 achieved a partial response, 2 stable disease, and 1 had progressive disease, for an overall clinical benefit rate of 75 %. An additional dog had clinically stable disease that was not confirmed via imaging. The toceranib-specific median overall survival time was 89.5 days (range: 14–506 days).

Conclusions

Although limited in patient number, this small study suggests that toceranib may have biologic activity in dogs with pancreatic carcinoma. Larger, prospective studies are needed to confirm these preliminary results and define the use of toceranib in the microscopic disease setting.

Evaluation of palliative therapy, alone or in combination with toceranib phosphate, in dogs diagnosed with metastatic or recurrent beta-cell neoplasia

AIMS

To compare survival in dogs with recurrent or metastatic insulinomas that were treated with palliative therapy, alone or in combination with toceranib phosphate and to assess tolerability of the combined therapy in dogs.

MATERIALS AND METHODS

Dogs diagnosed with insulinoma were retrospectively identified in the records of the Veterinary Teaching Hospital Complutense (Madrid, Spain). Diagnosis of insulinoma was based on clinical signs of hypoglycaemia, concentrations in serum of glucose <3.3 mmol/L and insulin >10 μIU/mL and presence of a pancreatic mass on diagnostic imaging. Dogs were treated surgically or medically, according to clinical stage established by imaging techniques, and monitored with blood and urine analyses monthly and abdominal ultrasonography every 3 months until death. Dogs that presented with metastatic disease at diagnosis or with recurrent hypoglycaemia after surgery were treated, according to the owner's decision, with one of two treatment protocols: palliative therapy alone (control group, n=7: diet, prednisone, famotidine or omeprazole, ±octreotide) or palliative therapy in combination with toceranib (treatment group, n=5; median dose of toceranib 2.52 mg/kg). Overall survival time (OST) and adverse events were compared between the two treatment groups.

RESULTS

The OST was longer in the treatment group (median 399, min 125, max 476 days) compared to the control group (median 67, min 23, max 387 days; p=0.042). Dogs in the treatment group had a higher incidence of grade 1-2 gastrointestinal toxicity (diarrhoea) than dogs in the control group (p=0.010). In all cases, gastrointestinal toxicity was solved by temporarily discontinuing toceranib.

CONCLUSIONS AND CLINICAL RELEVANCE

The use of toceranib combined with palliative treatment in dogs with suspect metastatic or recurrent insulinomas increased survival time and was adequate tolerated.

Response and outcome following toceranib phosphate treatment for stage four anal sac apocrine gland adenocarcinoma in dogs: 15 cases (2013-2017)

OBJECTIVE

To assess response and outcome in dogs with stage 4 anal sac apocrine gland adenocarcinoma (ASAGA) treated with toceranib phosphate as the sole chemotherapeutic agent.

DESIGN

Retrospective case series.

ANIMALS

15 client-owned dogs with stage 4 ASAGA treated with toceranib phosphate between March 2013 and June 2017.

PROCEDURES

Medical records were reviewed, and data collected included signalment, clinical signs, results of physical examinations and diagnostic procedures, treatments, response, follow-up information, and outcomes. Adverse events and response to treatment were assessed according to standard guidelines, and the Kaplan-Meier product limit method was used for analyses of progression-free interval and survival time.

RESULTS

No dogs had a complete or partial response to treatment with toceranib; however, 13 dogs had signs of clinical benefit. No dogs had signs of toxic effects related to toceranib or were withdrawn completely from treatment because of adverse events. Median progression-free interval and median survival time were 354 and 356 days, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Results of the present study indicated that dogs with stage 4 ASAGA treated with toceranib had improved outcomes, compared with outcomes previously reported for dogs with ASAGA that had received non-tyrosine kinase inhibitor treatments. Some dogs had improvement in clinical signs, but euthanasia was often performed because of signs of locoregional failure; therefore, toceranib alone may not be an appropriate treatment for dogs with marked clinical signs attributed to ASAGA, particularly when signs suggest limited quality of life. Further study of toceranib in multimodality treatments for dogs with advanced ASAGA is warranted.

Assessment of postoperative adjuvant treatment using toceranib phosphate against adenocarcinoma in dogs

Background

Toceranib phosphate (TOC) could be made widely available for treating tumors in dogs if evidence shows that TOC inhibits recurrence after surgery.

Objectives

To investigate how postoperative adjuvant treatment with TOC modulates the tumor microenvironment (TME), by assessing effects on angiogenic activity, tumor‐infiltrating regulatory T cells (Tregs), and intratumoral hypoxia.

Animals

Ninety‐two client‐owned dogs were included: 28 with apocrine gland anal sac adenocarcinoma, 24 with small intestinal adenocarcinoma, 22 with lung adenocarcinoma, and 18 with renal cell carcinoma.

Methods

Retrospective, multicenter study comparing time to progression (TTP) between 42 dogs treated by surgery and TOC and 50 dogs treated by surgery alone. Differences were analyzed in the expression of vascular endothelial growth factor receptor‐2 (VEGFR2) and the number of Foxp3⁺ Tregs and hypoxia‐inducible factor (HIF)‐1α⁺ cells in tumor tissues sampled at the first and second (recurrence) surgeries.

Results

Median TTP for dogs treated by surgery and TOC (360 days) was higher than that for dogs treated by surgery alone (298 days; hazard ratio, 0.82; 95% confidence interval [CI], 0.65‐0.96; P = .02). In dogs treated by surgery and TOC, VEGFR2 expression and the number of Tregs and HIF‐1α⁺ cells were significantly lower in tissues sampled at the second surgery than in those sampled after the first surgery. In dogs treated by surgery alone, significant differences were found between samples from the 2 surgeries.

Conclusions and Clinical Importance

Toceranib phosphate could prove to be a useful postoperative adjuvant treatment because of its modulation of the TME.

Assessment of tumor enhancement by contrast-enhanced CT in solid tumor-bearing dogs treated with toceranib phosphate

In humans, contrast-enhanced CT (CECT) has been used to indirectly assess the antiangiogenic effects demonstrated by a number of tyrosine kinase inhibitors. This retrospective, cross-sectional study aimed to quantitatively evaluate changes in tumor contrast-enhancement (CE) using CECT in solid tumor-bearing dogs treated with toceranib phosphate (TOC). The changes in tumor size and CE were measured using the Hounsfield unit (HU) scale in CECT images before TOC treatment and between 30 and 90 days after initiating the treatment. Among the 36 dogs treated with TOC, eight (22.2%) showed a partial response, 22 (61.1%) showed stable disease, and six (16.7%) showed progressive disease. Thirty (83.3%) of 36 dogs showed a decrease in tumor CE (median: -20%, range: -1% to -48%) after initiating the treatment. The results indicated that tumor CE and size changes were observed in tumor-bearing dogs that were treated with TOC; however, tumor CE was not significantly correlated with tumor regression. We suggest that these results could serve as pilot data to evaluate the antiangiogenic effects associated with TOC.

Canine Thyroid Cancer: Molecular Characterization and Cell Line Growth in Nude Mice

Thyroid cancer is the most common endocrine malignancy in dogs. Dogs and humans are similar in the spontaneous development of thyroid cancer and metastasis to lungs; however, thyroid cancer has a higher incidence of metastasis in dogs. This study developed a preclinical nude mouse model of canine thyroid cancer using a canine thyroid adenocarcinoma cell line (CTAC) and measured the expression of important invasion and metastasis genes in spontaneous canine thyroid carcinomas and CTAC cells. CTAC cells were examined by electron microscopy. Short tandem repeat analysis was performed for both the original neoplasm and CTAC cells. CTAC cells were transduced with luciferase and injected subcutaneously and into the tail vein. Tumors and metastases were monitored using bioluminescent imaging and confirmed with gross necropsy and histopathology. Invasion and metastasis genes were characterized in 8 follicular thyroid carcinomas (FTCs), 4 C-cell thyroid carcinomas, 3 normal thyroids, and CTAC cells. CTAC cells grew well as xenografts in the subcutis, and they resembled the primary neoplasm. Metastasis to the kidney and lung occurred infrequently following subcutaneous and tail vein injection of CTAC cells. STR analysis confirmed that CTAC cells were derived from the original neoplasm and were of canine origin. Finally, 24 genes were differentially expressed in spontaneous canine thyroid carcinomas, CTAC, and normal thyroids. This study demonstrated the usefulness of a nude mouse model of experimental canine thyroid carcinoma and identified potential molecular targets of canine follicular and C-cell thyroid carcinoma.

Toceranib phosphate in the treatment of canine thyroid carcinoma: 42 cases (2009-2018)

Thyroid carcinoma is the most common endocrine malignancy in dogs. Thyroidectomy and radiation therapy control local disease, yet are not always feasible, and efficacious medical therapies need to be identified. Toceranib phosphate has been reported to provide clinical benefit (CB) in dogs with thyroid carcinoma, while its role in treatment-naïve thyroid tumours has not been well-described. The objective of this study was to describe the use of toceranib in the management of thyroid carcinomas in dogs in both the naïve-disease and prior therapy- settings. A medical record search identified 42 dogs diagnosed with thyroid carcinoma and treated with toceranib, of which 26 and 16 dogs were in settings of naïve-disease and after prior therapy, respectively. Twenty-three (88.4%) and twelve (75%) dogs experienced CB in the naïve and prior therapy settings, respectively. The median [95% confidence interval] progression free interval (PFI) for dogs in the naïve and prior therapy settings were 206 [106,740] and 1015 [92,1015] days, respectively. The median overall survival time (OST) for dogs in the naïve and prior therapy settings were 563 [246,916] and 1082 [289,1894] days, respectively. Overall, the data provided no evidence for differences in overall PFI (P > .20) or OST (P = .15) between settings. However, when asymptomatic at the time of diagnosis, dogs in the naïve setting showed poorer survival prognosis (estimated hazard ratio 17.2 [1.8, 163]) relative to dogs in the prior therapy setting. This study characterizes PFI, OST and CB with minimal AE in dogs with thyroid carcinoma treated with toceranib in both the naïve and prior therapy settings.

Investigation of thyroid function in dogs treated with the tyrosine kinase inhibitor toceranib

Tyrosine kinase inhibitors are widely utilized in veterinary oncology for the treatment of mast cell and solid tumours. In man, these drugs are associated with thyroid dysfunction: however, to date only one study has investigated this in dogs. The aim of this study was to prospectively assess thyroid function in a group of dogs with cancer receiving toceranib. Thirty-four dogs were prospectively enrolled at two referral hospitals into two groups; those receiving toceranib with prednisolone and those receiving toceranib alone. Total thyroxine (TT4) and thyroid stimulating hormone (TSH) was monitored at regular time points during treatment. Follow-up data was available for 19 dogs. Overall, 12 incidences of elevated TSH occurred but none of these dogs had concurrent low TT4 concentrations. There was a significant difference in median TSH at week six compared with baseline. Hypothyroidism was not diagnosed in any patient during the study period. Patient drop-out was higher than anticipated which prevented the assessment of longer term toceranib administration on thyroid function. Toceranib therapy was not associated with hypothyroidism in this study but did result in elevations in TSH which confirms what has been previously reported. Toceranib should be considered to cause thyroid dysfunction in dogs and monitoring is advised.

Long-Term Survival and Glycemic Control with Toceranib Phosphate and Prednisone for a Metastatic Canine Insulinoma

Canine insulinoma is a highly metastatic neoplasm that is associated with a guarded to poor prognosis in dogs with distant metastases. A median survival of 6 mo has been reported for dogs with metastatic insulinoma. The dog in this report, diagnosed with stage III pancreatic insulinoma, had long-term glycemic control with survival of over 24 mo while receiving prednisone and toceranib phosphate after partial pancreatectomy. Toceranib phosphate has been shown to be an efficacious therapy for canine mast cell tumors with increasing evidence that it may be beneficial in the medical management of neuroendocrine tumors.

Long-term clinical control of feline pancreatic carcinoma with toceranib phosphate

An 11-year-old, spayed female, domestic shorthair cat was presented with a non-resectable abdominal mass diagnosed as carcinomatosis of pancreatic origin. Treatment with toceranib phosphate was started. Abdominal ultrasound approximately 1 year after diagnosis revealed progressive disease. The cat was humanely euthanized approximately 792 days after initial presentation due to progressive clinical signs.

Immunogenicity and safety of xenogeneic vascular endothelial growth factor receptor-2 DNA vaccination in mice and dogs

Vascular endothelial growth factor receptor-2 (VEGFR-2) is an attractive target in oncology due to its crucial role in angiogenesis. In this study a DNA vaccine coding for human VEGFR-2 was evaluated in healthy mice and dogs, administered by intradermal injection and electroporation. In mice, three doses and vaccination schedules were evaluated. Cellular immune responses were measured by intracellular IFN-gamma staining and a cytotoxicity assay and antibodies by ELISA. Safety was assessed by measuring regulatory T cells and myeloid derived suppressor cells and a wound healing assay. The vaccine was subsequently evaluated in dogs, which were vaccinated three times with 100μg. Cellular immune responses were measured by intracellular IFN-gamma staining and antibodies by a flow cytometric assay. In mice, maximal cellular responses were observed after two vaccinations with 5μg. Humoral responses continued to increase with higher dose and number of vaccinations. No abnormalities in the measured safety parameters were observed. The vaccine was also capable of eliciting a cellular and humoral immune response in dogs. No adverse effects were observed, but tolerability of the electroporation was poor. This study will facilitate the evaluation of the vaccine in tumor bearing animals, ranging from rodent models to dogs with spontaneous tumors.

Expression of receptor tyrosine kinase targets PDGFR-β, VEGFR2 and KIT in canine transitional cell carcinoma

Transitional cell carcinoma (TCC) is the most common neoplasia of the canine urinary tract. It tends to be locally invasive and has a moderate metastatic rate. Receptor tyrosine kinases (RTKs) play an important role in promoting cell growth, differentiation and regulation of cell function. RTK inhibitor toceranib phosphate has been used anecdotally to treat TCC. The goal of this study was to evaluate archived normal urinary bladder, TCC and cystitis bladder samples for expression of toceranib phosphate targets: VEGFR2, PDGFR-β and stem cell factor receptor (KIT). A significant number of TCC samples expressed PDGFR-β compared with cystitis and normal bladder samples (P<.0001). While all the tumour samples stained positively for VEGFR2, there was no significant difference between tumour, cystitis and normal bladder samples in intensity scores or staining distribution. Minimal positive staining for KIT was noted in the tumour samples. Based on this proof of target study, further investigation is warranted to determine clinical response of TCC to toceranib phosphate.

Safety evaluation of combination carboplatin and toceranib phosphate (Palladia) in tumour-bearing dogs: A phase I dose finding study

Combining conventional cytotoxic maximum tolerated dose (MTD) chemotherapy with low-dose metronomic and/or anti-angiogenic agents is a exciting area of oncologic research. The objective of this study was to establish the MTD, safety and adverse event (AE) profile of 1 such drug combination. This prospective phase I dose-finding clinical trial assumed an open-label 3 + 3 cohort design. Client-owned dogs with 1 or more cytologically and/or histologically confirmed and macroscopically measurable, naive or recurrent, malignant tumours, were enrolled. No preference for tumour histology, grade or stage was expressed. Toceranib was administered at a dose of 2.75 mg kg^-1 by mouth (PO) every other day (EOD), and carboplatin administered intravenously (IV) every 21 days at a starting dose of 200 mg m^-2 . A total of 25% dose escalation was proposed for carboplatin, to a maximum of 300 mg m^-2 . AEs were graded according to the Veterinary Cooperative Oncology Group's common terminology criteria for AEs (VCOG-CTCAE). Grade 3 haematologic or gastrointestinal AEs were nominated dose-limiting. Response to therapy was evaluated according to the VCOG's revised RECIST criteria. Eleven dogs were enrolled. Tumour histologies included sinonasal carcinoma, osteosarcoma, thyroid carcinoma, melanoma and apocrine gland anal sac adenocarcinoma. MTDs of carboplatin and toceranib were identified as 200 mg m^-2 IV every 21 days and approximately 2.75 mg kg^-1 PO EOD, respectively. The dose-limiting toxicity was neutropenia. Two dogs experienced a partial response, and 6 maintained stable disease. Combination carboplatin and toceranib chemotherapy was well-tolerated. Clinical benefit was observed in most cases. This protocol warrants further investigation in phase II/III trials.

Receptor tyrosine kinase expression and phosphorylation in canine nasal carcinoma

Preliminary studies have supported use of toceranib phosphate (Palladia®) in treatment of canine nasal carcinomas, though the mechanisms of its activity are unknown. This study evaluated sixteen canine nasal carcinoma and five normal nasal epithelium samples for expression and phosphorylation of known targets of toceranib [vascular endothelial growth factor receptor-2 (VEGR2), platelet derived growth factor alpha (PDGFR-α), platelet derived growth factor receptor beta (PDGFR-β), and stem cell factor receptor (c-KIT)] and epidermal growth factor receptor 1 (EGFR1) using immunohistochemistry, RT-PCR and a receptor tyrosine kinase (RTK) phosphorylation panel. Protein for VEGFR2 was expressed in all carcinomas, PDGFR-α was noted in 15/16, whereas PDGFR-β was detected in 3/16 samples, but showed significant stromal staining. Protein expression for c-KIT was present in 4/16 and EGFR1 was noted in 14/16 samples. Normal tissue showed variable protein expression of the RTKs. Messenger RNA for VEGFR2, PDGFR-β, and c-KIT were noted in all samples. Messenger RNA for PDGFR-α and EGFR1 were detected in 15/16 samples. All normal nasal tissue detected messenger RNA. Phosphorylation of VEGFR2, PDGFR-α, PDGFR-β and c-KIT was not observed in any carcinoma or normal nasal sample, but phosphorylation of EGFR1 was noted in 10/16 carcinoma and 3/5 normal samples. The absence of phosphorylated RTK targets of toceranib suggests any clinical effect of toceranib occurs through inhibition of alternative unidentified RTK pathways in canine nasal carcinomas. The observed protein and message expression and phosphorylation of EGFR1 in the nasal carcinoma samples merits further inquiry into EGFR1 as a therapeutic target for this cancer.

Expression of VEGFR and PDGFR-α/-β in 187 canine nasal carcinomas

Radiotherapy represents the standard of care for intranasal carcinomas. Responses to tyrosine kinase inhibitors (TKIs) have been reported but data on expression of target receptor tyrosine kinases (rTKs) is limited. This study characterizes the expression of vascular endothelial growth factor receptor (VEGFR), platelet-derived growth factor receptor (PDGFR)-α and PDGFR-β in canine intranasal carcinomas. Histological samples from 187 dogs were retrieved. Immunohistochemistry was performed using commercially available antibodies. Expression of rTKs was classified into weak, moderate or intense and additionally recorded as cytoplasmic, membranous, cytoplasmic-membranous, nuclear or stromal. VEGFR was expressed in 158 dogs with predominantly moderate expression (36.9%) and a cytoplasmic-membranous expression pattern (70.9%). PDGFR-α was detected in 133 with predominantly weak expression (57.9%) and cytoplasmic pattern (87.9%). PDGFR-β was identified in 74 patients with a predominantly moderate expression (17.6%) and cytoplasmic expression pattern (63.5%). Co-expression of rTKs was common. These results confirm expression of VEGFR, PDGFR-α and PDGFR-β in canine intranasal carcinomas and support the utility of TKIs.

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.

Angiogenesis in spontaneous tumors and implications for comparative tumor biology

Blood supply is essential for development and growth of tumors and angiogenesis is the fundamental process of new blood vessel formation from preexisting ones. Angiogenesis is a prognostic indicator for a variety of tumors, and it coincides with increased shedding of neoplastic cells into the circulation and metastasis. Several molecules such as cell surface receptors, growth factors, and enzymes are involved in this process. While antiangiogenic therapy for cancer has been proposed over 20 years ago, it has garnered much controversy in recent years within the scientific community. The complex relationships between the angiogenic signaling cascade and antiangiogenic substances have indicated the angiogenic pathway as a valid target for anticancer drug development and VEGF has become the primary antiangiogenic drug target. This review discusses the basic and clinical perspectives of angiogenesis highlighting the importance of comparative biology in understanding tumor angiogenesis and the integration of these model systems for future drug development.

Canine pulmonary adenocarcinoma tyrosine kinase receptor expression and phosphorylation

BACKGROUND

This study evaluated tyrosine kinase receptor (TKR) expression and activation in canine pulmonary adenocarcinoma (cpAC) biospecimens. As histological similarities exist between human and cpAC, we hypothesized that cpACs will have increased TKR mRNA and protein expression as well as TKR phosphorylation. The molecular profile of cpAC has not been well characterized making the selection of therapeutic targets that would potentially have relevant biological activity impossible. Therefore, the objectives of this study were to define TKR expression and their phosphorylation state in cpAC as well as to evaluate the tumors for the presence of potential epidermal growth factor receptor (EGFR) tyrosine kinase activating mutations in exons 18-21. Immunohistochemistry (IHC) for TKR expression was performed using a tissue microarray (TMA) constructed from twelve canine tumors and companion normal lung samples. Staining intensities of the IHC were quantified by a veterinary pathologist as well as by two different digitalized algorithm image analyses software programs. An antibody array was used to evaluate TKR phosphorylation of the tumor relative to the TKR phosphorylation of normal tissues with the resulting spot intensities quantified using array analysis software. Each EGFR exon PCR product from all of the tumors and non-affected lung tissues were sequenced using sequencing chemistry and the sequencing reactions were run on automated sequencer. Sequence alignments were made to the National Center for Biotechnology Information canine EGFR reference sequence.

RESULTS

The pro-angiogenic growth factor receptor, PDGFRα, had increased cpAC tumor mRNA, protein expression and phosphorylation when compared to the normal lung tissue biospecimens. Similar to human pulmonary adenocarcinoma, significant increases in cpAC tumor mRNA expression and receptor phosphorylation of the anaplastic lymphoma kinase (ALK) tyrosine receptor were present when compared to the corresponding normal lung tissue. The EGFR mRNA, protein expression and phosphorylation were not increased compared to the normal lung and no activating mutations were identified in exons 18-21.

CONCLUSIONS

Canine pulmonary adenocarcinoma TKRs are detected at both the mRNA and protein levels and are activated. Further investigation into the contribution of TKR activation in cpAC tumorigenesis is warranted.