Phase I lead-in and subsequent randomized trial assessing safety and modulation of regulatory T cell numbers following a maximally tolerated dose doxorubicin and metronomic dose cyclophosphamide combination chemotherapy protocol in tumour-bearing dogs

Metronomic chemotherapy: bridging theory to clinical application in canine and feline oncology

Veterinary oncology has experienced significant evolution over the last few decades, with chemotherapy being currently applied to several neoplasms with therapeutic success. Traditionally, chemotherapy protocols are based on classic cytostatic drugs under the concept of maximum tolerated dose (MTD), which has been associated with a greater risk of toxicity and resistance. Thus, new therapeutic alternatives have emerged, such as metronomic chemotherapy (MC), introducing a new paradigm in cancer treatment. MC consists of administering low doses of chemotherapy drugs continuously over a long period of time, modulating the tumour microenvironment (TME) due to the combination of cytotoxic, antiangiogenic and immunomodulatory effects. This multi-targeted therapy has been described as a treatment option in several canine and feline cancers since 2007, with positive results already published in the literature, particularly in mammary carcinomas and soft tissue sarcomas in dogs. The aim of this review article is to describe the current knowledge about the use of MC in small animal oncology, with emphasis on its mechanisms of action, the most commonly used drugs and clinical outcome.

Metronomic Chemotherapy for Palliative Treatment of Malignant Oral Tumors in Dogs

The aim of this study was to evaluate the efficacy of metronomic chemotherapy in the palliative treatment of various malignant oral tumors in dogs. Our focus was to determine the effect of treatment on local disease control and to assess the tolerability and safety of the treatment in dogs with various oral malignancies. Metronomic chemotherapy with cyclophosphamide was used to treat 12 dogs and was combined with non-steroidal anti-inflammatory drugs in 6/12 (50%) of dogs. A clinical benefit was observed in 6/12 (50%) patients 1 month and in 4/12 (33%) 3 months after treatment initiation. The median survival time of the dogs was 155 days (range 21–529 days). At the end of the observation period, the disease had progressed in 10/12 (83.3%) of the patients. Sterile hemorrhagic cystitis was the most commonly reported side effect of treatment, occurring in 4/12 (33.3%) dogs. The results of our study suggest that metronomic chemotherapy with cyclophosphamide can be, in a subset of dogs, beneficial in the palliation of malignant oral tumors.

Sarcomas-A barren immunological wasteland or field of opportunity for immunotherapy?

Key advances in our understanding of immunobiology and the immunosuppressive mechanisms of the tumour microenvironment have led to significant breakthroughs in manipulating the immune system to successfully treat cancer. Remarkable therapeutic responses have occurred with tumours that carry a high mutational burden. In these cases, pre-existing tumour-specific T cells can be rejuvenated via checkpoint inhibition to eliminate tumours. Furthermore, durable remissions have been achieved in haematological malignancies following adoptive transfer of T cells that specifically target cell surface proteins where expression is restricted to the malignancy's cell of origin. Soft tissue sarcomas and bone sarcomas have a paucity of non-synonymous somatic mutations and do not commonly express known, targetable, tumour-specific antigens. Historically, soft tissue sarcomas have been considered immunologically 'cold' and as such, unlikely candidates for immune therapy. Here, we review the immune landscape of canine and feline sarcomas and the immunotherapeutic strategies that have been employed in veterinary clinical trials to improve patient outcome. We also provide insight into immunotherapeutic approaches being used to treat human sarcomas. Together, current data indicates that, rather than a barren immunological wasteland, sarcomas represent a field of opportunities for immunotherapies. Furthermore, we and others would suggest that strategic combinations of immunotherapeutic approaches may hold promise for more effective treatments for high grade soft tissue sarcomas and bone sarcomas.

Evaluation of metronomic cyclophosphamide chemotherapy as maintenance treatment for dogs with appendicular osteosarcoma following limb amputation and carboplatin chemotherapy

OBJECTIVE To determine the effectiveness of metronomic cyclophosphamide (MC) chemotherapy (primary treatment of interest) with adjuvant meloxicam administration as maintenance treatment for dogs with appendicular osteosarcoma following limb amputation and carboplatin chemotherapy. DESIGN Retrospective case series with nested cohort study. ANIMALS 39 dogs with a histologic diagnosis of appendicular osteosarcoma that underwent limb amputation and completed carboplatin chemotherapy from January 2011 through December 2015. PROCEDURES Dogs were grouped by whether carboplatin chemotherapy had been followed with or without MC chemotherapy (15 mg/m², PO, q 24 h) and meloxicam (0.1 mg/kg [0.045 mg/lb], PO, q 24 h). The Breslow rank test was used to assess whether MC chemotherapy was associated with overall survival time (OST) and disease progression-free time (PFT) after limb amputation. RESULTS 19 dogs received carboplatin and MC chemotherapy, and 20 dogs received only carboplatin chemotherapy. No differences were identified between these groups regarding age, reproductive status, body weight, serum alkaline phosphatase activity, tumor location, or histologic grade or subtype of osteosarcoma. Median duration of MC chemotherapy for dogs in the carboplatin-MC group was 94 days (range, 7 to 586 days); this treatment was discontinued for 11 (58%) dogs when cystitis developed. Overall, 11 (28%) dogs survived to the time of analysis, for a median follow-up period of 450 days (range, 204 to 1,400 days). No difference in median PFT or OST was identified between the 2 groups. CONCLUSIONS AND CLINICAL RELEVANCE Maintenance MC chemotherapy following limb amputation and completed carboplatin chemotherapy was associated with no increase in PFT or OST in dogs with appendicular osteosarcoma. Cystitis was common in MC-treated dogs, and prophylactic treatment such as furosemide administration could be considered to reduce the incidence of cystitis in such dogs.

Primary Hepatic Neuroendocrine Carcinoma Treated with Doxorubicin and Cyclophosphamide in a Dog

A 7 yr, 6 mo old male neutered Australian cattle dog cross presented to a referral hospital with a large abdominal mass. An abdominal ultrasound revealed multifocal lesions throughout the liver, which were suspicious for intrahepatic metastasis, with no evidence of extrahepatic metastatic disease. Cytology indicated neoplasia of epithelial origin, with neuroendocrine neoplasia the primary suspicion. The patient was started on a maximally tolerated chemotherapy protocol of doxorubicin and metronomic cyclophosphamide. Stable disease was found on repeat abdominal ultrasounds, and the patient tolerated the protocol well. On completion of five doxorubicin doses, the dog was continued on metronomic cyclophosphamide and meloxicam. Progressive hepatic disease was found at 10 mo. The patient was euthanized 15.5 mo (465 days) after commencing treatment. Histopathology and immunohistochemistry (synaptophysin) performed on liver collected postmortem indicated (primary) hepatic neuroendocrine carcinoma. Primary hepatic neuroendocrine carcinomas are rare in dogs, and there is no standard of care for treatment. To the authors' knowledge, this is the first report of a primary hepatic neuroendocrine carcinoma treated with high-dose doxorubicin and metronomic cyclophosphamide.

The use of low-dose metronomic chemotherapy in dogs-insight into a modern cancer field

The era of chemotherapy, which started in the middle of the last century, has been ruled by the routine use of dose-intense protocols, based on the "maximum-tolerated dose" concept. By promoting a balance between patient's quality of life and the goal of rapidly killing as many tumour cells as possible, these protocols still play a prominent role in veterinary oncology. However, with the opening of a new millennium, metronomic chemotherapy (MC) started to be considered a possible alternative to traditional dose-intense chemotherapy. Characterized by a long-term daily administration of lower doses of cytotoxic drugs, this new modality stands out for its unique combination of effects, namely on neovascularization, immune response and tumour dormancy. This article reviews the rationale for treatment with MC, its mechanism of action and the main studies conducted in veterinary medicine, and discusses the key challenges yet to be solved.

The effects of cryopreservation on the expression of canine regulatory T-cell markers

BACKGROUND

Regulatory T (Treg) cells have been described as key regulators in various immunological processes and are of growing interest in veterinary allergy. Cryopreservation of immune cells is performed routinely in human basic science research and in clinical studies. As such, it allows batch testing of collected samples at a single time point, resulting in a significant reduction in sample variability. Data which describe the effects of cryopreservation on Treg cell frequency and functionality in the canine species are important to inform future research.

HYPOTHESIS/OBJECTIVES

The purpose of this study was to establish a robust freeze/thaw procedure and flow cytometric staining protocol for canine Treg cells, and to compare the frequencies of different canine Treg cell phenotypes before and after cryopreservation.

ANIMALS

Nine privately owned dogs.

METHODS

Peripheral blood mononuclear cells were isolated and Treg cells stained and analysed by flow cytometry, before and after three months of cryopreservation. The recovery percentages and the corresponding correlations (fresh versus cryopreserved) for CD4⁺ CD25⁺ , CD4⁺ FOXP3⁺ and CD4⁺ CD25⁺ FOXP3⁺ cell populations were calculated.

RESULTS

A high recovery rate of 97.2 (r = 0.94, P < 0.0001), 93.9 (r = 0.77, P < 0.01) and 101.7% (r = 0.99, P < 0.0001) for CD4⁺ CD25⁺ , CD4⁺ FOXP3⁺ and CD4⁺ CD25⁺ FOXP3⁺ cell populations, respectively, was observed.

CONCLUSIONS

This study demonstrates an optimized protocol for freezing, thawing and quantifying canine Treg cells. These results indicate that cryopreservation does not substantially affect the expression of surface and intracellular markers of canine Treg cells; however, additional studies will be necessary to assess whether functionality of the cells is also maintained.