Vincristine and ivermectin combination chemotherapy in dogs with natural transmissible venereal tumor of different cyto-morphological patterns: A prospective outcome evaluation

https://doi.org/10.1016/j.anireprosci.2020.106358Get rights and content

Highlights

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    Most dogs with natural CTVT presented with moderate to severe clinical disease.

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    Plasmacytic CTVT cytomorphology was more frequent than lymphocytic or mixed patterns.

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    No tumor resistance to chemotherapy was seen regardless of cytomorphological pattern.

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    Combination ivermectin/vincristine promoted tumor remission without enhancing adverse effects.

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    Combination ivermectin/vincristine was safe and efficacious for CTVT chemotherapy.

Abstract

Vincristine is the first-line drug for the chemotherapy of canine transmissible venereal tumor (CTVT). Drug resistance is related to tumor cyto-morphological patterns of CTVT. There are anti-cancer properties of ivermectin, thus, a combination of ivermectin and vincristine could be an effective chemo-therapeutic treatment regimen for CTVT. Study aims, therefore, were to (1) assess the frequency of CTVT cyto-morphologies, and (2) evaluate treatment efficacy and possible adverse reactions to vincristine compared with a combination vincristine and ivermectin. Dogs (n = 41) with CTVT were characterized by tumor cyto-morphology and disease severity and of those, 20 were randomly allocated into two groups. There was a control group (G-Vin; n = 10) in which there was treatment with vincristine; and an experimental group (G-Iv/Vin; n = 10) in which there was treatment with the ivermectin/vincristine combination. Although dogs in the G-Iv/Vin group had more severe disease at the beginning of the study (P = 0.0031), the number of weeks and chemotherapy sessions until tumor remission were similar among dogs of the two groups, indicating both treatments were effective. There was a decrease in the leukocyte counts (P = 0.0020), related to neutropenia (P = 0.0371) in the G-Vin but not the G-Iv/Vin treatment group. There was no tumor resistance that developed during the study regardless of the treatment regimen used or tumor cytomorphology. In summary, the use of the vincristine/ivermectin combination was well tolerated and efficacious for CTVT treatment.

Introduction

The canine transmissible venereal tumor (CTVT) affects the genital system of dogs and compromises the general clinical condition (Ganguly et al., 2016; Ferreira et al., 2017). The CTVT disease is globally distributed (Baez-Ortega et al., 2019). Among 90 countries throughout all continents of the globe, there was reporting that CTVT prevalence varies from 0.5 % in Australia to 10 % in Argentina, and there is a tendency for a lesser incidence in Europe and a greater incidence in South America (Strakova and Murchison, 2014).

In recent years, CTVT has been studied as a model for the comprehension of neoplastic diseases, owing to its peculiar immunological and metabolic properties associated with transmission and spontaneous regression in the natural host (Gonzalez et al., 2000; Ostrander et al., 2016; Ujvari et al., 2016; Fassati, 2018; Frampton et al., 2018).

Cytology assessments of tumor samples collected using fine-needle aspiration biopsy procedures is the routine method for confirmation of a clinical presumptive CTVT diagnosis and for cyto-morphological classification as lymphocytic, plasmacytic, or of mixed cell types (Amaral et al., 2007; Lima et al., 2013; Ganguly et al., 2016; Setthawongsin et al., 2016; Mascarenhas et al., 2017). Plasmacytic CTVTs are clinically more aggressive and considered resistant to chemotherapy (Flórez et al., 2017; Ballestero Fêo et al., 2018).

Vincristine sulfate is the first-line drug for CTVT treatment (Calvert et al., 1982; Nak et al., 2005), and is usually administered at weekly intervals until tumor remission (Scarpelli et al., 2010). As occurs with the use of other anti-neoplastic drugs, treatment with vincristine can result in adverse reactions affecting the bone marrow (Mealey et al., 2008; Hantrakul et al., 2014), or the gastrointestinal system (Ramadinha et al., 2016). Additionally, cases of CTVT resistance to vincristine have been reported (Brandão et al., 2002; Gaspar et al., 2010).

Treatments with ivermectin can result in a reversing of the resistance to antineoplastic drugs by inhibiting p-Glycoprotein (P-gp) production, with this being a protein that promotes the efflux of xenobiotics from within the tumor cell (Didier and Loor, 1996; Pouliot et al., 1997; Griffin et al., 2005; Lespine et al., 2006; Jiang et al., 2019). Ivermectin, therefore, has been proposed to be a therapeutic agent as an anticancer drug (Jiang et al., 2019; Markowska et al., 2019). Both vincristine and ivermectin are substrates for P-gp (Didier and Loor, 1996; Mealey and Fidel, 2015), and results from at least one clinical study indicate there is an association of ivermectin with vincristine in promotion of earlier remission of CTVT when compared with vincristine as a single drug (Lapa et al., 2012). More recently, diverse direct anti-cancer activities also have been listed as a result of the newly studied ivermectin properties (Crump, 2017; Dominguez-Gomez et al., 2018; Juarez et al., 2018).

It, therefore, was hypothesized that a chemotherapy based on the use of the combination of vincristine and ivermectin for treatment of dogs with CTVT could be effective. Considering that clinical studies on this subject are few, the aim of the present study was to evaluate the efficacy and occurrence of adverse reactions to a combined ivermectin/vincristine therapy. The dogs diagnosed with natural CTVT had categorization of the cyto-morphological patterns as plasmacytic, lymphocytic and mixtures of these cell types. The dogs had been admitted to a teaching veterinary hospital located in an endemic area for the disease.

Section snippets

Animals, experimental design and ethics

Dogs of different breeds, ages and both sexes with genital tumors were examined at the Teaching Hospital of Veterinary Medicine of the Federal University of Bahia, in Salvador, Brazil. The clinical diagnosis of CTVT was confirmed by cytological examination of tumor smears from samples collected with fine-needle aspiration biopsy. Inclusion criteria for dogs in the study were a confirmed CTVT diagnosis when there was a cytological examination of the tumor using procedures that have been

CTVT frequency and cyto-morphological patterns

From January 2017 to August 2018, 472 dogs with neoplasias were admitted to the Teaching Hospital of Veterinary Medicine of the Federal University of Bahia, of which 51 (10.8 %; 51/472) were diagnosed with CTVT using cytology procedures. There were ten of these 51 dogs excluded for subsequent study because the owners chose not to participate in the study.

The characteristics of the 41 dogs with CTVT are described in Table 2. The mean age of the dogs was 5.0 years ± 3.11 SD. Four dogs had genital

Discussion

The present study spanned 17 months and CTVT comprised 10.8 % (an average frequency of three cases per month) of all canine neoplasia cases at the largest veterinary hospital of Salvador, a city with an estimated canine population of 443,000 dogs in 2019 (personal communication). The findings in the present study were within the range of reported frequencies of CTVT cases in teaching hospitals in other areas (De Nardi et al., 2002; Araujo et al., 2016).

Considering the epidemiological nature of

CRediT authorship contribution statement

Laiane Ferreira Bulhosa: Methodology, Investigation, Writing - original draft. Alessandra Estrela-Lima: Conceptualization, Methodology, Writing - review & editing. Manuela da Silva Solcà: Data curation, Formal analysis, Writing - review & editing. Gabriel Saraiva Diniz Gonçalves: Methodology, Investigation. Daniela Farias Larangeira: Methodology, Investigation. Flaviane Alves de Pinho: Methodology, Data curation, Writing - review & editing. Stella Maria Barrouin-Melo: Supervision,

Declaration of Competing Interest

There are no conflicts of interest to report.

Acknowledgements

The study was supported by the Brazilian National Council for Scientific and Technological Development (CNPq - PQ Researcher scholarship for SMBM: Proc. 307813/2018-5, and for AESL: Proc. 305938/2018-5), by the Bahia Research Foundation (FAPESB - Grant n. PRONEM: 498/2011-PNE 0002/2011), and by the Coordination for Improvement of Higher Education Personnel – CAPES (MSc scholarship for LFB n. 1654450). We thank Dr. Aroldo Carneiro (Center for Zoonosis Control, Municipal Health Secretariat -

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