Combination therapy using intratumoral bacillus Calmette-Guerin (BCG) and vincristine in dogs with transmissible venereal tumours: therapeutic efficacy and histological changes

Clinical Guidelines for Canine Transmissible Venereal Tumour Treatment: Systematic Review and Meta-Analysis

The treatment of canine transmissible venereal tumour (CTVT) has evolved since its initial description in 1810. Initially considered untreatable in the early 20th century, extensive research over time has significantly advanced our understanding of its aetiopathogenesis. This led to successful chemotherapy treatments, which have shown superior outcomes compared to surgical interventions. Vincristine, in particular, has proven effective in treating CTVT. However, the development of chemoresistance underscores the need to explore alternative therapeutic options. This systematic review provides a comprehensive analysis of CTVT treatment practices from 1950 to 2023, aiming to establish a gold standard and enhance clinical decision-making. Initially, 3633 studies were identified, with 42 meeting the eligibility criteria. Our findings suggest that vincristine sulphate monotherapy is the recommended first-line treatment for CTVT. Administering vincristine intravenously at a dosage of 0.5-0.75 mg/m2 weekly for 4-6 sessions resulted in a 93.1% (67.4%-100%) complete response rate in dogs. Extending the treatment to eight sessions increased the complete response rate to 98.9% (83.3%-100%). Radiation therapy, lomustine and doxorubicin are viable second-line treatment options; however, extensive cohort studies are required to confirm their efficacy in achieving remission in vincristine-resistant cases. Additionally, no clear criteria could be established for initiating treatment with drugs other than vincristine in previously untreated dogs. Surgery is considered a third-line option. Notably, complete remission is anticipated following recommended systemic and local therapies in nearly all cases. Despite concerns about chemoresistance, current guidelines indicate a favourable response to suggested treatments even in resistant cases.

Tumor-associated macrophages: Prognostic and therapeutic targets for cancer in humans and dogs

Macrophages are ancient, phagocytic immune cells thought to have their origins 500 million years ago in metazoan phylogeny. The understanding of macrophages has evolved to encompass their foundational roles in development, homeostasis, tissue repair, inflammation, and immunity. Notably, macrophages display high plasticity in response to environmental cues, capable of a strikingly wide variety of dynamic gene signatures and phenotypes. Macrophages are also involved in many pathological states including neural disease, asthma, liver disease, heart disease, cancer, and others. In cancer, most tumor-associated immune cells are macrophages, coined tumor-associated macrophages (TAMs). While some TAMs can display anti-tumor properties such as phagocytizing tumor cells and orchestrating an immune response, most macrophages in the tumor microenvironment are immunosuppressive and pro-tumorigenic. Macrophages have been implicated in all stages of cancer. Therefore, interest in manipulating macrophages as a therapeutic strategy against cancer developed as early as the 1970s. Companion dogs are a strong comparative immuno-oncology model for people due to documented similarities in the immune system and spontaneous cancers between the species. Data from clinical trials in humans and dogs can be leveraged to further scientific advancements that benefit both species. This review aims to provide a summary of the current state of knowledge on macrophages in general, and an in-depth review of macrophages as a therapeutic strategy against cancer in humans and companion dogs.

Evaluation of lymphocyte-specific programmed cell death protein 1 receptor expression and cytokines in blood and urine in canine urothelial carcinoma patients

Urothelial carcinoma (UC) is the most common urinary tumour in dogs. Despite a range of treatment options, prognosis remains poor in dogs. In people, breakthroughs with checkpoint inhibitors have established new standards of care for muscle-invasive bladder cancer patients and elevated levels of programmed cell death protein 1 (PD-1) suggest immune checkpoint blockade may be a novel target for therapy. The goal of this study was to determine if canine UC patients express elevated levels of lymphocyte-specific PD-1 and/or urinary cytokine biomarkers compared to healthy dogs. Paired blood and urine were evaluated in 10 canine UC patients, five cystitis patients and 10 control dogs for lymphocyte-specific PD-1 expression via flow cytometry and relative cytokine expression. In UC patients, PD-1 expression was significantly elevated on CD8⁺ lymphocytes in urine samples. UC patients had a higher CD4:CD8 ratio in their urine compared to healthy dogs, however, there was no significant variation in the CD8:Treg ratio between any group. Cystitis patients had significantly elevated levels of CD4⁺ T cells, CD8⁺ T cells and Tregs in their blood samples compared to UC patients and healthy dogs. Cytokine analysis demonstrated significant elevations in urinary cytokines (granulocyte-macrophage colony-stimulating factor, interferon-gamma [IFN-γ], interleukin (IL)-2, IL-6 IL-7, IL-8 and IL-15, IP-10, KC-like, IL-18, monocyte chemoattractant protein-1 and tumour necrosis factor-alpha). Several of these cytokines have been previously correlated with both lymphocyte-specific PD-1 expression (IFN-γ, IL-2, IL-7 and IL-15) in muscle-invasive urothelial carcinoma in humans. Our results provide evidence of urinary lymphocyte PD-1 expression and future studies could elucidate whether veterinary UC patients will respond favourably to anti-PD-1 immune checkpoint inhibitor therapy.

Repurposing Infectious Diseases Vaccines Against Cancer

Vaccines used to prevent infections have long been known to stimulate immune responses to cancer as illustrated by the approval of the Bacillus Calmette-Guérin (BCG) vaccine to treat bladder cancer since the 1970s. The recent approval of immunotherapies has rejuvenated this research area with reports of anti-tumor responses with existing infectious diseases vaccines used as such, either alone or in combination with immune checkpoint inhibitors. Here, we have reviewed and summarized research activities using approved vaccines to treat cancer. Data supporting a cancer therapeutic use was found for 16 vaccines. For 10 (BCG, diphtheria, tetanus, human papillomavirus, influenza, measles, pneumococcus, smallpox, typhoid and varicella-zoster), clinical trials have been conducted or are ongoing. Within the remaining 6, preclinical evidence supports further evaluation of the rotavirus, yellow fever and pertussis vaccine in carefully designed clinical trials. The mechanistic evidence for the cholera vaccine, combined with the observational data in colorectal cancer, is also supportive of clinical translation. There is limited data for the hepatitis B and mumps vaccine (without measles vaccine). Four findings are worth highlighting: the superiority of intravesical typhoid vaccine instillations over BCG in a preclinical bladder cancer model, which is now the subject of a phase I trial; the perioperative use of the influenza vaccine to limit and prevent the natural killer cell dysfunction induced by cancer surgery; objective responses following intratumoral injections of measles vaccine in cutaneous T-cell lymphoma; objective responses induced by human papillomavirus vaccine in cutaneous squamous cell carcinoma. All vaccines are intended to induce or improve an anti-tumor (immune) response. In addition to the biological and immunological mechanisms that vary between vaccines, the mode of administration and sequence with other (immuno-)therapies warrant more attention in future research.

Factor Analysis for Bicluster Acquisition (FABIA) revealed vincristine-sensitive transcript pattern of canine transmissible venereal tumors

Chemotherapeutic treatment for Canine transmissible venereal tumor (CTVT) commonly relies on vincristine administration. Since the treatment outcomes can vary among CTVT cases, gaining insight into the tumor cell mechanisms influencing vincristine's potency should render veterinarians novel knowledge to enhance its therapeutic effect. This study aimed to attain such knowledge from a meta-analysis of CTVT mRNA sequencing (mRNA-seq) transcriptome data using Factor Analysis for Bicluster Acquisition (FABIA) biclustering. FABIA biclustering identified 459 genes consistently expressed among mRNA-seq transcription profiling of CTVT samples regressed by vincristine. These genes were also differentially expressed from those of progressive CTVT (FDR ≤ 0.001). Enrichment analysis illustrated the affiliation of these genes with "Antigen presentation" and "Lysosome" GO terms (FDR ≤ 0.05). Several genes in "Lysosome" term involved 5 cell mechanisms-antigen presentation, autophagy, cell-adhesion, lysosomal membrane permeabilization (LMP), and PI3K/mTOR signaling. This study integrated FABIA biclustering in CTVT transcriptome analysis to gain insight into cell mechanisms responsible for vincristine-sensitive characteristics of the tumor, in order to identify new molecular targets augmenting therapeutic effect of vincristine. Interestingly, the analysis indicated LMP targeting by lysosome destabilizing agent-siramesine as the promising vincristine's enhancer for future study. As far as we know, this is the first canine tumor transcriptomic meta-analysis applying FABIA biclustering for the betterment of future CTVT therapy. This study hereby provided an interesting manifestation to acquire such knowledge in other canine neoplasia.

Intratumoral recombinant human interferon alpha-2a and vincristine combination therapy in canine transmissible venereal tumour

Canine transmissible venereal tumour (CTVT) is a naturally occurring contagious neoplasm of dogs located mainly on the external genitalia of both sexes. The course of vincristine chemotherapy, the most effective and practical therapy, is affected by the immune status of the host. The aim was to investigate recombinant human interferon alpha‐2a (rhIFNα‐2a) and vincristine for treatment of CTVT. A total of 21 female dogs were included. In group I (n = 9), vincristine (0.025 mg/kg, IV) was administered weekly. In group II (n = 6), dogs were injected intratumorally weekly with 1.5 million IU rhIFNα‐2a. In group III (n = 6), rhIFNα‐2a and vincristine were combined. No tumour regression was observed after three injections of rhIFNα‐2a in group II and weekly vincristine was administered. The number of tumour infiltrating lymphocytes (TILs), mitotic figures and apoptotic cells were counted in subsequent incisional tumour biopsies. The Kaplan–Meier Method was used to analyse survival using complete tumour regression as the outcome and Breslow Test was used for comparison of survival curves. Differences in TILs, cell proliferation and apoptosis between groups were assessed by analysis of covariance. Complete regression was observed in all animals included. Mean duration of vincristine treatment for complete regression was shorter in group II (3.50 weeks, 95% CI, 3.06–3.94, P < 0.05) and group III (3.17 weeks, 95% CI, 2.84–3.49, P < 0.01) compared to group I (5.11 weeks, 95% CI, 4.42–5.80). Vincristine and rhIFNα‐2a combination increased TILs in CTVT biopsies compared to vincristine treatment (P = 0.017) and vincristine treatment after rhIFNα‐2a (P = 0.049). Vincristine treatment after rhIFNα‐2a (Group II; P < 0.001) and rhIFNα‐2a and vincristine combination (Group III; P < 0.001) decreased apoptosis. The results indicate that intratumoral rhIFNα‐2a treatment alone is not effective in CTVT. However, combination of rhIFNα‐2a and vincristine shortens the duration of treatment compared to vincristine therapy.

Spontaneous regression of tumour and the role of microbial infection--possibilities for cancer treatment

This review deals with the role of microorganisms in spontaneous regression of a tumour. Spontaneous cancer regression is a phenomenon that has been described for many centuries. One of the most well known methods of inducing spontaneous regression of cancer is the application of Coley's toxin (heat-killed Streptococcus pyogenes and Serratia marcescens), which has been used for the successful treatment of sarcomas, carcinomas, lymphomas, myelomas and melanomas. In clinical practice, the use of Bacillus Calmette-Guérin vaccine for the treatment of superficial urinary bladder cancer is the most common instance of the application of microorganisms for the treatment of cancer. This review provides further information on other tested bacteria--Clostridium spp., Bifidobacterium spp., Lactobacillus spp. and Salmonella spp.--in this field of study. Among new age methods, bactofection, alternative gene therapy, combination bacteriolytic therapy and bacteria-directed enzyme prodrug therapy are some of the potential cancer treatment modalities that use microorganisms. We have also provided information about the interconnection among microorganisms, immune system response, and the possible mechanisms involved in the spontaneous regression of tumours.

Cancer immunotherapy in veterinary medicine: Current options and new developments

Excitement in the field of tumor immunotherapy is being driven by several remarkable breakthroughs in recent years. This review will cover recent advances in cancer immunotherapy, including the use of T cell checkpoint inhibitors, engineered T cells, cancer vaccines, and anti-B cell and T cell antibodies. Inhibition of T cell checkpoint molecules such as PD-1 and CTLA-4 using monoclonal antibodies has achieved notable success against advanced tumors in humans, including melanoma, renal cell carcinoma, and non-small cell lung cancer. Therapy with engineered T cells has also demonstrated remarkable tumor control and regression in human trials. Autologous cancer vaccines have recently demonstrated impressive prolongation of disease-free intervals and survival times in dogs with lymphoma. In addition, caninized monoclonal antibodies targeting CD20 and CD52 just recently received either full (CD20) or conditional (CD52) licensing by the United States Department of Agriculture for clinical use in the treatment of canine B-cell and T-cell lymphomas, respectively. Thus, immunotherapy for cancer is rapidly moving to the forefront of cancer treatment options in veterinary medicine as well as human medicine.

Vincristine modulates the expression of Ki67 and apoptosis in naturally occurring canine transmissible venereal tumor (TVT)

We investigated eight adult dogs that were brought to veterinary clinics with a history of transmissible venereal tumors (TVT). Our goal was to demonstrate the occurrence of apoptosis and the cessation of cell proliferation at every phase of scheduled chemotherapy for naturally occurring TVT. Tissue samples were collected immediately after weekly treatments with vincristine sulfate and processed for histological purposes. Sections 5 μm thick were stained by the TUNEL reaction for apoptosis and immunostained for Ki67 as a proliferation marker. We observed that after vincristine applications, tumor cell proliferation ceased and apoptosis increased. Ki67 HSCORE values were significantly lowered after the first and second treatments with the chemotherapeutic agent compared to controls, whereas TUNEL HSCORE values were significantly higher after two applications of vincristine compared to controls. Our results suggest that scheduled vincristine sulfate applications stabilize the induction of tumor regression by inducing apoptosis and preventing cell proliferation.