Cytokine-enhanced vaccine and suicide gene therapy as adjuvant treatments of metastatic melanoma in a horse

Programmed Cell Death-Ligand 1 (PD-L1) Immunohistochemical Expression in Equine Melanocytic Tumors

Currently available treatments for equine melanocytic tumors have limitations, mainly due to mass localization and dimension, or the presence of metastases. Therefore, a search for new therapies is necessary. Programmed cell death-ligand 1 (PD-L1) is expressed by several tumors, blocking T cell-mediated elimination of the tumor cells by binding to programmed cell death protein 1 (PD-1). A novel therapeutic approach using PD-1/PD-L1 blockade in human melanoma resulted in tumor regression and prolonged tumor-free survival. This study aimed to evaluate the immunohistochemical expression of PD-L1 in equine melanocytic tumors. A total of 77 melanocytic tumors were classified as benign or malignant and evaluated by extension of labeling. A total of 59.7% of the tumors showed >50% of immunolabeled cells. Regarding malignant tumors, 24/38 tumors presented >50% of labeled cells, 13 tumors presented between 25-50% and one tumor presented <10%. Regarding benign tumors, 22/39 tumors presented >50% of labeled cells, nine tumors presented 25-50%, three tumors presented 10-25%, two tumors presented <10% and three tumors did not present expression. Our results suggest that PD-L1 blockade may be a potential target for immunotherapy in equine melanocytic tumors and that future clinical research trials into the clinical efficacy of the anti-PD-L1 antibody are necessary.

Administration and detection of gene therapy in horses: A systematic review

Gene therapy uses genetic modification of cells to produce a therapeutic effect. Defective or missing genes can be repaired or replaced, or gene expression can be modified using a variety of technologies. Repair of defective genes can be achieved using specialized gene editing tools. Gene addition promotes gene expression by introducing synthetic copies of genes of interest (transgenes) into cells where they are transcribed and translated into therapeutic proteins. Protein production can also be modified using therapies that regulate gene expression. Gene therapy is currently prohibited in both human and equine athletes because of the potential to induce production of performance-enhancing proteins in the athlete's body, also referred to as "gene doping." Detection of gene doping is challenging and necessitates development of creative, novel analytical methods for doping control. Methods for detection of gene doping must be specific to and will vary depending on the type of gene therapy. The purpose of this paper is to present the results of a systematic review of gene editing, gene therapy, and detection of gene doping in horses. Based on the published literature, gene therapy has been administered to horses in a large number of experimental studies and a smaller number of clinical cases. Detection of gene therapy is possible using a combination of PCR and sequencing technologies. This summary can provide a basis for discussion of appropriate and inappropriate uses for gene therapy in horses by the veterinary community and guide expansion of methods to detect inappropriate uses by the regulatory community.

Equine Melanocytic Tumors: A Narrative Review

Adult grey horses have a high incidence of melanocytic tumors. This article narratively reviews the role of some genetic features related to melanoma formation in horses, such as STX17 mutation, ASIP or MITF alterations, and the link between the graying process and the development of these tumors. A clear system of clinical and pathological classification of melanocytic tumors in naevus, dermal melanoma, dermal melanomatosis and anaplastic malignant melanoma is provided. Clinical and laboratorial methods of diagnosing are listed, with fine needle aspiration and histopathology being the most relevant. Relevance is given to immunohistochemistry, describing potentially important diagnostic biomarkers such as RACK1 and PNL2. Different therapeutical options available for equine practitioners are mentioned, with surgery, chemotherapy and electroporation being the most common. This article also elucidatesnew fields of research, perspectives, and new therapeutic targets, such as CD47, PD-1 and COX-2 biomarkers.

Interventions for treatment of cutaneous melanoma in horses: a structured literature review

Several therapies have been developed to treat equine cutaneous melanoma, but formal comparisons among different treatment options are currently unavailable. It was our intent to assess the efficacy of different treatment protocols and the quality of the studies based on the original published data, and summarize the knowledge concerning the outcome after equine cutaneous melanoma management. This structured review followed PRISMA procedure to search for treatment protocols on equine cutaneous melanoma published from 1960 until June 2021. Studies were assessed for the risk of bias. A descriptive analysis was performed, considering the disease control rate, the recurrence rate of the tumor, comorbidities, need for anesthesia, and horses' welfare. Twenty-three studies were included, from which the treatment outcomes of 173 horses were assessed. The homogeneity of the included trials was low. The percentages of each treatment arm achieving a partial response and curative effects accounted for 93.1% (surgical intervention), 90% (medication), and 39.4% (immunotherapies), respectively. A variable efficacy of different therapies of equine cutaneous melanoma was observed. Surgical intervention performed the best from the perspective of local antitumor effects alone. This literature review and descriptive analysis can serve as a source to assist in designing quality therapy research and can potentially aid in providing a clinical treatment reference for equine cutaneous melanoma.

Surgical excision of a malignant metastatic melanoma located in a skeletal muscle of the lateral thorax of a horse

BACKGROUND

A 20-year-old grey Warmblood gelding that had history of dermal melanomatosis.

OBJECTIVE

To report surgical treatment of a 6-cm large malignant metastatic melanoma located in the cutaneous trunci muscle of the left lateral thorax of a horse.

METHODS

A 20-year-old grey Warmblood gelding was referred for evaluation of a large, rapidly growing, thoracic mass. Clinical examination revealed an ovoid, firm, non-painful, movable mass, approximately 6 cm in diameter, located in the cutaneous trunci muscle of the left lateral thorax. Multiple melanocytic nodules were also found at the perianal region and ventral tail. Rectal examination, ultrasonography and endoscopy of the respiratory tract revealed no melanomas internally. Haematological and biochemical values were within normal limits. Surgical excision of both the thoracic mass and perianal nodules was the treatment of choice. Histopathology of the distant thoracic mass confirmed the diagnosis of malignant metastatic melanoma secondary to the perineal lesions that were confirmed as dermal melanomatosis.

RESULTS

The horse recovered uneventfully. Up until 3 years post surgery there was no tumour regrowth at the excision sites.

CONCLUSION

Surgical excision of the metastatic melanoma was performed and considered successful, with no gross evidence of tumour reoccurrence. Despite the fact that surgical excision is considered a treatment option regarding equine dermal melanomatosis, there is no previously published study proposing surgical removal of distant malignant metastatic melanocytic masses. This is the first report of a successful surgical excision of a large (6 cm) metastatic melanocytic tumour from the skeletal muscle of the lateral thorax of a horse.

Targeted gene therapy of the HSV-TK/hIL-12 fusion gene controlled by the hSLPI gene promoter of human non-small cell lung cancer in vitro

The incidence of lung cancer and lung cancer-associated mortality have markedly increased worldwide, and gene-targeted therapy has emerged as a promising treatment strategy. The present study aimed to explore the targeted antitumor effect of the herpes simplex virus-thymidine kinase/human interleukin-12 (HSV-TK/hIL-12) fusion gene regulated by the human secretory leukocyte protease inhibitor (hSLPI) promoter of human non-small cell lung cancer (hNSCLC). There were four recombinant eukaryotic expression vectors: pcDNA3.1-CMV-TK, pcDNA3.1-CMV-TK/hIL-12, pcDNA3.1-phSLP-TK and pcDNA3.1-phSLP-TK/hIL-12. These were constructed and transfected into the A549, SPC-A1 and HepG2 cell lines in vitro. The expression of the HSV-TK/hIL-12 fusion gene was detected with reverse transcription-polymerase chain reaction (RT-PCR), and the content of hIL-12 was measured using an ELISA. The antitumor effect of the fusion gene on the A549, SPC-A1 and HepG2 cell lines was determined using an MTT assay. Analysis of the experimental data demonstrated that genes regulated by the cytomegalovirus promoter were expressed at the same level in three different tumor cell lines. Genes regulated by the hSLPI promoter were expressed in the A549 and SPC-A1 cell lines, but not in the HepG2 cell line. Coincidentally, the hIL-12 expression levels were similar to those observed in previous RT-PCR findings. In the Pcmv-TK/Pcmv-TK-hIL-12 group for all three cell lines, as well as in the PSLPI-TK/PSLPI-TK-hIL-12 group for the A549 and SPC-A1 cell lines, the cell survival rate declined significantly and the fusion gene transfection group indicated a lower cell survival rate, when compared with single gene transfection group. The present study indicated that the fusion gene regulated by the hSLPI promoter had a targeted antitumor effect on hNSCLC, and that the combined suicide gene and immune gene therapy had a stronger antitumor effect, compared with single gene therapy.

Clinical trials of immunogene therapy for spontaneous tumors in companion animals

Despite the important progress obtained in the treatment of some pets' malignancies, new treatments need to be developed. Being critical in cancer control and progression, the immune system's appropriate modulation may provide effective therapeutic options. In this review we summarize the outcomes of published immunogene therapy veterinary clinical trials reported by many research centers. A variety of tumors such as canine melanoma, soft tissue sarcomas, osteosarcoma and lymphoma, feline fibrosarcoma, and equine melanoma were subjected to different treatment approaches. Both viral and mainly nonviral vectors were used to deliver gene products as cytokines, xenogeneic tumor associated antigens, specific ligands, and proapoptotic regulatory factors. In some cases autologous, allogenic, or xenogeneic transgenic cytokine producing cells were assayed. In general terms, minor or no adverse collateral effects appeared during this kind of therapies and treated patients usually displayed a better course of the disease (longer survival, delayed or suppressed recurrence or metastatic spread, and improvement of the quality of life). This suggests the utility of these methodologies as standard adjuvant treatments. The encouraging outcomes obtained in companion animals support their ready application in veterinary clinical oncology and serve as preclinical proof of concept and safety assay for future human gene therapy trials.

Malignant melanoma in a grey horse: case presentation and review of equine melanoma treatment options

A 15 year-old grey Thoroughbred gelding presented for investigation of chronic weight loss and recent onset of respiratory difficulty. Clinical examination confirmed tachypnoea with increased respiratory effort. Thoracic ultrasound examination detected pleural effusion. The dyspnoea was related to the large volume of pleural effusion and, following post-mortem examination, to the presence of a large mediastinal mass. Multiple pigmented masses, likely melanomas, were detected peri-anally. Thoracic radiography, cytological examination of the pleural fluid and a fine needle aspirate of a thoracic mass led to a presumptive diagnosis of malignant melanoma and this was confirmed at post mortem examination. Further metastatic spread to the central nervous system and right guttural pouch was also identified. In conclusion this case manifests the potential malignant behaviour of equine melanomas, and a review of proposed therapies for melanoma treatment highlights the therapeutic options and current areas of research.

IL-12 based gene therapy in veterinary medicine

The use of large animals as an experimental model for novel treatment techniques has many advantages over the use of laboratory animals, so veterinary medicine is becoming an increasingly important translational bridge between preclinical studies and human medicine. The results of preclinical studies show that gene therapy with therapeutic gene encoding interleukin-12 (IL-12) displays pronounced antitumor effects in various tumor models. A number of different studies employing this therapeutic plasmid, delivered by either viral or non-viral methods, have also been undertaken in veterinary oncology. In cats, adenoviral delivery into soft tissue sarcomas has been employed. In horses, naked plasmid DNA has been delivered by direct intratumoral injection into nodules of metastatic melanoma. In dogs, various types of tumors have been treated with either local or systemic IL-12 electrogene therapy. The results of these studies show that IL-12 based gene therapy elicits a good antitumor effect on spontaneously occurring tumors in large animals, while being safe and well tolerated by the animals. Hopefully, such results will lead to further investigation of this therapy in veterinary medicine and successful translation into human clinical trials.

Enforced effect of tk-MCP-1 fusion gene in ovarian cancer

OBJECTIVE

The efficiency of HSV-tk/GCV system is not high because of insufficient gene transfer and incompletely initiative of host antineoplastic potency. The present study was designed to assess the antitumor efficacy of tk-MCP-1 on ovarian cancer in vitro and vivo.

METHODS

A novel bicistronic expression system can help to improve the expression level of a gene in a stable manner. pLXSN/tk-MCP-1 co-expressing tk and MCP-1 genes was constructed using a pLXSN retroviral vector and an internal ribosome entry site sequence by restriction enzyme. Western blot was performed to determine tk and MCP-1 expression in the infected SKOV3. The GCV-sensitively tumoricidal activities of SKOV3/tk-MCP-1 with or without monocytes were compared to those of SKOV3 expressing HSV-tk or MCP-1. We investigated the growth of subcutaneous tumors in SCID mice immuno-reconstituted, and evaluated the antitumor effect of MCP-1 in conjunction with suicide gene.

RESULTS

The significant GCV-sensitively tumoricidal activity of pLXSN/tk-MCP-1 was observed when compared with those of pLXSN/tk, pLXSN/MCP-1 and pLXSN/neo, especially when monocytes were added. The growth of subcutaneous tumors in SCID mice immuno-reconstituted was markedly suppressed by co-delivery of HSV-tk and MCP-1 genes, and the enhanced antitumor effect was associated with the recruitment of monocytes.

CONCLUSION

These results demonstrated pLXSN/tk-MCP-1 presented an enhanced antitumor effects on ovarian cancer by orchestration of immune responses.