p53 expression and apoptosis in melanomas of dogs and cats

Development of a UPLC-MS/MS method for quantifying KPT-335 (Verdinexor) in feline plasma for a study of PK

KPT-335 (Verdinexor) is a novel SINE that potently inhibits the nucleoprotein Exportin 1 (XPO1/CRM1) of tumor cell lines and reduces the replication level of the influenza virus. KPT-335 is mainly used for the treatment of canine tumors. Drugs for the effective treatment of feline tumors are currently unavailable in China. KPT-335 may have potential in the treatment of cat tumors. However, the effects of KPT-335 in cats are unreported, and no relevant methodology has been established for pharmacokinetic studies. In this study, a UPLC-MS/MS method was developed to determine KPT-335 concentrations in cat plasma, followed by pharmacokinetic studies. Briefly, plasma proteins are precipitated with acetonitrile, and the supernatant was collected for detection after centrifugation. The linearity for KPT-335 in cat plasma was in the range of 5-1,000 ng/mL. Satisfactory accuracy and precision were obtained. The intra-day accuracy was between -4.10% and 10.48%, the precision was ≤4.65%; the inter-day accuracy was between -0.11% and 8.09%, and the precision was ≤5.85%. Intra-day and inter-day accuracy and precision were within regulatory limits. The results of preliminary pharmacokinetic studies were as follows: Tmax was 1.46 ± 0.51 h; Cmax was 239.54 ± 190.60 ng·mL-1; T1/2 was 5.16 ± 2.30 h; AUC0-t was 1439.85 ± 964.64 ng·mL-1·h. The AUC0-∞ was 1589.82 ± 1003.75 ng·mL-1·h. The purpose of this study was to develop a rapid and simple UPLC-MS/MS method to detect KPT-335 concentration in cat plasma and to conduct preliminary pharmacokinetic studies to support the future application of KPT-335 in felines.

Canine melanoma diagnosis: RACK1 as a potential biological marker

Melanoma diagnosis in dogs can be challenging due to the variety of histological appearances of canine melanocytic neoplasms. Markers of malignancy are needed. Receptor for activated C-kinase 1 (RACK1) was found to characterize melanomas in other mammals. We investigated the value of RACK1 detection in the classification of 19 cutaneous and 5 mucosal melanocytic neoplasms in dogs. These tumors were categorized as melanocytomas or benign and melanomas or malignant after evaluation of their morphology, mitotic index, and Ki-67 growth fraction. Using immunofluorescence, we confirmed microphthalmia-associated transcription factor (MITF) as a marker of normal and transformed melanocytic cells in dog tissues. All control (n = 10) and tumoral (n = 24) samples stained positively for MITF (34/34, 100%). Whereas RACK1 was not detected in healthy skin melanocytes, melanocytic lesions were all positive for RACK1 signal (24/24, 100%). RACK1 cytoplasmic staining appeared with 2 distinct distribution patterns: strong, diffuse, and homogeneous or granular and heterogeneous. All melanoma samples (13/13, 100%) stained homogeneously for RACK1. All melanocytomas (11/11, 100%) stained heterogeneously for RACK1. Immunohistochemistry was less consistent than immunofluorescence for all labelings in melanocytic lesions, which were often very pigmented. Thus, the fluorescent RACK1-MITF labeling pattern helped to distinguish melanomas from melanocytomas. Furthermore, RACK1 labeling correlated with 2 of 11 morphological features linked to malignancy: cell and nuclear size. These results suggest that RACK1 may be used as a marker in dog melanomas.

Reactivity of p53 protein in canine transmissible venereal tumor

The expression of p53 protein was evaluated in canine transmissible venereal tumor (CTVT), as following: natural occurrence (n=8); resistant to chemotherapy (n=4); and allogeneic transplanted in progression (n=8), stable (n=8), and regression (n=8)stages. The collected specimens were submitted to GM1 immunohistochemical reaction. Results showed a mean percentage of immunomarked cells around 18.6% in CTVT of natural occurrence, 23.8% in CTVT resistant to chemotherapy, 22.9% in allogeneic transplanted CTVT in both progression and stable stages, and 35.8% in transplanted CTVT in regression stage. The results suggest that there is a functional abnormality in p53 gene and its products in the studied tumors; although, it is not possible to correlate the percentage of cells marked by p53 and a prognosis.

Establishment of a dog model for the p53 family pathway and identification of a novel isoform of p21 cyclin-dependent kinase inhibitor

Spontaneous tumors in the dog offer a unique opportunity as models to study human cancer etiology and therapy. p53, the most commonly mutated gene in human cancers, is found to be altered in dog cancers. However, little is known about the role of p53 in dog tumorigenesis. Here, we found that on exposure to DNA damage agents or MDM2 inhibitor nutlin-3, canine p53 is accumulated and capable of inducing its target genes, MDM2 and p21. We also found that on DNA damage, canine p53 is accumulated in the nucleus, followed by MDM2 nuclear translocation and increased 53BP1 foci formation. In addition, we found that canine p63 and p73 are up-regulated by DNA damage agents. Furthermore, colony formation assay showed that canine tumor cells are sensitive to DNA damage agents and nutlin-3 in a p53-dependent manner. Surprisingly, canine p21 is expressed as two isoforms. Thus, we generated multiple canine p21 mutants and found that amino acids 129 to 142 are required, whereas amino acid 139 is one of the key determinants, for the expression of two p21 isoforms. Finally, we showed that although the full-length human p21 cDNA expresses one polypeptide, amino acid 139 seems to play a similar role as that in canine p21 for various migration patterns. Taken together, our results indicate that canine p53 family proteins have biological activities similar to human counterparts. These similarities make the dog an excellent outbred spontaneous tumor model, and the dog can serve as a translation model from benchtop to cage side and then to bedside.

Survival of Dogs Following Surgical Excision of Histologically Well-differentiated Melanocytic Neoplasms of the Mucous Membranes of the Lips and Oral Cavity

Postsurgical follow-up information was obtained on 64 dogs with 69 histologically well-differentiated melanocytic neoplasms that involved the mucous membranes of the lips and oral cavity. The patients received no adjunct therapy. Sixty one of 64 dogs (95%) were alive at the end of the study or had died of causes unrelated to the tumor, with a mean survival of 23.4 months and a median survival of 34 months after surgery. Twenty-eight dogs alive at the end of the study had a mean survival of 31.3 months after surgery. There were 2 dogs, which had recurrent tumors, that were still alive at the end of the study. All dogs that died of tumor-related causes (3) and all dogs with recurrent tumors (2) had tumors in the oral cavity.

Results of this study indicate that a favorable clinical course and prolonged survival can be expected in most dogs with histologically well-differentiated melanocytic neoplasms of the mucous membranes of the lips and oral cavity, with only local excision of the lesions and no adjunct therapy.

A Comprehensive Test System to Identify Suitable Antibodies Against p53 for Immunohistochemical Analysis of Canine Tissues

The tumour suppressor p53 is commonly detected in tissues of companion animals by means of antibodies raised against the human protein. The following three-step procedure was devised to test the suitability of such antibodies for immunohistochemistry on canine tissues. (1) Western blot and immunohistochemical analyses on bacterially expressed recombinant canine protein to assess human-to-canine cross-reactivity. (2) Immunohistochemistry of cultured, UVB-irradiated canine keratinocytes to evaluate suitability for detection of endogenous p53. (3) Immunohistochemistry on tissue arrays to further substantiate suitability of the antibodies on a panel of normal and neoplastic human and canine tissues. Five of six antibodies cross-reacted with recombinant canine p53. Three of these (PAb122, PAb240, CM-1) also immunolabelled stabilized wild type p53 in cell cultures and elicited a consistent, characteristic labelling pattern in a subset of tumours. However, two alternative batches of polyclonal antibody CM-1 failed to detect p53 in cell cultures, while showing a characteristic labelling pattern of a completely different subset of tumours and unspecific labelling of normal tissues. The test system described is well suited to the selection of antibodies for immunohistochemical p53 detection. The results emphasize the need to include appropriate controls, especially for polyclonal antibodies.

Prognostic and predictive markers in canine tumours: rationale and relevance. A review

Cancer is one of the most common causes of death in dogs. The availability of multiple treatment modalities and novel therapeutic targets make the correct diagnosis, prognostic stratification, and the identification of treatment effect predictive factors an issue of major debate in cancer management. Selection of high and low risk patients and the type of systemic or local treatment is important in cancer management. The search for better prognostic markers and predictive factors is now focused on the molecular mechanisms which underlie tumour behaviour, such as altered cell cycle progression, proliferation, apoptosis, and angiogenesis. The ultimate goal is to identify reliable markers that can accurately diagnose and stage a tumour and predict tumour's clinical behaviour, prognosis and response to therapy. In this review, the current state of prognostication in canine tumours and promising new molecular markers are discussed. The markers are allocated to four groups according to their function: (i) proliferation markers, (ii) apoptosis, (iii) extracellular matrix and cell adhesion molecules, (iv) angiogenesis and (v) cell cycle regulators. Clinicopathological factors and histopathological grading remain the most practical parameters in decision-making. Although experimental research has shown that molecular markers have a good potential to be used as diagnostic, prognostic or predictive markers in canine tumours, insufficient evidence exists on their efficacy for routine use in veterinary oncology.

The Basic Biology of Malignant Melanoma: Molecular Mechanisms of Disease Progression and Comparative Aspects

Malignant melanoma (MM) is a life-threatening disease characterized by a highly aggressive biologic behavior in both humans and dogs. Despite improvements in diagnosis and patient care, most deaths from MM are due to metastases that are resistant to conventional treatment modalities. To ultimately reduce the mortality associated with metastatic disease, it is necessary to better define the fundamental molecular mechanisms of malignant tumor progression. The progression of disease is a consequence of the complex interactions between malignantly transformed cells and host factors. Characterization of the stages of tumor progression and the changes occurring in highly malignant cells is important for the development of effective treatment regimens. The dys-regulated molecular mechanisms of transformed melanocytes are presently being characterized. In this review, we summarize the current understanding of the molecular phases in the progression of MM, which include genetic instability, dysregulated proliferation of melanocytes, increased invasion and metastasis, and angiogenesis.

Mechanisms of anticancer drug resistance

Chemotherapy agents are extremely important in the treatment of liquid malignancies, such as lymphoma, myeloma, and chronic lymphocytic leukemia. In addition, chemotherapy agents have proven effective in the adjuvant treatment of solid tumors, such as osteosarcoma, hemangiosarcoma, transitional cell carcinoma, and others. Unfortunately, chemotherapy resistance in these situations is the most significant cause of treatment failure. Therefore, the ability to predict, treat, or circumvent resistance is extremely likely to improve clinical outcomes. This article has reviewed the most widely investigated forms of chemotherapy resistance, such as reduced drug accumulation, increased DNA damage repair, decreased apoptosis, and others; however, new mechanisms are being found at an alarming pace. In addition, investigations to date have routinely centered on single-cell mechanisms of drug resistance, and cancer is truly a three dimensional disease. The elucidation of mechanisms surrounding (1) how tumors interact with their normal microenvironment, (2) how tumors interact in a three-dimensional environment, and (3) a better understanding of basic tumor physiology and biology may supersede in importance those previously elucidated single-cell mechanisms of chemoresistance.

A comparative review of melanocytic neoplasms

Melanoma is a devastating disease frequently encountered within both veterinary and human medicine. Molecular changes linked with neoplastic transformation of melanocytes include mutations in genes that encode proteins intrinsic to the regulatory pathways of two tumor suppressor proteins (retinoblastoma protein and p53), proto-oncogene mutation to oncogenes, altered expression of epithelial cadherin and CD44 adhesion molecules, and upregulation of angiogenic factors and other growth factors. Histologic evaluation of the primary mass is the most common means of diagnosis, with cytology used more frequently to document metastasis. Melanoma's highly variable histologic and cytologic patterns can make diagnosis by either method problematic. Adherent epithelioid morphology, including signet ring forms, and nonadherent round and spindle forms are recognized, with pigmentation an inconsistent finding. The site of the tumor, the thickness of the primary tumor or depth of invasion, and the number of mitotic figures per high-power field or per millimeter are used histologically to predict biologic behavior, whereas site and degree of pleomorphism are typically used for cytologic preparations. Diagnosis of amelanotic melanoma can be aided by ancillary diagnostic techniques. Tumor cells are usually positive for vimentin, S100, neuron-specific enolase, and Melan-A, and negative for cytokeratin. Melan-A as a positive marker is not as sensitive as the others are but is likely more specific. Monoclonal antibodies to human melanosome-specific antigens 1 and 5 cross-react with canine antigens for a combined sensitivity rate of 83%. Mouse monoclonal antibody IBF9 specifically recognizes canine melanoma antigen and also has good sensitivity. Serologic markers, including cytokines, cell adhesion molecules, and melanoma-inhibitory activity, are being investigated as potential sentinels of melanoma. Currently, there is no single diagnostic technique capable of differentiating benign from malignant melanocytic neoplasms or predicting survival time.