Synergistic Effect of Toceranib and Nanohydroxyapatite as a Drug Delivery Platform-Physicochemical Properties and In Vitro Studies on Mastocytoma Cells.

A new combination of Toceranib (Toc; 5-[(5Z)-(5-Fluoro-2-oxo-1,2-dihydro-3H-indol-3-ylidene)methyl]-2,4-dimethyl-N-[2-(pyrrolidin-1-yl)ethyl]-1H-pyrrole-3-carboxamide) with nanohydroxyapatite (nHAp) was proposed as an antineoplastic drug delivery system. Its physicochemical properties were determined as crystallinity, grain size, morphology, zeta potential and hydrodynamic diameter as well as Toceranib release. The crystalline nanorods of nHAp were synthesised by the co-precipitation method, while the amorphous Toceranib was obtained by its conversion from the crystalline form during nHAp-Toc preparation. The surface interaction between both compounds was confirmed using Fourier-transform infrared spectroscopy (FT-IR), ultraviolet-visible spectroscopy (UV-Vis) and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS). The nHAp-Toc showed a slower and prolonged release of Toceranib. The release behaviour was affected by hydrodynamic size, surface interaction and the medium used (pH). The effectiveness of the proposed platform was tested by comparing the cytotoxicity of the drug combined with nHAp against the drug itself. The compounds were tested on NI-1 mastocytoma cells using the Alamar blue colorimetric technique. The obtained results suggest that the proposed platform shows high efficiency (the calculated IC50 is 4.29 nM), while maintaining the specificity of the drug alone. Performed analyses confirmed that nanohydroxyapatite is a prospective drug carrier and, when Toceranib-loaded, may be an idea worth developing with further research into therapeutic application in the treatment of canine mast cell tumour.

Long-term in-vitro glucocorticoid treatment induces glucocorticoid resistance in canine mast cell tumors.

Although glucocorticoid administration has produced impressive results in treating canine mast cell tumors (MCTs), in some cases, glucocorticoids fail to reduce the tumor volume, leading to tumor relapse even after treatment. To date, mechanisms involved in glucocorticoid resistance in canine MCTs remain poorly defined. The objective of this study was to establish glucocorticoid-resistant canine MCT cell lines derived from glucocorticoid-sensitive cell lines after prolonged treatment with dexamethasone (Dex). Real-time polymerase chain reaction (RT-PCR) revealed that elevation of glucocorticoid receptor (GR)-regulated gene expression was suppressed in Dex-resistant cell lines after Dex stimulation compared with parent Dex-sensitive cell lines. This indicated that GR-regulated transcription was suppressed in Dex-resistant cell lines. Insufficient expression of GRs was not detected in Dex-resistant cell lines. Possible inhibitors of GR-regulated transcription were increased in mRNA expression in Dex-resistant cell lines. In addition, it was determined that mRNA expression of drug efflux pumps and anti-apoptosis factors was higher in Dex-resistant cell lines. In conclusion, glucocorticoid-resistant canine MCT cell lines have been established that are derived from glucocorticoid-sensitive cell lines. These cell lines suggest that multiple mechanisms contribute to glucocorticoid resistance in canine MCT cells. The mechanisms of glucocorticoid resistance after long-term treatment can be further investigated using these cell lines and a novel therapeutic strategy for glucocorticoid-resistant canine MCT cells can be developed.

Bien que l'administration de glucocorticoïdes ait produit des résultats impressionnants dans le traitement des mastocytomes (MCT) canins, dans certains cas, les glucocorticoïdes ne parviennent pas à réduire le volume tumoral, entraînant une rechute de la tumeur même après le traitement. À ce jour, les mécanismes impliqués dans la résistance aux glucocorticoïdes dans les MCT canins restent mal définis. L'objectif de cette étude était d'établir des lignées cellulaires MCT canines résistantes aux glucocorticoïdes dérivées de lignées cellulaires sensibles aux glucocorticoïdes après un traitement prolongé avec de la dexaméthasone (Dex). La réaction d'amplification en chaîne par polymérase en temps réel (RT-PCR) a révélé que l'élévation de l'expression génique régulée par le récepteur des glucocorticoïdes (GR) était supprimée dans les lignées cellulaires résistantes à Dex après stimulation par Dex par rapport aux lignées cellulaires parentales sensibles à Dex. Cela indiquait que la transcription régulée par GR était supprimée dans les lignées cellulaires résistantes à Dex. Une expression insuffisante des GR n'a pas été détectée dans les lignées cellulaires résistantes à Dex. Les inhibiteurs possibles de la transcription régulée par GR étaient augmentés dans l'expression de l'ARNm dans les lignées cellulaires résistantes à Dex. De plus, il a été déterminé que l'expression de l'ARNm des pompes d'efflux de médicaments et des facteurs anti-apoptose était plus élevée dans les lignées cellulaires résistantes au Dex. En conclusion, des lignées cellulaires canines MCT résistantes aux glucocorticoïdes ont été établies qui sont dérivées de lignées cellulaires sensibles aux glucocorticoïdes. Ces lignées cellulaires suggèrent que de multiples mécanismes contribuent à la résistance aux glucocorticoïdes dans les cellules MCT canines. Les mécanismes de résistance aux glucocorticoïdes après un traitement à long terme peuvent être étudiés plus en détail à l'aide de ces lignées cellulaires et une nouvelle stratégie thérapeutique pour les cellules MCT canines résistantes aux glucocorticoïdes peut être développée.(Traduit par Docteur Serge Messier).

Effects of ibrutinib on proliferation and histamine release in canine neoplastic mast cells.

The Bruton's tyrosine kinase (BTK) inhibitor ibrutinib is effective in the treatment of human chronic lymphocytic leukaemia and mantle cell lymphoma. Recent data have shown that ibrutinib also blocks IgE-dependent activation and histamine release in human basophils (BAs) and mast cells (MCs). The aim of this study was to investigate whether BTK serves as a novel therapeutic target in canine mast cell tumours (MCTs). We evaluated the effects of ibrutinib on two canine MC lines, C2 and NI-1 and on primary MCs obtained from canine MCTs (n = 3). Using flow cytometry, we found that ibrutinib suppresses phosphorylation of BTK and of downstream STAT5 in both MC lines. In addition, ibrutinib decreased proliferation of neoplastic MCs, with IC50 values ranging between 0.1 and 1 µM in primary MCT cells and between 1 and 3 µM in C2 and NI-1 cells. In C2 cells, the combination "ibrutinib + midostaurin" produced synergistic growth-inhibitory effects. At higher concentrations, ibrutinib also induced apoptosis in both MC lines. Finally, ibrutinib was found to suppress IgE-dependent histamine release in primary MCT cells, with IC50 values ranging from 0.05 to 0.1 µM in NI-1 cells, and from 0.05 to 1 µM in primary MCT cells. In summary, ibrutinib exerts anti-proliferative effects in canine neoplastic MCs and counteracts IgE-dependent histamine release in these cells. Based on our data, ibrutinib may be considered as a novel therapeutic agent for the treatment of canine MCT. The value of BTK inhibition in canine MCT patients remains to be elucidated in clinical trials.

Reactive Oxygen Species-Mediated Apoptosis and Cytotoxicity of Newly Synthesized Pyridazin-3-Ones In P815 (Murin Mastocytoma) Cell Line.

BACKGROUND: In cancer cells, the intracellular antioxidant capacity and the redox homeostasis are mainly maintained by the glutathione- and thioredoxin-dependent systems which are considered as promising targets for anticancer drugs. Pyridazinones constitute an interesting source of heterocyclic compounds for drug discovery. The present investigation focused on studying the in-vitro antitumor activity of newly synthesized Pyridazin-3(2h)-ones derivatives against P815 (Murin mastocytoma) cell line. METHODS: The in-vitro cytotoxic activities were investigated toward the P815 cell line using tetrazolium-based MTT assay. Lipid peroxidation and the specific activities of antioxidant enzymes were also determined. RESULTS: The newly compounds had a selective dose-dependent cytotoxic effect without affecting normal cells (PBMCs). Apoptosis was further confirmed through the characteristic apoptotic morphological changes and DNA fragmentation. Two compounds (6F: and 7H: ) were highly cytotoxic and were submitted to extend biological testing to determine the likely mechanisms of their cytotoxicity. Results showed that these molecules may induce cytotoxicity via disturbing the redox homeostasis. Importantly, the anticancer activity of 6F: and 7H: could be due to the intracellular reactive oxygen species hypergeneration through significant loss of glutathione reductase and thioredoxin reductase activities. This eventually leads to oxidative stress-mediated P815 cell apoptosis. Furthermore, the co-administration of 6F: or 7H: with Methotrexate exhibited a synergistic cytotoxic effect. CONCLUSIONS: considering their significant anticancer activity and chemosensitivity, 6F: and 7H: may improve the therapeutic efficacy of the current treatment for cancer.

Comparative oncology: The paradigmatic example of canine and human mast cell neoplasms.

In humans, advanced mast cell (MC) neoplasms are rare malignancies with a poor prognosis. Only a few preclinical models are available, and current treatment options are limited. In dogs, MC neoplasms are the most frequent malignant skin tumours. Unlike low-grade MC neoplasms, high-grade MC disorders usually have a poor prognosis with short survival. In both species, neoplastic MCs display activating KIT mutations, which are considered to contribute to disease evolution. Therefore, tyrosine kinase inhibitors against KIT have been developed. Unfortunately, clinical responses are unpredictable and often transient, which remains a clinical challenge in both species. Therefore, current efforts focus on the development of new improved treatment strategies. The field of comparative oncology may assist in these efforts and accelerate human and canine research regarding diagnosis, prognostication, and novel therapies. In this article, we review the current status of comparative oncology approaches and perspectives in the field of MC neoplasms.

The JAK2/STAT5 signaling pathway as a potential therapeutic target in canine mastocytoma.

BACKGROUND: Mastocytoma are frequently diagnosed cutaneous neoplasms in dogs. In non-resectable mastocytoma patients, novel targeted drugs are often applied. The transcription factor STAT5 has been implicated in the survival of human neoplastic mast cells (MC). Our study evaluated the JAK2/STAT5 pathway as a novel target in canine mastocytoma. MATERIALS AND METHODS: We employed inhibitors of JAK2 (R763, TG101348, AZD1480, ruxolitinib) and STAT5 (pimozide, piceatannol) and evaluated their effects on 2 mastocytoma cell lines, C2 and NI-1. RESULTS: Activated JAK2 and STAT5 were detected in both cell lines. The drugs applied were found to inhibit proliferation and survival in these cells with the following rank-order of potency: R763 > TG101348 > AZD1480 > pimozide > ruxolitinib > piceatannol. Moreover, synergistic anti-neoplastic effects were obtained by combining pimozide with KIT-targeting drugs (toceranib, masitinib, nilotinib, midostaurin) in NI-1 cells. CONCLUSION: The JAK2/STAT5 pathway is a novel potential target of therapy in canine mastocytoma.

Cellular effects of a turmeric root and rosemary leaf extract on canine neoplastic cell lines.

BACKGROUND: The use of nutraceuticals is gaining in popularity in human and canine oncology with a relatively limited understanding of the effects in the vastly different tumor types seen in canine oncology. We have previously shown that turmeric root (TE) and rosemary leaf (RE) extracts can work synergistically to reduce neoplastic cell growth, but the mechanisms are poorly understood and require further elucidation. RESULTS: Three different canine cell lines (C2 mastocytoma, and CMT-12 mammary carcinoma, D17 osteosarcoma) were treated with 6.3 µg mL-1 extract individually, or 3.1 µg mL-1 of each extract in combination based on studies showing synergy of these two extracts. Apoptosis, antioxidant effects, cellular accumulation of curcumin, and perturbation of signaling pathways were assessed. The TE + RE combination treatment resulted in Caspase 3/7 activation and apoptosis in all cell lines, beyond the effects of TE alone with the CMT-12 cell line being most susceptible. Both extracts had antioxidant effects with RE reducing reactive oxygen species (ROS) by 40-50% and TE reducing ROS by 80-90%. In addition RE treatment enhanced the c-jun N-terminal kinase (JNK) activity in the C2 cell line and TE + RE exposure increased activated JNK by 4-5 times in the CMT-12 cell line. Upon further examination, it was found that RE treatment caused a significant increase in the cellular accumulation of curcumin by approximately 30% in the C2 and D17 cell lines, and by 4.8-fold in the CMT-12 cell line. This increase in intracellular curcumin levels may play a role in the synergy exhibited when using TE and RE in combination. CONCLUSIONS: The use of RE in combination with TE induces a synergistic response to induce apoptosis which is better than either extract alone. This appears to be related to a variable increased TE uptake in cells and activation of pathways involved in the apoptotic response.

Outcome of adjuvant chemotherapy with lomustine, vinblastine and chlorambucil on management of canine mast cell tumour of high to intermediate risk / Resultado da quimioterapia adjuvante com lomustina, vimblastina e clorambucil no manejo do mastocitoma canino de risco alto a intermediário

In spite of the many available protocols, the use of chemotherapy for the management of canine mast cell tumours (MCT) remains empirical, and there is lack of criteria for the choice of protocol and definition of patients who may benefit from treatment. The objective of this study was to evaluate the outcome of dogs with MCT after adjuvant chemotherapy according to the risk of recurrence or metastasis proposed on the literature. This prospective study included 89 followed up dogs with prognosis assesment including clinical, histological, immunohistochemical and genetic features of canine MCT. Patients were grouped according to risk of recurrence and metastasis and recommended treatment with lomustine followed by chlorambucil if considered at high-risk, or vinblastine followed by chlorambucil if a patient was at intermediate risk. Outcome was defined by disease-free interval (DFI) and overall survival (OS) estimated by Kaplan-Meier curve. Adjuvant lomustine was useful for control of canine MCT of high-risk of recurrence or metastasis, but only when sequentially associated to chlorambucil with a DFI of 686 days and not reached OS. There was no difference in outcome in the intermediate-risk group despite choosen treatment. Patients at intermediate-to-low risk may not require adjuvant treatments, even in the absence of free surgical margins.(AU)

Apesar dos inúmeros protocolos disponíveis, o uso da quimioterapia permanece empírico para o mastocitoma canino e faltam critérios para escolha do protocolo e da definição dos pacientes que poderiam se beneficiar do tratamento. O objetivo deste estudo foi avaliar o resultado de cães com mastocitoma após a quimioterapia adjuvante, de acordo com o risco de recorrência ou metástase proposto na literatura. Este estudo prospectivo incluiu 89 cães com acompanhamento clínico e avaliação prognóstica, incluindo características clínicas, histológicas, imuno-histoquímicas e genéticas dos mastocitomas. Os pacientes foram agrupados segundo o risco de recorrência ou metástase, sendo recomendado tratamento com lomustina seguida de clorambucila, se considerados sob alto risco, ou vimblastina seguida de clorambucila, se estivessem sob risco intermediário. O resultado final foi definido pelo intervalo livre de doença (ILD) e pela sobrevida global (SG), estimados pela curva de Kaplan-Meier. Na adjuvância, a lomustina foi útil no controle do mastocitoma canino de alto risco, mas apenas quando associada ao clorambucila, com um ILD de 686 dias, sem atingir a mediana para SG. Não houve diferença no grupo de risco intermediário, independentemente do tratamento escolhido. Pacientes de risco intermediário podem não necessitar de tratamentos adjuvantes, mesmo na ausência de margens cirúrgicas livres.(AU)

Tratamento de um mastocitoma de alto grau na língua de um cão por meio de radioterapia e quimioterapia: relato de caso / Treatment of a canine high grade lingual mast cell tumor with radiation therapy and chemotherapy: case report

Um canino da raça Boxer, fêmea, de oito anos de idade, foi atendido com salivação, halitose e disfagia. No exame clínico, foi observada uma massa ulcerada no terço médio da língua medindo 3,5 x 4,0cm. A histopatologia e a imuno-histoquímica levaram ao diagnóstico de um mastocitoma de alto grau. O tratamento cirúrgico (glossectomia parcial) foi declinado pelo proprietário, sendo a radioterapia indicada em seu lugar. O protocolo radioterápico empregado foi 15 frações de 300cGy, realizadas cinco vezes por semana. O equipamento utilizado foi de ortovoltagem. A lesão neoplásica apresentou remissão clínica completa a partir da quarta sessão radioterápica. O único efeito colateral observado foi mucosite leve na região irradiada, que, entretanto, não levou a sintomas clínicos. A quimioterapia sistêmica consistiu de vimblastina e lomustina, alternadas a cada 14 dias, durante quatro meses. Até o momento (22 meses após o tratamento), não há evidências de recidiva local ou metástases do mastocitoma. A associação da radioterapia e da quimioterapia pode ser considerada uma alternativa terapêutica nos casos de mastocitomas irressecáveis, já que, neste caso, levou à remissão completa e duradoura de um tumor agressivo, com ótima tolerância do paciente ao tratamento e posterior qualidade de vida.(AU)

An 8 year old female boxer was presented with salivation, halitosis and dysphagia. In the clinical examination, an ulcerated mass in the middle third of the tongue was observed, measuring 3.5 x 4.0cm. Histopathology and immunohistochemistry the confirmed diagnosis of a high-grade mast cell tumor. Surgical treatment (partial glossectomy) was declined by owner, and radiotherapy was indicated. The protocol consisted of fifteen daily fractions of 300 cGy each. The equipment used was an orthovoltage unit. The tumor had complete clinical remission after the fourth session, and mild mucositis was the only side effect observed. Systemic chemotherapy was performed with vinblastine and lomustine, alternated every 14 days, during four months. There is no evidence of local recurrence or metastasis in this patient twenty-two months after treatment. The combination of radiation therapy and chemotherapy can be considered as an alternative therapy in cases of unresectable mast cell tumors. It led to complete and durable remission of an aggressive tumor, with great quality of life.(AU)

Presumed masitinib-induced nephrotic syndrome and azotemia in a dog.

Masitinib mesylate is a tyrosine-kinase inhibitor approved for the treatment of nonresectable or recurrent, Grade 2 or 3 mast cell tumors in dogs. This report describes nephrotic syndrome and acute kidney injury attributed to masitinib and illustrates the need for regular monitoring of serum creatinine concentration, urinalysis, and urine protein:creatinine ratio during its use.

Présomption de syndrome néphrotique et d'azotémie induits par le masitinib chez un chien. Le mésylate de masitinib est un inhibiteur de la tyrosine-kinase homologué pour le traitement des mastocytes non résécables ou récurrents de grade 2 ou 3 chez les chiens. Ce rapport décrit le syndrome néphrotique et une blessure aiguë au rein attribués au masitinib et illustre le besoin d'une surveillance régulière de la concentration sérique de créatinine, des analyses d'urine et du ratio protéine:créatinine urinaire durant son utilisation.(Traduit par Isabelle Vallières).

Curcumin analogue, A13, exhibits anti-leukemia effect via inhibiting STAT3.

Abnormal activation of signal transducer and activator of transcription 3 (STAT3) was reported in some leukemia, and inhibition of STAT3 can be the strategy for the leukemia treatment in clinic. In this study, we tested the anti-tumor effect of compound A13, a water-soluble analogue of curcumin, in vitro and in vivo. Herein, we show that A13 was able to reduce the viability of mastocytoma (P815 cells) and reticulum cell sarcoma (A20 cells) as measured by MTS assay. This effect was accompanied by a marked increase in the proportion of apoptotic cells as measured by flow cytometry. Furthermore, Western blot analysis suggested that the anti-leukemia effect of A13 was realized via STAT3 inhibition. In addition, systemic treatment with A13 in the A20-bearing mice for 60 days resulted in a significant improvement of survival rate and marked reduction of liver metastasis. In summary, our data show that the A13 treatment could effectively be applied to acute leukemia via inhibiting STAT3 signaling pathway.

A retrospective review of treatment and response of high-risk mast cell tumours in dogs.

This retrospective case series evaluates survival outcome of 94 dogs with high metastatic risk mast cell tumours (MCT). Patients were treated with a cytotoxic chemotherapy protocol or the tyrosine kinase inhibitor masitinib, in the presence of gross disease or as an adjunct to surgical resection of the primary tumour. In patients presenting with metastatic disease, surgical resection of the primary tumour with adjunctive therapy with any chemotherapy incurred a significant survival advantage [median survival time (MST): 278 days] compared to patients receiving chemotherapy without surgical excision of the primary tumour (MST: 91 days, P < 0.0001). Patients with a surgically excised Patnaik grade II tumour and high Ki-67 in the absence of metastatic disease treated with vinblastine and prednisolone showed a significantly longer survival (MST: 1946 days) than those treated with masitinib (MST: 369 days, P = 0.0037). Further prospective case-controlled clinical trials of high-risk MCTs are required to make precise evidence-based treatment decisions for individual patients.

Subcutaneous administration of paclitaxel in dogs with cancer: A preliminary study.

Intravenous paclitaxel has been underused in dogs due to severe and acute hypersensitivity reactions. Subcutaneous (SC) administration of paclitaxel and its safety are unknown. In this preliminary study, SC administration of paclitaxel was evaluated for hypersensitivity reactions and toxicity in 21 dogs with advanced cancer. Dogs received 1 to 5 paclitaxel doses, ranging from 85 to 170 mg/m(2), SC every 14 or 21 days. A total of 40 paclitaxel doses were administered and none of the 21 dogs developed systemic or acute local hypersensitivity reactions. Severe skin lesions at the injection site developed in 2 dogs after the 4th injection at the same location. Grade 4 neutropenia was observed in 50% of the dogs 5 days after the first treatment at 115 mg/m(2) (n = 14). Two animals developed Grade 5 diarrhea and died likely due to hemodynamic failure or sepsis. Paclitaxel can be administered SC in dogs with no hypersensitivity reaction.

Administration sous-cutanée de paclitaxel chez des chiens atteints du cancer: une étude préliminaire. Le paclitaxel intraveineux a été sous-utilisé chez les chiens en raison de réactions d'hypersensibilité graves et aiguës. L'administration sous-cutanée (SC) de paclitaxel et son innocuité ne sont pas connues. Dans cette étude préliminaire, l'administration SC de paclitaxel a été évaluée pour des réactions d'hypersensibilité et de toxicité chez 21 chiens atteints d'un cancer avancé. Les chiens ont reçu de 1 à 5 doses de paclitaxel, allant de 85 à 170 mg/m2 SC tous les 14 ou 21 jours. Un total de 40 doses de paclitaxel ont été administrées et aucun des 21 chiens n'a développé de réactions d'hypersensibilité systémique ou locale aiguë. Des lésions cutanées graves au site d'injection se sont développées chez deux chiens après la quatrième injection au même endroit. Une neutropénie de grade 4 a été observée chez 50 % des chiens 5 jours après le premier traitement à 115 mg/m2 (n = 14). Deux animaux ont développé une diarrhée de grade 5 et sont morts probablement à cause d'une insuffisance hémodynamique ou d'une sepsie. Le paclitaxel peut être administré SC chez les chiens sans une réaction d'hypersensibilité.(Traduit par Isabelle Vallières).

Outcome and Prognostic Indicators in Cats Undergoing Splenectomy for Splenic Mast Cell Tumors.

This was a multi-institutional retrospective study evaluating the outcome and clinical parameters associated with the postoperative prognosis of 36 cats with splenic mast cell tumors treated with splenectomy. Clinical parameters reviewed included signalment, clinical history, results of staging tests, surgical variables, administration of blood products, presence of metastasis, postoperative complications, administration of chemotherapy postoperatively, chemotherapy protocol, and response to chemotherapy. Overall median survival time was 390 days (range, 2-1737 days). Administration of a blood product (P < .0001), metastasis to a regional lymph node (P = .022), and evidence of either concurrent or historical neoplasia (P = .037) were negatively associated with survival. Response to chemotherapy (P = .0008) was associated with an improved median survival time. Larger-scale prospective studies evaluating different chemotherapy protocols are required to elucidate the discrepancy between lack of survival benefit with administration of chemotherapy and improvement in survival time with positive response to chemotherapy.

Novel thiazole amine class tyrosine kinase inhibitors induce apoptosis in human mast cells expressing D816V KIT mutation.

Gain-of-function mutations of receptor tyrosine kinase KIT play a critical role in the pathogenesis of systemic mastocytosis (SM) and gastrointestinal stromal tumors. D816V KIT mutation, found in ∼80% of SM, is resistant to the currently available tyrosine kinase inhibitors (TKIs) (e.g. imatinib mesylate). Therefore, development of promising TKIs for the treatment of D816V KIT mutation is still urgently needed. We synthesized thiazole amine compounds and chose one representative designated 126332 to investigate its effect on human mast cells expressing KIT mutations. We found 126332 inhibited the phosphorylation of KIT and its downstream signaling molecules Stat3 and Stat5. 126332 inhibited the proliferation of D816V KIT expressing cells. 126332 induced apoptosis and downregulated levels of Mcl-1 and survivin. Furthermore, 126332 inhibited the tyrosine phosphorylation of ß-catenin, inhibited ß-catenin-mediated transcription and DNA binding of TCF. Moreover, 126332 also exhibited in vivo antineoplastic activity against cells harboring D816V mutation. Our findings suggest thiazole amine compounds may be promising agents for the treatment of diseases caused by KIT mutation.

Development of an in vitro model of acquired resistance to toceranib phosphate (Palladia®) in canine mast cell tumor.

BACKGROUND: Mast cell tumors (MCTs) are the most common skin tumors in dogs and exhibit variable biologic behavior. Mutations in the c-kit proto-oncogene are associated with the tumorigenesis of MCTs, resulting in growth factor-independent and constitutive phosphorylation of the KIT receptor tyrosine kinase (RTK). Toceranib (TOC) phosphate (Palladia®) is a KIT RTK inhibitor that has biological activity against MCTs. Despite these benefits, patients ultimately develop resistance to TOC. Therefore, there is a need to identify distinguishing clinical and molecular features of resistance in this population. RESULTS: The canine C2 mastocytoma cell line contains an activating mutation in c-kit. Three TOC-resistant C2 sublines (TR1, TR2, TR3) were established over seven months by growing cells in increasing concentrations of TOC. TOC inhibited KIT phosphorylation and cell proliferation in a dose-dependent manner in the treatment-naïve, parental C2 line (IC50 < 10 nM). In contrast, the three sublines were resistant to growth inhibition by TOC (IC50 > 1,000 nM) and phosphorylation of the KIT receptor was less inhibited compared to the TOC-sensitive C2 cells. Interestingly, sensitivity to three structurally distinct KIT RTK inhibitors was variable among the sublines, and all 3 sublines retained sensitivity to the cytotoxic agents vinblastine and lomustine. Sequencing of c-kit revealed secondary mutations in the juxtamembrane and tyrosine kinase domains of the resistant sublines. These included point mutations in TR1 (Q574R, M835T), TR2 (K724R), and TR3 (K580R, R584G, A620S). Additionally, chronic TOC exposure resulted in c-kit mRNA and KIT protein overexpression in the TOC-resistant sublines compared to the parental line. C2, TR1, TR2, and TR3 cells demonstrated minimal P-glycoprotein (P-gp) activity and no functional P-gp. CONCLUSIONS: This study demonstrates the development of an in vitro model of acquired resistance to targeted therapy in canine MCTs harboring a c-kit-activating mutation. This model may be used to investigate the molecular basis of and strategies to overcome TOC resistance.

Repeated administration of inhibitors for ion pumps reduce markedly tumor growth in vivo.

INTRODUCTION: Measurements of extracellular pH show that the micro environment of malignant tumors is more acidic than that of normal cells, whereas pH does not differ appreciable in normal and malignant cells. The acid micro environment of tumors is created by the secretion of tumor factors and ATP hydrolysis in hypoxic tumor tissue. In order to survive in a low pH-environment tumor cells develop regulatory mechanisms which keep their intracellular pH stable. Two of the most important systems are the Na+/H+ ion pump and the Na-dependent HCO3-/Cl- pump of stilbenian derivatives. MATERIAL AND METHODS: Experiments were carried out on DBA mice of both sexes at the age of 4 month. Laboratory animals were grown in our institute and supplied with food and aqua ad libitum. RESULTS: After termination of the experiments the mean tumor diameter in the control group was 12.4 +/- 0.8mm, in group A it was 6.9 +/- 0.6mm, and in group B we measured 6.6 +/- 3.1mm. At the final day the tumor size in treated animals was twice as small as in the control group. In addition we observed the rate of survival. In the control group only 18% of the animals were still alive at day 18. Considering the rate of survival a statistically significant difference between treated and untreated animals was observed. The survival of tumor cells is dependent on the function of these ion pumps which keep their intracellular pH values constant in the setting of an acid extracellular environment. CONCLUSION: The activity of the ion pump is especially important at the beginning of cell division and in cell proliferation. Our in vivo experiments demonstrate that prolonged administration of intratumoral ion pump inhibitors suppresses tumor growth as well as enhances survival of tumor-bearing animals. Research of inhibitors of ion pumps and their action in tumor growth opens new perspectives into pathophysiology of malignant tumors and may create new therapeutic options.