Efficacy and toxicity of paclitaxel (Taxol) for the treatment of canine malignant tumors

Anti-cancer effects of DHP107 on canine mammary gland cancer examined through in-vitro and in-vivo mouse xenograft models

BACKGROUND

Canine mammary gland cancer (CMGC) is a common neoplasm in intact bitches. However, the benefit of adjuvant chemotherapy is unclear. The aim of this study was to investigate the anti-proliferative effects of paclitaxel on CMGC in in-vitro and in-vivo settings.

RESULTS

Paclitaxel dose-dependently inhibited viability and induced G2/M phase cell cycle arrest and apoptosis in both primary and metastatic CMGC cell lines (CIPp and CIPm). In animal experiments, the average tumour volume decreased significantly in proportion to the administered oral paclitaxel dose. By examining tumour tissue using a TUNEL assay and immunohistochemical staining with anti-CD31 as a marker of endothelial differentiation, respectively, it was confirmed that oral paclitaxel induced apoptosis and exerted an anti-angiogenetic effect in tumour tissues. Further, downregulation of cyclin D1 in tumour tissues suggested that oral paclitaxel induced cell cycle arrest in tumour tissues in-vivo.

CONCLUSIONS

Our results suggest that paclitaxel may have anti-cancer effects on CMGC through cell cycle arrest, induction of apoptosis, and anti-angiogenesis. This study could provide a novel approach to treat CMGC.

mTOR pathway as a potential therapeutic target for cancer stem cells in canine mammary carcinoma

Mammary adenocarcinoma, the most common cancer in female dogs, often exhibits the lymph node and lung metastases and has a higher mortality rate. However, mammary adenocarcinoma has no established treatment, except early surgical excision. Canine mammary carcinoma has many common features with human mammary carcinoma, including clinical characteristics, heterogeneity, and genetic aberrations, making it an excellent spontaneous tumor model for human breast cancer. Diverse cancers comprised heterogeneous cell populations originating from cancer stem cells (CSCs) with self-renewal ability. Therefore, in addition to conventional therapy, therapeutic strategies targeting CSCs are essential for cancer eradication. The present study aimed to extract inhibitors of canine mammary CSCs that suppress their self-renewal ability. Sphere-formation assay, which evaluates self-renewal ability, was performed for the canine mammary cancer cell lines CTBp and CNMp. The spheres formed in this assay were used in inhibitor library screening, which identified various signaling pathways such as proteosome, stress inducer, and mammalian target of rapamycin (mTOR). The present study focused on the mTOR signaling pathway. Western blotting showed higher levels of phosphorylated mTOR in sphere-forming CTBp and CNMp cells than in adherent cells. Drug sensitivity examination using the mTOR inhibitors everolimus and temsirolimus revealed dose-dependent reductions in viability among both sphere-forming cells and adherent cells. Expression of phosphorylated mTOR in adherent and sphere-forming cells decreased by everolimus and temsirolimus treatment. In mice transplanted with CTBp-derived spheres, everolimus treatment significantly decreased tumor volume compared to control. These results reveal that the mTOR signaling pathway may be a potential to be a therapeutic target in both cancer cells and CSCs. Novel therapeutic strategies for canine mammary carcinoma are expected to benefit to human breast carcinoma as well.

Assessment of Efficacy and Toxicity of Cyclophosphamide Chemotherapy in Canines with Malignant Mammary Tumor: A Retrospective Study

Surgical excision with chemotherapy is a commonly used treatment modality to treat canine mammary tumor (CMT), but it is unclear whether different treatment modalities may have similar efficacies and toxicities. The objective of this clinical study was to evaluate the efficacy and toxicity of cyclophosphamide chemotherapy along with surgical excision of malignant mammary tumor in canines by clinical, haemato-biochemical, radiographical, and histopathological evaluation before and after treatment. Eighteen dogs with malignant mammary tumor, reported to Teaching Veterinary Hospital, were divided into two groups consisting of nine dogs in each group. Group I (n = 9) dogs were treated with surgical excision of malignant mammary tumor alone, and group II (n = 9) was treated with surgical excision of mammary tumor with cyclophosphamide chemotherapy at 50-100 mg/m2 intravenously in weekly doses by three consecutive weeks. In group II, 7 dogs (78%) showed complete regression of tumor after the third dose of cyclophosphamide and showed increase in the quality and survival life and remaining two dogs showed recurrence of tumor after one year. Some dogs showed common adverse reactions such as lethargy, moderate alopecia, vomiting, anorexia, anemia, and haematuria after the third dose of chemotherapy. To conclude, surgical excision combined with cyclophosphamide chemotherapy is an effective protocol for management of malignant mammary tumor in canines with minimal toxicity and it could be possible to increase the quality and survival life of patients.

From Conventional to Precision Therapy in Canine Mammary Cancer: A Comprehensive Review

Canine mammary tumors (CMTs) are the most common neoplasm in intact female dogs. Canine mammary cancer (CMC) represents 50% of CMTs, and besides surgery, which is the elective treatment, additional targeted and non-targeted therapies could offer benefits in terms of survival to these patients. Also, CMC is considered a good spontaneous intermediate animal model for the research of human breast cancer (HBC), and therefore, the study of new treatments for CMC is a promising field in comparative oncology. Dogs with CMC have a comparable disease, an intact immune system, and a much shorter life span, which allows the achievement of results in a relatively short time. Besides conventional chemotherapy, innovative therapies have a large niche of opportunities. In this article, a comprehensive review of the current research in adjuvant therapies for CMC is conducted to gather available information and evaluate the perspectives. Firstly, updates are provided on the clinical-pathological approach and the use of conventional therapies, to delve later into precision therapies against therapeutic targets such as hormone receptors, tyrosine kinase receptors, p53 tumor suppressor gene, cyclooxygenases, the signaling pathways involved in epithelial-mesenchymal transition, and immunotherapy in different approaches. A comparison of the different investigations on targeted therapies in HBC is also carried out. In the last years, the increasing number of basic research studies of new promising therapeutic agents on CMC cell lines and CMC mouse xenografts is outstanding. As the main conclusion of this review, the lack of effort to bring the in vitro studies into the field of applied clinical research emerges. There is a great need for well-planned large prospective randomized clinical trials in dogs with CMC to obtain valid results for both species, humans and dogs, on the use of new therapies. Following the One Health concept, human and veterinary oncology will have to join forces to take advantage of both the economic and technological resources that are invested in HBC research, together with the innumerable advantages of dogs with CMC as a spontaneous animal model.

Case Report: Microfragmented Adipose Tissue Drug Delivery in Canine Mesothelioma: A Case Report on Safety, Feasibility, and Clinical Findings

Mesothelioma is a rare lethal tumor of dogs and humans involving cavities of the body. Dogs are considered a model for new drugs and therapeutic methods since they present spontaneous diseases similar to humans. Microfragmented adipose tissue (MFAT) uploaded by paclitaxel (PTX) is a drug delivery medium providing slow release of chemotherapic drugs. A dog affected by pleural, pericardial, and peritoneal mesothelioma was treated by 17 intracavitary ultrasound-guided injections of MFAT-PTX over 22 months. A long-lasting improvement of general conditions was observed, treatment was well-tolerated, and no toxicity or hypersensitivity was reported. Pharmacokinetic (PK) data indicated low drug localization in the circulatory system and a tendency to enter or remain in the extravascular compartments of the body. Indeed, low levels of free-circulating drugs for a short time produced low toxicity, whereas, a higher intracavitary PTX concentration can have major pharmacological efficacy. To our knowledge, this is the first time that mesothelioma has been treated using such a procedure, and this should be considered as a novel therapeutic approach. The low systemic absorption suggests the possible role of MFAT-PTX for loco-regional/intratumoral therapy also useful in other types of tumors, and further investigation is warranted.

Cytotoxic and Apoptotic Effect of Nanoclinoptilolite on Canine Osteosarcoma Cell Lines

Introduction

Clinoptilolite has antiviral, antibacterial, anti-inflammatory, antidiabetic, and anticancer properties due to its biological activities. In various cancer cell culture studies, it has been reported effective against tumour cells and gave positive results in treatment of various tumours in dogs. No study was found on the effects of the nanoparticulate form, nanoclinoptilolite, on cancer cells. The aim of this study was to determine its cytotoxic and apoptotic effects in canine osteosarcoma (OSA) cell culture.

Material and Methods

Doses at 50% inhibitory concentration were determined by measuring the dose- and duration-dependent cytotoxicity of nanoclinoptilolite on canine D-17 osteosarcoma cells by methylthiazol tetrazolium (MTT) test for 24 h, 48 h, and 72 h. Murine caspase-3 and -7 activity and expression levels of the BAX and BCL2 genes were measured using RT-PCR to investigate the apoptotic effect.

Results

Nanoclinoptilolite decreased cell viability and induced caspase-3- and -7-mediated apoptosis in treated canine OSA cells. Furthermore, its application to canine OSA cells downregulated the expression of BCL2 and upregulated the expression of proapoptotic BAX.

Conclusion

Clinoptilolite, which was previously demonstrated to have anticancer properties, decreased cell viability effectively and rapidly and increased the apoptotic cell ratio in a novel use in nanoparticle form, exhibiting this effect by increasing the BAX/BCL2 ratio.

Photohyperthermal therapy using liposomally formulated indocyanine green for feline nasal lymphoma: A case report

Our previous research has focused on the development of a novel cancer therapy by using photohyperthermal therapy (PHT) with indocyanine green (ICG) as an optical sensitizer. ICG-Lipo is a liposomally formulated ICG derivative in which ICG is tagged with an octadeca-alkyl chain to incorporate into liposome bilayers, and contains antitumor drugs such as carboplatin and paclitaxel within the inner membrane space. The present study reported a case of feline nasal lymphoma that was treated with combination therapy of PHT with ICG-Lipo. An antitumour effect was observed, and the patient entered remission. Complications from the radiation treatment included skin burns and bleeding from the irradiated hard palate. Serious side effects related to the drugs were not observed. This report suggested that PHT using ICG-Lipo enabled efficient and safe treatment of lymphoma, and that treatment with a liposomal drug delivery system was enhanced by PHT.

Use of oral paclitaxel for the treatment of bladder tumors in dogs

An oral paclitaxel formulation that overcomes the hypersensitivity reaction of paclitaxel has been evaluated for safety and efficacy in humans, but not in dogs. We present the first case report on the use of oral paclitaxel in dogs. In this study, oral paclitaxel was well-tolerated in four dogs with either transitional cell carcinoma or prostate cancer; adverse effects were limited to mild neutropenia. Each of the dogs had progressive disease at the end, but clinical responses, including changes in mass size and improvement of clinical symptoms, were confirmed in some of the animals following oral paclitaxel chemotherapy. Although this study is somewhat limited by a small sample size, it suggests that oral paclitaxel may be a chemotherapeutic option for malignant tumors in dogs.

Dog-specific hemorrhagic changes induced by liposomal formulations, in the liver and the gallbladder

Although several liposomal drugs, including liposomal doxorubicin, have been approved, the etiology of the pathological responses caused by their physicochemical properties remains unknown. Herein, we investigated the pathological changes in the liver and the gallbladder of dogs following a single injection of liposomal doxorubicin (1 or 2.5 mg/kg) or an empty liposomal formulation (i.e., liposomal formulation without doxorubicin, ca. 21 mg/kg as lipid content). Injection of liposomal doxorubicin or the empty liposomal formulation induced hemorrhagic changes in the liver and the gallbladder. These changes were accompanied by minimal cellular infiltration with no obvious changes in the blood vessels. As there were no differences in the incidence and severity of hemorrhage between the groups administered comparable amounts of total lipid, the physicochemical properties of the liposomal formulation rather than an active pharmacological ingredient, doxorubicin, were associated with the hemorrhagic changes. Furthermore, decreased cytoplasmic granules with low electron density in mast cells beneath the endothelium of the hepatic vein were observed in the liver of dogs treated with liposomal doxorubicin or empty liposomal formulation. Injection of compound 48/80, a histamine releaser induced comparable hemorrhage in dogs, implying that hemorrhage caused by injection of liposomal doxorubicin or the empty liposomal formulation could be attributed to the histamine released from mast cells. The absence of similar hemorrhagic lesions in other species commonly used in toxicology studies (i.e., rats and monkeys), as well as humans, is due to the lack of mast cells beneath the endothelium of the hepatic vein in these species.

Review of oncological emergencies in small animal patients

Oncological emergencies can occur at any time during the course of a malignancy and need to be recognized promptly to maximize successful outcomes. Emergencies are characterized as chemotherapy-induced, paraneoplastic syndromes, or directly related to the neoplasm. Prompt identification with treatment of these emergencies can prolong survival and improve quality of life, even in the setting of terminal illness. This review aims to educate the reader on the pathophysiology, clinical presentation and treatment of some of these emergencies, and to review the current veterinary literature to help educate veterinarians in primary and tertiary facilities to know how to diagnose and treat these serious conditions.

Suicide Gene Therapy By Amphiphilic Copolymer Nanocarrier for Spinal Cord Tumor

Spinal cord tumors (SCT) are uncommon neoplasms characterized by irregular growth of tissue inside the spinal cord that can result in non-mechanical back pain. Current treatments for SCT include surgery, radiation therapy, and chemotherapy, but these conventional therapies have many limitations. Suicide gene therapy using plasmid encoding herpes simplex virus-thymidine kinase (pHSV-TK) and ganciclovir (GCV) has been an alternative approach to overcome the limitations of current therapies. However, there is a need to develop a carrier that can deliver both pHSV-TK and GCV for improving therapeutic efficacy. Our group developed a cationic, amphiphilic copolymer, poly (lactide-co-glycolide) -graft-polyethylenimine (PgP), and demonstrated its efficacy as a drug and gene carrier in both cell culture studies and animal models. In this study, we evaluated PgP as a gene carrier and demonstrate that PgP can efficiently deliver reporter genes, pGFP in rat glioma (C6) cells in vitro, and pβ-gal in a rat T5 SCT model in vivo. We also show that PgP/pHSV-TK with GCV treatment showed significantly higher anticancer activity in C6 cells compared to PgP/pHSV-TK without GCV treatment. Finally, we demonstrate that PgP/pHSV-TK with GCV treatment increases the suicide effect and apoptosis of tumor cells and reduces tumor size in a rat T5 SCT model.

A novel canine histiocytic sarcoma cell line: initial characterization and utilization for drug screening studies

BACKGROUND

Histiocytic sarcoma is a rare disorder in humans, however it is seen with appreciable frequency in certain breeds of dogs, such as Bernese mountain dog. The purpose of this study was to fully characterize a novel canine histiocytic sarcoma cell line, and utilize it as a tool to screen for potential therapeutic drugs.

METHODS

The histiocytic sarcoma cell line was characterized by expression of cellular markers as determined by immunohistochemistry and flow cytometry techniques. The neoplastic cells were also evaluated for their capability of phagocytizing beads particles, and their potential to grow as xenograft in an immunodeficient mouse. We investigated the in vitro cytotoxic activity of a panel of thirteen compounds using the MTS proliferation assay. Inhibitory effects of different drugs were compared using one-way ANOVA, and multiple means were compared using Tukey's test.

RESULTS

Neoplastic cells expressed CD11c, CD14, CD18, CD45, CD172a, CD204, MHC I, and vimentin. Expression of MHC II was upregulated after exposure to LPS. Furthermore, the established cell line clearly demonstrated phagocytic activity similar to positive controls of macrophage cell line. The xenograft mouse developed a palpable subcutaneous soft tissue mass after 29 days of inoculation, which histologically resembled the primary neoplasm. Dasatinib, a tyrosine kinase pan-inhibitor, significantly inhibited the growth of the cells in vitro within a clinically achievable and tolerable plasma concentration. The inhibitory response to dasatinib was augmented when combined with doxorubicin.

CONCLUSIONS

In the present study we demonstrated that a novel canine histiocytic sarcoma cell line presents a valuable tool to evaluate novel treatment approaches. The neoplastic cell line favorably responded to dasatinib, which represents a promising anticancer strategy for the treatment of this malignancy in dogs and similar disorders in humans.

A Review of Paclitaxel and Novel Formulations Including Those Suitable for Use in Dogs

Paclitaxel is a commonly used chemotherapeutic agent with a broad spectrum of activity against cancers in humans. In 1992, paclitaxel was approved by the U.S. Food and Drug Administration (FDA) as Taxol(®) for use in advanced ovarian cancer. Two years later, it was approved for the treatment of metastatic breast cancer. Paclitaxel was originally isolated from the bark of the Pacific yew tree, Taxus brevifolia in 1971. Taxanes are a family of microtubule inhibitors. As a member of this family, paclitaxel suppresses spindle microtubule dynamics. This activity results in the blockage of the metaphase-anaphase transitions, and ultimately in the inhibition of mitosis, and induction of apoptosis in a wide spectrum of cancer cells. Additional anticancer activities of paclitaxel have been defined that are independent of these effects on the microtubules and may include the suppression of cell proliferation as well as antiangiogenic effects. Based on its targeting of a fundamental feature of the cancer phenotype, the mitotic complex, it is not surprising that paclitaxel has been found to be active in a wide variety of cancers in humans. This review summarizes the evidence in support of paclitaxel's broad anticancer activity and introduces the rationale for, and the progress in development of novel formulations of paclitaxel that may preferentially target cancers and that are not associated with the risks for hypersensitivity in dogs. Of note, a novel nanoparticle formulation of paclitaxel that substantially limits hypersensitivity was recently given conditional approval by the FDA Center for Veterinary Medicine for use in dogs with resectable and nonresectable squamous cell carcinoma and nonresectable stage III, IV and V mammary carcinoma.

Species differences in tumour responses to cancer chemotherapy

Despite advances in chemotherapy, radiotherapy and targeted drug development, cancer remains a disease of high morbidity and mortality. The treatment of human cancer patients with chemotherapy has become commonplace and accepted over the past 100 years. In recent years, and with a similar incidence of cancer to people, the use of cancer chemotherapy drugs in veterinary patients such as the dog has also become accepted clinical practice. The poor predictability of tumour responses to cancer chemotherapy drugs in rodent models means that the standard drug development pathway is costly, both in terms of money and time, leading to many drugs failing in Phase I and II clinical trials. This has led to the suggestion that naturally occurring cancers in pet dogs may offer an alternative model system to inform rational drug development in human oncology. In this review, we will explore the species variation in tumour responses to conventional chemotherapy and highlight our understanding of the differences in pharmacodynamics, pharmacokinetics and pharmacogenomics between humans and dogs. Finally, we explore the potential hurdles that need to be overcome to gain the greatest value from comparative oncology studies.

Hypersensitivity and nanoparticles: update and research trends

Nanotechnology holds a great promise for a wide range of medical-intent applications (diagnostic, treatment and prophylaxis of various diseases). Their advantages are due to their size, versatility and potential for multiple simultaneous applications. However, concerns have been formulated by scientific world due to insufficient data on toxicity of nanomaterials. One area of interest is represented by the interactions between nanoparticles and the components of the immune system. We review herein reported data on hypersensitivity reactions. The role exerted by nanoparticles in both immunostimulation and immunosuppression in allergen-driven mechanisms was studied, as well as future trends in worldwide research.

Cytotoxic and antiangiogenic paclitaxel solubilized and permeation-enhanced by natural product nanoparticles

Paclitaxel (PTX) is one of the most potent intravenous chemotherapeutic agents to date, yet an oral formulation has been problematic because of its low solubility and permeability. Using the recently discovered solubilizing properties of rubusoside (RUB), we investigated the unique PTX-RUB formulation. PTX was solubilized by RUB in water to levels of 1.6-6.3 mg/ml at 10-40% weight/volume. These nanomicellar PTX-RUB complexes were dried to a powder, which was subsequently reconstituted in physiologic solutions. After 2.5 h, 85-99% of PTX-RUB remained soluble in gastric fluid, whereas 79-96% remained soluble in intestinal fluid. The solubilization of PTX was mechanized by the formation of water-soluble spherical nanomicelles between PTX and RUB, with an average diameter of 6.6 nm. Compared with Taxol, PTX-RUB nanoparticles were nearly four times more permeable in Caco-2 cell monocultures. In a side-by-side comparison with dimethyl sulfoxide-solubilized PTX, PTX-RUB maintained the same level of cytotoxicity against three human cancer cell lines with IC50 values ranging from 4 to 20 nmol/l. In addition, tubule formation and migration of human umbilical vein endothelial cells were inhibited at levels as low as 5 nmol/l. These chemical and biological properties demonstrated by the PTX-RUB nanoparticles may improve oral bioavailability and enable further pharmacokinetic, toxicologic, and efficacy investigations.

Evaluation of the drug sensitivity and expression of 16 drug resistance-related genes in canine histiocytic sarcoma cell lines

Canine histiocytic sarcoma (HS) is an aggressive tumor type originating from histiocytic cell lineages. This disease is characterized by poor response to chemotherapy and short survival time. Therefore, it is of critical importance to identify and develop effective antitumor drugs against HS. The objectives of this study were to examine the drug sensitivities of 10 antitumor drugs. Using a real-time RT-PCR system, the mRNA expression levels of 16 genes related to drug resistance in 4 canine HS cell lines established from dogs with disseminated HS were determined and compared to 2 canine lymphoma cell lines (B-cell and T-cell). These 4 canine HS cell lines showed sensitivities toward microtubule inhibitors (vincristine, vinblastine and paclitaxel), comparable to those in the canine B-cell lymphoma cell line. Moreover, it was shown that P-gp in the HS cell lines used in this study did not have enough function to efflux its substrate. Sensitivities to melphalan, nimustine, methotrexate, cytarabine, doxorubicin and etoposide were lower in the 4 HS cell lines than in the 2 canine lymphoma cell lines. The data obtained in this study using cultured cell lines could prove helpful in the developing of advanced and effective chemotherapies for treating dogs that are suffering from HS.

Clinical characteristics and prognostic factors in dogs with histiocytic sarcomas in Japan

Canine histiocytic sarcoma (HS) is a rare neoplasm that originates from dendritic cells or macrophages, and there have been a number of cases experienced in Japan. To identify the characteristics and prognostic variables that determine outcome in dogs with HS in Japan, medical records of 73 dogs with HS were retrospectively analyzed. Signalment, clinical signs, complete blood count (CBC), blood chemistry profiles, treatment, response to treatment and overall survival (OS) were analyzed. Diagnosis of HS was determined histologically in 44 cases and cytologically in 29 cases. The most frequently diagnosed breeds were Flat-Coated Retrievers (n=16, odds ratio [OR] 62.0), Pembroke Welsh corgis (n=15, OR 9.7) and Bernese Mountain dogs (n=14, OR 45.0). Median survival time for all dogs in this study was 43 days. In the dogs that received no treatment or only symptomatic treatment, the median OS was 12 days (range 2–254 days) compared with that of dogs that received surgical treatment and/or chemotherapy (85 days, range 4–360 days). Univariate analysis identified anemia, thrombocytopenia, hypoalbuminemia, hypoproteinemia and not receiving antitumor treatment (chemotherapy and/or surgery) as factors significantly associated with shorter OS. Multivariate analysis confirmed that platelet counts, localized/disseminated lesional pattern and whether the dog received antitumor treatment were significantly predictive of survival.

A randomized trial investigating the efficacy and safety of water soluble micellar paclitaxel (Paccal Vet) for treatment of nonresectable grade 2 or 3 mast cell tumors in dogs

BACKGROUND

Effective treatments for dogs with advanced stage mast cell tumors (MCT) remain a pressing need. A micellar formulation of paclitaxel (paclitaxel [micellar]) has shown promise in early-phase studies.

HYPOTHESIS/OBJECTIVES

The objective was to demonstrate greater activity for paclitaxel (micellar) compared with lomustine. The null hypothesis was μ(p) = μ(L) (ie, proportion of responders for the paclitaxel [micellar] and lomustine groups, respectively).

ANIMALS

Two hundred and fifty-two dogs with advanced stage nonresectable grade 2 or 3 MCT.

METHODS

Prospective multicenter randomized double-blind positive-controlled clinical trial. The primary endpoint was confirmed overall response rate (CORR) at 14 weeks. A secondary endpoint, biologic observed response rate (BORR), also was calculated. Safety was assessed by the characterization and grading of adverse events (AE).

RESULTS

Overall CORR (7% versus 1%; P = .048) and BORR (23% versus 10%; P = .012) were greater for paclitaxel (micellar) compared with lomustine. Paclitaxel (micellar)-treated dogs were 6.5 times more likely to have a confirmed response and 3.1 times more likely to experience a biologic observed response. The majority of AE with paclitaxel (micellar) were transient and clinically manageable. Twenty-seven dogs (33%) receiving lomustine were discontinued because of hepatopathy compared with 3 dogs (2%) receiving paclitaxel (micellar) (P < .0001; odds ratio 26.7).

CONCLUSIONS AND CLINICAL IMPORTANCE

Paclitaxel (micellar)'s activity and safety profile are superior to lomustine. The addition of an active and novel taxane to the veterinary armamentarium could fill a substantial need and, as its mechanism of action and AE profile do not overlap with currently available TKI, its availability could lead to effective combination protocols.

Delayed onset of paresis in rats with experimental intramedullary spinal cord gliosarcoma following intratumoral administration of the paclitaxel delivery system OncoGel

OBJECT

Treatment options for anaplastic or malignant intramedullary spinal cord tumors (IMSCTs) remain limited. Paclitaxel has potent cytotoxicity against experimental intracranial gliomas and could be beneficial in the treatment of IMSCTs, but poor CNS penetration and significant toxicity limit its use. Such limitations could be overcome with local intratumoral delivery. Paclitaxel has been previously incorporated into a biodegradable gel depot delivery system (OncoGel) and in this study the authors evaluated the safety of intramedullary injections of OncoGel in rats and its efficacy against an intramedullary rat gliosarcoma.

METHODS

Safety of intramedullary OncoGel was tested in 12 Fischer-344 rats using OncoGel concentrations of 1.5 and 6.0 mg/ml (5 μl); median survival and functional motor scores (Basso-Beattie-Bresnahan [BBB] scale) were compared with those obtained with placebo (ReGel) and medium-only injections. Efficacy of OncoGel was tested in 61 Fischer-344 rats implanted with an intramedullary injection of 9L gliosarcoma containing 100,000 cells in 5 μl of medium, and randomized to receive OncoGel administered on the same day (in 32 rats) or 5 days after tumor implantation (in 29 rats) using either 1.5 mg/ml or 3.0 mg/ml doses of paclitaxel. Median survival and BBB scores were compared with those of ReGel-treated and tumor-only rats. Animals were killed after the onset of deficits for histopathological analysis.

RESULTS

OncoGel was safe for intramedullary injection in rats in doses up to 5 μl of 3.0 mg/ml of paclitaxel; a dose of 5 μl of 6.0 mg/ml caused rapid deterioration in BBB scores. OncoGel at concentrations of 1.5 mg/ml and 3.0 mg/ml paclitaxel given on both Day 0 and Day 5 prolonged median survival and preserved BBB scores compared with controls. OncoGel 1.5 mg/ml produced 62.5% long-term survivors when delivered on Day 0. A comparison between the 1.5 mg/ml and the 3.0 mg/ml doses showed higher median survival with the 1.5 mg/ml dose on Day 0, and no differences in median survival or BBB scores after treatment on Day 5.

CONCLUSIONS

OncoGel is safe for intramedullary injection in rats in doses up to 5 μl of 3.0 mg/ml, prolongs median survival, and increases functional motor scores in rats challenged with an intramedullary gliosarcoma at the doses tested. This study suggests that locally delivered chemotherapeutic agents could be of temporary benefit in the treatment of malignant IMSCTs under experimental settings.

Phase I dose escalation safety study of nanoparticulate paclitaxel (CTI 52010) in normal dogs

Background

Paclitaxel is highly effective in the treatment of many cancers in humans, but cannot be routinely used in dogs as currently formulated due to the exquisite sensitivity of this species to surfactant-solubilizing agents. CTI 52010 is a formulation of nanoparticulate paclitaxel consisting of drug and normal saline. Our objectives were to determine the maximally tolerated dose, dose-limiting toxicities, and pharmacokinetics of CTI 52010 administered intravenously to normal dogs.

Methods

Three normal adult hound dogs were evaluated by physical examination, complete blood count, chemistry profile, and urinalysis. Dogs were treated with staggered escalating dosages of CTI 52010 with a 28-day washout. All dogs were treated with a starting dosage of 40 mg/m², and subsequent dosages were escalated at 50% (dog 1), 100% (dog 2), or 200% (dog 3) with each cycle, to a maximum of 240 mg/m². Dogs were monitored by daily physical assessment and weekly laboratory evaluation. Standard criteria were used to grade adverse events. Plasma was collected at regular intervals to determine pharmacokinetics. Dogs were euthanized humanely, and necropsy was performed one week after the last treatment.

Results

The dose-limiting toxicity was grade 4 neutropenia and the maximum tolerated dosage was 120 mg/m². Grade 1–2 gastrointestinal toxicity was noted at higher dosages. Upon post mortem evaluation, no evidence of organ (liver, kidney, spleen) toxicity was noted.

Conclusion

CTI 52010 was well tolerated when administered intravenously to normal dogs. A starting dosage for a Phase I/II trial in tumor-bearing dogs is 80 mg/m².

A novel paclitaxel microemulsion containing a reduced amount of Cremophor EL: pharmacokinetics, biodistribution, and in vivo antitumor efficacy and safety

The purpose of this study was to prepare a novel paclitaxel (PTX) microemulsion containing a reduced amount of Cremophor EL (CrEL) which had similar pharmacokinetics and antitumor efficacy as the commercially available PTX injection, but a significantly reduced allergic effect due to the CrEL. The pharmacokinetics, biodistribution, in vivo antitumor activity and safety of PTX microemulsion was evaluated. The results of pharmacokinetic and distribution properties of PTX in the microemulsion were similar to those of the PTX injection. The antitumor efficacy of the PTX microemulsion in OVCRA-3 and A 549 tumor-bearing animals was similar to that of PTX injection. The PTX microemulsion did not cause haemolysis, erythrocyte agglutination or simulative reaction. The incidence and degree of allergic reactions exhibited by the PTX microemulsion group, with or without premedication, were significantly lower than those in the PTX injection group (P < .01). In conclusion, the PTX microemulsion had similar pharmacokinetics and anti-tumor efficacy to the PTX injection, but a significantly reduced allergic effect due to CrEL, indicating that the PTX microemulsion overcomes the disadvantages of the conventional PTX injection and is one way of avoiding the limitations of current injection product while providing suitable therapeutic efficacy.

In vitro and in vivo evaluation of combined calcitriol and cisplatin in dogs with spontaneously occurring tumors

PURPOSE

Calcitriol potentiates cisplatin-mediated activity in a variety of tumor models. We examine here, the effect of calcitriol and cisplatin pre-clinically and clinically in canine spontaneous tumors through in vitro studies on tumor cells and through a phase I study of calcitriol and cisplatin to identify the maximum-tolerated dosage (MTD) of this combination in dogs with cancer and to characterize the pharmacokinetic disposition of calcitriol in dogs.

METHODS

Canine tumor cells were investigated for calcitriol/cisplatin interactions on proliferation using an MTT assay in a median-dose effect analysis; data were used to derive a combination index (CI). Cisplatin was given at a fixed dosage of 60 mg/m2. Calcitriol was given i.v. and the dosage was escalated in cohorts of three dogs until the MTD was defined. Serum calcitriol concentrations were quantified by radioimmunoassay.

RESULTS

In vitro, CIs < 1.0 were obtained for all combinations of calcitriol/cisplatin examined. The MTD was 3.75 microg/kg calcitriol in combination with cisplatin, and hypercalcemia was the dose-limiting toxicosis. The relationship between calcitriol dosage and either Cmax or AUC was linear. Calcitriol dosages >1.5 microg/kg achieved Cmax > or = 9.8 ng/mL and dosages >1.0 microg/kg achieved AUC > or = 45 h ng/mL.

CONCLUSIONS

Calcitriol and cisplatin have synergistic antiproliferative effects on multiple canine tumor cells and high-dosages of i.v. calcitriol in combination with cisplatin can be safely administered to dogs. Cmax and AUC at the MTD 3.75 microg/kg calcitriol exceed concentrations associated with antitumor activity in a murine model, indicating this combination might have significant clinical utility in dogs.

Local intracerebral administration of Paclitaxel with the paclimer delivery system: toxicity study in a canine model

INTRODUCTION

Paclitaxel, a microtubule binding agent with potent anti-glioma activity in vitro, exhibits poor penetrance to the CNS when delivered systemically. To minimize toxicity and reach therapeutic concentrations in the CNS, paclitaxel was previously incorporated into biodegradable microspheres (Paclimer), and the efficacy of Paclimer was determined in a rat model of malignant glioma. In this study we report the safety of intracranial Paclimer in a canine dose escalation toxicity study to prepare its translation into clinical scenarios.

METHODS

Twelve normal beagle dogs underwent a right parieto-occipital craniectomy and were randomized to receive either Paclimer at 2-mg/kg (n=5), empty microspheres at 2-mg/kg (n=1), Paclimer at 20-mg/kg (n=5), or empty microspheres at 20-mg/kg (n=1). Post-operatively, dogs were observed daily for signs of neurotoxicity. Complete blood counts and plasma levels of paclitaxel were obtained weekly. CSF levels and MRI scans were obtained on days 14-120. Paclitaxel concentrations were quantified by LC-MS.

RESULTS

Animals treated with 20-mg/kg Paclimer had minimal paclitaxel levels in plasma (range 0-7.84 ng/ml) and CSF (range 0-1.16 ng/ml). Animals treated with 2 mg/kg Paclimer had undetectable levels of paclitaxel in plasma, CSF was not obtained to minimize animal suffering. All animals exhibited normal behavior and weight gain, and were alive post-operatively through the last day of the study (day 60-120) without signs of neurological toxicity. There was no evidence of systemic toxicity or myelosuppression. MR imaging was comparable between Paclimer animals and controls. Adverse effects included wound infections and a brain abscess, all of which responded to antibiotic therapy, and one ventriculomegaly due to communicating hydrocephalus.

CONCLUSIONS

Paclimer-based delivery of paclitaxel is safe for intraparenchymal delivery at the tested doses in normal dogs.

Identification of 12Cysbeta on tubulin as the binding site of tubulyzine

We have undertaken quantitative binding site studies in order to identify the binding site of the known microtubule destabilizing agents, the tubulyzines, in the tubulin dimer. Two different approaches were employed that utilized the tubulyzines and their derivatives. The first approach was based on a chemical affinity labeling method using tubulyzine affinity derivatives, and the second approach employed the mass spectrometric measurement of the differential reactivity of cysteines using the tubulyzines and monobromobimane. Based on overlapping data from these two approaches, we propose that the tubulyzines bind at the guanosine-5'-triphosphate binding site of beta-tubulin. Interestingly, we also show that the tubulyzines' binding to tubulin induces a conformational change in tubulin that prevents further interaction of the 239Cysbeta with other reagents.