Precision Medicine in Veterinary Science.

Precision medicine focuses on the clinical management of the individual patient, not on population-based findings. Successes from human precision medicine inform veterinary oncology. Early evidence of success for canines shows how precision medicine can be integrated into practice. Decreasing genomic profiling costs will allow increased utilization and subsequent improvement of knowledge base from which to make better informed decisions. Utility of precision medicine in canine oncology will only increase for improved cancer characterization, enhanced therapy selection, and overall more successful management of canine cancer. As such, practitioners are called to interpret and leverage precision medicine reports for their patients.

Effects of a high-protein, increased-fibre, dry diet supplemented with omega-3 fatty acids on quality of life in dogs undergoing chemotherapy.

Quality of life (QOL) in dogs with cancer is a key consideration in the assessment of cancer treatment options. Despite interest in dietary strategies to improve management of oncology patients, there have been very few clinical studies showing the impact of diet on adverse effects of chemotherapy in dogs. This study was a randomised, controlled, double-blinded, multicenter clinical trial to investigate a high-protein, increased-fibre diet supplemented with omega-3 fatty acids, for dogs with cancer undergoing standard-of-care chemotherapy. Client-owned dogs with newly diagnosed grade 2 or higher mast cell tumours (or non-resectable/incompletely resected tumours) or multicentric lymphoma were randomised to receive the test diet (n = 24) or control diet (n = 21) for 8 weeks. Primary outcomes were QOL assessments, faecal scores, and blood concentrations of C-reactive protein and monocyte chemoattractant protein-1. Of 12 QOL parameters, 10 significantly improved from baseline to Week 8 in the test group compared with one in the control group. However, differences between the two groups were only statistically significant for 'frequency of signs of illness' (P = .009). There were no significant differences in the incidence of any adverse events, including gastrointestinal adverse events or clinically significant differences in laboratory parameters or faecal scores between the two groups. The absence of an observed negative impact of the test diet, combined with the magnitude of QOL improvements associated with the diet, suggest that a larger trial is warranted.

Identification of genomic alterations with clinical impact in canine splenic hemangiosarcoma.

Canine hemangiosarcoma (HSA) is an aggressive cancer of endothelial cells with short survival times. Understanding the genomic landscape of HSA may aid in developing therapeutic strategies for dogs and may also inform therapies for the rare and aggressive human cancer angiosarcoma. The objectives of this study were to build a framework for leveraging real-world genomic and clinical data that could provide the foundation for precision medicine in veterinary oncology, and to determine the relationships between genomic and clinical features in canine splenic HSA. One hundred and nine dogs with primary splenic HSA treated by splenectomy that had tumour sequencing via the FidoCure® Precision Medicine Platform targeted sequencing panel were enrolled. Patient signalment, weight, metastasis at diagnosis and overall survival time were retrospectively evaluated. The incidence of genomic alterations in individual genes and their relationship to patient variables including outcome were assessed. Somatic mutations in TP53 (n = 44), NRAS (n = 20) and PIK3CA (n = 19) were most common. Survival was associated with presence of metastases at diagnosis and germline variants in SETD2 and NOTCH1. Age at diagnosis was associated with somatic NRAS mutations and breed. TP53 and PIK3CA somatic mutations were found in larger dogs, while germline SETD2 variants were found in smaller dogs. We identified both somatic mutations and germline variants associated with clinical variables including age, breed and overall survival. These genetic changes may be useful prognostic factors and provide insight into the genomic landscape of hemangiosarcoma.

Shared hotspot mutations in oncogenes position dogs as an unparalleled comparative model for precision therapeutics.

Naturally occurring canine cancers have remarkable similarities to their human counterparts. To better understand these similarities, we investigated 671 client-owned dogs from 96 breeds with 23 common tumor types, including those whose mutation profile are unknown (anal sac carcinoma and neuroendocrine carcinoma) or understudied (thyroid carcinoma, soft tissue sarcoma and hepatocellular carcinoma). We discovered mutations in 50 well-established oncogenes and tumor suppressors, and compared them to those reported in human cancers. As in human cancer, TP53 is the most commonly mutated gene, detected in 22.5% of canine tumors overall. Canine tumors share mutational hotspots with human tumors in oncogenes including PIK3CA, KRAS, NRAS, BRAF, KIT and EGFR. Hotspot mutations with significant association to tumor type include NRAS G61R and PIK3CA H1047R in hemangiosarcoma, ERBB2 V659E in pulmonary carcinoma, and BRAF V588E (equivalent of V600E in humans) in urothelial carcinoma. Our findings better position canines as a translational model of human cancer to investigate a wide spectrum of targeted therapies.

Analyses of canine cancer mutations and treatment outcomes using real-world clinico-genomics data of 2119 dogs.

Spontaneous tumors in canines share significant genetic and histological similarities with human tumors, positioning them as valuable models to guide drug development. However, current translational studies have limited real world evidence as cancer outcomes are dispersed across veterinary clinics and genomic tests are rarely performed on dogs. In this study, we aim to expand the value of canine models by systematically characterizing genetic mutations in tumors and their response to targeted treatments. In total, we collect and analyze survival outcomes for 2119 tumor-bearing dogs and the prognostic effect of genomic alterations in a subset of 1108 dogs. Our analysis identifies prognostic concordance between canines and humans in several key oncogenes, including TP53 and PIK3CA. We also find that several targeted treatments designed for humans are associated with a positive prognosis when used to treat canine tumors with specific genomic alterations, underscoring the value of canine models in advancing drug discovery for personalized oncology.

The Use of Oligo Fucoidan in Cancer Bearing Dogs Undergoing Chemotherapy: A Double-Blinded Study.

We evaluated the effect of oligo fucoidan (Laminina Japonica) derived from oceanic brown seaweed on the quality of life in dogs with cancer undergoing chemotherapy in a double-blinded case control study. Included in this prospective study were 100 dogs with a confirmed diagnosis of cancer that were being treated with chemotherapy. Dogs were randomly assigned to be treated with oligo fucoidan (treated group; n = 68) or placebo (placebo group; n = 32). Dogs were evaluated every 2-3 weeks for 3 months with a complete blood count (CBC) and serum biochemistry profile, and a complete history and physical examination by blinded clinicians at The Veterinary Cancer Center. The owners of the dogs enrolled in the study were required at each visit to complete a Quality-of-Life Questionnaire specifically designed for cancer-bearing veterinary patients. The owners were also blinded as to whether their dog was receiving oligo fucoidan or placebo. There were no significant differences between the CBC parameters or the serum biochemical parameters of the dogs in the treated and placebo-controlled groups. There was no significant difference in the median quality of life scores between the 2 cohorts, however, when evaluating the individual quality of life metrics, 5 out of the 23 metrics showed statistically significant improvement, and none of the quality-of-life metrics declined in the oligo fucoidan group as compared to the placebo group. All of the dogs that had a positive change in overall quality of life scores were dogs that received oligo fucoidan. There were minimal adverse side effects of giving the oligo fucoidan to dogs. Treatment with oligo fucoidan was safe and improved some of the quality-of-life metrics in dogs who were being treated with chemotherapy for cancer.

Multicenter, randomized, double-blinded, placebo-controlled study of rabacfosadine in dogs with lymphoma.

BACKGROUND: Rabacfosadine (RAB, Tanovea-CA1) is a novel chemotherapy agent conditionally approved for the treatment of lymphoma in dogs. HYPOTHESIS/OBJECTIVES: To determine the efficacy and safety of RAB in dogs with lymphoma. ANIMALS: One hundred and fifty-eight client-owned dogs with naïve or relapsed multicentric lymphoma were prospectively enrolled from January to October 2019. METHODS: Dogs were randomized to receive RAB or placebo at a 3 : 1 ratio. Treatment was given every 21 days for up to 5 treatments. Study endpoints included progression-free survival (PFS), overall response rate (ORR) at a given visit, best overall response rate (BORR), and percent progression free 1 month after treatment completion. Safety data were also collected. RESULTS: The median PFS was significantly longer in the RAB group compared to placebo (82 vs 21 days; P < .0001, HR 6.265 [95% CI 3.947-9.945]). The BORR for RAB-treated dogs was 73.2% (50.9% complete response [CR], 22.3% partial response [PR]) and 5.6% (0% CR, 5.6% PR) for placebo-treated dogs (P < .0001). One month after the last treatment, 37 RAB-treated dogs (33%) were progression free compared with no placebo-treated dogs (P < .0001). The most common adverse events observed in the RAB group were diarrhea (87.5%), decreased appetite (68.3%), and vomiting (68.3%) and were generally low grade and reversible. Serious adverse events were reported in 24 RAB-treated (20%) and 5 placebo-treated dogs (13%). CONCLUSIONS AND CLINICAL IMPORTANCE: Rabacfosadine demonstrated statistically significant antitumor efficacy in dogs with lymphoma when administered every 21 days for up to 5 treatments as compared to placebo.

Vaccine-induced ErbB (EGFR/HER2)-specific immunity in spontaneous canine cancer.

Epidermal Growth Factor Receptor (EGFR) is overexpressed on a number of human cancers, and often is indicative of a poor outcome. Treatment of EGFR/HER2 overexpressing cancers includes monoclonal antibody therapy (cetuximab/trastuzumab) either alone or in conjunction with other standard cancer therapies. While monoclonal antibody therapy has been proven to be efficacious in the treatment of EGFR/HER2 overexpressing tumors, drawbacks include the lack of long-lasting immunity and acquired resistance to monoclonal therapy. An alternative approach is to induce a polyclonal anti-EGFR/HER2 tumor antigen response by vaccine therapy. In this phase I/II open-label study, we examined anti-tumor immunity in companion dogs with spontaneous EGFR expressing tumors. Canine cancers represent an outbred population in which the initiation, progression of disease, mutations and growth factors closely resemble that of human cancers. Dogs with EGFR expressing tumors were immunized with a short peptide of the EGFR extracellular domain with sequence homology to HER2. Serial serum analyses demonstrated high titers of EGFR/HER2 binding antibodies with biological activity similar to that of cetuximab and trastuzumab. Canine antibodies bound both canine and human EGFR on tumor cell lines and tumor tissue. CD8 T cells and IgG deposition were evident in tumors from immunized dogs. The antibodies inhibited EGFR intracellular signaling and inhibited tumor growth in vitro. Additionally, we illustrate objective responses in reducing tumors at metastatic sites in host animals. The data support the approach of amplifying anti-tumor immunity that may be relevant in combination with other immune modifying therapies such as checkpoint inhibitors.

Rabacfosadine for naïve canine intermediate to large cell lymphoma: Efficacy and adverse event profile across three prospective clinical trials.

While current lymphoma therapies induce remission in most dogs, drug-resistant relapse is common, creating a need for novel agents. Rabacfosadine (RAB), a double prodrug of the acyclic nucleotide phosphonate 9-(2-phosphonylmethoxyethel) guanine (PMEG), preferentially targets lymphoma cells with reduced systemic toxicity compared with PMEG. Previous studies evaluating RAB administered every 21 days have suggested efficacy in both naïve and relapsed subjects; however, no large studies of RAB as a single agent have been reported in previously untreated dogs with intermediate to large cell lymphoma. The purpose of this study was to evaluate the safety and efficacy of RAB in dogs with previously untreated (excluding corticosteroids) lymphoma. Sixty-three dogs received up to five RAB treatments every 21 days (16 at 0.82 mg/kg and 47 at 1.0 mg/kg) as a 30 minutes intravenous infusion, with (n = 23) or without (n = 40) concurrent corticosteroids. Response assessment and adverse event (Ae) evaluation were performed every 21 days via Veterinary Cooperative Oncology Group (VCOG) criteria. The overall response rate was 87% (52% CR, 35% PR). The overall median progression free interval was 122 days (199 for CR, 89 for PR and 153 days for all responders). T-cell immunophenotype and corticosteroid pre-treatment were predictive of inferior outcomes on multivariate analysis. AEs were most commonly of gastrointestinal origin (hyporexia/diarrhoea) and generally resolved with supportive treatment and/or dosage adjustment. Three dogs experienced VCOG-CTCAE grade 5 delayed pulmonary fibrosis. In conclusion, RAB administered every 3 weeks is generally well tolerated and demonstrates substantial antitumour activity in dogs with previously untreated intermediate to large cell lymphoma.

Concurrent use of rabacfosadine and L-asparaginase for relapsed or refractory multicentric lymphoma in dogs.

BACKGROUND: Rabacfosadine (RAB), a novel antineoplastic agent conditionally licensed for the treatment of lymphoma in dogs, is efficacious in both naïve and previously treated dogs. Its use in combination with L-asparaginase (L-ASP) has not been studied. HYPOTHESIS/OBJECTIVES: To evaluate the safety and efficacy of L-ASP given concurrently with RAB in dogs with relapsed multicentric lymphoma. ANIMALS: Fifty-two dogs with relapse of lymphoma after treatment with at least 1 doxorubicin-based chemotherapy protocol. METHODS: Open-label, multicenter, prospective single-arm clinical trial. Dogs were treated with RAB at 1.0 mg/kg IV every 21 days for up to a total of 5 doses. L-asparaginase was administered at 400 IU/kg SQ concurrently with the first 2 treatments of RAB. RESULTS: The overall response rate (ORR) for all dogs was 67%, with 19 dogs (41%) achieving a complete response (CR). The median progression-free survival time (MPFS) was 63 days (range 5-428 days). Dogs experiencing a CR as their best response had an MPFS of 144 days (range 44-428 days). Adverse events were similar to previous studies evaluating single agent RAB. Failure to achieve a CR and having previously received L-ASP were negative prognostic factors on multivariate analysis. CONCLUSIONS AND CLINICAL IMPORTANCE: Concurrent RAB/L-ASP appears to be both efficacious and safe for treating relapsed multicentric lymphoma in dogs. Adverse events were most often mild and no unexpected toxicoses were observed.

Somatic inactivating PTPRJ mutations and dysregulated pathways identified in canine malignant melanoma by integrated comparative genomic analysis.

Canine malignant melanoma, a significant cause of mortality in domestic dogs, is a powerful comparative model for human melanoma, but little is known about its genetic etiology. We mapped the genomic landscape of canine melanoma through multi-platform analysis of 37 tumors (31 mucosal, 3 acral, 2 cutaneous, and 1 uveal) and 17 matching constitutional samples including long- and short-insert whole genome sequencing, RNA sequencing, array comparative genomic hybridization, single nucleotide polymorphism array, and targeted Sanger sequencing analyses. We identified novel predominantly truncating mutations in the putative tumor suppressor gene PTPRJ in 19% of cases. No BRAF mutations were detected, but activating RAS mutations (24% of cases) occurred in conserved hotspots in all cutaneous and acral and 13% of mucosal subtypes. MDM2 amplifications (24%) and TP53 mutations (19%) were mutually exclusive. Additional low-frequency recurrent alterations were observed amidst low point mutation rates, an absence of ultraviolet light mutational signatures, and an abundance of copy number and structural alterations. Mutations that modulate cell proliferation and cell cycle control were common and highlight therapeutic axes such as MEK and MDM2 inhibition. This mutational landscape resembles that seen in BRAF wild-type and sun-shielded human melanoma subtypes. Overall, these data inform biological comparisons between canine and human melanoma while suggesting actionable targets in both species.

Exceptional responders in conservation.

Conservation operates within complex systems with incomplete knowledge of the system and the interventions utilized. This frequently results in the inability to find generally applicable methods to alleviate threats to Earth's vanishing wildlife. One approach used in medicine and the social sciences has been to develop a deeper understanding of positive outliers. Where such outliers share similar characteristics, they may be considered exceptional responders. We devised a 4-step framework for identifying exceptional responders in conservation: identification of the study system, identification of the response structure, identification of the threshold for exceptionalism, and identification of commonalities among outliers. Evaluation of exceptional responders provides additional information that is often ignored in randomized controlled trials and before-after control-intervention experiments. Interrogating the contextual factors that contribute to an exceptional outcome allow exceptional responders to become valuable pieces of information leading to unexpected discoveries and novel hypotheses.

Retrospective evaluation of toceranib phosphate (Palladia) use in cats with mast cell neoplasia.

Objectives The purpose of this study was to solicit and compile data from practicing veterinary specialists regarding their use of toceranib in cats with mast cell neoplasia and to provide initial assessment of possible clinical benefit and adverse events. Methods The American College of Veterinary Internal Medicine and Oncology listservs were used to solicit data pertaining to cases in which toceranib was used in the treatment of feline mast cell neoplasia. Cases were included if the following data were received: signalment (age, sex, breed), diagnosis of mast cell neoplasia by either cytology or histopathology, anatomic classification of disease (cutaneous, splenic/hepatic, gastrointestinal, other), previous and concurrent treatment, toceranib dose (mg/kg) and schedule, duration of therapy, best response and documentation of adverse events. Results Case data from 50 cats with cutaneous (n = 22), splenic/hepatic (visceral) (n = 10), gastrointestinal (n = 17) or other (n = 1) mast cell neoplasia were received. Clinical benefit was seen in 80% (40/50), including 86% (19/22) with cutaneous, 80% (8/10) with visceral and 76% (13/17) with gastrointestinal involvement. A majority of cats (n = 35) received glucocorticoids during toceranib treatment. Median duration of treatment in cats experiencing clinical benefit was 36 weeks (range 4-106 weeks), 48 weeks (range 12-199 weeks) and 23 weeks (range 13-81 weeks) for cutaneous, visceral and gastrointestinal cases, respectively. Toceranib was administered at a median dose of 2.5 mg/kg (range 1.6-3.5 mg/kg); in 90% (45/50) the drug was given three times per week. Treatment was generally well tolerated with 60% (30/50) of cats experiencing adverse events. The majority of these events were low-grade (grade 1 or 2) gastrointestinal or hematologic events that resolved with treatment break and/or dose adjustment. Conclusions and relevance Toceranib appears to be well tolerated in feline patients with mast cell neoplasia. Biologic activity of this drug is evident in the studied cats; however, further prospective studies are needed to elucidate fully its role in treatment of this disease.

Tolerability of toceranib phosphate (Palladia) when used in conjunction with other therapies in 35 cats with feline oral squamous cell carcinoma: 2009-2013.

Objectives Squamous cell carcinoma (SCC) is the most common oral tumor in cats and typically carries a poor prognosis with current treatment options. The objective of this study was to evaluate the toxicity of toceranib phosphate (Palladia; Pfizer) in cats with oral SCC in combination with other treatment modalities. Methods In this study, 35 cats were retrospectively evaluated to determine toxicity when treated with toceranib in combination with other treatment modalities. Cats received toceranib at a median dose of 2.75 mg/kg (range 1.9-4.17 mg/kg) 3 days a week. Cats also underwent additional therapies, including surgical excision, radiation therapy, chemotherapy and/or use of non-steroidal anti-inflammatory drugs. Results Toxicity was seen in six cats, with five cases of grade 1 or 2 gastrointestinal (GI) toxicity and one grade 4 metabolic toxicity. Toceranib was discontinued in one cat and two cats received dose reductions. None of the cats required treatment delays or hospitalization due to toxicity. Median toceranib treatment duration was 77 days (range 7-741 days). Conclusions and relevance This study revealed that toceranib was well tolerated by the majority of cats, with five cases of low-grade GI toxicity and one case of metabolic toxicity. Given the favorable toxicity profile, future studies further evaluating the safety and efficacy of toceranib for cats with oral SCC should be considered.

KTN0158, a Humanized Anti-KIT Monoclonal Antibody, Demonstrates Biologic Activity against both Normal and Malignant Canine Mast Cells.

Purpose: KTN0158 is a novel anti-KIT antibody that potently inhibits wild-type and mutant KIT. This study evaluated the safety, biologic activity, and pharmacokinetic/pharmacodynamics profile of KTN0158 in dogs with spontaneous mast cell tumors (MCT) as a prelude to human clinical applications.Experimental Design: Cell proliferation, KIT phosphorylation, and mast cell degranulation were evaluated in vitro KTN0158 was administered to 4 research dogs to assess clinical effects and cutaneous mast cell numbers. Thirteen dogs with spontaneous MCT were enrolled into a prospective phase I dose-escalating open-label clinical study of KTN0158 evaluating 3 dose levels and 2 schedules and with weekly assessments for response and clinical toxicities.Results: KTN0158 was a potent inhibitor of human and dog KIT activation and blocked mast cell degranulation in vitro In dogs, KTN0158 was well tolerated and reduced cutaneous mast cell numbers in a dose-dependent manner. Clinical benefit of KTN0158 administration in dogs with MCT (n = 5 partial response; n = 7 stable disease) was observed regardless of KIT mutation status, and decreased KIT phosphorylation was demonstrated in tumor samples. Histopathology after study completion demonstrated an absence of neoplastic cells in the primary tumors and/or metastatic lymph nodes from 4 dogs. Reversible hematologic and biochemical adverse events were observed at doses of 10 and 30 mg/kg. The MTD was established as 10 mg/kg.Conclusions: KTN0158 inhibits KIT phosphorylation, demonstrates an acceptable safety profile in dogs, and provides objective responses in canine MCT patients with and without activating KIT mutations, supporting future clinical evaluation of KTN0158 in people. Clin Cancer Res; 23(10); 2565-74. ©2016 AACR.

Impact of Toceranib/Piroxicam/Cyclophosphamide Maintenance Therapy on Outcome of Dogs with Appendicular Osteosarcoma following Amputation and Carboplatin Chemotherapy: A Multi-Institutional Study.

BACKGROUND: We hypothesized that the addition of toceranib to metronomic cyclophosphamide/piroxicam therapy would significantly improve disease-free interval (DFI) and overall survival (OS) in dogs with appendicular osteosarcoma (OSA) following amputation and carboplatin chemotherapy. METHODS AND FINDINGS: This was a randomized, prospective clinical trial in which dogs with OSA free of gross metastatic disease (n = 126) received carboplatin chemotherapy (4 doses) following amputation. On study entry, dogs were randomized to receive piroxicam/cyclophosphamide with or without toceranib (n = 63 each) after completing chemotherapy. Patient demographics were not significantly different between both groups. During or immediately following carboplatin chemotherapy, 32 dogs (n = 13 toceranib; n = 19 control) developed metastatic disease, and 13 dogs left the study due to other medical conditions or owner preference. Following carboplatin chemotherapy, 81 dogs (n = 46 toceranib; n = 35 control) received the metronomic treatment; 35 dogs (n = 20 toceranib; n = 15 control) developed metastatic disease during the maintenance therapy, and 26 dogs left the study due to other medical conditions or owner preference. Nine toceranib-treated and 11 control dogs completed the study without evidence of metastatic disease 1-year following amputation. Toceranib-treated dogs experienced more episodes of diarrhea, neutropenia and weight loss than control dogs, although these toxicities were low-grade and typically resolved with supportive care. More toceranib-treated dogs (n = 8) were removed from the study for therapy-associated adverse events compared to control dogs (n = 1). The median DFI for control and toceranib treated dogs was 215 and 233 days, respectively (p = 0.274); the median OS for control and toceranib treated dogs was 242 and 318 days, respectively (p = 0.08). The one year survival rate for control dogs was 35% compared to 38% for dogs receiving toceranib. CONCLUSIONS: The addition of toceranib to metronomic piroxicam/cyclophosphamide therapy following amputation and carboplatin chemotherapy did not improve median DFI, OS or the 1-year survival rate in dogs with OSA.

Intratumoral injection of Clostridium novyi-NT spores induces antitumor responses.

Species of Clostridium bacteria are notable for their ability to lyse tumor cells growing in hypoxic environments. We show that an attenuated strain of Clostridium novyi (C. novyi-NT) induces a microscopically precise, tumor-localized response in a rat orthotopic brain tumor model after intratumoral injection. It is well known, however, that experimental models often do not reliably predict the responses of human patients to therapeutic agents. We therefore used naturally occurring canine tumors as a translational bridge to human trials. Canine tumors are more like those of humans because they occur in animals with heterogeneous genetic backgrounds, are of host origin, and are due to spontaneous rather than engineered mutations. We found that intratumoral injection of C. novyi-NT spores was well tolerated in companion dogs bearing spontaneous solid tumors, with the most common toxicities being the expected symptoms associated with bacterial infections. Objective responses were observed in 6 of 16 dogs (37.5%), with three complete and three partial responses. On the basis of these encouraging results, we treated a human patient who had an advanced leiomyosarcoma with an intratumoral injection of C. novyi-NT spores. This treatment reduced the tumor within and surrounding the bone. Together, these results show that C. novyi-NT can precisely eradicate neoplastic tissues and suggest that further clinical trials of this agent in selected patients are warranted.

Hydrophilic agarose macrobead cultures select for outgrowth of carcinoma cell populations that can restrict tumor growth.

Cancer cells and their associated tumors have long been considered to exhibit unregulated proliferation or growth. However, a substantial body of evidence indicates that tumor growth is subject to both positive and negative regulatory controls. Here, we describe a novel property of tumor growth regulation that is neither species nor tumor-type specific. This property, functionally a type of feedback control, is triggered by the encapsulation of neoplastic cells in a growth-restricting hydrogel composed of an agarose matrix with a second coating of agarose to form 6- to 8-mm diameter macrobeads. In a mouse cell model of renal adenocarcinoma (RENCA cells), this process resulted in selection for a stem cell-like subpopulation which together with at least one other cell subpopulation drove colony formation in the macrobeads. Cells in these colonies produced diffusible substances that markedly inhibited in vitro and in vivo proliferation of epithelial-derived tumor cells outside the macrobeads. RENCA cells in monolayer culture that were exposed to RENCA macrobead-conditioned media exhibited cell-cycle accumulation in S phase due to activation of a G(2)/M checkpoint. At least 10 proteins with known tumor suppression functions were identified by analysis of RENCA macrobead-conditioned media, the properties of which offer opportunities to further dissect the molecular basis for tumor growth control. More generally, macrobead culture may permit the isolation of cancer stem cells and other cells of the stem cell niche, perhaps providing strategies to define more effective biologically based clinical approaches to treat neoplastic disease.

A phase I clinical trial evaluating imatinib mesylate (Gleevec) in tumor-bearing cats.

A phase I clinical trial evaluating the toxicity of orally-administered imatinib mesylate was performed in 9 tumor-bearing cats. Imatinib is a small molecule, tyrosine kinase inhibitor, which selectively blocks the function of overexpressed proteins associated with various malignancies. Cats included in the study had diagnoses of fibrosarcoma, squamous cell carcinoma, and mast cell tumor, and each cat was staged using CBC and serum biochemistry; urinalysis, thoracic radiographs, and abdominal ultrasonography were performed in some cats. Most cats were treated previously by surgery, radiation therapy, chemotherapy, or some combination of these treatments. None of the cats received any concurrent chemotherapy. Six cats were treated with imatinib mesylate at 1-2 mg/kg PO q24h. Dose escalations were made to 2, 4, and 10 mg/kg PO q24h in 5 cats. Two cats started therapy at 10 mg/kg PO q24h, and 1 cat started therapy at 15 mg/kg PO q24h; all 3 cats remained at these dosages. No signs of toxicity, as evaluated by CBC and serum biochemistry, were noted in 8 of the 9 cats, and minimal gastrointestinal toxicity was observed. Due to the low frequency of adverse effects, further evaluation of imatinib is ongoing at a dosage of 10 mg/kg PO q24h.

Phase I dose-escalating study of SU11654, a small molecule receptor tyrosine kinase inhibitor, in dogs with spontaneous malignancies.

PURPOSE: The purpose of the following study was to investigate the safety and efficacy of the novel multitargeted indolinone receptor tyrosine kinase (RTK) inhibitor, SU11654, using a canine model of spontaneous tumors. This p.o. bioavailable compound exhibits potent inhibitory activity against members of the split kinase family of RTKs, including vascular endothelial growth factor receptor, platelet-derived growth factor receptor, Kit, and Flt-3, resulting in both direct antitumor and antiangiogenic activity. EXPERIMENTAL DESIGN: This was a Phase I trial in which successive cohorts of dogs with spontaneous tumors that had failed standard treatment regimens received escalating doses of SU11654 as oral therapy. Pharmacokinetics, toxicity, and tumor response were assessed. RESULTS: Fifty-seven dogs with a variety of cancers were enrolled; of these, 10 experienced progressive disease within the first 3 weeks. Measurable objective responses were observed in 16 dogs (including 6 complete responses), primarily in mast cell tumors (n = 11), mixed mammary carcinomas (n = 2), soft tissue sarcomas (n = 2), and multiple myeloma (n = 1), for an overall response rate of 28% (16 of 57). Stable disease of sufficient duration to be considered clinically meaningful (>10 weeks) was seen in an additional 15 dogs, for a resultant overall biological activity of 54% (31 of 57). CONCLUSIONS: This study provides the first evidence that p.o. administered kinase inhibitors can exhibit activity against a variety of spontaneous malignancies. Given the similarities of canine and human cancers with regard to tumor biology and the presence of analogous RTK dysregulation, it is likely that such agents will demonstrate comparable antineoplastic activity in people.