Cancer Therapy: Clinical Multi-center, Placebo-controlled, Double-blind, Randomized Study of Oral Toceranib Phosphate (SU11654), a Receptor Tyrosine Kinase Inhibitor, for the Treatment of Dogs with Recurrent (Either Local or Distant) Mast Cell Tumor Following Surgical Excision

Purpose: The purpose of this study was to determine the objective response rate (ORR) following treatment of canine mast cell tumors (MCT) with toceranib phosphate (Palladia, SU11654), a kinase inhibitor with both antitumor and antiangiogenic activity through inhibition of KIT, vascular endothelial growth factor receptor 2, and PDGFRβ. Secondary objectives were to determine biological response rate, time to tumor progression, duration of objective response, health-related quality of life, and safety of Palladia. Experimental Design: Dogs were randomized to receive oral Palladia 3.25 mg/kg or placebo every other day for 6 weeks in the blinded phase. Thereafter, eligible dogs received open-label Palladia. Results: The blinded phase ORR in Palladia-treated dogs (n = 86) was 37.2% (7 complete response, 25 partial response) versus 7.9% (5 partial response) in placebo-treated dogs (n = 63; P = 0.0004). Of 58 dogs that received Palladia following placebo-escape, 41.4% (8 complete response, 16 partial response) experienced objective response. The ORR for all 145 dogs receiving Palladia was 42.8% (21 complete response, 41 partial response); among the 62 responders, the median duration of objective response and time to tumor progressionwas 12.0 weeks and 18.1 weeks, respectively. Palladia-treated responders scored higher on health-related quality of life versus Palladia-treated nonresponders (P = 0.030). There was no significant difference in the number of dogs with grade 3/4 (of 4) adverse events; adverse events were generally manageable with dose modification and/or supportive care. Conclusions: Palladia has biological activity against canine MCTs and can be administered on a continuous schedule without need for routine planned treatment breaks. This clinical trial further shows that spontaneous tumors in dogs are good models to evaluate therapeutic index of targeted therapeutics in a clinical setting. Mast cell tumors (MCT) are the second most common malignant tumors in dogs. Most originate in the skin or s.c. tissues but they can occur as primary tumors in the intestines, liver, or spleen (1). Canine MCTs possess a wide range of biological behaviors, from benign to extremely aggressive leading to metastasis and eventual death. Several prognostic factors have been identified that help predict the biological behavior of a MCT, although histologic grade using the Patnaik system Authors' Affiliations: School of Veterinary Medicine, University of California, Davis, California; Pfizer Animal Health, Kalamazoo, Michigan; Animal Clinical Investigation at Friendship Hospital for Animals, Washington, District of Columbia; Veterinary Cancer Referral Group, Tustin, California; Department of Veterinary Medicine and Surgery, University of Missouri, Columbia, Missouri; Angel Care Cancer Clinic for Animals, Memphis, Tennessee; Southwest Veterinary Oncology, Tucson, Arizona; Veterinary Specialty Center, Buffalo Grove, Illinois; Animal Medical Center, New York, New York; College of Veterinary Medicine, The Ohio State University, Columbus, Ohio; and School of VeterinaryMedicine, Louisiana State University, Baton Rouge, Louisiana Received7/10/08; revised12/4/08;accepted12/16/08;publishedOnlineFirst5/26/09. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked advertisement in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. Note: Supplementary data for this article are available at Clinical Cancer Research Online (http://clincancerres.aacrjournals.org/). Current affiliation for C.A. London: College of Veterinary Medicine, The Ohio State University, Columbus, OH. Current affiliation for J.G. Hintermeister: Capital Area Veterinary Specialists, Round Rock, TX. Current affiliation for P.J. Bergman: Brightheart Veterinary Centers, Armonk, NY. Current affiliation for G.N. Mauldin: Western Veterinary Specialist Centre, Alberta, Canada. Requests for reprints: Gina M. Michels, Pfizer Animal Health, 7000 Portage Road, Kalamazoo, MI 49001. Phone: 269-833-2713; Fax: 646-441-4456; E-mail: [email protected]. F 2009 American Association for Cancer Research. doi:10.1158/1078-0432.CCR-08-1860 3856 Clin Cancer Res 2009;15(11) June 1, 2009 www.aacrjournals.org Research. on April 15, 2017. © 2009 American Association for Cancer clincancerres.aacrjournals.org Downloaded from (grade 1, low; 2, intermediate; 3, high) has proven to be the most reliable (2, 3). Treatment for dogs with MCTs consists of surgical excision followed by local radiation therapy if complete tumor removal is not possible (1). Chemotherapy (lomustine, vinblastine, cyclophosphomide, prednisone) is used when metastatic disease has been identified, or negative prognostic indicators are present, although no standard of care is currently established (4–9). Unfortunately, dogs with aggressive MCTs rarely survive beyond 6 months postdiagnosis even after treatment with surgery, chemotherapy, and/or radiation therapy (1). The potential role of the receptor tyrosine kinase Kit in mast cell disorders was first recognized in 1994 when point mutations inducing ligand-independent activation were identified in the catalytic domain of c-Kit in malignant mast cell lines (10–12). Subsequently, point mutations in the catalytic domain of c-Kit were shown in up to 90% of human patients with aggressive systemic mastocytosis, supporting the notion that Kit dysfunction may contribute to the malignant transformation of mast cells (13–15). An investigation of Kit dysregulation in dog MCTs showed the presence of novel mutations consisting of internal tandem duplications (ITD) in the juxtamembrane domain that resulted in constitutive activation of Kit in the absence of ligand binding (16, 17). The prevalence of Kit mutations in canine MCTs is approximately 9% to 30%, with higher-grade tumors more likely to possess a mutation (16, 18–20). Additionally, Kit ITDs are associated with increased risk of metastasis and local recurrence, a higher tumor proliferation index, and aberrant Kit localization (16, 18–20). More recently, activating point mutations in the extracellular domain of c-Kit (exons 8 and 9) have been identified in a proportion of MCTs (21). These mutations are similar to those found in acute myelogenous leukemia, suggesting that the spectrum of Kit dysregulation in dog cancer resembles that of human cancer (22–24). Given the presence of activating Kit mutations in canine MCTs and the importance of wild-type Kit in mast cell growth and survival, it was reasoned that these tumors would likely respond to a small-molecule Kit inhibitor. Additionally, as mast cells are known to produce vascular endothelial growth factor (VEGF) and contribute to the process of angiogenesis, inhibition of VEGF receptor 2 (VEGFR2) signaling might also display biological activity against MCTs. A phase I trial was conducted to explore the biologic activity of Palladia (SU11654), a multitargeted inhibitor active against the split kinase family of receptor tyrosine kinases (Kit, VEGFR2, PDGFRβ) in dogs with spontaneous tumors (25). Eleven of 22 dogs with MCTs in this study had tumors that possessed the c-Kit ITD. Response rates were approximately 90% in dogs with MCTs possessing a c-Kit ITD, and 25% in dogs without c-Kit mutations. A subsequent study showed down-regulation of Kit phosphorylation in vivo in previously untreated MCTs after a single dose of Palladia, thereby establishing a distinct pharmacokinetic/pharmacodynamic relationship (26). The observed responses provided evidence that a kinase inhibitor with activity against Kit, VEGFR2 and PDGFRβ could exhibit biological activity against canine MCTs in vivo. Furthermore, adverse events observed following Palladia administration, including anorexia, diarrhea, and lethargy, were predictive of those subsequently observed in human cancer patients treated with similar multitargeted kinase inhibitors (27). Lastly, activity of Palladia against MCTs possessing Kit juxtamembrane domain mutations predicted activity of similar multitargeted agents against human gastrointestinal stromal tumors with Kit juxtamembrane domain mutations (28, 29). The following study was a randomized, placebo-controlled, double-blind, multicenter study to evaluate the efficacy and safety of Palladia in dogs with recurrent, Patnaik grade 2 or 3 MCTs with or without lymph node involvement for the purpose of registration of Palladia as a new veterinary drug. Observed response rates were analyzed for an association with treatment (Palladia versus placebo), tumor grade, the presence or absence of regional lymph node metastasis, and the presence or absence of c-Kit mutation. Materials and Methods Patient selection. Dogs >1 y of age and with ≥5 kg body weight with pathologically confirmed recurrent MCT and at least 1 measurable MCT ≥20 mm in its longest diameter were included. Recurrence was defined as the postoperative occurrence of a new MCT, whether locally within/ near the original surgery site or distant to the previously excised tumor; the nature of the lesion(s) was not determined by clonality. Eligibility criteria included performance status of 0 or 1 on Karnovsky's performance scale modified for dogs (30), life expectancy of >12 wk, up to 1 previous radiation therapy regimen and/or 1 systemic chemotherapy regimen completed at least 14 d prior to enrollment, and adequate hematologic, renal, and hepatic function. Dogs were excluded if they were intended for breeding or had evidence of gastrointestinal bleeding, a Translational Relevance Small-molecule inhibitors are used to treat several human cancers. While clinical responses are observed, toxicities can be substantial and resistance develops over time. Unfortunately, murine models often fail to predict both the spectrum of toxicities and appropriate dosing regimens. The following clinical trial describes the first large-scale, registrational evaluation of a small-molecule inhibitor of a vascular endothelial growth factor receptor/ PDGFR/Kit (Palladia [SU11654]) for use in dogs. A phase I study of Palladia in dogs with cancer predicted that a vascular endothelial growth factor receptor/PDGFR/Kit inhibitor would have activity in several tumor types, particularly those harboring Kit juxtamembrane domain mutations, and accurately predicted the spectrum of clinical toxicities subsequently observed in people treated with similarly targeted tyrosine kinase inhibitors. The present study expands on these previous findings, demonstrating that Palladia can be administered on an alternating day schedule, avoiding the need for long treatment breaks to address toxicity. Furthermore, these data show that malignant mast cell disease is responsive to Palladia, supporting the notion that human mast cell and eosinophil disorders responsive to Gleevec (systemic mastocytosis, hypereosinophilic syndrome) will be responsive to other similarly targeted tyrosine kinase inhibitors. Lastly, this work again supports the notion that spontaneous tumors in dogs can serve as strong predictors of both clinical toxicities and response to therapy for targeted therapeutics. 3857 Clin Cancer Res 2009;15(11) June 1, 2009 www.aacrjournals.org Palladia Treatment for Canine Mast Cell Tumors Research. on April 15, 2017. © 2009 American Association for Cancer clincancerres.aacrjournals.org Downloaded from serious systemic disorder incompatible with the study, evidence of systemic MCT, and/or involvement of more than one lymph node region. Baseline evaluations included medical history, physical examination, thoracic and abdominal radiographs, abdominal ultrasound, fineneedle aspiration cytology from lymph nodes, splenic or hepatic lesions suspicious for MCT, assessment of performance status, complete blood count, biochemical profile, prothrombin time, partial thromboplastin time, and urinalysis. Tumor samples were obtained prior to study entry to assess for c-Kit mutation. Dogs were excluded if they received corticosteroids within 14 d prior to enrollment due to their potential effect (e.g., anti-inflammatory) on tumor size. Dog owners were required to give written informed consent. The study was conducted in compliance with the principles of Good Clinical Practice (31). Study design. This study was a double-blind, centrally randomized, multicenter group sequential clinical trial. Dogs were randomized to receive either Palladia or placebo in a 4:3 ratio. Dogs were stratified based on regional lymph nodemetastasis (yes or no) and tumor grade (2 or 3). Randomization grade was based on a histopathology report available at enrollment whereas analysis was based on the results of a central pathology review. The interim analysis assessed sample size and futility (n = 70). Treatment plan. Dogs received either Palladia (3.25 mg/kg orally every other day) or an equivalent number of placebo-matched tablets. Dose reductions and dose interruptions for up to 2 wk were permitted to manage adverse events (Supplemental Data, Table 1). Dogs in both treatment groups that showed complete response, partial response, or stable disease at the end of the 6-week blinded phase and placebotreated dogs that showed progressive disease at any time during the blinded phase were permitted to enter the open-label phase and receive Palladia. Dogs receiving Palladia during the blinded phase that had progressive disease at the final blinded phase visit were discontinued from study. Any dog experiencing a grade 4 adverse event at the end of the blinded phase was not eligible to enroll in the open-label phase. Concomitant medications, other than corticosteroids, were permitted to manage adverse events. Treatment continued until approximately 6 mo after the last dog enrolled; thereafter, eligible dogs could continue receiving Palladia under a separate continuation protocol where formal collection of efficacy and safety data was discontinued and, hence, is