Julie M. Cherrington

SU11248 inhibits tumor growth and CSF-1R-dependent osteolysis in an experimental breast cancer bone metastasis model.

The aim of the study was to investigate inhibitory effects of the receptor tyrosine kinase (RTK) inhibitor SU11248 against CSF-1R and osteoclast (OC) formation. We developed an in vivo model of breast cancer metastasis to evaluate efficacy of SU11248 against tumor growth and tumor-induced osteolysis in bone. The in vitro effects of SU11248 on CSF-1R phosphorylation, OC formation and function were evaluated. Effects on 435/HAL-Luc tumor growth in bone were monitored by in vivo bioluminescence imaging (BLI), and inhibition of osteolysis was evaluated by measurement of serum pyridinoline (PYD) concentration and histology. Phosphorylation of the receptor for M-CSF (CSF-1R) expressed by NIH3T3 cells was inhibited by SU11248 with an IC50 of 50–100 nM, consistent with CSF-1R belonging to the class III split kinase domain RTK family. The early M-CSF-dependent phase of in vitro murine OC development and function were inhibited by SU11248 at 10–100 nM. In vivo inhibition of osteolysis was confirmed by significant lowering of serum PYD levels following SU11248 treatment of tumor-bearing mice (P=0.047). Using BLI, SU11248 treatment at 40 mg/kg/day for 21 days showed 64% inhibition of tumor growth in bone (P=0.006), and at 80 mg/kg/day showed 89% inhibition (P=0.001). Collectively, these data suggest that SU11248 may be an effective and tolerated therapy to inhibit growth of breast cancer bone metastases, with the additional advantage of inhibiting tumor-associated osteolysis.

New paradigms for the treatment of cancer: The role of anti-angiogenesis agents

Angiogenesis, the sprouting of new blood vessels, plays a role in diverse disease states including cancer, diabetic retinopathy, age-related macular degeneration, rheumatoid arthritis, psoriasis, atherosclerosis, and restenosis. With regard to cancer, the clinical association of tumor vascularity with tumor aggressiveness has been clearly demonstrated in numerous tumor types. The observation of increased microvessel density in tumors not only serves as an independent prognostic indicator, but also suggests that anti-angiogenic therapy may be an important component of treatment regimens for cancer patients. The complexity of the angiogenic process, which involves both positive and negative regulators, provides a number of targets for therapy. Many positive regulators, including growth factor receptors, matrix metalloproteinases, and integrins, have been correlated with increased vascularity of tumors and poor prognosis for patient survival. Thus, these serve as ideal targets for anti-angiogenesis therapy. Many inhibitors of these targets are currently undergoing clinical evaluation as potential anti-cancer agents. In this article, we discuss the role of positive regulators in angiogenesis and tumor growth and describe the anti-angiogenic agents under development.

Expression profiling of blood samples from an SU5416 Phase III metastatic colorectal cancer clinical trial: a novel strategy for biomarker identification

BackgroundMicroarray-based gene expression profiling is a powerful approach for the identification of molecular biomarkers of disease, particularly in human cancers. Utility of this approach to measure responses to therapy is less well established, in part due to challenges in obtaining serial biopsies. Identification of suitable surrogate tissues will help minimize limitations imposed by those challenges. This study describes an approach used to identify gene expression changes that might serve as surrogate biomarkers of drug activity.MethodsExpression profiling using microarrays was applied to peripheral blood mononuclear cell (PBMC) samples obtained from patients with advanced colorectal cancer participating in a Phase III clinical trial. The PBMC samples were harvested pre-treatment and at the end of the first 6-week cycle from patients receiving standard of care chemotherapy or standard of care plus SU5416, a vascular endothelial growth factor (VEGF) receptor tyrosine kinase (RTK) inhibitor. Results from matched pairs of PBMC samples from 23 patients were queried for expression changes that consistently correlated with SU5416 administration.ResultsThirteen transcripts met this selection criterion; six were further tested by quantitative RT-PCR analysis of 62 additional samples from this trial and a second SU5416 Phase III trial of similar design. This method confirmed four of these transcripts (CD24, lactoferrin, lipocalin 2, and MMP-9) as potential biomarkers of drug treatment. Discriminant analysis showed that expression profiles of these 4 transcripts could be used to classify patients by treatment arm in a predictive fashion.ConclusionsThese results establish a foundation for the further exploration of peripheral blood cells as a surrogate system for biomarker analyses in clinical oncology studies.

Phase II study of SU5416, a small molecule vascular endothelial growth factor tyrosine kinase receptor inhibitor, in patients with refractory multiple myeloma

Purpose: Increased bone marrow angiogenesis and vascular endothelial growth factor (VEGF) levels are of adverse prognostic significance in patients with multiple myeloma (MM). VEGF, a soluble circulating angiogenic molecule, acts via receptor tyrosine kinases, including VEGF receptor 2. SU5416 is a small molecule VEGF receptor 2 inhibitor. Experimental Design: Adult patients with advanced MM were entered on a multicenter phase II study. Results: Twenty-seven patients (median age 69, range 39–79), median 4 (0–10) lines of prior therapy, 14 with prior thalidomide therapy, received SU5416 at 145 mg/m2 twice weekly i.v. for a median of two 4-week cycles (range 0.2–9). Grade 3/4 toxicities were rarely observed; the most frequent was thrombocytopenia (12%). Mild-to-moderate toxicities included nausea (63%), headache (56%), diarrhea, vomiting (both 37%), and fatigue (33%). There were three thromboembolic episodes and five cases of new onset hypertension. Two (7%) patients did not complete the first 4-week cycle of therapy because of adverse events (pneumonia and headache). There were no objective responses. Four patients had disease stabilization for ≥4 months. A decrease in median VEGF plasma levels was observed in patients with stable disease (n = 7) compared with patients with progressive disease (n = 5). Overall median survival was 42 weeks (range 3–92+). Conclusions: Although SU5416 had minimal clinical activity, signs of biological activity (decrease in plasma VEGF levels) suggest that angiogenic modulation may be of value in patients with MM.

Gene expression profiling of human colon xenograft tumors following treatment with SU11248, a multitargeted tyrosine kinase inhibitor.

Biomarkers that indicate biological activity and/or efficacy are a potentially useful tool in the development of molecularly targeted therapeutics. It is useful, though challenging, to identify biomarkers during preclinical development in order to impact decision-making during early clinical development. SU11248 is an oral, selective multitargeted tyrosine kinase inhibitor currently in Phase II oncology clinical trials. It exhibits direct antitumor and antiangiogenic activity via inhibition of the receptor tyrosine kinases PDGFR, VEGFR, KIT and FLT3. To identify clinically translatable biomarkers of SU11248 activity, expression profiling was performed on Colo205 human xenograft tumors following treatment with SU11248. Over 100 transcripts changed in abundance in SU11248 as compared to vehicle-treated tumors. Nine candidate transcripts, chosen based on putative function, were also analysed and validated by TaqMan. One such potential biomarker, cadherin-11, was further evaluated at the protein level and was found to have increased expression in xenograft tumors after SU11248 treatment. Interestingly, cadherin-11 expression was also detected via immunohistochemical analysis of archived solid tumors, indicating the technical feasibility of translating this putative biomarker to clinical studies. Importantly, SU11248 treatment also resulted in increased expression of cadherin-11 protein in human tumor biopsies in three out of seven patients examined and confirms the feasibility of using transcriptional profiling of preclinical models to identify clinically translatable biomarkers.

FLT3 K663Q is a novel AML-associated oncogenic kinase: determination of biochemical properties and sensitivity to Sunitinib (SU11248)

Somatic mutations of FLT3 resulting in constitutive kinase activation are the most common acquired genomic abnormality found in acute myeloid leukemia (AML). The majority of these mutations are internal tandem duplications (ITD) of the juxtamembrane region (JM). In addition, a minority of cases of AML are associated with mutation of the FLT3 activation loop (AL), typically involving codons D835 and/or I836. We hypothesized that other novel mutations of FLT3 could also contribute to leukemogenesis. We genotyped 109 cases of AML and identified two novel gain-of-function mutations. The first mutation, N841 H, is similar to previously described mutations involving amino-acid substitutions of codon 841. The other novel mutation, FLT3 K663Q, is the first AML-associated gain-of-function mutation located outside the JM and AL domains. Of note, this mutation was potently inhibited by Sunitinib (SU11248), a previously described FLT3 kinase inhibitor. Sunitinib reduced the proliferation and induced apoptosis of transformed Ba/F3 cells expressing FLT3 K663Q. The potency of Sunitinib against FLT3 K663Q was similar to its potency against FLT3 ITD mutations. We conclude that FLT3 mutations in AML can involve novel regions of the TK1. Future studies are needed to define the incidence and prognostic significance of FLT3 mutations outside the well-established JM and AL regions.