Phase I Evaluation of STA-1474, a Prodrug of the Novel HSP90 Inhibitor Ganetespib, in Dogs with Spontaneous Cancer

The novel water soluble compound STA-1474 is metabolized to ganetespib (formerly STA-9090), a potent HSP90 inhibitor previously shown to kill canine tumor cell lines in vitro and inhibit tumor growth in the setting of murine xenografts. The purpose of the following study was to extend these observations and investigate the safety and efficacy of STA-1474 in dogs with spontaneous tumors.This was a Phase 1 trial in which dogs with spontaneous tumors received STA-1474 under one of three different dosing schemes. Pharmacokinetics, toxicities, biomarker changes, and tumor responses were assessed. Twenty-five dogs with a variety of cancers were enrolled. Toxicities were primarily gastrointestinal in nature consisting of diarrhea, vomiting, inappetence and lethargy. Upregulation of HSP70 protein expression was noted in both tumor specimens and PBMCs within 7 hours following drug administration. Measurable objective responses were observed in dogs with malignant mast cell disease (n = 3), osteosarcoma (n = 1), melanoma (n = 1) and thyroid carcinoma (n = 1), for a response rate of 24% (6/25). Stable disease (>10 weeks) was seen in 3 dogs, for a resultant overall biological activity of 36% (9/25).This study provides evidence that STA-1474 exhibits biologic activity in a relevant large animal model of cancer. Given the similarities of canine and human cancers with respect to tumor biology and HSP90 activation, it is likely that STA-1474 and ganetespib will demonstrate comparable anti-cancer activity in human patients

Characterization of STAT3 activation and expression in canine and human osteosarcoma

Abstract Background Dysregulation of signal transducer and activator of transcription 3 (STAT3) has been implicated as a key participant in tumor cell survival, proliferation, and metastasis and is often correlated with a more malignant tumor phenotype. STAT3 phosphorylation has been demonstrated in a subset of human osteosarcoma (OSA) tissues and cell lines. OSA in the canine population is known to exhibit a similar clinical behavior and molecular biology when compared to its human counterpart, and is often used as a model for preclinical testing of novel therapeutics. The purpose of this study was to investigate the potential role of STAT3 in canine and human OSA, and to evaluate the biologic activity of a novel small molecule STAT3 inhibitor. Methods To examine STAT3 and Src expression in OSA, we performed Western blotting and RT-PCR. OSA cells were treated with either STAT3 siRNA or small molecule Src (SU6656) or STAT3 (LLL3) inhibitors and cell proliferation (CyQUANT), caspase 3/7 activity (ELISA), apoptosis (Western blotting for PARP cleavage) and/or viability (Wst-1) were determined. Additionally, STAT3 DNA binding after treatment was determined using EMSA. Expression of STAT3 targets after treatment was demonstrated with Western blotting, RT-PCR, or gel zymography. Results Our data demonstrate that constitutive activation of STAT3 is present in a subset of canine OSA tumors and human and canine cell lines, but not normal canine osteoblasts. In both canine and human OSA cell lines, downregulation of STAT3 activity through inhibition of upstream Src family kinases using SU6656, inhibition of STAT3 DNA binding and transcriptional activities using LLL3, or modulation of STAT3 expression using siRNA, all resulted in decreased cell proliferation and viability, ultimately inducing caspase-3/7 mediated apoptosis in treated cells. Furthermore, inhibition of either Src or STAT3 activity downregulated the expression of survivin, VEGF, and MMP2, all known transcriptional targets of STAT3. Conclusion These data suggest that STAT3 activation contributes to the survival and proliferation of human and canine OSA cells, thereby providing a potentially promising target for therapeutic intervention. Future investigational trials of LLL3 in dogs with spontaneous OSA will help to more accurately define the role of STAT3 in the clinical setting.</p

Mean pharmacokinetic parameters of STA-9090.

<p>*NR: not reportable due to insufficient terminal phase characterization.</p

Structure of STA-1474.

<p>Shown is the chemical structure of STA-1474, a water-soluble phosphate prodrug of ganetespib.</p

Response of metastatic thyroid carcinoma and OSA to STA-1474 treatment.

<p>a) Patient #14 had a locally recurrent thyroid carcinoma with metastatic disease to the lungs. This patient received STA-1474 on the 8 hour infusion protocol and experienced a partial response to therapy of both the locally recurrent and metastatic disease. Shown are representative radiographs before and after 15 treatments with STA-1474. The yellow arrows point to the metastatic pulmonary nodules. b) Patient #18 had metastatic OSA to the lungs following amputation and chemotherapy for an appendicular OSA. This patient received STA-1474 on the 8 hour infusion protocol and experienced a partial response to therapy. Shown are representative radiographs before and after 4 treatments with STA-1474. The yellow arrows point to the metastatic pulmonary nodules.</p

Serial CT demonstrating regression of oral malignant melanoma following treatment with STA-1474.

<p>Patient # 5 had an aggressive oral malignant melanoma that had invaded into the nasal cavity. During the 4^th treatment cycle with STA-1474, an extravasation event occurred resulting in altered drug pharmacokinetics. A marked decrease in the oral mass was observed 7 days later and a subsequent CT scan confirmed a partial response to therapy. Shown are two representative matched CT images of tumor before and after treatment.</p

Subject demographics.

<p>Subject demographics.</p