Purpose Cabozantinib, an orally available multi-tyrosine kinase inhibitor with activity against MET and vascular endothelial growth factor receptor 2 (VEGFR2), induces resolution of bone scan lesions in men with castration-resistant prostate cancer bone metastases. The purpose of this study was to determine whether cabozantinib elicited a direct anti-tumor effect, an indirect effect through modulating bone, or both. Experimental Design Using human prostate cancer xenograft studies in mice we determined cabozantinib's impact on tumor growth in soft tissue and bone. In vitro studies with cabozantinib were performed using (1) prostate cancer cell lines to evaluate its impact on cell growth, invasive ability and MET and (2) osteoblast cell lines to evaluate its impact on viability and differentiation and VEGFR2. Results Cabozantinib inhibited progression of multiple prostate cancer cell lines (Ace-1,C4-2B, and LuCaP 35) in bone metastatic and soft tissue murine models of prostate cancer, except for PC-3 prostate cancer cells in which it inhibited only subcutaneous growth. Cabozantinib directly inhibited prostate cancer cell viability and induced apoptosis in vitro and in vivo and inhibited cell invasion in vitro. Cabozantinib had a dose-dependent biphasic effect on osteoblast activity and inhibitory effect on osteoclast production in vitro, that was reflected in vivo. It blocked MET and VEGFR2 phosphorylation in prostate cancer cells and osteoblast-like cells, respectively. Conclusion These data indicate that cabozantinib has direct anti-tumor activity; and that its ability to modulate osteoblast activity may contribute to its anti-tumor efficacy.

Members of the human epidermal growth factor receptor (HER) family play a significant role in bladder cancer progression and may underlie the development of chemotherapy resistance. Dacomitinib is an irreversible tyrosine kinase inhibitor with structural specificity for the catalytic domains of epidermal growth factor receptor (EGFR), HER2 and HER4 that has exhibited vigorous efficacy against other solid tumors. We evaluated the antitumor activity of dacomitinib in human bladder cancer cell lines expressing varying levels of HER family receptors. These cell lines also were established as bladder cancer xenografts in nonobese diabetic/severe combined immunodeficiency (NOD/SCID) mice to assess dacomitinib activity in vivo. Significant cytotoxic and cytostatic effects were noted in cells expressing elevated levels of the dacomitinib target receptors with apoptosis and cell cycle arrest being the predominant mechanisms of antitumor activity. Cells expressing lower levels of HER receptors were much less sensitive to dacomitinib. Interestingly, dacomitinib was more active than either trastuzumab or cetuximab in vitro, and exhibited increased growth inhibition of bladder tumor xenografts compared with lapatinib. Pharmacodynamic effects of dacomitinib included decreased E-cadherin (E-cad) expression, reduction of EGFR and extracellular signal-regulated kinase (ERK) phosphorylation and reduced mitotic count. Dacomitinib also inhibited tumor growth in a chemotherapy-resistant xenograft and, when combined with chemotherapy in a sensitive xenograft, exhibited superior antitumor effects compared with individual treatments. Evaluation in xenograft-bearing mice revealed that this combination was broadly feasible and well tolerated. In conclusion, dacomitinib exhibited pronounced activity both as a single agent and when combined with chemotherapy in human bladder cancer models. Further investigation of dacomitinib in the preclinical and clinical trial settings is being pursued.

Advanced prostate carcinoma (PCa) is usually complicated by the presence of bone metastases. Current therapies targeting bone metastases are suboptimal as the metastases progress in spite of therapy. Accordingly, novel therapeutics are needed to target these lesions. The Wnt inhibitor Dickkopf-1 (DKK-1) appears to play an important role in progression of PCa bone metastases. Overexpression of DKK-1 by PCa promotes tumor growth and bone lysis in laboratory studies and DKK1 is present in clinical PCa bone metastases. Development of a fully humanized anti-DKK-1 neutralizing antibody, BHQ880 (Novartis), provides a potential therapeutic strategy to target PCa bone metastases. The goal of this study was to test if BHQ880 could impact PCa bone metastases. PC-3-luc cells (2.5x105) were injected intratibially into mice. Treatment with anti-DKK-1 or isotype control antibody (n=12 mice per group) was initiated 0, 7, or 14 days post-tumor injection. Mice were treated three times weekly by intraperitoneal injection with 200 μg/mouse (approximately 10 mg/kg) Tumor growth and bone lysis were assessed by weekly bioluminescence and bi-weekly radiography, respectively. All mice were euthanized 31 days post-tumor injection, tumor bearing limbs were formalin fixed and serum was obtained. Tumor bearing limbs were analyzed by dual energy x-ray absorptiometry (DEXA) and histology. Serum was assayed for the bone turnover biomarkers alkaline phosphatase (ALP), osteocalcin (OC), and tartate-resistant acid phosphatase 5b (TRAP5b). BHQ880 was well tolerated with no significant side effects observed. Significant inhibition of tumor growth was observed in mice where treatment was initiated 7 or 14 days post-tumor challenge when established tumors were present. Two mice from the 14-day treatment group had tumor regressions after treatment with BHQ880. Treatment with BHQ880 resulted in decreased bone lysis as determined using DEXA. Furthermore, increased serum concentrations of ALP and OC in mice treated with BHQ880 suggest increased bone production; no significant difference in TRAP5b concentration between treated and untreated mice was found. Treatment with the DKK-1 neutralizing antibody BHQ880 was found to inhibit tumor growth, tumor-induced osteolysis and increase serum bone remodeling markers associated with increased bone production in a murine model of PCa bone metastasis. These data suggest that anti-DKK-1 treatment is a plausible mechanism for inhibition of progression of PCa bone metastases. These data suggest that inhibition of DKK-1 may be an effective strategy to inhibit PCa growth in bone. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3794. doi:1538-7445.AM2012-3794

<p>PDF file 173K, Impact of cabozantinib on MET, phospho-MET, VEGFR2 and phospho-VEGFR2 expression of subcutaneous LuCaP 35 and intratibial C4-2B tumors in mice</p>

<div>Abstract<p><b>Purpose:</b> Cabozantinib, an orally available multityrosine kinase inhibitor with activity against mesenchymal epithelial transition factor (MET) and VEGF receptor 2 (VEGFR2), induces resolution of bone scan lesions in men with castration-resistant prostate cancer bone metastases. The purpose of this study was to determine whether cabozantinib elicited a direct antitumor effect, an indirect effect through modulating bone, or both.</p><p><b>Experimental Design:</b> Using human prostate cancer xenograft studies in mice, we determined the impact of cabozantinib on tumor growth in soft tissue and bone. <i>In vitro</i> studies with cabozantinib were performed using (i) prostate cancer cell lines to evaluate its impact on cell growth, invasive ability, and MET and (ii) osteoblast cell lines to evaluate its impact on viability and differentiation and VEGFR2.</p><p><b>Results:</b> Cabozantinib inhibited progression of multiple prostate cancer cell lines (Ace-1, C4-2B, and LuCaP 35) in bone metastatic and soft tissue murine models of prostate cancer, except for PC-3 prostate cancer cells in which it inhibited only subcutaneous growth. Cabozantinib directly inhibited prostate cancer cell viability and induced apoptosis <i>in vitro</i> and <i>in vivo</i> and inhibited cell invasion <i>in vitro</i>. Cabozantinib had a dose-dependent biphasic effect on osteoblast activity and inhibitory effect on osteoclast production <i>in vitro</i> that was reflected <i>in vivo</i>. It blocked MET and VEGFR2 phosphorylation in prostate cancer cells and osteoblast-like cells, respectively.</p><p><b>Conclusion:</b> These data indicate that cabozantinib has direct antitumor activity, and that its ability to modulate osteoblast activity may contribute to its antitumor efficacy. <i>Clin Cancer Res; 20(3); 617–30. ©2013 AACR</i>.</p></div>

<div>Abstract<p><b>Purpose:</b> Cabozantinib, an orally available multityrosine kinase inhibitor with activity against mesenchymal epithelial transition factor (MET) and VEGF receptor 2 (VEGFR2), induces resolution of bone scan lesions in men with castration-resistant prostate cancer bone metastases. The purpose of this study was to determine whether cabozantinib elicited a direct antitumor effect, an indirect effect through modulating bone, or both.</p><p><b>Experimental Design:</b> Using human prostate cancer xenograft studies in mice, we determined the impact of cabozantinib on tumor growth in soft tissue and bone. <i>In vitro</i> studies with cabozantinib were performed using (i) prostate cancer cell lines to evaluate its impact on cell growth, invasive ability, and MET and (ii) osteoblast cell lines to evaluate its impact on viability and differentiation and VEGFR2.</p><p><b>Results:</b> Cabozantinib inhibited progression of multiple prostate cancer cell lines (Ace-1, C4-2B, and LuCaP 35) in bone metastatic and soft tissue murine models of prostate cancer, except for PC-3 prostate cancer cells in which it inhibited only subcutaneous growth. Cabozantinib directly inhibited prostate cancer cell viability and induced apoptosis <i>in vitro</i> and <i>in vivo</i> and inhibited cell invasion <i>in vitro</i>. Cabozantinib had a dose-dependent biphasic effect on osteoblast activity and inhibitory effect on osteoclast production <i>in vitro</i> that was reflected <i>in vivo</i>. It blocked MET and VEGFR2 phosphorylation in prostate cancer cells and osteoblast-like cells, respectively.</p><p><b>Conclusion:</b> These data indicate that cabozantinib has direct antitumor activity, and that its ability to modulate osteoblast activity may contribute to its antitumor efficacy. <i>Clin Cancer Res; 20(3); 617–30. ©2013 AACR</i>.</p></div>

<p>PDF file 95K, Cabozantinib does not inhibit progression of PC-3luc PCa cells in bone in vivo</p>

<p>PDF file 183K, Impact of cabozantinib on MET, phospho-MET, VEGFR2 and phospho-VEGFR2 expression of subcutaneous and intratibial PC-3 tumors in mice</p>