Improved targeted therapies are needed to combat metastatic prostate cancer. Here, we report the identification of the spleen kinase SYK as a mediator of metastatic dissemination in zebrafish and mouse xenograft models of human prostate cancer. Although SYK has not been implicated previously in this disease, we found that its expression is upregulated in human prostate cancers and associated with malignant progression. RNAi-mediated silencing prevented invasive outgrowth in vitro and bone colonization in vivo, effects that were reversed by wild-type but not kinase-dead SYK expression. In the absence of SYK expression, cell surface levels of the progression-associated adhesion receptors integrin α2β1 and CD44 were diminished. RNAi-mediated silencing of α2β1 phenocopied SYK depletion in vitro and in vivo, suggesting an effector role for α2β1 in this setting. Notably, pharmacologic inhibitors of SYK kinase currently in phase I–II trials for other indications interfered similarly with the invasive growth and dissemination of prostate cancer cells. Our findings offer a mechanistic rationale to reposition SYK kinase inhibitors for evaluation in patients with metastatic prostate cancer. Cancer Res; 75(1); 1–11. ©2014 AACR.

Improved targeted therapies are needed to combat metastatic prostate cancer. Here we report the identification of the spleen kinase SYK as a mediator of metastatic dissemination in zebrafish and mouse xenograft models of human prostate cancer. While SYK has not been implicated previously in this disease, we found that its expression is upregulated in human prostate cancers and associated with malignant progression. RNAi-mediated silencing prevented invasive outgrowth in vitro and bone colonization in vivo, effects that were reversed by wild-type but not kinase-dead SYK expression. In the absence of SYK expression, cell surface levels of the progression-associated adhesion receptors integrin α2β1 and CD44 were diminished. RNAi-mediated silencing of α2β1 phenocopied SYK depletion in vitro and in vivo, suggesting an effector role for α2β1 in this setting. Notably, pharmacological inhibitors of SYK kinase currently in Phase I-II trials for other indications interfered similarly with the invasive growth and dissemination of prostate cancer cells. Our findings offer a mechanistic rationale to reposition SYK kinase inhibitors for evaluation in patients with metastatic prostate cancer.

Traditionally, cell-mediated immune responses to vaccination in animal models are evaluated by invasive techniques such as biopsy and organ extraction. We show here that by combining two noninvasive imaging technologies, MRI and bioluminescence imaging (BLI), we can visualize both the afferent and efferent arms of cellular events following vaccination longitudinally. To this end, we evaluated the immune response elicited by a novel Toll-like receptor 4 agonist vaccine adjuvant, glucopyranosyl lipid A (GLA), using a whole-cell tumor vaccine. After magnetovaccination, MRI was used to visualize antigen-presenting cell-mediated antigen capture and subsequent migration to draining lymph nodes (DLN). Paradoxically, we observed that the incorporation of GLA in the vaccine reduced these critical parameters of the afferent immune response. For the efferent arm, the magnitude of the ensuing antigen-specific T-cell response in DLN visualized using BLI correlated with antigen delivery to the DLN as measured by MRI. These findings were confirmed using flow cytometry. In spite of the GLA-associated reduction in antigen delivery to the DLN, however, the use of GLA as a vaccine adjuvant led to a massive proliferation of vaccine primed antigen-specific T cells in the spleen. This was accompanied by an enhanced tumor therapeutic effect of the vaccine. These findings suggest that GLA adjuvant changes the temporal and anatomical features of both the afferent and efferent arms of the vaccine response and illustrates the utility of quantitative noninvasive imaging as a tool for evaluating these parameters during vaccine optimization. Cancer Res; 75(1); 1–11. ©2014 AACR.

Traditionally, cell-mediated immune responses to vaccination in animal models are evaluated by invasive techniques such as biopsy and organ extraction. We show here that by combining two non-invasive imaging technologies, magnetic resonance imaging (MRI) and bioluminescence imaging (BLI), we can visualize both the afferent and efferent arms of cellular events following vaccination longitudinally. To this end, we evaluated the immune response elicited by a novel toll-like receptor 4 agonist vaccine adjuvant, glucopyranosyl lipid A (GLA), using a whole cell tumor vaccine. Following magnetovaccination, MRI was used to visualize antigen presenting cell-mediated antigen capture and subsequent migration to draining lymph nodes (DLN). Paradoxically, we observed that the incorporation of GLA in the vaccine reduced these critical parameters of the afferent immune response. For the efferent arm, the magnitude of the ensuing antigen-specific T cell response in DLN visualized using BLI correlated with antigen delivery to the DLN as measured by MRI. These findings were confirmed using flow cytometry. In spite of the GLA associated reduction in antigen delivery to the DLN however, the use of GLA as a vaccine adjuvant led to a massive proliferation of vaccine primed antigen-specific T cells in the spleen. This was accompanied by an enhanced tumor therapeutic effect of the vaccine. These findings suggest that GLA adjuvant changes the temporal and anatomical features of both the afferent and efferent arms of the vaccine response and illustrates the utility of quantitative non-invasive imaging as a tool for evaluating these parameters during vaccine optimization.

Vascular tumors are endothelial cell neoplasms whose mechanisms of tumorigenesis are poorly understood. Moreover, current therapies, particularly those for malignant lesions, have little beneficial effect on clinical outcomes. In this study, we show that endothelial activation of the Akt1 kinase is sufficient to drive de novo tumor formation. Mechanistic investigations uncovered opposing functions for different Akt isoforms in this regulation, where Akt1 promotes and Akt3 inhibits vascular tumor growth. Akt3 exerted negative effects on tumor endothelial cell growth and migration by inhibiting activation of the translation regulatory kinase S6-Kinase (S6K) through modulation of Rictor expression. S6K in turn acted through a negative feedback loop to restrain Akt3 expression. Conversely, S6K signaling was increased in vascular tumor cells where Akt3 was silenced, and the growth of these tumor cells was inhibited by a novel S6K inhibitor. Overall, our findings offer a preclinical proof of concept for the therapeutic utility of treating vascular tumors, such as angiosarcomas, with S6K inhibitors. Cancer Res; 75(1); 1–11. ©2014 AACR.