Tim C. Cao

Granulocyte-colony stimulating factor promotes lung metastasis through mobilization of Ly6G+Ly6C+ granulocytes

Priming of the organ-specific premetastatic sites is thought to be an important yet incompletely understood step during metastasis. In this study, we show that the metastatic tumors we examined overexpress granulocyte-colony stimulating factor (G-CSF), which expands and mobilizes Ly6G+Ly6C+ granulocytes and facilitates their subsequent homing at distant organs even before the arrival of tumor cells. Moreover, G-CSF–mobilized Ly6G+Ly6C+ cells produce the Bv8 protein, which has been implicated in angiogenesis and mobilization of myeloid cells. Anti–G-CSF or anti-Bv8 antibodies significantly reduced lung metastasis. Transplantation of Bv8 null fetal liver cells into lethally irradiated hosts also reduced metastasis. We identified an unexpected role for Bv8: the ability to stimulate tumor cell migration through activation of one of the Bv8 receptors, prokineticin receptor (PKR)-1. Finally, we show that administration of recombinant G-CSF is sufficient to increase the numbers of Ly6G+Ly6C+ cells in organ-specific metastatic sites and results in enhanced metastatic ability of several tumors.

Wnt Isoform-Specific Interactions with Coreceptor Specify Inhibition or Potentiation of Signaling by LRP6 Antibodies

β-catenin-dependent Wnt signaling is initiated as Wnt binds to both the receptor FZD and coreceptor LRP5/6, which then assembles a multimeric complex at the cytoplasmic membrane face to recruit and inactivate the kinase GSK3. The large number and sequence diversity of Wnt isoforms suggest the possibility of domain-specific ligand-coreceptor interactions, and distinct binding sites on LRP6 for Wnt3a and Wnt9b have recently been identified in vitro. Whether mechanistically different interactions between Wnts and coreceptors might mediate signaling remains to be determined. It is also not clear whether coreceptor homodimerization induced extracellularly can activate Wnt signaling, as is the case for receptor tyrosine kinases. We generated monoclonal antibodies against LRP6 with the unexpected ability to inhibit signaling by some Wnt isoforms and potentiate signaling by other isoforms. In cell culture, two antibodies characterized further show reciprocal activities on most Wnts, with one antibody antagonizing and the other potentiating. We demonstrate that these antibodies bind to different regions of LRP6 protein, and inhibition of signaling results from blocking Wnt binding. Antibody-mediated dimerization of LRP6 can potentiate signaling only when a Wnt isoform is also able to bind the complex, presumably recruiting FZD. Endogenous autocrine Wnt signaling in different tumor cell lines can be either antagonized or enhanced by the LRP6 antibodies, indicating expression of different Wnt isoforms. As anticipated from the roles of Wnt signaling in cancer and bone development, antibody activities can also be observed in mice for inhibition of tumor growth and in organ culture for enhancement of bone mineral density. Collectively, our results indicate that separate binding sites for different subsets of Wnt isoforms determine the inhibition or potentiation of signaling conferred by LRP6 antibodies. This complexity of coreceptor-ligand interactions may allow for differential regulation of signaling by Wnt isoforms during development, and can be exploited with antibodies to differentially manipulate Wnt signaling in specific tissues or disease states.

USP1 Deubiquitinates ID Proteins to Preserve a Mesenchymal Stem Cell Program in Osteosarcoma

Inhibitors of DNA binding (IDs) antagonize basic-helix-loop-helix (bHLH) transcription factors to inhibit differentiation and maintain stem cell fate. ID ubiquitination and proteasomal degradation occur in differentiated tissues, but IDs in many neoplasms appear to escape degradation. We show that the deubiquitinating enzyme USP1 promotes ID protein stability and stem cell-like characteristics in osteosarcoma. USP1 bound, deubiquitinated, and thereby stabilized ID1, ID2, and ID3. A subset of primary human osteosarcomas coordinately overexpressed USP1 and ID proteins. USP1 knockdown in osteosarcoma cells precipitated ID protein destabilization, cell-cycle arrest, and osteogenic differentiation. Conversely, ectopic USP1 expression in mesenchymal stem cells stabilized ID proteins, inhibited osteoblastic differentiation, and enhanced proliferation. Consistent with USP1 functioning in normal mesenchymal stem cells, USP1-deficient mice were osteopenic. Our observations implicate USP1 in preservation of the stem cell state that characterizes osteosarcoma and identify USP1 as a target for differentiation therapy.

Quantifying Antivascular Effects of Monoclonal Antibodies to Vascular Endothelial Growth Factor: Insights from Imaging

Purpose: Little is known concerning the onset, duration, and magnitude of direct therapeutic effects of anti–vascular endothelial growth factor (VEGF) therapies. Such knowledge would help guide the rational development of targeted therapeutics from bench to bedside and optimize use of imaging technologies that quantify tumor function in early-phase clinical trials. Experimental Design: Preclinical studies were done using ex vivo microcomputed tomography and in vivo ultrasound imaging to characterize tumor vasculature in a human HM-7 colorectal xenograft model treated with the anti-VEGF antibody G6-31. Clinical evaluation was by quantitative magnetic resonance imaging in 10 patients with metastatic colorectal cancer treated with bevacizumab. Results: Microcomputed tomography experiments showed reduction in perfused vessels within 24 to 48 h of G6-31 drug administration (P ≤ 0.005). Ultrasound imaging confirmed reduced tumor blood volume within the same time frame (P = 0.048). Consistent with the preclinical results, reductions in enhancing fraction and fractional plasma volume were detected in patient colorectal cancer metastases within 48 h after a single dose of bevacizumab that persisted throughout one cycle of therapy. These effects were followed by resolution of edema (P = 0.0023) and tumor shrinkage in 9 of 26 tumors at day 12. Conclusion: These data suggest that VEGF-specific inhibition induces rapid structural and functional effects with downstream significant antitumor activity within one cycle of therapy. This finding has important implications for the design of early-phase clinical trials that incorporate physiologic imaging. The study shows how animal data help interpret clinical imaging data, an important step toward the validation of image biomarkers of tumor structure and function. (Clin Cancer Res 2009;15(21):6674–82)Purpose Little is known concerning the onset, duration and magnitude of direct therapeutic effects of anti-VEGF therapies. Such knowledge would help guide the rational development of targeted therapeutics from bench to bedside and optimize use of imaging technologies that quantify tumor function in early phase clinical trials.

Hedgehog signaling regulates the generation of ameloblast progenitors in the continuously growing mouse incisor

In many organ systems such as the skin, gastrointestinal tract and hematopoietic system, homeostasis is dependent on the continuous generation of differentiated progeny from stem cells. The rodent incisor, unlike human teeth, grows throughout the life of the animal and provides a prime example of an organ that rapidly deteriorates if newly differentiated cells cease to form from adult stem cells. Hedgehog (Hh) signaling has been proposed to regulate self-renewal, survival, proliferation and/or differentiation of stem cells in several systems, but to date there is little evidence supporting a role for Hh signaling in adult stem cells. We used in vivo genetic lineage tracing to identify Hh-responsive stem cells in the mouse incisor and we show that sonic hedgehog (SHH), which is produced by the differentiating progeny of the stem cells, signals to several regions of the incisor. Using a hedgehog pathway inhibitor (HPI), we demonstrate that Hh signaling is not required for stem cell survival but is essential for the generation of ameloblasts, one of the major differentiated cell types in the tooth, from the stem cells. These results therefore reveal the existence of a positive-feedback loop in which differentiating progeny produce the signal that in turn allows them to be generated from stem cells.

Global defects in collagen secretion in a Mia3/TANGO1 knockout mouse

Mia3’s contribution to protein secretion is broader than previously realized—its absence impairs collagen deposition and normal development of cartilage and bone.

RIPK3 deficiency or catalytically inactive RIPK1 provides greater benefit than MLKL deficiency in mouse models of inflammation and tissue injury

Necroptosis is a caspase-independent form of cell death that is triggered by activation of the receptor interacting serine/threonine kinase 3 (RIPK3) and phosphorylation of its pseudokinase substrate mixed lineage kinase-like (MLKL), which then translocates to membranes and promotes cell lysis. Activation of RIPK3 is regulated by the kinase RIPK1. Here we analyze the contribution of RIPK1, RIPK3, or MLKL to several mouse disease models. Loss of RIPK3 had no effect on lipopolysaccharide-induced sepsis, dextran sodium sulfate-induced colitis, cerulein-induced pancreatitis, hypoxia-induced cerebral edema, or the major cerebral artery occlusion stroke model. However, kidney ischemia–reperfusion injury, myocardial infarction, and systemic inflammation associated with A20 deficiency or high-dose tumor necrosis factor (TNF) were ameliorated by RIPK3 deficiency. Catalytically inactive RIPK1 was also beneficial in the kidney ischemia–reperfusion injury model, the high-dose TNF model, and in A20−/− mice. Interestingly, MLKL deficiency offered less protection in the kidney ischemia–reperfusion injury model and no benefit in A20−/− mice, consistent with necroptosis-independent functions for RIPK1 and RIPK3. Combined loss of RIPK3 (or MLKL) and caspase-8 largely prevented the cytokine storm, hypothermia, and morbidity induced by TNF, suggesting that the triggering event in this model is a combination of apoptosis and necroptosis. Tissue-specific RIPK3 deletion identified intestinal epithelial cells as the major target organ. Together these data emphasize that MLKL deficiency rather than RIPK1 inactivation or RIPK3 deficiency must be examined to implicate a role for necroptosis in disease.

Death Receptors DR6 and TROY Regulate Brain Vascular Development

Signaling events that regulate central nervous system (CNS) angiogenesis and blood-brain barrier (BBB) formation are only beginning to be elucidated. By evaluating the gene expression profile of mouse vasculature, we identified DR6/TNFRSF21 and TROY/TNFRSF19 as regulators of CNS-specific angiogenesis in both zebrafish and mice. Furthermore, these two death receptors interact both genetically and physically and are required for vascular endothelial growth factor (VEGF)-mediated JNK activation and subsequent human brain endothelial sprouting in vitro. Increasing beta-catenin levels in brain endothelium upregulate DR6 and TROY, indicating that these death receptors are downstream target genes of Wnt/beta-catenin signaling, which has been shown to be required for BBB development. These findings define a role for death receptors DR6 and TROY in CNS-specific vascular development.

Anti-VEGF antibody therapy does not promote metastasis in genetically engineered mouse tumour models†

Resistance to anti‐angiogenic therapy can occur via several potential mechanisms. Unexpectedly, recent studies showed that short‐term inhibition of either VEGF or VEGFR enhanced tumour invasiveness and metastatic spread in preclinical models. In an effort to evaluate the translational relevance of these findings, we examined the consequences of long‐term anti‐VEGF monoclonal antibody therapy in several well‐validated genetically engineered mouse tumour models of either neuroendocrine or epithelial origin. Anti‐VEGF therapy decreased tumour burden and increased overall survival, either as a single agent or in combination with chemotherapy, in all four models examined. Importantly, neither short‐ nor long‐term exposure to anti‐VEGF therapy altered the incidence of metastasis in any of these autochthonous models, consistent with retrospective analyses of clinical trials. In contrast, we observed that sunitinib treatment recapitulated previously reported effects on tumour invasiveness and metastasis in a pancreatic neuroendocrine tumour (PNET) model. Consistent with these results, sunitinib treatment resulted in an up‐regulation of the hypoxia marker GLUT1 in PNETs, whereas anti‐VEGF did not. These results indicate that anti‐VEGF mediates anti‐tumour effects and therapeutic benefits without a paradoxical increase in metastasis. Moreover, these data underscore the concept that drugs targeting VEGF ligands and receptors may affect tumour metastasis in a context‐dependent manner and are mechanistically distinct from one another. Copyright

Modeling Targeted Inhibition of MEK and PI3 Kinase in Human Pancreatic Cancer

Activating mutations in the KRAS oncogene occur in approximately 90% of pancreatic cancers, resulting in aberrant activation of the MAPK and the PI3K pathways, driving malignant progression. Significant efforts to develop targeted inhibitors of nodes within these pathways are underway and several are currently in clinical trials for patients with KRAS-mutant tumors, including patients with pancreatic cancer. To model MEK and PI3K inhibition in late-stage pancreatic cancer, we conducted preclinical trials with a mutant Kras-driven genetically engineered mouse model that faithfully recapitulates human pancreatic ductal adenocarcinoma development. Treatment of advanced disease with either a MEK (GDC-0973) or PI3K inhibitor (GDC-0941) alone showed modest tumor growth inhibition and did not significantly enhance overall survival. However, combination of the two agents resulted in a significant survival advantage as compared with control tumor-bearing mice. To model the clinical scenario, we also evaluated the combination of these targeted agents with gemcitabine, the current standard-of-care chemotherapy for pancreatic cancer. The addition of MEK or PI3K inhibition to gemcitabine, or the triple combination regimen, incrementally enhanced overall survival as compared with gemcitabine alone. These results are reminiscent of the survival advantage conferred in this model and in patients by the combination of gemcitabine and erlotinib, an approved therapeutic regimen for advanced nonresectable pancreatic cancer. Taken together, these data indicate that inhibition of MEK and PI3K alone or in combination with chemotherapy do not confer a dramatic improvement as compared with currently available therapies for patients with pancreatic cancer. Mol Cancer Ther; 14(1); 40–47. ©2014 AACR.