Cardiac Toxicity of Cancer Chemotherapy

With the aging of the population, the number of patients diagnosed with cancer has grown significantly over the past few decades. In parallel, survival rates have improved due to the increased efficacy and tolerability of cancer treatments. As such, the acute and long-term toxicities of cancer therapies have become increasingly prominent as contributors to morbidity and mortality in cancer survivors. Cardiac toxicity can occur with a broad range of cancer treatments, from conventional cytotoxic agents to newer targeted and immune-based therapies. Common manifestations of chemotherapy-associated cardiotoxicity include asymptomatic left ventricular dysfunction, congestive heart failure, myocardial ischemia, myocarditis, QT prolongation, and arrhythmia. In this review, we will describe antitumor agents that have commonly been associated with an increased risk of cardiac toxicity, with an emphasis on clinical manifestations, underlying mechanisms, and cardioprotective strategies that can be implemented in this setting.

σ1 receptor ligands control a switch between passive and active threat responses

Humans and many animals show 'freezing' behavior in response to threatening stimuli. In humans, inappropriate threat responses are fundamental characteristics of several mental illnesses. To identify small molecules that modulate threat responses, we developed a high-throughput behavioral assay in zebrafish (Danio rerio) and evaluated 10,000 compounds for their effects on freezing behavior. We found three classes of compounds that switch the threat response from freezing to escape-like behavior. We then screened these for binding activity across 45 candidate targets. Using target profile clustering, we identified the sigma-1 (σ1) receptor as having a role in the mechanism of behavioral switching and confirmed that known σ1 ligands also disrupt freezing behavior. Furthermore, mutation of the gene encoding σ1 prevented the behavioral effect of escape-inducing compounds. One compound, which we call finazine, potently bound mammalian σ1 and altered threat-response behavior in mice. Thus, pharmacological and genetic interrogation of the freezing response revealed σ1 as a mediator of threat responses in vertebrates.

Zebrafish behavioral profiling identifies multitarget antipsychotic-like compounds

Many psychiatric drugs act on multiple targets and therefore require screening assays that encompass a wide target space. With sufficiently rich phenotyping and a large sampling of compounds, it should be possible to identify compounds with desired mechanisms of action on the basis of behavioral profiles alone. Although zebrafish (Danio rerio) behavior has been used to rapidly identify neuroactive compounds, it is not clear what types of behavioral assays would be necessary to identify multitarget compounds such as antipsychotics. Here we developed a battery of behavioral assays in larval zebrafish to determine whether behavioral profiles can provide sufficient phenotypic resolution to identify and classify psychiatric drugs. Using the antipsychotic drug haloperidol as a test case, we found that behavioral profiles of haloperidol-treated zebrafish could be used to identify previously uncharacterized compounds with desired antipsychotic-like activities and multitarget mechanisms of action.

Single Amino Acid Variation Underlies Species-Specific Sensitivity to Amphibian Skin-Derived Opioid-like Peptides

It has been suggested that the evolution of vertebrate opioid receptors (ORs) follow a vector of increased functionality. Here, we test this idea by comparing human and frog ORs. Interestingly, some of the most potent opioid peptides known have been isolated from amphibian skin secretions. Here we show that such peptides (dermorphin and deltorphin) are highly potent in the human receptors and inactive in frog ORs. The molecular basis for the insensitivity of the frog ORs to these peptides was studied using chimeras and molecular modeling. The insensitivity of the delta OR (DOR) to deltorphin was due to variation of a single amino acid, Trp7.35, which is a leucine in mammalian DORs. Notably, Trp7.35 is completely conserved in all known DOR sequences from lamprey, fish, and amphibians. The deltorphin-insensitive phenotype was verified in fish. Our results provide a molecular explanation for the species selectivity of skin-derived opioid peptides.

Chemical Screening in Zebrafish

Phenotypic small molecule screens in zebrafish have gained popularity as an unbiased approach to probe biological processes. In this chapter we outline basic methods for performing chemical screens with larval zebrafish including breeding large numbers of embryos, plating larval fish into multi-well dishes, and adding small molecules to these wells. We also highlight important considerations when designing and interpreting the results of a phenotypic screen and possible follow-up approaches, including popular methods used to identify the mechanism of action of a chemical compound.

Progesterone receptor membrane component-1 regulates hepcidin biosynthesis

Iron homeostasis is tightly regulated by the membrane iron exporter ferroportin and its regulatory peptide hormone hepcidin. The hepcidin/ferroportin axis is considered a promising therapeutic target for the treatment of diseases of iron overload or deficiency. Here, we conducted a chemical screen in zebrafish to identify small molecules that decrease ferroportin protein levels. The chemical screen led to the identification of 3 steroid molecules, epitiostanol, progesterone, and mifepristone, which decrease ferroportin levels by increasing the biosynthesis of hepcidin. These hepcidin-inducing steroids (HISs) did not activate known hepcidin-inducing pathways, including the BMP and JAK/STAT3 pathways. Progesterone receptor membrane component-1 (PGRMC1) was required for HIS-dependent increases in hepcidin biosynthesis, as PGRMC1 depletion in cultured hepatoma cells and zebrafish blocked the ability of HISs to increase hepcidin mRNA levels. Neutralizing antibodies directed against PGRMC1 attenuated the ability of HISs to induce hepcidin gene expression. Inhibiting the kinases of the SRC family, which are downstream of PGRMC1, blocked the ability of HISs to increase hepcidin mRNA levels. Furthermore, HIS treatment increased hepcidin biosynthesis in mice and humans. Together, these data indicate that PGRMC1 regulates hepcidin gene expression through an evolutionarily conserved mechanism. These studies have identified drug candidates and potential therapeutic targets for the treatment of diseases of abnormal iron metabolism.

A Small Molecule that Induces Intrinsic Pathway Apoptosis with Unparalleled Speed

Apoptosis is generally believed to be a process that requires several hours, in contrast to non-programmed forms of cell death that can occur in minutes. Our findings challenge the time-consuming nature of apoptosis as we describe the discovery and characterization of a small molecule, named Raptinal, which initiates intrinsic pathway caspase-dependent apoptosis within minutes in multiple cell lines. Comparison to a mechanistically diverse panel of apoptotic stimuli reveals that Raptinal-induced apoptosis proceeds with unparalleled speed. The rapid phenotype enabled identification of the critical roles of mitochondrial voltage-dependent anion channel function, mitochondrial membrane potential/coupled respiration, and mitochondrial complex I, III, and IV function for apoptosis induction. Use of Raptinal in whole organisms demonstrates its utility for studying apoptosis in vivo for a variety of applications. Overall, rapid inducers of apoptosis are powerful tools that will be used in a variety of settings to generate further insight into the apoptotic machinery.

Visnagin protects against doxorubicin-induced cardiomyopathy through modulation of mitochondrial malate dehydrogenase

Doxorubicin is a highly effective anticancer chemotherapy agent, but its use is limited by its cardiotoxicity. To develop a drug that prevents this toxicity, we established a doxorubicin-induced cardiomyopathy model in zebrafish that recapitulates the cardiomyocyte apoptosis and contractility decline observed in patients. Using this model, we screened 3000 compounds and found that visnagin (VIS) and diphenylurea (DPU) rescue the cardiac performance and circulatory defects caused by doxorubicin in zebrafish. VIS and DPU reduced doxorubicin-induced apoptosis in cultured cardiomyocytes and in vivo in zebrafish and mouse hearts. VIS treatment improved cardiac contractility in doxorubicin-treated mice. Further, VIS and DPU did not reduce the chemotherapeutic efficacy of doxorubicin in several cultured tumor lines or in zebrafish and mouse xenograft models. Using affinity chromatography, we found that VIS binds to mitochondrial malate dehydrogenase (MDH2), a key enzyme in the tricarboxylic acid cycle. As with VIS, treatment with the MDH2 inhibitors mebendazole, thyroxine, and iodine prevented doxorubicin cardiotoxicity, as did treatment with malate itself, suggesting that modulation of MDH2 activity is responsible for VIS' cardioprotective effects. Thus, VIS and DPU are potent cardioprotective compounds, and MDH2 is a previously undescribed, druggable target for doxorubicin-induced cardiomyopathy.

Zebrafish as tools for drug discovery

The zebrafish has become a prominent vertebrate model for disease and has already contributed to several examples of successful phenotype-based drug discovery. For the zebrafish to become useful in drug development more broadly, key hurdles must be overcome, including a more comprehensive elucidation of the similarities and differences between human and zebrafish biology. Recent studies have begun to establish the capabilities and limitations of zebrafish for disease modelling, drug screening, target identification, pharmacology, and toxicology. As our understanding increases and as the technologies for manipulating zebrafish improve, it is hoped that the zebrafish will have a key role in accelerating the emergence of precision medicine.

Engineered CRISPR-Cas9 nucleases with altered PAM specificities

Although CRISPR-Cas9 nucleases are widely used for genome editing^{1, 2}, the range of sequences that Cas9 can recognize is constrained by the need for a specific protospacer adjacent motif (PAM)^3–6. As a result, it can often be difficult to target double-stranded breaks (DSBs) with the precision that is necessary for various genome editing applications. The ability to engineer Cas9 derivatives with purposefully altered PAM specificities would address this limitation. Here we show that the commonly used Streptococcus pyogenes Cas9 (SpCas9) can be modified to recognize alternative PAM sequences using structural information, bacterial selection-based directed evolution, and combinatorial design. These altered PAM specificity variants enable robust editing of endogenous gene sites in zebrafish and human cells not currently targetable by wild-type SpCas9, and their genome-wide specificities are comparable to wild-type SpCas9 as judged by GUIDE-Seq analysis⁷. In addition, we identified and characterized another SpCas9 variant that exhibits improved specificity in human cells, possessing better discrimination against off-target sites with non-canonical NAG and NGA PAMs and/or mismatched spacers. We also found that two smaller-size Cas9 orthologues, Streptococcus thermophilus Cas9 (St1Cas9) and Staphylococcus aureus Cas9 (SaCas9), function efficiently in the bacterial selection systems and in human cells, suggesting that our engineering strategies could be extended to Cas9s from other species. Our findings provide broadly useful SpCas9 variants and, more importantly, establish the feasibility of engineering a wide range of Cas9s with altered and improved PAM specificities.

Pharmacological HIF2α inhibition improves VHL disease-associated phenotypes in zebrafish model

Patients with a germline mutation in von Hippel-Lindau (VHL) develop renal cell cancers and hypervascular tumors of the brain, adrenal glands, and pancreas as well as erythrocytosis. These phenotypes are driven by aberrant expression of HIF2α, which induces expression of genes involved in cell proliferation, angiogenesis, and red blood cell production. Currently, there are no effective treatments available for VHL disease. Here, using an animal model of VHL, we report a marked improvement of VHL-associated phenotypes following treatment with HIF2α inhibitors. Inactivation of vhl in zebrafish led to constitutive activation of HIF2α orthologs and modeled several aspects of the human disease, including erythrocytosis, pathologic angiogenesis in the brain and retina, and aberrant kidney and liver proliferation. Treatment of vhl(-/-) mutant embryos with HIF2α-specific inhibitors downregulated Hif target gene expression in a dose-dependent manner, improved abnormal hematopoiesis, and substantially suppressed erythrocytosis and angiogenic sprouting. Moreover, pharmacologic inhibition of HIF2α reversed the compromised cardiac contractility of vhl(-/-) embryos and partially rescued early lethality. This study demonstrates that small-molecule targeting of HIF2α improves VHL-related phenotypes in a vertebrate animal model and supports further exploration of this strategy for treating VHL disease.

Intravital correlated microscopy reveals differential macrophage and microglial dynamics during resolution of neuroinflammation

Many brain diseases involve activation of resident and peripheral immune cells to clear damaged and dying neurons. Which immune cells respond in what way to cues related to brain disease, however, remains poorly understood. To elucidate these in vivo immunological events in response to brain cell death we used genetically targeted cell ablation in zebrafish. Using intravital microscopy and large-scale electron microscopy, we defined the kinetics and nature of immune responses immediately following injury. Initially, clearance of dead cells occurs by mononuclear phagocytes, including resident microglia and macrophages of peripheral origin, whereas amoeboid microglia are exclusively involved at a later stage. Granulocytes, on the other hand, do not migrate towards the injury. Remarkably, following clearance, phagocyte numbers decrease, partly by phagocyte cell death and subsequent engulfment of phagocyte corpses by microglia. Here, we identify differential temporal involvement of microglia and peripheral macrophages in clearance of dead cells in the brain, revealing the chronological sequence of events in neuroinflammatory resolution. Remarkably, recruited phagocytes undergo cell death and are engulfed by microglia. Because adult zebrafish treated at the larval stage lack signs of pathology, it is likely that this mode of resolving immune responses in brain contributes to full tissue recovery. Therefore, these findings suggest that control of such immune cell behavior could benefit recovery from neuronal damage.

The zebrafish as a tool to identify novel therapies for human cardiovascular disease

Over the past decade, the zebrafish has become an increasingly popular animal model for the study of human cardiovascular disease. Because zebrafish embryos are transparent and their genetic manipulation is straightforward, the zebrafish has been used to recapitulate a number of cardiovascular disease processes ranging from congenital heart defects to arrhythmia to cardiomyopathy. The use of fluorescent reporters has been essential to identify two discrete phases of cardiomyocyte differentiation necessary for normal cardiac development in the zebrafish. These phases are analogous to the differentiation of the two progenitor heart cell populations in mammals, termed the first and second heart fields. The small size of zebrafish embryos has enabled high-throughput chemical screening to identify small-molecule suppressors of fundamental pathways in vasculogenesis, such as the BMP axis, as well as of common vascular defects, such as aortic coarctation. The optical clarity of zebrafish has facilitated studies of valvulogenesis as well as detailed electrophysiological mapping to characterize the early cardiac conduction system. One unique aspect of zebrafish larvae is their ability to oxygenate through diffusion alone, permitting the study of mutations that cause severe cardiomyopathy phenotypes such as silent heart and pickwick^m171, which mimic titin mutations observed in human dilated cardiomyopathy. Above all, the regenerative capacity of zebrafish presents a particularly exciting opportunity to discover new therapies for cardiac injury, including scar formation following myocardial infarction. This Review will summarize the current state of the field and describe future directions to advance our understanding of human cardiovascular disease.

PTPMT1 Inhibition Lowers Glucose through Succinate Dehydrogenase Phosphorylation

Virtually all organisms seek to maximize fitness by matching fuel availability with energy expenditure. In vertebrates, glucose homeostasis is central to this process, with glucose levels finely tuned to match changing energy requirements. To discover new pathways regulating glucose levels in vivo, we performed a large-scale chemical screen in live zebrafish and identified the small molecule alexidine as a potent glucose-lowering agent. We found that alexidine inhibits the PTEN-like mitochondrial phosphatase PTPMT1 and that other pharmacological and genetic means of inactivating PTPMT1 also decrease glucose levels in zebrafish. Mutation of ptpmt1 eliminates the effect of alexidine, further confirming it as the glucose-lowering target of alexidine. We then identified succinate dehydrogenase (SDH) as a substrate of PTPMT1. Inactivation of PTPMT1 causes hyperphosphorylation and activation of SDH, providing a possible mechanism by which PTPMT1 coordinates glucose homeostasis. Therefore, PTPMT1 appears to be an important regulator of SDH phosphorylation status and glucose concentration.

15 years of zebrafish chemical screening

In 2000, the first chemical screen using living zebrafish in a multi-well plate was reported. Since then, more than 60 additional screens have been published describing whole-organism drug and pathway discovery projects in zebrafish. To investigate the scope of the work reported in the last 14 years and to identify trends in the field, we analyzed the discovery strategies of 64 primary research articles from the literature. We found that zebrafish screens have expanded beyond the use of developmental phenotypes to include behavioral, cardiac, metabolic, proliferative and regenerative endpoints. Additionally, many creative strategies have been used to uncover the mechanisms of action of new small molecules including chemical phenocopy, genetic phenocopy, mutant rescue, and spatial localization strategies.

Discovery of therapeutic targets by phenotype-based zebrafish screens

The easy identification of phenotypes in the transparent zebrafish embryo has enabled numerous genetic, antisense morpholino oligonucleotide, and small molecule screens. Can zebrafish screens also be used for unbiased discovery of novel drug targets?:

Methods for targeted mutagenesis in zebrafish using TALENs

The transcription activator-like effector (TALE) nucleases, or TALENs, are customizable restriction enzymes that may be used to induce mutations at nearly any investigator-specified DNA sequence in zebrafish. The DNA-binding specificities of TALENs are determined by a protein array comprised of four types of TALE repeats, where each repeat recognizes a different DNA base. Here, we describe methods for constructing TALEN vectors that have been shown to achieve high success rates and mutation efficiencies in zebrafish. In addition, we discuss simple techniques and protocols that can be used to detect TALEN-induced mutations at almost any genomic locus. These methods should enable zebrafish researchers to quickly generate targeted mutations at their genes-of-interest.

Zebrafish models of cerebrovascular disease

Perturbations in cerebral blood flow and abnormalities in blood vessel structure are the hallmarks of cerebrovascular disease. While there are many genetic and environmental factors that affect these entities through a heterogeneous group of disease processes, the ultimate final pathologic insult in humans is defined as a stroke, or damage to brain parenchyma. In the case of ischemic stroke, blood fails to reach its target destination whereas in hemorrhagic stroke, extravasation of blood occurs outside of the blood vessel lumen, resulting in direct damage to brain parenchyma. As these acute events can be neurologically devastating, if not fatal, development of novel therapeutics are urgently needed. The zebrafish (Danio rerio) is an attractive model for the study of cerebrovascular disease because of its morphological and physiological similarity to human cerebral vasculature, its ability to be genetically manipulated, and its fecundity allowing for large-scale, phenotype-based screens.

New mechanisms of 5-nitrofuran toxicity

Phenotypic screens and the target identification that follows can lead to surprising new connections between small molecules and targets. In this issue of Chemistry & Biology, Zhou and colleagues seek to understand the pigmentation of fish skin and end up uncovering an interesting clinical hypothesis about the trypanocidal compound nifurtimox.

AUTOMATED QUANTIFICATION OF ZEBRAFISH TAIL DEFORMATION FOR HIGH-THROUGHPUT DRUG SCREENING

Zebrafish (Danio rerio) is an important vertebrate model organism in biomedical research thanks to its ease of handling and translucent body, enabling in vivo imaging. Zebrafish embryos undergo spinal deformation upon exposure to chemical agents that inhibit DNA repair. Automated image-based quantification of spine deformation is therefore attractive for whole-organism based assays for use in early-phase drug discovery. We propose an automated method for accurate high-throughput measurement of tail deformations in multi-fish micro-plate wells. The method generates refined medial representations of partial tail-segments. Subsequently, these disjoint segments are analyzed and fused to generate complete tails. Based on estimated tail curvatures we reach a classification accuracy of 91% on individual animals as compared to known control treatment. This accuracy is increased to 95% when combining scores for fish in the same well.

A zebrafish model of chordoma initiated by notochord-driven expression of HRASV12

Chordoma is a malignant tumor thought to arise from remnants of the embryonic notochord, with its origin in the bones of the axial skeleton. Surgical resection is the standard treatment, usually in combination with radiation therapy, but neither chemotherapeutic nor targeted therapeutic approaches have demonstrated success. No animal model and only few chordoma cell lines are available for preclinical drug testing, and, although no druggable genetic drivers have been identified, activation of EGFR and downstream AKT-PI3K pathways have been described. Here, we report a zebrafish model of chordoma, based on stable transgene-driven expression of HRASV12 in notochord cells during development. Extensive intra-notochordal tumor formation is evident within days of transgene expression, ultimately leading to larval death. The zebrafish tumors share characteristics of human chordoma as demonstrated by immunohistochemistry and electron microscopy. The mTORC1 inhibitor rapamycin, which has some demonstrated activity in a chordoma cell line, delays the onset of tumor formation in our zebrafish model, and improves survival of tumor-bearing fish. Consequently, the HRASV12-driven zebrafish model of chordoma could enable high-throughput screening of potential therapeutic agents for the treatment of this refractory cancer.

Abstract C1: Functional normalization of the breast cancer vasculature through activation of Tie2 using a vascular-endothelial protein tyrosine phosphatase inhibitor

Background: The solid tumor microvasculature is characterized by structural immaturity and functional abnormality, and mediates several deleterious aspects of tumor behavior. The vascular endothelial protein tyrosine phosphatase (VE-PTP) attenuates the activity of the endothelial cell (EC) Tie-2 receptor tyrosine kinase, a key mediator of vessel maturation. Here we determine the role of VE-PTP in the vasculature of primary and metastatic mammary carcinomas.

Methods: AKB-9778 is a first-in-class pharmacologic VE-PTP inhibitor. We systematically examined its effects in vitro and in vivo. First we studied the effects of AKB-9778 on Tie-2 signaling in two endothelial cell lines in vitro, and also measured its impact on Tie-2 activation in normal and tumor ECs in mice. We next used embryonic zebrafish assays to determine the effects of AKB-9778 on embryonic angiogenesis. We also studied the impact of AKB-9778 therapy on the tumor vasculature, tumor growth and metastatic progression using orthotopic models of murine mammary carcinoma as well as spontaneous and experimental metastasis models (4T1, E0771, P0008, MMTV-PyMT). Finally, we used endothelial nitric oxide synthase (eNOS) deficient mice to establish the role of eNOS in mediating the effects of VE-PTP inhibition.

Results: AKB-9778 induced ligand-independent Tie-2 activation in ECs in vitro and in vivo, and impaired embryonic zebrafish angiogenesis. In mouse models of breast cancer, AKB-9778 (i) delayed the early phase of mammary tumor growth by maintaining vascular maturity; (ii) slowed the growth of spontaneous micrometastases by preventing extravasation of tumor cells into distant organ parenchyma (prolonging survival above adjuvant chemotherapy alone); and (iii) matured established primary tumor blood vessels (increased pericyte coverage, reduced permeability) in turn enhancing tumor perfusion, reducing hypoxia, and improving radiation response. Experiments using eNOS knockout mice showed that the effects of AKB-9778 on tumor vessels were mediated in part by eNOS activation.

Conclusions: Phosphatase inhibition is a relatively unexplored field in cancer, and this is to our knowledge the first demonstration of the effects of VE-PTP inhibition in any disease. Our results demonstrate that pharmacological VE-PTP inhibition can normalize the structure and function of tumor vessels through Tie-2 activation, which delays tumor growth, slows metastatic progression, and enhances response to concomitant cytotoxic treatments. Furthermore we provide genetic evidence for the causal role of eNOS in mediating the beneficial effects of VEPTP inhibition in established tumors. By using models of adjuvant therapy (combined with chemotherapy) and radiation treatment, our results indicate possible avenues for further studying the clinical translatability of VE-PTP inhibition in cancer.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C1.

Citation Format: Shom Goel, Nisha Gupta, Brian P. Walcott, Matija Snuderl, Cristina T. Kesler, Benjamin J. Vakoc, Randall T. Peterson, Timothy P. Padera, Dan G. Duda, Dai Fukumura, Rakesh K. Jain. Functional normalization of the breast cancer vasculature through activation of Tie2 using a vascular-endothelial protein tyrosine phosphatase inhibitor. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C1.

Effects of vascular-endothelial protein tyrosine phosphatase inhibition on breast cancer vasculature and metastatic progression

BACKGROUND

The solid tumor microvasculature is characterized by structural and functional abnormality and mediates several deleterious aspects of tumor behavior. Here we determine the role of vascular endothelial protein tyrosine phosphatase (VE-PTP), which deactivates endothelial cell (EC) Tie-2 receptor tyrosine kinase, thereby impairing maturation of tumor vessels.

METHODS

AKB-9778 is a first-in-class VE-PTP inhibitor. We examined its effects on ECs in vitro and on embryonic angiogenesis in vivo using zebrafish assays. We studied the impact of AKB-9778 therapy on the tumor vasculature, tumor growth, and metastatic progression using orthotopic models of murine mammary carcinoma as well as spontaneous and experimental metastasis models. Finally, we used endothelial nitric oxide synthase (eNOS)-deficient mice to establish the role of eNOS in mediating the effects of VE-PTP inhibition. All statistical tests were two-sided.

RESULTS

AKB-9778 induced ligand-independent Tie-2 activation in ECs and impaired embryonic zebrafish angiogenesis. AKB-9778 delayed the early phase of mammary tumor growth by maintaining vascular maturity (P < .01, t test); slowed growth of micrometastases (P < .01, χ(2) test) by preventing extravasation of tumor cells (P < 0.01, Fisher exact test), resulting in a trend toward prolonged survival (27.0 vs 36.5 days; hazard ratio of death = 0.33, 95% confidence interval = 0.11 to 1.03; P = .05, Mantel-Cox test); and stabilized established primary tumor blood vessels, enhancing tumor perfusion (P = .03 for 4T1 tumor model and 0.05 for E0771 tumor model, by two-sided t tests) and, hence, radiation response (P < .01, analysis of variance; n = 7 mice per group). The effects of AKB-9778 on tumor vessels were mediated in part by endothelial nitric oxide synthase activation.

CONCLUSIONS

Our results demonstrate that pharmacological VE-PTP inhibition can normalize the structure and function of tumor vessels through Tie-2 activation, which delays tumor growth, slows metastatic progression, and enhances response to concomitant cytotoxic treatments.

Heritable and precise zebrafish genome editing using a CRISPR-Cas system

We have previously reported a simple and customizable CRISPR (clustered regularly interspaced short palindromic repeats) RNA-guided Cas9 nuclease (RGN) system that can be used to efficiently and robustly introduce somatic indel mutations in endogenous zebrafish genes. Here we demonstrate that RGN-induced mutations are heritable, with efficiencies of germline transmission reaching as high as 100%. In addition, we extend the power of the RGN system by showing that these nucleases can be used with single-stranded oligodeoxynucleotides (ssODNs) to create precise intended sequence modifications, including single nucleotide substitutions. Finally, we describe and validate simple strategies that improve the targeting range of RGNs from 1 in every 128 basepairs (bps) of random DNA sequence to 1 in every 8 bps. Together, these advances expand the utility of the CRISPR-Cas system in the zebrafish beyond somatic indel formation to heritable and precise genome modifications.