Abstract 413: Engineering Targeted Growth Factors for Selective Pro-survival Signaling in Apoptotic Cardiomyocytes Following Ischemic Injury

Background: Despite the benefits of reperfusion therapy after myocardial infarction (MI), most patients still progress to heart failure. MI patients suffer irreversible loss of heart function due to cardiomyocyte (CM) death and tissue scarring. Growth factors (GFs) reduce scar size and limit CM apoptosis in preclinical studies, however native GFs have poor drug-like qualities and have not been successful in the clinic. Silver Creek Pharmaceuticals is developing a new class of targeted, growth factor-based therapeutics (Smart Growth Factors) that are engineered to have optimized pharmacokinetics, dynamics and safety profiles. Our first generation of SGFs use annexin-V (AnxV) to target IGF-1 to damaged CMs and selectively activate pro-survival signaling.

Methods and Results: We used biophysical simulation to design an IGF-1-based SGF that selectively activated the PI3K pathway in damaged cells. SGFs were engineered to target IGF-1 to damaged cells through the binding of AnxV to phosphatidylserine exposed on the surface of apoptotic cells. These bispecific proteins were constructed with half-life modulators and linkers, then screened for their ability to selectively increase pAKT levels in apoptotic iPSC-derived human CMs. We identified a subset of SGFs that were able to selectively increase pAKT levels in apoptotic cells as compared to healthy cells (p<0.05). Based on these data, we tested the ability of SGFs to activate pro-survival signaling and reduce infarct size in a rat ischemia/reperfusion model of acute MI (AMI). SGFs were able to selectively prolong pAKT in the infarcted region of the left ventricle without activating signaling in remote healthy tissue out to 2 hours post-reperfusion (n=3-6/group, p<0.05). For efficacy studies, rats were subjected to 60 minutes of ischemia followed by 72 hours of reperfusion. A single IV dose of SGF (600 pmol/kg) administered at time of reperfusion was able to significantly reduce infarct size relative to the area-at-risk (infarct/AAR%) as compared to controls (p<0.05; SGF 12.7±5% n=10; wt IGF-1 20.3±3% n=8 and vehicle 27.6±7% n=12).

Conclusions: This work demonstrates that SGFs selectively activate pro-survival signals in distressed CMs and lead to reduced infarct size in vivo without off-target effects.

Abstract 233: Engineering Growth Factors For Cardiomyocyte Survival and Regeneration Following Ischemic Injury

Background: Despite the benefits of reperfusion therapy after myocardial infarction (MI), one-year mortality and morbidity rates remain high. Silver Creek Pharmaceuticals is engineering a new class of protein therapeutics, termed Smart Growth Factors (SGFs), designed to act directly on cardiomyocytes (CMs) to promote survival and regeneration after ischemia/reperfusion (I/R) injury. Our approach is to maximize pro-survival growth factor signaling in damaged cells by creating targeted molecules with optimized pharmacokinetics and dynamics.

Methods and Results: Computer model simulations guided the design of a panel of SGFs comprising various growth factors, targeting arms, half-life modulators, and linkers. SGF constructs were cloned and subsequently produced using a HEK 293F expression system. This panel was screened in vitro for signaling pathway activation and target affinity. The top hits were assayed for pro-survival activity in a chemical injury model in human CMs, where a targeted SGF significantly reduced caspase activation (p<0.0084; SGF-treated 3.82±0.64-fold, IGF1-treated 16.25±3.6-fold) Based on these data and additional simulations, a class of SGFs that utilized annexin V to target IGF1 to apoptotic cells via phosphatidylserine binding was selected for screening in animal models. In vivo, these SGFs extended pAKT signaling in heart tissue compared to wild-type IGF1 and had increased accumulation in the infarcted region of mouse hearts after MI. Preliminary data suggests that a single low intravenous dose (16 pmol) of SGF delivered one hour after LAD ligation could significantly reduce scar size in animals assessed at 12 weeks post MI (p<0.05; SGF-treated 9.3±1.3%, n=10; vehicle 18.1±3.13%, n=8). Finally, SGF treatment at the time of reperfusion in a rat I/R model was able to significantly reduce infarct size (p<0.05; SGF-treated 27.0±1.8% n=7; vehicle 33.6±1.92% n=8).

Conclusions: This work demonstrates an enhanced ability of SGFs in preventing apoptosis in vitro and reducing infarct sizes in animal models of MI. By taking a systems biology approach to SGF engineering, Silver Creek is developing cardioprotective therapies with the hope of improving patient health and addressing unmet medical need.

Transcriptional program of ciliated epithelial cells reveals new cilium and centrosome components and links to human disease

Defects in the centrosome and cilium are associated with a set of human diseases having diverse phenotypes. To further characterize the components that define the function of these organelles we determined the transcriptional profile of multiciliated tracheal epithelial cells. Cultures of mouse tracheal epithelial cells undergoing differentiation in vitro were derived from mice expressing GFP from the ciliated-cell specific FOXJ1 promoter (FOXJ1:GFP). The transcriptional profile of ciliating GFP+ cells from these cultures was defined at an early and a late time point during differentiation and was refined by subtraction of the profile of the non-ciliated GFP- cells. We identified 649 genes upregulated early, when most cells were forming basal bodies, and 73 genes genes upregulated late, when most cells were fully ciliated. Most, but not all, of known centrosome proteins are transcriptionally upregulated early, particularly Plk4, a master regulator of centriole formation. We found that three genes associated with human disease states, Mdm1, Mlf1, and Dyx1c1, are upregulated during ciliogenesis and localize to centrioles and cilia. This transcriptome for mammalian multiciliated epithelial cells identifies new candidate centrosome and cilia proteins, highlights similarities between components of motile and primary cilia, and identifies new links between cilia proteins and human disease.

Methylation by Set9 modulates FoxO3 stability and transcriptional activity

The FoxO family of transcription factors plays an important role in longevity and tumor suppression by regulating the expression of a wide range of target genes. FoxO3 has recently been found to be associated with extreme longevity in humans and to regulate the homeostasis of adult stem cell pools in mammals, which may contribute to longevity. The activity of FoxO3 is controlled by a variety of post-translational modifications that have been proposed to form a ‘code’ affecting FoxO3 subcellular localization, DNA binding ability, protein-protein interactions and protein stability. Lysine methylation is a crucial post-translational modification on histones that regulates chromatin accessibility and is a key part of the ‘histone code’. However, whether lysine methylation plays a role in modulating FoxO3 activity has never been examined. Here we show that the methyltransferase Set9 directly methylates FoxO3 in vitro and in cells. Using a combination of tandem mass spectrometry and methyl-specific antibodies, we find that Set9 methylates FoxO3 at a single residue, lysine 271, a site previously known to be deacetylated by Sirt1. Methylation of FoxO3 by Set9 decreases FoxO3 protein stability, while moderately increasing FoxO3 transcriptional activity. The modulation of FoxO3 stability and activity by methylation may be critical for fine-tuning cellular responses to stress stimuli, which may in turn affect FoxO3's ability to promote tumor suppression and longevity.

A shared molecular mechanism underlies the human rasopathies Legius syndrome and Neurofibromatosis-1

The Ras/mitogen-activated protein kinase (MAPK) pathway plays a critical role in transducing mitogenic signals from receptor tyrosine kinases. Loss-of-function mutations in one feedback regulator of Ras/MAPK signaling, SPRED1 (Sprouty-related protein with an EVH1 domain), cause Legius syndrome, an autosomal dominant human disorder that resembles Neurofibromatosis-1 (NF1). Spred1 functions as a negative regulator of the Ras/MAPK pathway; however, the underlying molecular mechanism is poorly understood. Here we show that neurofibromin, the NF1 gene product, is a Spred1-interacting protein that is necessary for Spred1's inhibitory function. We show that Spred1 binding induces the plasma membrane localization of NF1, which subsequently down-regulates Ras-GTP levels. This novel mechanism for the regulation of neurofibromin provides a molecular bridge for understanding the overlapping pathophysiology of NF1 and Legius syndrome.

The centriolar satellite proteins Cep72 and Cep290 interact and are required for recruitment of BBS proteins to the cilium

The ciliopathy-associated proteins Cep290 and BBS4 localize to cytoplasmic particles called centriolar satellites, yet the significance of this association is unknown. A new component of satellites, Cep72, is identified. Its role in the regulation of Cep290 and BBS4 is described, as are developmental defects resulting from loss of satellites in zebrafish.

Defects in centrosome and cilium function are associated with phenotypically related syndromes called ciliopathies. Centriolar satellites are centrosome-associated structures, defined by the protein PCM1, that are implicated in centrosomal protein trafficking. We identify Cep72 as a PCM1-interacting protein required for recruitment of the ciliopathy-associated protein Cep290 to centriolar satellites. Loss of centriolar satellites by depletion of PCM1 causes relocalization of Cep72 and Cep290 from satellites to the centrosome, suggesting that their association with centriolar satellites normally restricts their centrosomal localization. We identify interactions between PCM1, Cep72, and Cep290 and find that disruption of centriolar satellites by overexpression of Cep72 results in specific aggregation of these proteins and the BBSome component BBS4. During ciliogenesis, BBS4 relocalizes from centriolar satellites to the primary cilium. This relocalization occurs normally in the absence of centriolar satellites (PCM1 depletion) but is impaired by depletion of Cep290 or Cep72, resulting in defective ciliary recruitment of the BBSome subunit BBS8. We propose that Cep290 and Cep72 in centriolar satellites regulate the ciliary localization of BBS4, which in turn affects assembly and recruitment of the BBSome. Finally, we show that loss of centriolar satellites in zebrafish leads to phenotypes consistent with cilium dysfunction and analogous to those observed in human ciliopathies.

Kinetics and longevity of ΦC31 integrase in mouse liver and cultured cells

The ΦC31 integrase system provides genomic integration of plasmid DNA that may be useful in gene therapy. For example, the ΦC31 system has been used in combination with hydrodynamic injection to achieve long-term expression of factor IX in mouse liver. However, a concern is that prolonged expression of ΦC31 integrase within cells could potentially stimulate chromosome rearrangements or an immune response. Western blot and immunofluorescence analyses were performed to investigate the duration of ΦC31 integrase expression in mouse liver. Integrase was expressed within 2 to 3 hr after hydrodynamic injection of a plasmid expressing ΦC31 integrase. Expression peaked between 8 and 16 hr and fell to background levels by 24-48 hr postinjection. Analysis of the amount of integrase plasmid DNA present in the liver over time suggested that the brief period of integrase expression could largely be accounted for by rapid loss of the bulk of the plasmid DNA, as well as by silencing of plasmid expression. PCR analysis of integration indicated that ΦC31 integrase carried out genomic integration of a codelivered attB-containing plasmid by 3 hr after plasmid injection. Integrase was expressed for longer times and at higher levels in transfected cultured cells compared with liver. Inhibitor studies suggested that the enzyme had a short half-life and was degraded by the 26S proteasome. The short duration of integrase expression in liver and rapid integration reaction appear to be features favorable for use in gene therapy.