Improved gene expression using low molecular weight peptides produced from protamine sulfate

DNA-protamine condensates under low salt conditions: molecular dynamics simulation with a simple coarse-grained model focusing on electrostatic interactions

Protamine, a small, strongly positively-charged protein, plays a key role in achieving chromatin condensation inside sperm cells and is also involved in the formulation of nanoparticles for gene therapy and packaging of mRNA-based vaccines against viral infection and cancer. The detailed mechanisms of such condensations are still poorly understood especially under low salt conditions where electrostatic interaction predominates. Our previous study, with a refined coarse-grained model in full consideration of the long-range electrostatic interactions, has demonstrated the crucial role of electrostatic interaction in protamine-controlled reversible DNA condensation. Therefore, we herein pay our attention only to the electrostatic interaction and devise a coarser-grained bead-spring model representing the right linear charge density on protamine and DNA chains but treating other short-range interactions as simply as possible, which would be suitable for real-scale simulations. Effective pair potential calculations and large-scale molecular dynamics simulations using this extremely simple model reproduce the phase behaviour of DNA in a wide range of protamine concentrations under low salt conditions, again revealing the importance of the electrostatic interaction in this process and providing a detailed nanoscale picture of bundle formation mediated by a charge disproportionation mechanism. Our simulations also show that protamine length alters DNA overcharging and in turn redissolution thresholds of DNA condensates, revealing the important role played by entropies and correlated fluctuations of condensing agents and thus offering an additional opportunity to design tailored nanoparticles for gene therapy. The control mechanism of DNA-protamine condensates will also provide a better microscopic picture of biomolecular condensates, i.e., membraneless organelles arising from liquid-liquid phase separation, that are emerging as key principles of intracellular organization. Such condensates controlled by post-translational modification of protamine, in particular phosphorylation, or by variations in protamine length from species to species may also be responsible for the chromatin-nucleoplasm patterning observed during spermatogenesis in several vertebrate and invertebrate species.

Peptide vectors for gene delivery: from single peptides to multifunctional peptide nanocarriers

The therapeutic use of nucleic acids relies on the availability of sophisticated delivery systems for targeted and intracellular delivery of these molecules. Such a gene delivery should possess essential characteristics to overcome several extracellular and intracellular barriers. Peptides offer an attractive platform for nonviral gene delivery, as several functional peptide classes exist capable of overcoming these barriers. However, none of these functional peptide classes contain all the essential characteristics required to overcome all of the barriers associated with successful gene delivery. Combining functional peptides into multifunctional peptide vectors will be pivotal for improving peptide-based gene delivery systems. By using combinatorial strategies and high-throughput screening, the identification of multifunctional peptide vectors will accelerate the optimization of peptide-based gene delivery systems.

Cell-penetrating peptides meditated encapsulation of protein therapeutics into intact red blood cells and its application

Red blood cells (RBCs) based drug carrier appears to be the most appealing for protein drugs due to their unmatched biocompatability, biodegradability, and long lifespan in the circulation. Numerous methods for encapsulating protein drugs into RBCs were developed, however, most of them induce partial disruption of the cell membrane, resulting in irreversible alterations in both physical and chemical properties of RBCs. Herein, we introduce a novel method for encapsulating proteins into intact RBCs, which was meditated by a cell penetrating peptide (CPP) developed in our lab-low molecular weight protamine (LMWP). l-asparaginase, one of the primary drugs used in treatment of acute lymphoblastic leukemia (ALL), was chosen as a model protein to illustrate the encapsulation into erythrocytes mediated by CPPs. In addition current treatment of ALL using different l-asparaginase delivery and encapsulation methods as well as their associated problems were also reviewed.

Cell permeable cocaine esterases constructed by chemical conjugation and genetic recombination

Cocaine esterase (CocE) is the most efficient cocaine-metabolizing enzyme tested in vivo to date, displaying a rapid clearance of cocaine and a robust protection against cocaine's toxicity. Two potential obstacles to the clinical application of CocE, however, lie in its proteolytic degradation and induced immune response. To minimize these potential obstacles, we attempted nondisruptive cell encapsulation by creating a cell permeable form of CocE, which was achieved by covalently linking a thermally stable CocE mutant (dmCocE) with cell penetrating peptides (CPPs). Two types of CPPs, Tat and the low molecular weight protamine (LMWP), were used in this study. Two types of disulfide-bridged chemical conjugates, Tat-S-S-dmCocE and LMWP-S-S-dmCocE, were synthesized and then purified by heparin affinity chromatography. In addition, four recombinant CPP-dmCocE fusion proteins, Tat-N-dmCocE, LMWP-N-dmCocE, dmCocE-C-Tat, and dmCocE-C-LMWP, were constructed, expressed in Escherichia coli, and purified as soluble proteins. Among these six CPP-dmCocE variants, LMWP-S-S-dmCocE showed the highest cocaine-hydrolyzing activity, and dmCocE-C-Tat had the highest production yield. To evaluate their cellular uptake behavior, a covalently linked fluorophore (FITC) was utilized to visualize the cellular uptake of all six CPP-dmCocE variants in living HeLa cells. All the six variants exhibited cellular uptake, but their intracellular distribution phenotypes differed. While the chemical conjugates showed primarily cytoplasmic distribution, which was likely due to the reduction of the disulfide linkage between CPP and dmCocE, all the other four recombinant fusion proteins displayed both nuclear and cytoplasmic localization, with dmCocE-C-CPP exhibiting higher cytoplasmic distribution during cellular uptake. Based on a balanced consideration of essentials for clinical application, including parameters such as high cocaine-hydrolyzing efficiency, large production yield, major cytoplasmic distribution, etc., the dmCocE-C-Tat fusion protein seems to be the best candidate from this investigation. Further in vivo studies of the cell-encapsulated dmCocE-C-Tat in hydrolyzing cocaine and alleviating immunogenicity and proteolytic degradation in established, clinically relevant mouse models are currently underway in our laboratories. Findings from this research are not only useful for developing other new CPP-CocE constructs but also valuable for establishing a nondisruptive cell-encapsulation technology for other protein therapeutics that are known to be immunogenic for direct clinical application.

High-content screening of peptide-based non-viral gene delivery systems

High-content screening (HCS) uses high-capacity automated fluorescence imaging for the quantitative analysis of single cells and cell populations. Here, we developed an HCS assay for rapid screening of non-viral gene delivery systems as exemplified by the screening of a small library of peptide-based transfectants. These peptides were simultaneously screened for transfection efficiency, cytotoxicity, induction of cell permeability and the capacity to transfect non-dividing cells. We demonstrated that HCS is a valuable extension to the already existing screening methods for the in vitro evaluation of non-viral gene delivery systems with the added value that multiple parameters can be screened in parallel thereby obtaining more information from a single screening event, which will accelerate the development of novel gene delivery systems.

Accelerated stem cell labeling with ferucarbotran and protamine

OBJECTIVE

To develop and characterize a clinically applicable, fast and efficient method for stem cell labeling with ferucarbotran and protamine for depiction with clinical MRI.

METHODS

The hydrodynamic diameter, zeta potential and relaxivities of ferucarbotran and varying concentrations of protamine were measured. Once the optimized ratio was found, human mesenchymal stem cells (MSCs) were labeled at varying incubation times (1-24 h). Viability was assessed via Trypan blue exclusion testing. 150,000 labeled cells in Ficoll solution were imaged with T1-, T2- and T2*-weighted sequences at 3 T, and relaxation rates were calculated.

RESULTS

Varying the concentrations of protamine allows for easy modification of the physicochemical properties. Simple incubation with ferucarbotran alone resulted in efficient labeling after 24 h of incubation while assisted labeling with protamine resulted in similar results after only 1 h. Cell viability remained unaffected. R2 and R2* relaxation rates were drastically increased. Electron microscopy confirmed intracellular iron oxide uptake in lysosomes. Relaxation times correlated with results from ICP-AES.

CONCLUSION

Our results show internalization of ferucarbotran can be accelerated in MSCs with protamine, an approved heparin antagonist and potentially clinically applicable uptake-enhancing agent.