Expression and functional characterization of a recombinant targeted toxin with an uPA cleavable linker in Pichia pastoris

Recent developments in animal venom peptide nanotherapeutics with improved selectivity for cancer cells

Animal venoms are a rich source of bioactive peptides that efficiently modulate key receptors and ion channels involved in cellular excitability to rapidly neutralize their prey or predators. As such, they have been a wellspring of highly useful pharmacological tools for decades. Besides targeting ion channels, some venom peptides exhibit strong cytotoxic activity and preferentially affect cancer over healthy cells. This is unlikely to be driven by an evolutionary impetus, and differences in tumor cells and the tumor microenvironment are probably behind the serendipitous selectivity shown by some venom peptides. However, strategies such as bioconjugation and nanotechnologies are showing potential to improve their selectivity and potency, thereby paving the way to efficiently harness new anticancer mechanisms offered by venom peptides. This review aims to highlight advances in nano- and chemotherapeutic tools and prospective anti-cancer drug leads derived from animal venom peptides.

A pH-dependent Antibacterial Peptide Release Nano-system Blocks Tumor Growth in vivo without Toxicity

In this study, we designed a nano-system where a novel antibacterial peptide RGD-hylin a1 with reduced hemolysis than the commonly studied melittin was loaded onto mesoporous silica (HMS). We found out that the designed nano-system, RGD-hylin a1-HMS, released RGD-hylin a1 in a pH-dependent manner. It caused apoptosis of cancer cells at low dosage of the antibacterial peptide at pH = 5.5, but was safe to the cells at pH = 7. The hemolytic activity of RGD-hylin a1 itself was reduced by 50~100% by the nano-system depending on the dosage. When this nano-system was administered to tumor-bearing mice at low dosage via intravenous injection, the growth of the solid tumor was blocked by the RGD-hylin a1-HMS nano-system with a 50–60% inhibition rate relative to the PBS-treated control group in terms of tumor volume and weight. Further, the hemolytic activity of RGD-hylin a1 was completely eliminated within the delivery system with no other side effects observed. This study demonstrates that this smart pH-dependent antibacterial peptide release nano-system has superior potential for solid tumor treatments through intravenous administration. This smart-releasing system has great potential in further clinical applications.

Active Expression of Human Tissue Plasminogen Activator (t-PA) c-DNA from Pulmonary Metastases in the Methylotrophic Yeast Pichia Pastoris KM71H Strain

Background:

Human tissue-type plasminogen activator (t-PA) is a key protease of the trypsin family. It catalyzes the activation of zymogen plasminogen to the fibrin-degrading proteinase, plasmin, leading to digestion of fibrin clots. The recombinant enzyme produced by recombinant technology issued to dissolve blood clots in treatment of various human diseases such as coronary artery thrombosis, pulmonary embolism, acute ischemic stroke (AIS). Pichia pastoris expression system is a unique system for the production of high level of recombinant proteins. GS115 and KM71H are two kinds of Pichia pastoris strains whilst production of recombinant proteins in these strains is not predictable. The aim of the study was evaluation of t-PA expression in KM71H strains.

Methods:

In this study, the cDNA of the t-PA gene was amplified by PCR, sequenced and cloned into Pichia pastoris KM71H host strain using pPICZalphaA expression vector that allows methanol-induced expression and secretion of the protein.

Results:

Dot blotting results confirmed the presence oft-PA in the cell supernatant. Western blotting test revealed the approximate size of 70 KDa for recombinant t-PA. Quantitative ELISA experiment showed 810 µg/L of t-PA in the supernatant samples. Zymography analysis confirmed the proteolytic activity and biological function of the expressed recombinant t-PA.

Conclusions:

Correspondingly, Pichia pastoris KM71H is an appropriate strain for production of active recombinant protein.

Preparation and Characterization of Gelonin-Melittin Fusion Biotoxin for Synergistically Enhanced Anti-Tumor Activity

PURPOSE

To investigate the applicability of fusion biotoxins combining pore-forming toxins (PFTs) and ribosome-inactivating proteins (RIPs) for the anti-cancer treatment.

METHODS

Membrane active PFTs tend to destabilize cell membranes of tumor cells, but lack a warhead inducing significant cause of cell death. Cell-impermeable RIPs possess a powerful warhead, yet not able to enter the tumor cells. To address these challenges for anti-tumor effects, we introduced a fusion strategy of conjugating melittin (a PFT) and gelonin (a type 1 RIP) via chemical and recombinant methods, followed by in vitro assays and in vivo animal studies.

RESULTS

In vitro characterization results confirmed that the chimeric gelonin-melittin fusion proteins retained equivalent intrinsic activity to that of unmodified gelonin in inhibiting protein translation. However, chemically conjugated gelonin-melittin (cGel-Mel) and recombinant chimeric gelonin-melittin fusion (rGel-Mel) exhibited greater cell uptake, yielding a significantly enhanced cytotoxic activity over treatment of gelonin, melittin or physical mixture of gelonin and melittin. Remarkably, cGel-Mel and rGel-Mel displayed 32- and 10-fold lower IC50 than gelonin in the cell lines. The superior anti-tumor efficacy of multivalent cGel-Mel to monovalent rGel-Mel suggested that valency could be a crucial factor for the extent of melittin-mediated cell uptake. Tumoricidal effects observed from animal studies were in good accordance with our findings from the cellular assays.

CONCLUSIONS

This study successfully demonstrated that fusion of biotoxins could provide a simple yet effective way to synergistically augment their anti-tumor activity.

The anti-cancer potency and mechanism of a novel tumor-activated fused toxin, DLM

Melittin, which acts as a membrane-disrupting lytic peptide, is not only cytotoxic to tumors, but also vital to normal cells. Melittin had low toxicity when coupled with target peptides. Despite significant research development with the fused toxin, a new fused toxin is needed which has a cleavable linker such that the fused toxin can release melittin after protease cleavage on the tumor cell surface. We describe a novel fused toxin, composed of disintegrin, uPA (urokinase-type plasminogen activator)-cleavable linker, and melittin. Disintegrin is a single strand peptide (73 aa) isolated from Gloydius Ussuriensis venom. The RGD (Arg-Gly-Asp) site of disintegrin dominates its interaction with integrins on the surface of the tumor cells. uPA is over-expressed and plays an important role in tumor cell invasiveness and metastatic progression. The DLM (disintegrin-linker-melittin) linker is uPA-cleavable, enabling DLM to release melittin. We compared binding activity of our synthesized disintegrin with native disintegrin and report that DLM had less binding activity than the native form. uPA-cleavage was evaluated in vitro and the uPA-cleavable linker released melittin. Treating tumors expressing uPA with DLM enhanced tumor cell killing as well as reduced toxicity to erythrocytes and other non-cancerous normal cells. The mechanism behind DLM tumor cell killing was tested using a DNA ladder assay, fluorescent microscopy, flow cytometry, and transmission electron microscopy. Data revealed tumor cell necrosis as the mechanism of cell death, and the fused DLM toxin with an uPA-cleavable linker enhanced tumor selectivity and killing ability.