rAdinbitor, a disintegrin from Agkistrodon halys brevicaudus stejneger, inhibits tumorigenicity of hepatocarcinoma via enhanced anti-angiogenesis and immunocompetence

Emerging anticancer potential and mechanisms of snake venom toxins: A review

Animal-derived venom, like snake venom, has been proven to be valuable natural resources for the drug development. Previously, snake venom was mainly investigated in its pharmacological activities in regulating coagulation, vasodilation, and cardiovascular function, and several marketed cardiovascular drugs were successfully developed from snake venom. In recent years, snake venom fractions have been demonstrated with anticancer properties of inducing apoptotic and autophagic cell death, restraining proliferation, suppressing angiogenesis, inhibiting cell adhesion and migration, improving immunity, and so on. A number of active anticancer enzymes and peptides have been identified from snake venom toxins, such as L-amino acid oxidases (LAAOs), phospholipase A2 (PLA2), metalloproteinases (MPs), three-finger toxins (3FTxs), serine proteinases (SPs), disintegrins, C-type lectin-like proteins (CTLPs), cell-penetrating peptides, cysteine-rich secretory proteins (CRISPs). In this review, we focus on summarizing these snake venom-derived anticancer components on their anticancer activities and underlying mechanisms. We will also discuss their potential to be developed as anticancer drugs in the future.

Snake venom toxins: Potential anticancer therapeutics

Snake venom contains a cocktail of compounds dominated by proteins and peptides, which make up the toxin. The toxin components of snake venom attack several targets in the human body including the neuromuscular system, kidney and blood coagulation system and cause pathologies. As such, the venom toxins can be managed and used for the treatment of these diseases. In this regard, Captopril used in the treatment of cardiovascular diseases was the first animal venom toxin-based drug approved by the US Food and Drug Administration and the European Medicines Agency. Cancers cause morbidity and mortality worldwide. Due to side effects associated with the current cancer treatments including chemotherapy, radiotherapy, immunotherapy, hormonal therapy and surgery, there is a need to improve the efficacy of current treatments and/or develop novel drugs from natural sources including animal toxin-based drugs. There is a long history of earlier and ongoing studies implicating snake venom toxins as potential anticancer therapies. Here, we review the role of crude snake venoms and toxins including phospholipase A2, L-amino acid oxidase, C-type lectin and disintegrin as potential anticancer agents tested in cancer cell lines and animal tumour models in comparison to normal cell lines. Some of the anti-tumour activities of snake venom toxins include induction of cytotoxicity, apoptosis, cell cycle arrest and inhibition of metastasis, angiogenesis and tumour growth. We thus propose the advancement of multidisciplinary approaches to more pre-clinical and clinical studies for enhanced bioavailability and targeted delivery of snake venom toxin-based anticancer drugs.

Cloning, Expression and Inhibitory Effects on Lewis Lung Carcinoma Cells of rAj-Tspin from Sea Cucumber (Apostichopus japonicus)

In recent years, sea cucumber has become a favorite healthcare food due to its characteristic prevention of cardiovascular diseases, suppression of tumors, as well as enhancement of immunity. In order to screen the anti-tumoral proteins or peptides from sea cucumber (Apostichopus japonicus), its cDNA library was analyzed, and a disintegrin-like and metalloproteinase with thrombospondin type 1 motif, member 13 (ADAMTS13)-like was found. ADAMTS13-like contains 10 thrombospondin 1 (TSP1) domains. Based on analysis of bioinformatics, the third TSP1 domain of this protein, which is further named Aj-Tspin, contains an arginine-glycine-aspartate (RGD) motif. Since our previous studies showed that the recombinant RGD-containing peptide from lampreys showed anti-tumoral activity, the third TSP1 domain of ADAMTS13-like was chosen to evaluate it's effect on tumor proliferation and metastasis, despite the fact it shares almost no homologue with disintegrins from other species. After artificial synthesis, its cDNA sequence, Aj-Tspin, which is composed of 56 amino acids, was subcloned into a pET23b vector and expressed as a recombinant Aj-Tspin (rAj-Tspin) in a soluble form with a molecular weight of 6.976 kDa. Through affinity chromatography, rAj-Tspin was purified as a single protein. Both anti-proliferation and immunofluorescence assays showed that rAj-Tspin suppressed the proliferation of Lewis lung carcinoma (LLC) cells through apoptosis. Adhesion assay also displayed that rAj-Tspin inhibited the adhesion of LLC cells to ECM proteins, including fibronectin, laminin, vitronectin and collagen. Lastly, rAj-Tspin also suppressed the migration and invasion of LLC cells across the filter in transwells. Thus, the above indicates that rAj-Tspin might act as a potential anti-tumoral drug in the future and could also provide information on the nutritional value of sea cucumber.

Recombinant and Chimeric Disintegrins in Preclinical Research

Disintegrins are a family of small cysteine-rich peptides, found in a wide variety of snake venoms of different phylogenetic origin. These peptides selectively bind to integrins, which are heterodimeric adhesion receptors that play a fundamental role in the regulation of many physiological and pathological processes, such as hemostasis and tumor metastasis. Most disintegrins interact with integrins through the RGD (Arg-Gly-Asp) sequence loop, resulting in an active site that modulates the integrin activity. Some variations in the tripeptide sequence and the variability in its neighborhood result in a different specificity or affinity toward integrin receptors from platelets, tumor cells or neutrophils. Recombinant forms of these proteins are obtained mainly through Escherichia coli, which is the most common host used for heterologous expression. Advances in the study of the structure-activity relationship and importance of some regions of the molecule, especially the hairpin loop and the C-terminus, rely on approaches such as site-directed mutagenesis and the design and expression of chimeric peptides. This review provides highlights of the biological relevance and contribution of recombinant disintegrins to the understanding of their binding specificity, biological activities and therapeutic potential. The biological and pharmacological relevance on the newest discoveries about this family of integrin-binding proteins are discussed.