Recent investigations in vitro and in vivo have demontrated that scorpion venom has tha ability to induce apoptosis and inhibition of DNA synthesis in a variety of cancerous cells.
Althought, today, chemo- and radiotherapyare used as conventional options of cancer therapy by inducing apoptosis or inhibit proliferation in neoplastic cells, researchers have been studying alternative forms of cancer therapy by using potential biological molecules to target neoplastic
tumors. One type of investigations which looks promising is based on scorpion’s venom.
Scorpions’ venoms are liquid brew of several components such as mucopolysaccharides, serotonin, phospholipase, hyaluronidase, enzyme inhibitors, histamine and neurotoxic peptides with a wide range of biological properties and activity in cells. some isolated peptides from scorpions showed anticancer activity by induction of apoptosis and inhibition of proliferation in cancerous cells.
Cells for the first in vitro experiment were SH-SY5Y (human neuroblastoma) and MCF7 (breast cancer).
Cells were cultured in sterile plates and were exposed to different concentrations of scorpion venom. After 24h incubation researchers find out venom effect on cells.
They found out that some polypeptides present in scorpion venom could increase the oxidative stress in cells by inducing iNOS and NADPH oxidase (production of ROS and RNI).
Nitric oxide and superoxide damage a lot of structural components of the cell; for example they cause peroxidation of cardiolipin, an unusual phospholipid which is typically found in bacterial plasma membrane. Peroxidation of cardiolipin leads to dissociation of cytochrome c and its release in the cytosol where it takes part to the formation of a structure called apoptosome (cyt c, APAF-1, procaspase 9), that starts apoptosis.
Scorpion venom, furthermore, induce the assembly of mitochondrial permeability transition pore, the loss of mitochondrial membrane potential and the realise of cytc and other proapoptptic protein in the citosol. These events cause cells’ death by apoptosis.
After these experiments, scientists discover and isolated a polypeptide from venom scorpion, called chlorotoxin, that binds to some surface proteins averexpressed by many types of tumors, expecially in brain cancer. In particular chlorotoxin can bind to MMP-2 (Matrix metalloproteinase), a surface protein overexpressed in highly invasive tumors, such as brain cancer. When chlorotoxin binds to MMP-2, both get drawn into the cancerous cell via a clathrin-dependent pathway.
Metalloproteases constitute a family of enzymes from the group of proteases whose catalytic mechanism involves a metal (most metalloproteases are zinc-dependent, but some use cobalt).
These proteins are involved in the breakdown of extracellular matrix in normal physiological processes, such as embryonic development, reproduction and tissue remodeling, as well as in disease processes, such as arthritis and metastasis.
MMP-2 is specifically upregulated in gliomas and related cancers, and the anti-invasive effect of chlorotoxin on glioma cells can be explained by its interaction with MMP-2.
MMP-2 is unregulated only in glioma cells but not in normal glial cells and neurons; so CTX has been show to bind specifically to glioma cells surface and not to healthy cells.
Following experiments shown CTX bind also to cells of a wide variety of tumors, including prostate cancer, intestinel cancer and sarcoma, suggesting wider application of this targeting agent against other forms of cancer. In fact MMP-2 shows signt of being overactive in cancers of breast, colon, skin, lung, prostate and ovaries.
Furthermore, once CTX and MMP-2 are inside cancerous cell, they inhibit the machinery that allows cells to change shape, yet another step required for tumor cells to slip through the body.
Recently annexin A2 was identified as a binding partner for CTX in many human tumor cell lines and normal human endothelial cells. Annexin 2 is involved in diverse cellular processes such as cell motility, linkage of membrane-associated protein complexes to the actin cytoskeleton and cell matrix interactions . Annexin A2 is a member of this calcium-dependent phospholipid-binding protein family play a role in the regulation of cellular growth and in signal transduction pathways.
Maybe the abundant presence of annexin on endothelial cells can explain the anti-angiogenic effects of CTX that was demonstrated injecting the compound intravenously in vivo in mice.
In recent studies ANXA2 has been identified as a novel cellular redox regulatory protein that plays a significant role in cells undergoing oxidative stress and in particular during tumorigenesis. Annexin A2 is unique among the annexins in that it possesses redox sensitive cysteine(s). The ubiquitous and abundant expression of ANXA2 in cells and its reactivity with hydrogen peroxide led us to hypothesize that this protein could play a role in cellular redox regulation. Depletion of ANXA2 resulted in the elevation of cellular reactive oxygen species (ROS) upon oxidative stress, increased activation of the ROS-induced pro-apoptotic kinases, JNK, p38 and Akt and elevated sensitivity to ROS-mediated cellular damage/death. ANXA2-null mice showed significantly elevated protein oxidation. ANXA2 depleted cancer cells showed enhanced cellular protein oxidation concomitant with decreased tumor growth compared to control cancer cells. In fact ex-vivo human cancer studies showed that up-regulation of the reduced form of ANXA2 is associated with protection of the tumor proteins from oxidation.
Reactive oxygen species (ROS) are oxygen-containing reactive chemical species which include such biologically important molecules as superoxide, nitric oxide, hydroxyl radical and hydrogen peroxide (H2O2). Endogenous H2O2 is a by-product of mitochondrial respiration. In addition, various signaling molecules, including growth factors, cytokines, hormones and neurotransmitters induce increases in intracellular H2O2 through the activation of NADPH oxidases (Nox). H2O2-dependent signaling has been implicated in diverse processes such as regulation of cell proliferation, differentiation, migration and apoptosis.
The production of a cytotoxic molecule has obvious potential risks to the cells as H2O2 is a major contributor to DNA damage, protein oxidation and lipid peroxidation.
Cancer cells typically express higher levels of ROS compared to normal cells which gives them both a proliferative advantage and also promotes malignant progression. In order to balance the proliferative advantage of ROS up-regulation versus its potential risks due to protein, lipid and DNA damage, cancer cells induce over-expression of ANXA2.
ANXA2 possesses redox cysteine (Cys8) that is oxidated by H2O2 and reduced by the thioredoxin system.
Common chemotherapeutic agents induce oxidative stress in target cells. Unfortunately cancer cells overexpress ANXA2 and so they are more resistant to ROS induced death.
So the use of CTX, blocking the expression in cancer cells might constitute a potential therapeutic strategy to support chemiotherapeutic terapy.
In conclusion, all these studies indicate the presence of apoptotic, anti-proliferative and anti-angiogenic compuonds in scorpion venom which, in future, can lead to development of new drugs for cancer and other incurable desease.