, 2000). Bubien et al. (2004), using this peptide, inhibited

Na+ currents in high-grade human GSK2118436 molecular weight astrocytoma cells (glioblastoma multiforme, or GBM). However, when the same experiment was performed on normal human astrocytes, the toxin failed to inhibit the whole-cell current, suggesting that Psalmotoxin 1 may be used in the diagnosis as well as in therapeutic treatments of malignant gliomas. Gao et al. (2005a) studied the inhibitory effect of the venom of the spider Macrothele raveni on the proliferation of human hepatocellular carcinoma cell line BEL-7402 and its molecular mechanism. Using the MTT assay, the venom was shown to inhibit cell proliferation in a dose- and time-dependent manner,

with IC50 of 20 μg/ml (48 h), also inhibiting DNA synthesis by the treated cells. Flow cytometry analyses showed an arrest in the cell cycle in the G(0)/G(1) phase and an increase in the number of apoptotic cells. Furthermore, the expression of c-myc, a transcription factor responsible for activation of a large number of genes, was down-regulated. McLachlan et al., 2005 and Kekre et al., 2005 and Siedlakowski et al. (2008) studied the effects of Pancratistatin (PST) upon human neuroblastoma cells (SHSY-5Y), human lymphoma (Jurkat) and breast cancer (MCF-7), respectively. PST, a natural molecule isolated from the lily spider Pancratium littorale, was shown to have apoptotic effects specifically upon these cells, and not upon their homologous non-tumoral lines. The most interesting finding is that this molecule does not affect normal MS-275 cells when compared to other drugs employed in clinical treatments of cancer, such as Etoposide (Vp-16) and Paclitaxel (Taxol). In cancer cell lines, PST induced permeabilization of mitochondria and activation Janus kinase (JAK) of caspases, leading cells to apoptosis and also increasing ROS production, while the mitochondria of normal cells were not affected. It is worth mentioning that PST induced apoptosis in cancer cells acting upon non-genomic targets (with no DNA damage) and,

even more remarkable is the fact that this molecule does not seem to have any effect upon non-cancer cells, representing an important candidate in the development of anti-cancer therapies with no toxic consequences to the organism. The anti-tumor activity of gomesin, a potent anti-microbial peptide isolated from hemocytes of the spider Acanthoscurria gomesiana, was tested in vitro and in vivo ( Rodrigues et al., 2008). C57BL/6 mice received subcutaneous injection of 105 melanoma cells B16F10-Nex2 followed by topic treatment with gomesin as a cream, which significantly reduced tumor growth and increased survival compared to control. Gomesin displayed cytotoxic effects, reducing the viability of a number of tumor cell lines, such as melanoma, breast cancer and colon carcinoma.