Drug Discov Ther. 2011;5(6):266-278. (DOI: 10.5582/ddt.2011.v5.6.266)
Effective neurofibromatosis therapeutics blocking the oncogenic kinase PAK1.
Maruta H
Neurofibromatosis (NF) is a family of genetic diseases which are caused by dysfunction of either NF1 gene or NF2 gene. One in 3,000 people suffer from this tumor-carrying NF. NF1 gene product is a RAS GTPase activating protein (GAP) of 2,818 amino acids, which normally attenuates the GTP-dependent signal transducing activity of the G protein RAS. Dysfunction of this GAP leads to the abnormal activation of RAS, and eventually an oncogenic kinase called PAK1 as well. NF2 gene product is ''Merlin'' which directly inactivates PAK1. Thus, dysfunction of Merlin causes the abnormal activation of PAK1. In other words, dysfunction of NF1 gene (causing type 1 NF) is basically the same as dysfunction of NF2 gene (causing type 2 NF). In fact the growth of both NF1 and NF2 tumors requires PAK1, and all PAK1 blockers, synthetic chemicals or natural products, suppress the growth of these NF tumor cells both in vitro (cell culture) and in vivo (mice). However, until recently, no FDA-approved effective NF therapeutics is available on the market. Here a series of anti-PAK1 products shall be introduced, which would be potentially useful for the life-long treatment of NF patients in the future. These include the most potent HDAC (histone deacetylase) inhibitor FK228 (IC50: around 1 nM), that eventually blocks PAK1, the direct PAK1 inhibitor PF3758309 (IC50: around 10 nM), a CAPE (caffeic acid phenethyl ester)-based propolis extract called ''Bio 30'' from NZ (New Zealand), and an ARC (artepillin C)-based green propolis extract (GPE) from Brazil. Although the first two drugs are potent, none of them is available on the market as yet. The last two natural (bee-made) products are available on the market, and have been used for the therapy of NF and tuberous sclerosis (TSC) as well as many PAK1-dependent solid cancers such as breast and pancreatic cancers as well as glioma, which altogether represent more than 70% of all human cancers. Since PAK1 is not essential for the normal cell growth, propolis extracts cause no side effects.
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