Lesson 6: CK2 (Casein Kinase 2) is also essential for the activation of PAK1 in cells

At least three distinct Tyr-kinases (ETK, JAK2 and FYN) are essential for the activation of PAK1 in cells. These kinases act down-stream of the oncogenic RAS. Recently another kinase was found to activate PAK1 in a RAS-dependent manner, too. It is called CK2 (Casein Kinase 2) which phosphorylates PAK1 at Ser 223 (1). The CK2-PAK1 interaction requires another protein called CKIP1, a PH domain protein. Furthermore, it is also known that PI-3 kinase acts upstream of the oncogenic CKIP1-CK2-PAK1 pathway. Thus, RAS-PI-3 kinase-CKIP1-CK2-PAK1 cascade has been established. In other words, CK2 inhibitors would block PAK1.

So I wonder what sort of CK2 inhibitors have been developed till now. Among several CK2 inhibitors, "D11 " is among the most potent, with the IC50 around 5 nM in vitro (2). It  was recently developed by a Danish group led by Barbara Guerra, and inhibits the PAK1-dependent growth of pancreatic cancer cells with the IC50 around 50 micro M in cell culture. Another potent CK2 inhibitor called "TF" (IC50=50 nM in vitro) inhibits the growth of cancer cells with IC50 around 50 micro M. Thus, their cell-permeability is extremely poor. I wonder if there is any potent CK2 inhibitor(s)  inhibiting the growth of cancer cells with IC50 at low nM levels.

So far CX-4945 (developed by Cylene Pharmaceuticals in US) is the most potent among CK2 inhibitors, with IC50=1 nM (in vitro) but 1 micro M (in cell culture), and inhibits the growth of human pancreatic cancer grafted in mice by 93 % with the daily dose of 75 mg/kg orally (3).

If I understand correctly, Senhwa Biosciences in Taiwan/US is currently conducting the phase1/2 clinical trials of CX-4945 for cancer therapy in combination with gemcitabin and cisplatin, hinting that CX-4945 alone is not sufficient for the complete cure of cancers.

References:

1. Kim YB, Shin YJ, Roy A, Kim JH.　The Role of the Pleckstrin Homology Domain-Containing Protein CKIP-1 in Activation of p21-activated Kinase 1 (PAK1). J Biol Chem. 2015 Jul 9.

2. Guerra B, Hochscherf J, Jensen NB, Issinger OG. Identification of a novel potent, selective and cell permeable inhibitor of protein kinase CK2 from the NIH/NCI Diversity Set Library. Mol Cell Biochem. 2015 May 12.

3. Siddiqui-Jain A¹, Drygin D, Streiner N, Chua P,et al. CX-4945, an orally bioavailable selective inhibitor of protein kinase CK2, inhibits prosurvival and angiogenic signaling and exhibits antitumor efficacy. Cancer Res. 2010; 70: 10288-98.
 

The Direct Target of CAPE: AKR1B10 ("Aldo-Keto-Reductase" ) that is essential for RAS/RAC/PAK1 signaling

CAPE (caffeic acid phenethyl ester), the major anti-cancer ingredient in propolis such as Bio 30, has been known to down-regulate RAC that is essential for the activation of the major oncogenic/ageing kinase PAK1. However, the direct target of CAPE remained unknown till recently. 

A few years ago, a group at Gifu College of Pharmacy in Japan identified AKR1B10 ("Aldo-Keto-Reductase" ) as the direct target of CAPE with the IC50=80 nM, and developed a more potent CAPE derivative (called "10C") with the IC50=6 nM (1).  AKR1B10 is essential for the activation of RAS and RAC, which eventually activate PAK1 in cells.  Thus, we wonder if "Nepofein" is more potent than the compound 10C or not in cell culture and in vivo. The cell-permeability of "compound 10C" is still very low, and the IC50 against cancer cell growth (or AKR1B10 ) in cell culture is around 300 nM, indicating that only 1/50 of this compound enters cells.

References:

1. Soda M, Hu D, Endo S, Takemura M, Li J, Wada R, Ifuku S, Zhao HT, El-Kabbani O, Ohta S, Yamamura K, Toyooka N, Hara A, Matsunaga T.

Design, synthesis and evaluation of caffeic acid phenethyl ester (CAPE) -based inhibitors targeting a selectivity pocket in the active site of human aldo-keto reductase 1B10. Eur J Med Chem. 2012 ; 48:321-9.

Nepofein: Nepodin-Caffeic Acid Ester for Therapy of Cancers and Diabetes?

We recently heard from an old Korean friend that a naphthalene called “Nepodin” (MW=216) from roots of an Okinawa weed is a potent anti-diabetic compound which activates the anti-oncogenic kinase AMPK (1).  It is effective at the daily dose of 2-10 mg/kg in mice. Interestingly, it was shown by a leading Korean pharmaceutical company (CKD) to be a potent anti-malaria drug as well (2).  

Almost all herbal AMPK activators are PAK1-blockers, and both diabetes (type 2) and malaria infection require the oncogenic/ageing kinase PAK1. Thus, it is not unreasonable to suspect that Nepodin also blocks PAK1. Interestingly, CAPE (caffeic acid phenethyl ester), the major anti-cancer/anti-PAK1 ingredient in propolis, is made simply by condensation of CA (caffeic acid) and phenethyl alcohol.  Thus, by analogy, it would be quite easy to synthesize a new ester called “Nepofein” by condensation of Nepodin and CA, and test its anti-cancer and anti-diabetic property, in which the CKD Pharm would be surely interested. http://www.ckdpharm.com

References:

1.   Ha BG, Yonezawa T, Son MJ, Woo JT, Ohba S, Chung UI, Yagasaki K. Antidiabetic effect of nepodin, a component of Rumex roots, and its modes of action in vitro and in vivo. Biofactors. 2014; 40(4): 436-47.

2.  Lee KH¹, Rhee KH. Antimalarial activity of nepodin isolated from Rumex crispus. Arch Pharm Res. 2013; 36(4):430-5.