3-OH Hispidin is a "luciferin" for a Brazilian glowing mushroom! Does this PAK1/PKC-inhibitor extend the healthy lifespan of C. elegans?

According to a recent work by an international team led by Prof. Cassius Stevani at University of San Paulo in Brazil, a hispidin derivative called "3-OH hispidin" is a green bio-LED (fluorescence) for a Brazilian glowing mushroom (1).  For detail, see the following website:
https://www.sciencenews.org/blog/science-ticker/how-mushroom-gets-its-glow

A few years ago, we found that hispidin, a metabolite of DK (5,6-dehydrokawain), inhibits PAK1 directly with IC50 around 6 micro M (2).  However, it is not specific for PAK1:  it inhibits PKC as well with IC50 around 2 micro M (3). 

According to our structure-function analysis, it is most likely that 3-OH hispidin also a PAK1-inhibitor (2). Since PAK1-deficient mutant (RB689) of C. elegans lives far longer than the wild-type (4), and a potent PAK1-blocker called "15K" also extends the healthy lifespan of this worm (5),  we wonder if this luciferin also could extend the lifespan of this worm, and make this "transparent" worm "glow greenly" as a Brazilian mushroom, under certain "oxidative" conditions. According to a recent e-mail from Prof. Ilia Yampolsky in Moscow,  his Russian team has cloned the mushroom-specific  "luciferase" cDNA, and it is unlikely that C. elegans possesses such a luciferase homologue.

According to this Russian team, by changing the side chain of "phenolic ring" of 3-OH hispidin, they could change the color of this luciferin from red to blue, just like rainbow or GFP mutants (1).  

The mushroom luciferin (3-OH hispidin) is converted by this luciferase to oxyluciferin, emitting the fluorescence, and then further converted to caffeic acid (CA) during night (6). In daytime, after sun rises, CA is reconverted to hispidin by mushroom (solar) "recyclase" in the presence of ATP and maronyl CoA in a temperature-dependent manner (6). Thus, these components consist of mushroom "solar battery" supporting this bio-LED system. 

Interestingly, just like CA, oxyluciferin carries a COOH, and if it still inhibits PAK1 directly, 
we can boost its cell-permeability by CC (click chemistry), as we have done with CA and a few other PAK1-blockers. Thus, we started collaborating with this Russian group on the mushroom luciferin.

References:  

1. Kaskova ZM, Dörr FA, Petushkov VN et al (2017). Mechanism and color modulation of fungal bioluminescence. Sci Adv. 3: e1602847. 
 

6. Oba Y, Suzuki Y, Martins GNR, et al.  Photochem Photobiol Sci. 2017 Aug 2. doi: 10.1039/c7pp00216e. Identification of hispidin as a bioluminescent active compound and its recycling biosynthesis in the luminous fungal fruiting body.

Our 2017 Mini-Review for “Eur. J. Med. Chem” (special issue on “Cancer Research”)

(On-line Publication on August 9, 2017)

From Bench (Laboratory) to Bed (Hospital/Home): How to Explore Effective Natural and Synthetic PAK1-blockers/Longevity-promoters for Cancer Therapy.  

Hiroshi Maruta ^a*, Mok-Ryeon Ahn ^b

^a PAK Research Center, Melbourne, Australia

^b Dong-A University, Busan, Korea

* Corresponding author.

E-mail address:  maruta20420@yahoo.co.jp 

ABSTRACT

PAK family kinases are RAC/CDC42-activated kinases that were first found in a soil amoeba 4 decades ago, and 2 decades later, were discovered in mammals as well. Since then at least 6 members of this family have been identified in mammals. One of them called PAK1 has been best studied so far, mainly because it is essential not only for malignant cell growth and metastasis, but also for many other diseases/disorders such as diabetes (type 2), AD (Alzheimer’s disease), hyper-tension, and a variety of inflammatory or infectious diseases, which definitely shorten our lifespan.  

Moreover, PAK1-deficient mutant of C. elegans lives longer than the wild-type by 60%, clearly indicating that PAK1 is not only an oncogenic but also ageing kinase. Thus, in theory, both anti-oncogenic and longevity-promoting activities are among the “intrinsic” properties or criteria of “clinically useful’ PAK1-blockers. There are a variety of PAK1-blocking natural products such as propolis and curcumin which indeed extend the healthy lifespan of small animals such as C. elegans by inducing the autophagy. 

Recently, we managed to synthesize a series of potent water-soluble and highly cell-permeable triazolyl esters of COOH-bearing PAK1-blockers such as Ketorolac, ARC (artepillin C) and CA (caffeic acid) via “Click Chemistry” that boosts their anti-cancer activity over 500-fold, mainly by increasing their cell-permeability, and one of them called 15K indeed extends the lifespan of C. elegans.  In this mini-review we shall discuss both synthetic and natural PAK1-blockers, some of which would be potentially useful for cancer therapy with least side effect (rather promoting the longevity as well). 

Acknowledgment

We are grateful to Dr. Yoshihiro Uto and Mr. Hideaki Takahashi for their synthesis of a series of triazolyl esters of COOH-bearing PAK1-blockers discussed in this review, and Dr. Binh Nguyen for his unpublished observations on 15K and YK155. 

Table 1

Anti-cancer activity (IC₅₀) of natural and synthetic PAK1-blockers

“Natural” PAK1-blockers	Anti-cancer (IC50)		“Synthetic” PAK1-blockers	Anti-cancer (IC50)
FK228 Daumone Triptolide Cucurbitacins Mycophenolate Frondoside A DIF-3            Nymphaeols CAPE Curcumin Ursolic acid	0.025-0.05 0.02 0.03 0.14 0.05-0.5 0.6 2-3 4-7 10 16 20		AG879/GL2003 15K* PP1/PP2 PP12 YM155 2013UA* 15C* NOV-3 FRAXs/G-5555 CEP-1347 MIA-602	0.005 0.006-0.024 0.01 0.05 0.134 0.1 0.225 0.25 >1 1 1-5
ARC	25		WR-PAK18	5
Resveratrol	30		Selbex (GGA)	10
Melatonin	1300		IPA-3	30

IC₅₀ value (against the growth of A549 cancer cells etc ) is in μM. 

*Triazolyl esters of COOH-bearing PAK1-blockers