Abstract of Our 2017 Brief Paper for Drug Discov. Ther.

(DDT-17-01009-BR) : accepted for the publication (April 14, 2017)

1,2,3-Triazolyl Esterization of PAK1-blocking Propolis Ingredients, Artepillin C (ARC) and Caffeic Acid (CA), for Boosting Their Anti-cancer/Anti-PAK1 Activities along with  Cell-permeability.

Hideaki Takahashi^1# , Binh Cao Quan Nguyen^2#,  Yoshihiro Uto¹, Md. Shahinozzaman^2,3, Shinkichi Tawata², Hiroshi Maruta⁴*.

¹Tukushima University, Tokushima, Japan.

²PAK Research Center (Lab), Okinawa, Japan.

³Kagoshima University, Kagoshima, Japan.

⁴PAK Research Center (Office), Melbourne, Australia.

# These authors contributed equally to this study.

*Corresponding authors:  

Hiroshi Maruta, PAK Research Center, Melbourne, Australia. E-mail:  maruta20420@yahoo.co.jp

Keywords:  PAK1, Artepillin C, Caffeic Acid, Click Chemistry, Triazolyl esters

Abstract:

Artepillin C (ARC) and Caffeic acid (CA) are among the major anti-cancer ingredients of propolis, and block the oncogenic/melanogenic/ageing kinase PAK1. However, mainly due to their COOH moiety, cell-permeability of these herbal compounds is rather limited. Thus, in this study, in an attempt to increase their cell-permeability without any significant loss of their water-solubility, we have esterized both ARC and CA with the water-soluble 1,2,3-Triazolyl alcohol through Click Chemistry. We found that this esterization boosts the anti-cancer activity of ARC and CA by 100 and over 400 folds, respectively, against the PAK-dependent growth of A549 lung cells, but show no effect on the PAK1-independent growth of B16F10 melanoma cells. 

Confirming this “selective” toxicity, these esters are still capable of blocking the kinase PAK1 strongly in cell culture (with IC₅₀ around 5 micro M), and the anti-PAK1 activity of 15A (ARC ester) and 15C (CA ester) appears to be 30-fold and 140-fold higher than ARC and CA, respectively. The 15A and 15C are 8-fold and 70-fold more cell-permeable (through the multi-drug resistant cell line EMT6) than ARC and CA、respectively. 

These data altogether suggest that both 15A and 15C would be far more useful than propolis for the treatment of a wide variety of PAK1-dependent diseases/ disorders such as cancers, Alzheimer’s diseases (AD), hypertension, diabetes (type 2), and hyper-pigmentation.

Table 1.  Increase in anti-cancer activity of several herbal acids by their esterization

___________________________________________________________________________

                                                                                       IC₅₀ (micro M)

                                                  ---------------------------------------------------------------------------

                                                           A549                       B16F10                         EMT6

___________________________________________________________________________                                                  

ARC                                                     25                            ND                                170

15A (ester of ARC)                          0.25                             >1                                  22

CA                                                      100                            ND                              1000

15C (ester of CA)                             0.225                           >1                                    8

Ketorolac^a                                            13                            30                               4000

15K (ester of Ketorlac)^a                   0.024                        0.006                              450

UA^b                                                       20                            ND                               ND

13U (ester of UA)^b                             0.10                           ND                               ND

___________________________________________________________________________

a, reference 7; b, reference 6; UA, ursolic acid