Combination of immunoprecipitation (IP)-ATP_Glo kinase assay and melanogenesis for the assessment of potent and safe PAK1-blockers in cell culture

Rapamycin vs TORin-1 or Gleevec vs Nilotinib: Simple chemical evolution that converts PAK1-blockers to TOR-blockers or vice versa?

Both PAK1 (RAC/CDC42-activating kinase 1) and TOR (Target of Rapamycin) are among the major oncogenic/ageing kinases. However, they play the opposite role in our immune system, namely immune system is suppressed by PAK1, while it requires TOR. Thus, PAK1-blockers, would be more effective for therapy of cancers, than TOR-blockers. Since 2015 when we discovered genetically that PDGF-induced melanogenesis depends on "PAK1", we are able to screening a series of PAK1-blockers as melanogenesis-inhibitors which could eventually promote longevity. Interestingly, rapamycin, the first TOR-inhibitor, promotes melanogenesis, clearly indicating that TOR suppresses melanogenesis. However, a new TOR-inhibitor called TORin-1 no longer suppresses immune system, and blocks melanogenesis in cell culture. These observations strongly indicate that TORin-1 acts as PAK1-blockers, instead of TOR-blockers, in vivo. Thus, it is most likely that melanogenesis in cell culture could enable us to discriminate PAK1-blockers from TORblockers.

Cucurbitacin promotes hair growth in mice by inhibiting the expression of fibroblast growth factor 18

BACKGROUND

The inhibition of fibroblast growth factor 18 (FGF18) promotes the transition of hair follicles (HFs) from the telogen phase to the anagen phase. Cucurbitacin has been shown to have a good effect in promoting hair cell growth. This study explored the potential effect of cucurbitacin on hair growth and its effect on FGF18 expression in mice.

METHODS

Male C57BL/6J mice were randomly divided into the following two groups: (I) the vehicle group; and (II) the cucurbitacin group. Matrix cream and cucurbitacin cream were applied to the depilated skin on the back of the vehicle group mice and the cucurbitacin group mice, respectively. On days 3, 6, 9, 12, 15, and 18, the hair growth in the depilated dorsal skin of the mice was recorded with a digital camera and a HF detector, and the HF cycle status of the mice was observed by hematoxylin and eosin (H&E) staining. In addition, the level of FGF18 messenger ribonucleic acid (mRNA) in the dorsal skin was measured on days 15 and 18 by quantitative real-time polymerase chain reaction (qRT-PCR), while the level of FGF18 protein was measured by western blot and immunofluorescence staining.

RESULTS

The dorsal skin to which the cucurbitacin cream was applied began to darken on day 6 and grew hairs on day 9, which was 3 days earlier than the dorsal skin to which the matrix cream was applied. The H&E staining revealed a transition from the telogen phase to the anagen phase 3 days earlier for the cucurbitacin cream-treated skin than the matrix cream-treated skin. In addition, the skin treated with cucurbitacin cream also showed a significant decrease in FGF18 mRNA as seen by qRT-PCR, and reduced FGF18 protein levels as detected by western blot and immunofluorescence staining compared to the skin treated with matrix cream only.

CONCLUSIONS

Cucurbitacin significantly reduced the levels of FGF18 mRNA and protein in the dorsal skin of mice to accelerate the HFs to enter the anagen phase earlier, thereby promoting the regeneration of hair. Thus, cucurbitacin can be considered a new and valuable agent for the development of anti-hair loss products.

Use of cucurbitacins for lung cancer research and therapy

As the main substance in some traditional Chinese medicines, cucurbitacins have been used to treat hepatitis for decades in China. Currently, the use of cucurbitacins against cancer and other diseases has achieved towering popularity among researchers worldwide, as detailed in this review with summarized tables. Numerous studies have reported the potential tumor-killing activities of cucurbitacins in multiple aspects of human malignancies. Continuous research on its anticancer activity mechanisms also brings a glimmer of light to the treatment of patients with lung cancer. In line with the promising roles of cucurbitacins against cancer, through various molecular signaling pathways, it is justifiable to propose the use of cucurbitacins as a potential mainline chemotherapy before the onset and after the diagnosis of lung cancers. Here, this article mainly summarized the findings about the biological functions and underlying mechanisms of cucurbitacins on lung cancer pathogenesis and treatment. In addition, we also discussed the safety and efficacy of their application for further research and even clinical practice.

A computational approach to explore and identify potential herbal inhibitors for the p21-activated kinase 1 (PAK1)

The oncogenic kinase PAK1 (p21-activated kinase 1) is involved in developing many diseases including cancers, neurofibromatosis, Alzheimer's disease, diabetes (type 2), and hypertension. Thus, it is thought to be a prominent therapeutic target, and its selective inhibitors have a huge market potential. Recently, herbal PAK1 inhibitors have gained immense interest over synthetic ones mainly due to their non-toxic effects. Till date, many herbal compounds have been suggested to inhibit PAK1, but their information on selectivity, bioavailability, ADMET (absorption, distribution, metabolism, excretion, and toxicity) properties, and molecular interactions with PAK1 has not been explored. Hence, this study was designed with computational approaches to explore and identify the best herbal PAK1-blockers showing good ADMET properties, druggable features and binding affinity with PAK1. Herbal inhibitors reported here were initially filtered with Lipinski's rule of five (RO5). Then, molecular docking between these inhibitors and PAK1 catalytic sites was performed using AutoDock Vina and GOLD suite to determine the binding affinity and interactions. Finally, 200 ns molecular dynamics (MD) simulations on three top-ranked inhibitors including cucurbitacin I (C-I), nymphaeol A (NA), and staurosporine (SPN) were carried out. The binding free energies and interactions revealed that NA can strongly bind with the PAK1 catalytic cleft. PASS prediction and ADMET profiling supported that NA is appeared to be a more selective and safer inhibitor than C-I and SPN. These results conform to the previous experimental evidences, and therefore, NA from Okinawa propolis could be a promising inhibitor for treating PAK1-dependent illnesses.Communicated by Ramaswamy H. Sarma.

Cucurbitacin I induces pro-death autophagy in A549 cells via the ERK-mTOR-STAT3 signaling pathway

Natural products are a great source of cancer chemotherapeutic agents. In the present study, the anticancer effects of cucurbitacin I on A549 cells were investigated. Cucurbitacin I decreased cell viability, inhibited colony formation, and induced apoptosis in A549 cells. Cucurbitacin I caused accumulation of autophagosome and dose-dependent expression of LC3II protein. Autophagy inhibitors 3-methyladenine (3-MA) inhibited autophagy induced by cucurbitacin I and relieved cucurbitacin I-triggered cell death and apoptosis in A549 Cells. Cucurbitacin I treatment inhibits the ERK activation and the downstream phosphorylation level of mTOR and STAT3, but not the PI3K/Akt pathway. Furthermore, treatment with the mTOR activator MHY-1485, which also suppressed cucurbitacin I-induced LC3II expression, and also reversed cucurbitacin I-induced cell death and apoptosis. Taken together, these results suggest that cucurbitacin I induced pro-death autophagy through ERK/mTOR/STAT3 signaling cascade in A549 cells.

Frondoside A from sea cucumber and nymphaeols from Okinawa propolis: Natural anti-cancer agents that selectively inhibit PAK1 in vitro

A sulfated saponin called "Frondoside A" (FRA) from sea cucumber and ingredients from Okinawa propolis (OP) have been previously shown to suppress the PAK1-dependent growth of A549 lung cancer as well as pancreatic cancer cells. However, the precise molecular mechanism underlying their anti-cancer action still remains to be clarified. In this study, for the first time, we found that both FRA and OP directly inhibit PAK1 in vitro in a selective manner (far more effectively than two other oncogenic kinases, LIMK and AKT). Furthermore, at least two major anti-cancer ingredients of OP, nymphaeols A and C, also directly inhibit PAK1 in vitro in a selective manner. To the best of our knowledge, FRA is the first marine compound that selectively inhibits PAK1. Likewise, these nymphaeols are the first propolis ingredients that selectively inhibit PAK1.

1,2,3-Triazolyl ester of Ketorolac: A "Click Chemistry"-based highly potent PAK1-blocking cancer-killer

An old anti-inflammatory/analgesic drug called Toradol is a racemic form of Ketorolac (50% R-form and 50% S-form) that blocks the oncogenic RAC-PAK1-COX-2 (cyclooxygenase-2) signaling, through the direct inhibition of RAC by the R-form and of COX-2 by the S-form, eventually down-regulating the production of prostaglandins. However, due to its COOH moiety which is clearly repulsive to negatively-charged phospholipid-based plasma membrane, its cell-permeability is rather poor (the IC₅₀ against the growth of human cancer cells such as A549 is around 13 μM). In an attempt to boost its anti-cancer activity, hopefully by increasing its cell-permeability through abolishing the negative charge, yet keeping its water-solubility, here we synthesized a 1,2,3-triazolyl ester of Toradol through "Click Chemistry". The resultant water-soluble "azo" derivative called "15K" was found to be over 500 times more potent than Toradol with the IC₅₀ around 24 nM against the PAK1-dependent growth of A549 cancer cells, inactivating PAK1 in cell culture with the apparent IC₅₀ around 65 nM, and inhibiting COX-2 in vitro with the IC₅₀ around 6 nM. Furthermore, the Click Chemistry boosts the anti-cancer activity of Ketorolac by 5000 times against the PAK1-independent growth of B16F10 melanoma cells. Using a multi-drug-resistant (MDR) cancer cell line (EMT6), we found that the esterization of Ketorolac boosts its cell-permeability by at least 10 folds. Thus, the Click Chemistry dramatically boosts the anti-cancer activity of Ketorolac, at least in three ways: increasing its cell-permeability, the anti-PAK1 activity of R-form and anti-COX-2 activity of S-form. The resultant "15K" is so far among the most potent PAK1-blockers, and therefore would be potentially useful for the therapy of many different PAK1-dependent diseases/disorders such as cancers.

The serum/PDGF-dependent "melanogenic" role of the minute level of the oncogenic kinase PAK1 in melanoma cells proven by the highly sensitive kinase assay

We previously demonstrated that the oncogenic kinase PAK4, which both melanomas and normal melanocytes express at a very high level, is essential for their melanogenesis. In the present study, using the highly sensitive "Macaroni-Western" (IP-ATP-Glo) kinase assay, we investigated the melanogenic potential of another oncogenic kinase PAK1, which melanoma (B16F10) cells express only at a very minute level. After transfecting melanoma cells with PAK1-shRNA for silencing PAK1 gene, melanin content, tyrosinase activity, and kinase activity of PAK1 were compared between the wild-type and transfectants. We found that (i) PAK1 is significantly activated by melanogenic hormones such as IBMX (3-isobutyl-1-methyl xanthine) and α-MSH (melanocyte-stimulating hormone), (ii) silencing the endogenous PAK1 gene in melanoma cells through PAK1-specific shRNA reduces both melanin content and tyrosinase activity in the presence of both serum and melanogenic hormones to the basal level, (iii) the exogenously added wild-type PAK1 in the melanoma cells boosts the α-MSH-inducible melanin level by several folds without affecting the basal, and (iv) α-MSH/IBMX-induced melanogenesis hardly takes place in the absence of either serum or PAK1, clearly indicating that PAK1 is essential mainly for serum- and α-MSH/IBMX-dependent melanogenesis, but not the basal, in melanoma cells. The outcome of this study might provide the first scientific basis for explaining why a wide variety of herbal PAK1-blockers such as CAPE (caffeic acid phenethyl ester), curcumin and shikonin in cosmetics are useful for skin-whitening.

Effect of Okinawa Propolis on PAK1 Activity, Caenorhabditis elegans Longevity, Melanogenesis, and Growth of Cancer Cells

Propolis from different areas has been reported to inhibit oncogenic/aging kinase PAK1, which is responsible for a variety of conditions, including cancer, longevity, and melanogenesis. Here, a crude extract of Okinawa propolis (OP) was tested against PAK1 activity, Caenorhabditis elegans (C. elegans) longevity, melanogenesis, and growth of cancer cells. We found that OP blocks PAK1 and exhibits anticancer activity in the A549 cell (human lung cancer cell) line with IC50 values of 6 μg/mL and 12 μg/mL, respectively. Most interestingly, OP (1 μg/mL) significantly reduces reproduction and prolongs the lifespan of C. elegans by activating the HSP-16.2 gene, as shown in the PAK1-deficient strain. Furthermore, OP inhibits melanogenesis in a melanoma cell line (B16F10) by downregulating intracellular tyrosinase activity with an IC50 of 30 μg/mL. Our results suggest that OP demonstrated a life span extending effect, C. elegans, anticancer, and antimelanogenic effects via PAK1 inactivation; therefore, this can be a potent natural medicinal supplement against PAK1-dependent diseases.

PAKs in Human Cancer Progression: From Inception to Cancer Therapeutic to Future Oncobiology

Since the initial recognition of a mechanistic role of p21-activated kinase 1 (PAK1) in breast cancer invasion, PAK1 has emerged as one of the widely overexpressed or hyperactivated kinases in human cancer at-large, allowing the PAK family to make in-roads in cancer biology, tumorigenesis, and cancer therapeutics. Much of our current understanding of the PAK family in cancer progression relates to a central role of the PAK family in the integration of cancer-promoting signals from cell membrane receptors as well as function as a key nexus-modifier of complex, cytoplasmic signaling network. Another core aspect of PAK signaling that highlights its importance in cancer progression is through PAK's central role in the cross talk with signaling and interacting proteins, as well as PAK's position as a key player in the phosphorylation of effector substrates to engage downstream components that ultimately leads to the development cancerous phenotypes. Here we provide a comprehensive review of the recent advances in PAK cancer research and its downstream substrates in the context of invasion, nuclear signaling and localization, gene expression, and DNA damage response. We discuss how a deeper understanding of PAK1's pathobiology over the years has widened research interest to the PAK family and human cancer, and positioning the PAK family as a promising cancer therapeutic target either alone or in combination with other therapies. With many landmark findings and leaps in the progress of PAK cancer research since the infancy of this field nearly 20 years ago, we also discuss postulated advances in the coming decade as the PAK family continues to shape the future of oncobiology.

Artepillin C and Other Herbal PAK1-blockers: Effects on Hair Cell Proliferation and Related PAK1-dependent Biological Function in Cell Culture

PAK1 (RAC/CDC42-activated kinase 1) is the major oncogenic kinase, and a number of herbal PAK1-blockers such as propolis and curcumin have been shown to be anti-oncogenic and anti-melanogenic as well as anti-alopecia (promoting hair growth). Previously, we found several distinct PAK1-inhibitors in Okinawa plants including Alpinia zerumbet (alpinia). Thus, here, we tested the effects of these herbal compounds and their derivatives on the growth of cancer or normal hair cells, and melanogenesis in cell culture of A549 lung cancer, hair follicle dermal papilla cell, and B16F10 melanoma. Among these herbal PAK1-inhibitors, cucurbitacin I from bitter melon (Goya) turned out to be the most potent to inhibit the growth of human lung cancer cells with the IC50 around 140 nM and to promote the growth of hair cells with the effective dose around 10 nM. Hispidin, a metabolite of 5,6-dehydrokawain from alpinia, inhibited the growth of cancer cells with the IC50 of 25 μM as does artepillin C, the major anti-cancer ingredient in Brazilian green propolis. Mimosine tetrapeptides (MFWY, MFYY, and MFFY) and hispidin derivatives (H1-3) also exhibited a strong anti-cancer activity with the IC50 ranging from 16 to 30 μM. Mimosine tetrapeptides and hispidin derivatives strongly suppressed the melanogenesis in melanoma cells.