Song Yi Bae

6″-Debromohamacanthin A, a Bis (Indole) Alkaloid, Inhibits Angiogenesis by Targeting the VEGFR2-Mediated PI3K/AKT/mTOR Signaling Pathways

Hamacanthins, bis (indole) alkaloids, are found in a few marine sponges, including Spongosorites sp. Hamacanthins have been shown to possess cytotoxic, antibacterial and antifungal activities. However, the precise mechanism for the biological activities of hamacanthins has not yet been elucidated. In the present study, the anti-angiogenic effects of 6″-debromohamacanthin A (DBHA), an active component of isolated hamacanthins, were evaluated in cultured human umbilical vascular endothelial cells (HUVEC) and endothelial-like cells differentiated from mouse embryonic stem (mES) cells. DBHA significantly inhibited vascular endothelial growth factor (VEGF)-induced cell proliferation, migration and tube formation in the HUVEC. DBHA also suppressed the capillary-like structure formation and the expression of platelet endothelial cell adhesion molecule (PECAM), an endothelial biomarker, in mES cell-derived endothelial-like cells. To further understand the precise molecular mechanism of action, VEGF-mediated signaling pathways were analyzed in HUVEC cells and mES cell-derived endothelial-like cells. DBHA suppressed the VEGF-induced expression of MAPKs (p38, ERK and SAPK/JNK) and the PI3K/AKT/mTOR signaling pathway. In addition, DBHA inhibited microvessel sprouting in mES/EB-derived embryoid bodies. In an ex vivo model, DBHA also suppressed the microvessel sprouting of mouse aortic rings. The findings suggest for the first time that DBHA inhibits angiogenesis by targeting the vascular endothelial growth factor receptor 2 (VEGFR2)-mediated PI3K/AKT/mTOR signaling pathway in endothelial cells.

Induction of Cell Cycle Arrest and Apoptosis by Physcion, an Anthraquinone Isolated From Rhubarb (Rhizomes of Rheum tanguticum ), in MDA-MB-231 Human Breast Cancer Cells

Background: Physcion is an anthraquinone from rhubarb (rhizomes of Rheum tanguticum) and has been reported to have anti-inflammatory, hepatoprotective, antifungal, and anti-cancer activities. However, the growth inhibitory activity against human cancer cells and the underlying molecular mechanisms have been poorly determined. This study was designed to investigate the anti-proliferative activity of physcion by induction of cell cycle arrest and apoptosis in human MDA-MB-231 triple negative breast cancer cell line. Methods: MDA-MB-231 cells were treated with physcion, and the anti-proliferative activity was evaluated by the sulforhodamine B assay. The mechanisms of action for the growth inhibitory activity of physcion were evaluated by flow cytometry for cell cycle distribution, and by Western blot for the assessment of potential target proteins. Results: Physcion showed a significant anti-proliferative activity against MDA-MB-231 human breast cancer cells. Flow cytometric analysis indicated that physcion markedly induced the accumulation of cells in the G0/G1 phase and the increase of cell population in the sub-G1 phase. The G0/G1 cell cycle arrest by physcion was associated with the down-regulation of Cyclin D1, Cyclin A, CDK4, CDK2, c-Myc and phosphorylated Rb protein expressions. The increase of sub-G1 peak by physcion was closely correlated with the induction of apoptosis, which was confirmed by the induction of cleaved poly-(adenosine diphosphate ribose) polymerase, activation of Caspases, and suppression of Bid and Bcl-2 expression. Conclusions: The induction of G0/G1 cell cycle arrest and apoptosis might be one of the plausible mechanisms of actions for the anti-proliferative activity of physcion in human breast cancer cells.

Deguelin Analogue SH-1242 Inhibits Hsp90 Activity and Exerts Potent Anticancer Efficacy with Limited Neurotoxicity

The Hsp90 facilitates proper folding of signaling proteins associated with cancer progression, gaining attention as a target for therapeutic intervention. The natural rotenoid deguelin was identified as an Hsp90 inhibitor, but concerns about neurotoxicity have limited prospects for clinical development. In this study, we report progress on deguelin analogues that address this limitation, focusing on the novel analogue SH-1242 as a candidate to broadly target human lung cancer cells, including those that are chemoresistant or harboring KRAS mutations. In a KRAS-driven mouse model of lung cancer, SH-1242 administration reduced tumor multiplicity, volume, and load. Similarly, in human cell line-based or patient-derived tumor xenograft models, SH-1242 induced apoptosis and reduced tumor vasculature in the absence of detectable toxicity. In contrast to deguelin, SH-1242 toxicity was greatly reduced in normal cells and when administered to rats did not produce obvious histopathologic features in the brain. Mechanistic studies revealed that SH-1242 bound to the C-terminal ATP-binding pocket of Hsp90, disrupting the ability to interact with its co-chaperones and clients and triggering a degradation of client proteins without affecting Hsp70 expression. Taken together, our findings illustrate the superior properties of SH-1242 as an Hsp90 inhibitor and as an effective antitumor and minimally toxic agent, providing a foundation for advancing further preclinical and clinical studies.

Anti-proliferative effect of (19Z)-halichondramide, a novel marine macrolide isolated from the sponge Chondrosia corticata, is associated with G2/M cell cycle arrest and suppression of mTOR signaling in human lung cancer cells.

Five oxazole-containing macrolides isolated from the marine sponge Chondrosia corticata were evaluated for their anti-proliferative activity in a panel of human solid cancer cell lines. (19Z)-Halichondramide ((19Z)-HCA), a novel trisoxazole-containing macrolide, exhibited the highest potency among the macrolides, with IC50 values in the submicro-molar ranges. Prompted by the high potency of growth inhibition of cancer cells, we investigated the mechanism of action of the anti-proliferative activity of (19Z)-HCA in human A549 lung cancer cells. (19Z)-HCA induced cell cycle arrest in the G2/M phase, and this event was highly correlated with the expression of checkpoint proteins, including the up-regulation of p53 and GADD45α and the down-regulation of cyclin B1, cyclin A, CDC2, and CDC25C. In addition, the growth inhibition by (19Z)-HCA was associated with the suppression of mTOR and its downstream effector molecules 4EBP1 and p70S6K. The modulation of mTOR signaling by (19Z)-HCA was found to be mediated by the regulation of upstream proteins, including the down-regulation of Akt and p38 MAPK and the up-regulation of AMPK. These data suggest the potential of (19Z)-HCA to serve as a candidate for cancer chemotherapeutic agents derived from marine organisms by virtue of arresting the cell cycle in the G2/M phase and the modulation of mTOR/AMPK signaling pathways.

Honokiol Inhibits Vascular Vessel Formation of Mouse Embryonic Stem Cell-Derived Endothelial Cells via the Suppression of PECAM and MAPK/mTOR Signaling Pathway

Embryonic stem cells, which are characterized by pluripotency and self-renewal, have recently been highlighted in drug discovery. In particular, the potential of ES cells to differentiate into specific-cell types make them an extremely useful tool in the evaluation of the biological activity of test compounds. Honokiol, a major neolignan derived from the bark of Magnolia obovata, has been shown an anti-tumor activity. However, the precise mechanism of action in the anti-tumor activity of honokiol is still poorly understood. Here, we evaluated the antiangiogenic activity of honokiol using mouse ES cell-derived embryoid bodies. mES-derived EBs were formed using hanging drop cultures and vascular formation was induced on gelatincoated plates in EGM-2 medium. The growth inhibition of honokiol was found to be more sensitive in the differentiated EB-derived endothelial cells compared to the undifferentiated EB-derived cells. Honokiol also inhibited the vascular formation of mES cells on 3-D collagen gel and decreased the expression of endothelial biomarkers VEGFR2 and PECAM in the differentiated EB-derived endothelial cells. In addition, honokiol suppressed the MAPK and mTOR signaling pathways in the EB-derived endothelial cells. Therefore, the anti-angiogenic activity of honokiol is associated in part with the suppression of PECAM and MAPK/mTOR pathways in EB-derived endothelial cells.

Antitumor Activity of Americanin A Isolated from the Seeds of Phytolacca americana by Regulating the ATM/ATR Signaling Pathway and the Skp2-p27 Axis in Human Colon Cancer Cells.

The antiproliferative and antitumor activities of americanin A (1), a neolignan isolated from the seeds of Phytolacca americana, were investigated in human colon cancer cells. Compound 1 inhibited the proliferation of HCT116 human colon cancer cells both in vitro and in vivo. The induction of G2/M cell-cycle arrest by 1 was concomitant with regulation of the ataxia telangiectasia-mutated/ATM and Rad3-related (ATM/ATR) signaling pathway. Treatment with 1 activated ATM and ATR, initiating the subsequent signal transduction cascades that include checkpoint kinase 1 (Chk1), checkpoint kinase 2 (Chk2), and tumor suppressor p53. Another line of evidence underlined the significance of 1 in regulation of the S phase kinase-associated protein 2 (Skp2)-p27 axis. Compound 1 targeted selectively Skp2 for degradation and thereby stabilized p27. Therefore, compound 1 suppressed the activity of cyclin B1 and its partner cell division cycle 2 (cdc2) to prevent entry into mitosis. Furthermore, prolonged treatment with 1 induced apoptosis by producing excessive reactive oxygen species. The intraperitoneal administration of 1 inhibited the growth of HCT116 tumor xenografts in nude mice without any overt toxicity. Modulation of the ATM/ATR signaling pathway and the Skp2-p27 axis might be plausible mechanisms of action for the antiproliferative and antitumor activities of 1 in human colon cancer cells.

Anti-Melanogenic Activity of Gagunin D, a Highly Oxygenated Diterpenoid from the Marine Sponge Phorbas sp., via Modulating Tyrosinase Expression and Degradation

Tyrosinase is the rate-limiting enzyme critical for melanin synthesis and controls pigmentation in the skin. The inhibition of tyrosinase is currently the most common approach for the development of skin-whitening cosmetics. Gagunin D (GD), a highly oxygenated diterpenoid isolated from the marine sponge Phorbas sp., has exhibited cytotoxicity toward human leukemia cells. However, the effect of GD on normal cells and the molecular mechanisms remain to be elucidated. In the present study, we identified for the first time the anti-melanogenic activity of GD and its precise underlying mechanisms in mouse melan-a cells. GD significantly inhibited melanin synthesis in the melan-a cells and a reconstructed human skin model. Further analysis revealed that GD suppressed the expression of tyrosinase and increased the rate of tyrosinase degradation. GD also inhibited tyrosinase enzymatic activity. In addition, GD effectively suppressed the expression of proteins associated with melanosome transfer. These findings suggest that GD is a potential candidate for cosmetic formulations due to its multi-functional properties.

Asperphenins A and B, Lipopeptidyl Benzophenones from a Marine-Derived Aspergillus sp. Fungus

Asperphenins A (1) and B (2), novel diastereomeric lipopeptidyl benzophenone metabolites, were isolated from a marine-derived Aspergillus sp. fungus. On the basis of the results of combined spectroscopic analyses, the structures of these compounds were determined to be linear assemblies of three motifs: a hydroxy fatty acid, a tripeptide, and a trihydroxybenzophenone. The absolute configurations were assigned using chemical modifications and electronic circular dichroism (ECD) calculations. The novel compounds exhibited significant cytotoxicity on diverse cancer cells.

Anti-Tumor Activity of Yuanhuacine by Regulating AMPK/mTOR Signaling Pathway and Actin Cytoskeleton Organization in Non-Small Cell Lung Cancer Cells

Yuanhuacine (YC), a daphnane diterpenoid from the flowers of Daphne genkwa, exhibited a potential growth inhibitory activity against human non-small cell lung cancer (NSCLC) cells. YC also suppressed the invasion and migration of lung cancer cells. However, the precise molecular mechanisms remain to be elucidated. In the present study, we report that YC significantly activated AMP-activated protein kinase (AMPK) signaling pathway and suppressed mTORC2-mediated downstream signaling pathway in H1993 human NSCLC cells. AMPK plays an important role in energy metabolism and cancer biology. Therefore, activators of AMPK signaling pathways can be applicable to the treatment of cancer. YC enhanced the expression of p-AMPKα. The co-treatment of YC and compound C (an AMPK inhibitor) or metformin (an AMPK activator) also confirmed that YC increases p-AMPKα. YC also suppressed the activation of the mammalian target of rapamycin (mTOR) expression, a downstream target of AMPK. Further study revealed that YC modulates mTORC2-associated downstream signaling pathways with a decreased expressions of p-Akt, p-protein kinase C alpha (PKCα), p-ras-related C3 botulinum toxin substrate 1 (Rac1) and filamentous actin (F-actin) that are known to activate cell growth and organize actin cytoskeleton. In addition, YC inhibited the tumor growth in H1993 cell-implanted xenograft nude mouse model. These data suggest the YC could be a potential candidate for cancer chemotherapeutic agents derived from natural products by regulating AMPK/mTORC2 signaling pathway and actin cytoskeleton organization.

Targeting Nicotinamide N-Methyltransferase and miR-449a in EGFR-TKI-Resistant Non-Small-Cell Lung Cancer Cells

Epidermal growth factor receptor tyrosine kinase inhibitors (EGFR-TKIs) are used clinically as target therapies for lung cancer patients, but the occurrence of acquired drug resistance limits their efficacy. Nicotinamide N-methyltransferase (NNMT), a cancer-associated metabolic enzyme, is commonly overexpressed in various human tumors. Emerging evidence also suggests a crucial loss of function of microRNAs (miRNAs) in modulating tumor progression in response to standard therapies. However, their precise roles in regulating the development of drug-resistant tumorigenesis are still poorly understood. Herein, we established EGFR-TKI-resistant non-small-cell lung cancer (NSCLC) models and observed a negative correlation between the expression levels of NNMT and miR-449a in tumor cells. Additionally, knockdown of NNMT suppressed p-Akt and tumorigenesis, while re-expression of miR-449a induced phosphatase and tensin homolog (PTEN), and inhibited tumor growth. Furthermore, yuanhuadine, an antitumor agent, significantly upregulated miR-449a levels while critically suppressing NNMT expression. These findings suggest a novel therapeutic approach for overcoming EGFR-TKI resistance to NSCLC treatment.