New Structures, Spectrometric Quantification, and Inhibitory Properties of Cardenolides from Asclepias curassavica Seeds.

Cardiac glycosides are a large class of secondary metabolites found in plants. In the genus Asclepias, cardenolides in milkweed plants have an established role in plant-herbivore and predator-prey interactions, based on their ability to inhibit the membrane-bound Na+/K+-ATPase enzyme. Milkweed seeds are eaten by specialist lygaeid bugs, which are the most cardenolide-tolerant insects known. These insects likely impose natural selection for the repeated derivatisation of cardenolides. A first step in investigating this hypothesis is to conduct a phytochemical profiling of the cardenolides in the seeds. Here, we report the concentrations of 10 purified cardenolides from the seeds of Asclepias curassavica. We report the structures of new compounds: 3-O-ß-allopyranosyl coroglaucigenin (1), 3-[4'-O-ß-glucopyranosyl-ß-allopyranosyl] coroglaucigenin (2), 3'-O-ß-glucopyranosyl-15-ß-hydroxycalotropin (3), and 3-O-ß-glucopyranosyl-12-ß-hydroxyl coroglaucigenin (4), as well as six previously reported cardenolides (5-10). We test the in vitro inhibition of these compounds on the sensitive porcine Na+/K+-ATPase. The least inhibitory compound was also the most abundant in the seeds-4'-O-ß-glucopyranosyl frugoside (5). Gofruside (9) was the most inhibitory. We found no direct correlation between the number of glycosides/sugar moieties in a cardenolide and its inhibitory effect. Our results enhance the literature on cardenolide diversity and concentration among tissues eaten by insects and provide an opportunity to uncover potential evolutionary relationships between tissue-specific defense expression and insect adaptations in plant-herbivore interactions.

Allicin Overcomes Hypoxia Mediated Cisplatin Resistance in Lung Cancer Cells through ROS Mediated Cell Death Pathway and by Suppressing Hypoxia Inducible Factors.

BACKGROUND/AIMS: The hypoxic microenvironment in NSCLC has been widely accepted as a contributor to both therapeutic resistance and tumor progression. In this study, we have explored Allicin, a key organosulfur compound present in garlic for its previously unreported effectiveness in the heterogeneous hypoxic tumor microenvironment of NSCLC. METHODS: The effect of Allicin on the viability of NSCLC cells was determined by MTT assay. To determine the migration rate of treated cells compared to the control, scratch and transwell migration assays were performed. Flowcytometry was done to explore cell cycle distribution, apoptosis and ROS production in cells. Fluorescence microscopy was used to examine autophagy and DNA damage in cells. Dot blot was done to check genome wide methylation. RNA expression was detected by RT-PCR and protein expression by western blotting. RESULTS: Allicin significantly decreases cell viability, proliferation and migration of NSCLC cells in both normoxia and hypoxia. It elicits both apoptosis and autophagy pathway in A549 cells by ROS accumulation and facilitating S/G2-M phase arrest in both normoxia as well as hypoxia. We suggest that ROS/MAPK and ROS/JNK signaling pathway together govern the cytotoxic effect of allicin in NSCLC cells. Notably, allicin suppresses the expression of HIF-1α and HIF-2α in hypoxic cells, pointing towards a mechanism of its effectiveness in hypoxia. A long term passive demethylation was observed, with decreased mC and no change in TET expression, thereby ruling out active demethylation by allicin. Furthermore, allicin synergistically enhances growth inhibitory activity of low dose cisplatin to effectively overcome hypoxia induced cisplatin resistance in A549 cells. CONCLUSION: Altogether, our results elucidate a potential use of allicin in sensitizing hypoxic and chemoresistant NSCLC to cisplatin-based chemotherapy and provide new, affordable therapeutic strategy with reduced side effects.

Nucleic acid binding properties of allicin: spectroscopic analysis and estimation of anti-tumor potential.

BACKGROUND: Allicin has received much attention due to its anti-proliferative activity and not-well elucidated underlying mechanism of action. This work focuses towards determining the cellular toxicity of allicin and understanding its interaction with nucleic acid at molecular level. METHODS: MTT assay was used to assess the cell viability of A549 lung cancer cells against allicin. Fourier transform infrared (FTIR) and UV-visible spectroscopy were used to study the binding parameters of nucleic acid-allicin interaction. RESULTS: Allicin inhibits the proliferation of cancer cells in a concentration dependent manner. FTIR spectroscopy exhibited that allicin binds preferentially to minor groove of DNA via thymine base. Analysis of tRNA allicin complex has also revealed that allicin binds primarily through nitrogenous bases. Some amount of external binding with phosphate backbone was also observed for both DNA and RNA. UV visible spectra of both DNA allicin and RNA allicin complexes showed hypochromic shift with an estimated binding constant of 1.2×10(4)M(-1) for DNA and 1.06×10(3)M(-1)for RNA binding. No major transition from the B-form of DNA and A-form of RNA is observed after their interaction with allicin. CONCLUSIONS: The results demonstrated that allicin treatment inhibited the proliferation of A549 cells in a dose-dependent manner. Biophysical outcomes are suggestive of base binding and helix contraction of nucleic acid structure upon binding with allicin. GENERAL SIGNIFICANCE: The results describe cytotoxic potential of allicin and its binding properties with cellular nucleic acid, which could be helpful in deciphering the complete mechanism of cell death exerted by allicin.

Hypoxia-induced inhibin promotes tumor growth and vascular permeability in ovarian cancers.

Hypoxia, a driver of tumor growth and metastasis, regulates angiogenic pathways that are targets for vessel normalization and ovarian cancer management. However, toxicities and resistance to anti-angiogenics can limit their use making identification of new targets vital. Inhibin, a heteromeric TGFß ligand, is a contextual regulator of tumor progression acting as an early tumor suppressor, yet also an established biomarker for ovarian cancers. Here, we find that hypoxia increases inhibin levels in ovarian cancer cell lines, xenograft tumors, and patients. Inhibin is regulated primarily through HIF-1, shifting the balance under hypoxia from activins to inhibins. Hypoxia regulated inhibin promotes tumor growth, endothelial cell invasion and permeability. Targeting inhibin in vivo through knockdown and anti-inhibin strategies robustly reduces permeability in vivo and alters the balance of pro and anti-angiogenic mechanisms resulting in vascular normalization. Mechanistically, inhibin regulates permeability by increasing VE-cadherin internalization via ACVRL1 and CD105, a receptor complex that we find to be stabilized directly by inhibin. Our findings demonstrate direct roles for inhibins in vascular normalization via TGF-ß receptors providing new insights into the therapeutic significance of inhibins as a strategy to normalize the tumor vasculature in ovarian cancer.

Inhibin Is a Novel Paracrine Factor for Tumor Angiogenesis and Metastasis.

Inhibin is a heterodimeric TGFß family ligand that is expressed in many cancers and is a selective biomarker for ovarian cancers; however, its tumor-specific functions remain unknown. Here, we demonstrate that the α subunit of inhibin (INHA), which is critical for the functionality of dimeric inhibin A/B, correlates with microvessel density in human ovarian tissues and is predictive of poor clinical outcomes in multiple cancers. We demonstrate that inhibin-regulated angiogenesis is necessary for metastasis. Although inhibin had no direct impact on tumor cell signaling, both tumor cell-derived and recombinant inhibin elicit a strong paracrine response from endothelial cells by triggering SMAD1/5 activation and angiogenesis in vitro and in vivo Inhibin-induced angiogenesis was abrogated via anti-inhibin α antibodies. The endothelial-specific TGFß receptor complex comprising ALK1 and endoglin was a crucial mediator of inhibin signaling, offering a molecular mechanism for inhibin-mediated angiogenesis. These results are the first to define a role for inhibin in tumor metastasis and vascularization and offer an antibody-based approach for targeting inhibin therapeutically.Significance: Inhibin is a predictor of poor patient survival in multiple cancers and is a potential target for antiangiogenic therapies. Cancer Res; 78(11); 2978-89. ©2018 AACR.

Scriptaid overcomes hypoxia-induced cisplatin resistance in both wild-type and mutant p53 lung cancer cells.

Non-small cell lung cancer (NSCLC), comprising 85% of lung cancer cases, has been associated with resistance to chemo/radiotherapy. The hypoxic tumor micro-environment, where insufficient vasculature results in poor drug penetrance and sub-optimal chemotherapy in the tumor interiors contributes heavily to this resistance. Additionally, epigenetic changes in tumorigenic cells also change their response to different forms of therapy. In our study, we have investigated the effectiveness of a combination of cisplatin with scriptaid [a pan-Histone Deacetylase inhibitor (HDACi)] in a model that mimics the tumor microenvironment of hypoxia and sub-lethal chemotherapy. Scriptaid synergistically increases the efficacy of cisplatin in normoxia as well as hypoxia, accompanied with reduced metastasis and enhanced DNA damage. Addition of scriptaid also overcomes the cisplatin resistance exhibited in lung cancer cells with stabilized hypoxia inducible factor 1 (HIF1)-α (mutant) and mutant p53. Molecular studies showed that the combination treatment increased apoptotic cell death in both normoxia and hypoxia with a dual role of p38MAPK. Together, our results suggest that the combination of low dose cisplatin and scriptaid is cytotoxic to NSCLC lines, can overcome hypoxia induced resistance and mutant p53- induced instability often associated with this cancer, and has the potential to be an effective therapeutic modality.

Recent advances in targeted therapy for glioblastoma.

Glioblastomas are the most common form of brain tumor with a very dismal prognosis. While a standard treatment regimen of surgery followed by chemo/radiotherapy is currently used, this has only marginally improved the survival time of patients with little benefit on tumor recurrence. Although many molecular targets have already been identified and tested in clinical trials, very few are approved for use in clinics. Efforts are ongoing to target newer molecules that could be used for drug development. This review provides up-to-date information on the drugs and their molecular targets, which are currently in different stages of clinical trials. Since multiple signaling pathways are deregulated, it appears that the use of combination drugs along with personalized targeting approach would provide better therapy in the future.