Synthesis and active oxygen generation by new emodin derivatives and their gonadotropin-releasing hormone conjugates

Is Emodin with Anticancer Effects Completely Innocent? Two Sides of the Coin

Many anticancer active compounds are known to have the capacity to destroy pathologically proliferating cancer cells in the body, as well as to destroy rapidly proliferating normal cells. Despite remarkable advances in cancer research over the past few decades, the inclusion of natural compounds in researches as potential drug candidates is becoming increasingly important. However, the perception that the natural is reliable is an issue that needs to be clarified. Among the various chemical classes of natural products, anthraquinones have many biological activities and have also been proven to exhibit a unique anticancer activity. Emodin, an anthraquinone derivative, is a natural compound found in the roots and rhizomes of many plants. The anticancer property of emodin, a broad-spectrum inhibitory agent of cancer cells, has been detailed in many biological pathways. In cancer cells, these molecular mechanisms consist of suppressing cell growth and proliferation through the attenuation of oncogenic growth signaling, such as protein kinase B (AKT), mitogen-activated protein kinase (MAPK), HER-2 tyrosine kinase, Wnt/-catenin, and phosphatidylinositol 3-kinase (PI3K). However, it is known that emodin, which shows toxicity to cancer cells, may cause kidney toxicity, hepatotoxicity, and reproductive toxicity especially at high doses and long-term use. At the same time, studies of emodin, which has poor oral bioavailability, to transform this disadvantage into an advantage with nano-carrier systems reveal that natural compounds are not always directly usable compounds. Consequently, this review aimed to shed light on the anti-proliferative and anti-carcinogenic properties of emodin, as well as its potential toxicities and the advantages of drug delivery systems on bioavailability.

Identification and characterization of chemical constituents in Qi-Lin pills and their metabolites in rat bio-samples after oral administration using ultra-high performance liquid chromatography with quadrupole time-of-flight mass spectrometry

Qi-Lin pill (QLP), a traditional Chinese medicine prescription (TCMP), composed of fifteen herbal medicines, has been widely used for the treatment of male infertility. However, an in-depth understanding of the chemical constituents of QLP and its in vivo metabolic study is lacking. In this study, a method using ultra-performance liquid chromatography coupled with quadruple time-of-flight mass spectrometry (UPLC/Q-TOF-MS) was established for comprehensive analysis of chemical constituents of QLP and their metabolites in plasma, urine, bile and feces after gastric perfusion. The method guaranteed the fast discovery of representative structural fragment information and provided efficient structure clues for identification based on data from MS^E mode. As a result, a total of 202 constituents were unambiguously identified or tentatively characterized. In addition, a total of 203 QLP-related xenobiotics were characterized, including 41 (22 prototypes and 19 metabolites) in plasma, 144 (47 prototypes and 97 metabolites) in urine, 50 (27 prototypes and 23 metabolites) in bile and 68 (51 prototypes and 17 metabolites) in feces. The metabolism reactions included phase I reactions (demethylation, hydroxylation, deglycosylation, deoxygenation, hydrogenation, dehydration, oxidation and hydrolysis) and phase II reactions (methylation, conjugation with glucuronide and sulfate). This was the first comprehensive investigation on chemical constituents and metabolic profiles of QLP in vivo, and the results provided chemical foundation for further research on effective substances and action mechanism of QLP.

Generation of Reactive Oxygen Species by Photosensitizers and their Modes of Action on Proteins

In this review, we first survey the mechanisms underlying the chemical modification of amino acid residues in proteins by singlet oxygen elicited by photosensitizers. Singlet oxygen has the capacity to cause widespread chemical damage to cellular proteins. Its use in photodynamic therapy of tumors thus requires the development of methodologies for specific addressing of the photosensitizer to malignant cells while sparing normal tissue. We describe three targeting paradigms for achieving this objective. The first involves the use of a photosensitizer with a high affinity for its target protein; in this case, the photosensitizer is methylene blue for acetylcholinesterase. The second paradigm involves the use of the hydrophobic photosensitizer hypericin, which has the capacity to interact selectively with partially unfolded forms of proteins, including nascent species in rapidly dividing or virus-infected and cancer cells, acting preferentially at membrane interfaces. In this case, partially unfolded molten globule species of acetylcholinesterase serve as the model system. In the third paradigm, the photodynamic approach takes advantage of a general approach in 'state-of-the-art' chemotherapy, by coupling the photosensitizer emodin to a specific peptide hormone, GnRH, which recognizes malignant cells via specific GnRH receptors on their surface.

Redox-Active Quinone Chelators: Properties, Mechanisms of Action, Cell Delivery, and Cell Toxicity

SIGNIFICANCE

Chemotherapy is currently the principal method for treating many malignancies. Thus, the development of improved antitumor drugs with enhanced efficacy and selectivity remains a high priority. Recent Advances: Anthracycline antibiotics (AAs), for example, doxorubicin, daunomycin, and mitomycin C, belong to an important family of antitumor agents widely used in chemotherapy. These compounds are all quinones. They are, thus, capable of being reduced by appropriate chemicals or reductases. One of their important properties is that under aerobic conditions their reduced forms undergo oxidation, with concomitant generation of reactive oxygen species (ROS), namely, superoxide anion radicals, hydrogen peroxide, and hydroxyl radicals. The presence of metal ions is essential for the generation of ROS by AAs in biological systems.

CRITICAL ISSUES

A fundamental shortcoming of the AAs is their high cardiotoxicity. We have proposed, and experimentally realized, a new type of quinones that is capable of coordinating metal ions. We have demonstrated in vitro that they can be reduced by electron transfer chains and glutathione with concomitant generation of ROS. They can also produce ROS under photo-excitation. The mechanisms of these reactions have been characterized by using nuclear magnetic resonance and electron paramagnetic resonance.

FUTURE DIRECTIONS

To enhance their therapeutic effectiveness, and decrease cardiotoxicity and other side effects, we intend to conjugate the quinone chelators with monoclonal antibodies and peptide hormones that are specifically targeted to receptors on the cancer cell surface. Some such candidates have already been synthesized. An alternative approach for delivery of our compounds involves the use of specific peptide-based nanoparticles. In addition, our novel approach for treating malignancies is also suitable for photodynamic therapy. Antioxid. Redox Signal. 28, 1394-1403.

Synthesis and antitumor activity of emodin quaternary ammonium salt derivatives

A series of new emodin derivatives modified at the C-3 and the C-6 positions were synthesized, and evaluated for their anticancer activities in vitro and in vivo. Among them, Compounds 5g and 5h had more significant antiproliferative ability against HepG2, BGC-823, AGS cancer cell lines and low cytotoxicity to HELF normal cell line, respectively. Compounds 5g and 5h induced AGS cell cycle arrest at G0/G1 phase and induce apoptosis via activation of caspase-3 and caspase-9 enzyme. In vivo studies using H22 xenografts in Kunming mice were conducted with 5g and 5h. The results revealed that the medium dosage group (10 mg/kg) of 5g and the high dosage group (25 mg/kg) of 5h showed significant antitumor activity compared to the control group.

[GnRH analogues containing SV-40 virus T-antigen nuclear localization sequence]

To improve the efficiency of anticancer drugs due to their delivery to intracellular targets a set of GnRH analogues containing nuclear localization signal (NLS) of SV-40 virus large T-antigen have been synthesized. NLS was attached to the parent molecule via ε-amino group of D-Lysine in position 1 or 6 of peptide sequence using orthogonal protection strategy. The biological activity studies revealed that incorporation of NLS moiety significantly increases cytotoxic activity of palmitoyl-containing GnRH analogues in vitro. The influence of tested peptides on tumor cells does not accompanied by the destruction of cell membrane, as confirmed in experiments with normal fibroblasts, used as a control.