Synthesis and Biological Evaluation of Glycyrrhetic Acid Derivatives as Potential VEGFR2 Inhibitors

Amino-Acid-Conjugated Natural Compounds: Aims, Designs and Results

Protein is one of the essential macronutrients required by all living things. The breakdown of protein produces monomers known as amino acids. The concept of conjugating natural compounds with amino acids for therapeutic applications emerged from the fact that amino acids are important building blocks of life and are abundantly available; thus, a greater shift can result in structural modification, since amino acids contain a variety of sidechains. This review discusses the data available on amino acid–natural compound conjugates that were reported with respect to their backgrounds, the synthetic approach and their bioactivity. Several amino acid–natural compound conjugates have shown enhanced pharmacokinetic characteristics, including absorption and distribution properties, reduced toxicity and increased physiological effects. This approach could offer a potentially effective system of drug discovery that can enable the development of pharmacologically active and pharmacokinetically acceptable molecules.

Apoptotic and Cell Cycle Effects of Triterpenes Isolated from Phoradendron wattii on Leukemia Cell Lines

Current antineoplastic agents present multiple disadvantages, driving an ongoing search for new and better compounds. Four lupane-type triterpenes, 3α,24-dihydroxylup-20(29)-en-28-oic acid (1), 3α,23-dihydroxy-30-oxo-lup-20(29)-en-28-oic acid (2), 3α,23-O-isopropylidenyl-3α,23-dihydroxylup-20(29)-en-28-oic acid (3), and 3α,23-dihydroxylup-20(29)-en-28-oic acid (4), previously isolated from Phoradendron wattii, were evaluated on two cell lines of chronic (K562) and acute (HL60) myeloid leukemia. Compounds 1, 2, and 4 decreased cell viability and inhibit proliferation, mainly in K562, and exhibited an apoptotic effect from 24 h of treatment. Of particular interest is compound 2, which caused arrest in active phases (G2/M) of the cell cycle, as shown by in silico study of the CDK1/Cyclin B/Csk2 complex by molecular docking. This compound [3α,23-dihydroxy-30-oxo-lup-20(29)-en-28-oic acid] s a promising candidate for incorporation into cancer treatments and deserves further study.

Piperazine skeleton in the structural modification of natural products: a review

Piperazine moiety is a cyclic molecule containing two nitrogen atoms in positions 1 and 4, as well as four carbon atoms. Piperazine is one of the most sought heterocyclics for the development of new drug candidates with a wide range of applications. Over 100 molecules with a broad range of bioactivities, including antitumor, antibacterial, anti-inflammatory, antioxidant, and other activities, were reviewed. This article reviewed investigations regarding piperazine groups for the modification of natural product derivatives in the last decade, highlighting parameters that affect their biological activity.

Synergistic breast cancer suppression efficacy of doxorubicin by combination with glycyrrhetinic acid as an angiogenesis inhibitor

BACKGROUND

Therapeutic regimens of breast cancer treatment are increasingly inclined to adopt combination strategy based on the broad spectrum antitumor effect of doxorubicin (Dox). Currently, combination therapy comprises of conventional anti-cancer drugs and angiogenesis inhibitors have been corroborated as an effective approach in cancer treatment.

PURPOSE

We explored the ability of a natural anti-angiogenic compound glycyrrhetinic acid (GA), derived from an edible-medicinal herb licorice, to enhance the breast cancer suppression effect of Dox.

STUDY DESIGN

The drug ratio of GA and Dox with synergistic anticancer effect against MCF-7 cells was optimized by combination index (CI) value in vitro, followed by evaluation of the improved anticancer effects and reduced side-effects of this combination in vitro and in vivo.

METHODS

Cell viability was measured by MTT assay. Analyses of mitochondrial membrane potential and cell apoptosis on MCF-7 cells were performed by JC-1 dye and Annexin V-FITC/PI assays. The cellular accumulation of Dox when combined with GA was evaluated. Levels of apoptosis-related proteins in MCF-7 cells were measured by Western blot analysis. Synergistic anti-angiogenic effects on HUVECs were evaluated. A breast cancer mouse model was established to investigate the anti-tumor effects in vivo.

RESULTS

Based on the optimization by CI value, Dox and GA at 1:20 molar ratio was chosen as the optimal combination drug ratio that exhibited synergistic effect against MCF-7 breast cancer cells. In addition, the combination of GA and Dox exhibited significantly enhanced cytotoxicity, apoptosis, and loss of mitochondrial membrane potential via the upregulation of a mitochondrial-dependent apoptosis pathway against MCF-7 cells. Interestingly, the addition of GA increased the intracellular accumulation of Dox in MCF-7 cells. Moreover, VEGF-induced HUVECs proliferation, migration, and tube formation were strongly inhibited by Dox when used with GA via the significant down-regulation of VEGFR2-mediated pathway, indicating that the combination of Dox and GA could exhibit ideal synergistic anti-angiogenesis effect. Expectedly, the enhanced anti-tumor efficacy of Dox and reduced Dox-induced cardiotoxicity when used in combination with GA were evident in a mouse breast tumor model.

CONCLUSIONS

These findings support that the combination of Dox with GA is a novel and promising therapeutic strategy for the treatment of breast cancer.

Design, Synthesis and Biological Evaluation of Dimethyl Cardamonin (DMC) Derivatives as P-glycoprotein-mediated Multidrug Resistance Reversal Agents

Background:

P-glycoprotein (P-gp) has been regarded as an important factor in the multidrug resistance (MDR) of tumor cells within the last decade, which can be solved by inhibiting Pgp to reverse MDR. Thus, it is an effective strategy to develop inhibitor of P-gp.

Objective:

In this study, the synthesis of a series of derivatives had been carried out by bioisosterism design on the basis of Dimethyl Cardamonin (DMC). Subsequently, we evaluated their reversal activities as potential P-glycoprotein (P-gp)-mediated Multidrug Resistance (MDR) agents.

Methods:

Dimethyl cardamonin derivatives were synthesized from acetophenones and the corresponding benzaldehydes in the presence of 40% KOH by Claisen-Schmidt reaction. Their cytotoxicity and reversal activities in vitro were assessed with MTT. Moreover, the compound B4 was evaluated by Doxorubicin (DOX) accumulation, Western blot and wound-healing assays deeply.

Results and Conclusion:

The results showed that compounds B2, B4 and B6 had the potency of MDR reversers with little intrinsic cytotoxicity. Meanwhile, these compounds also demonstrated the capability to inhibit MCF-7 and MCF-7/DOX cells migration. Besides, the most compound B4 was selected for further study, which promoted the accumulation of DOX in MCF-7/DOX cells and inhibited the expressionof P-gp at protein levels.

Conclusion:

The above findings may provide new insights for the research and development of Pgp- mediated MDR reversal agents.

Efficient synthesis of piperazinyl amides of 18β-glycyrrhetinic acid

In the present study, a practical method to prepare piperazinyl amides of 18β-glycyrrhetinic acid was developed. Two main procedures for the construction of important intermediate 8 are discussed. One procedure involves the amidation of 1-Boc-piperazine with 3-acetyl-18β-glycyrrhetinic acid, prepared by the reaction of 18β-glycyrrhetinic acid with acetic anhydride without any solvent at 130 °C. The other procedure to prepare compound 8 involves the amidation of 18β-glycyrrhetinic acid followed by the esterification with acetic anhydride. Finally, compound 8 underwent N-Boc deprotection to prepare product 4. To ascertain the scope of the reaction, another C-3 ester derivative 17 was tested under the optimized reaction conditions. Furthermore, the reasons for the appearance of byproducts were elucidated. Crystallographic data of a selected piperazinyl amide is reported.

Synergistic inhibitory effect of resveratrol and TK/GCV therapy on melanoma cells

PURPOSE

To investigate the synergistic effect of resveratrol on the bystander effect of TK/GCV suicide gene system in melanoma cells.

METHODS

The effect of resveratrol on the growth of B16 cells and the synergistic effect of resveratrol with or without GCV were detected by MTT assay and high content screening assay. The effect of resveratrol on GJIC function was detected by flow cytometry combined with fluorescence tracer and fluorescence microscope, and the expression of gap junction protein was detected by western blotting. Synergistic killing effect of resveratrol plus TK/GCV was tested in vivo using transplanted melanoma model.

RESULTS

In vitro, resveratrol can enhanced GJ function and upregulated Cx32 and Cx43 protein expression in B16 cells. Resveratrol synergized with GCV to kill mixed B16 melanoma cells (20% TK⁺ cells and 80% TK^- cells) and to improve apoptosis rate of TK^- cells (the bystander effect of TK system), and the synergistic action was reversed by the GJ inhibitor AGA. In vivo, when B16 cells were mixed with 30% TK⁺ B16 cells, significantly reduced tumor weight and volume were observed after combinational treatment with resveratrol plus GCV as compared with GCV or resveratrol treatment alone.

CONCLUSIONS

Resveratrol could synergistically enhance the killing effect of TK/GCV suicide gene system in melanoma B16 cells and transplanted melanoma. It might be a promising adjuvant of TK/GCV therapy.

Design, synthesis and biological evaluation of novel amide-linked 18β-glycyrrhetinic acid derivatives as novel ALK inhibitors

A series of novel amide-linked 18β-glycyrrhetinic acid derivatives were developed by incorporating substituted piperazine amide fragments into the C30-COOH of 18β-glycyrrhetinic acid scaffold. The synthesized compounds were evaluated for their anticancer activity against Karpas299, A549, HepG2, MCF-7, and PC-3 cell lines by MTT assay. Besides, some compounds with electron-withdrawing groups on phenyl moieties exhibited noticeable antiproliferative activity. The most potent compound 4a was also found to be non-toxic to normal human hepatocytes LO2 cells. The compound 4a exhibited moderate inhibitory activity against wild-type ALK with an IC50 value of 203.56 nM and relatively weak potent activity to c-Met (IC50 > 1000 nM). Molecular docking studies were performed to explore the diversification in bonding patterns between the compound 4a and Crizotinib.

Synthesis and Antiproliferative Activity of Novel Heterocyclic Glycyrrhetinic Acid Derivatives

A new series of glycyrrhetinic acid derivatives has been synthesized via the introduction of different heterocyclic rings conjugated with an α,β-unsaturated ketone in its ring A. These new compounds were screened for their antiproliferative activity in a panel of nine human cancer cell lines. Compound 10 was the most active derivative, with an IC₅₀ of 1.1 µM on Jurkat cells, which is 96-fold more potent than that of glycyrrhetinic acid, and was 4-fold more selective toward that cancer cell line. Further biological studies performed in Jurkat cells showed that compound 10 is a potent inducer of apoptosis that activates both the intrinsic and extrinsic pathways.