Conjugation of Uridine with Oleanolic Acid Derivatives as Potential Antitumor Agents

Biological Activities of Novel Oleanolic Acid Derivatives from Bioconversion and Semi-Synthesis

Oleanolic acid (OA) is a vegetable chemical that is present naturally in a number of edible and medicinal botanicals. It has been extensively studied by medicinal chemists and scientific researchers due to its biological activity against a wide range of diseases. A significant number of researchers have synthesized a variety of analogues of OA by modifying its structure with the intention of creating more potent biological agents and improving its pharmaceutical properties. In recent years, chemical and enzymatic techniques have been employed extensively to investigate and modify the chemical structure of OA. This review presents recent advancements in medical chemistry for the structural modification of OA, with a special focus on the biotransformation, semi-synthesis and relationship between the modified structures and their biopharmaceutical properties.

Design, Synthesis, and Evaluation of Novel 2-Methoxyestradiol Derivatives as Apoptotic Inducers Through an Intrinsic Apoptosis Pathway

In order to discover novel derivatives in the anti-tumor field, reported anti-tumor pharmacophores (uridine, uracil, and thymine) were combined with 2-methoxyestradiol, which has been characterized as having excellent biological properties in terms of anti-tumor activity. Thus, 20 hybrids were synthesized through etherification at the 17β-OH or 3-phenolic hydroxyl group of 2-methoxyestradiol, and evaluated for their biological activities against the human breast adenocarcinoma MCF-7 cell lines, human breast cancer MDA-MB-231 cell lines, and the normal human liver L-O2 cell lines. As a result, all the uridine derivatives and single-access derivatives of uracil/thymine possessed good anti-proliferative activity against tested tumor cells (half maximal inhibitory concentration values from 3.89 to 19.32 µM), while only one dual-access derivative (21b) of thymine possessed good anti-proliferative activity (half maximal inhibitory concentration ≈ 25 µM). Among them, the uridine derivative 11 and the single-access derivative of uracil 12a possessed good anti-proliferative selectivity against tested tumor cells. Furthermore, basic mechanism studies revealed that hybrids 11 and 12a could induce apoptosis in MCF-7 cells through mitochondrial pathway. These hybrids induced morphological changes in MCF-7 cells, causing mitochondrial depolarization. These two hybrids also had the following effects: arrest of the cell cycle at the G2 phase; up regulation of Apaf-1, Bax, and cytochrome c; down regulation of Bcl-2 and Bcl-xL for both mRNA and protein; and increase of the expression for caspase-8 and -9. Finally, apoptotic effector caspase-3 was increased, which eventually caused nuclear apoptosis at least through an intrinsic pathway in the mitochondria. Additionally, hybrids 11 and 12a could specifically bind to estradiol receptor alpha in a dose-dependent manner.

Synthesis and antitumor activity of fluorouracil - oleanolic acid/ursolic acid/glycyrrhetinic acid conjugates

Due to the obvious adverse effects of 5-fluorouracil that limit its clinical usefulness and considering the diverse biological activities of pentacyclic triterpenes, twelve pentacyclic triterpene-5-fluorouracil conjugates were synthesized and their antitumor activities were evaluated. The results indicated that all the single substitution targeted hybrids (7a-12a) possessed much better antiproliferative activities than the double substitution targeted hybrids (7b-12b). Hybrid 12a exhibited good antiproliferative activities against all the tested MDR cell lines. Furthermore, it was revealed that 12a could induce intracellular calcium influx, the generation of ROS, arrest the cell proliferation at the G1 phase, and activate the apoptotic signaling caspase-8, which eventually activates the apoptotic effector caspase-3 and causes the later nuclear apoptosis.

Facile one-pot syntheses of new C-28 esters of oleanolic acid and studies on their antiproliferative effect on T cells

Structure-activity relationship studies on oleanolic acid (1) have resulted in facile syntheses of its new C-28 esters 2-7 by way of one-pot reaction of 1 with a variety of alkylating agents. Oleanolic acid and its new esters were studied for their in vitro antiproliferative effect on healthy human peripheral blood mononuclear cell isolated phytohemagglutinin activated T cells. Results showed that compounds 1, 3, and 5 exhibited significant inhibitory activity on T-cell proliferation. Compound 5 was found to be the most potent, with an IC50 value of 4.249 μg/mL, among all tested compounds, and its activity could be attributed to the presence of bromine atom in the molecule.

Development of an engineered carbamoyl phosphate synthetase with released sensitivity to feedback inhibition by site-directed mutation and casting error-prone PCR

Carbamoyl phosphate synthetase (CPS) is a key enzyme in both pyrimidine and arginine biosynthesis. However, it is inhibited strongly by uridine monophosphate (UMP), which is an intermediate of the de-novo synthesis of pyrimidine nucleoside. In this study, the native carbamoyl phosphate synthetase, from Escherichia coli, was evolved by site-directed mutation and casting error-prone PCR. Compared with the wild-type, the variant N1015 F had released sensitivity to UMP and exhibited 100% of the initial activity in the presence of UMP. Variant K1006A exhibited 0.14-fold improvement in initial activity and kept above 65% of relative activity under the saturated concentration of inhibitor. Structure analysis of variants demonstrated that the reduced sensitivity to inhibitor was largely attributed to the decreased hydrogen bonds, which could reduce the binding affinity with UMP. Also, Phe with large side chain could narrow the binding pocket and generate more steric hindrance. Based on the results in this study, N1015F was an ideal alternative catalyst for the wild-type CPS for pyrimidine biosynthesis.

Synthesis and in vitro antiproliferative evaluation of PEGylated triterpene acids

A set of PEGylated derivatives of oleanolic and maslinic acids has been semi-synthesised, attaching ethylene glycol, diethylene glycol, triethylene glycol or tetraethylene glycol to the C-28 carboxyl group of these natural triterpenes and some derivatives. Another set of PEGylated derivatives has been semi-synthesised by connecting the same four ethylene glycols to the hydroxyl groups of the A ring of these triterpenic acids, through a carbonate linker, by reaction with trichloromethyl chloroformate. The aqueous solubility of some of these PEGylated derivatives has been compared with that of maslinic acid. The cytotoxic effects of 28 triterpenic PEGylated derivatives in three cancer-cell lines (B16-F10, HT29, and Hep G2) have been assayed. The best results have been achieved with the HT29 cell line, and specifically with the oleanolic acid derivatives having ethylene glycol or tetraethylene glycol attached to the C-28 carboxyl group, which are approximately 27-fold more effective than their natural precursor. Eight PEGylated derivatives have been selected to compare the cytotoxicity results in the HT29 cancer-cell line with those of a non-tumour cell line of the same tissue (IEC-18), four of which were less cytotoxic in the non-tumour cell line. These compounds showed apoptotic effects on treated cells, with percentages of total apoptosis between 20% and 53%, relative to control, at 72h and IC₅₀ concentration, and between 29% to 62%, relative to control, for the same time and IC₈₀ concentration. We have also found that with the treatment of these compounds in HT29 cancer cells, cell-cycle arrest occurred in the G0/G1 phase. Finally, we have also studied changes in mitochondrial membrane potential during apoptosis of HT29 cancer cells, and the results suggest an activation of the extrinsic apoptotic pathway for these compounds.

Improvement of uridine production of Bacillus subtilis by atmospheric and room temperature plasma mutagenesis and high-throughput screening

In the present study, a novel breeding strategy of atmospheric and room temperature plasma (ARTP) mutagenesis was used to improve the uridine production of engineered Bacillus subtilis TD12np. A high-throughput screening method was established using both resistant plates and 96-well microplates to select the ideal mutants with diverse phenotypes. Mutant F126 accumulated 5.7 and 30.3 g/L uridine after 30 h in shake-flask and 48 h in fed-batch fermentation, respectively, which represented a 4.4- and 8.7-fold increase over the parent strain. Sequence analysis of the pyrimidine nucleotide biosynthetic operon in the representative mutants showed that proline 1016 and glutamate 949 in the large subunit of B. subtilis carbamoyl phosphate synthetase were of importance for the allosteric regulation caused by uridine 5′-monophosphate. The proposed mutation method with efficient high-throughput screening assay was proved to be an appropriate strategy to obtain uridine-overproducing strain.