A novel synthetic oleanolic acid derivative with amino acid conjugate suppresses tumour growth by inducing cell cycle arrest

Imidazo[1,2-a]quinoxalines Derivatives Grafted with Amino Acids: Synthesis and Evaluation on A375 Melanoma Cells

Imiqualines (imidazoquinoxaline derivatives) are anticancer compounds with high cytotoxic activities on melanoma cell lines. The first generation of imiqualines, with two lead compounds (EAPB0203 and EAPB0503), shows remarkable in vitro (IC₅₀ = 1 570 nM and IC₅₀ = 200 nM, respectively, on the A375 melanoma cell line) and in vivo activity on melanoma xenografts. The second generation derivatives, EAPB02302 and EAPB02303, are more active, with IC₅₀ = 60 nM and IC₅₀ = 10 nM, respectively, on A375 melanoma cell line. The aim of this study was to optimize the bioavailability of imiqualine derivatives, without losing their intrinsic activity. For that, we achieved chemical modulation on the second generation of imiqualines by conjugating amino acids on position 4. A new series of twenty-five compounds was efficiently synthesized by using microwave assistance and tested for its activity on the A375 cell line. In the new series, compounds 11a, 9d and 11b show cytotoxic activities less than second generation compounds, but similar to that of the first generation ones (IC₅₀ = 403 nM, IC₅₀ = 128 nM and IC₅₀ = 584 nM, respectively). The presence of an amino acid leads to significant enhancement of the water solubility for improved drugability.

Synthesis, anti-tumor and anti-angiogenic activity evaluations of asiatic Acid amino Acid derivatives

Fifteen semi-synthetic derivatives of asiatic acid (AA) have been synthesized and evaluated for their biological activities. The successful modification of these compounds at the C-2, C-3, C-23 and C-28 positions was confirmed using NMR, MS and IR spectra. Further, their anti-tumor effects were evaluated in vitro using different cancer cell lines (HeLa, HepG2, B16F10, SGC7901, A549, MCF7 and PC3), while their anti-angiogenic activities were evaluated in vivo using a larval zebrafish model. Among the derivatives, compounds 4–10 showed more potent cytotoxic and anti-angiogenic effects than AA, while compounds 11–17 had significantly less effects. The new derivative 10 was also included in finished formulations to evaluate its stability using HPLC due to its potential topical use. The derivative 10 had markedly better anti-tumor activities than both AA and other derivatives, with similar stability as its parent compound AA.

Amino acid derivatives of ligustrazine-oleanolic acid as new cytotoxic agents

A series of novel ligustrazine-oleanolic acid (TOA) derivatives were designed, and synthesized by conjugating amino acids to the 3-hydroxy group of TOA by ester bonds. Their cytotoxicity was evaluated on four cancer cell lines (HepG2, HT-29, Hela and BGC-823) by standard MTT assays. The ClogP values were calculated by means of computer simulation, and logP values of both 3β-glycine ester olean-12-en-28-oic acid-3,5,6-trimethylpyrazin-2-methyl ester (6a) and TOA were determined using a shake flask-ultraviolet spectrophotometry method. It was found that 6a and the 3β-L-lysine ester-6g not only displayed good cytotoxicity (IC50<3.5 μM) but also possessed better hydrophilicity than TOA. Moreover, 6a (IC50=4.884 μM) had lower nephrotoxicity than both 6g (IC50=2.310 μM) and cisplatin (CDDP, IC50=3.691 μM) on MDCK cells. Combining Giemsa and DAPI staining, it was further verified that 6a could induce HepG2 apoptosis via nuclei fragmentation and had lower nephrotoxicity. In addition, the structure-activity relationships of these derivatives are briefly discussed.

Olean-12-eno[2,3-c] [1,2,5]oxadiazol-28-oic acid (OEOA) induces G1 cell cycle arrest and differentiation in human leukemia cell lines

Oleanolic acid (3β-hydroxy-olea-12-en-28-oic acid) is a natural pentacyclic triterpenoic acid found in many fruits, herbs and medicinal plants. In the past decade, increasing evidence has suggested that oleanolic acid exhibits inhibitory activities against different types of cancer including skin cancer and colon cancer, but not leukemia. We report here that a derivative of oleanolic acid, olean-12-eno[2,3-c] [1], [2], [5]oxadiazol-28-oic acid (designated OEOA) effectively blocks the proliferation of human leukemia cells. OEOA significantly reduces cell proliferation without inducing cell death in three types of leukemia cell lines, including K562, HEL and Jurket. Moreover, exposure of K562 cells to OEOA results in G1 cell cycle arrest, with a concomitant induction of cyclin-dependent kinase inhibitor p27 and downregulation of cyclins and Cdks that are essential for cell cycle progression. Interestingly, OEOA also enhances erythroid differentiation in K562 cells through suppressing the expression of Bcr-Abl and phosphorylation of Erk1/2. These findings identify a novel chemical entity for further development as therapeutics against leukemia.