Keguang Cheng

Synthesis of oleanolic acid dimers linked at C-28 and evaluation of anti-tumor activity

Five dimeric oleanolic acids linked at C-28 by 1,6-hexanediamine, or built around the carbon chains of varying lengths between two carboxyl groups were synthesized, to investigate the effect of internal spacer length and species upon the stereochemical features and anti-tumor activity of the resultant bis-oleanolic acids. The IC50 values of these dimeric compounds for cytotoxicity evaluation in vitro against Hep-G2, A549, BGC-823, MCF-7 and PC-3 tumor cell lines, were mainly under 10.0 μM. This result was much better than the inhibition of proliferation against tested tumor cell lines of the monomer oleanolic acid and the commercial anticancer drug 5-fluorouracil. The cytotoxicity selectivity detection revealed that dimer 11c exhibited low cytotoxicity towards normal human liver cell HL-7702. A combination of fluorescence staining observation and flow cytometric analysis indicated that 11c could induce Hep-G2 cell apoptosis. Molecular mechanism studies suggested that 11c induced apoptosis is mediated through the intrinsic apoptotic pathway with changes in mitochondrial membrane potential by finally activating effector caspase-3/9 to trigger cell apoptosis. Further studies revealed that 11c caused cell cycle arrest at G1 phase in Hep-G2 cells. Taken together, these results suggest that 11c may be a potential candidate for further cancer research.

Oridonin, a Promising ent-Kaurane Diterpenoid Lead Compound

Oridonin belongs to ent-kaurane tetracyclic diterpenoid and was first isolated from Isodon species. It exhibits inhibitory activities against a variety of tumor cells, and pharmacological study shows that oridonin could inhibit cell proliferation, DNA, RNA and protein synthesis of cancer cells, induce apoptosis and exhibit an antimutagenic effect. In addition, the large amount of the commercially-available supply is also very important for the natural lead oridonin. Moreover, the good stability, suitable molecular weight and drug-like property guarantee its further generation of a natural-like compound library. Oridonin has become the hot molecule in recent years, and from the year 2010, more than 200 publications can be found. In this review, we summarize the synthetic medicinal chemistry work of oridonin from the first publication 40 years ago and share our research experience of oridonin for about 10 years, which may provide useful information to those who are interested in this research field.

Synthesis, Biological Activity, and Apoptotic Properties of NO-Donor/Enmein-Type ent-Kauranoid Hybrids

Herein, we reported on a series of synthetic nitric oxide-releasing enmein-type diterpenoid hybrids (9a–i). All the target compounds showed potent antibacterial activity against selected Gram-positive bacteria S. aureus and B. subtilis. The antiproliferative activity against human tumor K562, MGC-803, CaEs-17 and Bel-7402 cells, and human normal liver cells L-02 was tested and the structure activity relationships (SARs) were also concluded. Compounds 9b and 9d showed the best activity against S. aureus and B. subtilis with the same minimal inhibitory concentrations (MICs) of 4 and 2 μg/mL, respectively. The derivative 9f displayed IC50 values of 1.68, 1.11, 3.60 and 0.72 μM against the four cancer cell lines above and 18.80 μM against normal liver cells L-02; meanwhile, 9f also released a high level of NO at the time point of 60 min of 22.24 μmol/L. Furthermore, it was also found that 9f induced apoptosis via the mitochondria-related pathway and arrested cell cycle of Bel-7402 cells at S phase. These findings might be important to explore new chemical entities for the main causes of in-hospital mortality of S. aureus infection, combined with a solid tumor.

Antitumor and Antibacterial Derivatives of Oridonin: A Main Composition of Dong-Ling-Cao

Isodon rubescens has been used as a traditional green tea for more than 1000 years and many medicinal functions of I. rubescens are also very useful, such as its well-known antitumor and antibacterial activities. Oridonin, a bioactive ent-kaurane diterpenoid, is the major ingredient of this medicinal tea. Herein, 22 novel oridonin derivatives were designed and synthesized. The antibacterial activity was evaluated for the first time. Compound 12 was the most promising one with MIC of 2.0 μg/mL against B. subtilis, which was nearly 3-fold stronger than positive control chloromycetin. The antiproliferative property was also assayed and compound 19 showed stronger activity than taxol. The apoptosis-inducing ability, cell cycle arrest effect at S phase and influence of mitochondrial membrane potential by 19 in CaEs-17 cancer cells were first disclosed. Based on the above results, the cell apoptosis induced by compound 19 in CaEs-17 cells was most probably involved in the intrinsic apoptotic pathway.

Conjugation of uridine with oleanolic acid derivatives as potential antitumor agents

According to fused two bioactive moieties together by bonds covalently and available as a new single hybrid entity known as pharmacophore hybridization, a total of 10 targeted uridine–oleanolic acid hybrids were synthesized. Most of these hybrids showed excellent proliferation inhibition against tested Hep‐G2, A549, BGC‐823, MCF‐7, and PC‐3 tumor cell lines (IC50 < 8 μm), even with some IC50 values under 0.1 μm. The detection of cytotoxicity selectivity revealed that hybrids 5 and 18 exhibited low cytotoxicity toward normal human liver cell HL‐7702. Further studies revealed that selected hybrid 5 could induce apoptosis in Hep‐G2 cells through the investigation of acridine orange/ethidium bromide, Hoechst 33258 fluorescence stainings, and annexin V/propidium iodide assay. It was also found that hybrid 5 could induce mitochondrial membrane potential disruption, arrest Hep‐G2 cell line at G1 phase, and activate effector caspase‐3/9 to trigger cell apoptosis.

Synthesis and cytotoxic evaluation of several oleanolic acid–uracil/thymine conjugates

A total of 16 targeted oleanolic acid–uracil/thymine hybrids were designed and synthesized as potential cytotoxic agents. Most IC50 values were under 10.0 μM, with some of them under 0.1 μM in vitro test against tested cells (Hep-G2, A549, BGC-823, MCF-7 and PC-3). These hybrids displayed much more potent inhibitory activities compared with oleanolic acid and commercial anticancer drug 5-fluorouracil (5-FU). The combination of fluorescence staining observation and flow cytometric analysis suggested that selected oleanolic acid–uracil hybrid 6a possessed clear cell apoptosis inducing effects. And the underlying mechanisms for the antitumor activity were associated with loss of the mitochondrial membrane potential, arrest of the Hep-G2 cell line at the G1 phase and activation of effector caspase-3/9 to trigger cell apoptosis.

Synthesis, Cytotoxicity and Antimicrobial Activity of New Enmein-type Kauranoid Diterpenoid Derivatives

BACKGROUND Recently, we devoted to disclosing the antibacterial activities of enmein-type 6,7-seco-ent-kauranoid derivatives. OBJECTIVE Eleven new enmein-type diterpenoid derivatives with different substituents and drug-like properties were designed and synthesized. METHOD The antimicrobial activities against E. coli, S. aureus, B. subtilis and M. albicans were disclosed. The antiproliferative activities against human cancer Bel-7402, K562, MGC-803 and CaEs-17 cells and non-cancerous L-02 cells were also measured by MTT method. RESULTS The results revealed that enmein-type diterpenoids showed more promising activities against tested gram-positive bacteria than gram-negative bacterium and fungus. Compound 9 with R of 2-quinolyl group exhibited the strongest antimicrobial activities with MIC values of 7.81 µg/ml and 0.98 µg/ml against S. aureus and B. subtilis, respectively. All the target derivatives exhibited superior cytotoxic activities to compounds 1 and 2 against tumor cells, and slight selectivity between cancerous cells and normal liver cells. Compound 12 with R of 3-(2-chloropyridyl) group and IC50 values of 0.7 µM, 0.9 µM, 0.8 µM and 2.0 µM agaist four tumor cells, respectively, was selected for further mechanism study in Bel-7402 cell line. CONCLUSION Compound 12 could induce S phase cell cycle arrest and apoptosis at low concentrations via mitochondria-related pathways. The effects of compound 12 on some apoptosis related proteins showed that CDK2 was up regulated and ATM and cyclin A1 were down-regulated which confirmed the apoptosis and cell cycle effects.

Synthesis of scutellarein derivatives with antiproliferative activity and selectivity through the intrinsic pathway

To explore antitumor agents with potent efficacy and low toxicity, scutellarein derivatives with benzoic acid mustard (10a-c, 11a-c and 13a-c) were designed and synthesized. The antiproliferative activities of the target derivatives against A549, MCF-7 and Bel-7402 cancer cell lines were tested. Compound 10a showed the strongest potency with an IC50 value of 1.50 μM against MCF-7 cell line, and displayed low toxicity against human liver L-O2 normal cells (IC50 > 50 μM), showing specificity between normal and malignant cells. The mechanism studies revealed that 10a could induce apoptosis in MCF-7 cells, arrest MCF-7 cell cycle at the G1 phase and cause mitochondrial dysfunction in a concentration-dependant manner. Furthermore, the enhanced expression of the pro-apoptotic proteins caspase-9, caspase-3, Bax and cytochrome c, and the reduced expression of the anti-apoptotic protein Bcl-2 confirmed that 10a induced the intrinsic apoptosis pathway in MCF-7 cells. The potent antiproliferative activity and good selectivity guaranteed 10a a lead compound for the further development into anticancer therapeutics, especially for breast cancer.

Synthesis and Cytotoxicity Evaluation of Pentacyclic Triterpene–Phenol Nitrogen Mustard Conjugates

Using a reported pharmacophore, 4-[N,N-bis(2-chloroethyl)-amino]phenol, and pentacyclic triterpenes, pharmacologically and structurally diverse components of natural products, six pentacyclic triterpene-4-[N,N-bis(2-chloroethyl)-amino]phenol conjugates were synthesized by click chemistry. Their cytotoxicities against the BEL-7404 and NCI-H460 tumor cell lines were evaluated by the MTT assay. The in vitro results from the cytotoxicity assay indicated that at a compound concentration of 20 μM, these conjugates showed low toxicity (< 16%) toward the tested tumor cells in culture.

Discovery of Novel Quinazolines as Potential Anti-tubulin Agents Occupying Three Zones of Colchicine domain

A series of novel quinazolines as tubulin inhibitors occupying three zones of colchicine domain have been designed and synthesized inspired by the recently disclosed crystal structure of verubulin analogue 6 with tubulin. Among the newly synthesized compounds, 19c showed noteworthy potency against K562, HepG2, KB, HCT-8 and MDB-MB-231 cancer cells. In vitro microtubule polymerization assays identified 19c as a potent tubulin assembly inhibitor, the binding mode of which with tubulin was confirmed by molecular modeling studies to occupy three zones of tubulin domain. Furthermore, 19c disrupted the intracellular microtubule network, caused G2/M phase arrest, induced cell apoptosis and depolarized mitochondria of K562 cells. 19c also reduced the cell migration and disrupted the capillary-like tube formation of human umbilical vein endothelial cells (HUVECs). Importantly, 19c significantly and dose dependently inhibited tumor growth in H22 liver cancer xenograft mouse model. All these results suggested that 19c deserves further research as a novel and potential anti-tubulin agent for the treatment of cancers.