Synthesis And Anticancer Activity Study Of P-Terphenyl Topoisomerase Inhibitors

Currently cancer is a terrible disease of mankind. The screening of effective anticancer reagent is an important work of oncotherapy. One main way of the discovery of new anticancer drugs or lead compounds is looking from natural products. Natural active ingredients in plants, animals, marine organisms and microorganisms, some of them have antitumor activity and many have been used clinically. Because of the special environment for the growth of microorganisms and marine organisms, their secondary metabolites are usually very special and these compounds have the structural complexity and diversity. Our group isolated variety types of natural products from endophytes of medicinal plants and marine microbes, and some of the products showed antitumor activity, such as ANSA neomycin,16-membered macrolide and terphenyl compounds.Research I:In our previous study,8p-terphenyl compounds isolated from the marine fungal strain Aspergillus sp. AF119were found showing cytotoxicity against MDA-MB-435cell line. In order to find the basic pharmacophore of p-terphenyls and novel derivatives as potential anticancer compounds, eight new p-terphenyl derivatives H1-H8were successfully synthesized and their antitumor activities have been evaluated.Compound H2, showing the best antiproliferative activity with IC50<1μM against MDA-MB-435cells, was further investigated. Compound H2, inhibited the enzyme activity of topoisomerase Ⅰ (TOP Ⅰ) and topoisomerase Ⅱα (TOP Ⅱ a) by interfering predominantly with the enzyme, could be topoisomerase (TOP) suppressors instead of TOP poisons. We deduced that compound H2represented a novel class of TOP catalytic suppressor, which could develop into new chemotherapeutic agents in the future. By observing in vivo activity of compound H2showed that the compound group vs. control group had no difference. Possible reasons were:Firstly, the compound H2had poor water solubility, low bioavailability and absorption; Secondly, the compound H2had some toxicity, the larger quantity H2were given the higher mortality of mice were observed. So need to further optimize the structure of the compound.Research II:Topoisomerases are the essential enzymes that control and modify the topological state of DNA during cellular processes. DNA topoisomerases required for all organisms are enzymes that regulate the overwinding or underwinding of DNA and play an important role in regulating cellular processes, such as replication, transcription and chromosomal segregation by altering DNA topology. They are viewed as important therapeutic targets for cancer chemotherapy. Some chemotherapy drugs called topoisomerase inhibitors worked by interfering with eukaryotic mammalian-type topoisomerases in cancer cells. This induces breaks in the DNA that ultimately lead to programmed cell death.Compound H2and H6had a strong inhibitory effect on the TOP, hut the activity of compounds H6was lower than H2. The structural difference between the two compounds was the ring B, which H2had no phenolic hydroxyl groups substituted. To find more active TOP inhibitors, we optimize the structure of the compound H2and obtained59derivatives:Y1-Y16, Q1-Q21, S1-S10, T1-T7and W1-W5. The antitumor activity showed that compound T2, T4, T5and W2had higher activity, in addition compound Tl, T7also showed good activity. Studying the structure of these compounds was easy to find that the phenolic hydroxyl group of the ring A was the key factor to activity intensity; carboxyl decreased the activity of the compounds; nitro substituting did not affect the activity; NH2-substituted had a different effect on the activity:substituted the ring C has little effect on the activity of the compound, but the ring A has a significant impact on the activity.4-amino-substituted Yl and Y2performed higher activity than3-amino-substituted W3and W4.Research Ⅲ:DNA topoisomerase Ⅱ (TOP Ⅱ) which have two major isoforms is a well-known anticancer target. The two isoforms, TOP Ⅱα and TOP Ⅱβ, are differentially regulated and are involved in different cellular processes. In rapidly growing cancer cells, TOP Ⅱα is highly expressed and its expression is cell cycle-regulated. TOP Ⅱβ which is dispensable for cell survival is expressed in quiescent cells in all tissues throughout the whole cell cycle. TOP Ⅱα inhibitors fall into two major classes that are "TOP Ⅱα poisons" and "TOP Ⅱα inhibiters", based on their mechanisms of action."TOP Ⅱα poisons" convert the essential enzyme into a highly cytotoxic DNA-damaging agent through the formation of cleavable complex, in which a TOP Ⅱα linked DNA strand-passing intermediate is stabilized."TOP Ⅱ α inhibitors" interrupt the binding of TOP Ⅱα and DNA by binding enzymes and some intercalating DNA with high affinity. So, TOP Ⅱα-tagged agents is a valuable novel approach for cancer chemotherapy. Among compounds H1-H8, only compounds H4and H8selectively inhibited TOP Ⅱα and the structural difference of them was the ring B. The ring B of H4was only one phenolic hydroxyl group substituted and the ring B of compound H2substituted no phenolic hydroxyl group. For cytotoxic activity, although compound H2was the strongest, but its inhibition was unselective against TOP Ⅱα. These illustrated that selective inhibition of TOP Ⅱα might originate from the middle of the phenolic hydroxyl groups on the B ring. The activity of compound H8against MDA-MB-435cells line was higher than compound H4. Therefore, basing on structure of the compound H8, substituted with different substituents,17derivatives were designed and synthesized. They were D1-D17, meantime obtained5byproduct:D18-D22.The antitumor activity showed that compound D17was the highest one, and its structure was similar to the compound H8. These results similar to those derivatives of compound H2, which showing phenolic hydroxyl of ring A was a key group. When phenolic hydroxyl groups were protected, the activities of the compounds significantly reduced, but the compound D12and D15showed differences, making the substitution position activity relationship needed further confirmation. Similar to H2derivatives substituted carboxyl group, the activities of carboxyl group-containing compound D3, D4, D5, D6and D8were very low, and the positional relationship was not for sure. When the carboxyl groups were esterified, the compound D1and D2had shown some activity and the substitution position of the esterified carboxyl was related to their activities:substituted on the C3of ring A was significantly lower than C4. The byproduct biphenyl compound D20showed some antitumor activity, and the activity of other biphenyls were low, their structure activity relationship needed to further study.Research Ⅳ:Drugs with hetero atoms or heterocyclic is widely used in clinical application. Here are representative drugs:Diazepam, Phenobarbital, Chlorpromazine, Morphine, Atropine, Reserpine, Indomethacin, Chlorpheniramine Maleate, Omeprazole, Fluorouracil, Norfloxacin, Benzylpenicillin, Vitamin B6etc. These drugs provided a reference to synthesis derivatives. Based on the relationship of activity and structure of H2and H8derivatives and learned from the results of other experiments which replacing benzene ring with heterocyclic would increase cytotoxic activity, we synthesized16heterocyclic derivatives Z1-Z16. These compounds mainly contained N, O, and S, substituted the ring A or C. However, the activities of the compounds Z8-Z15were not very high. But there is still hope that the demethylations will show higher activity.The compounds represented by H2were novel TOP inhibitor. However, their water solubility were poor, oral bioavailability were low, so needed to be improved in these areas in the future. The compounds represented by H8were new selective inhibitors of TOP Ⅱα. But now the activities of synthetic derivatives had not been greatly improved, which needing for further structural optimization in the future. As TOP Ⅱα favorite drugs may be a valuable novel approach for cancer treatment, more active compounds targeting TOP II a need to be further explored. It is hoped that the discussion herein will contribute to the development of more potent and effective TOP Ⅱα inhibitors and an enhanced understanding of the structure activity relationship.