Study Of Novel Small Molecule Tumor-targeting Ligands Based On Carbohydrates

Malignant neoplasm exists as a most serious threat to human life and health,and medication has always been playing an important role in tumor treatment.Chemotherapeutics,with their strong capability of killing tumor cells,still occupy a crucial position in the clinic,but make their patients suffer insufferable side effects.On the other hand,targeting-drugs bring the patients better quality of life,but resistance and relapse are usually inevitable.To utilize both the bioactivity of chemotherapeutics and the tumor-targeting ability of targeting-drugs,the targeting-ligand drug conjugates emerged.With the success of antibody-drug conjugates,this new field is attracting more and more attention.This work focused on the targeting ability of some small molecular targeting ligands based on carbohydrate.We studied two groups of small molecular ligands from two different angels,which included five small molecular sugars and three phenylboronic acids with the ability of targeting at the sialic acid groups on the surface of tumor cells.The tumor-targeting abilities of these two types were compared respectively in the same systems.In the first part,we first accomplished the gram-scale total syntheses of two kinds of bleomycin disaccharides.L-gulose subunit 2-7 was accomplished with a novel and short route in six steps and 37% overall yield from 2-47,which could be easily prepared from the commercially available inexpensive material D-sorbitol,while 6-deoxy-Lgulose subunit was synthesized in 7 steps in 22% yield from 2-63,which could be prepared from D-glucolactone.The mannose subunit was prepared in 8 steps in 13% yield from mannose.The disaccharides were then prepared in a previously reported glycosidation coupling of the 3-O-carbamoyl-mannosyl donor with the Lgulopyranoside acceptors.Both disaccharides were finally obtained in gram-scale,laying the foundations for the further study of their abilities in targeting tumor cells.Then we synthesized five sugar-contained conjugates,in which the dye was prepared via the modification of a reported DCM dye.Fluorescence microscopy imaging in human lung cancer A549 cells was then carried out and the three bleomycin di-or mono saccharides showed at least comparable affinities for the cells.At last,we conjugated mannose and 3-carbamoyl mannose to SN-38 respectively and cell uptake experiments and the MTT assays were then conducted.The results showed that both saccharides could improve the cell uptake of the conjugates,and 3-carbamoyl mannose exhibited the best ability in mediating cell uptake.In the second part,3-nitrophenylboronic acid was first used as a targeting ligand,which was conjugated to SN-38 at its C10 or C20 positions via two different linkers with different lengths,to achieve four conjugates.The MTT assays showed that the conjugates with the ligand linked at the C20 position exerted comparable antitumor activities as SN-38.The structural instability made them unfit for the study of the targeting ligands.Conjugating at the C10 position of SN-38 resulted in more stable compounds,making it more convenient to compare the targeting abilities of different phenylboronic acids,but we failed to get their fluorescence pictures via fluorescence microscopy imaging.Then three phenylboronic acid-contained fluorescent probes were prepared to compare the targeting abilities of different commonly-used phenylboronic acids.By cellular uptake experiment,two probes which were based on 4-carboxyphenylboronic acid and 3-amino-benzoxaborole showed enhanced cell uptake abilities compared with two no-PBA contained counterparts.4-carboxyphenylboronic acid and 3-amino-benzoxaborole were then conjugated to SN-38 respectively and cell uptake experiments were then conducted in two ways where the results were tested by confocal laser scanning microscope and HPLC.Compounds decorated with PBAs showed enhanced cell uptake abilities,while 4-carboxyphenylboronic acid conjugate the most significantly.All conjugates didn't exhibited stronger antitumor activities compared to irinotecan.In summary,the bleomycin di-or mono saccharides showed at least comparable affinities for the tumor cells compared to glucose and mannose.Especially 3-carbamoyl mannose exhibited the best ability in targeting tumor cells.On the other hand,4-carboxyphenylboronic acid and 3-amino-benzoxaborole significantly enhanced the uptake of DCM dyes and SN-38 in tumor cells.The two types of small molecules showed great potency in developing novel small molecular targeting ligands and further studies are of great worth.