Modification And SAR Study Of Lead Compounds As Novel Tublin Inhibitors

During the past decade,a novel class of antitumor agents termed tumor-vascular disrupting agents（tumor-VDAs）have been investigated intensively.Unlike angiogenesis inhibitors（AIs）,tumor-VDAs target established tumor blood vessels and exert an almost immediate effect on these vessels,thus leading to a rapid vascular collapse and subsequent tumor cell death via extensive necrosis and apoptosis.Due to the morphological vasculature difference between normal tissues and solid tumors,tumor-VDAs preferentially block the blood flow of solid tumors,while the blood flow in normal tissues remains relatively intact.Currently,more than a dozen tumor-VDA drug candidates are undergoing clinical trials and the most advanced candidate CA-4P,a phosphate prodrug of combretastatin A-4（CA-4）,is in phase III trials for anaplastic thyroid cancer and Phase II trials for non-small cellular lung cancer（NSCLC）.Even though the exact mechanism（s）of action of tumor-VDAs are still not known,most of these compounds show common pharmacological characteristics,including inhibition of microtubule polymerization,competitive binding to the colchicine binding site on tubulin,and disruption of the tumor cell cytoskeleton.In our prior studies on novel antitumor agents,we discovered a series of new N-aryl-1,2,3,4-tetrahydroquinoline compounds with high anti-proliferative activity in cellular assays,exemplied by lead 1 shown in the Figure below.Subsequent lead optimizationon of the C-ring（skeleton hopping）led to the discovery of 7-methoxy-4-（2-methylquinazolin-4-yl）-3,4-dihydroquinoxalin-2（1H）-one（2）as a new lead compound.Leads 1 and 2 show high anti-proliferative activity,with GI50 values of 1.5–1.7 and 1.9-3.2 n M,respectively,and they also inhibit tubulin polymerization with IC50 values of 0.93 and 0.77 μM,respectively,which are comparable or higher potent than those of the CA4,a clinic drug candidate,in the same assays.Further studies indicated that our previous lead compounds with new scaffold（s）（1 and 2）not only inhibited tumor cell proliferation and tubulin polymerization targeting at the colchicine binding site,but also showed disrupted tumor vasculature activity.Therefore,this kind of new compounds represent a novel class of tubulin-binding tumor-vascular disrupting agents（tumor-VDAs）,and will be developed as potential new anti-tumor drug candidates.Meanwhile,our severally previous studies also revealed some necessary pharmacophores for our lead compounds as a novel class of anti-tumor agents.As a continue study,current research aimed at exploring and/or expanding new structure-activity relationships（SARs）for this new class of anti-tumor agents.Based on leads 1 and 2,current optimizations focused on the A/B ring,C ring,and substituents（R₁,R₂ and R₃）successively.As results,twenty four of new derivatives were designed,synthesized,and evaluated.All new compounds were tested against a human tumor cell line panel,including A549,KB,KBvin,MDA-MB-231,and MCF-7.Among these new derivatives,compounds 9b,11 a,and 11 b all showed high anti-tumor potency with low nanomolar GI50 values about 5 n M in the tested human tumor cell lines,similar to those of leads 1 and 2 in the same assays.Furthermore,a few active compounds were tested in tubulin assembly and colchicine binding assays,thus confirming that new active compounds should have the same mechanism as leads.On the other hand,new compounds 7a and 8c with a changed C ring exhibited dramatically decreased activity（GI50>10μM）,indicating the C-ring was an important moiety related to anti-tumor activity.Moreover,this study also revealed more structure-function relationships,which will provide more information and be helpful for further study in this project.