Mechanism Of Action Of Natural Boxwood Alkaloids KBA01 Targeting Mutant P53

Malignant tumor serious threat to human health.Colorectal cancer is the third mortality rate cancer in the world,and its incidence and mortality is increasing year by year in our country.Currently,cancer treatment mostly uses surgery,radiation and chemotherapy,etc.However,after treatment by them,the survival time of patients are still short,the prognosis effect is still poor.Many anticancer drugs were extract from natural plants,these small molecular drugs can target to tumor cell and kill them.However,these natural plants utilization rate is very low in clinical,and the pharmacological mechanism also needs to more research.Wild-type p53(wtp53)is a tumor suppressor,and it also is a transcription factor.wtp53 can regulate cell cycle,cell apoptosis,aging,and other cell phenomenon.However;there are more than 50%of p53 mutations and more than 2000 kinds of p53 mutation types in tumors.The expression of mutant p53(mutp53)is higher in tumor cells,and this phenomenon is more common in colon cancer,breast cancer,lung cancer.In tumor cells,heat shock protein(often highly expressed in tumor cells,and will be the target of tumor therapy),such as Hsp90/Hsp70/Hsp40,which plays a molecular partner role in cells.The present study suggests that heat shock protein(Hsp90/Hsp70/Hsp40)can form a stable complex with mutp53,which result in mutp53 half-life extending(more than 24h),gathered in cells.The stable complex is difficult to degrade,sometimes can further promoting the development of tumor.Therefore,the mutp53 can gain a function,which called Gain of function(GOF).Hence,the mutp53 becomes a target of tumor therapy.In tumor cells,we need to more researches to recomprehensive understanding the GOF of mutp53,which will find out more tumor therapeutic targets.mutp53 can promote heat shock transcription factor 1(HSF1)phosphorylation,and induce heat shock response.However,heat shock protein,such as Hsp90,Hsp27,Hsp70/72 and Hsp40,which have anti-apoptotic effect in tumor cells.Researches show that some of Hsp90 inhibitors could block the bandage between Hsp90 and mutp53,so some of Hsp90 inhibitors have antitumor function.However,at the same time,these small molecular compounds can active HSF1(HSF1 often high express in tumor cells,and will be a new type of targets in tumor therapy),then induce heat shock response.This negative feedback regulation,can further promoting the expression of heat shock protein,and further promoting the development of cancer.This is why the research about application of Hsp90 inhibitors in clinical is very hard.KBA01,a natural alkaloid,which come from lobular boxwood extract.It is more researched in the treatment of cardiovascular disease,while less study focus on anti-tumor.In recent years,many studies shown that the steroidal alkaloid composition has antitumor activity.Meanwhile,our previous study discovered that the activity structure of KBA01(an Hsp90 inhibitors,exist in thunder god vine)is similarly to celastrol structure.Our previous studies also found that the toxic activity of KBA01 in HT29 cell(a colon cancer cell,p53R273H)was four-fold higher than the cytotoxic activity in HCT116 cells(a colon cancer cell,wtp53),and 10 times higher than the cytotoxic activity in MRC-5 cell.Therefore,in order to further research the antitumor activity and mechanism of KBA01,we chose the HT29 cells.Our previous studies found that KBA01 had killing effect to HT29 cell.The compound could inhibit the growth of tumor cells,change the shape and inhibit clone formation of HT29 cell.At the same time,when HT29 cell treated with KBA01,the expression of p53R273H would reduce,the expression of HSF1 and phosphorylation HSF1(p-Ser326)were also reduced,and then reduce the heat shock response,overcome the effect of negative feedback which lead to by Hsp90 inhibitors and while could activate HSF1.The lower expression of Hsp90,which would lead to destabilization of mutp53 and make depolymerization of the stable complexes,as well as reduce the p53R273H half-life.We suspected that the lower expression of Hsp90 speed up the degradation of mutp53 would through the ubiquitin-proteasome pathway.On the other hand,our further study found that KBA01 could restore the wild-type p53 activity function of mutp53,thus induced some protein express,which are downstream of p53(such as P21,PUMA,NOXA,etc.).This result would lead to tumor cell cycle arrest and induce tumor cell apoptosis.Therefore,KBA01 can accelerate the degradation of mutp53,and can reduce the heat shock response which caused by other small molecules.KBA01 will be become an important compound for personalized therapy of cancer,and our research result will open a wider range road for personalized targeted therapy of cancer.