Mechanistic Study Of Synthetic Lethal Vulnerability In Malignant Tumors Harboring ERBB3 Or P53 Gene Mutations

Tumor,a collection of genetic diseases,can be classified as benign and malignant cancerous,in which the malignant tumors are highly invasive and lethal.It is well known that malignant tumors have long been the leading cause of death worldwide.Although much progress has been made to improve the efficacy of cancer treatment,the options are still limited.Currently,in addition to the conventional chemo-radiotherapeutics,molecular targeted therapies is emerging as one of the effective cancer treatments.However,targeted therapy are still facing many problems in clinic.On the one hand,tumor cells could escape the targeted gene signaling pathway and acquire a new survival way,leading to the failure of targeted drugs;on the other hand,many known oncogenes are not druggable.It is therefore urgent to identify novel molecular targets.Synthetic lethality refers to the biological effect that cell death occurs upon two genes mutated or inactivated simultaneously.While inactivation of either one of these two mutated genes does not lead to cell death.One of such successful examples is the discovery of PARP inhibitors,which has been approved to treat BRCA1/2 mutated cancer in clinic.Since then,synthetic lethal screening has become an important approach to discover novel cancer targets.In this study,we performed chemical screens to identify new synthetic targets for mutant ERBB3 and mutant p53,respectively.In addition,we explore potential molecular mechanisms.In project 1,we firstly found that the mutation frequency of ERBB3 gene in human gastrointestinal cancer is relatively high through analyzing the cancer genome atlas(TCGA)database.Then,we carried out a viability screen in a panel of human gastrointestinal cancer cell lines with or without ERBB3 mutations using a collection of tyrosine kinase inhibitors(TKIs).Interestingly,we found that tumor cell lines with ERBB3-E928 G mutations were significantly resistant to FGFR1 inhibitors(BGJ398 and PD173074).In addition,either knocking down of Mut-ERBB3 or specific inhibition of ERBB3 activity through LJM716,specific antibody against ERBB3,could effectively reverse the resistance of ERBB3-E928 G mutant tumor cells to FGFR1 inhibitors by increasing apoptosis.Meanwhile,we functionally validated the in vivo tumor killing effect by co-targeting Mut-ERBB3 and FGFR1 in those tumor-bearing mouse models.Furthermore,we found that E928 G mutated ERBB3 could interact with FGFR1 protein to promote tumor growth by activating its downstream MEK/ERK signaling pathway.Our results suggest that ERBB3 mutated gastrointestinal tumors could be resistant to TKIs,such as FGFR1 inhibitors,and the combinatory inhibition of Mut-ERBB3 and FGFR1 might serve as a promising treatment regimen for gastrointestinal cancer.In project 2,we screened a panel of cancer cell lines carried either mutated p53 gene(Mut-p53)or wild-type p53 gene(WT-p53)using 43 of epigenetic drugs,including HDAC inhibitor,SIRT1 inhibitors/activator and methyltransferase/demethylation inhibitors.SIRT1 activators were found as more potent compounds to specifically suppress cell viability of Mut-p53 tumor cells.We also found that SIRT1 activators arrested Mut-p53 tumor cells at cell cycle of S-phase.Mechanistically,we found that minichromosomal maintenance protein(MCM)complex,a DNA helicase complex might participate in this process based on both proteomics and gene interference(RNAi)screening.Further functional studies validated that knocking-down of MCM2 rescued the death of Mut-p53 cells induced by SIRT1 activation.Importantly,we demonstrated that activation of SIRT1(either by activator or by overexpression of SIRT1)could specifically inhibit tumor growth of Mut-p53 in mice.In conclusion,our findings suggest that activation of SIRT1 inhibits the growth of Mut-p53 cells by regulating MCM2,which provides a new avenue for targeting p53 mutated tumors.In conclusion,our functional studies revealed FGFR1 and SIRT1 as novel synthetic lethal targets for malignant tumors carried either ERBB3 kinase mutations or p53 missense mutations respectively.Notably,in preclinical tumor models,we demonstrated genetic and pharmacological targeting FGFR1 or SIRT1 significantly suppressed ERBB3-and p53-mutated tumor growth,providing supporting evidence for further testing the implications of these mechanisms for clinical practice.