PROJECT SUMMARY/ABSTRACT: PROJECT 1 – WEE1 inhibition in uterine serous carcinomas or p53-mutated uterine cancers Uterine serous carcinomas (USC) are a distinct histologic subtype of uterine cancer with poor prognosis, comprising up to 40% of uterine cancer deaths. Similarly, data from the The Cancer Genome Atlas (TCGA) has shown that p53-mutated uterine cancers are often “serous-like” and have decreased overall survival compared to other subtypes of uterine cancer. Therapeutic options for this group of patients are limited; in the recurrent setting, chemotherapy has limited activity and few effective therapies have been identified beyond the recently FDA-approved regimen of combination pembrolizumab and lenvatinib. Molecularly, these cancers are characterized by features that suggest the frequent presence of concomitant cell cycle dysregulation (alterations in TP53, CCNE1, RB1) and high oncogene-driven replication stress (alterations in MYC, KRAS/NRAS, ERBB2), which might make these cancers particularly vulnerable to targeting replication stress via WEE1 inhibition. A previous clinical trial of the WEE1 adavosertib in USC at our institution demonstrated significant clinical activity with a response rate of 29.4%, although targeted next generation sequencing did not reveal any correlation between specific molecular alterations and clinical activity. The overall objectives of this project are to (a) assess the correlation between anti-tumor activity of WEE1-targeting agents with functional and IHC measures of replication stress, (b) explore how IHC measures of replication stress correlate with the activity of WEE1 inhibition in PDX and GEMM models of p53-mutated endometrial cancers and clinical samples, and (c) evaluate the correlation of functional and IHC measures of replication stress with clinical activity of WEE1 inhibition in uterine serous cancer in a biopsy-driven trial. We hypothesize that sensitivity of p53-mutated uterine cancers is correlated with levels of replication stress and/or the effect of WEE1 inhibition on replication stress. To test this hypothesis, we will investigate in vitro the effect of WEE1 inhibition on replication fork dynamics in established endometrial cancer PDO models and the correlation between functional and IHC measures of replication stress with sensitivity to WEE1 inhibition in these PDOs. We will further investigate how IHC measures of DNA damage or RS, including γH2AX, pRPA, pKAP1, or pCHK1, change in vivo after exposure to WEE1 inhibition and whether these measures correlate with in vivo activity across a panel of established endometrial cancer PDX and GEMMs. Finally, we will assess the correlation of functional and IHC measures of RS with clinical activity in a biomarker study of the WEE1 inhibitor Zn-c3 in USC through the establishment of co-clinical PDO models from trial biopsy samples. The findings from these studies will provide important mechanistic insight into how RS underlies sensitivity to WEE1 i...