Defining Mechanistic Targets and Circulating Biomarkers of Therapeutic Response and Resistance to Clinical ATR and Chk1 Inhibitors in High-Grade Ovarian Cancer
Abstract
Advances in ovarian cancer treatment have modestly improved 5-year survival rates from 33.7% in 1975 to 46.5% in 2017, based on both more aggressive surgery and improved chemotherapy. Small molecule inhibitors targeting proteins that promote DNA damage response (DDR), such as inhibitors of ataxia telangiectasia and Rad3-related protein (ATR) and checkpoint kinase 1 (Chk1), are among new strategies to combat recurrent disease. One critical issue to increasing long-term survival for ovarian cancer patients is improving the management of treatment resistance. How ovarian cancer cells become resistant to ATRi and Chk1i remains largely unexplored and we seek to rectify this deficiency as there are currently 19 active clinical trials testing ATR and Chk1 inhibitors to treat diverse cancers, including high-grade and recurrent ovarian cancers (clinicaltrials.gov). We have generated and characterized unique models of ATRi (Chk1i) resistance established by metronomic treatment of ovarian cancer cell lines (OVCAR3, OV90, TOV-21G) with the ATR inhibitor AZD6738 (Astra Zeneca). The models are resistant to ATRi as well as inhibitors of Chk1, a protein directly regulated by ATR. This proposal is focused on two main goals: The first is to improve our understanding of a novel mechanism identified by our group that confers resistance to ATRi and Chk1i in ovarian cancer cells, i.e., loss of cyclin-dependent kinase 6 (CDK6) expression. Secondly, we aim to leverage our ATRi (Chk1i) resistance models to establish biomarkers that will lead to the development of blood tests that can aid clinicians to identify patients with ATRi (Chk1i)-resistant disease as well as to track treatment response to these drugs and potent ATRi combinations that are highly effective at killing ovarian cancer cells, namely, with poly (ADP-ribose) polymerase inhibitors (PARPi), ATR and Chk1 protein kinases that promote the repair of damaged DNA, such as that caused by chemotherapy, as well as regulate DNA replication, a process required for tumor cell proliferation. Characterization of ATRi (Chk1i) resistance models has shown that ATRi-resistant cells treated with ATRi exhibit a cell cycle arrest that halts DNA replication. Analysis of proteins that drive cells to replicate DNA has shown that expression of a key replication checkpoint protein, cyclin-dependent kinase 6 (CDK6) is lost in ATRi-resistance models (OVCAR3). We further confirm that CDK6 is important in mediating response to ATRi (Chk1i) by showing that inhibition of CDK6 activity, using small molecule inhibitors or cells engineered to not express CDK6, results in resistance to ATRi and Chk1i treatment. Review of public data and recent literature shows that gains in CDK6 gene copy number occur in ~20% of ovarian cancers and a recent analysis of over 1,000 ovarian cancer patients showed that elevated CDK6 expression significantly correlated with an increased risk to experience poor disease outcome. As we have found, ovarian cancer cells that express CDK6 are responsive to ATRi (Chk1i); this suggests that patients with high CDK6 expression may be excellent candidates for treatment with clinical ATRi and Chk1i. We propose herein to further understand how CDK6 protein expression is lost in ATRi (Chk1i)-resistant ovarian cancer cells as we have established that this is not due to loss of CDK6 gene expression. This knowledge may lead to novel applications of ATRi (Chk1i) therapies for the treatment of ovarian cancer patients with high CDK6 expressing disease. We also propose to capitalize on the conserved biology exhibited by ATRi (Chk1i)-resistant cells in response to ATRi treatment, i.e., cell cycle arrest that halts DNA replication, to define protein markers actively secreted by ovarian cancer cells that can indicate whether cells are resistant to ATRi (Chk1i). We also aim to establish protein markers indicating response to ATRi, Chk1i as well as to potent ATRi/PARPi combination treatments. We will use cutting-
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Oct 29, 2018
- Source ID
- W81XWH1810044
Entities
People
- Nicholas W Bateman
Organizations
- Henry M. Jackson Foundation for the Advancement of Military Medicine
- United States Army