Targeting Senescence and the senescent secretome to impact breast cancer formation

Project Summary Senescence and the senescence associated secretory phenotype (SASP) have long been implicated in driving tumorigenesis. However, the pro-tumorigenic mechanism(s) of senescence are still not fully understood, pointing to a need for better model systems to study the role of senescence in tumorigenesis. We recognized that a breast

cancer model that used irradiation of cleared mammary fat pads followed by implantation of syngeneic Comma- D cells could be an ideal system to study senescence effects on tumorigenesis. Implantation of Comma-D alone does not result in outgrowth of tumors, but requires pre-irradiation of the gland for tumorigenesis. Similarly,

treatment of the mammary fat pad with chemicals prior to implantation can also drive tumorigenesis. Both these types of treatments are also known to induce senescence, and indeed we found that irradiation induces massive senescence in the tissue. Thus, we hypothesize that tumorigenesis in this model system relies on induction of

senescence to drive tumor formation, and that targeting the senescent cells or specific SASP factors will impair tumorigenesis. We propose to study this model system further to show that tumorigenesis requires induction of senescence in two specific aims. In the first aim, we will treat irradiated animals with senolytic drugs to remove

senescent cells prior to implantation of SCp2 and other mammary cells, and compare tumor incidence in this group to a control arm that are treated with vehicle alone. Our preliminary data indicates that targeted removal of senescent cells with navitoclax blocks tumor formation. Extension of our studies will establish that senescence

can drive early tumorigenesis in multiple models. In the second aim, we will examine how senescence drives pre-neoplastic cell growth, survival, and differentiation in vivo using multiplex immunofluorescence. We will perform RNAseq to identify SASP factors that are upregulated in response to irradiation. We will test these

factors for their ability to enhance growth of SCp2 and human mammary epithelial cells (HMECs) in vitro. SASP factors that enhance growth and survival of these cells will be selected for targeting to determine their role in tumor formation. We will use small molecule inhibitors of receptors or interfering antibodies for SASP factors to

determine how blocking these putative growth promoting factors impacts tumor formation. Successful completion of these studies will establish whether tumorigenesis in a luminal mammary cell implantation system is driven by senescence, will identify mechanisms by which senescence drives tumorigenesis, and will demonstrate the

ability of senolytics or small molecule inhibitors targeting SASP factors to impair tumorigenesis. These represent the first steps in gaining mechanistic understanding of the role of senescence in early mammary tumorigenesis, with a long term goal of developing anti-senescence approaches for the prevention or treatment of human breast

cancer.