OBJECTIVES/GOALS: The objective of my study is to test my overall hypothesis that CDK4/6 inhibitor-induced cellular senescence has long-lasting consequences on the tumor microenvironment that affect tumor growth and disease progression. METHODS/STUDY POPULATION: There is a lack of mechanistic understanding of the crosstalk of drug effects on different cellular pathways. One less-studied consequence of CDK4/6 inhibitors (CDKI) is their ability to induce cellular senescence in the non-malignant host cells (“stroma”), which causes secretion of a plethora of proteins that have lasting effects on the tumor microenvironment. Stromal cells are known to be able to enter senescence and promote a state of chronic inflammation that contributes to disease progression. I propose to study the stromal contribution to the tumor microenvironment and how this affects tumor growth and disease progression by using genetically engineered mouse models of breast cancer. RESULTS/ANTICIPATED RESULTS: We have found that palbociclib, a CDKI, inhibited growth and induced senescence of breast cancer cell lines xenografted into mice, and that while most on-target effects of palbociclib were reversed after treatment cessation, there was long-lasting down-regulation of interferon-γ and inflammatory response signaling pathways in the mouse host stroma that persisted after cessation of palbociclib treatment. In syngeneic models, we have found that palbociclib treatment influenced migration of T cells into CDKI-resistant tumors. DISCUSSION/SIGNIFICANCE: These studies will shed light on how senescence-inducing anticancer therapies, such as CDKI, affect tumor growth and disease progression. My studies will help elucidate new therapeutic avenues in combination with CDKI to combat therapeutic resistance in advanced breast cancer.