Targeting ULK3 for the treatment of triple negative breast cancer

PROJECT SUMMARY / ABSTRACT Clinical significance: Triple negative breast cancer (TNBC) is the most aggressive subtype of breast cancer and represents 15-20% of new cases (1). Given that TNBC lacks molecular expression of hormonal receptors and HER2 amplification, chemotherapy remains the go-to treatment option (2). The prognosis for TNBC patients is

grim, and after initial surgery/chemotherapy, patients often relapse with metastases to lung, brain, liver, and bone (3). Understanding the mechanisms that govern TNBC progression and metastasis can reveal new targets for therapeutic intervention which is an urgent and unmet clinical need for this patient population (4,5).

Rationale: Autophagy is a metabolic program that is highly utilized by TNBC cells to survive, particularly upon exposure to chemotherapy (6). While reagents such as chloroquine can block autophagy, their clinical impact is yet to be realized due to unknown mechanisms of action and toxicity (7,8). However, focusing on specific key

nodes that regulate the program with highly selective inhibitors is possible. Investigating upstream initiators of the autophagy program, emerging evidence from our group demonstrates that Unc-51 like kinase 3 (ULK3) expression, as opposed to the more commonly studied ULK1, correlates with TNBC aggressiveness. Further,

genetic analyses confirm a key role for ULK3 in controlling TNBC autophagy and survival. No ULK3 inhibitors currently exist but excitingly, we have generated novel ULK3 selective inhibitors that are effective in preliminary in vitro experiments. Here, we plan to focus on our lead ULK3 inhibitor, RF1024, to test our hypothesis that ULK3

is a tractable and therapeutic target for the effective treatment of triple negative breast cancer. Proposed studies: In Aim 1 we will assess the efficacy of RF1024 in limiting TNBC growth in vitro using immortalized cell lines and in vivo using two preclinical metastatic TNBC models (4T1, SUM159). In Aim 2, we

will determine ULK3 expression in TNBC patients. We will also investigate autophagy status and ULK3 levels as a response/prognosis biomarker in a robust data set of TNBC patient biopsies. We propose to determine a retrospective study (patient samples from 2010 - to date) on TNBC patient specimens collected at Moffitt with

the purpose to validate for the first time ULK3 protein as a possible biomarker. At the conclusion of our studies, we expect to have fully interrogated the efficacy of a novel ULK3 inhibitor that can be rapidly translated to the clinical setting for the treatment of TNBC patients