A novel cellular identity regulatory pathway that drives anokis resistance-mediated TNBC growth and metastasis

Women in the United States have a 1 in 8 PROJECT SUMMARY lifetime risk of developing breast cancer. Among the various breast cancer subtypes, triple-negative breast cancer (TNBC) carries the worst prognosis and only 11% TNBC patients with distal metastasis are expected to survive beyond 5-years. Furthermore, current therapies for TNBC also

provide marginal and in most cases only short-term clinical benefits. Therefore, novel and more efficacious drugs for TNBC treatment are in urgent need. Most epithelial cells are dependent upon contacts with the extracellular matrix (ECM) for survival and undergo apoptosis when they lose contact with the ECM, a process termed anoikis.

However, tumor cells, upon detachment from the ECM, are capable of evading anoikis. The acquisition of anoikis resistance is a critical step that contributes prominently to TNBC tumor growth and metastasis. Thus, anoikis inducers represent valuable therapeutic targets for TNBC treatment. However, the molecular drivers of anoikis

resistance that can be therapeutically targeted in TNBC remain largely unknown. Protein kinases are excellent drug targets with over 25 drugs targeting kinases are approved by US FDA for treating a wide-variety of cancers in clinic. Therefore, to identify kinases that confer anoikis resistance in TNBC cells, we performed a kinome-wide

shRNA screen and identified the PDZ Binding Kinase (PBK) as a driver of anoikis resistance in TNBC cells. We found that PBK was overexpressed in TNBC and predicted poor prognosis. Furthermore, genetic or pharmacological inhibition of PBK induced anoikis in TNBC cells. Based on these results, we hypothesize that

PBK confers anoikis resistance to drive TNBC tumor growth and metastasis. The overall objective is to determine the in vivo role of PBK in TNBC tumor growth and metastasis and evaluate pharmacological targeting of PBK for TNBC therapy. Aim 1 studies will determine the in vivo role of PBK as a driver of TNBC tumor growth and

metastasis. First, using mammary fat-pad injection-based orthotopic mouse model of TNBC tumor growth and metastasis we will determine if genetic inhibition of PBK suppresses TNBC tumor growth and metastasis. We will also measure circulating tumor cell (CTC) load in vivo in this mouse model to monitor the effect of PBK

inhibition on anoikis induction in vivo. Next, based on our preliminary results, we will test the role of PBK- dependent phosphorylation of transcription factor TWIST1 in reprogramming TNBC cells to acquire mesenchymal cell state and thereby acquiring anoikis resistance. Aim 2 studies will ascertain the efficacy of PBK

inhibitor in vivo for TNBC treatment. To do so, we will determine if a highly-potent and efficacious PBK inhibitor, OTS-964 can effectively suppress TNBC tumor growth and metastasis utilizing established TNBC cell lines, and patient-derived xenografts (PDXs)-based models. Taken together, our findings will have strong scientific impact

by establishing a novel role of PBK in driving cell state regulatory pathway that facilitate TNBC tumor growth and metastasis as well as by establishing PBK targeting as an effective approach for treating TNBC.