Mechanistic Evaluation of Macrocyclic Diterpenoids with Selective Triple Negative Breast Cancer Activity

PROJECT SUMMARY Triple-negative breast cancer (TNBC) is a highly heterogeneous disease largely devoid of targeted therapy due to the absence of estrogen, progesterone, and HER2 receptors. Due to this, conventional chemotherapy is the only systemic pharmacological option used to treat TNBC patients. However many women do not have a lasting response to this treatment alone particularly in the later stages of the disease. Therefore, the identification of agents that can selectively target molecularly defined subtypes of TNBC would be beneficial. To this end, we have pioneered the screening of natural product extracts for TNBC subtype-selective constituent, resulting in the identification of the macrocyclic diterpenoid yuanhuacine. This proposal thus focuses on elucidating the molecular mechanisms by which yuanhuacine mediates TNBC subtype-selective cytotoxicity and which pharmacophores in the structure modulate such activity. This work will test the central hypothesis that the epoxide on carbon 6,7 of ring B on the macrocyclic diterpene ester skeleton is pivotal in mediating potent and selective cytotoxicity against the basal-like 2 (BL2) subtype of TNBC through a protein kinase C (PKC) dependent pathway. Preliminary studies suggest that the PKC βII isozyme of PKC may mediate the sensitivity of BL2 TNBC cells towards yuanhuacine. In Specific Aim 1, we will determine whether PKC βII isozyme expression is both necessary and sufficient for these activities, and how the compound alters PKC kinase activity in both sensitive and resistant cells. Previous studies comparing the potency of macrocyclic diterpenoids that lack the epoxide group on carbons 6 and 7 to those that do, demonstrate a significant loss in cytotoxicity potency when compared to the epoxidated derivatives. In Specific Aim 2, we will define additional structural pharmacophores that are critical to mediating the potent and selective cytotoxicity against the BL2 TNBC cells and further establish the importance of the epoxide group by comparing the activity of a series of established and newly synthesized derivatives representatives of the distinct subclasses of macrocyclic diterpenoids. Successful completion of the proposed studies will provide insights into an unanticipated druggable oncogenic pathway and a companion drug to advance the development of targeted therapies against TNBC. Additionally, the integrative approaches proposed here will serve as a platform for me to obtain new mentored career training and pave the way to establishing a sustainable research program at a primarily undergraduate institution (PUI) conducive to excellence in biomedical research.