Abstract BS2-2: PTEN loss by exosomal microRNA primes brain metastasis outgrowth

Abstract

Abstract Of 1.6 million newly diagnosed breast cancer patients per year, about 10-16% will develop brain metastases. Among the different subtypes of breast cancer, HER2-overexpressing (HER2+) and triple-negative breast cancers (TNBC) have the highest incidence of brain metastasis. Recently, advances in targeted therapies for breast cancer (e.g., trastuzumab, T-DM1, and lapatinib) have prolonged patient survival through better control of the systemic disease. However, when patients have disease recurrence, their brain metastasis incidence doubles, which represents an imposing challenge. Current treatment options are limited and merely palliative for those patients with brain-metastatic breast cancer, and their one year survival is less than 20%. To develop effective treatments for brain metastasis, we strived to gain global understanding of the mechanisms of brain metastasis to guide rapid development of novel and clinically applicable targeted therapies. We recently found that the brain astrocytes secrete exosomes that contain PTEN-targeting miR-19a, among other biomolecules. After brain metastatic tumor cells uptake these astrocytes-derived exosomes, miR-19a reversibly downregulates PTEN expression in metastatic tumor cells, thereby increasing Akt and NF-kB signaling, leading to an increased secretion of CCL2 cytokine. CCL2 then recruits CCR2 positive and Iba1 positive myeloid cells that promote proliferation and inhibit apoptosis of brain metastatic tumor cells and facilitate metastatic tumor outgrowth to symptomatic brain metastasis. Importantly, inhibition of exosome secretion or stable ablation of CCL2 inhibits brain metastasis outgrowth in vivo, demonstrating the potential of exosome- and CCL2-targeting for therapeutic intervention of life-threatening brain metastases (Nature, 11/2015). Currently, we are exploring the clinical potential by systematic preclinical testing in animal models. Citation Format: Yu D. PTEN loss by exosomal microRNA primes brain metastasis outgrowth [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr BS2-2.