PROJECT SUMMARY Centrosome amplification (CA) is highly prevalent in cancer and strongly associated with tumor progression and worse prognosis in several different cancers, including breast, prostate, ovarian and lung. Centrosome amplified cells also demonstrate increased motility and invasiveness leading to metastasis. Moreover, CA is associated with genetic aberrations, such as p53 mutation that are commonly observed in aggressive forms of cancers, such as the triple negative breast cancer (TNBC). Our long-term goal is to target the growth and metastatic dissemination of aggressive breast tumors with CA that will ultimately lead to improved patient outcome. The overall objectives of this project are to (i) inhibit tumor growth in breast cancer models with CA via inducing centrosome de-clustering and formation of multipolar spindles upon targeting transforming acidic coiled-coil 3 (TACC3), and to (ii) block local invasion and metastatic dissemination in CA models by preventing cell polarization, migration and invasion upon inhibition of TACC3. The central hypothesis is that TACC3 inhibition will, on one hand, prevent active clustering of amplified centrosomes into two spindle poles during mitotic cell division leading to multipolar mitosis and apoptotic cell death in p53 altered cells, and on the other hand disrupts centrosome and Golgi re-orientation, microtubule nucleation and cell polarization in interphase cells leading to decreased migration. The rationale for this project is that TACC3 inhibition represents a unique opportunity to eliminate the most aggressive tumors that have supernumerary centrosomes, while sparing the normal cells. The central hypothesis will be tested by pursing two specific aims: 1.) To inhibit tumor growth in aggressive breast cancer models with CA by targeting TACC3, and 2.) To prevent metastasis in aggressive breast cancer models with CA by targeting TACC3. State-of-the-art experimental settings with translatable approaches will be employed, including tumor organoids, patient- derived xenografts and immunocompetent transgenic mouse model of advanced breast cancer that we characterized in terms of CA. The research proposed in this project is innovative as it aims to study mitosis/interphase-specific interactomes of TACC3 that are essential for TACC3-mediated cell division in mitotic cells and cell polarity in interphase cells that we propose to block using our novel and highly potent TACC3 inhibitor as well as using CRISPR-mediated knock-out. The proposed project is significant because it is expected to provide key mechanistic and phenotypic pre-clinical data to support the notion that targeting TACC3 concomitantly inhibits tumor growth and metastasis in breast cancer models with CA, which will then dramatically reduce mortality rates among patient subpopulation with highly aggressive cancers.