Modular Nanoparticle Probes for Personalized in Vitro and in Vivo Imaging of Cancer Cell Populations

P.D. Nallathamby, K. Cowden-Dahl, R.K. Roeder
University of Notre Dame,
United States

Keywords: ovarian cancer, cancer stem cell, hafnia, gadolinia, gold, bioconjugation, immunooncotherapeutic, platform technology, modular assembly, nanoparticle system, theranostics, multi-modal, fluorescence, X-ray CT

Summary:

The high mortality and poor prognosis for women diagnosed with ovarian cancer is mainly due to late diagnosis. Improved detection of primary tumors and recurrence after chemotherapy is, therefore, crucial to reduce ovarian cancer mortality and improve progression-free survival. However, current clinical screening and diagnostic imaging methods are limited by low sensitivity and/or specificity Molecular imaging approaches for targeting cell surface receptors, including ovarian cancer stem cells (CSCs), have shown promise in preclinical cell culture and tumor models with large and homogeneous cell populations. Contrast-enhanced computed tomography (CT) and spectral (color) X-ray CT have the potential to enable molecular imaging with CT as a lower cost and higher resolution alternative to PET and MRI. Therefore, we have developed a modular approach for the design and scalable synthesis of core-shell nanoparticle (NPs) imaging probes enabling multi-modal imaging (e.g., fluorescence, MRI, X-ray, plasmonic), dosed delivery of therapeutics, and active targeting through molecular surface functionalization. For the purpose of imaging distinct cancer cell populations both in vitro and in vivo, we prepared Au@SiO2 core-shell NPs comprising a gold core ~10 nm in diameter encapsulated in a tunable silica shell, 1-15 nm in thickness, which enabled controlled loading of fluorophores and bimodal imaging by fluorescence and CT. Antibodies and other small molecules were efficiently conjugated to the silica shell using appropriate CLICK chemistry to enable cell surface receptor targeting. The bioactivity and orientation of antibodies conjugated to NPs were confirmed through agglomeration assays and electron microscopy. Quantitative assays reported a steady conjugation efficiency of 75%-80%. For proof-of-concept, Au@SiO2 NPs were successfully targeted to CD133(+) SKOV3-IP cells, which are known to be over-expressed in chemoresistant ovarian cancer metastases. Quantitative fluorescence imaging was used to measure the binding kinetics and confirm that the cell lines were targeted with high specificity in co-cultures in vitro. The intracellular distribution of NPs was characterized spatiotemporally at single NP sensitivity using confocal microscopy and electron microscopy. Ensemble statistics about the percentage of CD133(+) SKOV-IP cells in total cell population was determined using flow cytometry. Finally, a murine xenograft model of ovarian cancer was developed using CD133(+) SKOV3-IP cells. Importantly, the tumor location and margin could be determined noninvasively by CT and was correlated with in vivo fluorescence imaging. The modular approach allows us to plug in core compositions of other modalities such as gadolinium oxide, iron oxide, and hafnium oxide. It also enables us to easily vary the targeting molecules and therapeutic molecules that can be conjugated or volume loaded onto this core-shell NPs system.