PROGRAM | Biomedical Engineering

By: Danielle Valcourt Chair: Emily Day

ABSTRACT

Triple-negative breast cancer (TNBC) is an aggressive disease that accounts for 15-25% of all breast cancer cases and is characterized by its cells’ lack of expression of the three most common surface receptors detected on other subtypes: estrogen receptor, progesterone receptor, and human epidermal growth factor receptor 2. This lack of expression makes TNBC unsusceptible to current targeted or hormonal therapies, so new treatment strategies are desperately needed. This thesis makes progress towards this goal by developing poly(lactic co-glycolic acid) (PLGA) nanoparticles that can enable treatment of TNBC through three distinct mechanisms. PLGA is an ideal carrier material because the Food and Drug Administration (FDA) has already approved this polymer for human clinical use, and it readily degrades into non-toxic byproducts in the body, allowing for the creation of safe and effective therapeutics. Chapter 1 of this thesis provides an introduction to TNBC biology and the current state of cancer nanomedicine, while Chapter 2 describes common methods used in this work. The remaining Chapters discuss the specific therapies developed in this dissertation and provide insight on directions for future development.

The first objective of this thesis was to enable photothermal therapy (PTT) of TNBC using a biodegradable nanoparticle platform. PTT utilizes nanoparticles embedded in tumors as exogenous energy absorbers to convert externally applied near-infrared (NIR) light into heat to ablate cancer cells, and it has shown much promise as a novel cancer treatment strategy. Historically, PTT has utilized gold-based nanoparticles to produce heat, but these materials will remain in the body indefinitely with unknown long-term health effects. To enable PTT with a biodegradable platform, we loaded PLGA nanoparticles with the NIR-absorbing dye, IR820. In Chapter 3, we demonstrate that these IR820-NPs are potent mediators of pro-apoptotic TNBC cell death in vitro and can significantly reduce tumor burden in murine TNBC xenograft models in vivo.

While PTT can be used to treat relatively superficial or accessible tumors, it is not well suited for treatment of tumors located in regions where NIR light cannot penetrate. Thus, the second and third objectives of this thesis developed a more widely applicable therapeutic strategy: using PLGA nanoparticles as delivery vehicles to regulate oncogenic signaling pathways in TNBC cells and tumors. In TNBC, the anti-apoptotic protein Bcl-2 is overexpressed, contributing to drug resistance. Prior studies have shown that the small molecule drug ABT-737, which inhibits Bcl-2 to reinstate apoptotic signaling, is a promising candidate for TNBC therapy. However, ABT-737 is poorly soluble in aqueous conditions and its orally bioavailable derivative causes severe thrombocytopenia. To enable targeted delivery of ABT-737 to TNBC and enhance its therapeutic efficacy, we encapsulated the drug in PLGA nanoparticles that were functionalized with Notch-1 antibodies to produce N1-ABT-NPs. The antibodies in this nanoparticle platform enable both TNBC cell-specific binding and suppression of Notch signaling within TNBC cells by locking the Notch-1 receptors in a ligand unresponsive state. This Notch inhibition potentiates the effect of ABT-737 by up-regulating Noxa, resulting in effective killing of TNBC cells. In Chapter 4, we present the results of in vitro studies that demonstrate N1-ABT-NPs can preferentially bind TNBC cells versus non-cancerous breast epithelial cells to effectively regulate Bcl-2 and Notch signaling to induce cell death. Further, we show that N1-ABT-NPs can accumulate in subcutaneous TNBC xenograft tumors in mice following systemic administration to reduce tumor burden and extend animal survival.

In Chapter 5, we introduce an alternative treatment strategy for TNBC that exploits its overexpression of Notch-1 receptors to enable targeted microRNA (miRNA) delivery. Studies have shown that introducing mimics of the tumor suppressive miRNA miR-34a to TNBC cells can effectively inhibit cancer growth, but miR-34a cannot be administered in the clinic without a carrier. To enable delivery of miR-34a to TNBC cells, we encapsulated miR-34a mimics in PLGA nanoparticles that were functionalized with Notch-1 antibodies to produce N1-34a-NPs. As in our second objective, the antibodies in this formulation not only enable binding of Notch-1 receptors overexpressed on the surface of TNBC cells, but also facilitate suppression of Notch signaling through signal cascade interference. The results presented in Chapter 5 demonstrate that N1-34a-NPs can regulate Notch signaling and downstream miR-34a targets in TNBC cells to induce senescence and reduce cell proliferation and migration. Thus, these nanoparticles are worthy of continued development as promising tools to combat TNBC.

In summary, this dissertation describes the development of three novel nanoparticles that can treat TNBC through distinct mechanisms: photothermal therapy, targeted drug delivery, and targeted miRNA replacement therapy. Future directions for this research are summarized in Chapter 6. With continued development and implementation, each of these nanoparticle formulations has great potential to improve patient outcomes.

Back >