Transmembrane Cell Signaling by Targeted Ultrasound Contrast Agents in Cancer Therapy

Here we describe the development of non-immunogenic, functionalized PLA UCA for use in targeted breast cancer therapy. We believe that the use of a targeting ligand in conjunction with polyethylene glycol (PEG) will help to shield the UCA from immune recognition and improve the treatment efficacy at the target site. For ultrasound (US) imaging with polymeric contrast agents, it is necessary to modify the shell to create "stealth" microbubbles but without these modifications sacrificing the agent's ability to interact with the focused US beam. We hypothesize that addition of the classic immune shielding molecule PEG to a polylactide (PLA) microbubble shell will affect the acoustic and physical properties of the resulting agents.;In an effort to determine the best formulation to achieve a balance between stealth and acoustic activity, we compared two PEGylation techniques; addition of increasing amounts of PEG-PLA copolymer and employing incorporation of a PEG lipid (LipidPEG) into the shell. Loss of acoustic enhancement occurred in a dose-dependent manner for both types of PEGylated agents (loss of signal occurred at >5 wt% PEG-PLA and >1 wt% LipidPEG), while immune activation was also reduced in a dose-dependent manner for the PEG-PLA agents. This study shows that the balance between acoustic behavior and improved immune avoidance was scalable and successful to different degrees with both PEGylation methods, and was best achieved using for PEG-PLA at 5 wt% and for LipidPEG at 1 wt%.;The added advantage to the use of the targeting ligand, specifically tumor necrosis factor-related apoptosis inducing ligand (TRAIL), is that it also induces tumor cell death upon binding to the cell surface receptors DR4 and DR5 and initiating a transmembrane apoptosis signal. Healthy cells possess decoy receptors (DcR1 and DcR2) that cannot process the apoptotic signal, therefore being protected from non-specific binding. Additionally, the UCA were designed to co-encapsulate the chemotherapeutic drug doxorubicin (Dox) that can be released from the polymer shell in response to US focused at the tumor site, shielding healthy tissues from the toxic substance while also increasing the potency and efficiency of treatment to the tumor tissue. The ability of the ligand to cause cell death was tested against ligand-sensitive MDA-MB-231 human breast adenocarcinoma cells and ligand-resistant MCF7 human breast adenocarcinoma cells, comparing the efficacy of the microbubble formulations. It is believed that co-administration of Dox to cancer cells that are normally resistant to TRAIL increases the expression of death receptors on the cell surface, sensitizing the cell to TRAIL and improving its efficacy. For the MDA-MB-231 cells, cell viability was reduced by approximately 25-50% (52.84+/-11.65% to 76.34+/-3.25% live cells) upon incubation with the TRAIL-ligated US-generated nanoshards, and was further reduced to approximately 40-80% (20.32+/-6.91% to 64.19+/-2.68% live cells) with the addition of doxorubicin compared to TRAIL alone. TRAIL-resistant MCF7 cells showed little apoptotic response to TRAIL-ligated nanoshards (93.44+/-2.88% to 98.18+/-1.04% live cells); however, co-administration of doxorubicin increased apoptosis and reduced cell viability (37.37+/-5.39% to 67.78+/-3.98% live cells), supporting the sensitization effect of the drug. Healthy MCF-12A human breast epithelial cells were also tested, to confirm the selective targeting and apoptotic activity of TRAIL to cancer cells and not healthy cells. These cells exhibited from 90.64+/-2.54% to 97.46+/-0.62% cell viability when incubated with TRAIL-ligated nanoshards, confirming their insensitivity to TRAIL-induced death. However, cell viability was greatly decreased (44.73+/-15.26% to 68.79+/-6.89% live cells) when also exposed to doxorubicin, demonstrating the toxic effects of the chemotherapeutic agent on surrounding healthy cells during systemic treatment.;Overall, this work has resulted in the production of effective ultrasound-triggered, non-immunogenic, targeted drug delivery agents for potential use in cancer therapy. This platform has many advantages over the systemic administration of chemotherapeutic drugs, and represents a promising treatment to better serve the population with breast cancer, and solid cancerous tumors as a whole. (Abstract shortened by ProQuest.).