The effectiveness of localized ultrasound and aptamer surface modification on nanoemulsions for drug delivery to spheroids.
Date on Master's Thesis/Doctoral Dissertation
JB Speed School of Engineering
Spheroid; Nanoemulsion; Ultrasound; Drug Delivery; AS1411; aptamer
Cancer is a group of diseases that affects 1.6 million and kills nearly 600,000 Americans each year. The National Cancer Institute defines it as “diseases in which abnormal cells divide without control and can invade nearby tissues” and it is often treated with one or more of the following: chemotherapy, radiation, surgery. The expense for these treatments is expected to rise to $156 billion by 2020. Localized delivery can improve effectiveness and cancer survival rates, decrease the cost of treatment, and decrease the side effects of chemotherapy. This paper addresses models for this localized delivery through nanoemulsions. Nanoemulsions are a spherical layer of a hydrophobic substance holding and surrounded by hydrophilic substances or a spherical layer of a hydrophilic substance surrounded by and holding hydrophobic substances with a diameter less than one micrometer. Nanoemulsions are in development for cancer treatment due to their thermodynamic stability, which improves shelf-life.
While nanoemulsions on their own do not provide specific targeting, two potential options for targeted and local delivery are addressed here. This paper explores the effect of AS1411, an aptamer which can target some cancer cells, on nanoemulsions for chemotherapy delivery. AS1411 binds to nucleolin, which is overexpressed in many cancer cells and appears on their surface, allowing AS1411 to target them. AS1411 also has the ability to inhibit cancer cell functions and kill cancer cells selectively. When taken into healthy cells, AS1411 is removed through exocytosis or efflux instead of damaging them. Using AS1411 on nanoemulsions should cause the cancerous cells to actively absorb the nanodroplets while limiting uptake by healthy cells.
Ultrasound-induced vaporization is also explored as a way to cause nanoemulsions to release their payload into cancer cells. Vaporization of the nanoemulsion droplets weakens surrounding membranes and forces drugs out of nanoemulsions as microjets. This method can be used on many cancers, especially those near to the skin as there is less interference. One caveat is that ultrasound may not be safe for lung cancer treatments, as ultrasound cannot penetrate air in the lungs and the reflected waves may damage healthy lung tissue. These additions to systemic nanoemulsion treatment, both combined and separate, are tested on both traditional single-layer MDA-MB-231 breast cancer cells and on artificially grown tumors, called spheroids. This spheroid testing allows for a look into how these treatments may be affected by avascular tumors, which are more drug resistant than normal cancer.
To test the effects of these treatment options, FITC-labeled or doxorubicin-loaded nanoemulsions were produced and applied on top of the cancerous cells. Doxorubicin was used due to its chemotherapeutic properties and its lack of interference with MTT assay readings. Some samples were created with AS1411 covalently bound to the outside while others were created with no payload or targeting to act as a control. After a period of incubation the nanoemulsions in some samples are ultrasonicated while others remain untouched as control. Following further incubation, the cells were harvested and assayed for analysis, using flow cytometry for FITC detection and an MTT assay for doxorubicin-induced cytotoxicity detection.
The results of these tests showed that ultrasound improved cytotoxicity in doxorubicin-treated spheroids but worsened FITC uptake. This reduced FITC uptake may be caused by holes in the cell membrane induced by ultrasound, allowing FITC to leak back out of the cells. AS1411, both with and without ultrasound, had an insignificant effect on cytotoxicity in this study. The lack of consistent improvement by AS1411 may be due to the use of cancerous cells exclusively in our spheroids, which result in all of the nanoemulsions releasing their payloads onto the cancer regardless of whether or not they bind to their nucleolin. Another theory is that the incubation times were too long, so the passive uptake of the nanoemulsions was able to overshadow to the active uptake stimulated by AS1411. The results of this research encourage further study into the potential efficacy of these treatment options.
Hodge, Daniel A., "The effectiveness of localized ultrasound and aptamer surface modification on nanoemulsions for drug delivery to spheroids." (2018). Electronic Theses and Dissertations. Paper 3004.
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