Predicted by the National Center for Health Statistics, 600,920 Americans will die of cancer by the end of 2017, and 24,500 will be victims of leukemia.[1] Leukemia aggressively attacks bone marrow, forming abnormal leukocytes and preventing normal red blood cell production. To treat this disease, doctors use chemotherapy drugs such as daunorubicin to eliminate the tumor cells. However, free chemotherapy drugs do not have a consistent or efficient treatment time. Research suggests that nanoscale drug delivery vehicles will have promising results in treating cancer more effectively.[2] Current nanotechnology used for drug delivery includes nanoparticles and DNA origami. Nanoparticles as drug delivery devices are polymerized and loaded with a chemotherapy drug to sent into the body. However, nanoparticles consist of foreign materials and thus pose toxicity concerns;[3] the components may not be compatible with the human body, and the cells may remove the substances via efflux pumps. However, intercalating chemotherapy drugs into DNA origami nanostructures benefits drug delivery because of DNA’s compatibility with the human body, bypassing drug resistance mechanisms before taken up into the cells.[4]

DNA origami involves the nanoscale folding of DNA into predesigned 2D or 3D shapes by attaching complementary sequences to a scaffold.[5] Short oligonucleotides, also known as staple strands, bind to specific parts of the scaffold to form distinct nanostructure shapes. The DNA origami structure elements are heated to denature the DNA and then annealed by slowly cooling to the desired temperature, allowing the elements to interact and bind properly. DNA assembles via Watson-Crick base pairing, allowing for efficient manufacturing of designs on the scale of 10-100 nm.[6] Some examples of DNA origami applications include biosensory devices, nanomechanical research, nanoelectronic research, and drug delivery. We chose to focus on drug delivery aspects as they pertain to chemotherapy treatments. Previous studies have proven the potential in using DNA origami structures as chemotherapy drug delivery vehicles for treating cancers such as breast cancer[7] and leukemia.[8]

Background Figure

Figure B.1. A.Examples of objects built with scaffolded DNA origami.[9] B. Intercalation of cancer drugs into DNA origami nanostructures to circumvent drug resistance in tumor cells. [10] C. Twisted DNA origami structure allows more room for cancer drugs to attach and slower release.[11] D. Clamshell structure for delivery of a payload. [12] E. Free daunorubicin drug enters cell by passive diffusion. F. in vivo delivery of the chemotherapeutic doxorubicin into mouse tumors through intercalation into DNA origami structures. [13]

A study done by researchers at the Ohio State University showed that a DNA origami structure named the “Trojan Horse” effectively delivered loaded daunorubicin to a cell via endocytosis, bypassing the cell’s drug resistance mechanisms to enter the cell.[8] The Horse provided a protective mechanism for the drug because the cell recognized the DNA structure as a familiar material, and therefore did not destroy it. Even though the Horse was tested for its drug delivery abilities, it was not compared to other types of rod-shaped structures. Other structure characteristics such as lattice cross section, surface area, length, presence of overhangs, and amount of twist could possess advantages over others. For example, in a study done Xidian University in China, 2D triangular-shaped DNA origami structures proved to accumulate at cancer cells more efficiently than 3D tube-shaped structures.[2] Shape and structure design may also affect the amount of drug retention. Retaining the drug prior to cancer cell uptake prevents the drug from affecting other parts of the body; also, maximizing drug retention allows the drug to affect the cancer cells most efficiently, lowering cell viability. Nanotechnology has shown promising results for drug retention in cancer treatments.[14],[15] Research regarding drug retention at Ohio State University showed that over a 24 hour incubation period, 31% and 50% of the drug leaked out of the Horse structure from suspension in PBS (10 mM MgCl2) and culture media (clear RPMI 1640, 20% Fetal Bovine Serum).[2] We hope to determine if structures with increased surface area might allow increased drug retention. Also, twisted structures were proven to have increased efficiency in loading, retaining, and releasing the chemotherapy drug doxorubicin in a study at Karolinska Institute.[7] A twisted version of a rod-shaped structure may alter the amount of drug retained.

Background Figure

Figure B.2. Twisted structure design for better daunorubicin retention created with caDNAno software.

Several DNA origami structures were tested to compare physiological environment stability, drug loading stability, drug retention capacity, and cell uptake. These structures included the Horse, Square 18, Branch, Symmetric 18, and LPP. Using these results, we plan to create a physiologically stable and efficient structure design using caDNAno that maximizes drug retention. We plan to test a twisted version of the horse to determine if it has a higher capacity to protect the drug from the environment and deliver more to the cell, decreasing cancer cell viability. This process has potential for increasing efficacy in cancer treatments.

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