Avidity-Driven Targeting of a Versatile Nanoscale Carrier Engineered for High Payload and Extended Release of Anticancer Drugs
Katherine A. Windham1, 2, Ricky J. Whitener1, 2, 3, Jacek Wower1, 3, Mark E. Byrne2, 3, 4
1 RNA Biochemistry Laboratories, Department of Animal and Dairy Sciences, College of Agriculture
2 Biomimetic & Biohybrid Materials, Biomedical Devices, and Drug Delivery Laboratories, Department of Chemical Engineering, Auburn University
3 US Dept of Education GAANN Graduate Fellowship Program in Biological & Pharmaceutical Engineering
4 Biomimetic & Biohybrid Materials, Biomedical, Drug Delivery Laboratories, Department of Biomedical Engineering, Rowan University
Our work uses a nanoparticle consisting of a gold core coated with DNA strands creating a flexible and versatile nanocarrier with detection, drug carrying, and specific recognition and targeting capabilities driven to bind to cells by an avidity process. Gold nanoparticles (AuNps) were selected because of a large of number properties advantageous to our DNA based targeting and drug delivery approach. They are easy to synthesize, modify, and known to not elicit an immune response. We combine the properties of AuNps with recently developed small-cell lung carcinoma (SCLC) specific DNA aptamers in order to target and treat SCLC tumors. This allows us to construct a nanocarrier with the ability to modulate quantity of drug and specificity towards targeting of SCLC cells while resulting in an avidity driven process rather than affinity.
The first step is to functionalize 15-nm gold nanoparticles with single stranded DNA strands (anchor DNAs) modified with a thiol group on the 5’ end. Slight deviations in nanoparticle size can affect their color due to surface plasmon resonance, an advantage of AuNps that can be used to determine successful functionalization of the particles. Previous work in our lab has shown that we can bind up to 101 +/- 8 of our anchor DNAs to a 15-nm AuNp using optimized experimental procedures. Due to the size of our functionalized AuNps we can target SCLC cells by a passive targeting approach. Additionally, our nanocarrier possesses an active targeting mechanism with the inclusion of SCLC-cell-specific DNA aptamers found in the literature. We have successfully engineering these aptamers to hybridize with our anchor DNAs.
Using known optimal triplet base pairs for binding of doxorubicin, one of the best drugs for treating SCLC, we can control the location and quantity of drug bound to our nanocarrier. This is done by creating a double stranded DNA region containing a series of the triplet base pair sequences, the length of which determines how many drugs can bind. Since doxorubicin is a DNA intercalator, it needs a double stranded region to bind to our nanocarrier. This property allows us to control the location of the drug on our nanoparticle platform. By extending this drug carrying region onto our DNA aptamer strands, we can introduce this ability to our nanocarrier without the need for additional components. We have been able to attach a maximum of ~1,100 molecules of drug to a 15-nm gold nanoparticle with our current design, which is much greater than the average drug loading of any 15-nm nanoparticle found in the literature.
The flexibility and versatility of this platform is evident in each of the components. The nanoparticle, the anchor strand sequence, the doxorubicin binding sequences, the aptamer sequences, and even the drug can each be individually modified depending on a patient’s medical status and the heterogeneity of the SCLC tumor. By modifying the nucleic acid strands which bind the drug, we can regulate both the drug binding and control release as needed. Extending the sequence of the double stranded DNA segment of the nanocarrier increases the drug payload. Furthermore, the nanocarrier can be programmed to bind specifically to targeted cells by using either a single type of aptamer or an array of SCLC-cell-specific aptamers.
Currently, we are investigating regulation of the specificity and binding constant of our nanocarrier by modulating use of the aptamers. By attaching multiple DNA aptamers, the resulting nanoparticle is expected to act as a “molecular octopus” increasing the binding constant of our platform by avidity, and is able to target different markers on the surface of many SCLC cell lines. This means that once the SCLC cell lines present in a tumor are identified, our nanocarrier can specifically target that particular tumor as opposed to general small-cell lung cancer cases. Furthermore, the exact amount of drug needed to kill the tumor can be delivered to a patient, rather than targeting the cancer with an excess of drugs. The use of biohybrid strategies in the creation of novel controlled and targeted drug release carriers has significant potential to affect a number of cancer treatment regimes. We have synthesized, characterized, and optimized a novel gold nanoparticle platform that utilizes an avidity driven process capable of finely tuning the size of the carrier, quantity of drug, binding constant, and specificity towards particular cell lines, created as an application for a personalized treatment regime to individual cancer patients.