Abstract 3913: Conjugate-SELEX, a novel screening method, identifies aptamers that deliver payload to the cytosol of target cells
Authors: Mu Qingshan , Annapragada Akshaya , Srivastava Mayank , Thiviyanathan Varatharasa , Li Xin , Gorenstein David , Annapragada Annanth , Vigneswaran Nadarajah 
Published: July 2016

Abstract
Introduction: Delivery of a nanoparticle payload to a specific cellular compartment is a prized goal of cancer nanomedicine. The well-known SELEX (systematic evolution of ligands by exponential enrichment) process is often used to identify aptamers that localize to target cellular compartments, but such aptamers cannot be guaranteed to traffic an attached payload nanoparticle to the target as well. We hypothesized that to find an aptamer capable of trafficking a nanoparticle to a specific cellular compartment, the screened library must consist of aptamer-nanoparticle conjugates. We therefore designed a screening procedure we call “Conjugate-SELEX”. In this process, the aptamer library is conjugated to liposomal nanoparticles, creating a nanoparticle-aptamer conjugate library for screening. At each round of Conjugate-SELEX, aptamers recovered from the desired cellular compartment are amplified, and used to create the conjugate library for the next round of Conjugate-SELEX. Negative screens against off-target cells (e.g. hepatocytes, unwanted uptake in which, causes many of the toxicities associated with nanoparticle therapeutics) facilitate the identification of an aptamer that efficiently transports payload into target cells while minimizing the uptake in off-target cells. Using fluorescently tagged particles, imaging the cells at each stage verifies the successful transport of the payload particles into the cytosol.
Methods: We used conjugate-SELEX to screen for aptamers that carried an attached nanoparticle payload to the cytosol of UM-SCC-22A oral cancer cell line, while not being taken up by THLE-3 hepatocytes. IonTorrent sequencing of the remaining aptamers after each round demonstrated convergence to a small family of sequences with only one base difference between members. Mass spectrometric proteomics identified the surface receptor bound by these sequences as the neuroblast differentiation-associated protein AHNAK (desmoyokin) a ubiquitous intracellular protein with surface expression exclusively in certain epithelial cell types. Uptake studies with concertedly synthesized hit aptamer sequences showed enhanced uptake of targeted nanoparticles over controls, and increased cytotoxicity of doxorubicin in the nanoparticles over controls.
Conclusions: Conjugate-SELEX is an excellent means of identifying aptamers with the ability to transport attached nanoparticle payloads to targeted cellular compartments, while minimizing off target effects. The technique also lends itself to the identification of surface receptors mediating the trafficking.[D.G., A.A., and N.V. contributed equally to this work.]
Citation Format: Qingshan Mu, Akshaya Annapragada, Mayank Srivastava, Varatharasa Thiviyanathan, Xin Li, David Gorenstein, Annanth Annapragada, Nadarajah Vigneswaran. Conjugate-SELEX, a novel screening method, identifies aptamers that deliver payload to the cytosol of target cells. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3913.