Conjugate-SELEX: A High-throughput Screening of Thioaptamer-liposomal Nanoparticle Conjugates for Targeted Intracellular Delivery of Anticancer Drugs

Patients with advanced head and neck squamous cell carcinoma receiving chemotherapy have a poor prognosis partly due to normal tissue toxicity; therefore, development of a tumor-targeted drug delivery platform to minimize collateral toxicity is a goal of cancer nanomedicine. Aptamers can achieve this purpose. While conventional Systematic Evolution of Ligands by Exponential Enrichment (SELEX) screens aptamer-only libraries and conjugates them to delivery vehicles after selection, we hypothesized that specific delivery requires screening libraries with aptamer-nanoparticle conjugates. We designed a procedure called, Conjugate-SELEX, where liposomal nanoparticles (LNP) conjugated with aptamers is screened to identify aptamers that carried attached LNPs to the human head and neck squamous cell carcinoma cell cytosol. Aptamer-LNPs were simultaneously selected for a low affinity to human hepatocytes, minimizing hepatoxicity and LNP clearance. Post-SELEX Next Generation sequencing demonstrated convergence to a family of sequences with one base difference. Affinity pulldown and proteomics analysis identified the uptake-mediating surface receptor as the neuroblast differentiation-associated protein AHNAK (Desmoyokin), a ubiquitous intracellular protein expressed in certain epithelial cell types. Uptake studies with the lead aptamer-conjugates showed enhanced uptake and increased cytotoxicity induced by doxorubicin in cells treated with aptamer-conjugated LNPs over LNP controls. Conjugate-SELEX identifies aptamers capable of targeted cytosolic delivery of attached LNPs payload, while minimizing off-target delivery. The technique lends itself to identification of uptake-mediating surface receptors.