Next-generation aptamers for faster, safer, more sensitive in vivo PET imaging - Abstract
Significance: ImmuoPET is a powerful in vivo imaging technique with unique advantages over standard of care ex vivo
methods to improve cancer diagnosis, monitoring and treatment selection. Despite ImmunoPET’s potential, standard
antibody-based targeting methods result in long multi-day procedures, insufficient specificity and contrast for early detection,
and risk of adverse immunological response with repeated use. While solutions such as minibodies or affibodies can resolve
some of these issues, no complete solution to all three of these challenges is available. Aptamers, single-stranded nucleic
acid ligands, can yield high binding affinity and specificity to a target, favorable pharmacokinetics, and a highly non-
immunogenic composition. However, aptamers have been stymied in clinical imaging due to rapid nuclease-mediated
degradation and difficulty retaining affinity in vivo within biological environments, preventing them from accumulating in
target tissue in sufficient quantities. Hypothesis: Next-gen aptamer targeting agents, designed with increased longevity and
performance within in vivo environments, offer a non-immunogenic alternative to antibody-based targeting agents with the
possibility of increased imaging quality and favorable pharmacokinetics. Preliminary Data: Aptitude has developed
Chemically-Augmented Particle Display (CAPD), a novel platform that yields next-gen aptamers with unprecedented
affinity, specificity, and in vivo stability via a novel non-SELEX approach of ultra-high-throughput quantitative screening.
Aims: In this proposal, we aim to utilize CAPD to develop and validate an initial suite of next-gen aptamer-based
immunoPET imaging agents, and then compare to established antibody-based methods in an animal model. First, we will
use CAPD to create next-gen aptamers to an angiogenesis marker, VEGF, and a checkpoint marker, PD-L1. We will
synthetize and conjugate aptamers for radiolabeling, and characterize their affinity, specificity, and stability in human serum.
We will validate our 68Ga-labeled anti-VEGF aptamer in vivo, and with an ovarian cancer xenograft model, assess image
development time, sensitivity and biodistribution. We will compare to 89Zr-labeled-bevacizumab, the radiolabeled form of
Avastin, an FDA-approved anti-VEGF therapy, previously validated in immunoPET imaging. If successful, this study will
support both the validation of our aptamer imaging agents and the applicability of our aptamer generation platform, which
we plan to use to create a broad suite of safer, faster, and more sensitive in vivo imaging agents for PET.
