Abstract 705: In vivo audition of tumor homing peptides using high-throughput sequencing and q-PCR

Abstract

Abstract In vivo peptide phage display has been widely used to explore tumor vascular heterogeneity and to develop targeting ligands for the delivery of anticancer drugs and imaging agents. Numerous tumor homing peptides with various targeting specificities have been identified. To select a suitable targeting ligand for a particular tumor from an existing peptide panel, it is crucial to perform unbiased quantitative assessment of in vivo peptide homing. Here we describe an approach for parallel evaluation of in vivo tumor homing of peptide-displaying phage clones. Mice bearing orthotopic xenografts of gliomas, breast tumors, and prostate tumors were intravenously injected with equimolar mix of phage clones displaying 12 different tumor homing or control peptides. After 30 min circulation and removal of blood by perfusion, representation of each phage clone in tumors and control organs was determined by high throughput sequencing (HTS) and quantitative PCR (qPCR). The ratiometric analysis demonstrated a clear and reproducible homing signature for each tumor model. Calibrated copy number data obtained by qPCR correlated well with the HTS analysis. Selected phage clones were validated for tumor homing by conventional single-phage homing studies using immunofluorescence, phage titration, and qPCR. Our study shows that the ratiometric in vivo phage biodistribution analysis can be used to rapidly identify peptides that efficiently deliver payloads to particular tumor types. As the peptides are evaluated side-by-side in a same animal, inter-animal variability is eliminated and the number of animals required is dramatically decreased. The choice of analysis (HTS vs qPCR) depends on the complexity of phage pool to be audited. HTS enables the analysis of highly complex phage pools, but introduces a potential bias owing to multiple DNA amplification steps. On the other hand, qPCR allows precise quantification of the copy number of the target sequences, and is suitable for low complexity pools. Narrowing down a complex pool with HTS followed by precise evaluation with qPCR can be a potential combination of the two analytical methods. Citation Format: Kadri Toome, Tarmo Mölder, Kuldar Kõiv, Pille Säälik, Kazuki N. Sugahara, Erkki Ruoslahti, Tambet Teesalu. In vivo audition of tumor homing peptides using high-throughput sequencing and q-PCR. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 705. doi:10.1158/1538-7445.AM2014-705