A new generic platform for PET imaging based on 68Ga-labeled Pept-insTM: from infectious disease to cancer imaging

70 Objectives: The Pept-in technology is based on a highly specific beta-sheet aggregation of a target protein, induced by short amyloidogenic peptides called Pept-ins (7-20 AA). Pept-In sequences are derived from aggregation-prone regions present in the target protein. They provide a generic platform for diagnostics similar to antibodies and derivatives. However, the rapid production by solid-phase peptide synthesis results in lower cost for production and a higher production throughput with lower batch-to-batch variation compared to antibodies and derivatives. Gallardo et al. (2016, Science) designed an amyloidogenic peptide called vascin that inhibits VEGFR2 function by inducing aggregation of this receptor with high specificity. Furthermore, Khodaparast et al. (2018, Nature Communications) showed that the sequence specificity of beta-sheet aggregation can also be exploited to target redundant aggregation-prone regions in the E. coli proteome by the Colpeptin1 amyloidogenic peptide, thereby inducing proteostatic collapse leading to bacterial cell death. The observed specificity of the amyloid toxicity indicates the large potential of radiolabeled Pept-ins to be developed for PET imaging. Methods: Vascin and Colpeptin1 were modified for 68Ga-labeling by synthesis of [68Ga]Ga-NODAGA-PEG4-vascin and [68Ga]Ga-NODAGA-PEG2-Colpeptin1. Since proline is a known beta-sheet structure breaker, proline-mutated variants were synthesized as controls to obtain [68Ga]Ga-NODAGA-PEG4-vascin(Pro) and [68Ga]Ga-NODAGA-PEG2-Colpeptin1(Pro). Specific in vivo accumulation at the target site was evaluated by dynamic 3 hour µPET imaging in a mouse melanoma tumor model for vascin and in an E. coli muscle infection model for radiolabeled Colpeptin1. Biodistribution studies were executed in the same mouse models. Results: Radiolabeled vascin and Colpeptin1 provided good target-to-background contrast in PET images with high specificity, since for vascin tumor-to-muscle SUV ratios (T/M SUVR, foreleg muscle as reference tissue of non-specific binding) were significantly higher than for its proline-mutated variant at all time points (p