PO-517 Peptide-based diagnostic in vivo targeting of membrane Hsp70 positive tumours

Abstract

IntroductionHeat shock protein 70 (Hsp70, HSP1A1), the major stress-inducible stress response protein, is frequently overexpressed in tumour cells of many entities. Hsp70 plays a promotive role in the development, viability and metastatic spread of tumour cells, in vivo. In contrast to normal cells, next to its cytoplasmic localization Hsp70 is additionally found on the plasma membrane of many different tumour types. For tumour cell-selective in vivo targeting, we developed an membrane Hsp70 specific, peptide-based tumour targeting probe, termed ‘Tumour cell penetrating peptide’ (TPP).Material and methodsThe internalisation kinetics of the Hsp70 peptide tracer into tumour cells was determined by flow cytometry. The in vivotumour targeting capacity of fluorescence- or 89Zr radio-labelled TPP based probes were assessed by near infrared fluorescence imaging and PET/CT measurements, following intravenous administration of the compounds. For in vivo imaging, preclinical tumour models of syngeneic, spontaneous, chemically or genetically induced as well as xenografted tumours were used.Results and discussionsBy mimicking the oligomerization domain of Hsp70, binding specificity and affinity (Kd=19 nM) of TPP was achieved. Following the rapid intracellular turnover rate of membrane bound Hsp70, TPP is continuously internalised into tumour cells, leading to a rapid intracellular accumulation. In accordance, following intravenous administration in tumour bearing mice, the tracer is effectively protected from body clearance, which results in a high tumor-to-normal tissue signal ratio and precise tumour delineation within 24 hour after injection. In vivo, TPP accumulation reliably reflects the mHsp70 expression profiles of differently Hsp70 expressing tumour types. The peptide thereby differentiates between tumour cells and cells of the tumour microenvironment, such as tumor-associated macrophages and fbroblasts, which were found to be membrane-Hsp70 negative. Compared to a small molecule αvβ3-integrin antagonist probe, TPP based probes offer preferably high tumor-to-background contrast and tumor-specific signal intensity in the tested tumour models.ConclusionTPP provides a useful tool for multimodal imaging of tumours and metastases that might help to improve our understanding of tumour biology and allow the establishment of improved diagnostic procedures and more accurate therapeutic monitoring. TPP might also be a promising platform for tumor-specific drug delivery and other Hsp70- based targeted therapies.