SPECT/CT Imaging, Biodistribution and Radiation Dosimetry of a 177Lu-DOTA-Integrin αvβ6 Cystine Knot Peptide in a Pancreatic Cancer Xenograft Model

Sachindra Sachindra; Teresa Hellberg; Samantha Exner; Sonal Prasad; Nicola Beindorff; Stephan Rogalla; Richard Kimura; Sanjiv Sam Gambhir; Bertram Wiedenmann; Carsten Grötzinger

doi:10.3389/fonc.2021.684713

SPECT/CT Imaging, Biodistribution and Radiation Dosimetry of a ¹⁷⁷Lu-DOTA-Integrin αvβ6 Cystine Knot Peptide in a Pancreatic Cancer Xenograft Model

Front Oncol. 2021 May 31:11:684713. doi: 10.3389/fonc.2021.684713. eCollection 2021.

Authors

Affiliations

¹ Department of Hepatology and Gastroenterology, Charité - Universitätsmedizin Berlin, Berlin, Germany.
² Berlin Experimental Radionuclide Imaging Center (BERIC), Charité - Universitätsmedizin Berlin, Berlin, Germany.
³ Department of Nuclear Medicine, Charité-Universitätsmedizin Berlin, Berlin, Germany.
⁴ Department of Radiology, Molecular Imaging Program at Stanford, Canary Center for Cancer Early Detection, Stanford University, Stanford, CA, United States.
⁵ Molecular Cancer Research Center (MKFZ), Charité - Universitätsmedizin Berlin, Berlin, Germany.
⁶ German Cancer Consortium (DKTK), Berlin, Germany.
⁷ German Cancer Research Center (DKFZ), Heidelberg, Germany.

Abstract

Introduction: Pancreatic ductal adenocarcinoma (PDAC) is one of the most aggressive malignant neoplasms, as many cases go undetected until they reach an advanced stage. Integrin αvβ6 is a cell surface receptor overexpressed in PDAC. Consequently, it may serve as a target for the development of probes for imaging diagnosis and radioligand therapy. Engineered cystine knottin peptides specific for integrin αvβ6 have recently been developed showing high affinity and stability. This study aimed to evaluate an integrin αvβ6-specific knottin molecular probe containing the therapeutic radionuclide ¹⁷⁷Lu for targeting of PDAC.

Methods: The expression of integrin αvβ6 in PDAC cell lines BxPC-3 and Capan-2 was analyzed using RT-qPCR and immunofluorescence. In vitro competition and saturation radioligand binding assays were performed to calculate the binding affinity of the DOTA-coupled tracer loaded with and without lutetium to BxPC-3 and Capan-2 cell lines as well as the maximum number of binding sites in these cell lines. To evaluate tracer accumulation in the tumor and organs, SPECT/CT, biodistribution and dosimetry projections were carried out using a Capan-2 xenograft tumor mouse model.

Results: RT-qPCR and immunofluorescence results showed high expression of integrin αvβ6 in BxPC-3 and Capan-2 cells. A competition binding assay revealed high affinity of the tracer with IC₅₀ values of 1.69 nM and 9.46 nM for BxPC-3 and Capan-2, respectively. SPECT/CT and biodistribution analysis of the conjugate ¹⁷⁷Lu-DOTA-integrin αvβ6 knottin demonstrated accumulation in Capan-2 xenograft tumors (3.13 ± 0.63%IA/g at day 1 post injection) with kidney uptake at 19.2 ± 2.5 %IA/g, declining much more rapidly than in tumors.

Conclusion: ¹⁷⁷Lu-DOTA-integrin αvβ6 knottin was found to be a high-affinity tracer for PDAC tumors with considerable tumor accumulation and moderate, rapidly declining kidney uptake. These promising results warrant a preclinical treatment study to establish therapeutic efficacy.

Keywords: dosimetry; integrin αvβ6; knottin peptide; pancreatic ductal adenocarcinoma; radioligand therapy; tumor targeting.