[Lu]pentixather: Comprehensive Preclinical Characterization of a First CXCR4-directed Endoradiotherapeutic Agent.

Based on the clinical relevance of the chemokine receptor 4 (CXCR4) as a molecular target in cancer and on the success of [Ga]pentixafor as an imaging probe for high-contrast visualization of CXCR4-expression, the spectrum of clinical CXCR4-targeting was expanded towards peptide receptor radionuclide therapy (PRRT) by the development of [Lu]pentixather. CXCR4 affinity, binding specificity, hCXCR4 selectivity and internalization efficiency of [Lu]pentixather were evaluated using different human and murine cancer cell lines. Biodistribution studies (1, 6, 48, 96h and 7d p.i.) and metabolite analyses were performed using Daudi-lymphoma bearing SCID mice. Extrapolated organ doses were cross-validated with human dosimetry (pre-therapeutic and during [Lu]pentixather PRRT) in a patient with multiple myeloma (MM). [Lu]pentixather binds with high affinity, specificity and selectivity to hCXCR4 and shows excellent stability. Consequently, and supported by >96% plasma protein binding and a logP=-1.76, delaying whole-body clearance of [Lu]pentixather, tumor accumulation was high and persistent, both in the Daudi model and the MM patient. Tumor/background ratios (7d p.i.) in mice were 499±202, 33±7, 4.0±0.8 and 116±22 for blood, intestine, kidney and muscle, respectively. In the patient, high tumor/kidney and tumor/liver dose ratios of 3.1 and 6.4 were observed during [Lu]pentixather PRRT (7.8 GBq), with the kidneys being the dose-limiting organs. [Lu]pentixather shows excellent CXCR4-targeting characteristics and a suitable pharmacokinetic profile, leading to high tumor uptake and retention and thus high radiation doses to tumor tissue during PRRT, suggesting high clinical potential of this [Ga]pentixafor/[Lu]pentixather based CXCR4-targeted theranostic concept.