[177Lu]pentixather: Comprehensive Preclinical Characterization of a First CXCR4-directed Endoradiotherapeutic Agent

Abstract

Purpose: Based on the clinical relevance of the chemokine receptor 4 (CXCR4) as a molecular target in cancer and on the success of [⁶⁸Ga]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 [¹⁷⁷Lu]pentixather. Experimental design: CXCR4 affinity, binding specificity, hCXCR4 selectivity and internalization efficiency of [¹⁷⁷Lu]pentixather were evaluated using different human and murine cancer cell lines. Biodistribution studies (1, 6, 48, 96h and 7d p.i.) and in vivo metabolite analyses were performed using Daudi-lymphoma bearing SCID mice. Extrapolated organ doses were cross-validated with human dosimetry (pre-therapeutic and during [¹⁷⁷Lu]pentixather PRRT) in a patient with multiple myeloma (MM). Results: [¹⁷⁷Lu]pentixather binds with high affinity, specificity and selectivity to hCXCR4 and shows excellent in vivo stability. Consequently, and supported by >96% plasma protein binding and a logP=-1.76, delaying whole-body clearance of [¹⁷⁷Lu]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 [¹⁷⁷Lu]pentixather PRRT (7.8 GBq), with the kidneys being the dose-limiting organs. Conclusions: [¹⁷⁷Lu]pentixather shows excellent in vivo 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 [⁶⁸Ga]pentixafor/[¹⁷⁷Lu]pentixather based CXCR4-targeted theranostic concept.

Keywords: CXCR4; PRRT; endoradiotherapy.; pentixafor; pentixather.

Figure 1

Chemical structures of [⁶⁸Ga]pentixafor and [¹⁷⁷Lu]pentixather

Figure 2

A: Binding of [¹⁷⁷Lu]pentixather to wild type (wt) CHO-K1 cells and CHO-K1 cells transiently transfected with HA-tagged hCXCR4, mCXCR4, hCXCR7 and mCXCR7. Cells were incubated with [¹⁷⁷Lu]pentixather (1 nM) at 37°C for 60 min in the absence (white bars) and presence (grey bars) of competitor (100 µM AMD3100). Experiments were carried out in triplicate, and data are means±SD. B: Binding and internalization kinetics of [¹⁷⁷Lu]pentixather (1 nM) in Daudi lymphoma cells (37°C). Data are corrected for non-specific binding/internalization in the presence of 100 µM AMD3100. Experiments were performed in triplicate, and data are means±SD. C: Binding of [¹⁷⁷Lu]pentixather to different lymphoma (Daudi), AML (MV4-11, THP-1, Molm-13) and multiple myeloma (MM.1S, RPMI, OPM-2) cell lines. Cells were incubated with [¹⁷⁷Lu]pentixather (1 nM) at 37°C for 60 min. Data are corrected for non-specific binding in the presence of 100 µM AMD3100. Experiments were performed in triplicate, and data are means±SD. D: CXCR4 expression levels on the assayed cell lines determined via flow cytometry. E: Binding of [¹⁷⁷Lu]pentixather to human blood cells. Whole blood from a healthy donor was incubated with [¹⁷⁷Lu]pentixather at RT for 15 min in the absence (white bars) and presence (grey bars) of 100 µM AMD3100. Experiments were performed in triplicate, and data are means±SD.

Figure 3

A: Comparative biodistribution of [⁶⁸Ga]pentixafor and [¹⁷⁷Lu]pentixather in Daudi (human B cell lymphoma) xenograft bearing CB17-SCID mice (groups of n=5) at 90 and 60 min p.i., respectively. Uptake values are given in %iD/g and are means±SD. B: Comparison of the tracer kinetics of [¹⁷⁷Lu]pentixather in kidneys and liver of the multiple myeloma patient (f, 54y) in this study with mouse biodistribution data. Total organ uptake is given in % of the injected activity (%iD). Patient data are depicted in green (pre-therapeutic injection, 197 MBq [¹⁷⁷Lu]pentixather) and black ([¹⁷⁷Lu]pentixather therapy, 7.8 GBq), mouse data are depicted in red. Open circles represent data for kidneys, filled dots data for liver. C: Whole body planar imaging of the multiple myeloma patient in this study at 22h after [¹⁷⁷Lu]pentixather therapy (7.8 GBq). D: Corresponding SPECT/CT images at 23h after [¹⁷⁷Lu]pentixather therapy (7.8 GBq).