Development and evaluation of CXCR4 receptor targeted probes for medical imaging applications

Lee, Rhiannon Elizabeth

Abstract

The chemokine receptor CXCR4 has been shown to be overexpressed in over 23 different types of cancers, making it an attractive target for therapeutic and imaging agents. Molecular imaging techniques, such as positron emission tomography (PET) and single photon emission tomography (SPECT), are being used for the development of CXCR4 receptor targeted cancer diagnostic agents. This work exploits the properties of tetraazamacrocycles and their known affinity for the chemokine receptor CXCR4. The inclusion of copper-64, gallium-68, fluorine-18, technetium-99m and optical probes allows the high affinity macrocyclic compounds to be developed as imaging agents.
Copper-64 labelled CXCR4 targeted PET tracers have been reported in the literature (AMD3100 and AMD3465), however, they suffer from transchelation and loss of the radiolabel in vivo. Novel tetraazamacrocyclic tracers [64Cu][Cu5(OAc)](OAc) and [64Cu][Cu25(OAc)2](OAc)2 were produced in a decay corrected RCY of 41.6 ± 4.6% and 75.4 ± 1.5%. Calcium signalling assays gave an IC50 value of 60 nM and 4 nM, respectively. In vitro cell binding experiments showed that [64Cu][Cu5(OAc)](OAc) had a higher affinity for the CXCR4 receptor when compared to other CXCR4 imaging tracers. In vivo experiments carried out in mice revealed the tracer [64Cu][Cu5(OAc)](OAc) to be specific to CXCR4 with an 8-fold higher uptake seen in the CXCR4 positive cell lines compared to the negative; (23.6 ± 2.7; 3.0 ± 0.5 respectively). Importantly no liver uptake was seen when a blocking dose was administered, indicating the improved stability of the CB cyclam structure.
Several approaches for developing a novel gallium-68 CXCR4 targeted PET tracer were investigated. In vitro and in vivo data showed that the inclusion of DOTAGA in [Zn229(OAc)2](OAc)2 resulted in a decrease in affinity. Alternative PEG chain spacer and pretargeted approaches were investigated to overcome this issue. A THP analogue of Pentixafor (P5) was synthesised and radiolabelled in a 76.8% decay corrected RCY. In vivo studies were carried out and showed that the lipophilicity of the THP moiety is detrimental to the biodistribution of the tracer. Inorganic radiofluorination was attempted for the synthesis of fluorine-18 labelled CXCR4 targeting PET probes; with the antagonist [Zn2AlF43(OAc)2](OAc)2 showing high affinity towards the receptor (IC50 = 20 nM).
Novel CXCR4 targeted SPECT tracers such as [99mTc][Cu2Tc51(OAc)2](OAc)2 (IC50 = 16 nM) were synthesised and radiolabelled at up to 46.0% RCY. Optical imaging CXCR4 probes were also developed including a novel aza-BODIPY labelled peptide (P7). The antagonist maintained high affinity (IC50 = 42 nM) towards the CXCR4 receptor with initial confocal experiments indicating that the NIR probe is worthy of further investigation.

Citation

Lee, R. E. Development and evaluation of CXCR4 receptor targeted probes for medical imaging applications. (Thesis). University of Hull. https://hull-repository.worktribe.com/output/4224548

• Thesis Type: Thesis
• Deposit Date: Jan 5, 2023
• Publicly Available Date: Feb 24, 2023
• Keywords: Chemistry
• Public URL: https://hull-repository.worktribe.com/output/4224548
• Additional Information: Department of Chemistry, The University of Hull
• Award Date: Nov 1, 2017