Synthesis and biological evaluation of CXCR4 chemokine receptor antagonists

Nicholson, Kate Louise

Abstract

The CXCR4 chemokine receptor is known to be overexpressed in many types of cancer as well as being involved in several stages of metastasis, which is responsible for the majority of deaths in cancer patients. Molecular imaging techniques, such as positron emission tomography (PET), are being used in the design of early stage CXCR4 expressing cancer diagnosis agents which can be followed by the administration of CXCR4 specific drugs targeting to an individual’s specific cancer treatment requirements to prevent the spread of cancer. Incorporation of positron emitting radioisotopes such as ¹⁸F and ⁶⁴Cu into a CXCR4 specific compound allows visualisation of the locations that the drug has accumulated. This can facilitate the diagnosis of a CXCR4 expressing cancer as large volumes of emission signals will be detected in tumours. Following diagnosis, high CXCR4-affinity targeted compounds can be administrated which prevent CXCR4’s binding partner, CXCL12, activating the receptor and enabling metastasis. This work focuses on the development of high affinity CXCR4 antagonists which can be used in therapeutic and diagnostic applications.

A series of configurationally restricted complexes of copper(II), zinc(II) and nickel(II), where the metal ion is coordinated to tris-macrocycles, were synthesised. Tris-macrocycles have the potential to show improved affinity for the CXCR4 receptor because the third macrocyclic ring can facilitate more interactions with the CXCR4 receptor than reported bis-macrocycles, due to the extra interactions possible with the aspartate rich receptor surface. Biological studies revealed the tris-macrocyclic series has high affinity for CXCR4. [Zn₃18] ⁶⁺ showed nanomolar activity with an IC₅₀ value of 0.84 nM, 14 times more potent than the FDA approved drug AMD3100. Another high affinity tris-macrocycle, [Zn₃19] ⁶⁺ showed an IC₅₀ value of 1.86 nM also significantly lower than ADM3100. The high affinity compounds, [Zn₃18] ⁶⁺ and [Zn₃19] ⁶⁺, were radiolabelled with ⁶⁴Cu via transmetalation. Crude-radiochemical yields (crude-RCY) of 79% and 62% were achieved for ⁶⁴CuZn₂[18] and ⁶⁴CuZn₂[19] respectively. The complexes were identified as strongly hydrophilic with calculated LogP values of -3.69 and -2.20 for ⁶⁴CuZn₂[18] and ⁶⁴CuZn₂[19] respectively.

A series of rigidified bis-macrocycle copper(II) and zinc(II) complexes were synthesised and explored as imaging agents. Routes to incorporate ¹⁸F and ⁶⁸Ga into the bis-macrocycles for applications in PET imaging were explored. Mono-macrocycles were synthesised and used in a series of test reactions to evaluate a range of pendant arm functionalisations including nitro, amine, azide and alkyne. Subsequently, azide functionalised rigidified bis-macrocycle copper(II) and zinc(II) complexes for use in copper-free click reactions were synthesised which provided an effective route to incorporate ¹⁸F into macrocycles. Biological studies identified that the functionalised bis-macrocycle complexes showed high affinity towards the CXCR4 receptor. The key compound was [Zn₂32] ⁴⁺ which showed IC₅₀ values of 3.22 nM, more than 3 times lower than AMD3100.

A series of surface plasmon resonance (SPR) experiments were conducted to develop a method to determine the residence time of macrocycles on the CXCR4 receptor. A range of approaches, such as intact cell immobilisation, intact cell capture and receptor capture, were studied but all methods had drawbacks therefore association and dissociation rates of macrocycles and the CXCR4 receptor were not ascertained.

This work highlights important steps towards the diagnosis of CXCR4 expressing cancers with the use of highly stable tris-macroycles. Furthermore, initial steps to incorporate the most readily available radioisotope, ¹⁸F, into macrocycles have been identified. Progress towards the development of high affinity, anti-metastatic therapeutic agents, in CXCR4 expressing cancers, has been made with the synthesis and in vitro evaluation of configurationally restricted tris-macrocycle metal complexes. Key compounds in this series were [Zn₃18] ⁶⁺ and [Zn₃19] ⁶⁺ which showed significantly better affinity for the CXCR4 receptor than AMD3100 and low toxicity.

Citation

Nicholson, K. L. Synthesis and biological evaluation of CXCR4 chemokine receptor antagonists. (Thesis). University of Hull. https://hull-repository.worktribe.com/output/4222198

• Thesis Type: Thesis
• Deposit Date: Feb 26, 2020
• Publicly Available Date: Feb 23, 2023
• Keywords: Chemistry
• Public URL: https://hull-repository.worktribe.com/output/4222198
• Additional Information: Department of Chemistry, The University of Hull
• Award Date: Dec 1, 2014