A first-in-human study of [68Ga]Ga-CDI: a positron emitting radiopharmaceutical for imaging tumour cell death.

PURPOSE: This study assesses human biodistribution, radiation dosimetry, safety and tumour uptake of cell death indicator labelled with 68Ga ([68Ga]Ga-CDI), a novel radiopharmaceutical that can image multiple forms of cell death. METHODS: Five participants with at least one extracranial site of solid malignancy > 2 cm and no active cancer treatment in the 8 weeks prior to the study were enrolled. Participants were administered 205 ± 4.1 MBq (range, 200-211 MBq) of [68Ga]Ga-CDI and 8 serial PET scans acquired: the first commencing immediately and the last 3 h later. Participants were monitored for clinical, laboratory and electrocardiographic side effects and adverse events. Urine and blood radioactivity was measured. Spherical volumes of interest were drawn over tumour, blood pool and organs to determine biodistribution and calculate dosimetry. In one participant, tumour specimens were analysed for cell death using terminal deoxynucleotidyl transferase dUTP nick end labelling (TUNEL) staining. RESULTS: [68Ga]Ga-CDI is safe and well-tolerated with no side effects or adverse events. [68Ga]Ga-CDI is renally excreted, demonstrates low levels of physiologic uptake in the other organs and has excellent imaging characteristics. The mean effective dose was 2.17E - 02 ± 4.61E - 03 mSv/MBq. It images constitutive tumour cell death and correlates with tumour cell death on histology. CONCLUSION: [68Ga]Ga-CDI is a novel cell death imaging radiopharmaceutical that is safe, has low radiation dosimetry and excellent biodistribution and imaging characteristics. It has potential advantages over previously investigated radiopharmaceuticals for imaging of cell death and has progressed to a proof-of-concept trial. TRIAL REGISTRATION: ACTRN12621000641897 (28/5/2021, retrospectively registered).

Preclinical Assessment of [68Ga]Ga-Cell Death Indicator (CDI): A Novel hsp90 Ligand for Positron Emission Tomography of Cell Death.

BACKGROUND: 4-(N-(S-glutathionylacetyl)amino) phenylarsonous acid (GSAO) when conjugated with a bifunctional chelator 2,2'-(7-(1-carboxy-4-((2,5-dioxopyrrolidin-1-yl)oxy)-4- oxobutyl)-1,4,7-triazonane-1,4-diyl)diacetic acid (NODAGA) (hereafter referred to as Cell Death Indicator [CDI]), enters dead and dying cells and binds to 90kDa heat shock proteins (hsp90). OBJECTIVE: This study assesses stability, biodistribution, imaging, and radiation dosimetry of [68Ga]- Ga-CDI for positron emission tomography (PET). METHODS: Preparation of [68Ga]Ga-CDI was performed as previously described. Product stability and stability in plasma were assessed using high-performance liquid chromatography. Biodistribution and imaging were conducted in ten healthy male Lewis rats at 1 and 2 h following intravenous [68Ga]Ga-CDI injection. Human radiation dosimetry was estimated by extrapolation for a standard reference man and calculated with OLINDA/EXM 1.1. RESULTS: Radiochemical purity of [68Ga]Ga-CDI averaged 93.8% in the product and 86.7% in plasma at 4 h post-synthesis. The highest concentration of [68Ga]Ga-CDI is observed in the kidneys; [68Ga]Ga-CDI is excreted in the urine, and mean retained activity was 32.4% and 21.4% at 1 and 2 h post-injection. Lower concentrations of [68Ga]Ga-CDI were present in the small bowel and liver. PET CT was concordant and additionally demonstrated focal growth plate uptake. The effective dose for [68Ga]Ga-CDI is 2.16E-02 mSv/MBq, and the urinary bladder wall received the highest dose (1.65E-02 mSv/Mbq). CONCLUSION: [68Ga] Ga-CDI is stable and has favourable biodistribution, imaging, and radiation dosimetry for imaging of dead and dying cells. Human studies are underway.

Preparation of a Dithiol-Reactive Probe for PET Imaging of Cell Death.

Conjugates of 4-(N-(S-glutathionylacetyl)amino)phenylarsonous acid (GSAO) with optical or radionuclide probes are able to image cell death in vivo. GSAO conjugates are retained in the cytosol of dying and dead cells via the formation of covalent bonds between the As(III) ion and the thiol groups of proximal cysteine residues. Here we describe the method for preparing a NODAGA-GSAO conjugate and its radiolabeling with gallium-68 (68Ga-NODAGA-GSAO) for positron-emission tomography (PET) imaging of cell death.