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.