ImmunoPET for mesothelin positive tissues using bio-orthogonal in-vivo click chemistry

Mesothelin is a membrane bound antigen overexpressed in a wide array of cancers including ovarian, pancreatic, lung, and triple negative breast cancers. Here a full-length IgG antibody developed against mesothelin, called MESO-HSS1 was conjugated for immunoPET imaging and assessed in-vivo in a H956 mesothelin positive model. Furthermore, random lysine conjugation as well as a site selective conjugation method were compared in two pretargeting models for overall tumor uptake alongside non target organs and tumor to organ ratios. Overall, [⁸⁹Zr]Zr-DFO-MESO-HSS1 was found to be a suitable immunoPET radiotracer for the detection of the mesothelin low cancer line H596 as early as 24 h post injection with up to 20.1 % injected dose per gram by 144 h. Furthermore, in pretargeted models, lysine conjugation of TCO-Lys-MESO-HSS1 with [⁶⁴Cu]Cu-Sar-Tz yielded the highest tumor uptake at 2.6 % injected dose per gram at 24 h. Imaging 4 h post injection of [¹⁸F]F-Al-NOTA-PEG₇-Tz however was best with TCO-SS-MESO-HSS1 with improved tumor to organ ratios as expected from site selective modifications. High tumor to pancreas ratios suggests mesothelin imaging could be a highly effective diagnostic for pancreatic cancer identification. Together these data show MESO-HSS1 as a direct immunoPET or pretargeting agent as a viable immunoPET system for imaging mesothelin positive cancers.