Granzyme B PET Imaging of Immune Checkpoint Inhibitor Combinations in Colon Cancer Phenotypes

Abstract

Purpose Immune checkpoint inhibitor (ICI) monotherapy and combination regimens are being actively pursued as strategies to improve durable response rates in cancer patients. However, the biology surrounding combination therapies is not well understood and may increase the likelihood of immune-mediated adverse events. Accurate stratification of ICI response by non-invasive PET imaging may help ensure safe therapy management across a wide number of cancer phenotypes. Procedures We have assessed the ability of a fluorine-labelled peptide, [18F]AlF-mNOTA-GZP, targeting granzyme B, to stratify ICI response in two syngeneic models of colon cancer, CT26 and MC38. In vivo tumour uptake of [18F]AlF-mNOTA-GZP following ICI monotherapy, or in combination with PD-1 was characterised and correlated with changes in tumour-associated immune cell populations. Results [18F]AlF-mNOTA-GZP showed good predictive ability and correlated well with changes in tumour-associated T cells, especially CD8+ T cells; however, overall uptake and response to monotherapy or combination therapies was very different in the CT26 and MC38 tumours, likely due to the immunostimulatory environment imbued by the MSI-high phenotype in MC38 tumours. Conclusions [18F]AlF-mNOTA-GZP uptake correlates well with changes in CD8+ T cell populations and is able to stratify tumour response to a range of ICIs administered as monotherapies or in combination. However, tracer uptake can be significantly affected by preexisting phenotypic abnormalities potentially confusing data interpretation.

Granzyme B PET Imaging of Combined Chemotherapy and Immune Checkpoint Inhibitor Therapy in Colon Cancer

“…[ 18 F]AlF-mNOTA-GZP Radiochemistry NOTA-β-Ala-Gly-Gly-Ile-Glu-Phe-Asp-CHO (mNOTA-GZP) was synthesized using standard Fmoc chemistry and characterized by HPLC and mass spectroscopy as previously described [14]. [ 18 F]AlF-mNOTA-GZP was synthesized as previously described [15]. Briefly, aqueous [ 18 F]fluoride was trapped on a preconditioned Sep-Pak® light (46 mg) Accell™ plus QMA carbonate cartridge, washed with water (5 mL), and eluted with 0.9% w/v saline (0.2 mL).…”

“…Successful therapy response in this preclinical model was determined by the comparison of day 6 baseline tumor volumes with day 21 post therapy tumor volumes separating the treatment arms into two groups, treatment responders (combining complete responders and partial responders into a single group, TR) and treatment non-responders (TNR). This reductionist approach has been used previously to the assessment of the utility of imaging to stratify responders from non-responders but may introduce bias [15,[18][19][20][21]. TRs were identified as final tumor volumes less than 850 mm 3 and include tumors with stable or decreased volumes (tumor volumes are shown in Supplementary Table S1).…”

The aluminium-[18F]fluoride revolution: simple radiochemistry with a big impact for radiolabelled biomolecules

“…Preclinical imaging distinguished between responders and non-responders to monotherapy (anti-PD-1) and combination immunotherapy (anti-PD-1 and anti-CTLA-4) with excellent predictive ability (Larimer et al 2017 ; Goggi et al 2020b ). Goggi et al ( 2020a ) radiolabelled the peptide with the [ 18 F]AlF complex to improve PET sensitivity and spatial resolution. Formulated [ 18 F]AlF-mNOTA-GZP was produced in 50 min from [ 18 F]fluoride in a 17–25% RCY (n.d.c) and a molar activity of 45–90 GBq/μmol.…”

“…The enzyme inhibition efficiency of both 68 Ga and [ 18 F]AlF peptides were similar. The uptake of [ 18 F]AlF-mNOTA-GZP correlated with changes in T cell populations and distinguished responders and non-responders to monotherapy and combination immunotherapy (Goggi et al 2020a ). An automated radiosynthesis of [ 18 F]AlF-mNOTA-GZP has not yet been described.…”

Colorectal Cancer and Immunity: From the Wet Lab to Individuals

“…Western blotting or RT-qPCR can also be performed to assess post-translational modifications or protein/genes expression levels. The whole set of data thus generated then improves our understanding of the mechanisms involved in either sensitivity or resistance to therapeutic interventions ( Figure 3 ) [ 116 , 117 , 118 , 119 , 120 ]. Another major advantage of using syngeneic models is that engrafted cells can easily be manipulated and genetically modified in vitro prior to inoculation.…”