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

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.

Enhancing Specific Disruption of Intracellular Protein Complexes by Hydrocarbon Stapled Peptides Using Lipid Based Delivery.

Linear peptides can mimic and disrupt protein-protein interactions involved in critical cell signaling pathways. Such peptides however are usually protease sensitive and unable to engage with intracellular targets due to lack of membrane permeability. Peptide stapling has been proposed to circumvent these limitations but recent data has suggested that this method does not universally solve the problem of cell entry and can lead to molecules with off target cell lytic properties. To address these issues a library of stapled peptides was synthesized and screened to identify compounds that bound Mdm2 and activated cellular p53. A lead peptide was identified that activated intracellular p53 with negligible nonspecific cytotoxicity, however it still bound serum avidly and only showed a marginal improvement in cellular potency. These hurdles were overcome by successfully identifying a pyridinium-based cationic lipid formulation, which significantly improved the activity of the stapled peptide in a p53 reporter cell line, principally through increased vesicular escape. These studies underscore that stapled peptides, which are cell permeable and target specific, can be identified with rigorous experimental design and that these properties can be improved through use with lipid based formulations. This work should facilitate the clinical translation of stapled peptides.