ImmunoPET Imaging of TIM‐3 in Murine Melanoma Models

Abstract

T cell immunoglobulin and mucin domain-containing-3 (TIM-3) is an immune checkpoint expressed mainly on CD4 + and CD8 + T cells. In addition to negatively regulating inflammatory T cell function, TIM-3 is a promising immunotherapy target. Herein, the aim is to develop an immuno-positron emission tomography (immunoPET) probe for noninvasively characterizing TIM-3 expression. Flow cytometry is used to detect the expression levels of TIM-3 in B16F10 cells. RMT3-23, a rat antimouse TIM-3-specific monoclonal antibody, is radiolabeled with 64 Cu and the performance of 64 Cu-NOTA-RMT3-23 is interrogated by immunoPET in murine melanoma models before and after radiation therapies. Biodistribution and immunofluorescent staining studies are carried out after the immunoPET imaging studies. TIM-3 is negatively expressed in B16F10 cells, and its expression is not induced by radiation therapies. ImmunoPET imaging with 64 Cu-NOTA-RMT3-23 precisely tracks the unique distribution of TIM-3-positive lymphocytes in immunocompetent melanoma models, and tumor uptake of the radiotracer is not affected by either single-dose or fractionated radiation therapies. The 64 Cu-NOTA-RMT3-23 immunoPET imaging results are further mirrored by the immunofluorescent staining studies. These results demonstrate the feasibility of 64 Cu-NOTA-RMT3-23 immunoPET in tracking TIM-3 and highlight a new opportunity to optimize TIM-3-targeted immunotherapies with this novel imaging strategy. 1. Introduction With the clinical use of chimeric antigen receptor (CAR)modified T cells and immune checkpoint inhibitors, cancer

ImmunoPET: Antibody-Based PET Imaging in Solid Tumors

“…Some common obstacles to the wide implementation of immunoPET include the high costs, advanced technology to commercially produce pure mAbs, difficulties in conjugation and in vivo tracer stability, as well as high circulation time and physiologic uptake after administration. Recent developments are answering these needs ( 97 , 411 ) and will continue to evolve. Although immunoPET can become a diagnostic tool in specific conditions, its primary role seems to be a complementary imaging tool for therapy guidance.…”

“…Moreover, radiotherapy-induced PD-L1 upregulation was demonstrated in melanoma mouse models, using radiolabeled anti-PD-L1 Abs ( 348 , 349 ). Another immune checkpoint, T-cell immunoglobulin and mucin domain-containing-3 (TIM-3), was a successful target for murine melanoma models ( 97 ). One clinical study evaluated [ 89 Zr]Zr-pembrolizumab in melanoma, reporting relations between tracer uptake and response to therapy and survival in patients with advanced or metastatic disease ( 347 ).…”

Molecular imaging to support cancer immunotherapy

“…[ 89 Zr]Zr-TIGITmAb detected TIGIT+tumor infiltrating lymphocytes in a melanoma allograft mouse model. 32 T cell immunoglobulin and mucin domain-containing-3 (TIM-3) is another immune checkpoint for which a PET tracer was developed, 33 namely a rat anti-mouse TIM-3specific monoclonal antibody [ 64 Cu]Cu-NOTA-RMT3-23.…”

Current state and upcoming opportunities for immunoPET biomarkers in lung cancer

“…To our knowledge, only one study has been performed with a TIM-3 targeting tracer. Wei et al (2020) have developed 64 Cu-NOTA-RMT3-23 to visualize TIM-3 expression in murine models [43]. Their study showed the presence on TIM-3 positive cells on the edge of the tumors as well as high uptake in the liver and spleen.…”