Preclinical evaluation of a novel CEA‐targeting near‐infrared fluorescent tracer delineating colorectal and pancreatic tumors

Abstract

Surgery is the cornerstone of oncologic therapy with curative intent. However, identification of tumor cells in the resection margins is difficult, resulting in non-radical resections, increased cancer recurrence and subsequent decreased patient survival. Novel imaging techniques that aid in demarcating tumor margins during surgery are needed. Overexpression of carcinoembryonic antigen (CEA) is found in the majority of gastro-intestinal carcinomas, including colorectal and pancreas. We developed ssSM3E/800CW, a novel CEA-targeted near-infrared fluorescent (NIRF) tracer, based on a disulphide stabilized single-chain antibody fragment (ssScFv), to visualize colorectal and pancreatic tumors in a clinically translatable setting. The applicability of the tracer was tested for cell and tissue binding characteristics and dosing using immunohistochemistry, flow cytometry, cell-based plate assays and orthotopic colorectal (HT-29, well differentiated) and pancreatic (BXPC-3, poorly differentiated) xenogeneic human-mouse models. NIRF signals were visualized using the clinically compatible FLARE™ imaging system. Calculated clinically relevant doses of ssSM3E/800CW selectively accumulated in colorectal and pancreatic tumors/cells, with highest tumor-to-background ratios of 5.1±0.6 at 72 h post-injection, which proved suitable for intra-operative detection and delineation of tumor boarders and small (residual) tumor-nodules in mice, between 8 h and 96 h post-injection. Ex vivo fluorescence imaging and pathologic examination confirmed tumor-specificity and the distribution of the tracer. Our results indicate that ssSM3E/800CW shows promise as a diagnostic tool to recognize colorectal and pancreatic cancers for fluorescent-guided surgery applications. If successful translated clinically, this tracer could help improve the completeness of surgery and thus survival.

Setting Standards for Reporting and Quantification in Fluorescence-Guided Surgery

“…Noise is the sum of autofluorescence, scattering and reflection events and can make it difficult to discern the actual fluorescence signal. A SBR 9 2 is generally considered adequate to differentiate target from background [25]. Nevertheless, there are clinical trials in which SBR values below 2 are described as sufficient for intraoperative FI [26].…”

A promising cancer diagnosis and treatment strategy: targeted cancer therapy and imaging based on antibody fragment

“…For instance, Tolner et al constructed a nearinfrared fluorescent tracer based on scFv. The fluorescent tracer selectively accumulates at the tumour site and has an excellent biodistribution, and can be applied to identify colorectal cancer and pancreatic cancer with good clinical transformation prospects [62].…”

Les anticorps, outils de choix pour la chirurgie guidée par fluorescence

“…Pour ces raisons, plusieurs équipes s'intéressent à l'éva-analyse aux anticorps et à leurs fragments et, plus précisément, aux molécules ayant été évaluées en clinique. En effet, les anticorps monoclonaux (AcM) et certaines molécules dérivées de ces anticorps semblent être la meilleure option pour délivrer les colorants NIR aux sites tumoraux puisque les conjugués anticorps-colorant peuvent combiner la spécificité tumorale exceptionnelle des anticorps avec des performances de fluorescence optimales de colorants dédiés [15][16][17][18][19][20][21]. Il aura fallu plus de vingt ans pour passer de la souris à l'homme [15,16] et des travaux des pionniers [17] aux nombreuses études cliniques actuelles, mais l'application clinique de l'immunophotodétection (IPD, c'est-à-dire l'utilisation de colorants couplés de façon covalente à des anticorps spécifiques pour la détection peropératoire des tumeurs) semble maintenant très proche [22].…”

“…Avec de plus en plus de molécules en études cliniques [11,12], dont deux en phase III (NCT03180307 pour vasculaires [42]. Il existe actuellement un consensus pour utiliser des colorants dans le proche infra-rouge (650-900 nm [19,44] ou les nanobodies [45,46], en se fondant sur l'argument qu'une cinétique courte est plus favorable et que de petites entités peuvent pénétrer plus profondément dans les nodules tumoraux. Les différentes études réalisées jusqu'à présent montrent que les conjugués préparés avec des anticorps intacts pénètrent également bien dans les tumeurs, y compris dans des tumeurs réputées difficiles d'accès telles que les adénocarcinomes du pancréas [39].…”