96: Targeting Gastric Cancer Metastatic Lymph Nodes with a NIR-fluorescent anti-CEA Antibody Enables Their Identification for Resection in Orthotopic Mouse Models

Friday, March 22, 2024

11:42am – 11:52am ET

Location: C102

Abstract Presenter(s)

Kristin Cox, MD (she/her/hers)

Resident Physician
Department of Surgery, University of California San Diego, La Jolla, CA
San Diego, California, United States

Submitter(s)

Kristin Cox, MD (she/her/hers)

Resident Physician
Department of Surgery, University of California San Diego, La Jolla, CA
San Diego, California, United States

Author(s)

Kristin Cox, MD (she/her/hers)

Resident Physician
Department of Surgery, University of California San Diego, La Jolla, CA
San Diego, California, United States
SA

Siamak Amirfakhri, PhD

Post-doctoral research scientist
VA San Diego Healthcare System, San Diego, CA, United States
Thinzar M. Lwin, MD (she/her/hers)

Assistant Professor
Department of Surgical Oncology, City of Hope National Medical Center, Duarte, CA, California, United States
PG

Pradipta Ghosh, MD

Professor
Department of Cellular and Molecular Medicine, University of California San Diego, La Jolla, CA, United States
MO

Marygorret Obonyo, PhD

Associate Professor
Department of Medicine, University of California San Diego, La Jolla, CA, United States
RH

Robert Hoffman, PhD

Scientist
AntiCancer Inc., San Diego CA, United States
PY

Paul Yazaki, PhD

Professor
Department of Immunology and Theranostics, Beckman Research Institute of the City of Hope, Duarte, CA, United States
Michael Bouvet, MD

Professor
Department of Surgery, University of California San Diego, United States

Disclosure(s):

Kristin Cox, MD: No financial relationships to disclose

Introduction: Gastric cancer poses a major diagnostic and therapeutic challenge. Improved visualization of tumor margins and nodal disease with tumor-specific fluorescent markers could improve outcomes.

Methods: To establish orthotopic models, 10⁶ cells of the gastric cancer cell line, MKN45, were suspended in 50 µl of equal parts PBS and Matrigel. A 1cm incision was made in anesthetized athymic mice through which the stomach was delivered. Using a 29 g needle, the cells were injected into the gastric wall before it was returned to the abdomen and the incision was closed. Tumors were allowed to grow for 2 – 3 months prior to performing imaging studies. For tumor labeling, M5A (humanized anti-CEA mAb) and IgG as a control, were conjugated with the near infrared dye IRDye800CW. Mice received 50 µg M5A-IR800 (n = 16) or 50 µg IgG-IR800 (n = 10) intravenously and were imaged 72 hours later. Fluorescence imaging was performed using the LI-COR Pearl Imaging System. A tumor to background ratio (TBR) was calculated by dividing mean fluorescence intensity of the tumor versus adjacent stomach tissue. After imaging the gastric tumors, the stomach and part of the liver were removed to image and collect lymph nodes. Lymph nodes were sectioned fully and reviewed for presence or absence of cancer.

Results: Flat infiltrative tumors were identified in 20 of the 26 mice (11 treated with M5A-IR800 and 9 treated with IgG-IR800). M5A-IR800 administration resulted in bright labeling of otherwise invisible tumors with an average TBR of 4.08 (SE ± 0.42). Labeling with IgG-IR800 was non-specific, with an average TBR of 0.79 (SE ± 0.23). 10 lymph nodes were collected from the mice treated with M5A-IR800, of which 7 were found to contain cancer. In the mice treated with IgG-IR800, 11 of the 14 lymph nodes contained cancer. The TBR for cancer-positive nodes treated with M5A-IR800 was 2.84 (SE ± 0.96) while those negative for cancer had a TBR of 1.56 (SE ± 0.29). IgG-IR800 treated mice had an average TBR of 0.73 (SE ± 0.05) for cancer-positive lymph nodes, while those negative for cancer had a TBR of 0.62 (SE ± 0.12). A statistically significant difference was seen in the TBRs of cancer-positive lymph nodes labeled with M5A-IR800 and IgG-IR800, p-value < 0.001 (Figure 1C).

Conclusions: Humanized anti-CEA (M5A) antibodies conjugated to fluorescent dyes provide bright labeling of lymph nodes containing metastatic gastric cancer. This tumor-specific fluorescent antibody is a promising potential clinical tool for identifying metastatic gastric cancer.

Learning Objectives:

Recognize the need for improved tools for identifying metastatic disease in gastric cancer.
Critically appraise a fluorescent antibody's ability to label lymph nodes containing metastatic gastric cancer.
Understand the role of fluorescent labeling of tumors for improved visualization at time of surgical resection.