Abstract 6027: 89Zr-matuzumab and 225Ac-matuzumab as a theranostic for epidermal growth factor receptor-positive KRAS wild-type colorectal and breast cancer xenografts

Abstract

Abstract Background: About 80% of colorectal cancer (CRC) and 50 % of Triple-Negative breast cancer (TNBC) patients overexpress epidermal growth factor receptor (EGFR). Mutations in the KRAS oncogene (present in 40% of mCRC) lead to constitutive over-activation of EGFR and drive de novo resistance to anti-EGFR drugs. Here, we propose to target KRAS-mutant/BRAF mutant EGFR positive mCRC and TNBC using 225Ac-labeled matuzumab, a humanized anti-EGFR monoclonal antibody. Methods: p- -SCN-macropa was used to conjugate matuzumab for radiolabeling with 225Ac and SCN-deferoxamine was used to conjugate matuzumab for labelling with 89Zr. The radioimmunoconjugates were characterized by flow cytometry, HPLC and iTLC. in vitro cytotoxicity was evaluated in EGFR-positive mCRC, TNBC cell lines and 3D spheroids with different levels of EGFR density. Tumor growth was monitored using digital caliper. Mice were treated with either 10 MBq of 89Zr-matuzumab for imaging or three doses of 13 KBq/dose administered of 225Ac-matuzumab 10 days apart. In vivo study endpoint was tumor volume greater than or equal to 1500 mm3. Results: Flow cytometry showed about 95% binding to the cells in all EGFR-positive colorectal cell lines (DLD-1, SW620, SNU-C2B, HT-29) and breast cancer cell lines (MDA-MB-468, MDA-MB-231). in vitro studies showed enhanced cytotoxicity of 225Ac-matuzumab compared with matuzumab. IC50 in the MDA-MB-468 cell line for 225Ac-matuzumab (1.86 ± nM) was 35 times more effective than matuzumab (65.25± 7 nM). Similar trends were observed in the other KRAS-mutant mCRC cell lines and breast cancer cell lines. In 3D spheroid models, the IC50 of 225Ac-matuzumab (3.0 ± 2 nM) in MDA-MB-468, was 20.79 times more effective than matuzumab (62.3 ± 1.38 nM). Similar trends were observed for all the other spheroid models as well. High uptake of 89Zr-matuzumab was observed in both mCRC and TNBC xenografts. 225Ac-matuzumab slowed tumor growth rate in MDA-MB-468 and MDA-MB-231 tumors models compared with control antibody or non-treated controls for 30 days. This study is still ongoing and will last for 2 more months. Conclusion: 225Ac-matuzumab shows very promising outcomes in KRAS-mutant mCRC models and breast cancer models and warrants further investigation. Citation Format: Florence Anjong Tikum, Humphrey Fonge, Fabrice Njotu, Hanan Babeker, Jessica K. Pougoue, Nikita Henning, Alireza Doroudi. 89Zr-matuzumab and 225Ac-matuzumab as a theranostic for epidermal growth factor receptor-positive KRAS wild-type colorectal and breast cancer xenografts [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6027.