# Carbonic Anhydrase-IX Is a Specific and Sensitive Theragnostic Target for Imaging and Radioimmunotherapy in Metastatic Colorectal Cancer

## TL;DR

Carbonic anhydrase IX (CA-IX) is a promising target for both imaging and treating metastatic colorectal cancer, with high expression in tumors and low toxicity in preclinical models.

## Contribution

This study is the first to demonstrate the theragnostic potential of radiolabeled girentuximab in clinically relevant metastatic colorectal cancer models.

## Key findings

- CA-IX was expressed in 87% of colorectal cancer liver metastasis samples.
- Radiolabeled girentuximab enabled high-resolution imaging of CA-IX-expressing lesions.
- Therapeutic doses of [177Lu]Lu-girentuximab reduced tumor burden in mouse models without toxicity.

## Abstract

Over 40% of colorectal cancer (CRC) patients develop metastatic disease. Their survival outlook is very low, highlighting the urgent need to improve the detection and therapeutic management of metastatic colorectal cancer (mCRC), particularly when metastases are not surgically resectable. Our study aimed to characterize the preclinical utility of targeting carbonic anhydrase IX (CA-IX) for metastasis imaging and for therapeutic purposes in patients with CRC liver metastases.

CA-IX expression was characterized in 46 liver metastasis samples using RNA sequencing and immunohistochemical staining. We labeled girentuximab, a clinical grade CA-IX antibody, with zirconium-89 ([89Zr]Zr) or lutetium-177 ([177Lu]Lu), and characterized its biodistribution in vivo. Using radiolabeled girentuximab in patient-derived liver metastasis organoids (PDOs) and xenograft models, we then characterized the preclinical utility of CA-IX imaging and therapeutic targeting in mCRC.

CA-IX mRNA and/or protein expression was detected in 87% of CRC liver metastasis samples, with little to no expression in surrounding liver tissue. Both [89Zr]Zr- and [177Lu]Lu-girentuximab exhibited excellent biodistribution characteristics in mice xenografted with PDOs. Positron emission tomography imaging showed that [89Zr]Zr-girentuximab enabled specific and high-resolution detection of CA-IX-expressing lesions at subcutaneous and hepatic sites compared to [18F]F-fluoro deoxy-glucose. Finally, single-dose [177Lu]Lu-girentuximab treatment induced cytotoxicity in PDOs in vitro and strongly reduced tumor burden in 2 independent xenografted mouse models, with no signs of toxicity.

Our results demonstrate that CA-IX is a relevant target for a theragnostic strategy in mCRC, and provide the first demonstration in clinically-relevant models of metastasis that radiolabeled girentuximab can be used as a scouting agent to stratify and monitor mCRC patients and as a therapeutic alternative for patients with CA-IX-expressing tumors.