Epiregulin: A Novel Antibody Drug Conjugate Target for Treating Colorectal Cancer
Introduction
Colorectal cancer (CRC) is the second leading cause of cancer related deaths in the U.S. This is largely due to metastasis, tumor relapse, and the vast differences in CRC tumors leading to treatment failure. Epiregulin (EREG) is a protein highly expressed in treatment-resistant CRCs of various mutation statuses, providing a target for combating drug resistance in CRC. Therefore, I hypothesize that EREG can mediate CRC tumor growth and metastasis and an EREG-targeted antibody-drug conjugate (ADC) can act as a guided missile to deliver cytotoxic drugs to EREG-expressing tumors for targeting treatment resistant CRC.
Methods
To characterize epiregulin’s role in CRC progression, I generated EREG knockout (KO) and knockdown lines using DLD-1 cells. To develop a novel EREG ADC, I cloned an EREG monoclonal antibody (mAb) and tested for binding affinity and internalization. Using the EREG mAb as well as a non-targeting IgG1 control antibody (cmAb) we performed radiolabeling with Zr89 to trace antibody tumor uptake in vivo using a CRC cell line xenograft model. We then conjugated the EREG mAb and cmAb to potent cytotoxic agents using various linker strategies. Our EREG ADCs were evaluated in vitro against a wide panel of CRC cells. Drug efficacy was determined using cytotoxicity assays to measure cell survival given varying doses of the cmAb and EREG mAb as well as control ADC (cADC) or EREG ADC. Tumor growth was monitored in vivo using a cell line xenograft model. Tolerability was measured by clinical chemistry analysis in C57/ BL6 mice.
Results
EREG silencing resulted in decreased proliferation, migration, invasion, and slowed tumor growth in vivo. Our EREG antibody showed high binding affinity, internalization and lysosomal colocalization in vitro and tumor specificity in vivo. While the EREG mAb alone does not produce significant cytotoxicity, conjugated to a chemical payload, the EREG ADC has a much higher efficacy at lower concentrations in causing cytotoxicity compared to cADC. Safety and therapeutic efficacy studies of the EREG ADC in vivo revealed no observable systemic toxicity and reduced tumor growth.
Conclusion
Future studies include development of new EREG mAbs and combination therapies. By targeting EREG, we can develop an ADC capable of acting as a potent clinical drug to eliminate colorectal cancer resistance and recurrence.