As colorectal cancer remains a leading cause of cancer-related death, identifying therapeutic targets and approaches is essential to improve patient outcomes. The EGFR ligand epiregulin (EREG) is highly expressed in RAS wild-type (WT) and mutant colorectal cancer, with minimal expression in normal tissues, making it an attractive target for antibody–drug conjugate (ADC) development. In this study, we produced and purified an EREG mAb, H231, which had high specificity and affinity for human and mouse EREG. H231 also internalized to lysosomes, which is important for ADC payload release. ImmunoPET and ex vivo biodistribution studies showed significant tumor uptake of zirconium-89–labeled H231, with minimal uptake in normal tissues. H231 was conjugated to either cleavable dipeptide or tripeptide chemical linkers attached to the DNA-alkylating payload duocarmycin DM, and the cytotoxicity of EREG ADCs was assessed in a panel of colorectal cancer cell lines. EREG ADCs incorporating tripeptide linkers demonstrated the highest potency in EREG-expressing colorectal cancer cells irrespective of RAS mutations. Preclinical safety and efficacy studies showed that EREG ADCs were well tolerated, neutralized EGFR pathway activity, caused significant tumor growth inhibition or regression, and increased survival in colorectal cancer cell line and patient-derived xenograft models. These data suggest that EREG is a promising target for the development of ADCs for treating colorectal cancer and other cancer types that express high levels of EREG. Although the efficacy of clinically approved anti-EGFR mAbs is largely limited by RAS mutational status, EREG ADCs may show promise for both RAS mutant and WT patients, thus improving existing treatment options. Significance: EREG-targeting antibody-drug conjugates demonstrate acceptable safety and robust therapeutic efficacy in RAS mutant and wild-type colorectal cancer, suggesting their potential as an alternative to EGFR-targeted therapy to benefit a broader patient population.

Current therapies targeting the human epidermal growth factor receptor (HER) family, including monoclonal antibodies (mAbs) and tyrosine kinase inhibitors (TKIs), are limited by drug resistance and systemic toxicities. Antibody–drug conjugates (ADCs) are one of the most rapidly expanding classes of anti-cancer therapeutics with 13 presently approved by the FDA. Importantly, ADCs represent a promising therapeutic option with the potential to overcome traditional HER-targeted therapy resistance by delivering highly potent cytotoxins specifically to HER-overexpressing cancer cells and exerting both mAb- and payload-mediated antitumor efficacy. The clinical utility of HER-targeted ADCs is exemplified by the immense success of HER2-targeted ADCs including trastuzumab emtansine and trastuzumab deruxtecan. Still, strategies to improve upon existing HER2-targeted ADCs as well as the development of ADCs against other HER family members, particularly EGFR and HER3, are of great interest. To date, no HER4-targeting ADCs have been reported. In this review, we extensively detail clinical-stage EGFR-, HER2-, and HER3-targeting monospecific ADCs as well as novel clinical and pre-clinical bispecific ADCs (bsADCs) directed against this receptor family. We close by discussing nascent trends in the development of HER-targeting ADCs, including novel ADC payloads and HER ligand-targeted ADCs.

The epidermal growth factor receptor (EGFR) plays a critical role in regulating essential cellular processes that are frequently hijacked to promote cancer. In colorectal cancer (CRC) in particular, the EGFR signaling pathway is frequently hyperactivated via receptor and/or ligand overexpression and downstream oncogenic mutations. Current EGFR-targeted therapies for metastatic CRC (mCRC) include the mAbs cetuximab and panitumumab. However, intrinsic and acquired resistance to EGFR-targeted mAbs are commonly observed. Thus, additional biomarkers are necessary to better understand patient sensitivity to EGFR-targeted therapies. Furthermore, therapeutic targeting of alternative EGFR pathway components may serve as one mechanism to overcome EGFR-targeted mAb resistance. In this review, we discuss the mounting evidence supporting EGFR ligands epiregulin (EREG) and amphiregulin (AREG), which are overexpressed in CRC with potential key roles in tumor progression, as predictive biomarkers for EGFR-targeted therapy sensitivity, as well as mediators of therapy resistance, though further studies are necessary to validate the prognostic roles and mechanisms by which these ligands contribute to resistance. Additionally, we review recent advances towards therapeutic targeting of EREG and AREG in cancer through the development and use of EREG- and AREG-targeted mAbs as well as antibody–drug conjugates (ADCs). We conclude with a discussion on the roadblocks to clinical implementation of EREG and AREG as biomarkers, as well as approaches to enhance the efficacy of current EREG- and AREG-targeted strategies.

As colorectal cancer (CRC) remains a leading cause of cancer-related death, identifying therapeutic targets and approaches is essential to improve patient outcomes. The EGFR ligand epiregulin (EREG) is highly expressed in RAS wildtype and mutant CRC with minimal expression in normal tissues, making it an attractive target for antibody-drug conjugate (ADC) development. In this study, we produced and purified an EREG monoclonal antibody (mAb), H231, that had high specificity and affinity for human and mouse EREG. H231 also internalized to lysosomes, which is important for ADC payload release. ImmunoPET and ex vivo biodistribution studies showed significant tumor uptake of ⁸⁹ Zr-labeled H231 with minimal uptake in normal tissues. H231 was conjugated to either cleavable dipeptide or tripeptide chemical linkers attached to the DNA-alkylating payload duocarmycin DM, and cytotoxicity of EREG ADCs was assessed in a panel of CRC cell lines. EREG ADCs incorporating tripeptide linkers demonstrated the highest potency in EREG-expressing CRC cells irrespective of RAS mutations. Preclinical safety and efficacy studies showed EREG ADCs were well-tolerated, neutralized EGFR pathway activity, caused significant tumor growth inhibition or regression, and increased survival in CRC cell line and patient-derived xenograft models. These data suggest EREG is a promising target for the development of ADCs for treating CRC and other cancer types that express high levels of EREG. While the efficacy of clinically approved anti-EGFR mAbs are largely limited by RAS mutational status, EREG ADCs may show promise for both RAS mutant and wildtype patients, thus improving existing treatment options. Significance: EREG-targeting antibody-drug conjugates demonstrate acceptable safety and robust therapeutic efficacy in RAS mutant and wildtype colorectal cancer, suggesting their potential as an alternative to EGFR-targeted therapy to benefit a broader patient population.

Colorectal cancer (CRC) remains a significant contributor to cancer-associated deaths worldwide, indicating the need for new therapeutic targets and modalities. Antibody-drug conjugates (ADCs) have demonstrated remarkable potential for the treatment of various cancer types, although their efficacy as monotherapies is often limited by insufficient targeting of tumor heterogeneity, dose-limiting toxicities, and drug resistance. Accordingly, multi-targeting therapeutic strategies, such as bispecific ADCs (bsADCs), which simultaneously target two cancer-associated antigens or non-overlapping epitopes on the same antigen, may prove more effective at overcoming resistance and eliminating tumors compared to monospecific ADCs. In this work, we describe the development of EGFR:LGR5 bispecific antibodies (bsAbs) and bsADCs. EGFR:LGR5 bsAbs were shown to internalize to the lysosome to a greater extent than EGFR- and LGR5-targeting monoclonal antibodies (mAbs) and drive EGFR lysosomal degradation in an LGR5-mediated fashion. However, EGFR:LGR5 bsAbs exerted suboptimal cytotoxicity in CRC cell lines. We therefore engineered an EGFR:LGR5 bsADC that demonstrated 100- to 1000-fold enhanced efficacy over a previously developed LGR5-targeting monospecific ADC (8E11-CPT2) with an identical linker-payload in CRC cell lines of various genetic backgrounds and EGFR and LGR5 expression levels. EGFR:LGR5 bsADC potency was strongly correlated with cell line sensitivity to the CPT2 payload. EGFR:LGR5 bsADC induced tumor regression in select RASMUT CRC xenograft models and demonstrated superior antitumor activity and prolonged survival benefit in all evaluated models versus EGFR mAb cetuximab (CTX), bsAb, and 8E11-CPT2. These findings strongly support the further development of EGFR and LGR5 dual-targeting approaches for CRC and other EGFR- and LGR5-expressing malignancies.

Bispecific antibodies (bsAbs) and bispecific antibody–drug conjugates (bsADCs) represent promising classes of emerging targeted therapeutics with the potential to overcome tumor heterogeneity and resistance in colorectal cancer (CRC). BsAbs can simultaneously engage multiple tumor antigens or immune cells or bind two distinct epitopes within a single target, enabling mechanisms of action beyond the capabilities of monoclonal antibodies. Bispecific T cell engagers facilitate targeted destruction of tumors through immune cell recruitment, while dual immune checkpoint inhibitors enhance immune activation by blocking T cell inhibitory signals. Furthermore, bsAbs can mediate dual signaling pathway inhibition through binding multiple receptor tyrosine kinase receptors or other tumor cell surface proteins. BsADCs integrate the dual-antigen recognition of bsAbs with targeted payload delivery, utilizing receptor-mediated endocytosis to deliver potent cytotoxic payloads selectively to CRC cells, while minimizing systemic toxicity. Recent advances in bsAb engineering, linker chemistry, site-specific conjugation, and payload design have accelerated the development of bsADCs for solid tumors, including CRC. BsAbs and bsADCs provide opportunities to improve tumor selectivity, enhance internalization, overcome antigen escape, and expand the population of CRC patients eligible for targeted therapy. Emerging preclinical studies demonstrate encouraging anti-tumor activity for bispecific modalities in CRC, while early clinical trials are beginning to establish their translational potential. This review summarizes the current landscape of bsAbs and bsADCs in therapeutic development for CRC, highlighting key biological targets, engineering strategies, mechanisms of action, and clinical status. We also discuss the major challenges facing clinical translation and provide perspectives on future directions for bispecific therapies in CRC.