Dual Targets, Double Impact: Advancing HER2 x TROP2 Bispecific ADCs in Preclinical Development

Homing in on the tumor: the magic bullet of cancer therapy

Antibody-drug conjugates (ADCs) have revolutionized oncotherapy, achieving significant clinical success in multiple cancer types. Hailed as a “magic bullet” of precision medicine, ADCs improved therapeutic success in oncology, offering patients more targeted treatment with reduced collateral damage to healthy tissues. New generation ADCs has become one of the most highly pursued biologics in the competitive oncology landscape. Their versatility and specificity enable a finely tuned approach to drug design and development. More recently, researchers have explored advanced biologics, such as antibodies equipped with dual cytotoxic warheads or payloads designed not for direct cell destruction but for immune modulation. Ultimately, bispecific antibody-drug conjugates (bsADCs) have been developed, featuring distinct paratopes on each arm that simultaneously target different proteins, enabling a dual mechanism of action. Most recently, a new class of biparatopic antibody-drug conjugates (bpADCs) has emerged, designed to target two distinct epitopes on the same protein, enhancing binding affinity and therapeutic precision.

Precision reloaded: enhancing ADC efficacy through dual targeting

Using bispecific antibodies eliminates sequential dosing for single target antibodies, however it comes with its own set of challenges. Each biologic’s efficacy and toxicity profile is shaped by the intricate design of its key components – the antibody, the linker, and the payload. The ideal drug will bind specifically and strongly to cancer cells, remain stable in the bloodstream, and retain its toxic payload until it reaches its target. Upon reaching the cancer cell, the drug should be promptly internalized and release its lethal warhead inside the cell – and, in an optimal scenario, allow the toxin to diffuse to the neighboring malignant cells within the tumor microenvironment. [1]

Two targets, one mission: seek and destroy

Proper dual target identification is the key for effective bispecific antibody design. The major challenge of biologics in oncology is finding targets that are predominantly expressed on the surface of tumor cells, with little to no expression in healthy tissue. High-affinity antibodies against such targets are ideal candidates for drugs that selectively kill tumors while minimizing on-target, off-tumor toxicities. With bsADCs two tumor-specific proteins can be targeted, which can increase tumor cell binding affinity and internalization, leading to enhanced payload delivery and better therapeutic efficacy. BsADCs can also be effective in targeting cells with varying expression levels of each antigen. To develop reliable bsADC preclinical validation platform ChemPartner’s scientists selected dual tumor-associated antigens (TAA), Human Epidermal Growth Factor Receptor 2 (HER2) and Trophoblast cell surface antigen 2 (TROP2), which are commonly expressed and co-expressed by multiple tumor types, including gastric, colorectal, bladder, breast, and non-small-cell lung cancer (NSCLC). TROP2 has recently become an attractive target for ADC design due to its rare expression in normal cells. [2][3]

We then developed a versatile cell-binding assay platform to evaluate the specificity of antibodies and ADCs to cells exhibiting varying levels of HER2 and TROP2 expression. Our binding panel includes well established human cell lines including a non-small cell lung cancer cell line NCI-H1975, an ovarian cancer cell line SK-OV-3, a gastric adenocarcinoma cell line NCI-N87, and a lung mucoepidermoid carcinoma cell line NCI-H292.

Here are two examples of different binding profiles for cell lines with different expression patterns for the two TAAs

INTERESTED TO SEE MORE DATA? Scroll down to request our poster from 2025 Antibody Engineering & Therapeutics

For an ADC to function effectively after binding to its target, it must be internalized by the cancer cell. We developed an antibody internalization assay and tested it on cell lines characterized by different expression levels of HER2 and TROP2 including a non-small cell lung cancer cell line NCI-H1975 and a gastric adenocarcinoma cell line NCI-N87.

INTERESTED TO SEE MORE DATA? Scroll down to request our poster from 2025 Antibody Engineering & Therapeutics

Tethered for impact: engineering therapeutically efficient linkers

The chemistry of the linker plays a critical role in determining the efficacy and toxicity of antibody-drug conjugates. Both cleavable and non-cleavable linkers offer distinct advantages and pose unique challenges. For example, cleavable linkers can be less stable in plasma, but they allow the payload to diffuse outside of the targeted cell and affect other cancer cells in the tumor microenvironment. Conversely, non-cleavable linkers allow delivery only to the cells displaying target antigen and being more stable in plasma, offer larger therapeutic window. Scientists have engineered highly sophisticated linkers that are cleaved under precisely defined conditions. One of the most common linkers are stable in the extracellular surroundings but are cleaved in the acidic environment of a lysosome. Other linkers utilize disulfide bonds which can be reductively cleaved by glutathione present in intracellular spaces but are intact while circulating in plasma. Others yet, can contain peptides or glucuronide and utilize specific hydrolytic enzymes inside the cells or tumor microenvironment to release the payload. [1]

We developed fully human bsADCs by using lysosomal-cleavable dipeptide, valine-citrulline (vc) to attach monomethyl auristatin E (MMAE) as the payload, with an average (Drug to Antibody Ratio) DAR of 4.2. We then used multiple cell lines to confirm the bsADCs cytotoxicity.

INTERESTED TO SEE MORE DATA? Scroll down to request our poster from 2025 Antibody Engineering & Therapeutics

Ultimate preclinical test: in vivo tumor model validation

We have tested the ADCs in two subcutaneous xenograft models: NCI-H1975 cell lines from non-small cell lung cancer, and JIMT-1 a breast cancer model. For the NCI-H1975, both bsADCs showed good dose-response at three different dose levels and at medium and high dose level significantly prolonged survival of the animals. In JIMT-1 model, BsADC at high dose treatment significantly reduced tumor volume compared to the vehicle treated animals. The bsADCs showed similar efficacy as mono-specific ADCs at the same levels.

BsADC efficacy in a subcutaneous NCI-H1975 model (NSCLC)

BsADC efficacy in a subcutaneous JIMT-1 model (breast cancer)

Next-gen ADCs demand next-gen preclinical platform

The development of bispecific ADCs targeting HER2 and TROP2 marks an exciting leap forward in precision oncology, particularly for tumors with heterogeneous TAAs expression. In our model, the anti-HER2 and TROP2 bispecific antibodies with vcMMAE payload, induced fast internalization and exhibited greater tumor killing efficiency and specificity, with an IC50 in the sub-nanomolar range in cell lines with high TROP2 and medium/low HER2 expression. Furthermore, our xenograft in vivo studies demonstrated favorable safety profiles, pharmacokinetics, and superior antitumor efficacy compared to monotherapy ADCs targeting either HER2 or TROP2 alone. These results confirm the transformative potential of bsADCs in the clinic – but also highlight the critical need for a robust and comprehensive preclinical evaluation platform. As interest in bispecific ADCs continues to surge across the biotech and pharma oncology landscape, establishing validated preclinical systems to benchmark efficacy, specificity, internalization, and safety will be essential for identifying new life-saving therapies. In this competitive and rapidly evolving field, rigorous, high-throughput preclinical validation is not just a foundation – it’s a competitive advantage.

Our preclinical bsADC platform capabilities are presented at 2025 Antibody Engineering & Therapeutics Europe, 10 – 12 June, 2025 at Congress Center, Basel Switzerland

REQUEST THE POSTER BY CLICKING ON THE IMAGE BELOW:

---

References

[1] Schlam, I., Moges, R., Morganti, S., Tolaney, S. M., & Tarantino, P. (2023). Next-generation antibody-drug conjugates for breast cancer: Moving beyond HER2 and TROP2. Critical reviews in oncology/hematology, 190, 104090.

[2] Su, P. L., Furuya, N., Asrar, A., Rolfo, C., Li, Z., Carbone, D. P., & He, K. (2025). Recent advances in therapeutic strategies for non-small cell lung cancer. Journal of hematology & oncology, 18(1), 35. https://doi.org/10.1186/s13045-025-01679-1

[3] Davis, A. A., Hesse, J., Pereira, P. M. R., & Ma, C. X. (2025). Novel treatment approaches utilizing antibody-drug conjugates in breast cancer. NPJ breast cancer, 11(1), 42. https://doi.org/10.1038/s41523-025-00743-w