Advancing ADC development: Overcoming preclinical challenges with Labcorp Discovery Oncology

Author: Gunisha Arora, PhD, Medical and Scientific Writer, Scientific Development
Date: May 2025

Antibody-drug conjugates (ADCs) have transformed cancer treatment by merging the accuracy of targeted therapies with the strength of chemotherapy. These treatments utilize monoclonal antibodies to deliver potent chemotherapy drugs directly to cancer cells, sparing healthy cells from damage. This precise targeting has proven highly effective in treating various cancers, such as breast, lung, and hematologic malignancies, particularly in patients who have not responded to other treatments. As research progresses, ADCs are poised to become an increasingly crucial component of oncology.

While the advent of ADCs has led to notable improvements in patient outcomes and provides new hope for those with difficult-to-treat or advanced cancers, ADCs still face many challenges. Namely, complexities within the preclinical research phase of ADC development can result in a translational gap, in which promising preclinical study results do not translate to human trials. This issue often is exacerbated by inconsistent study designs, leading to data that is difficult to reproduce. Additionally, the high costs and extended timelines required for preclinical research present substantial obstacles, necessitating considerable financial and time investments. Overcoming these challenges is essential to enhance the efficiency and success rate of translating ADC preclinical discoveries into effective clinical treatments.

Recognizing this complexity, Labcorp offers comprehensive preclinical services that span the entire ADC development pathway, from drug target identification, antibody characterization, through in vitro and in vivo efficacy studies into IND-enabling toxicology packages. Our scientific team provides the necessary support to accelerate the journey of promising ADC candidates from early discovery to clinical development, ultimately enhancing the success rate of translating preclinical discoveries into effective cancer treatments. Our approach is detailed below, alongside insights on the role that in vivo tumor models, in vitro efficacy studies, and antibody assays play in helping bridge the gap between promising ADC candidates in early discovery and clinical development.

In vivo tumor models offer critical insights

In vivo tumor models are critical to the preclinical development of ADCs because they offer invaluable insights into drug behavior within an organism. These models allow researchers to evaluate the ADC's pharmacokinetics, pharmacodynamics, and therapeutic efficacy in a complex biological environment, which is crucial for predicting how the ADC will perform in humans. By observing the ADC's ability to target and eliminate cancer cells, as well as its distribution and potential off-target effects, scientists can also optimize the ADC's design and dosing. Additionally, mouse models help identify the maximum tolerated dose and any adverse reactions, providing confidence that only the safest and most effective ADC candidates progress to clinical trials. This comprehensive evaluation is vital for developing drugs that can effectively and safely treat patients.

Figure 1: Targeting Trop-2 with sacituzumab and Nectin-4 with enfortumab inhibits subcutaneous non-small cell lung carcinoma cell line-derived xenograft tumor growth in vivo.

The assessment of ADC efficacy is a crucial endpoint of in vivo studies. Robust anti-tumor activity measurements, such as the reduction of tumor size or tumor growth inhibition, provides compelling evidence of the ADC's effectiveness. Moreover, in vivo efficacy studies help fine-tune the dosing regimen and treatment schedule, to help ensure the ADC delivers optimal therapeutic benefits with minimal side effects. To help demonstrate, shown are examples of two non-small cell lung carcinoma (NSCLC) cell line-derived xenograft (CDX) models (Calu-3 and NCI-H322M), and their responses to sacituzumab and enfortumab, respectively (Figure 1). Labcorp Discovery Oncology offers approximately 350 CDX models spanning most histotypes, and a growing biobank of more than 300 implantable patient-derived xenograft models. Many of these models have been well characterized in vivo for responsiveness to standard of care therapies and are all available to our drug development partners for preclinical support.

Figure 2A: HER-2 binding and specificity measurements for trastuzumab antibody. Trastuzumab (HER-2 antibody alone) or trastuzumab-Dxd (HER-2 ADC) were incubated with breast carcinoma CDX lines that express divergent levels of HER-2 (SK-BR-3 [HER-2 high] and Hs 578T [HER-2 low]). Cells were then incubated with PE-labeled trastuzumab to determine the percentage of free HER-2 molecules. 

Figure 2B: ADC IC50 measurements by Promega® CellTiter-Glo®. Trastuzumab (HER-2 antibody alone), DM1 (payload alone), or trastuzumab-DM1 (HER-2 ADC) were incubated with breast carcinoma CDX lines that express divergent levels of HER-2 (SK-BR-3 and Hs 578T). RLU = relative light units. 

In vitro efficacy is a vital measurement 

Similarly to in vivo efficacy, in vitro efficacy is a vital measurement for the preclinical development of ADCs. Conducted in controlled laboratory settings, in vitro studies provide crucial insights into the ADC's ability to bind to target antigens, internalize within cancer cells, and induce cell death. These studies help determine the ADC's potency and specificity, which are essential for its therapeutic potential. By identifying the most promising ADC candidates for further in vivo testing, in vitro efficacy studies streamline the development process. 

In vitro efficacy can also serve as an important component of model selection, helping confirm the CDX or patient-derived xenograft model selected not only expresses the therapeutic target of interest but is responsive to treatment. Thus in vitro testing is an important de-risking step prior to downstream in vivo studies where the labor and financial resources required are greater. To help demonstrate, shown are in vitro assays confirming the relative protein expression levels of HER-2 in two breast cancer CDX lines, and the specificity of the trastuzumab anti-HER-2 ADC against these lines (Figure 2A). The sensitivity of each model to cytolysis triggered by trastuzumab treatment is also shown (Figure 2B). In this example, the data would predict the SK-BR-3 model would likely respond more robustly in an in vivo tumor-bearing animal study setting compared to Hs578t tumors. Taken together, in vitro efficacy can serve as an early indicator of the ADC's effectiveness, guiding subsequent in vivo studies and helping ensure only the most viable approaches advance toward in-human trials.

Figure 3: Trastuzumab-DM1 was incubated with HER-2 positive SK-BR-3 breast carcinoma cells. Trastuzumab loaded cells were labeled with lysotracker (to detect lysosomes) and a secondary antibody targeting the ADC. Internalized ADCs were observed as green punctate staining. Lysotracker (red) and ADCs (green) were co-localized when ADCs were internalized (punctate, white arrow).

Antibody assays: Important tools for characterizing the ADC profile

Antibody internalization assays and bystander killing assays are other tools used to characterize the profile of ADCs during preclinical development. Internalization assays measure how effectively an ADC is taken up by cancer cells after binding to its target antigen, which is crucial for the ADC to deliver its cytotoxic payload inside the tumor cell and induce cell death (Figure 3). Bystander killing assays, on the other hand, assess the ADC's ability to kill neighboring cancer cells that do not express the target antigen (depicted in Figure 4). This is particularly important in heterogeneous tumors where not all cancer cells uniformly express the target antigen. To demonstrate this in action, shown is a luciferase-based platform for bystander killing assessments that uses MDA-MB-231-Luc-D3H2LN bystander cells (HER-2 low), which express a luciferase reporter. When cocultured with MDA-MD-361 target cells (HER-2 high) treated with trastuzumab-DM1, bystander killing in the MDA-MB-231-Luc-D3H2LN cells was detected by a loss of luciferase signal when bystander cells were eliminated (Figure 5). By enabling the ADC to eliminate both target-positive and nearby target-negative cancer cells, bystander killing can significantly enhance the overall therapeutic efficacy of the ADC. Together, these assays provide valuable insights into the ADC's mechanism of action and its potential effectiveness.

Figure 4: Schematic representation of bystander cell killing activity of ADCs.

Figure 5: Luciferase bystander cell killing assay. Trastuzumab-DM1 (HER-2 ADC) was incubated for 72 hours with non-target MDA-MB-231-Luc-D3H2LN cells (HER-2 low) plus varying numbers of target MDA-MB-361 (HER-2 high) cells, shown as a percent of total antigen (Ag) positive cells. To detect bystander cell cytolysis, luciferase activity was measured in the bystander cells remaining in culture after incubation.

Labcorp is committed to enhancing the success rate of translating preclinical discoveries into effective cancer treatments, ultimately providing new hope for patients with difficult-to-treat or advanced cancers. 

To further explore our preclinical services supporting ADC development, connect with our scientific development team or visit our antibody-drug conjugate page. 

Note: Please note that all animal care and use was conducted according to animal welfare regulations in an AAALAC-accredited facility with IACUC protocol review and approval.