Biomarker and its role in ADC drug development
Part 01, Introduction to ADC
Antibody-Drug Conjugates (ADCs) are complex therapeutics created by linking a small-molecule toxin, known as the payload, to a tumor-targeting monoclonal antibody via a specialized linker. This design harnesses both the powerful cytotoxic effects of traditional chemotherapy agents and the precision targeting capabilities of antibody therapies [1]. Through the antibody's targeting function, ADCs deliver the small-molecule toxin directly into tumor cells, where it interacts with cellular DNA or microtubules to trigger apoptosis or cell death. Additionally, ADCs can eliminate tumor cells through mechanisms involving the antibody’s Fc fragment, including antibody-dependent cellular cytotoxicity (ADCC), antibody-dependent cellular phagocytosis (ADCP), and complement-dependent cytotoxicity (CDC). By binding specifically to tumor cell surface antigens, ADCs can also inhibit downstream signaling pathways of antigen receptors, further promoting apoptosis [2].
Part 02, Definition and Classification of Biomarkers
The value of biomarkers in the clinical development of anti-tumor drugs has become increasingly evident, establishing them as an essential tool in oncology drug research and development. Biomarkers are now widely used in patient screening, diagnosis, clinical studies, guiding therapeutic decisions, and prognosis. In December 2021, the CDE issued the Technical Guidelines for the Application of Biomarkers in the Clinical Development of Anti-Tumor Drugs, which provided a clear definition of biomarkers. Biomarkers are defined as objectively measurable indicators that reflect physiological or pathological processes or the biological effects of exposure or therapeutic interventions. The guidelines also classify biomarkers into six types: diagnostic biomarkers, prognostic biomarkers, predictive biomarkers, pharmacodynamic biomarkers, safety biomarkers, and monitoring biomarkers [3].
Part 03 Biomarker-Based Clinical Development of ADC Drugs
In the clinical development of ADC drugs for anti-tumor applications, biomarkers can be used to precisely identify potential responders, thereby improving the success rate of clinical trials. The Technical Guidelines for Clinical Development of Anti-Tumor Antibody-Drug Conjugates, issued by the CDE in April 2023, also encourages researchers to actively conduct in-depth exploratory biomarker studies early in clinical trials. These studies should explore predictive, prognostic, and pharmacodynamic biomarkers based on the target characteristics of the ADC [4]. Given the mechanism of action of ADC drugs, patient selection strategies in clinical development are primarily based on target antigen expression on tumor cells, using the target antigen as a biomarker for population enrichment and efficacy analysis. Several ADC drugs targeting specific antigens for patient selection have already been approved, such as trastuzumab deruxtecan and mirvetuximab soravtansine. The following section will use mirvetuximab soravtansine as an example to illustrate how biomarkers support ADC drug clinical development, enhancing the efficiency of ADC drug research.
Mirvetuximab soravtansine (brand name Elahere), developed by ImmunoGen, is an ADC targeting folate receptor alpha (FRα). It consists of a chimeric IgG1 antibody against FRα, a cleavable linker, and the microtubule-disrupting agent DM4 [5]. On November 14, 2022, the U.S. FDA granted accelerated approval for mirvetuximab soravtansine to treat adults with FRα-positive, platinum-resistant epithelial ovarian, fallopian tube, or primary peritoneal cancer who have received one to three prior systemic therapies.
In a Phase I expansion cohort study evaluating the safety and clinical activity of mirvetuximab soravtansine (IMGN853), patients were enriched based on FRα positivity (≥25% of tumor cells with an IHC staining intensity of ≥2+ as the inclusion criterion). Additionally, subgroup analyses were conducted based on FRα expression levels: low (25–49% of tumor cells with ≥2+ IHC staining intensity), medium (50–74% of tumor cells with ≥2+ IHC staining intensity), or high (≥75% of tumor cells with ≥2+ IHC staining intensity). The results indicated that FRα expression levels were associated with anti-tumor activity, with patients showing high FRα expression exhibiting a higher overall response rate (ORR) and longer median progression-free survival (mPFS). These findings suggest that FRα can serve as a predictive biomarker to accurately identify patients who are likely to benefit from IMGN853 treatment [6][7].
Based on Phase I trial results, ImmunoGen initiated FORWARD I (NCT02631876), a randomized, open-label Phase III trial designed to compare the safety and efficacy of MIRV (IMGN853) with investigator's choice chemotherapy in platinum-resistant patients with medium/high FRα expression (≥50% of tumor cells showing any FRα membrane staining under ≤×10 magnification) who had received three or fewer prior therapies.
The results of the FORWARD I trial [8] showed that, for the intent-to-treat (ITT) population, there was no significant difference in the primary endpoint of progression-free survival (PFS) between the MIRV and chemotherapy groups (HR, 0.98; 95% CI, 0.73–1.31; P=0.897), with median PFS values of 4.1 months and 4.4 months, respectively. However, on all secondary endpoints, the MIRV group demonstrated superior clinical efficacy compared to chemotherapy: confirmed overall response rate (ORR) (22% vs. 12%; P=0.049) and CA-125 response (51% vs. 27%; P < 0.001).
In the high FRα expression subgroup, the MIRV group showed a longer PFS compared to the chemotherapy group (mPFS of 4.8 months vs. 4.1 months; HR, 0.69; 95% CI, 0.48–1.00; P=0.049), though it did not meet the predefined significance threshold (P < 0.025) to be considered a primary endpoint success. For secondary endpoints, the MIRV group in the high FRα expression population also showed better clinical efficacy than the chemotherapy group: confirmed ORR (24% vs. 10%; P=0.014) and CA-125 response (53% vs. 25%; P < 0.001).
Exploratory analyses indicated that the FORWARD I trial used a simplified scoring method (10× scoring) to assess FRα expression in tumor samples, which inadvertently included patients with lower-than-expected FRα levels. When the scoring method from the Phase I clinical study (PS2+ scoring) was applied to re-evaluate the tumor samples from FORWARD I, a substantial proportion of patients were found to have low FRα expression. An exploratory efficacy analysis of FORWARD I patients using the PS2+ scoring method revealed that efficacy was correlated with FRα expression, with the high FRα expression group (n=116) showing the strongest treatment effects across all efficacy endpoints [9].
Building on the lessons learned from FORWARD I, ImmunoGen launched two subsequent Phase III trials of MIRV in platinum-resistant epithelial ovarian cancer (EOC) patients with high FRα expression (PS2+ scoring: ≥75% of tumor cells with ≥2+ IHC staining intensity): the pivotal SORAYA trial (NCT04296890) and the confirmatory MIRASOL trial (NCT04209855).
The SORAYA trial, a single-arm, multicenter study, reported an overall response rate (ORR) of 31.7% (95% CI: 22.9, 41.6) among 104 patients treated with mirvetuximab soravtansine, with a median duration of response (DOR) of 6.9 months (95% CI: 5.6, 9.7) [10]. Based on these results, the FDA granted accelerated approval for mirvetuximab soravtansine, and the VENTANA FOLR1 (FOLR-2.1) RxDx Assay was approved as a companion diagnostic tool for selecting patients with this indication.
MIRASOL is a randomized, open-label Phase III trial evaluating the safety and efficacy of MIRV versus investigator’s choice (IC) chemotherapy in platinum-resistant ovarian cancer (PROC) patients with high FRα expression (≥75% of tumor cells with ≥2+ IHC staining intensity). Compared to IC chemotherapy, MIRV demonstrated superior efficacy across progression-free survival (PFS), overall response rate (ORR), and overall survival (OS): mPFS (5.62 months vs. 3.98 months; HR, 0.65; 95% CI, 0.52–0.81; P < 0.0001), ORR (42% vs. 16%; P < 0.0001), and mOS (16.46 months vs. 12.75 months; HR, 0.67; 95% CI, 0.50–0.89; P = 0.0046) [11].
The successful approval of mirvetuximab soravtansine demonstrates how the strategic application of biomarkers can enhance clinical development efficiency. From the early clinical trials, exploratory studies on biomarkers were conducted for mirvetuximab soravtansine, and their value was continuously validated in subsequent pivotal trials. This process also involved assessing the appropriateness of biomarker cut-off values and developing companion diagnostic tools, effectively leveraging biomarkers to identify patient populations likely to benefit from treatment.
Part 04 – Introduction to Accurant FRα Assay
In normal or tumor tissues, FRα can be detected using the IHC method, with staining primarily localized on the cell membrane, sometimes accompanied by weaker cytoplasmic staining. Normal liver tissue is used as a negative control, while serous ovarian cancer tissue serves as a positive control.
Scoring Algorithm
Referencing the scoring method for FRα expression levels used in the Phase III SORAYA trial of MIRV, we established the H-score standard for FRα (as shown in the table below).
Part 05 – ?Biomarker and CDx Development Experience – Accurant Biotech
Accurant Biotech’s biomarker testing and companion diagnostic development platform is built on a comprehensive quality management system that complies with CAP and GCP standards. Designed to support the clinical testing and diagnostic development needs of pharmaceutical companies, the platform offers robust capabilities across various sample types. With extensive experience in biomarker detection, we deliver customized testing solutions spanning tissue, cellular, protein, genetic, and molecular dimensions. Additionally, we have developed proprietary methodologies for commonly studied biomarkers, a selection of which is highlighted below:
IHC Platform
Flow Cytometry Platform
Soluble Biomarker Testing (ELISA, MSD)
NGS Platform
PCR Platform
Mass Spectrometry Platform
Accurant Biotech has successfully established more than 200 IHC methodologies, encompassing key ADC drug targets such as HER2, HER3, EGFR, FRα, Trop2, Nectin-4, c-Met, Claudin18.2, B7-H3, and MSLN. Many of these methods have been validated and accredited through authoritative inter-laboratory quality evaluations.
Accurant Biotech has identified several monoclonal antibodies with strong potential for companion diagnostic (CDx) development and has successfully completed the initial stages of kit development. We are equipped to provide clients with comprehensive services, including antibody screening, assay development, sample analysis, and CDx reagent development. We are ready do serve your ADC development need. Please reach out to our BD specialist at [email protected] for more information.
Article credits to Accurant Biotech China team.
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