New-generation technologies for spatial tissue analysis, indispensable tools for deciphering intratumor heterogeneity in the development of antibody-drug conjugates and radio-immunoconjugates for cancer treatment

Unlocking the Potential: Biomarkers of Response to Antibody-Drug Conjugates

Antibody-drug conjugates (ADCs) have reshaped the cancer treatment landscape across a variety of different tumor types. ADCs' peculiar pharmacologic design combines the cytotoxic properties of chemotherapeutic agents with the selectivity of targeted therapies. At present, the approval of many ADCs used in clinical practice has not always been biomarker-driven. Indeed, predicting ADCs' activity and toxicity through the demonstration of specific biomarkers is still a great unmet need, and the identification of patients who can derive significant benefit from treatment with ADCs may often be uncertain. With the lack of robust predictive biomarkers to anticipate primary, intrinsic resistance to ADCs and no consolidated biomarkers to aid in the early identification of treatment resistance (ie, acquired resistance), the determination of precise biologic mechanisms of ADC activity and safety becomes priority in the quest for better patient-centric outcomes. Of great relevance, whether the target antigen expression is a determinant of ADCs' primary activity is still to be clarified, and available data remain quite controversial. Antigen expression assessment is typically performed on tissue biopsy, hence only providing information on a specific tumor site, therefore unable to capture heterogeneous patterns of tumor antigen expression. Quantifying the expression of the target antigen across all tumor sites would help better understand tumor heterogeneity, whereas molecularly characterizing tumor-intrinsic features over time might provide information on resistance mechanisms. In addition, toxicity can represent a critical concern, since most ADCs have a safety profile that resembles that of chemotherapies, with often unique adverse events requiring special management, possibly because of the differential in pharmacokinetics between the small-molecule agent versus payload of a similar class (eg, deruxtecan conjugate-related interstitial lung disease). As such, the identification of robust predictive biomarkers of safety and activity of ADCs has the potential to improve patient selection and enrich the population of patients most likely to derive a substantial clinical benefit, especially in those disease settings where different ADCs happen to be approved in competing clinical indications, with undefined biomarkers to make precise decision making and unclear data on how to sequence ADCs. At this point, the identification of clinically actionable biomarkers in the space of ADCs remains a top research priority.

Biomarkers for Antibody-Drug Conjugates in Solid Tumors

The clinical development and then the progressive entry in clinical practice of antibody-drug conjugates (ADC) have marked a transformative advancement in the overall cancer treatment. ADCs have been extensively tested for a large number of tumors, reporting heterogeneous clinical efficacy and safety results. In some diseases, the advent of ADCs has yielded significant changes in the prognostic trajectory, portending an improvement of the survival and/or quality of life. ADCs are targeted agents, capable of delivering highly cytotoxic payloads selectively to antigen-expressing cancer cells. As such, they have been intended as perfect "bullets" to enable the promise of precision medicine, toward high-efficacy and limited-toxicity treatment options. However, only some approved ADCs are intended for the use in biomarker-selected patient populations, restricting potentially the opportunity to be more precise. Yet, key characteristics of modern ADCs might allow the activity of ADCs in tumors with heterogeneous or low expression of cancer antigens, resulting in a clinical activity that could sublimate the classic paradigm of a drug-to-target perfect match. In our review, we portrayed the current landscape of approved ADCs, reporting data of activity as related to the expression of the cancer antigens, and elucidating possible determinants of the safety and efficacy, including when used in a therapeutic sequence.