Abstract 6442: Evaluation of drug target engagement on pharmacodynamic biomarkers in human plucked scalp hair
Authors: Tudor Greg , Ponthan Frida , Boanas Adam , Brown Matt , Booth Catherine 
Published: March 2024

Abstract
Plucked hair is a valuable surrogate tissue to monitor pharmacodynamic (PD) responses in a clinical trial. Hair collection is a minimally invasive, simple technique amenable to frequent sampling and hence patient compliance. We have developed a method to assess target expression changes following exposure of plucked hairs to chemotherapeutic agents and other potential therapeutics. Successful ex vivo responses provide proof of concept data prior to clinical studies. Since hairs are epithelial appendages, many signaling pathways active in other epithelial tissues, including cancers, are also present in hairs. Highly proliferative scalp hair can be utilized as a surrogate tissue to measure proliferation, phosphorylation and DNA damage responses after treatment. Furthermore, hairs are highly vascularized, suggesting administered Test Articles may be delivered efficiently to the hair in a similar manner to other highly vascularized tissues, including many tumor types. Human plucked scalp hair was placed in maintenance media in the presence of chemotherapeutic agents that have different mechanisms of action (e.g. Gemcitabine, Epirubicin, Erlotinib) for a range of timepoints. Hairs were fixed post-exposure and longitudinal sections were immunohistochemically labelled for markers relating to DNA damage/repair or signaling pathways directly relating to target engagement. Examples include p-Chk1, g-H2AX, p-ERK1/2, and p-AKT. Quantitative image analysis to measure the level of labelling was performed using an Aperio ScanScope®. The relative number of positively labelled cell nuclei or relative labelled tissue area (depending on the labelling pattern of the target), of the hair outer root sheath was analyzed, along with label intensity. In subsequent clinical trials, formaldehyde fixed hairs from patients were returned to the lab, sectioned, labelled and quantified. If antibody labelling is not possible or more detailed information on pathway modulation may be useful, drug treated plucked hairs can be subjected to Next Generation Sequencing (NGS) gene expression analysis. The expected changes in labelling were observed, reflecting known tumor responses. For example, Gemcitabine (linked to DNA polymerase inhibition) increased p-Chk1 labelling after 4 hours and strongly induced p53 by 24 hours. Epirubicin (anthracycline topoisomerase II inhibitor) increased g-H2AX labelling up to 24 hours. Erlotinib (EGFr pathway inhibitor) decreased levels of both p-ERK1/2 and p-AKT after only 10 minutes. We have demonstrated that plucked hair is a valuable PD biomarker tissue for various chemotherapy agents. Proof of concept studies performed ex vivo can inform the design of clinical studies by indicating optimum biomarkers and timepoints. Further, each hair is an independent unit thereby allowing replicate tissues (hairs) to be sampled, improving statistical confidence compared to single readout markers.
Citation Format: Greg Tudor, Frida Ponthan, Adam Boanas, Matt Brown, Catherine Booth. Evaluation of drug target engagement on pharmacodynamic biomarkers in human plucked scalp hair [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6442.