Abstract 4350: Pharmacodynamic biomarkers: Evaluation of oncology drug target engagement in human plucked scalp and beard hair

Abstract

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. Plucked hair is a valuable surrogate biomarker tissue to monitor pharmacodynamic (PD) responses in a clinical trial. The collection of hairs is minimally invasive, simple and is amenable to frequent sampling. Since hairs are epithelial appendages, many signaling pathways active in other epithelial tissues, including cancers, are also present in hairs. Highly proliferative plucked human 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 that 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 hair (either from the scalp or beard) was placed in maintenance media in the presence of conventional or targeted chemotherapeutic agents, known for their different mechanisms of action (e.g. Gemcitabine, Carboplatin, Tarceva), for a range of time points. Hairs were then fixed post-exposure and longitudinal sections immunohistochemically labelled for various markers including p-ERK1/2, p-AKT, p-Chk1, g-H2AX, Ki67 and androgen receptor. 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 tissue area (depending on the labelling pattern of the target), of the hair outer root sheath labelled was analyzed, along with label intensity. In subsequent trial patients, formaldehyde fixed plucked hairs were returned to the lab, similarly sectioned, labelled and quantified. In addition, where antibody labelling is not possible or more detailed information on the modulation of a pathway 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. For example, Gemcitabine, which is linked to DNA polymerase inhibition, increased p-Chk1 labelling 4-fold after 4-8 hours and strongly induced p53 by 24 hours. Tarceva, an inhibitor of the EGF pathway, decreased levels of both p-ERK1/2 and p-AKT 3-fold after only 10 minutes. The alkylating agent carboplatin increased g-H2AX labelling up to 12-fold after 24 hours. 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 validation studies by indicating optimum markers and timepoints. Further, each hair is an independent unit thereby allowing independent replicate tissues (hairs) to be sampled. Citation Format: Greg Tudor, Frida Ponthan, Adam Boanas, Aude-Marine Bonavita, Catherine Booth. Pharmacodynamic biomarkers: Evaluation of oncology drug target engagement in human plucked scalp and beard hair. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 4350.