On-Treatment DNA Damage Response Biomarkers in Surrogate Tissue Types

Abstract

Given the challenges associated with collection of tumor specimens for biomarker monitoring, collection of surrogate tissues (e.g., normal tissues such as hair or blood) may enable the assessment of pharmacodynamic (PD) biomarkers. For chemotherapeutic agents, limited work has been done to establish pharmacodynamic (PD) biomarkers in these surrogate specimens. This study aims to demonstrate that surrogate specimens, specifically hair follicles and whole blood, are a viable option for assessment of PD biomarkers in response to chemotherapy in the clinic.

Traditional chemotherapeutic agents act by targeting rapidly dividing cells, one of the hallmarks of most cancers and some normal cells such as bone marrow, hair follicles and cells that line the digestive tract. Many chemotherapeutic agents, such as anthracyclines, topoisomerase inhibitors, and alkylating agents (e.g., platinums), work by directly damaging a cell’s DNA in some or all phases of the cell cycle. The mechanism by which DNA damaging agents target erroneously dividing cells is indiscriminant and therefore results in DNA damage-induction in rapidly dividing healthy cells. The desire to better understand the biological reasons why cancer arises, propagates, and metastasizes, combined with a wider acceptance of personalized medicine, has led to the development of targeted therapies. However, despite, the development of multiple anti-cancer targeted agents, chemotherapy remains the mainstay of cancer therapeutics. As such, there is a need to further develop biomarkers that aid in our understanding of chemotherapeutic activity.

In order to study these specimens, consent was obtained from healthy volunteers for the collection of hair follicles and whole blood, treated ex vivo, and evaluated by immunohistochemistry and flow cytometry for biomarkers of DNA damage. As an expansion of the whole blood work, blood was also obtained from rats after in vivo exposure to various DNA damaging agents.

This study demonstrates that human hair follicles are a viable option for biomarker monitoring in oncology. Specifically, gH2AX can be used as a DNA damage marker. To enable robust assessment of DNA damage markers in surrogate specimens, multiple biological replicate must be collected given the expected variability in data generated. Results from this study also indicate that human whole blood will need more investigation before it is used clinically. Detection in whole blood was unsuccessful after ex vivo stimulation but in vivo exploration in rats yielded positive data.