Evaluation of pharmacodynamic responses to cancer therapeutic agents using DNA damage markers

Deborah F. Wilsker, Allison M. Barrett, Angie B. Dull, Scott M. Lawrence, Melinda G. Hollingshead, Alice Chen, Shivaani Kummar, Ralph E. Parchment, James H. Doroshow, Robert J. Kinders

Research output: Contribution to journalArticlepeer-review

14 Scopus citations


Purpose: We sought to examine the pharmacodynamic activation of the DNA damage response (DDR) pathway in tumors following anticancer treatment for confirmation of target engagement. Experimental Design: We evaluated the time course and spatial activation of 3 protein biomarkers of DNA damage recognition and repair (gH2AX, pS343-Nbs1, and Rad51) simultaneously in a quantitative multiplex immunofluorescence assay (IFA) to assess DDR pathway activation in tumor tissues following exposure to DNA-damaging agents. Results: Because of inherent biological variability, baseline DDR biomarker levels were evaluated in a colorectal cancer microarray to establish clinically relevant thresholds for pharmacodynamic activation. Xenograft-bearing mice and clinical colorectal tumor biopsies obtained from subjects exposed to DNA-damaging therapeutic regimens demonstrated marked intratumor heterogeneity in the timing and extent of DDR biomarker activation due, in part, to the cell-cycle dependency of DNA damage biomarker expression. Conclusions: We have demonstrated the clinical utility of this DDR multiplex IFA in preclinical models and clinical specimens following exposure to multiple classes of cytotoxic agents, DNA repair protein inhibitors, and molec-ularly targeted agents, in both homologous recombination–proficient and -deficient contexts. Levels exceeding 4% nuclear area positive (NAP) gH2AX, 4% NAP pS343-Nbs1, and 5% cells with 5 Rad51 nuclear foci indicate a DDR activation response to treatment in human colorectal cancer tissue. Determination of effect-level cutoffs allows for robust interpretation of biomarkers with significant inter-patient and intratumor heterogeneity; simultaneous assessment of biomarkers induced at different phases of the DDR guards against the risk of false negatives due to an ill-timed biopsy.

Original languageEnglish (US)
Pages (from-to)3084-3095
Number of pages12
JournalClinical Cancer Research
Issue number10
StatePublished - 2019
Externally publishedYes

ASJC Scopus subject areas

  • Oncology
  • Cancer Research


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