Abstract 1667: A phase Ib study to evaluate induction of pCDC2 in skin biopsies from patients with solid tumors treated with DNA-damaging chemotherapy
Authors: Sun Amy , Lam Raymond , Pavlick Anna C. , Iannone Robert , Herman Gary , Dauffenbach Lisa M. , Kerfoot Christopher A. , Harman Amy , Bergstrom Donald A. 
Published: February 2011

Background: Phospho-CDC2 (pCDC2) is a known substrate of Wee1 kinase, a regulator of the G2/M checkpoint. Therapies that induce DNA damage engage the G2/M checkpoint and lead to elevated levels of pCDC2. Measurement of pCDC2 levels could be a valuable target engagement biomarker for development of Wee1 kinase inhibitors, especially if these agents are used in the setting of DNA-damaging chemotherapy. Methods: The objective of this study was to measure pCDC2 in skin punch biopsies from patients receiving DNA-damaging chemotherapy for solid tumor to qualify pCDC2 as a target engagement biomarker for Wee1 kinase inhibitors. Skin punch biopsies were performed at baseline, 24, and 48 hours after the first infusion of standard regimens containing gemicitabine, cisplatin or carboplatin (Cohort 1), or 24, 32 and 48 hours post-infusion (Cohort 2). Samples were analyzed for pCDC2 and total CDC2 using chromogenic multiplex IHC with multispectral image analysis. Analyses included manual enumeration of pCDC2 and total CDC2 in epidermal cells, hair follicle and bulb, and all dermal and epidermal tissues combined. Histogram analysis and co-localization analysis using pixel-based methods were also performed to allow unbiased evaluation of staining intensity and grading of the intensity of both markers. Results: A total of 32 patients aged 30 to 88 were enrolled and completed the study. Three IHC parameters (out of a total of 16 analyzed) were pre-specified for the primary analysis and all three detected significant induction of pCDC2 in response to chemotherapy over the time course. One parameter, the proportion of cells positive for total CDC2 also positive for pCDC2 showed a 1.4 fold induction from baseline to 24 hours post-infusion (multiplicity-adjusted p=0.023) and a 2.1 fold increase from baseline to 48 hours (p&lt;0.001). pCDC2 levels 48 hours post-infusion were significantly higher than that at 24 hours (p=0.010) suggesting pCDC2 induction continues to increase between 24 and 48 hours post-infusion. Of the tissues studied, epidermis was most consistently evaluable across skin biopsies and demonstrated strong induction of pCDC2. Increases in pCDC2 were also observed in hair follicles and bulbs, but these tissues were present in fewer biopsies than epidermis limiting the number of informative specimens. Conclusion: To our knowledge, this is the first clinical study to evaluate pCDC2 with multiplex IHC methods at multiple time points in patients with solid tumors receiving DNA-damaging chemotherapy. The methods employed allow quantitative measurement of pCDC2 and have identified recommended analysis parameters and tissue types for future studies. The results suggest that pCDC2 in skin punch biopsies is a fit-for-purpose biomarker for assessing pCDC2 inhibition in early clinical studies of Wee1 kinase inhibitors.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 1667.