Abstract 5246: Use of γH2aX and other biomarkers to quantify distribution of drug activity in solid tumors

Abstract

Abstract Background: The disorganized vasculature within solid tumors leads to decreased drug delivery and poor penetration of drugs from blood vessels to the tumor cells. Our laboratory has used quantitative immunohistochemistry (IHC) to show limited intratumoral distribution of the auto-fluorescent drugs doxorubicin and mitoxantrone. Most anti-cancer drugs are not fluorescent and do not have antibodies that recognize them; there is a need for biomarkers that can be used to quantify their distribution and efficacy in different regions of solid tumors. The aim of the present study was to characterize the spatial distribution within solid tumors of biomarkers of drug effect that can be used to test drug efficacy. Methods: Cleaved caspase 3 (a marker of apoptosis), γH2aX (a marker of DNA damage) and Ki67 (a marker of cell proliferation) were quantified in tumor sections in relation to blood vessels (recognized by CD31) using monoclonal antibodies and IHC. To validate the use of these biomarkers we compared their time-dependent distribution with (i) the distribution of auto-fluorescent doxorubicin and (ii) the distribution of a fluorescent monoclonal antibody that detects melphalan-induced DNA adducts. The biomarkers were then used to study the distribution of docetaxel in relation to tumor blood vessels. Results: The distributions of doxorubicin in MCF7 & MDA-MB-231 xenografts and of melphalan-induced DNA adducts in MCF-7 & EMT-6 tumors decreased exponentially with increasing distance from tumor blood vessels; they were similar to the distribution of γH2aX at 10 minutes after injection of these drugs. The distributions of cleaved caspase 3 and of change in Ki-67 at 24 hours following treatment also mirrored the distribution of the drugs. The distribution of these biomarkers following injection of docetaxel also showed a sharp decrease in drug activity with increasing distance from tumor blood vessels in solid tumors (MCF-7, PC-3 & A431). Conclusions: Activation of γH2aX occurs within 10 minutes after injection of several drugs and is the preferred biomarker for studying distribution of drug activity in tumors. There is heterogeneity of activity of many anticancer drugs in solid tumors, with rapid decrease in activity with increasing distance from tumor blood vessels. Poor distribution of drugs to cells within tumors is an important cause of drug resistance. Supported by a research grant from the Canadian Institutes of Health Research Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 5246. doi:1538-7445.AM2012-5246