Abstract 1183: Phase 0 microdosing trial quantitating DNA adduct formation to identify platinum chemosensitivity: from bench to bedside.
Authors: Pan Chong-xian , Wang Sisi , He Miaoling , Li Tao , Lin Tzu-yin , Zhang Hongyong , Malfatti Michael , Gandara David , Li Tianhong , Yoneda Ken , Lee Joyce , Dall'Era Marc , Cimino George , de Vere White Ralph , Turteltaub Kenneth , Henderson Paul 
Published: August 2014

Abstract
Purpose: DNA adduct formation is a critical step in platinum(Pt)–induced cell death. The goal of this project is to measure carboplatin-DNA adducts after a single non-toxic microdose of [14C]carboplatin, use this information to predict efficacy before cancer patients receive toxic chemotherapy and assess the underlying chemoresistance mechanisms, thus enhancing personalized therapy.
Methods: Six non-small cell lung cancer (NSCLC) and six bladder cancer cell lines were treated with 1 μM (microdose) or 100 μM (therapeutic dose) carboplatin, but with equal amounts of [14C]carboplatin. Carboplatin-DNA monoadduct levels were determined by measuring 14C content in genomic DNA with accelerator mass spectrometry (AMS). Cellular sensitivity to carboplatin (IC50 values) was correlated with drug-DNA adduct levels. To validate the in vitro findings, a pilot Phase 0 trial with microdosing [14C]carboplatin was initiated to determine the recommended Phase II dose (RP2D) of [14C]carboplatin for optimal measurement of DNA monoadducts and pharmacokinetics (PK) in lung and bladder cancer. PK and DNA monoadduct levels in peripheral blood mononuclear cells and tumor tissues were determined by liquid scintillation counting and AMS, respectively, validated with inductively coupled plasma mass spectrometry (ICP-MS), and correlated with tumor response to chemotherapy.
Results: DNA monoadduct levels in cell lines induced by microdose and therapeutic concentrations of carboplatin were highly linearly proportional (r2 = 0.95, p &lt; 0.001) as measured by AMS, and correlated to the total Pt-DNA adduct levels induced by therapeutic carboplatin (r2 = 0.80, p &lt; 0.001) as measured by ICP-MS. DNA adduct levels were superior in predicting resistance to carboplatin when compared to the mRNA expression of ERCC1, a DNA repair gene commonly used as a resistant biomarker of Pt-based chemotherapy. Nine patients were recruited at the pilot Phase 0 trial. The Level I dose of [14C]carboplatin at 107 dpm/Kg with total carboplatin at 1% of therapeutic dose (area under curve of 6) was determined as the RP2D. No clinical toxicity was observed as a result of microdosing. The radiation exposure from 14C was less than a chest X-ray per patient. DNA monoadduct levels and PK parameters of carboplatin at the microdose and therapeutic doses were highly correlated (p&lt;0.001), suggesting that this non-toxic microdosing approach can be used to predict DNA adduct levels and PK of therapeutic doses. Patients with the highest DNA monoadduct levels responded best to carboplatin-based chemotherapy, although more data is needed to achieve statistical significance in the clinical data.
Conclusions: This novel microdosing approach predicts DNA monoadduct levels and PK of therapeutic carboplatin dosing; preliminary data suggest the feasibility of predicting chemosensitivity and the possibility of guiding personalized dosing.
Citation Format: Chong-xian Pan, Sisi Wang, Miaoling He, Tao Li, Tzu-yin Lin, Hongyong Zhang, Michael Malfatti, David Gandara, Tianhong Li, Ken Yoneda, Joyce Lee, Marc Dall'Era, George Cimino, Ralph de Vere White, Kenneth Turteltaub, Paul Henderson. Phase 0 microdosing trial quantitating DNA adduct formation to identify platinum chemosensitivity: from bench to bedside. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1183. doi:10.1158/1538-7445.AM2013-1183