Targeting anti-apoptotic XXXX by AT-101 to increase radiation efficacy: data from in vitro and clinical pharmacokinetic studies in head and neck cancer.

@entity1 @entity588 @entity2667 @entity5 @entity2455 @entity900 @entity213
BACKGROUND: Pro-survival @entity588 family members can promote @entity5 development and contribute to treatment resistance. @entity213 ( @entity213 ) is frequently characterized by overexpression of anti-apoptotic @entity588 family members. Increased levels of these anti-apoptotic proteins have been associated with radio- and chemoresistance and poor clinical outcome. Inhibition of anti-apoptotic @entity588 family members therefore represents an appealing strategy to overcome resistance to anti- @entity5 therapies. The aim of this study was to evaluate combined effects of radiation and the pan- @entity588 inhibitor AT-101 in @entity213 in vitro. In addition, we determined @entity1 plasma levels of AT-101 obtained from a phase I/II trial, and compared these with the effective in vitro concentrations to substantiate therapeutic opportunities. METHODS: We examined the effect of AT-101, radiation and the combination on apoptosis induction and clonogenic survival in two @entity213 cell lines that express the target proteins. Apoptosis was assessed by @entity2455 staining to detect morphological nuclear changes and/or by @entity2667 staining and flow-cytometry analysis to quantify sub-diploid apoptotic nuclei. The type of interaction between AT-101 and radiation was evaluated by calculating the Combination Index (CI) and by performing isobolographic analysis. For the pharmacokinetic analysis, plasma AT-101 levels were measured by HPLC in blood samples collected from @entity1 enrolled in our clinical phase I/II study. These @entity1 with locally advanced @entity213 were treated with standard @entity900 -based chemoradiotherapy and received dose-escalating oral AT-101 in a 2-weeks daily schedule every 3  weeks. RESULTS: In vitro results showed that AT-101 enhances radiation-induced apoptosis with CI's below 1.0, indicating synergy. This effect was sequence-dependent. Clonogenic survival assays demonstrated a radiosensitizing effect with a DEF37 of 1.3 at sub-apoptotic concentrations of AT-101. Pharmacokinetic analysis of @entity1 blood samples taken between 30  min and 24  h after intake of AT-101 showed a dose-dependent increase in plasma concentration with peak levels up to 300-700  ng/ml between 1.5 and 2.5  h after intake. CONCLUSION: AT-101 is a competent enhancer of radiation-induced apoptosis in @entity213 in vitro. In addition, in vitro radiosensitization was observed at clinically attainable plasma levels. These finding support further evaluation of the combination of AT-101 with radiation in @entity588 -overexpressing @entity5 .
