Role of the Microenvironment for Radiosensitization by Patupilone

Abstract

Purpose: The combined treatment modality of ionizing radiation (IR) and the clinically relevant microtubule-stabilizing compound patupilone (epothilone B, EPO906) is a promising approach for anticancer therapy. Here, we investigated the role of the tumor microenvironment for the supra-additive in vivo response in tumor xenografts derived from patupilone-sensitive and patupilone-resistant non-small cell lung cancer cells. Experimental Design:The treatment response to a combined regimen of patupilone and IR was investigated in vitro and in tumor xenografts derived from wild-type A549 and A549.EpoB40 cells, which are resistant to patupilone due to a h-tubulin mutation. Results: In both A549 and A549.EpoB40 cells, proliferative activity and clonogenicity were reduced in response to IR, whereas patupilone, as expected, inhibited proliferation of the mutant cell line with reduced potency. Combined treatment with patupilone and IR induced a cytotoxic effect in vitro in an additive way in A549 cells but not in the tubulin-mutated, patupilone-resistant A549.EpoB40 cells. A supra-additive tumor growth delay was induced by combined treatment in xenografts derived from A549 cells but not in xenografts derived from A549.EpoB40 cells. Histologic analysis revealed a significant decrease in tumor cell proliferation (Ki-67) and microvessel density and a treatment-dependent change of tumor hypoxia in A549 but not A549.EpoB40 xenografts. Conclusions: Using a genetically defined patupilone-sensitive and patupilone-resistant tumor model, we here showed that the major cytotoxic effect of the combined treatment modality of IR and patupilone is directed against the tumor cell compartment. The induced antiangiogenic effect derives indirectly from the tumor cell.

Regulation of VEGF-expression by patupilone and ionizing radiation in lung adenocarcinoma cells

“…Cells were preincubated with patupilone for 24 hours under normoxic conditions, followed by incubation in the hypoxia chamber or under hypoxia-mimicking conditions, using Dimethyloxaloylglycine (DMOG) (Biomol GmbH, Hamburg, Germany), a prolyl-4-hydroxylase inhibitor (0.25 and 1 mM, respectively) [2].…”

“…The use of microtubule interfering agents is therefore a promising strategy for anti-cancer therapy alone and as part of combined treatment modalities with cytotoxic agents [1]. The effects of microtubule interfering agents at the biochemical level are well investigated, but additional cytotoxic effects due to signaling interference have been identified, which merit further investigation [2][3][4][5].…”

“…We previously investigated the combined treatment modality of ionizing radiation (IR) with the novel, clinically relevant microtubule stabilizing agent patupilone (Epothilone B), and interestingly, the combination of patupilone with IR resulted in vitro only in an additive cytotoxic effect (against various cancer cell types) but in a supra-additive tumor growth delay against tumor xenografts derived from the same tumor cells [2,4]. The accumulation of tumor cells in the most radiosensitive G2-M phase of the cell cycle represents the major rationale for the sensitization to IR [6][7][8][9], though other Sphase progression-related mechanisms have been observed as well [4].…”

“…The accumulation of tumor cells in the most radiosensitive G2-M phase of the cell cycle represents the major rationale for the sensitization to IR [6][7][8][9], though other Sphase progression-related mechanisms have been observed as well [4]. Additional anti-vascular and anti-angiogenic effects might contribute to the supra-additive tumor growth delay observed in vivo, and indeed, direct targeting of endothelial cells [10][11][12] and indirect, anti-angiogenic interference with the secretion of pro-angiogenic factors from tumor cells have been proposed [2,13]. Microtubule stabilizing and destabilizing agents block the nuclear translocation and correct assembly of the hypoxia inducible factor (HIF) by disrupting the structural organization of the microtubule cytoskeleton.…”

“…Microtubule stabilizing and destabilizing agents block the nuclear translocation and correct assembly of the hypoxia inducible factor (HIF) by disrupting the structural organization of the microtubule cytoskeleton. In consequence, the downstream signaling of HIF-1 target genes in response to hypoxia is compromised [2][3]5]. A reduction of pro-angiogenic (and cytoprotective) cytokine secretion by patupilone via inhibition of HIF could contribute to this mechanism [14][15].…”