Interactions of Polyamine Analogs With Chromatin and the Relationship of Polyamine Analog Growth Inhibitory Activity to Extracellular Matrix Control of the Uveal Melanoma Cell Phenotype

Abstract

Purpose:: There is currently no effective treatment for metastatic uveal melanoma. This study was designed to investigate the mechanisms by which polyamine analogs might be used against highly invasive and metastatic uveal melanoma cells.

Methods:: We tested both eukaryotic and prokaryotic chromatin assays to (a) determine if polyamine analogs protect, compact, and reorganize DNA, whether or not histones or other nuclear proteins are present, and (b) protect DNA from nuclease digestion. We measured the compaction and reorganization activity of polyamine analogs on microsurgically-isolated eukaryotic chromatin that was removed under non-denaturing conditions. Three dimensional uveal melanoma cultures were also treated with polyamine analogs.

Results:: Polyamine analogs were active, independent of high ionic strength. The analogs reconstituted uveal melanoma chromosomes even after prior removal of chromatin proteins with trypsin, heparin, proteinase K, or after dissociation of GFP-labeled topoisomerase with high ionic strength solutions. Polyamine analogs were active within 30 minutes exposure to living uveal melanoma cells. 3-dimensional cultures employing pseudotissues constructed from metastatic tumor cells revealed that highly invasive and metastatic cells that had adopted an indolent phenotype by direct contact with laminin-rich extracellular matrix (ECM) proteins exhibited resistance to the killing action of polyamine analogs, while the same cells not associated with pseudotissue matrix, and which had adopted an invasive phenotype, were highly sensitive and were rapidly killed by the analogs.

Conclusions:: These results show for the first time that the sensitivity of highly invasive melanoma and cells to polyamine analogs can be controlled by the ECM microenvironment, independent of genotype. Therefore, the permeability of polyamine analogs into malignant melanomas and the relative non-toxicity of polyamine analogs to normal cells comprising these tumors, or tissue of normal architecture, suggests specific polyamine analogs may be a highly effective chemotherapeutic class of agents against the most invasive cells.

Keywords: melanoma • pathology: experimental • pathobiology