The treatment of uveal melanoma and its metastases has not evolved sufficiently over the last decades in comparison to other tumour entities, posing a great challenge in the field of ocular oncology. Despite improvements in the conventional treatment regime and new discoveries about the genetic and molecular background of the primary tumour, effective treatment strategies to either prevent tumours or treat patients with advanced or metastatic disease are still lacking. New therapeutic options are necessary in order to achieve satisfactory local tumour control, reduce the risk of metastasis development, and preserve the eyeball and possibly the visual function of the eye. The development of in vivo model systems remains crucial for the identification and investigation of potential novel treatment modalities. The aim of this study was the optimisation of the chorioallantoic membrane (CAM) model for uveal melanoma research. We analysed the established CAM assay and its modification after the implantation of three-dimensional spheroids. The chorioallantoic membrane of a chick embryo was used to implant uveal melanoma-cell-line-derived spheroids in order to study their growth rate, angiogenic potential, and metastatic capability. Using the UM 92.1, UPMD2, UPMM3, and Mel270 cell lines, we were able to improve the viability of the embryos from 20% to >80% and to achieve up to a fourfold volume increase of the transplanted spheroid masses. The results point to the value of an optimised chicken embryo assay as an in vivo model for testing novel therapies for uveal melanoma by simplifying the research conditions and by contributing to a considerable reduction in animal experiments.

Electrochemotherapy (ECT) is the combination of transient pore formation following electric pulse application with the administration of cytotoxic drugs, which enhances the cytotoxic effect of the applied agent due to membrane changes and permeabilization. Although EP represents an established therapeutic option for solid malignancies, recent advances shift to the investigation of non-cytotoxic agents, such as calcium, which can also induce cell death. The present study aims to evaluate the cytotoxic effect, the morphological changes in tumor spheroids, the effect on the cell viability, and the cell-specific growth rate following calcium electroporation (CaEP) in uveal melanoma (UM) 2D monolayer cell cultures as well as in 3D tumor spheroid models. The experiments were conducted in four cell lines, UM92.1, Mel270, and two primary UM cell lines, UPMD2 and UPMM3 (UPM). The 2D and 3D UM cell cultures were electroporated with eight rectangular pulses (100 µs pulse duration, 5 Hz repetition frequency) of a 1000 V/cm pulse strength alone or in combination with 0.11 mg/mL, 0.28 mg/mL, 0.55 mg/mL or 1.11 mg/mL calcium chloride or 1.0 µg/mL or 2.5 µg/mL bleomycin. The application of calcium chloride alone induced an ATP reduction only in the UM92.1 2D cell cultures. Calcium alone had no significant effect on ATP levels in all four UM spheroids. A significant decrease in the intracellular adenosine triphosphate (ATP) level was documented in all four 2D and 3D cell cultures for both CaEP as well as ECT with bleomycin. The results suggest a dose-dependent ATP depletion with a wide range of sensitivity among the tested UM cell lines, control groups, and the applied settings in both 2D monolayer cell cultures and 3D tumor spheroid models. The colony formation capacity of the cell lines after two weeks reduced significantly after CaEP only with 0.5 mg/mL and 1.1 mg/mL, whereas the same effect could be achieved with both applied bleomycin concentrations, 1.0 µg/mL and 2.5 µg/mL, for the ECT group. The specific growth rate on day 7 following CaEP was significantly reduced in UM92.1 cell lines with 0.5 and 1.1 mg/mL calcium chloride, while Mel270 showed a similar effect only after administration of 1.1 mg/mL. UM92.1 and Mel270 spheroids exhibited lower adhesion and density after CaEP on day three in comparison to UPM spheroids showing detachment after day 7 following treatment. CaEP and bleomycin electroporation significantly reduce cell viability at similar applied voltage settings. CaEP may be a feasible and inexpensive therapeutic option for the local tumor control with fewer side effects, in comparison to other chemotherapeutic agents, for the treatment of uveal melanoma. The limited effect on normal cells and the surrounding tissue has already been investigated, but further research is necessary to clarify the effect on the surrounding tissue and to facilitate its application in a clinical setting for the eye.