Identification of Spiro-Fused [3-azabicyclo[3.1.0]hexane]oxindoles as Potential Antitumor Agents: Initial In Vitro Evaluation of Anti-Proliferative Effect and Actin Cytoskeleton Transformation in 3T3 and 3T3-SV40 Fibroblast

Novel heterocyclic compounds containing 3-spiro[3-azabicyclo[3.1.0]hexane]oxindole framework (<b>4a</b>, <b>4b</b> and <b>4c</b>) have been studied as potential antitumor agents. The in silico ADMET (adsorption, distribution, metabolism, excretion and toxicity) analysis was performed on <b>4a</b>-<b>c</b> compounds with promising antiproliferative activity, previously synthetized and screened against human erythroleukemic cell line K562 tumor cell line. Cytotoxicity of <b>4a</b>-<b>c</b> against murine fibroblast 3T3 and SV-40 transformed murine fibroblast 3T3-SV40 cell lines were evaluated. The <b>4a</b> and <b>4c</b> compounds were cytotoxic against 3T3-SV40 cells in comparison with those of 3T3. In agreement with the DNA cytometry studies, the tested compounds have achieved significant cell-cycle perturbation with higher accumulation of cells in G0/G1 phase. Using confocal microscopy, we found that with <b>4a</b> and <b>4c</b> treatment of 3T3 cells, actin filaments disappeared, and granular actin was distributed diffusely in the cytoplasm in 82-97% of cells. The number of 3T3-SV40 cells with stress fibers increased to 7-30% against 2% in control. We discovered that transformed 3T3-SV40 cells after treatment with compounds <b>4a</b> and <b>4c</b> significantly reduced the number of cells with filopodium-like membrane protrusions (from 86 % in control cells to 6-18% after treatment), which indirectly suggests a decrease in cell motility. We can conclude that the studied compounds <b>4a</b> and <b>4c</b> have a cytostatic effect, which can lead to a decrease in the number of filopodium-like membrane protrusions.