## 4 Conclusions  
Cell migration plays a significant role in physiological conditions, such as embryonic morphogenesis, nervous system development, tissue homeostasis, and immune cell trafficking [46; 47], but can be deregulated as well, contributing to several pathological processes such as inflammation and cancer metastasis [48]. Tumor cell migration and invasion involve several events, including remodeling of the cell cytoskeleton, thus the employment of drugs targeting this structure is of notable interest in the pharmaceutical field. Here, we demonstrated that a synthetic derivative of RSV possesses a strong activity on two main proteins forming the cell cytoskeleton, namely tubulin and actin. Particularly, by using in silico and in vitro studies, we discovered that RSV derivative **2** is able to inhibit tubulin and actin polymerization and, most interestingly, induce the F-actin depolymerization, with a common and synergic final effect, i.e., the structural dysfunction of cancer cells cytoskeleton. These exciting features are responsible for the observed reduced metastatic and migration potentials of the breast cancer cells used as models, as demonstrated by wound healing, Boyden Chamber, and 3D-spheroid formation assays. We are confident  
Figure 9: Derivative **2** inhibits breast cancer cell 3D-spheroid formation. MCF-7 and MDA-MB-231 cells were plated on low-attachment plates and then left untreated (CTRL) or treated with derivative **2** (**2**) and RSV (20 \(\upmu\)M). Spheroid formation capability of untreated and treated cells was determined in a 3D spheroid assay as described in “Materials and Methods”. Tumor spheres formation efficiency (TSFE) was evaluated five days later (\(\lx@math@degree\)\(p<0.05\) vs. untreated cells). Images are from a representative experiment (magnification \(\times 100\), scale bar: 100 \(\upmu\)m). Right graphs represent the mean values \(\pm\) SD of three independent experiments of 3D-spheroids formed and expressed as fold change over untreated cells (CTRL) (\(\lx@math@degree\)\(p<0.05\) vs. CTRL).  
that these studies may support and push the research of anticancer drugs, derived from natural products, gifted with synergic multi-target effects and lower toxicity.  
Conceptualization, J.C., A.C. and D.I.; methodology, D.I. and A.C.; software, C.R. and G.C.V.; validation, D.I.; investigation, J.C. and A.D.L.; data curation, C.S. and V.P.; writing--original draft preparation, J.C. and A.C.; writing--review and editing, D.I. and M.S.S.; visualization, V.P. and C.S.; supervision, M.S.S.; funding acquisition, V.P., A.C., A.D.L. and C.R. All authors have read and agreed to the published version of the manuscript.  
This work was supported by a special award (Department of Excellence, Italian Law 232/2016) from the Italian Ministry of Research and University (MIUR) to the Department of Pharmacy, Health and Nutritional Sciences of the University of Calabria (Italy), and by MIUR ex 60% (V.P., A.C.) and by AIRC (Associazione Italiana per la Ricerca sul Cancro), projects n. IG20122. A.D.L. was supported by a fellowship from PAC (Progetto Strategico Regionale Calabria Alta Formazione) Calabria 2014/2020--Asse Prioritario 12, Linea B, Azione 10.5.12. C.R. acknowledges the support by a grant from the Italian Ministry of Health (Ricerca Corrente 2012). J.C. was supported by Italian Minister of University and Research [MIUR, D.M. 1062 del 10.08.2021]-PON R&L 2014-2020 \"Azione IV.6 \"Contratti di ricerca sul tematice Green\" 1062.R13_CREEN. M.S. was supported by PON 'R&l\" 2014-2020--project from Area di Specializzazione \"Salute\", ARSO1_00568 titled \"SI.F.I.PA.CRO.DE.--Sviluppo e industrializzazione farraci innovati per tarpia molecolare personalizzata PA. CRO. DE. for providing lab tools. GCV is supported by a fellow from the Italian Ministry of Health (5x1000 2018-2019).  
Not applicable.  
The authors declare no conflict of interest.