The superimposition of the X-ray complexes of cyclohexanediones (i.e., TUB015), described by our research group, and nocodazole, within the colchicine binding site of tubulin provided an almost perfect overlap of both ligands. This structural information led us to propose hybrids of TUB015 and nocodazole using a salicylanilide core structure. Interestingly, salicylanilides, such as niclosamide, are well-established signal transducers and activators of transcription (STAT3) inhibitors with anticancer properties. Thus, different compounds with this new scaffold have been synthesized with the aim to identify compounds inhibiting tubulin polymerization and/or STAT3 signaling. As a result, we have identified new salicylanilides (6 and 16) that showed significant antiproliferative activity against a panel of cancer cells. Both compounds were able to reduce the levels of p-STAT3Tyr705 without affecting the total expression of STAT3. While compound 6 inhibited tubulin polymerization and arrested the cell cycle of DU145 cells at G2/M, similar to TUB015, compound 16 showed a more potent effect on inhibiting STAT3 phosphorylation and arrested the cell cycle at G1/G0, similar to niclosamide. In both cases, no toxicity towards PBMC cells was detected. Thus, the salicylanilides described here represent a new class of antiproliferative agents affecting tubulin polymerization and/or STAT3 phosphorylation.

Department of Pharmacology and Toxicology Faculty of Pharmacy Masaryk University Palackeho tr 1946 1 612 42 Brno Czech Republic

Instituto de Quimica Medica c Juan de la Cierva 3 28006 Madrid Spain

KU Leuven Department of Microbiology Immunology and Transplantation Laboratory of Virology and Chemotherapy Rega Institute for Medical Research KU Leuven Herestraat 49 3000 Leuven Belgium

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