The present invention relates to an isoxazole derivative, the compound of formula (I) herein after referred to as GIT27-NO, which is the NO-donating structurally modified form of (S,R)-3-phenyl-4,5-dihydro-5-isoxazole acetic acid, herein after referred to as VGX-1027. Treatment of three tumor cell lines, rat astrocytoma C6, mouse fibrosarcoma L929, and mouse melanoma B16 cells with GIT27-NO resulted in a significant reduction of cell respiration and of number of viable cells, while VGX-1027 was completely ineffective. Hemoglobin, which act as NO-scavenger, restored cell viability, thus indicating the NO-mediated tumoricidal effect of compound (I). GIT27-NO triggered apoptotic cell death in L929 cell cultures, while autophagic cell death is mainly responsible for the diminished viability of C6 and B16 cells. Moreover, GIT27-NO induced the production of reactive oxygen species which can be neutralized by antioxidant N-acetyl cysteine (NAC), indicating that reactive oxygen species (ROS) are at least partly involved in the reduction of cell viability. The anti-tumor activity of GIT27-NO is mediated through activation of MAP kinases (ERK1/2, p38 and JNK) in cell-specific manner. The role of MAP kinases was further confirmed by specific inhibitors of these molecules, PD98059, SB202190, and SP600125. Finally, in vivo treatment with GIT27-NO significantly reduced tumor growth in syngeneic C57BL/6 mice implanted with B16 melanoma.