A cell-permeable poly(ADP-ribose) polymerase (PARP) inhibitor. Offers protection against peroxynitrite and hydroxyl radicals in vitro and in vivo and abrogates peroxynitrite-induced mitochondrial transmembrane potential (DYm) reduction. Also exhibits malignant phenotype reversal in cancer cells and inhibits HIV-1 IIIb replication in vitro.