Cisplatin and platinum drugs at the molecular level. (Review)

Over twenty years of intensive work toward improvement of cisplatin, and with hundreds of platinum drugs tested, has resulted in the introduction of the widely used carboplatin and of oxaliplatin used only for a very narrow spectrum of cancers. A number of interesting platinum compounds including the orally administered platinum drug JM216, nedaplatin, the sterically hindered platinum(II) complex ZD0473, the trinuclear platinum complex BBR3464, and the liposomal forms Lipoplatin and SPI-77 are under clinical evaluation. This review summarizes the molecular mechanisms of platinum compounds for DNA damage, DNA repair and induction of apoptosis via activation or modulation of signaling pathways and explores the basis of platinum resistance. Cisplatin, carboplatin, oxaliplatin and most other platinum compounds induce damage to tumors via induction of apoptosis; this is mediated by activation of signal transduction leading to the death receptor mechanisms as well as mitochondrial pathways. Apoptosis is responsible for the characteristic nephrotoxicity, ototoxicity and most other toxicities of the drugs. The major limitation in the clinical applications of cisplatin has been the development of cisplatin resistance by tumors. Mechanisms explaining cisplatin resistance include the reduction in cisplatin accumulation inside cancer cells because of barriers across the cell membrane, the faster repair of cisplatin adducts, the modulation of apoptotic pathways in various cells, the upregulation in transcription factors, the loss of p53 and other protein functions and a higher concentration of glutathione and metallothioneins in some type of tumors. A number of experimental strategies to overcome cisplatin resistance are at the preclinical or clinical level such as introduction of the bax gene, inhibition of the JNK pathway, introduction of a functional p53 gene, treatment of tumors with aldose reductase inhibitors and others. Particularly important are combinations of platinum drug treatments with other drugs, radiation and the emerging gene therapy regimens.