Human telomeres consist of noncoding repeats of the hexanucleotide sequence 5'-TTAGGG, which protect chromosomes from degradation and end fusion, two factors limiting a normal cell's life span.  In most tumors, the telomeres are relatively short compared to normal cells but are efficiently maintained by upregulated telomerase, rendering cancer cells immortal.  It has been proposed that cancer cells, therefore, might be extremely susceptible to therapies targeted at their telomeres, which have the potential to halt indefinite cell proliferation. Telomeres contain 3' single-stranded overhangs which fold into G-quadruplex structures. In a G-quartet, four guanine bases are linked by Hoogsteen hydrogen bonding. In this arrangement, N7 of guanine is protected from G_N7-directed, electrophilic agents, such as platinum-containing drugs. We are interested in designing a G4-specific platinum-based agent that specifically targets adenine in the loop regions of the quadruplex structure. Here we report on the interactions of two platinum derivatives with the G-quadruplex structure formed by the human telomeric sequence. PT-ACRAMTU ([PtCl(en)[ACRAMTU-S]](NO₃)₂; en = ethane-1,2-diamine; ACRAMTU = 1-[2-(acridin-9-ylamino)ethyl]-1,3-dimethylthiourea) has shown enhanced adenine affinity in double-stranded DNA, which prompted us to test its reactivity on G-quadruplex. Using acidic and enzymatic digestion assays, we demonstrated that indeed ~50% of PT-ACRAMTU binds to adenine; moreover, a kinetic assay showed that platination of adenine-N7 is kinetically preferred over guanine-N7.  To produce a truly G4- and adenine-specific drug, we replaced the acridine moiety of PT-ACRAMTU with a perylene derivative. Circular dichroism spectra indicate that this new platinum derivative not only stabilizes G-quadruplex, it also induces this structure.