About the Cover: Cover illustration by P. Podsiadlo and N. Kotov. 6-Mercaptopurine and its riboside derivatives are some of the most widely utilized anti-leukemic and anti-inflammatory drugs. Their short biological half-life and severe side effects limit their use. 6-Mercaptopurine-9-β-d-ribofuranoside, a prodrug of 6-mer captopurine, was used as a stabilizer of 4-5 nm diameter gold nanoparticles. In spite of covalent attachment of the drug to the surface of the nanocolloid via a strong S-Au bond which should decrease the drug's effectiveness, the conjugate showed improved in vitro anti-cancer efficacy over the drug in free form. The pictures show gradual uptake of the gold nanoparticles bearing the drug and FITC fluorescent dye by myeloid leukemia cells after 4 h (left) and 16 h (right) incubation. This study unveils basic steps in the metabolism of AuNPs in the cells involving enhanced transmembrane transport of particles by endocytosis and subsequent digestion in lysosomes where the drug is released due to low pH. For more information, see "Gold Nanoparticles Enhance the Anti- Leukemia Action of a 6-Mercaptopurine Chemotherapeutic Agent" by P. Podsiadlo, V. A. Sinani, J. H. Bahng, N. W. S. Kam, J. Lee, and N. A. Kotov on pages 568-574 of this issue. Copyright 2008 American Chemical Society View the article.