We have designed MI-219 as a potent, highly selective and orally active small-molecule inhibitor of the MDM2-p53 interaction. MI-219 binds to human MDM2 with a Ki value of 5 nM and is 10,000-fold selective for MDM2 over MDMX. It disrupts the MDM2-p53 interaction and activates the p53 pathway in cells with wild-type p53, which leads to induction of cell cycle arrest in all cells and selective apoptosis in tumor cells. MI-219 stimulates rapid but transient p53 activation in established tumor xenograft tissues, resulting in inhibition of cell proliferation, induction of apoptosis, and complete tumor growth inhibition. MI-219 activates p53 in normal tissues with minimal p53 accumulation and is not toxic to animals. MI-219 warrants clinical investigation as a new agent for cancer treatment.cancer therapy ͉ MDM2-p53 protein-protein interaction ͉ selective toxicity to tumors ͉ small-molecule inhibitor T he tumor suppressor p53 plays a central role in the regulation of cell cycle, apoptosis, DNA repair, and senescence (1-4). Because of the prominent role played by p53 in suppressing oncogenesis (5), it is not surprising that p53 function is impaired in all human cancers. Several distinct approaches have been pursued to restore p53 function as a new cancer therapeutic strategy (6-9). Three recent studies, using unique genetic mouse models, have demonstrated that the restoration of p53 leads universally to a rapid and robust regression of established sarcomas, lymphomas, and liver tumors (10)(11)(12)(13)(14). These studies provide strong evidence that established tumors remain persistently vulnerable to p53 tumorsuppressor function and that restoration of p53 function is therefore a powerful cancer therapeutic strategy (13).In Ϸ50% of human cancers, the gene encoding p53 is either deleted or mutated, rendering the p53 protein inactive (5, 15). In the remaining cancers, p53 retains its wild-type status but its function is effectively inhibited by its primary cellular inhibitor, the human MDM2 oncoprotein (mouse double minute 2, also termed HDM2 in humans) (5,16,17). One attractive pharmacological approach to p53 reactivation is to use a small molecule to block the MDM2-p53 interaction (6)(7)(8)18). The discovery of the Nutlins provided the important proof of the concept for this approach (7). Nutlins were shown to bind to MDM2, block the MDM2-p53 interaction, and activate wild-type p53 (7,(19)(20)(21). Nutlin-3a exhibits strong anti-tumor activity in multiple xenograft mouse models of human cancer (7,19). The discovery of the Nutlins has fueled enthusiasm for the development of small-molecule MDM2 inhibitors as a new class of anticancer therapy (6,8,22,23).One critical question in the development of MDM2 inhibitors for cancer treatment is their potential toxicity to normal tissues. This concern was heightened by a recent genetic study, which showed that p53 activation in the absence of the MDM2 gene causes severe toxicity to radiosensitive normal adult mouse tissues, leading to rapid animal death (24). Previous studies on ...

Potent, specific, non-peptide small-molecule inhibitors of the MDM2-p53 interaction were successfully designed. The most potent inhibitor (MI-63) has a K(i) value of 3 nM binding to MDM2 and greater than 10,000-fold selectivity over Bcl-2/Bcl-xL proteins. MI-63 is highly effective in activation of p53 function and in inhibition of cell growth in cancer cells with wild-type p53 status. MI-63 has excellent specificity over cancer cells with deleted p53 and shows a minimal toxicity to normal cells.

Poly(amidoamine), or PAMAM, dendrimers in the G5−G10 range were imaged by tapping mode atomic force microscopy (AFM). Individual dendrimer molecules could be clearly observed in the AFM images, which showed that these dendritic particles appear to be monodispersed, dome-shaped, and randomly distributed on the mica surface. Molecular diameter and height can also be measured from each particle's profile section from the AFM line scans. The diameter and height data were used to calculate the molecular volume of each single molecule. Absolute molecular weight and polydispersity were then estimated for each dendrimer generation. The calculated molecular weights for G5−G8 were in very good agreement with theoretical values. In addition, lower generation dendrimers, such as G4, were also studied by AFM. Although individual molecules of G4 dendrimer could not be imaged, the surface morphology of G4 dendrimer films on mica at different surface densities was observed by AFM.