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Cancer-specific inhibitors that reflect the unique metabolic needs of cancer cells are rare. Here we describe Gboxin, a small molecule that specifically inhibits the growth of primary mouse and human glioblastoma cells but not that of mouse embryonic fibroblasts or neonatal astrocytes. Gboxin rapidly and irreversibly compromises oxygen consumption in glioblastoma cells. Gboxin relies on its positive charge to associate with mitochondrial oxidative phosphorylation complexes in a manner that is dependent on the proton gradient of the inner mitochondrial membrane, and it inhibits the activity of F.sub.0F.sub.1 ATP synthase. Gboxin-resistant cells require a functional mitochondrial permeability transition pore that regulates pH and thus impedes the accumulation of Gboxin in the mitochondrial matrix. Administration of a metabolically stable Gboxin analogue inhibits glioblastoma allografts and patient-derived xenografts. Gboxin toxicity extends to established human cancer cell lines of diverse organ origin, and shows that the increased proton gradient and pH in cancer cell mitochondria is a mode of action that can be targeted in the development of antitumour reagents. Gboxin and its chemical derivatives inhibit the growth of primary human and mouse glioblastoma cells, but not of mouse embryonic fibroblasts or neonatal astrocytes, by targeting mitochondrial oxidative phosphorylation complexes., Author(s): Yufeng Shi [sup.1] [sup.2] , S. Kyun Lim [sup.3] [sup.4] [sup.8] , Qiren Liang [sup.3] , Swathi V. Iyer [sup.1] [sup.2] , Hua-Yu Wang [sup.3] , Zilai Wang [sup.1] [...]

Objectives: The tumor suppressor p53 plays a crucial role in the development of osteosarcoma. The primary objective of this study is to develop and optimize lipid based nanoparticle formulations that can carry siRNA and effectively silence mutant p53 in 318–1, a murine osteosarcoma cell line. Methods: The nanoparticles were composed of a mixture of two lipids (cholesterol and DOTAP) and either PLGA or PLGA-PEG and prepared by using an EmulsiFlex-B3 high pressure homogenizer. A series of studies that include using different nanoparticles, different amount of siRNAs, cell numbers, incubation time, transfection media volume, and storage temperature was performed to optimize the gene silencing efficiency. Key findings: Replacement of lipids by PLGA or PLGA-PEG decreased the particle size and overall cytotoxicity. Among all lipid-polymer nanoformulations, nanoparticles with 10% PLGA showed highest mutant p53 knockdown efficiency while maintaining higher cell viability when a nanoparticle to siRNA ratio equal to 6.8:0.66 and 75 nM siRNA was used. With long term storage the mutant p53 knockdown efficiency decreased to a greater extent. Conclusions: This study warrants a future evaluation of this formulation for gene silencing efficiency of mutant p53 in tissue culture and animal models for the treatment of osteosarcoma. [ABSTRACT FROM AUTHOR]

Many p53 hotspot mutants not only lose the transcriptional activity, but also show dominant-negative (DN) and oncogenic gain-of-function (GOF) activities. Increasing evidence indicates that knockdown of mutant p53 (mutp53) in cancer cells reduces their aggressive properties, suggesting that survival and proliferation of cancer cells are, at least partially, dependent on the presence of mutp53. However, these p53 siRNAs can downregulate both wild-type p53 (wtp53) and mutp53, which limits their therapeutic applications. In order to specifically deplete mutp53, we have developed allele-specific siRNAs against p53 hotspot mutants and validated their biological effects in the absence or presence of wtp53. First, the mutp53-specific siRNAs selectively reduced protein levels of matched p53 mutants with minimal reduction in wtp53 levels. Second, downregulation of mutp53 in cancer cells expressing a mutp53 alone (p53mut) resulted in significantly decreased cell proliferation and migration. Third, transfection of mutp53-specific siRNAs in cancer cells expressing both wtp53 and mutp53 also reduced cell proliferation and migration with increased transcripts of p53 downstream target genes, which became further profound when cells were treated with an MDM2 inhibitor Nutlin-3a or a chemotherapeutic agent doxorubicin. These results indicate that depletion of mutp53 by its specific siRNA restored endogenous wtp53 activity in cells expressing both wtp53 and mutp53. This is the first study demonstrating biological effects and therapeutic potential of allele-specific silencing of mutp53 by mutp53-specific siRNAs in cancer cells expressing both wtp53 and mutp53, thus providing a novel strategy towards targeted cancer therapies.