Structural and Functional Basis for Therapeutic Modulation of p53 Signaling
ABSTRACT Effective modulation of structural features and/or functional properties of the major tumor suppressor p53 as a wild-type or cancer-associated mutant protein represents a major challenge in drug development for cancer. p53 is an attractive target for therapeutic design because of its involvement as a mediator of growth arrest and apoptosis after exposure to chemoradiotherapy and/or radiotherapy. Although most clinically used cytotoxic agents target stabilization of wild-type p53, there are a number of approaches that hold promise for reactivation of mutant p53. On the other hand, brief blockade of p53 may reduce toxicity from systemic cytotoxic therapy. Screens for restoration of p53 transcriptional responses in p53-deficient cells may provide a functional means to develop anticancer therapeutics. Structure-based modulation continues to hold promise for development of peptides or small molecules capable of modulation of either wild-type or mutant p53 proteins.
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ABSTRACT: The cancer stem cell hypothesis suggests that rare populations of tumor-initiating cells may be resistant to therapy, lead to tumor relapse and contribute to poor prognosis for cancer patients. We previously demonstrated the feasibility of p53 pathway restoration in p53-deficient tumor cell populations using small molecules including ellipticine or its derivatives. We now establish a single cell p53-regulated green fluorescent protein (EGFP)-reporter system in human DLD1 colon tumor cells expressing mutant p53 protein. We use these p53-EGFP reporter DLD1 cells to investigate the status of p53 transcriptional activity in putative colon cancer stem cell populations following exposure to p53 pathway-restoring drugs and/or classical chemotherapy. We demonstrate induction of p53-specific EGFP reporter fluorescence following overexpression of p53 family member p73 by an Adenovirus vector. We further show that p53-reporter activity is induced in DLD1 putative cancer stem cell side-populations analyzed by their Hoechst dye efflux properties following treatment with the p53 pathway restoring drug ellipticine. Combination of ellipticine with the cytotoxic agent 5-fluorouracil resulted in increased cytotoxicity as compared to either agent alone and this was associated with depletion of putative cancer stem cell populations as compared with 5-FU alone treatment. Our results support the feasibility of therapeutic targeting of mutant p53 in putative cancer stem cells as well as the potential to enhance cytotoxic chemotherapy.Cancer biology & therapy 11/2009; 8(22):2186-93. DOI:10.4161/cbt.8.22.10446 · 3.63 Impact Factor
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ABSTRACT: Cisplatin is one of the most widely used and highly effective drug for the treatment of various solid tumors; however, it has dose-dependent side effects on the kidney, cochlear, and nerves. Nephrotoxicity is the most well-known and clinically important toxicity. Numerous studies have demonstrated that several mechanisms, including oxidative stress, DNA damage, and inflammatory responses, are closely associated with cisplatin-induced nephrotoxicity. Even though the establishment of cisplatin-induced nephrotoxicity can be alleviated by diuretics and pre-hydration of patients, the prevalence of cisplatin nephrotoxicity is still high, occurring in approximately one-third of patients who have undergone cisplatin therapy. Therefore it is imperative to develop treatments that will ameliorate cisplatin-nephrotoxicity. In this review, we discuss the mechanisms of cisplatin-induced renal toxicity and the new strategies for protecting the kidneys from the toxic effects without lowering the tumoricidal activity.Electrolyte & blood pressure: E & BP 12/2014; 12(2):55-65. DOI:10.5049/EBP.2014.12.2.55
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ABSTRACT: Osteosarcoma (OS) is the most common bone cancer in dogs. It is biologically aggressive and <20% survive >2 years with standard therapy. Hence, new approaches must be considered. TP53 is altered in ~50% of human and canine cancers, including OS, making it a candidate for targeted suicide gene therapy strategies. Canine OS is considered to be a good model for human OS. The aims of this study were to: examine the site incidence of canine OS retrieved from Glasgow University Veterinary School (GUVS) histology database; perform TP53 mutational analysis in canine OS cases diagnosed at GUVS; investigate delivery of exogenous wild-type canine TP53 into D17, CMT3, CMT7 and CMT8 canine OS cell lines; design and construct vectors for a TP53-targeted suicide gene strategy, which can selectively target canine OS cells containing accumulated TP53, and initially analyse using Dual-Luciferase® reporter assays (DLR); perform suicide gene/prodrug assays using nitroreductase (NTR) in combination with CB1954 or nitrofurazone (NFZ) in several canine cell lines; replace luciferase with NTR in vectors for TP53-targeted suicide gene strategy, and with CB1954, determine if survival of CMT7 cells possessing accumulated TP53 are reduced, in comparison to D17 cells, containing wild-type TP53. OS were most commonly found in appendicular areas, followed by axial and extraskeletal sites; this agrees with published findings. No TP53 mutations were found in 7 biopsies removed from 4 dogs, 5 were OS, due to analysis of a small sample number, but still fits within published data. TP53 expression did not have a significant negative effect on canine OS cell growth. Contrasting results have been shown in canine and human OS cells. Luciferase expression levels following transfection with designed constructs were higher in CMT7 cells, than in D17 cells. Similar results were shown in NTR/CB1954 assays as reductions in cell survival only occurred in CMT7 cells but not in D17 cells. NFZ was not suitable as a prodrug for NTR in canine cells as there were no differences in cell survival with cells not expressing NTR. Hence, the TP53-targeted suicide gene therapy strategy appears to selectively reduce survival of canine OS cells possessing accumulated TP53, warranting further investigation as a treatment modality for OS, in both dogs and humans.