http://hdl.handle.net/1721.1/7754 Search the Channel search http://dspace.mit.edu/simple-search http://hdl.handle.net/1721.1/34155 Title: The role of mismatch repair in mediating cellular sensitivity to cisplatin : the Escherichia coli methyl-directed repair paradigm <br/> <br/>Authors: Robbins, Jennifer L <br/> <br/>Abstract: The anticancer drug cisplatin is in widespread use but its mechanism of action is only poorly understood. Moreover, human cancers acquire resistance to the drug, which limits its clinical utility. A paradox in the field is how loss of mismatch DNA repair leads to clinical resistance to this widely used drug. The phenomenon of cisplatin tolerance in mismatch repair deficient cells was initially discovered in E. coli, where methylation deficient dam mutants show high sensitivity to cisplatin and dam mutants with an additional mutation in either of the mismatch repair genes mutS or mutL show near wildtype levels of resistance. A prevalent explanation for this observation is the abortive repair model, which proposes that in dam mutants, where the strand discrimination signal is lost, mismatch repair attempts futile cycles of repair opposite cisplatin-DNA adducts. Previous findings have supported this model to the extent that MutS, the E. coli mismatch recognition protein, specifically recognizes DNA modified with cisplatin. However it has recently been shown that MutS binding to cisplatin adducts may contribute to toxicity by instead preventing the recombinational repair of a cisplatin-modified substrate, and we have previously shown that recombination is an essential mechanism for tolerating cisplatin damage.; (cont.) In the present study, we examined the global transcriptional responses of wildtype, dam, dam mutS, and mutS mutant E. coli after treatment with a toxic dose of cisplatin. We also determined any dose-response at the transcriptional level of several SOS response genes and other genes involved in DNA repair by real time RT-PCR. Furthermore, we performed single-cell electrophoresis in order to determine the effect of mismatch repair on the level of double-strand break formation in cisplatin-treated cells. Our results show that Dam-deficient strains exhibit unique gene regulation that may be due to mismatch-repair induced DNA damage in the absence of adenine methylation. In addition, cisplatin treatment induces double-strand break formation and the SOS response in a dose-dependent manner, and both break formation and the SOS response are greatest in the hypersensitive dam mutant strain. The higher level of cisplatin-induced double-strand breaks in the dam mutant may be dependent on functional mismatch repair. <br/> <br/>Description: Thesis (Ph. D.)--Massachusetts Institute of Technology, Biological Engineering Division, 2006.; Includes bibliographical references (v. 2, leaves 195-258). http://hdl.handle.net/1721.1/35701 Title: Cisplatin cytotoxicity associated with tetracycline resistance determinants in Escherichia coli <br/> <br/>Authors: Froim, Doriana, 1973- <br/> <br/>Abstract: Tetracyclines, a broad-spectrum class of antibiotics, were discovered in the late 1940s, and became widely used because of their important advantages: they are inexpensive, safe, demonstrate good oral absorption, and are active against a broad range of bacterial pathogens. Unfortunately, as with most antibiotics, the emergence of microbial resistance to tetracyclines has become a serious problem. Today, most genera examined have tetracycline-resistant isolates, although the percentage varies according to species and geographic location. Due to the emergence of resistance, tetracyclines are no longer the antibiotics of choice in treatment of many conditions, although they are still extensively used to treat a variety of bacterial infections. Substantial research efforts have been directed towards reversing tetracycline resistance in bacteria. This work describes the development of a novel anti-bacterial treatment for diseases caused by bacteria resistant to tetracycline. It was found that tetracycline-resistant bacteria expressing the TnlO gene of tetracycline resistance, upon induction with tetracycline, became extremely susceptible to destruction by the DNA-damaging anti-cancer drug cisplatin. Tetracycline-resistant bacteria grown in tetracycline and subsequently treated with cisplatin in the presence of tetracycline were killed about 10⁵-fold more effectively than wild-type bacteria and tetracycline-resistant bacteria not exposed to tetracycline. This phenomenon was observed in different strains of tetracycline-resistant E. coli. Other antibiotics tested with respective antibiotic-resistant bacteria did not produce the same effect of sensitization to cisplatin, suggesting a unique relationship among cisplatin, tetracycline and the tetracycline resistance; (cont.) gene. It was determined that levels of platinum DNA damage were higher in sensitized tetracycline-resistant cells than in wild-type cells, although total cellular platinum levels in sensitized tetracycline-resistant cells were not increased. At this time, the mechanism of increased DNA damage formation and the mechanism underlying sensitization to cisplatin are still matters of speculation. The experiments reported here, however, demonstrate that cells expressing the genes of tetracycline resistance actually became primary targets for destruction by cisplatin. Based on this study, it is suggested that the therapeutic power of the tetracyclines could be restored and enhanced by using a complementary drug that, in combination with tetracycline, would induce selective destruction of tetracycline-resistant bacteria. <br/> <br/>Description: Thesis (Ph. D. in Molecular and Systems Toxicology and Pharmacology)--Massachusetts Institute of Technology, Biological Engineering Division, 2005.; Includes bibliographical references. http://hdl.handle.net/1721.1/40588 Title: Characterization of a substance from Chinese-style salted shrimp paste that causes DNA single-strand breaks in human cells <br/> <br/>Authors: Brunson, Don Carlos <br/> <br/>Description: Thesis (Ph. D.)--Massachusetts Institute of Technology, Division of Toxicology, 1996.; Includes bibliographical references (leaves 106-109). http://hdl.handle.net/1721.1/39922 Title: A dendrimer-based prodrug for use in an anti-cancer nanocell <br/> <br/>Authors: Awasthi, Samir <br/> <br/>Abstract: Cancer science is a heavily researched and rapidly changing field. Cutting edge research consistently reveals unique features of tumors that can be exploited for treatment. For example, it is well known that cells of varying tumor types have unique molecular markers and cell-surface receptors - fingerprints of sorts - that set cancerous cells apart from healthy cells. Furthermore, the tumor microenvironment has been explored to the point that its unique fluid mechanical and biochemical properties are well understood in the context of tumor growth and survival. However, very little of this research has penetrated clinical medicine. The purpose of this thesis is to present a recent concept in cancer therapy: an anti-cancer nanocell that is capable of the spatial and temporal targeting of drugs to tumor cells. The combination of targeting mechanisms designed into the nanocell is a product of our current understanding of tumors. The design serves to improve the effectiveness of inexpensive, out-of-patent cytotoxic and anti-angiogenic drugs to standards representative of modern research. Efforts towards improving the efficiency of the nanocell, with regards to both drug loading and tumor cell targeting, are presented and discussed.; (cont.) The synthesis of various polymer-ligand conjugates for use in the improved nanocell is reported, as is the development of a prodrug consisting of a generation three polyamidoamine dendrimer conjugated to methotrexate via an ester bond; cell studies demonstrating the effectiveness of the prodrug are included. The expandability of the nanocell is also explored, because ultimately, the nanocell must be robust enough to accommodate both tumor-type and population variability. <br/> <br/>Description: Thesis (M. Eng.)--Massachusetts Institute of Technology, Biological Engineering Division, 2007.; Includes bibliographical references.