Theses and Dissertations from UMD
Permanent URI for this communityhttp://hdl.handle.net/1903/2
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a give thesis/dissertation in DRUM
More information is available at Theses and Dissertations at University of Maryland Libraries.
Browse
3 results
Search Results
Item EVALUATING THE PHOTODYNAMIC AND SONODYNAMIC POTENTIAL OF CLINICALLY RELEVANT PHOTOSENSITIZERS AND DYES(2024) Vig, Shruti; Chiao Huang, Huang; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Light-activable agents such as fluorophores and photosensitizers are used for fluorescenceimaging and photodynamic therapy (PDT) applications in the clinic. These agents can absorb light at specific wavelengths and generate fluorescence and/or cytotoxic reactive molecular species (RMS). Photosensitizers can also interact with ATP-binding cassette (ABC) transporters on target cells. This interaction can affect the intracellular accumulation of photosensitizers and thereby influence imaging and treatment efficacy and outcomes. Currently, there are no well-established methods for screening photoactive agents for potential phototoxicity, creating a need for reliable iii testing methods. Comprehensive screening methods are essential for ensuring safe and effective imaging and therapeutic outcomes with light activable agents. Moreover, photosensitizers are currently being explored for sonodynamic therapy (SDT) with ultrasound in patients. Just like PDT, photosensitizers are thought to be activated by ultrasound-mediated light generation (sonoluminescence) to generate RMS. However, no evidence supporting this mechanism has been published with safe, monitorable, and reproducible SDT effects. Thus, rigorous test methods must be developed to evaluate photochemical activation of photosensitizers using clinically relevant SDT parameters. The results obtained through the studies in this dissertation resulted in (1) A modified invitro test method for assessing the photo-cytotoxic potential of light-activable agents at clinically relevant concentrations and illumination parameters, (2) Updated the ABC transporter substrate status of clinically relevant using in-vitro extraction and flowcytometry methods. (3) Confirmed lack of photochemical activation of clinically relevant photosensitizers during SDT as a potential mechanism of action using a phantom model. A comprehensive understanding of the mechanisms and factors affecting the safety and efficacy of fluorophores and photosensitizers is essential for advancing the field of fluorescence imaging, PDT, and SDT for cancer and other diseases.Item Mathematical Models of Tumor Heterogeneity and Drug Resistance(2015) Greene, James; Levy, Doron; Mathematics; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)In this dissertation we develop mathematical models of tumor heterogeneity and drug resistance in cancer chemotherapy. Resistance to chemotherapy is one of the major causes of the failure of cancer treatment. Furthermore, recent experimental evidence suggests that drug resistance is a complex biological phenomena, with many influences that interact nonlinearly. Here we study the influence of such heterogeneity on treatment outcomes, both in general frameworks and under specific mechanisms. We begin by developing a mathematical framework for describing multi-drug resistance to cancer. Heterogeneity is reflected by a continuous parameter, which can either describe a single resistance mechanism (such as the expression of P-gp in the cellular membrane) or can account for the cumulative effect of several mechanisms and factors. The model is written as a system of integro-differential equations, structured by the continuous ``trait," and includes density effects as well as mutations. We study the limiting behavior of the model, both analytically and numerically, and apply it to study treatment protocols. We next study a specific mechanism of tumor heterogeneity and its influence on cell growth: the cell-cycle. We derive two novel mathematical models, a stochastic agent-based model and an integro-differential equation model, each of which describes the growth of cancer cells as a dynamic transition between proliferative and quiescent states. By examining the role all parameters play in the evolution of intrinsic tumor heterogeneity, and the sensitivity of the population growth to parameter values, we show that the cell-cycle length has the most significant effect on the growth dynamics. In addition, we demonstrate that the agent-based model can be approximated well by the more computationally efficient integro-differential equations, when the number of cells is large. The model is closely tied to experimental data of cell growth, and includes a novel implementation of transition rates as a function of global density. Finally, we extend the model of cell-cycle heterogeneity to include spatial variables. Cells are modeled as soft spheres and exhibit attraction/repulsion/random forces. A fundamental hypothesis is that cell-cycle length increases with local density, thus producing a distribution of observed division lengths. Apoptosis occurs primarily through an extended period of unsuccessful proliferation, and the explicit mechanism of the drug (Paclitaxel) is modeled as an increase in cell-cycle duration. We show that the distribution of cell-cycle lengths is highly time-dependent, with close time-averaged agreement with the distribution used in the previous work. Furthermore, survival curves are calculated and shown to qualitatively agree with experimental data in different densities and geometries, thus relating the cellular microenvironment to drug resistance.Item Alterations in the Primary Structures of Ribosomal Proteins in Acquired Drug Resistance(2012) Lohnes, Karen Lynn; Fenselau, Catherine C; Biochemistry; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Acquired drug resistance is a multifactorial process that is one of the major causes for cancer treatment failure. The anticancer drug, mitoxantrone, was recently determined to inhibit ribosome biogenesis. Changes in ribosomal protein composition and efficiency with which the ribosomes incorporate 35S-methionine has been noted in a mitoxantrone resistant MCF7 cell line when compared with a drug-susceptible parental cell line. This dissertation evaluated three proteomic workflows in order to successfully characterize the changes in the primary structures of cytoplasmic ribosomal proteins isolated from a mitoxantrone resistant breast cancer cell line that could serve some functional significance to the resistance when compared with a parental drug-susceptible cell line. A combination of the data from the three workflows allowed for the identification of 76 of the 79 human ribosomal proteins with an average sequence coverage of 76%. The N-terminal ends of 52 of the ribosomal proteins were identified using bottom-up and middle-down mass spectrometric approaches. An additional 7 N-terminal fragments were identified by top-down high resolution mass spectrometric analysis. Forty of the 52 N-terminal peptides were observed to have lost their N-terminal methionine and 19 were acetylated. Identification of the N-terminal peptides was most successful using the middle-down approach. Internal acetylations (on lysine) and phosphorylations were only noted with trypsin in-gel digestion and HPLC fraction analysis. Gel arrays of the two ribosomal populations illustrated differences in the protein compositions. Comparative densitometry imaging software indicated the presence of two novel protein spots in the drug resistant cell line as well six additional spots with increased and decreased abundances. High coverage bottom-up mass spectrometric analysis allowed for these protein spots to be assigned as isoform pairs of RPS3, RPS10, RPL11 and RPL23A. Molecular masses and top-down analyses were used to define the alterations in the ribosomal proteins in conjunction with high coverage bottom up and middle-down analyses. The change in the primary structures of these four ribosomal proteins is believed to alter access to the mRNA tunnel in the ribosome. This suggests that these ribosomes may participate in differential selective translation to allow for the cell to produce the necessary proteins during cellular stress.