Browsing by Subject "Drug resistance"

Now showing 1 - 3 of 3
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    Development of effective anti-cancer agents targeting drug-resistant malignancies
    (2011-09) Das, Sonia Goutam Kumar
    Rapid development of multidrug resistance (MDR) against current therapies is a major barrier in the treatment of cancer. Over-expression of anti-apoptotic Bcl-2 proteins has been implicated in development of cancer and drug resistance. Hence, our research has focused on developing anti-apoptotic Bcl-2 inhibitors that can eliminate drug-resistant cancer cells. HA 14-1 was the first small-molecule reported to inhibit anti-apoptotic Bcl-2 proteins and selectively eliminated cancer cells over-expressing anti-apoptotic Bcl-2 proteins. However, previous work in our lab revealed that HA 14-1 is unstable and decomposes within 15 min in cell culture medium at 37°C. Therefore, the main aim of this thesis was to develop a stable, more potent analog of HA 14-1, which would retain its beneficial properties. In the current work we were able to design a stable analog of HA 14-1 (sHA 14-1) by removing the cyano group from HA 14-1. Although sHA 14-1 had beneficial properties like HA 14-1, it was 2-fold less potent in activity. Further SAR studies carried out to improve the activity of sHA 14-1 led to the discovery of CXL017, which was ~27 fold more potent than sHA 14-1 and ~12 fold more potent than HA 14-1. Biological studies on CXL017 revealed that CXL017 causes cell death via apoptosis characterized by caspase-3/7 activation and PARP cleavage. Furthermore, CXL017 selectively eliminated drug-resistant cancer cells both in vitro and in vivo. These interesting results, prompted us to investigate the effects of long-term exposure to CXL017 in drug-resistant cancer cells. Our results show that drug-resistant cells do not develop stable resistance to CXL017 upon prolonged exposure for 6 months. In addition, drug-resistant cells exposed to CXL017 for 4 months develop collateral sensitivity towards a variety of standard therapies. Mechanistic investigations suggests that the re-sensitization observed in drug-resistant cells exposed to CXL017 is caused due to the down-regulation of Mcl-1 and a decrease in ER calcium content in these cell lines. Taken together, the results demonstrated in this work show that CXL017 is a more potent stable analog of HA 14-1, which merits further investigation for its potential as a drug candidate for the treatment of MDR cancers.
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    Pharmacogenomic modeling of bortezomib resistance in B cell malignancies
    (2013-04) Stessman, Holly Annette-Feser
    Proteasome inhibitors are a class of drugs that have been largely successful in the treatment of cancer patients, particularly those with the plasma cell malignancy, multiple myeloma. The most successful of these drugs, bortezomib (Bz), has paved the way for the development of next-generation proteasome inhibitors. Although Bz has significantly contributed to improved outcomes in myeloma patients, acquired resistance to Bz is imminent. Furthermore, a portion of patients never initially respond to the drug. Therefore, the goal of these studies was to further characterize Bz resistance with the aim to better predict secondary therapies that may be used successfully with Bz to recapture drug sensitivity.In the first study, we describe the creation of an in vitro malignant mouse plasma cell system from which we create isogenic pairs of Bz-sensitive and -resistant cell lines. We further characterize the transcriptional responses of these cell line pairs to identify both conserved and unique expression signatures. Using the expression signatures that are unique to each pair of cell lines, we identify secondary therapies that may be useful for treatment of the Bz-refractory cell line using an in silico database called Connectivity Map (CMAP). This analysis predicted a unique response to histone deacetylase inhibitors, a class of drugs that are currently being tested for efficacy in myeloma, in only one mouse cell line pair. Indeed, we find that the predicted Bz-resistant cell line has increased sensitivity to this class of drugs (including the drug panobinostat). When these cells were transferred back into syngeneic recipient mice, panobinostat treatment could successfully extend the life of Bz-resistant animals suggesting that the Bz-resistant phenotype may select also for increased sensitivity to other drugs that may be identified through in silico approaches. In the second study, we follow up these observations by investigating other CMAP prediction patterns, such as those that are conserved across all cell line pairs. A second prediction of one class of these CMAP-predicted drugs using high-throughput drug screening of the cell lines revealed that a combination of these approaches may be highly successful for accurate prediction of secondary therapies. Based on these predictions, we further investigate the efficacy of topoisomerase inhibitors in combination with Bz for the treatment of Bz-resistant cell lines.In the third study, we provide further immunophenotypic characterization of the Bz-sensitive and -resistant mouse cell lines revealing not only cell surface markers that are associated with "acquired" and "innate" Bz resistance but perhaps a mechanism of resistance. Although Bz-sensitive mouse cells display a classic myeloma phenotype, homing to the bone marrow in vivo and expressing classic plasma cell markers, Bz-resistant mouse cells present as extramedullary disease and express a more B cell-like immunophenotype. We identify that differences in migration may be linked to the differential expression of the bone marrow homing protein, CXCR4. Lower expression of this gene in a Bz human clinical trial was also associated with inferior survival. Immunophenotypic characterization of these cell populations further revealed that forced differentiation of the Bz-resistant population could restore Bz-sensitivity.The final study investigates the acquisition of Bz-resistance in a B cell malignancy, Burkitt lymphoma, that is currently undergoing Bz clinical trials. In this particular malignancy, a DNA mutator, AID, is known to be expressed that may contribute to other types of drug resistance. Here, we identify that this is unlikely a mechanism for developing resistance to Bz. Furthermore, we provide evidence that AID activity is reduced in Bz-resistant clones and, in fact, that high AID expression may be selectively eliminated during Bz selection.
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    Pre-clinical Strategies to Overcome Drug-Resistant Multiple Myeloma: Predictive Transcriptomics and Targeting the Myeloma Epigenome
    (2018-04) Harding, Taylor
    Multiple myeloma remains an incurable hematological malignancy due to the failure of standard-of-care therapies to broadly target a genetically heterogeneous disease and an inability overcome inevitable drug-resistant relapse. This dissertation will address this outstanding problem through two approaches: transcriptomic profiling to predict resistance to proteasome inhibitors and pre-clinical evaluation of epigenetic-targeting therapies to broadly target the myeloma epigenome. First, our goal was to develop a gene expression signature that predicts response specific to proteasome inhibitor (PI) treatment in MM. Using a well-characterized panel of human myeloma cell lines (HMCLs) representing the biological and genetic heterogeneity of MM, we created an in vitro chemosensitivity profile in response to treatment with the four PIs as single-agents. Through gene expression profiling and machine learning-based computational approaches we identified a 42-gene expression signature that could not only distinguish good and poor PI-response in the HMCL panel, but could also be successfully applied to four different clinical datasets on MM patients undergoing PI-based chemotherapy to distinguish between extraordinary (good and poor) outcomes. Our results demonstrate the use of in vitro modeling and machine learning-based approaches to establish predictive biomarkers of response and resistance to drugs that may serve to better direct myeloma patient treatment options. Epigenetic abnormalities are abundantly present in multiple myeloma and accumulating evidence suggests that the histone methyltransferase EZH2 is aberrantly active in MM. We tested the efficacy of EZH2 specific inhibitors in a large panel of human MM cell lines (HMCLs) and found that only a subset of HMCLs demonstrate single agent sensitivity despite ubiquitous global H3K27 demethylation. Pre-treatment with EZH2 inhibitors greatly enhanced the sensitivity of HMCLs to the pan-HDAC inhibitor panobinostat in nearly all cases regardless of single agent EZH2 inhibitor sensitivity. Transcriptomic profiling revealed large-scale transcriptomic alteration by EZH2 inhibition highly enriched for cancer-related pathways. Further analysis demonstrated that combination treatment further perturbed oncogenic pathways and signaling nodes consistent with an antiproliferative/pro-apoptotic state. We conclude that combined inhibition of HDAC and EZH2 inhibitors is a promising therapeutic strategy to broadly target the epigenetic landscape of aggressive MM.