Browsing by Author "Kovalchuk, Olga"
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- ItemOpen AccessA suppressive role of guanine nucleotide-binding protein subunit beta-4 inhibited by DNA methylation in the growth of anti-estrogen resistant breast cancer cells(2018-08-13) Wang, Bo; Li, Dongping; Rodriguez-Juarez, Rocio; Farfus, Allison; Storozynsky, Quinn; Malach, Megan; Carpenter, Emily; Filkowski, Jody; Lykkesfeldt, Anne E; Kovalchuk, OlgaAbstract Background Breast cancer is the most common malignancy in women worldwide. Although the endocrine therapy that targets estrogen receptor α (ERα) signaling has been well established as an effective adjuvant treatment for patients with ERα-positive breast cancers, long-term exposure may eventually lead to the development of acquired resistance to the anti-estrogen drugs, such as fulvestrant and tamoxifen. A better understanding of the mechanisms underlying antiestrogen resistance and identification of the key molecules involved may help in overcoming antiestrogen resistance in breast cancer. Methods The whole-genome gene expression and DNA methylation profilings were performed using fulvestrant-resistant cell line 182R-6 and tamoxifen-resistant cell line TAMR-1 as a model system. In addition, qRT-PCR and Western blot analysis were performed to determine the levels of mRNA and protein molecules. MTT, apoptosis and cell cycle analyses were performed to examine the effect of either guanine nucleotide-binding protein beta-4 (GNB4) overexpression or knockdown on cell proliferation, apoptosis and cell cycle. Results Among 9 candidate genes, GNB4 was identified and validated by qRT-PCR as a potential target silenced by DNA methylation via DNA methyltransferase 3B (DNMT3B). We generated stable 182R-6 and TAMR-1 cell lines that are constantly expressing GNB4 and determined the effect of the ectopic GNB4 on cell proliferation, cell cycle, and apoptosis of the antiestrogen-resistant cells in response to either fulvestrant or tamoxifen. Ectopic expression of GNB4 in two antiestrogen resistant cell lines significantly promoted cell growth and shortened cell cycle in the presence of either fulvestrant or tamoxifen. The ectopic GNB4 induced apoptosis in 182R-6 cells, whereas it inhibited apoptosis in TAMR-1 cells. Many regulators controlling cell cycle and apoptosis were aberrantly expressed in two resistant cell lines in response to the enforced GNB4 expression, which may contribute to GNB4-mediated biologic and/or pathologic processes. Furthermore, knockdown of GNB4 decreased growth of both antiestrogen resistant and sensitive breast cancer cells. Conclusion GNB4 is important for growth of breast cancer cells and a potential target for treatment.
- ItemOpen AccessRadiation Dosimetry in the Presence of Gold Nanoparticles(2017) Koger, Brandon; Kirkby, Charles; Spencer, David; Yau, Andrew; Kovalchuk, OlgaThe use of gold nanoparticles (GNPs) to enhance the dose due to radiation, through increased photoelectric effect interactions, has shown promise in vivo and in vitro. Monte Carlo studies have worked towards quantifying the dose enhancement and the dosimetry surrounding GNPs. This thesis investigates the dosimetry in the presence of GNPs for several scenarios using PENELOPE Monte Carlo simulations. Accurate simulation of GNPs can be challenging due to the large number of particles present in realistic scenarios – up to 10^15 particles/cm^3. Because of this, many Monte Carlo studies have approximated GNPs in tissue as a homogeneous mixture of tissue and gold. However, such models ignore details of energy deposition on nanoscopic scales, including absorption of dose within the GNPs. In this thesis, we first quantified the dosimetric impact of this assumption, finding dose differences up to 31% for the scenarios investigated, and enabling fast, accurate simulation of macroscopic dose enhancement. The eventual clinical application of GNP-enhanced radiation therapy will rely on enhancement at macroscopic scales. We next investigated the general feasibility of using GNP-enhanced arc radiation therapy (GEART) to treat deep-seated tumours using kilovoltage photon beams. Applying the method established above, we quantified the quality of GEART treatments compared to conventional 6 MV treatments for a variety of tumour sizes and depths. We recommended those sites for which further investigation should be undertaken. In vivo and in vitro, GNPs are often coated with polyethylene glycol (PEG), a polymer that enables functionalization and biocompatibility. Monte Carlo studies, however, typically do not model these coatings, which may lead to dosimetric errors. We quantified the dose lost to PEG coatings for a variety of GNP sizes, coating thicknesses, and photon beam energies. Dose losses of up to 7.5% and 34% were seen on microscopic and nanoscopic scales, respectively. Through this work we aim to provide a basis for future studies examining clinical implementation of GNP dose enhancement, adding to the base of knowledge that can be drawn upon if GNP dose enhancement is to be brought into clinical use. Further research is needed to evaluate the radiobiological impact of the effects studied here.