16 results on '"Alexander De Los Reyes"'
Search Results
2. Defect-related temperature dependence of THz emission from GaAs/AlGaAs MQWs grown on off- and on-axis substrates
- Author
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Jessica P. C. Afalla, Alexander de los Reyes, Valynn Katrine Mag-usara, Lorenzo P. Lopez Jr., Kohji Yamamoto, Masahiko Tani, Armando S. Somintac, Arnel A. Salvador, and Elmer S. Estacio
- Subjects
Physics ,QC1-999 - Abstract
Simultaneous molecular beam epitaxial growth of GaAs/AlGaAs multiple quantum wells on two different substrates (one on GaAs (100) and another on a GaAs substrate misoriented by 4° in the (111) direction) resulted in samples of similar structure, but having different defect profiles. The on-axis sample had a higher defect density and more types of electron traps than the off-axis counterpart. Temperature-dependent terahertz (THz) emission and temperature-dependent photoluminescence were measured; in both cases, an intensity quenching was observed between 75 K – 250 K for the on-axis sample, but not in the off-axis sample. We attribute the THz emission quenching to the electron traps present in the sample, which decreases the photocarriers participating in setting up the surface field.
- Published
- 2017
- Full Text
- View/download PDF
3. A modulation-doped heterostructure-based terahertz photoconductive antenna emitter with recessed metal contacts
- Author
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Maria Angela Faustino, Elmer Estacio, Armando Somintac, Gerald Angelo Catindig, Masahiko Tani, Hannah Bardolaza, Jessica Afalla, Elizabeth Ann Prieto, Victor Dc Andres Vistro, Valynn Katrine Mag-usara, Arnel Salvador, Alexander De Los Reyes, Neil Irvin Cabello, John Paul Ferrolino, Karl Cedric Gonzales, and Hideaki Kitahara
- Subjects
Materials science ,Terahertz radiation ,Physics::Optics ,lcsh:Medicine ,Optical power ,02 engineering and technology ,01 natural sciences ,Article ,Ultrafast photonics ,Fiber laser ,0103 physical sciences ,lcsh:Science ,Terahertz optics ,Common emitter ,010302 applied physics ,Multidisciplinary ,Photonic devices ,business.industry ,Dynamic range ,Doping ,Energy conversion efficiency ,lcsh:R ,Heterojunction ,021001 nanoscience & nanotechnology ,Optoelectronics ,lcsh:Q ,0210 nano-technology ,business - Abstract
We present the implementation of an efficient terahertz (THz) photoconductive antenna (PCA) emitter design that utilizes high mobility carriers in the two-dimensional electron gas (2DEG) of a modulation-doped heterostructure (MDH). The PCA design is fabricated with recessed metal electrodes in direct contact with the 2DEG region of the MDH. We compare the performance of the MDH PCA having recessed contacts with a PCA fabricated on bulk semi-insulating GaAs, on low temperature-grown GaAs, and a MDH PCA with the contacts fabricated on the surface. By recessing the contacts, the applied bias can effectively accelerate the high-mobility carriers within the 2DEG, which increases the THz power emission by at least an order of magnitude compared to those with conventional structures. The dynamic range (62 dB) and bandwidth characteristics (3.2 THz) in the power spectrum are shown to be comparable with the reference samples. Drude-Lorentz simulations corroborate the results that the higher-mobility carriers in the MDH, increase the THz emission. The saturation characteristics were also measured via optical fluence dependence, revealing a lower saturation value compared to the reference samples. The high THz conversion efficiency of the MDH-PCA with recessed contacts at low optical power makes it an attractive candidate for THz-time domain spectroscopy systems powered by low power fiber lasers.
- Published
- 2020
4. Temperature-dependent terahertz time-domain spectroscopy of 3D, 2D, and 0D semiconductor heterostructures
- Author
-
Elmer Estacio, John Daniel Vasquez, Der-Jun Jang, Arnel Salvador, Neil Irvin Cabello, Alexander De Los Reyes, Che-Yung Chang, Lorenzo Lopez, Armando Somintac, and Hannah Bardolaza
- Subjects
Photoluminescence ,Materials science ,Terahertz radiation ,business.industry ,Physics::Optics ,Context (language use) ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Condensed Matter::Materials Science ,Semiconductor ,Electric field ,Optoelectronics ,Electrical and Electronic Engineering ,Terahertz time-domain spectroscopy ,business ,Spectroscopy ,Semiconductor heterostructures - Abstract
Carrier transport in semiconductors with different dimensionalities, i.e., 3D (bulk), 2D (QW), and 0D (QD), were investigated via temperature-dependent terahertz time-domain spectroscopy (THz-TDS). The optical properties and recombination dynamics in the samples were probed via photoluminescence spectroscopy. The temperature-dependence of the THz emission from the samples was explained in the context of the drift-diffusion model using the dominant THz radiation mechanism. The THz emission from diffusion-type THz emitters such as p- and n-InAs decreases as temperature increases due to mobility decrease. Conversely, the THz emission from drift-type THz emitters such as SI-GaAs, GaAs QW, and InAs QD was found to increase with temperature due to the increase in the driving electric field. In summary, THz-TDS can be utilized to gain qualitative insights on the temperature-dependent transport characteristics and establish dominant THz radiation mechanisms.
- Published
- 2020
5. Terahertz emission increase in GaAs films exhibiting structural defects grown on Si (100) substrates using a two-layered LTG-GaAs buffer system
- Author
-
Gerald Angelo Catindig, Horace Andrew Husay, Alexander De Los Reyes, Elizabeth Ann Prieto, Maria Angela Faustino, Arnel Salvador, Elmer Estacio, John Daniel Vasquez, Armando Somintac, Mae Agatha Tumanguil-Quitoras, and Karl Cedric Gonzales
- Subjects
Materials science ,Terahertz radiation ,Scanning electron microscope ,Physics::Optics ,Substrate (electronics) ,01 natural sciences ,GaAs thin films ,symbols.namesake ,Crystallinity ,Condensed Matter::Materials Science ,0103 physical sciences ,Terahertz (THz) emission ,Electrical and Electronic Engineering ,Thin film ,010302 applied physics ,business.industry ,Condensed Matter Physics ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Electron diffraction ,symbols ,Optoelectronics ,structural defects ,Raman spectroscopy ,business ,Molecular beam epitaxy - Abstract
Terahertz (THz) emission increase is observed for GaAs thin films that exhibit structural defects. The GaAs epilayers are grown by molecular beam epitaxy on exactly oriented Si (100) substrates at three different temperatures (Ts = 320ºC, 520ºC and 630ºC). The growth method involves the deposition of two low-temperature-grown (LTG)-GaAs buffers with subsequent in-situ thermal annealing at Ts = 600ºC. Reflection high energy electron diffraction confirms the layer-by-layer growth mode of the GaAs on Si. X-ray diffraction shows the improvement in crystallinity as growth temperature is increased. The THz time-domain spectroscopy is performed in reflection and transmission excitation geometries. At Ts = 320ºC, the low crystallinity of GaAs on Si makes it an inferior THz emitter in reflection geometry, over a GaAs grown at the same temperature on a semi-insulating GaAs substrate. However, in transmission geometry, the GaAs on Si exhibits less absorption losses. At higher Ts, the GaAs on Si thin films emerge as promising THz emitters despite the presence of antiphase boundaries and threading dislocations as identified from scanning electron microscopy and Raman spectroscopy. An intense THz emission in reflection and transmission excitation geometries is observed for the GaAs on Si grown at Ts = 520ºC, suggesting the existence of an optimal growth temperature for GaAs on Si at which the THz emission is most efficient in both excitation geometries. The results are significant in the growth design and fabrication of GaAs on Si material system intended for future THz photoconductive antenna emitter devices.
- Published
- 2021
6. Temperature dependence of THz emission and junction electric field of GaAs–AlGaAs modulation-doped heterostructures with different i-AlGaAs spacer layer thicknesses
- Author
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Elmer Estacio, John Daniel Vasquez, Miguel Bacaoco, Alexander De Los Reyes, Armando Somintac, Arnel Salvador, Lorenzo Lopez, Roland V. Sarmago, and Hannah Bardolaza
- Subjects
010302 applied physics ,Materials science ,Terahertz radiation ,business.industry ,Doping ,Heterojunction ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Layer thickness ,Emission intensity ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Electric field ,0103 physical sciences ,Optoelectronics ,Electrical and Electronic Engineering ,0210 nano-technology ,Spectroscopy ,business ,Gaas algaas - Abstract
Photocarrier dynamics in GaAs/AlGaAs modulation-doped heterostructures (MDH) having i-AlGaAs spacer layers of different thicknesses were investigated using temperature-dependent terahertz time-domain spectroscopy (THz-TDS) and photoreflectance spectroscopy. In particular, results are discussed in the framework of the temperature dependence of the heterojunction electric field and photocarrier velocity for two i-AlGaAs spacer layer thickness values. The junction electric field, THz emission intensity and bandwidth of the MDH samples all decrease as temperature decreases. In contrast, the THz emission intensity and bandwidth of a reference bulk undoped GaAs does not significantly vary with temperature. These results imply that THz emission of MDH’s originates primarily from carrier drift due to the GaAs/AlGaAs junction electric field. A general decrease in the THz emission bandwidth of the MDH’s is attributed to a decrease in carrier velocity at lower temperatures, presumably due to the weaker electric field. Moreover, the MDH sample with thinner spacer layer exhibited a higher junction electric field. This work demonstrates the study of temperature-dependent photocarrier transport and junction electric field measurements. The results may provide useful insights in the design of MDH-based devices.
- Published
- 2018
7. Low-temperature carrier dynamics in MBE-grown InAs/GaAs single- and multi-layered quantum dots investigated via photoluminescence and terahertz time-domain spectroscopy
- Author
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Elmer Estacio, Hannah Bardolaza, Armando Somintac, John Daniel Vasquez, Lorenzo Lopez, Arnel Salvador, Che-Yung Chang, Alexander De Los Reyes, and Der-Jun Jang
- Subjects
Photoluminescence ,Materials science ,business.industry ,Terahertz radiation ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Electronic, Optical and Magnetic Materials ,Terahertz spectroscopy and technology ,010309 optics ,Quantum dot ,Electric field ,0103 physical sciences ,Optoelectronics ,0210 nano-technology ,business ,Terahertz time-domain spectroscopy ,Spectroscopy ,Molecular beam epitaxy - Abstract
The photocarrier dynamics in molecular beam epitaxy (MBE)-grown single- (SLQD) and multi-layered (MLQD) InAs/GaAs quantum dots were studied. Photoluminescence (PL) spectroscopy has shown that the MLQD has more uniform QD size distribution as compared to the bimodal SLQD. Correlation between PL and THz-TDS has shown that photocarrier transport is more favored in the MLQD owing to this uniform QD size distribution, resulting to higher THz emission. The THz emission from the QD samples were found to be proportional to temperature. A drift-related photocarrier transport mechanism is proposed, wherein photocarriers generated in the QDs are accelerated by an interface electric field.
- Published
- 2019
8. Defect-related temperature dependence of THz emission from GaAs/AlGaAs MQWs grown on off- and on-axis substrates
- Author
-
Alexander De Los Reyes, Kohji Yamamoto, Elmer Estacio, Arnel Salvador, Masahiko Tani, Lorenzo Lopez, Valynn Katrine Mag-usara, Armando Somintac, and Jessica Afalla
- Subjects
Photoluminescence ,Materials science ,Terahertz radiation ,General Physics and Astronomy ,02 engineering and technology ,Substrate (electronics) ,Electron ,engineering.material ,01 natural sciences ,Gallium arsenide ,chemistry.chemical_compound ,0103 physical sciences ,010302 applied physics ,Quenching ,Maple ,business.industry ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,021001 nanoscience & nanotechnology ,lcsh:QC1-999 ,chemistry ,engineering ,Optoelectronics ,0210 nano-technology ,business ,lcsh:Physics ,Intensity (heat transfer) - Abstract
Simultaneous molecular beam epitaxial growth of GaAs/AlGaAs multiple quantum wells on two different substrates (one on GaAs (100) and another on a GaAs substrate misoriented by 4° in the (111) direction) resulted in samples of similar structure, but having different defect profiles. The on-axis sample had a higher defect density and more types of electron traps than the off-axis counterpart. Temperature-dependent terahertz (THz) emission and temperature-dependent photoluminescence were measured; in both cases, an intensity quenching was observed between 75 K – 250 K for the on-axis sample, but not in the off-axis sample. We attribute the THz emission quenching to the electron traps present in the sample, which decreases the photocarriers participating in setting up the surface field.
- Published
- 2017
9. Apoptotic action of 17beta-estradiol in raloxifene-resistant MCF-7 cells in vitro and in vivo
- Author
-
Eun Sook Lee, V. Craig Jordan, Jessica A. Loweth, Sandra Timm Pearce, Bin Chen, Csaba Gajdos, Clodia Osipo, Hong Liu, Laura K. Wing, Alexander De Los Reyes, and Kevin P. McKian
- Subjects
Selective Estrogen Receptor Modulators ,Cancer Research ,medicine.medical_specialty ,medicine.drug_class ,Ovariectomy ,Blotting, Western ,Estrogen receptor ,Mice, Nude ,Antineoplastic Agents ,Apoptosis ,Breast Neoplasms ,Biology ,Polymerase Chain Reaction ,Mice ,Internal medicine ,Cell Line, Tumor ,medicine ,Animals ,Humans ,Raloxifene ,RNA, Messenger ,RNA, Neoplasm ,skin and connective tissue diseases ,Estradiol ,NF-kappa B ,Antiestrogen ,Endocrinology ,Oncology ,MCF-7 ,Selective estrogen receptor modulator ,Estrogen ,Drug Resistance, Neoplasm ,Raloxifene Hydrochloride ,Female ,Tamoxifen ,medicine.drug - Abstract
BACKGROUND Resistance to tamoxifen, a selective estrogen receptor modulator (SERM), involves changes that prevent apoptosis and enhance cell proliferation and survival. Paradoxically, estrogen treatment inhibits the growth of long-term tamoxifen-treated breast tumors. Because of the increasing use of raloxifene, another SERM, to prevent osteoporosis and potentially reduce breast cancer risk, some women will develop raloxifene-resistant breast cancer. We developed a raloxifene-resistant MCF-7 cell model (MCF-7/Ral) and investigated the nature of raloxifene-resistant breast cancer and its response to estradiol. METHODS Raloxifene resistance and hormone responsiveness were assessed by proliferation assays and cell cycle analysis in parental MCF-7 and MCF-7/Ral cells. Nuclear factor kappaB (NF-kappaB) activity was investigated with a transient transfection assay. Apoptosis was investigated by annexin V staining, mRNA was measured by real-time polymerase chain reaction, and protein was measured by western blotting. Tumorigenesis was studied by injecting MCF-7 or MCF-7/Ral cells into ovariectomized athymic mice (10 per group) and monitoring tumor size weekly. All statistical tests were two-sided. RESULTS Basal NF-kappaB activity was higher in MCF-7/Ral cells (1.6 U, 95% confidence interval [CI] = 1.2 to 2.0 U) than in MCF-7 cells (0.8 U, 95% CI = 0.4 to 1.1 U; P =.004). When cultured with 1 microM raloxifene, MCF-7/Ral cells grew statistically significantly (P
- Published
- 2003
10. 796 15-Year Trend of Peptic Ulcer Complications in the United States: A Decline in Mortality, but at What Price?
- Author
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Marek Rudnicki, Alexander De Los Reyes, Samuel Jacob, and Vijay K. Maker
- Subjects
medicine.medical_specialty ,Hepatology ,business.industry ,Peptic ulcer ,General surgery ,Internal medicine ,Gastroenterology ,Medicine ,business ,medicine.disease - Published
- 2010
11. Tunneling dynamics and transport in MBE-grown GaAs/AlGaAs asymmetric double quantum wells investigated via photoluminescence and terahertz time-domain spectroscopy.
- Author
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De Los Reyes, Alexander, Prieto, Elizabeth Ann, Dasallas, Lean, Bardolaza, Hannah, Tumanguil-Quitoras, Mae Agatha, Cabello, Neil Irvin, Somintac, Armando, Salvador, Arnel, and Estacio, Elmer
- Subjects
TERAHERTZ spectroscopy ,TERAHERTZ time-domain spectroscopy ,QUANTUM wells ,SCANNING tunneling microscopy ,MOLECULAR beam epitaxy ,PHOTOLUMINESCENCE ,AUDITING standards - Abstract
We study the transport of photogenerated carriers in molecular beam epitaxy (MBE)-grown gallium arsenide/aluminum gallium arsenide (GaAs/AlGaAs) coupled (CDQW) and uncoupled (UDQW) double quantum wells. Photoluminescence (PL) spectroscopy was used to investigate the optical properties and establish differences in the tunneling properties between the CDQW and UDQW. Terahertz time-domain spectroscopy (THz-TDS) measurements have shown that the emissions from the CDQW and UDQW were 57 % and 31 % of the THz emission of p-InAs, 800 nm excitation wavelength. The higher THz emission from the CDQW is attributed to the tunneling of electrons from the NW to the WW leading to a larger dipole moment. Furthermore, excitation wavelength-dependent THz-TDS measurements have shown that when the NW is not photoexcited, high-frequency components appear in the frequency spectra. These results provide insights on the possible development of DQWs as THz optoelectronic devices. It also demonstrates the application of THz-TDS in investigating tunneling dynamics in DQWs in conjunction with established optical characterization techniques, such as PL spectroscopy. [ABSTRACT FROM AUTHOR]
- Published
- 2022
- Full Text
- View/download PDF
12. Terahertz emission increase in GaAs films exhibiting structural defects grown on Si (100) substrates using a two-layered LTG-GaAs buffer system.
- Author
-
Gonzales, Karl Cedric, Prieto, Elizabeth Ann, Catindig, Gerald Angelo, De Los Reyes, Alexander, Faustino, Maria Angela, Tumanguil-Quitoras, Mae Agatha, Husay, Horace Andrew, Vasquez, John Daniel, Somintac, Armando, Estacio, Elmer, and Salvador, Arnel
- Subjects
MOLECULAR beam epitaxy ,REFLECTION high energy electron diffraction ,AUDITING standards ,ANTIPHASE boundaries - Abstract
Terahertz (THz) emission increase is observed for GaAs thin films that exhibit structural defects. The GaAs epilayers are grown by molecular beam epitaxy on exactly oriented Si (100) substrates at three different temperatures (T
s = 320 °C, 520 °C and 630 °C). The growth method involves the deposition of two low-temperature-grown (LTG)-GaAs buffers with subsequent in-situ thermal annealing at Ts = 600 °C. Reflection high energy electron diffraction confirms the layer-by-layer growth mode of the GaAs on Si. X-ray diffraction shows the improvement in crystallinity as growth temperature is increased. The THz time-domain spectroscopy is performed in reflection and transmission excitation geometries. At Ts = 320 °C, the low crystallinity of GaAs on Si makes it an inferior THz emitter in reflection geometry, over a GaAs grown at the same temperature on a semi-insulating GaAs substrate. However, in transmission geometry, the GaAs on Si exhibits less absorption losses. At higher Ts , the GaAs on Si thin films emerge as promising THz emitters despite the presence of antiphase boundaries and threading dislocations as identified from scanning electron microscopy and Raman spectroscopy. An intense THz emission in reflection and transmission excitation geometries is observed for the GaAs on Si grown at Ts = 520 °C, suggesting the existence of an optimal growth temperature for GaAs on Si at which the THz emission is most efficient in both excitation geometries. The results are significant in the growth design and fabrication of GaAs on Si material system intended for future THz photoconductive antenna emitter devices. [ABSTRACT FROM AUTHOR]- Published
- 2021
- Full Text
- View/download PDF
13. Temperature-dependent terahertz time-domain spectroscopy of 3D, 2D, and 0D semiconductor heterostructures.
- Author
-
De Los Reyes, Alexander, Bardolaza, Hannah, Vasquez, John Daniel, Cabello, Neil Irvin, Lopez, Lorenzo, Chang, Che-Yung, Somintac, Armando, Salvador, Arnel, Jang, Der-Jun, and Estacio, Elmer
- Subjects
TERAHERTZ time-domain spectroscopy ,TERAHERTZ spectroscopy ,TERAHERTZ materials ,SEMICONDUCTORS ,OPTICAL properties ,ELECTRIC fields ,ELECTRIC drives - Abstract
Carrier transport in semiconductors with different dimensionalities, i.e., 3D (bulk), 2D (QW), and 0D (QD), were investigated via temperature-dependent terahertz time-domain spectroscopy (THz-TDS). The optical properties and recombination dynamics in the samples were probed via photoluminescence spectroscopy. The temperature-dependence of the THz emission from the samples was explained in the context of the drift-diffusion model using the dominant THz radiation mechanism. The THz emission from diffusion-type THz emitters such as p- and n-InAs decreases as temperature increases due to mobility decrease. Conversely, the THz emission from drift-type THz emitters such as SI-GaAs, GaAs QW, and InAs QD was found to increase with temperature due to the increase in the driving electric field. In summary, THz-TDS can be utilized to gain qualitative insights on the temperature-dependent transport characteristics and establish dominant THz radiation mechanisms. [ABSTRACT FROM AUTHOR]
- Published
- 2020
- Full Text
- View/download PDF
14. A modulation-doped heterostructure-based terahertz photoconductive antenna emitter with recessed metal contacts
- Author
-
Afalla, Jessica, De Los Reyes, Alexander, Cabello, Neil Irvin, Vistro, Victor DC Andres, Faustino, Maria Angela, Ferrolino, John Paul, Prieto, Elizabeth Ann, Bardolaza, Hannah, Catindig, Gerald Angelo R., Gonzales, Karl Cedric, Mag-usara, Valynn Katrine, Kitahara, Hideaki, Somintac, Armando S., Salvador, Arnel A., Tani, Masahiko, and Estacio, Elmer S.
- Published
- 2020
- Full Text
- View/download PDF
15. Defect-related temperature dependence of THz emission from GaAs/AlGaAs MQWs grown on off- and on-axis substrates.
- Author
-
Afalla, Jessica P. C., de los Reyes, Alexander, Mag-usara, Valynn Katrine, Lopez Jr., Lorenzo P., Yamamoto, Kohji, Tani, Masahiko, Somintac, Armando S., Salvador, Arnel A., and Estacio, Elmer S.
- Subjects
EPITAXY ,MOLECULAR beam epitaxy ,TERAHERTZ materials ,AUDITING standards ,ELECTRON traps ,ELECTRON emission ,QUANTUM wells - Abstract
Simultaneous molecular beam epitaxial growth of GaAs/AlGaAs multiple quantum wells on two different substrates (one on GaAs (100) and another on a GaAs substrate misoriented by 4° in the (111) direction) resulted in samples of similar structure, but having different defect profiles. The on-axis sample had a higher defect density and more types of electron traps than the off-axis counterpart. Temperature-dependent terahertz (THz) emission and temperature-dependent photoluminescence were measured; in both cases, an intensity quenching was observed between 75 K – 250 K for the on-axis sample, but not in the off-axis sample.We attribute the THz emission quenching to the electron traps present in the sample, which decreases the photocarriers participating in setting up the surface field. [ABSTRACT FROM AUTHOR]
- Published
- 2017
- Full Text
- View/download PDF
16. Apoptotic Action of 17β-Estradiol in Raloxifene-Resistance MCF-7 Cells In Vitro and In Vivo.
- Author
-
Hong Liu, Eun-Sook Lee, Steven K., Gajdos, Csaba, Pearce, Sandra Timm, Bin Chen, Clodia Osipo, Sandra Timm, Loweth, Jessica, McKian, Kevin, De Los Reyes, Alexander, Wing, Laura, and Jordan, V. Craig
- Subjects
TAMOXIFEN ,ESTROGEN receptors ,APOPTOSIS ,BREAST cancer treatment ,CANCER treatment ,ONCOLOGY - Abstract
Background: Resistance to tamoxifen, a selective estrogen receptor modulator (SERM), involves changes that prevent apoptosis and enhance cell proliferation and survival. Paradoxically, estrogen treatment inhibits the growth of longterm tamoxifen-treated breast tumors. Because of the increasing use of raloxifene, another SERM, to prevent osteoporosis and potentially reduce breast cancer risk, some women will develop raloxifene-resistant breast cancer. We developed a raloxifene-resistant MCF-7 cell model (MCF-7/ Ral) and investigated the nature of raloxifene-resistant breast cancer and its response to estradiol. Methods: Raloxifene resistance and hormone responsiveness were assessed by proliferation assays and cell cycle analysis in parental MCF-7 and MCF-7/Ral cells. Nuclear factor KB (NF-κB) activity was investigated with a transient transfection assay. Apoptosis was investigated by annexin V staining, mRNA was measured by real-time polymerase chain reaction, and protein was measured by western blotting. Tumorigenesis was studied by injecting MCF-7 or MCF-7/Ral cells into ovariectomized athymic mice (10 per group) and monitoring tumor size weekly. All statistical tests were two-sided. Resuits: Basal NF-κB activity was higher in MCF-7/Ral cells (1.6 U, 95% confidence interval [CI] = 1.2 to 2.0 U) than in MCF-7 cells (0.8 U, 95% CI = 0.4 to 1.1 U; P = .004). When cultured with 1 µM raloxifene, MCF-7/Ral cells grew statistically significantly (P<.001) faster than MCF-7 cells. Estradiol treatment of MCF-7/Ral cells arrested cells in G[sub 2]/M phase of the cell cycle, decreased NF-κB activity (0.2 U, 95% CI = 0.2 to 0.3 U; P<.001), increased expression of Fas protein and mRNA (4.5-fold, 95% CI = 2.8- to 6.3-fold versus 0.5-fold, 95% CI = 0.3- to 0.8-fold for control treatment; P<.001), and induced apoptosis. Treatment with either raloxifene or tamoxifen stimulated MCF-7/Ral tumor growth, suggesting that such tumors were resistant to both drugs. When a 9-week raloxifene or tamoxifen treatment was followed by a 5-week estradiol treatment, estradiol statistically significantly reduced the size of tumors stimulated by raloxifene or tamoxifen (at week 14, P = .004 for raloxifene and P<.001 for tamoxifen). Conclusions: Growth of raloxifeneresistant MCF-7/Ral cells in vitro and in vivo is repressed by estradiol treatment by a mechanism involving G[sub 2]/M-phase arrest, decreased NF-κB activity, and increased Fas expression to induce apoptosis. [ABSTRACT FROM AUTHOR]
- Published
- 2003
- Full Text
- View/download PDF
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