Page 246 - 2014 Printable Abstract Book
P. 246
st
-1
protonated form of the radical anion at pH 7 undergoes a kinetic 1 -order transformation at 125 ± 15 s ,
-1
6
-1
in competition to the back reaction with molecular oxygen of rate constant 3.3 ± 0.1 x 10 M s . Spin-
trapping experiments with N-tert-butylphenylnitrone (PBN) and 5-(diethoxyphosphoryl)-5-methyl-1-
pyrroline (DEPMPO) indicate both an aryl-type radical (a) and another oxidizing radical, trapped as a
carbon-centred radical (b), are formed upon bioreduction. Radical (b), also produced upon the one-
electron oxidation of the 2-electron reduced metabolite of SN30000, was shown to oxidize 2-deoxyribose,
a model for the site of damage on DNA leading to double strand breaks, with a rate constant of 6.3 ± 0.2
-1
x 10 M s . The one-electron reduction potentials of SN30000 and radical (b), determined using pulse
-1
6
radiolysis, are -401 ± 8 mV and +1.35 V respectively. In a head to head comparison with the BTO drug
tirapazamine (TPZ) using a plasmid system, approximately twice the amount of double strand breaks than
for TPZ are seen upon the bioreduction of SN30000 in hypoxia. This observation may reflect the greater
rate of metabolism and increased radical oxidizing power in line with the above reduction potentials being
greater than those of TPZ, as well as a higher proportion of aryl radicals (a) being formed upon the
bioreduction of SN30000. Such strong oxidizing radicals are candidate radicals underlying the known
toxicity of this class of bioreductive compounds. In addition, the above kinetic measurements give some
insight into the possible mechanism of hypoxia-selectivity of this class of bioreductive drugs, which will be
discussed.
1
(PS4-20) Icaritin enhances the radiosensitivity of 4T1 breast cancer cells. Zhenhuan Zhang, MD, PhD ;
2;3
1
Jinsheng Hong, MD, PhD ; Wenlong Lu, PhD ; Mei Zhang, MD ; Chun Chen, MD, PhD ; Shanmin Yang,
2
4
2
1
3
1
2;3
MD ; Shan Li, MD ; Lurong Zhang, MD, PhD ; Deping Han, MD, PhD ; Weijian Zhang, MD ; Steven G.
1
1
1
Swarts, PhD ; and Paul Okunieff, MD, University of Florida Health Cancer Center, Gainesville, FL ;
2
Department of Radiation Oncology, First Affiliated Hospital, Fujian Medical University, Fujian, China ;
Division of Radiation Biology, Central Research Lab, First Affiliated Hospital, Fuzhou, China ; and
3
Department of Pharmacology, School of Pharmacy, Fujian Medical University, Fujian, China
4
Overview: Icaritin (ICT) is a flavonoid glycoside derived from plants of the genus Epimedium. This
study was performed to determine if ICT might radiosensitize 4T1 breast cancer cells in vitro, and if so by
what potential mechanisms. Methods: Radiation-related and drug dose-related cell killing were studied
by clonogenic assay; proliferation by MTT; ERK1/2 and AKT by ELISA; and G2/M blockade by flow
cytometry. Angiogenesis was studied with a chorioallantoic membrane (CAM) assay. Results: The slope of
the clonogenic survival curve, 1/D0, at 0, 3, and 6μM of ICT was calculated for 4T1 cells exposed to 0, 2,
4, 6, or 8 Gy of ionizing radiation. This yielded radiosensitization (ratio of control to test D0) of 1.17 at 3
μM and 1.49 at 6 μM. The combination index (CI) was 0.38 and 0.19, and the dose-reducing index (DRI)
was 2.51 and 5.07, respectively. These results suggest that ICT is a radiosensitizer. This effect might be
related to the many bioactivities of ICT. ICT was shown to: (1) exert an antiproliferative effect in a dose-
dependent and time-dependent manner; (2) suppress radiation-induced activation of 2 survival pathways,
ERK1/2 and AKT; (3) induce G2/M blockage, a radiosensitive period in the cell cycle; and (4) enhance
radiation-related apoptosis. In addition, ICT suppressed angiogenesis in the CAM assay. Conclusions: ICT
exhibits antiproliferative and stem cell maturational effects. In this study, we show that ICT is also a
radiosensitizer in 4T1 cells. ICT may have clinical potential when used in combination with radiation.
244 | P a g e
-1
protonated form of the radical anion at pH 7 undergoes a kinetic 1 -order transformation at 125 ± 15 s ,
-1
6
-1
in competition to the back reaction with molecular oxygen of rate constant 3.3 ± 0.1 x 10 M s . Spin-
trapping experiments with N-tert-butylphenylnitrone (PBN) and 5-(diethoxyphosphoryl)-5-methyl-1-
pyrroline (DEPMPO) indicate both an aryl-type radical (a) and another oxidizing radical, trapped as a
carbon-centred radical (b), are formed upon bioreduction. Radical (b), also produced upon the one-
electron oxidation of the 2-electron reduced metabolite of SN30000, was shown to oxidize 2-deoxyribose,
a model for the site of damage on DNA leading to double strand breaks, with a rate constant of 6.3 ± 0.2
-1
x 10 M s . The one-electron reduction potentials of SN30000 and radical (b), determined using pulse
-1
6
radiolysis, are -401 ± 8 mV and +1.35 V respectively. In a head to head comparison with the BTO drug
tirapazamine (TPZ) using a plasmid system, approximately twice the amount of double strand breaks than
for TPZ are seen upon the bioreduction of SN30000 in hypoxia. This observation may reflect the greater
rate of metabolism and increased radical oxidizing power in line with the above reduction potentials being
greater than those of TPZ, as well as a higher proportion of aryl radicals (a) being formed upon the
bioreduction of SN30000. Such strong oxidizing radicals are candidate radicals underlying the known
toxicity of this class of bioreductive compounds. In addition, the above kinetic measurements give some
insight into the possible mechanism of hypoxia-selectivity of this class of bioreductive drugs, which will be
discussed.
1
(PS4-20) Icaritin enhances the radiosensitivity of 4T1 breast cancer cells. Zhenhuan Zhang, MD, PhD ;
2;3
1
Jinsheng Hong, MD, PhD ; Wenlong Lu, PhD ; Mei Zhang, MD ; Chun Chen, MD, PhD ; Shanmin Yang,
2
4
2
1
3
1
2;3
MD ; Shan Li, MD ; Lurong Zhang, MD, PhD ; Deping Han, MD, PhD ; Weijian Zhang, MD ; Steven G.
1
1
1
Swarts, PhD ; and Paul Okunieff, MD, University of Florida Health Cancer Center, Gainesville, FL ;
2
Department of Radiation Oncology, First Affiliated Hospital, Fujian Medical University, Fujian, China ;
Division of Radiation Biology, Central Research Lab, First Affiliated Hospital, Fuzhou, China ; and
3
Department of Pharmacology, School of Pharmacy, Fujian Medical University, Fujian, China
4
Overview: Icaritin (ICT) is a flavonoid glycoside derived from plants of the genus Epimedium. This
study was performed to determine if ICT might radiosensitize 4T1 breast cancer cells in vitro, and if so by
what potential mechanisms. Methods: Radiation-related and drug dose-related cell killing were studied
by clonogenic assay; proliferation by MTT; ERK1/2 and AKT by ELISA; and G2/M blockade by flow
cytometry. Angiogenesis was studied with a chorioallantoic membrane (CAM) assay. Results: The slope of
the clonogenic survival curve, 1/D0, at 0, 3, and 6μM of ICT was calculated for 4T1 cells exposed to 0, 2,
4, 6, or 8 Gy of ionizing radiation. This yielded radiosensitization (ratio of control to test D0) of 1.17 at 3
μM and 1.49 at 6 μM. The combination index (CI) was 0.38 and 0.19, and the dose-reducing index (DRI)
was 2.51 and 5.07, respectively. These results suggest that ICT is a radiosensitizer. This effect might be
related to the many bioactivities of ICT. ICT was shown to: (1) exert an antiproliferative effect in a dose-
dependent and time-dependent manner; (2) suppress radiation-induced activation of 2 survival pathways,
ERK1/2 and AKT; (3) induce G2/M blockage, a radiosensitive period in the cell cycle; and (4) enhance
radiation-related apoptosis. In addition, ICT suppressed angiogenesis in the CAM assay. Conclusions: ICT
exhibits antiproliferative and stem cell maturational effects. In this study, we show that ICT is also a
radiosensitizer in 4T1 cells. ICT may have clinical potential when used in combination with radiation.
244 | P a g e
