Page 304 - 2014 Printable Abstract Book
P. 304
However, methods to map the spatial variations in biologic effectiveness of protons are lacking, thus the
data necessary to guide novel treatment planning approaches is very limited. Methods: Monte Carlo
modeling was used to develop a high-throughput strategy to spatially map the biologic effectiveness of
scanned proton beams. 96-well plates were used to culture H460 NSCLC (non-small cell lung cancer) cells.
A stepwise fashioned irradiation apparatus was fabricated and used to attenuate the large-field scanned
proton beams (79.7 MeV) to deliver different dose-LET combinations to 12 columns of the 96-well plate.
By altering the total number of dose repaintings, numerous dose-LET configurations were examined to
effectively generate surviving fraction (SF) data over the entire Bragg curve. The clonogenic assay was
performed post-irradiation using an INCell Analyzer for colony quantification. SF data were fit to the
linear-quadratic model for analysis. Results: The cell survival data revealed that the SF at a dose of 2 Gy
(SF2) for the NSCLC H460 cell line was 0.46 for the low-LET (<10 keV/µm) protons and 0.33 for protons
with an LET of 10.35 keV/µm at the Bragg peak. Beyond the Bragg peak, in low dose, yet high LET areas,
we recorded lower yet SF values of 0.16 for 15.01 keV/µm, 0.02 for 16.79 keV/µm, and 0.004 for 18.06
keV/µm. Conclusion: Irradiation with increasing LETs resulted in decreased cell survival largely
independent of dose. This trend was obscured at the lower LET values in the plateau region of the Bragg
curve; however, it was clear for LET values at and beyond the Bragg peak. These findings represent the
first step toward the acquisition of data necessary for biologically optimized proton therapy and thereby
to a significant enhancement of the therapeutic potential for numerous cancer types. Moreover, the
methodologies developed may also be applied to other particles.
(PS5-30) Radiation-induced reprogramming of glioma stem cells. Erina Vlashi, PhD; MIlana Bochkur
Dratver; Yazeed Alhiyari; Alexandra McDonald; Patricia Frohnen; and Frank Pajonk, UCLA,Los Angeles, CA
Despite maximal surgical resection, followed by aggressive treatment with radiation and
temozolomide, GBM still remains one of the most lethal of cancers, with a median overall survival of only
~ 15 months and a rapid, aggressive tumor relapse after ~ 7 months. Such a rapid relapse suggests that a
subpopulation of the primary tumor cells that has the ability to regenerate a GBM tumor (i.e. GBM stem
cells) has been spared by the current, standard-of-care treatment approaches. Alternatively, or
simultaneously, current GBM treatments may be changing the phenotype of the primary tumor cells into
a more aggressive and treatment-refractory phenotype. Such a possibility is supported by recent evidence
from our laboratory, demonstrating that radiation therapy converts differentiated breast cancer cells into
treatment-resistant, induced-CSCs. These findings suggest that radiation therapy as an anti-cancer
treatment is being counteracted by the occurrence of these reprogramming events. The cancer stem cell
(CSC) hypothesis claims that most cancers, including GBM, are hierarchically organized with the CSCs at
the apex of cellular hierarchy. CSCs are defined experimentally by their exclusive ability to initiate and
propagate a tumor, while their progeny lack these features. The CSC theory predicts that long-term cures
will only be achieved if the CSC population of a tumor is eliminated. Radiation therapy is an indispensable
part of the current treatment approaches for GBM. In these studies we use a unique, fluorescent-based,
imaging system for GBM-SCs to demonstrate that radiation treatment induces reprogramming of non-
stem GBM cells into induced GBM stem cells (induced-GBM-SCs) in several primary GBM lines. Radiation-
induced GBM stem cells have higher sphere forming capacity and tumor initiating capability compared to
the non-irradiated cells. We further demonstrate that metabolic inhibitors can prevent these
reprogramming events from occurring. The studies proposed here provide critical insight into the
radiation-induced reprogramming of GBM cells, and begin to address potential ways of preventing
302 | P a g e
data necessary to guide novel treatment planning approaches is very limited. Methods: Monte Carlo
modeling was used to develop a high-throughput strategy to spatially map the biologic effectiveness of
scanned proton beams. 96-well plates were used to culture H460 NSCLC (non-small cell lung cancer) cells.
A stepwise fashioned irradiation apparatus was fabricated and used to attenuate the large-field scanned
proton beams (79.7 MeV) to deliver different dose-LET combinations to 12 columns of the 96-well plate.
By altering the total number of dose repaintings, numerous dose-LET configurations were examined to
effectively generate surviving fraction (SF) data over the entire Bragg curve. The clonogenic assay was
performed post-irradiation using an INCell Analyzer for colony quantification. SF data were fit to the
linear-quadratic model for analysis. Results: The cell survival data revealed that the SF at a dose of 2 Gy
(SF2) for the NSCLC H460 cell line was 0.46 for the low-LET (<10 keV/µm) protons and 0.33 for protons
with an LET of 10.35 keV/µm at the Bragg peak. Beyond the Bragg peak, in low dose, yet high LET areas,
we recorded lower yet SF values of 0.16 for 15.01 keV/µm, 0.02 for 16.79 keV/µm, and 0.004 for 18.06
keV/µm. Conclusion: Irradiation with increasing LETs resulted in decreased cell survival largely
independent of dose. This trend was obscured at the lower LET values in the plateau region of the Bragg
curve; however, it was clear for LET values at and beyond the Bragg peak. These findings represent the
first step toward the acquisition of data necessary for biologically optimized proton therapy and thereby
to a significant enhancement of the therapeutic potential for numerous cancer types. Moreover, the
methodologies developed may also be applied to other particles.
(PS5-30) Radiation-induced reprogramming of glioma stem cells. Erina Vlashi, PhD; MIlana Bochkur
Dratver; Yazeed Alhiyari; Alexandra McDonald; Patricia Frohnen; and Frank Pajonk, UCLA,Los Angeles, CA
Despite maximal surgical resection, followed by aggressive treatment with radiation and
temozolomide, GBM still remains one of the most lethal of cancers, with a median overall survival of only
~ 15 months and a rapid, aggressive tumor relapse after ~ 7 months. Such a rapid relapse suggests that a
subpopulation of the primary tumor cells that has the ability to regenerate a GBM tumor (i.e. GBM stem
cells) has been spared by the current, standard-of-care treatment approaches. Alternatively, or
simultaneously, current GBM treatments may be changing the phenotype of the primary tumor cells into
a more aggressive and treatment-refractory phenotype. Such a possibility is supported by recent evidence
from our laboratory, demonstrating that radiation therapy converts differentiated breast cancer cells into
treatment-resistant, induced-CSCs. These findings suggest that radiation therapy as an anti-cancer
treatment is being counteracted by the occurrence of these reprogramming events. The cancer stem cell
(CSC) hypothesis claims that most cancers, including GBM, are hierarchically organized with the CSCs at
the apex of cellular hierarchy. CSCs are defined experimentally by their exclusive ability to initiate and
propagate a tumor, while their progeny lack these features. The CSC theory predicts that long-term cures
will only be achieved if the CSC population of a tumor is eliminated. Radiation therapy is an indispensable
part of the current treatment approaches for GBM. In these studies we use a unique, fluorescent-based,
imaging system for GBM-SCs to demonstrate that radiation treatment induces reprogramming of non-
stem GBM cells into induced GBM stem cells (induced-GBM-SCs) in several primary GBM lines. Radiation-
induced GBM stem cells have higher sphere forming capacity and tumor initiating capability compared to
the non-irradiated cells. We further demonstrate that metabolic inhibitors can prevent these
reprogramming events from occurring. The studies proposed here provide critical insight into the
radiation-induced reprogramming of GBM cells, and begin to address potential ways of preventing
302 | P a g e
