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Translational research with small animal IGRT
Andrew Hope, MD
Staff Radiation OncologistRadiation Medicine ProgramPrincess Margaret Hospital
Assistant ProfessorDepartment of Radiation Oncology
University of Toronto
“Good” models for translational research
• Should assess both tumor control and normal tissue effects– Relevant tumor model
• Orthotopic tumor• Carcinogenesis
– Normal tissue endpoints in conjunction with tumor
• Longitudinal studies with non-invasive endpoints
• Physiologic measures• Imaging
µµµµCT µµµµSPECT µµµµPET MR – 7T
Pre-clinical imaging modalities
Gruene et al., Gamma Medica, Nature Medicine
µµµµUS µµµµOptical
Pre-clinical imaging modalities
Images courtesy of Visualsonics, Xenogen
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Biologic variation is a significant factor in the clinic
• Inherent radiosensitivityand/or response to treatment may be as important as the dose itself
• Small animal irradiation can minimize biologic variation– inbred strains
• Evaluation of radiotherapy, chemotherapy, and biologic agents without confounding genetic heterogenity
Yuan et al., JCO, 2009
A challenging problem
• Glioblastoma– Very poor long-term
prognosis – Radiotherapy alone
insufficient– Some improvements with
addition of temozolomide(~10% OS @ 5y)
• New treatments required– Novel targets continuously
being explored– How to test to see if they
improve outcomes?
Stupp, R. et al. N. Engl. J. Med 352, 987-996(2005).
A potential target
• Many brain tumors gliomas express CXCR4– G-protein coupled receptor
that drives cAMP levels
• Inhibition of CXCR4 with targeted agents slows tumor growth– Multiple cell lines
• Possible target for further clinical exploration?
Rubin, J.B. et al. Proc. Natl. Acad. Sci. U.S.A 100, 13513-13518(2003).
An exploitable mechanism
• Tumors drive cAMP down via CXCL12/CXCR4 to sustain growth
• CXCR4 suppression elevates cAMP– Elevated cAMP suppresses
tumor growth
• Rolipram (generic drug) elevated cAMP as well as more expensive ‘targeted’agent
Yang, L. et al. Cancer Res 67, 651-658(2007).
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An in vivo model
• Intracranially implanted bioluminescent tumors– U87-luc/NCR nude
• Growth can be tracked longitudinally with non-invasive imaging
• Tumor growth is slowed, but not halted
• What’s the next step?
Yang, L. et al. Cancer Res 67, 651-658(2007).
A rationale for pre-clinical IGRT
• High RT doses are needed to effectively treat brain tumors
• Concurrent chemotherapy with temozolomide is the current standard of care
• High RT doses in previous mouse model attempts was poorly tolerated– Adjacent critical structures! (Pharynx, esophagus, eye)– Concurrent chemotherapy
microRTmicroRTP
Kiehl, E.L. et al. Med Phys 35, 4735-4743(2008).
Experimental schema
• RT – 30 Gy / 6 (pragmatic, ~66 Gy equiv)• Temozolomide (21 mg/kg/d x 5d per month)• Rolipram (5mg / kg continuously)
RT: 6x5Gy MWFx2
TMZ TMZTMZ TMZ
Rolipram
Imaging Imaging Imaging Imaging Imaging Imaging
Goldhoff, P. et al. Clin Cancer Res 14, 7717-7725(2008).
An important observation in vivo
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A translatable result?
Goldhoff, P. et al. Clin Cancer Res 14, 7717-7725(2008).
Bench to mouse… to clinic?
• Translational path– From basic science observation– Clinical relevant (staining patient samples)– Shown to be effective alone in vivo– When added to ‘standard’ therapy in vivo cured
tumors
• Next stop…. the clinic?– Novel agent in trials of pediatric patients with
unresectable (and universally fatal) brain stem gliomas
A related clinical problem
• Radiation necrosis– Imaging methods currently don’t clearly differentiate from tumor– TMZ addition appears to make this effect more common
• Up to 10% rate
– Biopsy is usually required to prevent futile re-operation
Peca, C. et al. Clin Neurol Neurosurg 111, 331-334(2009).
An in vivo normal tissue model
• Using a micro-IGRT device, sub-totally irradiate murine brain– 60 Gy / 10 fractions
• Monitor with small animal MR
Jost, S.C. et al. Intl J Rad Onc Bio Phys In press,
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Jost, S.C. et al. Intl J Rad Onc Bio Phys In press,
Contrast-enhanced, T1-weighted, gradient-echo images
T2-weighted spin-echo images
2 months 4 months 6 months
Histology confirms necrosis
Jost, S.C. et al. Intl J Rad Onc Bio Phys In press,
Mouse Human
Tools for translation research• Orthotopic tumor and normal tissue models
– Biologic (targeted) agents– Chemotherapy– Timing– Combinations
• Modeling outcomes– Modulate dose to adjust TCP and NTCP – Model uncomplicated control
• Imaging questions– Novel imaging methods and modalities (PET tracers,
MR sequences, etc) • Imaging biomarkers to distinguish tumor from necrosis
• Therapy questions– Hypoxia targeting?– Sub-volume boosts to ‘resistant’ areas
Garbow et al., Clin Can Res 2008
Carcinogenesis models
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Respiratory correlated small animal CBCT and 4D IGRT
Amplitude 0
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Amplitude 0.2
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Amplitude 0.4
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Amplitude 0.6
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Amplitude 0.8
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Amplitude 1
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Moseley D., Lindsay, P. 2009
Endpoints: Pre-clinical and Clinical
• Clinical– Symptoms– Histology – Laboratory– Physiology– Imaging
• Anatomic
• Functional
– Tumor endpoints
• Pre-clinical
– Histology– Laboratory– Physiology– Imaging
• Anatomic
• Functional
– Tumor endpoints
Site3-WBP1:Flow WB FDP:Time
4.323.4562.5921.7280.8640
2
1.5
1
0.5
0
-0.5
-1
-1.5
Site1-WBP1:Flow WB FDP:Time
4.693.7522.8141.8760.9380
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1.5
1
0.5
0
-0.5
-1
-1.5
Conclusions• Potential for exploration with small
animal IGRT is immense– Internal normal control tissue for
experiments
• Many issues to consider for each potential application
– Biology• Species/strain• Tumor model• Endpoints
– Radiotherapy• Fractionation• Dose distribution• Motion• Validation
– Drugs• Timing• Sequencing
Acknowledgements:Washington University in St. Louis
• Daniel Low• Strahinja Stojadinovic• Enrique Izaguirre• Simon Powell• Joseph Deasy• Issam El Naqa• Jeffrey Bradley• Sasa Mutic• James Alaly• Divya Khullar• Aditya Aapte• Kate Malinowski• Erich Kiehl• And many more…
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Acknowledgements:Princess Margaret Hospital
• Patricia Lindsay• David Jaffray• Dick Hill• Amudha Venugopal• Steve Ansell• Salomeh Jelveh• Doug Moseley• James Chow• Graham Wilson• Precision X-ray, Inc.• (many more)