Biophysical Determinants of Photodynamic Therapy and Approaches to Improve Outcome

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Biophysical Determinants of Photodynamic Therapy
and Approaches to Improve Outcome

• Theresa M. Busch, Ph.D.
• Department of Radiation Oncology
• University of Pennsylvania, Philadelphia, PA

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What is Photodynamic Therapy?

• PDT is a directed, light-based method of damaging
  malignant or otherwise abnormal tissues.

Image from Wikipedia
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How Does it Work?
Type 2 Reaction
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How Does it Work?

• Mechanisms of PDT action
• Direct Cell Effects
• Direct 1O2-mediated toxicity to tumor cells
• Indirect Effects
• Vascular damage
• During light treatment
• Delayed development within several hours after
  light treatment
• Stimulation of host immune responses.
• Cell death may occur by apoptosis, necrosis,
  and/or autophagy

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PDT Variables

• Photosensitizer
• Drug type
• Dose
• Drug-light interval
• Light Delivery
• Wavelength
• Fluence
• Fluence rate

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What is it used for?

• Clinical Trials
• Pleural spread of nonsmall cell lung cancer
• Mesothelioma
• Intraperitoneal malignant tumors
• Head and Neck- pre-malignant through advanced
  disease
• Brain tumors
• Skin cancer
• Prostate cancer

• FDA-Approved Indications (Oncology)
• Obstructive esophageal cancer
• Obstructive endobronchial lung cancer
• Microinvasive endobronchial lung cancer
• Actinic keratosis
• Barretts esophagus/ high grade dysplasia
• for palliative intent

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Heterogeneity in PDT

• Photosensitizer distribution
• Tissue optical properties (light distribution)
• Microenvironment
• Tumor oxygenation
• Vascular network

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Heterogeneity in Photosensitizer Uptake A
Lesson From the Intraperitoneal PDT Clinical
Trial
Hahn SM, et al. Clin Cancer Res 125464-70, 2006
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How about light distribution?
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Light absorption and scattering affects the
fluence rate seen by the tissue.
Tumor surface
75 mW/cm2 630 nm
Normalized fluence rate
3 mm depth
Distance (mm)
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The tumor microenvironment is highly
heterogeneous.
Busch TM, et al. Clin. Cancer Res. 10
46304638, 2004
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. and PDT exacerbates heterogeneity in hypoxia
distribution
Control RIF Tumor
During PDT 5 mg/kg Photofrin 135 J/cm2, 75 mW/cm2
Busch TM, et al. Cancer Res. 62, 7273-7279,
2002
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Heterogeneity AboundsSo what to do?
?????Modify
?????Monitor
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Approach 1 Modify Light Delivery

• Rationale
• Lowering PDT fluence rate reduces the rate of
  photochemical oxygen consumption.
• Better maintenance of tumor oxygenation during
  illumination.
• Improves long-term tumor responses
• Enhanced direct cell kill
• Enhanced vascular shutdown in the treatment field

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Hypoxia Assay

• EF3 and EF5 are nitroimidazole-based drugs that
  binds to hypoxic cells as an inverse function of
  oxygen tension.
• Detection is by a fluorochrome-conjugated
  monoclonal antibody.
• Fluorescent micrographs are digitally analyzed
  for binding.

Section, Stain for EF3/5
Fluorescence microscopy
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Labeling of Hypoxia during PDT
PDT

• RIF murine tumor
• EF3 at 52 mg/kg
• Treated animals receive Photofrin-PDT at 75 or 38
  mW/cm2, 135 J/cm2
• Hoechst 33342 at 1.5 min before tumor excision
• Cryosectioning, immunohistochemistry,
  fluorescence microscopy

Hoechst (perfusion) Anti-EF3 Anti-CD31 Hoechst
(tissue label)
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Fluence rate effects on PDT-created hypoxia
EF3 Binding
EF3 Binding
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Low fluence rate reduces intratumor heterogeneity
in PDT-created hypoxia
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Causes of depth-dependent hypoxia during PDT

• Light distribution?

Tumor surface
Normalized fluence rate
3 mm depth
Distance (mm)
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Causes of depth-dependent hypoxia during PDT

• Photosensitizer distribution?

Photofrin Uptake (ng/mg)
S D
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Causes of depth-dependent hypoxia during PDT

• Does not appear to be a result of photochemical
  oxygen consumption.
• How about PDT-induced vascular effects?

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Getting at heterogeneity in vascular response
during PDT

• Diffuse Correlation Spectroscopy
• Measures the temporal correlation of fluctuations
  in the intensity of transmitted light (785 nm) to
  provide information on the motion of tissue
  scatters, e.g. red blood cells
• Data used to calculate relative blood flow, i.e.
  flow normalized to a pre-treatment baseline
• Monitoring throughout PDT is facilitated by a
  non-contact camera probe equipped with optical
  filters to block the 630 nm treatment light
• Separation distance between unique
  source-detector pairs determines the depth of
  tissue probed.

sources
detectors
Distance (mm)
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Substantial intratumor heterogeneity exists in
PDT-created vascular effects

• PDT induces an initial increase in blood flow.
• PDT leads to significant depth-dependent
  intratumor heterogeneity in blood flow response
  during illumination.

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Intratumor heterogeneity in vascular effects
(controls)
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Lower fluence rate reduces intratumor
heterogeneity in relative blood flow during PDT
Max rbf Max time (s) Min rbf Min time (s) CV () of values 0.75-1.00
75 mW/cm2 1.72 0.13 325 57 0.47 0.7 1195 172 15 3 13 2
38 mW/cm2 1.76 0.19 752 175 0.31 0.03 1647 249 9 1 26 5
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Low fluence rate reduces intratumor heterogeneity
in cytotoxic response.
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Low fluence rate improves long-term tumor response
of animals with tumors lt400 mm3
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Lowering PDT fluence rate improves therapeutic
outcome (summary)

• Delivering a light dose more slowly provides
• Less intra-tumor heterogeneity in PDT-created
  hypoxia during illumination
• Less intra-tumor heterogeneity in vascular
  responses during illumination
• Greater direct cell kill of tumor cells
• Better long-term treatment response

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Heterogeneity AboundsSo what to do?
?????Modify
?????Monitor
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Monitoring Rationale

• PDT can create significant hypoxia in even
  vascular-adjacent tumor cells.
• Vascular monitoring, including oxygenation and/or
  blood flow, may be indicative of tumor response.

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Monitoring Methods

• Diffuse optical spectroscopy
• Broadband reflectance spectroscopy with a
  noninvasive probe
• Measures tissue optical properties in the range
  of 600-800 nm
• Data used to calculate concentrations of
  oxyhemoglobin (HbO2) and deoxyhemoglobin (Hb)
• Tissue hemoglobin oxygen saturation (SO2 or StO2)
  HbO2/HbO2 Hb
• In mouse tissues SO2 of 50 at pO2 of 40 mmHg
• Diffuse correlation spectroscopy with a
  non-contact probe
• Measures temporal fluctuations in transmitted
  light (785 nm) to provide information on the
  motion of tissue scatters, e.g. red blood cells
• Data used to calculate relative blood flow, i.e.
  flow normalized to a pre-treatment baseline
• Monitoring throughout PDT is facilitated by a
  non-contact camera probe equipped with optical
  filters to block the 630 nm treatment light

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PDT induces variable changes in tumor hemoglobin
oxygen saturation
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Pre- or post-PDT SO2 is not associated with tumor
response
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The PDT-induced change in SO2 in individual
tumors is highly predictive of response
Relative SO2 SO2 after PDT SO2 before PDT
Time-to-400 mm3 (days)
Wang H-W, et al. Cancer Res. 64(20)7553-7561,
2004
Relative-SO2
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The PDT-induced change in blood flow is highly
predictive of response
Time to a tumor volume of 400 mm3 (days)
Slope of decrease in blood flow
Yu G, et al. Clin Cancer Res. 113543-52, 2005
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Monitoring (Summary)

• Pre-existing tumor SO2 of similarly-sized tumors
  of the same line can be highly heterogeneous.
• PDT-induced changes in SO2 and blood flow can
  vary from tumor-to-tumor, even for the same PDT
  treatment conditions.
• Individualized measurement of PDT effect on blood
  flow or blood oxygenation in a given tumor is
  predictive of long term response in that animal.
• Changes associated with better maintenance of
  tumor oxygen (smaller PDT-induced decreases in
  SO2 or blood flow) lead to better tumor
  response.
• Diffuse optical spectroscopy, can be readily
  applied in the clinic and thereby may provide a
  means for the rapid, individualized assessment of
  PDT outcome.

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Conclusions

• Both and clinical and preclinical studies
  indicate that tumors can be characterized by
  substantial heterogeneity in the essential
  components of PDT.
• MODIFICATION (e.g. light delivery or tumor
  microenvironment) can be used reduce physiologic,
  hemodynamic, and cytotoxic heterogeneity.
• MONITORING offers potential to optimize treatment
  through individualized, real-time dosimetry based
  on hemodynamic responses.

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PDT at Penn
Laser Specialist/Manager Carmen
Rodriguez Biostatistics Rosie Mick Mary
Putt Radiation Oncology Eli Glatstein Stephen
Hahn Robert Lustig James Metz Harry Quon Neha
Vapiwala Keith Cengel Veterinary Medicine Lilly
Duda Jolaine Wilson
Surgery Douglas Fraker Joseph Friedberg Scott
Cowan Bert OMalley S. Bruce Malkowicz Ara
Chalian Nursing Coordinators Debbie Smith Susan
Prendergast Melissa Culligan Medicine Dan
Sterman Colin Gilespie Andrew Haas Gregory
Ginsberg
Physicists Timothy Zhu Jarod Finlay Andreea
DiMofte Pre-clinical Researchers Theresa
Busch Sydney Evans Cameron Koch Stephen
Tuttle Keith Cengel Arjun Yodh Xioaman
Xing Dermatology Steve Fakharzadeh
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Acknowledgements

• Radiation Oncology
• Steve Hahn
• Eli Glatstein
• Keith Cengel
• Cameron Koch
• Sydney Evans
• Statistics/Image Analysis
• E. Paul Wileyto
• Mary Putt
• Kevin Jenkins
• Physics and Astronomy
• Arjun Yodh
• Xiaoman Xing
• Guoqiang Yu
• Hsing-Wen Wang

• Medical Physics
• Timothy Zhu
• Jarod Finlay
• Ken Wang
• Carmen Rodriguez
• Andreea Dimofte
• Busch lab
• Elizabeth Rickter
• Shirron Carter
• Min Yuan
• Amanda Maas
• Grant Support (NIH)
• R01 CA 85831
• P01 CA 87971