Photodynamic Therapy of Cancer: The Design and Characterization of Photosensitizing Agents

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Photodynamic Therapy of Cancer The Design and
Characterization of Photosensitizing Agents

• Angela Dann
• Monday, October 9, 2006

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• History
• Introduction
• Process of Photodynamic therapy (PDT)
• PDT to treat cancer
• Photosensitizing Agents
• Requirements
• Advancements
• Trials using PDT on tumor cells
• Conclusions
• Future applications

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History

• Light used as therapeutic agent for 3000 years
• Egyptian, Indian, and Chinese civilizations
• Psoriasis, rickets, vitiligo, skin cancer
• Photodynamic Therapy (PDT) developed within the
  last century

Nature 2003, 3, 380.
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History
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History

• Niels Finsen (late 19th century)
• Red light to prevent formation and discharge of
  small pox postules
• UV light from the sun to treat cutaneous
  tuberculosis
• Nobel Prize 1903
• Oscar Rabb (100 years ago)
• Acridine in combination with certain wavelengths
  of light
• Lethal to infusoria

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History

• Herman Von Tappeiner, A. Jesionek
• Defined photodynamic action
• Topically applied eosin and white light
• W. Hausmann
• 1st studies with haematoporphyrin and light
• Killed paramecium and red blood cells
• Friedrich Meyer-Betz (1913)
• 1st to treat humans with porphyrins
• Haematoporphyrin applied to skin, causing
  swelling/pain with light exposure

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History

• Samuel Schwartz (1960s)
• Developed haematoporphyrin derivative (HpD)
• Haematoporphyrin treated with acetic and sulfuric
  acids, neutralized with sodium acetate
• Lipson, E.J. Baldes
• HpD localization in tumor cells, fluorescence
• I. Diamond (1972)
• Use PDT to treat cancer

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History

• Thomas Dougherty (1975)
• HpD and red light
• Eradicated mammary tumor growth in mice
• J.F. Kelly (1976)
• 1st human trials using HpD
• Bladder cancer
• Canada (1999)
• 1st PDT drug approved

Nature 2003, 3, 380.
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IntroductionProcess of Photodynamic therapy

• Two individually non-toxic components brought
  together to cause harmful effects on cells and
  tissues
• Photosensitizing
• agent
• Light of specific
• wavelength

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IntroductionReaction Mechanisms

• Type 1
• Direct reaction with substrate (cell membrane or
  molecule)
• Transfer of H atom to form radicals
• Radicals react with O2 to form oxygenated
  products
• Type 2
• Transfer of energy to O2 to form 1O2

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IntroductionReaction Mechanisms

• Ratio of Type 1/Type 2 depends on
• Photosensitizing agent, concentration of
  substrate and O2, binding affinity of
  photosensitizing agent to substrate
• Reactive oxygenated species (ROS)
• Free radicals or 1O2
• Half-life of 1O2 lt 0.04 ms
• Radius affected lt 0.02 mm

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IntroductionType 1 and 2 Reactions
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IntroductionTreatment of cancer

• PDT best suited for
• Early stage tumors
• Inoperable for various reasons
• Limited success due to lack of specificity and
  potency of photosensitizing agents
• Three mechanisms of tumor damage

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IntroductionMechanism 1

• Direct Photodamage to Tumors by ROS
• Problems
• Non-homogenous distribution of photosensitizing
  agent within tumor
• Availability of O2 within tumor cells
• Reduction of O2 presence during PDT
• Overcoming O2 depletion
• Lower light fluence rate
• Pulse light delivery allow re-oxygenation

Nature 2003, 3, 380. J. of Nuclear Medicine
2006, 47, 1119.
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IntroductionMechanism 2

• Vascular Damage
• Blood vessels supply nutrients to tumor cells
• Effects
• Microvascular collapse
• Tissue hypoxia and anoxia
• Thrombus formation
• Associated with halting tumor growth
• Angiogenic factors upregulated

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2006, 47, 1119.
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IntroductionMechanism 3

• Immune Response
• Movement of lymphocytes, leukocytes, macrophages
  into treated tissue
• Difference in reactions toward normal and tumor
  tissues
• Upregulation of interleukin, not tumor necrosis
  factor-a
• Neutrophil slows tumor growth
• Required to purge remaining cells

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Photosensitizing AgentsRequirements

• Selectivity to tumor cells
• Photostability
• Biological stability
• Photochemical efficiency
• No cytotoxicity in absence of light
• Strong absorption 600-800 nm
• Good tissue penetration
• Long triplet excited state lifetime

J. of Photochemistry and Photobiology A
Chemistry 2002, 153, 245. Photochemistry and
Photobiology 2001, 74, 656.
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Photosensitizing AgentsClasses

• Porphyrin derivatives
• Most widely used
• Chlorins
• Reduced porphyrins
• Derivatives from chlorophyll or porphyrins
• Phthalocyanines
• 2nd generation
• Contain diamagnetic metal ion
• Porphycenes
• Synthetic porphyrins

Pharmaceutical Research 2000, 17, 1447.
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Photosensitizing AgentsExamples

• Photofrin
• Foscan
• 5-Aminolevulinic acid (5-ALA)
• Mono-L-aspartyl chlorin e6 (NPe6)
• Phthalocyanines
• Meso-tetra(hydroxyphenyl)porphyrins (mTHPP)
• Texaphyrins
• Tin ethyl etiopurpurin (SnET2, Purlytin)

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Photosensitizing AgentsPhotofrin

• 1st clinical approval (1999) in Canada
• Bladder cancer treatment
• Most commonly used photosensitizer
• Destroys mitochondria
• Dihematoporphyrin ether (DHE)
• bis-1-3(1-hydroxy-ethyl)deuteroporphyrin-8-yl
  ethyl ether
• Active component of HpD

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Photosensitizing AgentsPhotofrin

• Partially purified haematoporphyrin derivative
  (HpD)
• Mixture of mono-, di-, and oligomers
• Twice as phototoxic as crude haematoporphyrin
  (Hp)
• Crude Hp consists of range of porphyrins
• Convert to HpD by acetylation and reduction using
  acetic and sulfuric acids, filtering, and
  neutralizing with sodium acetate

Photochemistry and Photobiology 2001, 74, 656.
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Photosensitizing AgentsPhotofrin

• Limitations
• Contains 60 compounds
• Difficult to reproduce composition
• At 630 nm, molar absorption coefficient is low
  (1,170 M-1 cm-1)
• Main absorption at 400 nm
• High concentrations of drug and light needed
• Not very selective toward tumor cells
• Absorption by skin cells causes long-lasting
  photosensitivity (½ life 452 hr)

Nature 2003, 3, 380. J. of Photochemistry and
Photobiology A Chemistry 2002, 153, 245.
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Photosensitizing AgentsAdvancements

• Need to overcome limitations of Photofrin
• New photosensitizers developed according to ideal
  situations
• Increase specificity to tumor cells
• Increase potency
• Decrease time of sensitivity to sunlight after
  treatment

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Photosensitizing AgentsFoscan

• Chlorin photosensitizing agent
• Approved for treatment of head and neck cancer
• Low drug dose (0.1 mg/kg body weight)
• Low light dose (10 J/cm2)
• Complications due to potency

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Photosensitizing Agents5-Aminolevulinic acid
(5-ALA)

• Hydrophilic zwitterion at physiological pH
• Approved for treatment of actinic keratosis and
  BCC of skin
• Topical application most frequently used
• Endogenous photosensitizing agent
• 5-ALA not directly photosensitizing
• Creates porphyria-like syndrome
• Precursor to protoporphyrin IX (PpIX)

Nature 2003, 3, 380. Photochemistry and
Photobiology 2001, 74, 656. Pharmaceutical Res.
2000, 17, 1447.
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Photosensitizing AgentsMono-L-aspartyl chlorin
e6 (NPe6)

• 2nd generation hydrophilic chlorin
• Derived from chlorophyll a
• Chemically pure
• Absorption at 664 nm
• Localizes in lysosomes (instead of mitochondria)
• Reduced limitations compared to Photofrin
• Decreased sensitivity to sunlight (1 week)
• ½ life 105.9 hr

Photodermatol Photoimmunol Photomed 2005, 21, 72.
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Photosensitizing AgentsPhthalocyanines

• 2nd generation
• Ring of 4 isoindole units linked by N-atoms
• Stable chelates with metal cations
• Sulfonate groups increase water solubility
• Examples (AlPcS4, ZnPcS2)
• Aluminum chlorophthalocyanine sulfonate
• More prolonged photosensitization than HpD
• Less skin sensitivity in sunlight

Photochemistry and Photobiology 2001, 74, 656. J.
of Nuclear Medicine, 2006, 47, 1119.
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Photosensitizing AgentsPhthalocyanines

• Tetrasulfonated AlPcS4
• Hydrophilic
• Deposited in vascular stroma
• Affects vascular system indirect cell death
• Disulfonated ZnPcS2
• Amphophilic
• Transported by lipoproteins
• Direct cell death

Photochemistry and Photobiology 2001, 74, 656. J.
of Nuclear Medicine, 2006, 47, 1119.
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Photosensitizing AgentsMeta-tetra(hydroxyphenyl)
porphyrins (mTHPP)

• Commercially available as meta-tetra(hydroxyphenyl
  )chlorin (mTHPC)
• 2nd generation
• Improved red light absorption
• 25-30 times more potent than HpD
• More selective toward tumor cells
• Most active photosensitizer with low drug and
  light doses
• Not granted approval

Photochemistry and Photobiology 2001, 74, 656.
Int. J. Cancer 2001, 93, 720.
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Photosensitizing AgentsTexaphyrins

• Synthetic porphycene
• Water soluble
• Related to porphyrins
• Absorption between 720-760 nm (far red)
• Sufficiently penetrates tissue

Photochemistry and Photobiology 2001, 74, 656.
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Photosensitizing AgentsTin ethyl etiopurpurin

• SnET2, Purlytin
• Chlorin
• Treatment of cutaneous metastatic malignancies
• Results of phase III study (934 patients) not yet
  released

Photochemistry and Photobiology 2001, 74, 656.
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PDT Trials on Tumor CellsBreast Cancer

• Chest wall recurrences problem with mastectomy
  treatment (5-19)
• Study
• 7 patients, 57.6 years old (12.6)
• 89 metastatic nodes treated
• 11 PDT sessions
• Photosensitizing agent (m-THPC)
• meta-tetra(hydroxyphenyl)chlorin
• 2nd generation photosensitizing agent

Int. J. Cancer 2001, 93, 720.
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PDT Trials on Tumor CellsBreast Cancer

• Dosage
• Diode laser used to generate l 652 nm
• 3 patients
• 0.10 mg/kg total body weight
• 48 hr under 5 J/cm2
• 4 patients
• 0.15 mg/kg total body weight
• 96 hr under 10 J/cm2

Int. J. Cancer 2001, 93, 720.
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PDT Trials on Tumor CellsBreast Cancer

• Results
• Complete response in all 7 patients
• Pain 10 days, Healing 8-10 weeks
• Patients advised to use sun block or clothing to
  protect skin from light for 2 weeks
• 4 days after treatment 1 patient with skin
  erythema and edema from reading light
• 6 of 7 patients given medication for pain
• Mostly based on size, not lightdose
• Recurrences in 2 patients (2 months)

Int. J. Cancer 2001, 93, 720.
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PDT Trials on Tumor CellsSkin Cancer

• Traditional Treatments
• Surgery, electrodesiccation, cryosurgery, topical
  application of podophyllin or 5-fluorouracil,
  radiation
• Problems
• High cost, scarring, pigmentation changes, pain,
  inflammation, irritation

Pharmaceutical Research 2000, 17, 1447.
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PDT Trials on Tumor CellsSkin Cancer

• Most promising treatment using PDT
• Skin highly accessible to light exposure
• Most common method
• Topical administration of 5-ALA
• Non-invasive, short photosensitization period,
  treat multiple lesions, good cosmetic results,
  well accepted by patients, no side effects

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PDT Trials on Tumor CellsSkin Cancer

• Mechanism of 5-ALA use
• 5-ALA formed in vivo in mitochondria by
  condensation of glycine and succinyl CoA
  (catalyzed by ALA-syntase)
• Subsequent reactions produce protoporphyrin IX
  (PpIX)
• Converted to heme using ferrochelatase and Fe
• Heme inhibits synthesis of 5-ALA
• Excess administered 5-ALA passes through abnormal
  epidermis and converts to PpIX

Pharmaceutical Research 2000, 17, 1447.
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PDT Trials on Tumor CellsSkin Cancer

• Mechanism (continued)
• PpIX accumulates with minimized amount of
  ferrochelatase
• Tissues with increased concentration of PpIX
  undergo phototoxic damage upon light exposure
• 3PpIX is formed, energy transferred to create 1O2
• PpIX nearly completely cleared within 24 hr

Pharmaceutical Research 2000, 17, 1447.
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PDT Trials on Tumor CellsSkin Cancer

• Clinical Studies performed on superficial skin
  cancer types
• Actinic keratosis (AK)
• Basal cell carcinoma (BCC)
• Squamous cell carcinoma (SCC)
• Bowens disease (BD)
• Complete response (CR) no clinical or
  histopathologic signs after follow-up
• Minimal side effects

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PDT Trials on Tumor CellsSkin Cancer
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PDT Trials on Tumor CellsSkin Cancer

• Clinical trials with mono-L-aspartyl chlorin e6
  (NPe6)
• 14 patients 9 male, 5 female
• 46-82 years old (64 yrs average)
• BCC 22 lesions, SCC 13 lesions, papillary
  carcinoma 14 lesions

Photodermatol Photoimmunol Photomed 2005, 21, 72.
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PDT Trials on Tumor CellsSkin Cancer

• Clinical trials (continued)
• 5 different intravenous doses of NPe6 over 30
  minutes (0.5 mg/kg 3.5 mg/kg)
• 4-8 hr prior to light administration (due to
  number of lesions)
• Light dose 25-200 J/cm2
• Argon-pumped tunable dye laser set at 664 nm
• Dose dependent on tumor size/shape

Photodermatol Photoimmunol Photomed 2005, 21, 72.
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PDT Trials on Tumor CellsSkin Cancer
Photodermatol Photoimmunol Photomed 2005, 21, 72.
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PDT Trials on Tumor CellsSkin Cancer

• Results
• 4 weeks later 20 of 22 BCC CR, 18 of 27 other
  CR
• CR no evidence of tumor in treatment field
• PR gt50 reduction in tumor size
• Photosensitivity gone within 1 week (12 of 14)
• 3 patients mild to moderate pruritis, facial
  edema or blistering, erythema, tingling
• 1 patient severe intermittent burning pain
• 1 patient erythema, edema, moderate pain (gone
  within 2 weeks)

Photodermatol Photoimmunol Photomed 2005, 21, 72.
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Conclusions

• PDT of cancer regulated by
• Type of photosensitizing agent
• Type of administration
• Dose of photosensitizer
• Light dose
• Fluence rate
• O2 availability
• Time between administration of photosensitizer
  and light

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Conclusions

• Tumor cells show some selectivity for
  photosensitizing agent uptake
• Limited damage to surrounding tissues
• Less invasive approach
• Outpatient procedure
• Various application types
• Well accepted cosmetic results

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ConclusionsClinical Approval of Photosensitizers
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Future ApplicationsTreatment of Other Diseases

• Dermatology
• Psoriasis, scleroderma, vitiligo
• Rheumatology
• Arthritis
• Cardiovascular diseases
• Artherosclerotic plaque resolution, post-stent
  implantation
• Age-related eye diseases
• Macular degeneration
• Immunotherapy

Nature 2003, 3, 380. Photochemistry and
Photobiology 2001, 74, 656.
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Future ApplicationsTumor Detection Using
Fluorescence

• Mechanism by which HpD selectively accumulates in
  tumor cells not well understood
• High vascular permeability of agents?
• Testing photosensitizing agents
• Porphyrins, haematoporphyrins, HpD, ALA-D
• Administer photosensitizer and monitor
  fluorescence with endoscope
• SCC shows increased fluorescence
• More invasive tumors show even greater
  fluorescence

Nature 2003, 3, 380.
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Future ApplicationsTumor Detection Using
Fluorescence

• a Green vascular endothelial cells of a tumor
• b Red photosensitizing agent localizes to
  vascular endothelial cells after intravenous
  injection

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Future ApplicationsPhotosensitizing Drugs

• Improved Specificity and Potency
• Better photosensitizers developed and under
  investigation in clinical trials
• Use of carriers conjugated antibodies directed
  to tumor-associated antigens
• New compounds that absorb light of longer
  wavelength better tissue penetration
• New compounds with less skin photosensitivity
• Improved Efficacy
• Creating a preferred treatment of cancer

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Thank you