Angela Dann Monday, October 9, 2006 Photodynamic Therapy of Cancer: The Design and Characterization of Photosensitizing Agents Angela Dann Monday, October 9, 2006

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

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.

History Nature 2003, 3, 380.

History Niels Finsen (late 19th century) Oscar Rabb (100+ years ago) 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 Nature 2003, 3, 380.

History Herman Von Tappeiner, A. Jesionek W. Hausmann 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 Nature 2003, 3, 380.

History Samuel Schwartz (1960’s) Lipson, E.J. Baldes I. Diamond (1972) 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 Nature 2003, 3, 380.

History Thomas Dougherty (1975) J.F. Kelly (1976) Canada (1999) 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.

Introduction: Process of Photodynamic therapy Two individually non-toxic components brought together to cause harmful effects on cells and tissues Photosensitizing agent Light of specific wavelength Nature 2003, 3, 380.

Introduction: Reaction 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 Nature 2003, 3, 380.

Introduction: Reaction 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 < 0.04 ms Radius affected < 0.02 mm Nature 2003, 3, 380.

Introduction: Type 1 and 2 Reactions Nature 2003, 3, 380.

Introduction: Treatment 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 Nature 2003, 3, 380.

Introduction: Mechanism 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.

Introduction: Mechanism 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 Nature 2003, 3, 380. J. of Nuclear Medicine 2006, 47, 1119.

Introduction: Mechanism 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 Nature 2003, 3, 380.

Photosensitizing Agents: Requirements 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.

Photosensitizing Agents: Classes 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.

Photosensitizing Agents: Examples 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)

Photosensitizing Agents: Photofrin 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 Photochemistry and Photobiology 2001, 74, 656.

Photosensitizing Agents: Photofrin 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. Nature 2003, 3, 380.

Photosensitizing Agents: Photofrin 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.

Photosensitizing Agents: Advancements 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

Photosensitizing Agents: Foscan 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 Nature 2003, 3, 380.

Photosensitizing Agents: 5-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.

Photosensitizing Agents: Mono-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.

Photosensitizing Agents: Phthalocyanines 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.

Photosensitizing Agents: Phthalocyanines 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.

Photosensitizing Agents: Meta-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.

Photosensitizing Agents: Texaphyrins Synthetic – porphycene Water soluble Related to porphyrins Absorption between 720-760 nm (far red) Sufficiently penetrates tissue Photochemistry and Photobiology 2001, 74, 656.

Photosensitizing Agents: Tin 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.

PDT Trials on Tumor Cells: Breast 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.

PDT Trials on Tumor Cells: Breast 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.

PDT Trials on Tumor Cells: Breast 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.

PDT Trials on Tumor Cells: Skin 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.

PDT Trials on Tumor Cells: Skin 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 Pharmaceutical Research 2000, 17, 1447.

PDT Trials on Tumor Cells: Skin 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.

PDT Trials on Tumor Cells: Skin 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.

PDT Trials on Tumor Cells: Skin Cancer Clinical Studies performed on superficial skin cancer types: Actinic keratosis (AK) Basal cell carcinoma (BCC) Squamous cell carcinoma (SCC) Bowen’s disease (BD) Complete response (CR) – no clinical or histopathologic signs after follow-up Minimal side effects Pharmaceutical Research 2000, 17, 1447.

PDT Trials on Tumor Cells: Skin Cancer Pharmaceutical Research 2000, 17, 1447.

PDT Trials on Tumor Cells: Skin 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.

PDT Trials on Tumor Cells: Skin 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.

PDT Trials on Tumor Cells: Skin Cancer Photodermatol Photoimmunol Photomed 2005, 21, 72.

PDT Trials on Tumor Cells: Skin Cancer Results: 4 weeks later: 20 of 22 BCC – CR, 18 of 27 other – CR CR – no evidence of tumor in treatment field PR – >50% 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.

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

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

Conclusions: Clinical Approval of Photosensitizers Nature 2003, 3, 380.

Future Applications: Treatment 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.

Future Applications: Tumor 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.

Future Applications: Tumor Detection Using Fluorescence a: Green vascular endothelial cells of a tumor b: Red photosensitizing agent localizes to vascular endothelial cells after intravenous injection Nature 2003, 3, 380.

Future Applications: Photosensitizing 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 Nature 2003, 3, 380.

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