Porphyrins with applications in PDT of cancer
(Dr. R.-M. Ion)

Figure 2. Metals which can react with porphyrins

Figure 3. The Jablonski diagram

Figure 5.
The photodegradation
scheme of porphyrins

R

Name of the porphyrin

C6H5

5, 10,15,20-tetraphenylporphyrin (TPP)

C10 H8

5,10,15,20-tetra-1-naphthylporphyrin (TNP)

C6H4-SO3

5, 10,15, 20-tetra-p-sulfonatophenylporphyrin (TSPP)

C6H5-NH2

5,10,15,20-tetra(4-aminophenyl)porphyrin (TAPP)

C6H5-NO2

5,10,15,20-tetra(4-nitro-phenyl)porphyrin (TNPP)

C6H5-OH

5,10,15,20-tetra(4-hydroxyphenyl)porphyrin (THPP)

C6H5-CH3

5,10,15,20-tetra(4-methylphenyl)porphyrin (TMPP)

C6H5-OCH3

5,10,15,20-tetra(4-methoxyphenyl)porphyrin (TMOPP)

C10H7-SO3H

5,10,15,20-tetra(4-sulfonatonaphthyl)porphyrin (TSNP)

C10H7-OH

5,10,15,20-tetra(4-hydroxynaphthyl)porphyrin (THNP)

Figure 1. Structure of
the studied porphyrins

Table 1. Types of the different
meso-substituted porphyrins

Patient

Sensitizer / solvent

(mg / ml)

Irradiation conditions

time / dose / power density

(h) / (J/cm2) / (mW/cm2)

Incubation time

(h)

Tumor type

A

TSPP

0.1 (1)

4 / 14.3 / 1.05

24

Parasagial meningiom

B

TSPP

0.1 (2)

1 / 6.3 / 1.75

1

Right temporal

C

TSPP

0.1 (1)

2 / 12.6 / 1.75

2

Left parentheral

D

TPP

0.05 (2)

1 / 6.3 / 1.75

24

Left frontal

E

TNP

0.1 (1)

3 / 19 / 1.75

48

Malignant meningioma

F

TNP

0.1 (2)

3 / 19 / 1.75

48

Intraventricular

G

ZnTSPP

0.5

1 / 6.3 / 1.75

24

Left frontal

Figure 4. Experimental set-up for tumor irradiation (in vitro)

Contact Person

Topics of Interest

Structure and spectral characterization
Photophysical properties
Photochemical properties

Introduction

From The Oxford English Dictionary, porphyrins are "a large class of deeply coloured red or purple, fluorescent crystalline pigments, with natural or synthetic origin, having in common a substituted aromatic macrocyclic ring consisting of four pyrrole-type residues, linked togheter by four methine bridging groups".

Photodynamic Therapy of Cancer

Photodynamic therapy (also called PDT, photoirradiation therapy, phototherapy, or photochemotherapy) as a new modality for cancer treatment is the combination of light with a photosensitizing drug in an oxygen-rich environment. Photosensitizing drugs (porphyrins, porphycenes and phthalocyanines) are used according to their efficiency to generate singlet oxygen, the phototoxic intermediary.

The photosensitization of oxygen is a slightly different process. The sensitizer molecule, which has a singlet electronic ground state, absorb light energy and becomes electronically excited. This process occurs very rapidly (10-15s) and produces a singlet excited state of a sensitizer, 1S*.

Toxic oxygen species such as singlet oxygen and free radicals are thus formed. These chemicals are very reactive and can damage proteins, lipids (including phospholipids and cholesterol), nucleic acids and other cellular components and with certain a-aminoacids side chains in proteins (Trp, His, Met); these are all vital components of membranes (external and internal to the cell) and membrane damage in this way is a plausible macroscopic mechanism for cell damage and death.

Singlet oxygen is a powerful, fairly indiscriminant, oxidant that reacts with a variety of biological molecules and assemblies.

Seven golden rules for a good PDT agent

  1. It must be a pure compound;
  2. It must be activated at l 650 nm to ensure better absorption of tissue-penetrating red light, and also sensitization by an external light source;
  3. It must be non-toxic in the absence of light;
  4. Its triplet excited state must be long-lived enough to enable it to photosensitize the production of singlet oxygen;
  5. It must localize specifically in the tumor;
  6. It must clear rapidly from the body after it has done its work;
  7. It must be soluble in the body´s tissue fluids so that it can be injected and transported to the tumor site.
Porphyrins for Photodynamic Therapy of Human Brain Tumors

Photodynamic therapy (PDT) offers a more selective approach to the treatment of brain malignancies compared with other standard available treatment modalities. PDT may be of advantage in the treatment of tumors of combining it with radiotherapy, hyperthermia, chemotherapy, sonotherapy, and hyperoxygenation.

In-vitro samples of brain tumoral tissues were prelevated from human patients and impregnated with different porphyrin-sensitizers solutions (including with metallic complexes of porphyrins). The radiation of the nitrogen pulsed laser is emitted at 337.1 nm with a power density ranging from 1 to 3.5 mW/cm2.

Photosensitizers preferentially accumulate in malignant tissue whether via increased uptake due to an accelerated cellular proliferation rate, decreased intratumoral pH favoring photosensitizer retention, increased phagocytosis capabilities, leaky vasculature, decreased lymph drainage tumor-associated macrophage engulfing photosensitizers or specific uptake via receptors.

The experiments were made in vitro on tumoral tissues obtained from different types of cerebral tumors prelevated from 10 patients on whom there were made previously surgical interventions. The samples were obtained by cutting pieces from tumor tissues. An aseptically excised brain tissue was cut on a sterile paraffin plate into pieces about 1 mm of diameter. These fragments were washed in MEM and then were places into wells. MEM with 10% FCS in total volume of 0.15 ml was added into each wells. The sample was irradiated by laser after 24-48 h incubation time. The dye impregnation was done immediately after operation.

Measurement types:

Absorption spectra;

Fluorescence spectra;

The 3-fluorescence flow cytometry (Cytron Absolute, Ortho) equipped with an argon ion laser was used and with a peak fitting program using Gauss type functions on a PC computer program.

Optical microscopy for video recordings of the vascular effects for cells during the light irradiation, obtained by means of a Leitz microscope and a Leitz Aristoplan microscope.

Irradiation procedure with a nitrogen pulsed laser radiation.

The efficiency of the incorporation of these dyes into human blood cells changed in the same manner as the singlet oxygen generation: the sulfonated porphyrins was efficiently incorporated into leukocytes than into granulocytes and only in monomeric form.

The light led to a rapid necrosis of tumor which was not the result of the direct killing of tumor cells, but destruction of tumor microvasculature. It has been shown that the vascular damage expressed by a decreased blood flow stasis are immediate and major consequences of the photodynamic treatment with photodynamic systems introduced in these experiments.

The photodegradation reaction of porphyrinic agents

The porphyrins can be modified by light and oxygen, this process being called photodegradation or photobleaching.

It should be noted that the photobleaching does not decribe a "simple" photodegradation of the photosensitizer. It includes a chemical modification of the porphyrin, i.e. formation of photoproducts.

The main factors influencing the photodegradation rate:

Some References
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