1O2 Singlet Oxygen - PDT PhotoDynamic Therapy - Doctoral Thesis

Section 1.2.2: Mechanisms of Tumour Destruction

While it has long been known that the basis mode of cancer cell death in PDT is mediated through singlet oxygen generation and other reactive oxygen species, and that direct cellular damage and vascular shutdown contribute to destruction of the tumour, only in recent years the importance of immune responses have been recognized [3].

Direct Cellular Damage: It has been shown that exposure of tumours to PDT in vivo can reduce the clonogenic tumour cells thought direct photodamage, i.e., those cells able to reproduce a tumour. However, complete tumour eradication is not always fully realized by this mechanism mainly due to two reasons: non-homogeneous distribution of the photosensitiser within the tumour and oxygen availability within the tissue that is targeted by PDT [4,6].

Vascular Damage: The viability of tumour cells also depends on the amount of nutrients supplied by the blood vessels, which in turn depend on growth factors produced by tumour or host cells. The mechanisms underlying the vascular effects of PDT differ greatly with different photosensitizers but vascular constriction, thrombus formation and inhibition of tumour growth have been identify among the most important ones [13].

Immune Responses: Several studies have reported that infiltration of lymphocytes, leukocytes and macrophages into PDT-treated tissue produced an activation of the immune response that consequently eliminates surviving tumour cells that have escaped to the direct effects of PDT [14-16].

PDT effects on all these targets may influence each other, producing a plethora of responses. However, the relative importance of each for the overall tumour response is yet to be defined. Further, it is known that both necrosis and apoptosis occur following PDT [17,18], albeit to different degrees depending on the photosensitiser and treatment conditions.

Necrosis or passive cell death can either result from extreme external physical conditions or severe cellular damage induced by chemical processes. It is usually accompanied by a loss of membrane integrity and associated with characteristic morphological changes such as organelle and cell swelling, bleb formation, loss of integrity of mitochondrial, lysosomal and plasma membranes and eventual breakdown
of the cell, leading to release of its contents into the surrounding area [19].

Apoptosis represents regulated cell suicide. It is a mechanism whereby organisms initiate cellular death via a process that is normally part of the genetic apparatus [20]. The end result is fragmentation of nuclear DNA and dissociation of the cell into membrane-bound particles that are phagocyted by neighbouring cells, preventing uncontrolled leakage of intracellular material to the environment and thereby avoiding
damage to neighbouring cells and tissue inflammation [21]. Apoptosis has been shown to be a rapid and dominant form of cell death following PDT in multiple experimental settings utilising various photosensitisers and cell types [22-24].

1O2 Singlet Oxygen - PDT PhotoDynamic Therapy - "Thought" To Activate Immune System Too - Cancer Active - UK

Although we featured this benefit of PDT in our report on this exciting and potentially non-invasive therapy more than a year ago, a new report in the British Journal of Cancer claims the new discovery: that PDT can do more than treat the cancer it is directly attacking. In early studies using animal models, Roswell Park Researchers in the USA found that treatment with PDT stimulated the immune system to move out and attack cancer cells elsewhere in the body.

To recap, PDT uses an agent which attaches to the cancer cells. Then by shining light of a certain frequency onto the agent it produces free radical oxygen and kills the cancer cell.

Hitherto, many of the agents developed in the USA have essentially been ‘drugs’ and can kill healthy cells as well. A new breed of natural, algae based agents developed by the Russians has been seen to be far more targeted on cancer cells and to stimulate the immune system
throughout the body. Readers may care to read our report on our web site.

Meanwhile the Roswell Park ‘drug’ seems to have many of these immune system developing benefits too. Dr Sandra Gollnick, senior author of the research, explains:

“Solely treating the tumours in the shoulder worked as normal for PDT. But it also sparked off an immune response that reduced the number of tumours in the lungs as well. We made sure this wasn’t due to activated drug reaching the lung tumours, and we were able to identify the precise part of the immune system being activated.

“It’s the first time this effect has been seen and explained in such detail, although other scientists have predicted that PDT could trigger an immune response.”

PDT is almost one hundred years old,but with new laser delivery methods and new agents it is at last coming into its own.

1O2 Singlet Oxygen - PDT - PhotoDynamic Therapy Using a Protoporphyrinogen Oxidase Inhibitor

V H Fingar, T J Wieman, K S McMahon, P S Haydon, B P Halling, D A Yuhas, J W Winkelman

Division of Surgical Oncology, Henry Vogt Cancer Institute, University of Louisville, Kentucky 40292, USA.

Journal Article: Cancer Research (impact factor: 8.23). 11/1997; 57(20):4551-6.

Abstract

The use of endogenously created porphyrins as an alternative to photosensitizer injection for photodynamic therapy is a rapidly evolving area of study. One common method to induce porphyrin synthesis and accumulation in cells is the topical, oral, or parenteral administration of 5-aminolevulinic acid, a precursor for heme biosynthesis. Porphyrin accumulation may also be elicited by the use of enzyme inhibitors of the heme biosynthetic pathway.

Groups of DBA/2 mice bearing SMT-F mammary tumors were placed on a diet containing 0-4000 ppm of a protoporphyrinogen oxidase inhibitor, FP-846. This agent blocks a critical step in porphyrin metabolism and results in elevated intracellular levels of protoporphyrin IX.

* Light treatment of tumors produced both initial and long-term regression that was dependent on the amount of inhibitor, the duration of inhibitor exposure to animals, and the amount of light used in PDT.

* Tumor regression occurred without significant destruction of normal tissues in the treatment field and without initial vascular constriction or blood flow stasis.

* Tumor cure in animals given 4000 ppm FP-846 in feed for 3 days and 300 J/cm2 602-670 nm light (23% cure) was similar to the response in animals given 10 mg/kg Photofrin and the same light dose (20%).

Source: PubMed

1O2 Singlet Oxygen - Experimental Study on Photodynamic Diagnosis of Cancer Mediated by Chemiluminescenc Probe

The reaction of ozone with a number of biological molecules was found to produce singlet oxygen in high yield. At pH 7.0, the reaction of ozone with an equimolar amount of biological molecule produced the following singlet oxygen yields (mole of singlet oxygen/mole of ozone):

http://www.osti.gov/energycitations/product.biblio.jsp?query_id=1&page=0&osti_id=5639691

Cancer - 1O2 Singlet Oxygen - Study on Photodynamic Diagnosis of Cancer Mediated by Chemiluminescenc Probe

1O2 Singlet Oxygen - PDT PhotoDynamic Therapy - "Thought" To Activate Immune System Too - Cancer Active - UK

Although we featured this benefit of PDT in our report on this exciting and potentially non-invasive therapy more than a year ago, a new report in the British Journal of Cancer claims the new discovery: that PDT can do more than treat the cancer it is directly attacking. In early studies using animal models, Roswell Park Researchers in the USA found that treatment with PDT stimulated the immune system to move out and attack cancer cells elsewhere in the body.

To recap, PDT uses an agent which attaches to the cancer cells. Then by shining light of a certain frequency onto the agent it produces free radical oxygen and kills the cancer cell.
Hitherto, many of the agents developed in the USA have essentially been ‘drugs’ and can kill healthy cells as well. A new breed of natural, algae based agents developed by the Russians has been seen to be far more targeted on cancer cells and to stimulate the immune system
throughout the body. Readers may care to read our report on our web site.

Meanwhile the Roswell Park ‘drug’ seems to have many of these immune system developing benefits too. Dr Sandra Gollnick, senior author of the research, explains:
“Solely treating the tumours in the shoulder worked as normal for PDT. But it also sparked off an immune response that reduced the number of tumours in the lungs as well. We made sure this wasn’t due to activated drug reaching the lung tumours, and we were able to identify the precise part of the immune system being activated.

“It’s the first time this effect has been seen and explained in such detail, although other scientists have predicted that PDT could trigger an immune response.”

PDT is almost one hundred years old,but with new laser delivery methods and new agents it is at last coming into its own.

OBSERVATIONAL OUTCOMES ON ALL PATIENTS TREATED IN A 12 MONTH PERIOD WITH SYSTEMIC PHOTODYNAMIC AND SONODY­NAMIC THERAPY (SPDT/SDT) USING A TIN CHLOROPHYLLIN BASED SENSITIZER
By Dr Julian Kenyon, Medical Director Dove Clinic - February, 2007

Summary
Patient result

s reported here are very encouraging. In the majority of patients, biochemistry pre- and post­SPDT/SDT shows that there has been significant tumour cell destruction. This includes the destruction of tu­mours deep in the body. Almost all patients with bone secondaries develop increased pain post SPDT.

A clinic based in Australia (Opal Clinic, ed) also using SPDT/SDT has used photodynamic diagnosis to observe bony metastases. With this diaglostic technique, a laser light is used to stimulate fluorescent radiation from the sensitizer in tumours. The technique is only applicable to tumours relatively close to the skin. They treated a patient with non small cell lung cancer with bony metastases in the lumbar 4 vertebra.

Photodynamic diag­nosis showed that these tumours disappeared after SPDT/SDT therapy. The patient also reported that he felt " 50 % better° three months after starting SPDT/SDT, and was still well after 5 months. We are looking into the use of this diagnostic method In order to look at the bone secondary situation in more detail.

A small number of patients have had a complete response, it is too early to say if their tumours will recur. It would seem that a sensible woy forward with patients with significant tumour load, is to repeat this form of photodynamic therapy as necessary to continue tumour destruction and to cope with any recurrences. We are continuing to audit these cases in as detailed a way as possible.

Recently, there has been wide dissemination of information about the purported dangers of free radicals, which are being blamed for all the ills that mankind is subject to, from aging to heart attacks to cancer.

Free radicals are atoms with unpaired electrons, a natural occurrence in biochemical reactions. There could be no chemical reactions and thus no life without free radicals. The properties of free radicals vary widely. Some are toxic to all living cells, others only to the most vulnerable cells. Singlet oxygen, O1 is a highly reactive, beneficial free radical that acts as a scavenger of other harmful free radicals. The oxygen combines with some of them to render them harmless, thereby protecting cells from damage. Healthy cells produce enzymes that protect them from oxidation.

These enzymes are glutathione peroxidase, super-oxide dismutase, catalase, and reductase. Bacteria and viruses have no such enzyme
protection and are therefore oxidized. By this elegant mechanism, ozone distinguishes between friends and foes and attacks only toxins, pathogens, and cells that have been damaged, weakened and infected.