Targeted transcutaneous cancer therapy

Details Targeted transcutaneous cancer therapy Targeted transcutaneous cancer therapy

1999-03-18

2003-08-05

Gibson, Roy D. (Department: 3733)

Surgery: light, thermal, and electrical application

Light, thermal, and electrical application

Light application

C607S089000, C604S021000

Reexamination Certificate

active

06602274

ABSTRACT:

FIELD OF THE INVENTION
This invention generally relates to the delivery to a tumor target site of a therapeutically effective amount of a photosensitizing agent that is activated by a relatively low fluence rate or level of intensity of light administered over a prolonged period of time, and more specifically, to the delivery of a photosensitizing agent that is targeted to bind with cancerous cells at the target site.
BACKGROUND OF THE INVENTION
One form of energy activated therapy for destroying abnormal or diseased tissue is photodynamic therapy (PDT). PDT is a two-step treatment process, which has received increasing interest as a mode of treatment for a wide variety of different cancers and diseased tissue. The first step in this therapy is carried out by administering a photosensitive compound systemically by ingestion or injection, or topically applying the compound to a specific treatment site on a patient's body, followed by illumination of the treatment site with light having a wavelength or waveband corresponding to a characteristic absorption waveband of the photosensitizer. The light activates the photosensitizing compound, causing singlet oxygen radicals and other reactive species to be generated, leading to a number of biological effects that destroy the abnormal or diseased tissue, which has absorbed the photosensitizing compound. The depth and volume of the cytotoxic effect on the abnormal tissue, such as a cancerous tumor, depend in part on the depth of the light penetration into the tissue, the photosensitizer concentration and its cellular distribution, and the availability of molecular oxygen, which will depend upon the vasculature system supplying the abnormal tissue or tumor.
Various types of PDT light sources and their methods of use have been described in the prior art literature. However, publications describing appropriate light sources and the effects of transcutaneous light delivery to internal treatment sites within a patient's body, for PDT purposes, are relatively limited in number. It has generally been accepted that the ability of a light source external to the body to cause clinically useful cytotoxicity during PDT is limited in depth to a range of 1-2 cm or less, depending on the photosensitizer.
Treatment of superficial tumors in this manner has been associated with inadvertent skin damage due to accumulation of the photosensitizer in normal skin tissue, which is a property of all systemically administered photosensitizers in clinical use. For example, clinically useful porphyrins such as PHOTOPHRIN™ (a QLT, Ltd. brand of sodium porfimer) are associated with general dermal photosensitivity lasting up to six weeks. PURLYTIN™, which is a brand of purpurin, and FOSCAN™, which is brand of chlorin, sensitize the skin to light for at least several weeks, so that patients to whom these drugs are administered must avoid exposure to sunlight or other bright light sources during this time to avoid unintended phototoxic effects on the normal dermal tissue. Indeed, efforts have been made to develop photoprotectants to reduce skin photosensitivity (see, for example: Dillon et al., “Photochemistry and Photobiology,” 48(2): 235-238 (1988); and Sigdestad et al.,
British J. of Cancer
, 74:S89-S92, (1996)).
Recently, it has been reported that a relatively intense external laser light source might be employed transcutaneously to cause two-photon absorption by a photosensitizer at a greater depth within a patient's body, so that it is theoretically possible to cause a very limited volume of cytotoxicity in diseased tissue at greater depths than previously believed possible. However, no clinical studies exist to support this contention. One would expect that the passage of an intense beam of light through the skin would lead to the same risk of phototoxic injury to non-target normal tissues, such as skin and subcutaneous normal tissue, if this light is applied in conjunction with a systemically administered photosensitizer.
For example, one PDT modality discloses the use of an intense laser source to activate a photosensitizer drug within a precisely defined boundary (see: U.S. Pat. No. 5,829,448, Fisher et al., “Method for improved selectivity in photo-activation of molecular agents”). The two-photon methodology requires a high power, high intensity laser for drug activation using a highly collimated beam, with a high degree of spatial control. For a large tumor, this treatment is not practical, since the beam would have to be swept across the skin surface in some sort of set, repeating pattern, so that the beam encompasses the entire volume of the tumor. Patient or organ movement would be a problem, because the beam could become misaligned. Exposure of normal tissue or skin in the path of the beam and subcutaneous tissue photosensitivity is not addressed in the prior art literature. Any photosensitizer absorbed by normal tissue in the path of the beam will likely be activated and cause unwanted collateral normal tissue damage. Clearly, it would be preferable to employ a technique that minimizes the risk of damage to normal tissue and which does not depend upon a high intensity laser light source to produce two photon effects. Further, it would be preferable to provide a prolonged exposure of an internal treatment site with light at a lower fluence rate or lower intensity, which tends to reduce the risk of harm to non-target tissue or skin and subcutaneous normal tissue and reduces any collateral tissue damage due to phototoxicity.
Other PDT modalities have employed the use of a light source producing a low total fluence delivered over a short time period to avoid harm to skin caused by activation of a photosensitizer and have timed the administration of such drugs to better facilitate destruction of small tumors in animals (see, for example, U.S. Pat. No. 5,705,518, Richter et al.). However, although not taught or suggested by the prior art, it would be preferable to employ a light source that enables a relatively large total fluence PDT, but at a lower intensity so that larger tumor volumes can more readily be treated.
If, as is often the case, a target tumor tissue lies below an intact cutaneous layer of normal tissue, the main drawbacks of all transcutaneous illumination methods, whether they be external laser or external non-laser light sources, are: (1) the risk of damage to non-target tissues, such as the more superficial cutaneous and subcutaneous tissues overlying the target tumor mass; (2) the limited volume of a tumor that can be treated; and (3) the limitation of treatment depth. Damage to normal tissue lying between the light source and the target tissue in a tumor occurs due to the uptake of photosensitizer by the skin and other tissues overlying the tumor mass, and the resulting undesired photoactivation of the photosensitizer absorbed by these tissues. The consequences of inadvertent skin damage caused by transcutaneous light delivery to a subcutaneous tumor may include severe pain, serious infection, and fistula formation. The limited volume of tumor that can be clinically treated and the limitations of the light penetration below the skin surface in turn have led those skilled in this art to conclude that clinical transcutaneous PDT is only suitable for treatment of superficial, thin lesions.
U.S. Pat. No. 5,445,608, Chen et al., discloses the use of implanted light sources for internally administering PDT. Typically, the treatment of any internal cancerous lesions with PDT requires at least a minimally invasive procedure such as an endoscopic technique, for positioning the light source proximate to the tumor, or open surgery to expose the tumor site. There is some risk associated with any internal procedure performed on the body. Clearly, there would be significant advantage to a completely noninvasive form of PDT directed to subcutaneous and deep tumors, which avoids the inadvertent activation of any photosensitizer in skin and intervening tissues. To date, this capability has not been clinically demonstrated nor realized. O

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