James A. Hampton

A transient mathematical model of oxygen depletion during photodynamic therapy.

A transient one-dimensional mathematical model is presented to help visualize the qualitative and quantitative effects on inter-capillary tissue undergoing photodynamic therapy (PDT). The model is solved by a Crank-Nicholson finite difference formulation to provide time-dependent concentrations of the Type II mechanisms photo-oxidation species in the tissue surrounding a capillary. The time-dependent solution allows educated decisions to be made as to the optimum timing of light fractionation (on/off) cycles. Qualitative and quantitative optimization of the PDT process is considered along with a case study of data in the literature, the main goal being to provide optimized light therapy regimens for eventual clinical use.

Transperineal Photodynamic Ablation of the Canine Prostate

PURPOSE Experiments were undertaken to determine the effects of transperineal interstitial photodynamic therapy on the canine prostate. MATERIALS AND METHODS Mongrel dogs were injected intravenously with the photosensitizer, tin (II) ethyl etiopurpurin dichloride. Twenty-four hours later, 2 optical fibers were implanted in 1 hemisphere of the prostate, which was then treated with red light (660 nm.). RESULTS Acutely, the treated areas showed extensive hemorrhagic necrosis. At 3 and 6 weeks, the treated lobes were largely replaced by fibrous connective tissue. CONCLUSION Transperineal photodynamic therapy of the canine prostate is feasible. Further preclinical investigation is warranted to determine the applicability of this approach to the treatment of localized prostate cancer.

CURCUMIN PREVENTS INTRAVESICAL TUMOR IMPLANTATION OF THE MBT-2 TUMOR CELL LINE IN C3H MICE

PURPOSE The development of an effective nontoxic intravesical agent that may be used immediately after bladder tumor resection to prevent the implantation of tumor cells would be a significant clinical advancement. We report the cytotoxic effects of curcumin on bladder tumor cell lines as well as its effects on the intravesical implantation of tumor cells in C3H mice. MATERIALS AND METHODS UMUC human and MBT-2 mouse bladder cancer lines were incubated with 0 to 100 microM. curcumin in dimethyl sulfoxide for 30 minutes and cell viability was determined by clonal assay. Additional culture dishes were incubated with curcumin and processed for electron microscopy. Using the C3H mice and the MBT2 tumor lines the effects of intravesical curcumin on tumor implantation after bladder injury was studied. The 10 group 1 mice served as nontreatment controls. In the 18 group 2 mice 30 minutes after tumor cell implantation 100 microM. curcumin in 0.1% dimethyl sulfoxide were instilled intravesically for 30 minutes. The 15 group 3 mice served as treatment controls with 0.1% dimethyl sulfoxide or culture medium instilled intravesically for 30 minutes. Animals were sacrificed 7 to 10 days after treatment and the bladder was subjected to histological analysis for tumor. RESULTS At the 100 microM. dose curcumin was completely lethal to the 2 cell lines on clonal growth assay. Electron microscopy revealed apoptotic bodies after curcumin administration. The tumor implantation rate was 16.7% (3 of 18 mice) in curcumin treated bladders and 73% (11 of 15) in the vehicle control group. CONCLUSIONS At the 100 microm. concentration curcumin is a potent cytotoxic agent against the MBT and UMUC bladder tumor cell lines. In addition, curcumin effectively inhibits tumor implantation and growth in this murine bladder tumor model.

COPPER BENZOCHLORIN, A NOVEL PHOTOSENSITIZER FOR PHOTODYNAMIC THERAPY: EFFECTS ON A TRANSPLANTABLE UROTHELIAL TUMOR

Abstract— An iminum salt of octaethylbenzochlorin with copper in the aromatic ring, CDSI, was tested for its tumoricidal effects on theA–27 N‐[4‐(5‐notro‐2‐furyl)‐2‐thiazoly] formamide tumor line. CDSI was found to be an effective photosensitiz4r in vivo when used in combination with either a xenon arc lamp or a pulsed alexandrite laser. Hemodynamically, CDSI and light caused a rapid decrease in tumor blood flow. skin photosensitization was found to be minimal when drug‐injected mice werwe illuminated in a solar simulator.

MECHANISMS OF CELL KILLING IN PHOTODYNAMIC THERAPY USING A NOVEL in vivo DRUG/in vitro LIGHT CULTURE SYSTEM

Photodynamic therapy of certain neoplasms has emerged as a promising form of cancer treatment. This type of therapy involves the exogenous administration of a photosensitizer with subsequent exposure to light. The ensuing photochemical reaction results in destruction of the tumor. Whether tumor cells are destroyed directly by the photodynamic treatment or indirectly as a result of destruction of the tumor microvascular bed is unknown. To address this question, methods were adapted to test whether combinations of a photosensitizer and light resulted in direct cell killing of precision cut tissue slices placed in culture. The major advantages of this culture system are that photosensitizers are administered in vivo, tissue slices produced in minutes, placed in culture medium, and irradiated in vitro. Any resulting cellular destruction occurs in the absence of a functioning vascular system and indicates that photodynamic therapy acts through a direct cell killing mechanism. Tissue slice viability was monitored by two standard methods: assay for intracellular potassium and morphological examination at the electron microscopic level. The effects of hematoporphyrin derivative and light were examined on tissue slices produced from a prostate adenocarcinoma transplanted into male Copenhagen rats. The data indicate that direct killing of tumor slices occurs and is dependent on the irradiation protocol used.

Predictions of Mathematical Models of Tissue Oxygenation and Generation of Singlet Oxygen during Photodynamic Therapy

Photodynamic therapy (PDT) is a relatively new protocol for cancer treatment which has recently been approved for limited clinical use. Traditionally, the success of treatment with PDT has been compared on the basis of total light delivery. Using the mathematical model of Henning et al. (Radiat. Res. 142, 221-226, 1995), we have determined that when oxygen is not depleted from the tissue, the concentration of singlet oxygen that is generated is directly proportional to the product of the light fluence rate (phi) and the concentration of the photosensitizer (Cs). Therefore, phiCs is an appropriate parameter for comparing the potential success of PDT protocols under these conditions. For a treatment of time t, the observed photodynamic effect resulting from singlet oxygen exposure should be directly related to phiCst. For high phiCs, the model predicts that oxygen depletion occurs within the tumor tissue. As a result, the photodynamic effect is no longer proportional to phiCst. We have expanded the model of Henning et al. to include the changes in oxygen concentration which occur within the capillary as blood flows through the tissue. Our new predictions with the mathematical model for optimal PDT treatment conditions are significantly different from those predicted by the previous models. Predictions of the model are given using parameters relevant for treatment of solid tumors with Photofrin.

Exposure to Alkyllysophospholipids Inhibits in Vitro Invasion of Transitional Cell Carcinoma

Alkyllysophospholipids (ALP) are a group of synthetic analogs of a naturally occurring 2-lysophosphocholine. They are directly cytotoxic to a variety of neoplastic cell lines and can modulate the activation of macrophages against tumor cells. Moreover, recent reports have demonstrated the ability of racemic 1-octadecyl-2-methyl-sn-glycero-3-phosphocholine (ET-18-O-CH3) to prevent tumor cell invasion when given in noncytotoxic concentrations. Using an in vitro model, we studied the ability of ET-18-O-CH3 to prevent transitional cell carcinoma invasion. Cytostatic activity was determined by clonal growth assay (25,000 cells per plate). Suppression of colony growth was found at concentrations greater than 4 micrograms/ml. of ET-18-O-CH3 in rat and mouse transitional cell carcinoma (TCC) cell lines and greater than 2 micrograms/ml. in a human TCC line. Inhibition of tumor cell invasion was assessed by the effects on cell migration through Matrigel-coated 8 microns-pore polycarbonate filters (using 1 x 10(5) cells per chamber). Invasion was reduced to 50 to 70% of controls in both the mouse and rat TCC lines at the highest concentration (4.0 micrograms/ml.). In the human TCC line, invasion was reduced to less than 30% of controls at concentrations as low as 0.5 micrograms/ml. Motility (without invasion) of the human TCC line, as measured by cell migration through the micropore filter without the Matrigel coating, was inhibited at the same concentration of ET-18-O-CH3 found to inhibit invasion. The anti-invasive effect seen with noncytotoxic concentrations of ALP may prove useful in the treatment of transitional cell carcinoma.

THE ROLE OF LIPOPROTEINS IN THE DISTRIBUTION OF TIN ETIOPURPURIN (SnET2) IN THE TUMOR‐BEARING RAT

The role of plasma lipoproteins in the distribution of the photosensitizing agent tin etiopurpurin (SnET2) was examined in male rats bearing the N‐[4‐(5‐nitro‐2‐furyl)‐2‐thiazolyl]formamide‐induced tumor. Treatement with 17α‐ethinyl estradiol resulted in the depletion of total plasma cholesterol by > 70% and a corresponding decrease in plasma lipoproteins. To both control and estradiol‐treated animals, a therapeutic dose (1.5mg/kg) of SnET2 was administered and biodistribution measured 24 h later. Estradiol treatment was not associated with difference in the distribution of SnET2 to liver, skin or tumor, or in the pattern of affinity of SnET2 to plasma albumin and lipoprotein. These results indicate that a substantial decrease in circulating lipoprotein levels does not alter patterns of SnET2 biodistribution.

Photodynamic therapy : effect on the endothelial cell of the rat aorta

Previous studies in our laboratory have demonstrated that photodynamic therapy (PDT) of experimental bladder tumors leads to rapid destruction of the endothelial lining within the tumor micro vasculature. Endothelial cell death during PDT may be a consequence of direct cell injury resulting from retention of photosensitizer within the endothelial cell or, alternatively, result from intravascular activation of circulating photosensitizer with subsequent indirect endothelial damage. In the experiments described here, we investigated the possibility that photosensitizer retained within the endothelial cell was sufficient to cause endothelial cell injury in the absence of circulating drug. The experimental model was rat aorta photosensitized in vivo via the intravenous injection of tin(II) etiopurpurin dichloride (SnET2), and subsequent in situ or in vitro (in explant culture) light (670 nm) treatment from an argon pumped dye laser. Damage to the lining of the aorta was assessed morphome‐trically by determining the areal density of silver stained endothelial cells. Results indicate that purpurin SnET2‐PDT directly damages the endothelial lining.

Iminium salt benzochlorins: structure-activity relationship studies.

An iminium salt of copper(II) octaethylbenzochlorin (CDS1) is an effective new photosensitizer despite the fact that it does not produce singlet oxygen, does not fluoresce and the triplet state lifetime can only be less than 20 ns. A number of octaethylbenzochlorin derivatives were synthesized in order to determine the structural component(s) that is(are) responsible for the photodynamic action of these new photosensitizers. Studies utilizing the N‐(4‐[5‐nitro‐2‐furyl]‐2‐thiazolyl)formamide‐induced urothelial tumor revealed that the coexistence of the copper inside the aromatic ring and the iminium group at the meso position are required for the photodynamic effect.