Tumor versus vascular photodamage in a rat tumor model

The [4-(5-nitro-2-furyl)-2-thiazoyl] formamide (FANFT)-induced urothelial tumor in the rat is found to express the mdr gene. The resulting multidrug resistance (MDR) phenotype results in the expression of an outward transport system that prevents cellular accumulation of certain weakly cationic agents. Among the latter is a photosensitizer with known efficacy for the FANFT tumor, the copper benzochlorin iminium salt. FANFT cells are protected from direct cell kill mediated by this drug, suggesting that the substantial delay in tumor regrowth from this tumor/sensitizer combination can be attributed to vascular effects.

Photodynamic therapy

Photodynamic therapy involves administration of a tumor-localizing photosensitizing agent, which may require metabolic synthesis (i.e., a prodrug), followed by activation of the agent by light of a specific wavelength. This therapy results in a sequence of photochemical and photobiologic processes that cause irreversible photodamage to tumor tissues. Results from preclinical and clinical studies conducted worldwide over a 25-year period have established photodynamic therapy as a useful treatment approach for some cancers. Since 1993, regulatory approval for photodynamic therapy involving use of a partially purified, commercially available hematoporphyrin derivative compound (Photofrin) in patients with early and advanced stage cancer of the lung, digestive tract, and genitourinary tract has been obtained in Canada, The Netherlands, France, Germany, Japan, and the United States. We have attempted to conduct and present a comprehensive review of this rapidly expanding field. Mechanisms of subcellular and tumor localization of photosensitizing agents, as well as of molecular, cellular, and tumor responses associated with photodynamic therapy, are discussed. Technical issues regarding light dosimetry are also considered.

Sources of error in intra-arterial pressure measurements across a stenosis

OBJECTIVE

To investigate potential errors associated with different techniques of intra-arterial pressure measurement at angiography.

MATERIALS AND METHODS

An experimental model of an arterial stenosis was developed. Experiments were performed to assess the relevance of catheter position, catheter direction and catheter type on the recorded intraluminal pressure. Transstenotic pressure gradients were recorded with and without angiographic catheters crossing the stenosis.

RESULTS

At physiological flow rates angiographic catheter type does not influence the recorded pressure. At high flow rates through tight stenoses there is a significant catheter-related difference in recorded pressure adjacent to a stenosis. Downstream pressures may be altered by up to 85 mmHg when standard angiographic catheters are placed across a stenosis.

CONCLUSION

The different techniques employed to measure pressure differences across a model stenosis may introduce significant errors up to 85 mmHg. Care must be taken when pressure measurements alone are used to interpret the clinical significance of a stenosis. In low flow conditions there may not be a detectable pressure gradient across a 95% stenosis.

Photodynamic therapy of B16F10 murine melanoma with lutetium texaphyrin

Photodynamic therapy (PDT) of pigmented melanoma has generally been unsuccessful because of insufficient light penetration in such tissues. In this study, the responsiveness of the heavily pigmented B16F10 murine melanoma to lutetium texaphyrin (PCI-0123), a water-soluble sensitizer with strong absorbance in the near infrared (700-760 nm), was examined. These studies were carried out in both normal and ApoE deficient C57BL/6 mice. The latter strain exhibits a lipoprotein profile more like humans (low density lipoprotein > high density lipoprotein) than rodents (high density lipoprotein >> low density lipoprotein). Under optimal conditions of drug dose, light dose, and interval between drug administration and irradiation--the median survival time of C57BL/6 tumor bearing mice was approximately doubled (29 d) compared with tumor bearing control animals (13 d). The life-span of the ApoE knockout mice was greater (33 d) than the C57BL/6 animals (23 d) when irradiation occurred 3 h after administration of a 10 micromol per kg drug dose. The greater efficacy of PDT in the ApoE deficient mice was associated with more rapid clearance of drug from the blood, greater accumulation of sensitizer in tumor tissue, and substantially greater drug binding to the very low density lipoprotein/low density lipoprotein plasma fraction. Confocal laser scanning microscopy showed that the predominant subcellular site of photosensitizer binding was to melanosomes; costaining was performed with Mel-5. Melanosomes are susceptible to oxidative stress. Photo-oxidation, mediated by PCI-0123 PDT, could potentially overload an already highly oxidized stressed state leading to cell death. The good tissue penetration depth achieved by PCI-0213 mediated PDT and the activation of melanosomes makes PDT of pigmented melanoma, for the first time, clinically relevant.

Hemodynamic effects of 5-aminolevulinic acid in humans

Endogenous protoporphyrin IX (PpIX), which results from the oral administration of 5-aminolevulinic acid (ALA), is being investigated for its efficacy as a photosensitizing agent for photodynamic therapy (PDT). Clinical use of ALA has been associated with only mild gastrointestinal side effects. The hemodynamic effects of orally administered ALA in doses used for PDT are unknown. Six patients with a significant history of cardiac disease underwent Swan-Ganz catheterization prior to ALA administration and abdominal operation for PDT. Hemodynamic data collection began at least 1 h prior to ALA, and continued for at least 4 h subsequently, during which time no other medications were administered. When compared to measurements made prior to ALA administration, all patients displayed a significant decrease in systolic and diastolic blood pressures, pulmonary artery systolic and diastolic pressures as well as pulmonary vascular resistance. Five of the six patients also developed a decrease in systemic vascular resistance. No significant changes in pulmonary capillary wedge pressure, cardiac output or cardiac index was observed, but the mean pulse rate rose significantly. These findings cannot be explained on the basis of other cardiovascular depressants or to poor central volume status. Although no adverse sequela were appreciated as a result of the observed hemodynamic changes, this potential should be recognized in patients undergoing PDT using ALA.

Mitochondrial photodamage and PDT-induced apoptosis

Four photosensitizers with specific targets (mitochondria, lysosomes and plasma membrane) were used to delineate the mechanism of PDT-induced apoptosis in murine leukemia cells. Additional studies were carried out with two sensitizers which caused photodamage to both mitochondria and lysosomes, but varied with regard to membrane photodamage. PDT induced an apoptotic response after mitochondrial photodamage, but not after selective damage to lysosomes or to the cell membrane. Moreover, the latter could delay or inhibit the appearance of apoptosis after mitochondrial photodamage. We had previously reported that exposure of cells to high porphycene concentrations caused an apoptotic response in the dark; this was also associated with mitochondrial damage. These results are consistent with recent proposals that release of mitochondrial components can trigger an apoptotic response. ATP depletion after mitochondrial photodamage does not appear to play a role in initiation of the apoptotic program.

The induction of apoptosis by a positively charged methylene blue derivative

Identifying the cellular responses to photodynamic therapy (PDT) is important if the mechanisms of cell death are to be fully understood. PDT with a methylene blue analog DO15 yielded mitochondrial photodamage whilst membrane and lysosomal integrity were maintained. Apoptosis was detected using the DNA stain HO342, by the appearance of 50 kb fragments and by DNA ladder formation. The release of mono- and oligonucleosomes was further quantified using an ELISA protocol. Large DNA fragments were observed immediately following illumination, and nucleosomes were detected at 1-2 h post-treatment. Increasing the dose 4-fold accelerated the apoptotic response to PDT. This is the first report of a thiazine photosensitiser inducing apoptosis and is consistent with recent proposals suggesting that release of mitochondrial components may play an important role in the mechanism of cell death.

Initiation of apoptosis versus necrosis by photodynamic therapy with chloroaluminum phthalocyanine

While chloroaluminum phthalocyanine is a highly effective photosensitizer of murine leukemia P388 or L1210 cells, the mode of cell death varies as a function of the PDT dose. When cells were incubated with 0.3 microM of the sensitizer, a light dose of 45 mJ cm-2 (670 +/- 5 nm) yielded a 90% apoptotic cell population within 60 min. The sensitizer localized throughout the cytoplasm and catalyzed both lysosomal and mitochondrial photodamage at this light dose. Higher light doses yielded progressively more membrane photodamage and inhibited the apoptotic response as determined by the examination of Höchst dye HO 33342-labeled nuclei, DNA fragmentation on gels and a poly(adenosylribose) polymerase (PARP)-cleavage assay. Pulse-field gel electrophoresis revealed nonspecific DNA degradation to particles > or = 50 kbp at the higher PDT doses but neither PARP cleavage nor apoptotic nuclei.

Effects of fractionated 5-aminolevulinic acid administration on tissue levels of protoporphyrin in vivo

The photodynamic therapy (PDT) of malignant tissues can be achieved via the administration of 5-aminolevulinic acid (ALA), which is naturally converted to the photoreactive substance protoporphyrin IX (PP). This study compares bolus with fractionated ALA dosing in order to determine whether one of these methods results in a higher tissue concentration of PP. Mice bearing a subcutaneously implanted colon-26 tumor were treated with ALA (200 mg kg-1), given intravenously either as a single bolus or as three equally divided doses at 50 min intervals. Tissue samples of tumor, kidney, skin, liver, skeletal muscle, colon and plasma were obtained 2, 3, 4 and 6 h later for the analysis of PP concentrations. Fractionated dosing results in significantly higher concentrations of PP at 4 and 6 h for kidney, 3 and 6 h for skin, 3 h for colon and 6 h for liver. In contrast, fractionated dosing has no significant effect on the PP concentrations of muscle and plasma. Fractionated dosing results in a significantly greater PP concentration in the tumor at 3 h relative to that observed for the bolus dose. However, from a consideration of the time of PP measurement, it is concluded that fractionated dosing may not cause a significant increase in the PP concentration in colon-26 tumors relative to that observed for the bolus dose.

Analysis of renal artery geometry may assist in the design of new stents for endovascular aortic aneurysm repair

BACKGROUND

Endovascular repair of infrarenal aortic aneurysms is a feasible technique, but up to 30 per cent of patients may be excluded on the basis of a short proximal aortic neck.

METHODS

A dissection study was performed on 65 cadavers to measure the distance between the superior mesenteric and renal artery ostia, and to document the points of origin of the renal arteries.

RESULTS

The interostial distance did not differ significantly between aneurysmal and non-aneurysmal aortas (P = 0.90 for the left renal artery; P = 0.72 for the right). The median distance was 0.7 cm. The renal arteries originated between 2 and 4 o'clock on the left and between 9 and 10 o'clock on the right.

CONCLUSION

The relative consistency of the anatomy in this region may allow the development of a new stent which would increase the number of patients suitable for endovascular repair.

Pharmacokinetics of N-aspartyl chlorin e6 in cancer patients

We examined the pharmacokinetics of the photosensitizer N-aspartyl chlorin e6 in a group of cancer patients. While the drug persisted in plasma for as long as six weeks, there was no evidence of fluorescent NPe6 metabolites during this interval. Kinetics of drug elimination from plasma were consistent with a 2-compartment model with half-lives of approximately 9 hr (57%) and 134 hr (43%). The drug was bound to plasma albumin+other heavy proteins (65%) > HDL (35%) > > LDL (1-2%). These relative values did not change for as long as 21 days after drug administration. The long persistence of NPe6 in plasma was not associated with extended skin photosensitization.

On-line fluorescence of human tissues after oral administration of 5-aminolevulinic acid

It is important to have a frame of reference for the timing of photodynamic therapy (PDT) using 5-aminolevulinic acid (ALA) so that PDT can occur when the tissue levels of protoporphyrin IX (PP) are at a maximum. This study describes a non-invasive fluorescence technique for detecting tissue PP levels after systemic ALA administration in patients with gastrointestinal cancer. The data suggest that the intensity of tumor surface fluorescence correlates with the tumor PP concentration. Spectrophotofluorometric measurements of skin and buccal mucosa also offer an easily acquired and rapid means for determining changes in plasma concentrations of PP. A number of potential variables, including blood flow, affect the intensity of fluorescence. We report that fluorescence measurements in situ are best adapted to the measurement of changes in the porphyrin levels in tissues rather than the absolute concentrations.

Localization and efficacy analysis of the phototherapeutic lutetium texaphyrin (PCI-0123) in the murine EMT6 sarcoma model

Lutetium texaphyrin (PCI-0123) is a pure, water-soluble photodynamic therapy (PDT) agent that is activated by tissue-penetrating far red light. The sensitizer is highly fluorescent and exhibits a strong, broad emission signal at 750 nm. In vitro cellular uptake studies revealed an increase in sensitizer retention with incubation time. Confocal laser scanning microscopy demonstrated that the intracellular localization site of PCI-0123 is the lysosomes. Ensuing illumination of the EMT6 cells led to lysosomal breakup, extensive cytoplasmic blebbing and subsequent cell death. Noninvasive spectral imaging analysis of PCI-0123 fluorescence depicted selective drug uptake, compared to surrounding normal tissue, in EMT6 mammary sarcomas syngeneic to BALB/c mice. The PCI-0123 PDT was shown to effectively treat the EMT6 murine sarcoma. Irradiation (732 nm light) 3 h postintravenous injection of 10 mumol PCI-0123 per kg gave 100% cures (no evidence of cancer), whereas light exposure at 5 h resulted in 75% cures. Hematoxylin and eosin histologic examination of photoirradiated tumors indicated apoptosis of the EMT6 neoplasms at early times post-PDT progressing, with time, to extensive necrotic areas. Gel electrophoresis of extracted photoirradiated tumors showed the typical apoptotic DNA ladder pattern that increased in intensity following PDT treatment.

The role of subcellular localization in initiation of apoptosis by photodynamic therapy

Rapid initiation of apoptosis can be induced by photodynamic therapy, depending on the cell line and sensitizer employed. In this study, we evaluated the photodynamic responses to two structurally related photosensitizing agents, using the P388 murine leukemia cell line in culture. Photodamage mediated by tin etiopurpurin involved lysosomes and mitochondria and yielded a rapid apoptotic response; apoptotic nuclei were observed within 60 min after PDT. A drug analog, tin octaethylpurpurin amidine, targeted lysosomes, mitochondria and cell membranes; apoptotic nuclei were not observed until 24 h after PDT. These results, together with other recent reports, are consistent with the hypothesis that membrane photodamage can delay or prevent an apoptotic response to PDT.

Side effects and photosensitization of human tissues after aminolevulinic acid

Aminolevulinic acid (ALA) is being used as a "prodrug" for photodynamic therapy. The side effects of ALA have been only anecdotally reported and these effects as well as pharmacokinetics of the photosensitizing end product of ALA, protoporphyrin IX (PpIX), in patients undergoing operation are unknown. This study systematically determines the side effects of ALA and pharmacokinetics of PpIX in patients undergoing abdominal surgery. Patients were given 30 or 60 mg/kg ALA preoperatively, kept in subdued light for 48 hr, and monitored clinically and with laboratory tests for 5 to 7 days and for at least 2 months thereafter. Periodic plasma samples and tissue biopsies were analyzed for PpIX concentrations using a photodiode array system. No patient developed symptoms of porphyria other than nausea and vomiting, which occurred in 20%. Nearly one-quarter of patients developed transient abnormal liver functions. No patient developed cutaneous phototoxicity, abnormal neurologic function, or unexpected postoperative laboratory tests. The times of peak plasma, skin, skeletal muscle, omental, mucosal, muscularis mucosal, and tumor concentrations of PpIX varied among patients. In general, PpIX concentrations were significantly greater with the higher dose of ALA. Tumor PpIX concentrations were significantly greater than in other tissues except liver. In conclusion, ALA, up to 60 mg/kg, is associated with minimal side effects in patients undergoing operation. Actual tissue concentrations of PpIX suggest that endogenous photosensitization using systemically administered ALA is a mode of PDT feasible for treatment of adenocarcinomas of the gastrointestinal tract in humans.