PEG-m-THPC-mediated photodynamic effects on normal rat tissues

Photodynamic therapy (PDT) of malignancies uses light to activate a photosensitizer preferentially accumulated in cancer cells. The first pegylated photosensitizer, tetrakis-(m-methoxypolyethylene glycol) derivative of 7,8-dihydro-5,10,15,20-tetrakis(3-hydroxyphenyl)-21-23-[H]-porphyrin (PEG-m-THPC), was evaluated in non-tumor-bearing rats. The aim of this study was to assess the photodynamic threshold for damage and its sequelae in normal rat tissue. Thirty-five Fischer rats were sensitized with 3, 9 or 30 mg/kg body weight PEG-m-THPC. Colon, vagina and perineum were irradiated with laser light of 652 nm wavelength and an optical dose of 50, 150 or 450 J/cm fiber length. Temperature in the pelvis was measured during PDT. Three days following PDT the effect on skin, vagina, colon, striated muscle, connective tissue, nerves and blood vessels was assessed by histology. The healing of the above-mentioned tissues was assessed on two rats 3 and 8 weeks after PDT using 9 mg/kg PEG-m-THPC activated with 450 J/cm laser light. No dark toxicity was observed. PDT using 30 mg/kg PEG-m-THPC induced severe necrosis irrespective of the optical dose. Body weight of 9 or 3 mg/kg activated with less than 450 J/cm induced moderate or no damage. No substantial increase in body temperature was seen during PDT. Tissues with severe PDT-induced damage seem to have a good tendency to regenerate. We conclude that within the dose required for tumor treatment PEG-m-THPC is a safe photosensitizer with promising properties. PDT of the colon mucosa below 9 mg/kg PEG-m-THPC and 150 J/cm seems to be safe. All other tissues can be exposed to 9 mg/kg PEG-m-THPC activated with less than 450 J/cm laser light with little side effects.     

Tumor selectivity at short times following systemic administration of a liposomal temoporfin formulation in a murine tumor model

Meso-tetra(hydroxyphenyl)chlorin (mTHPC) (INN: Temoporfin) is one of the most potent photodynamically active substances in clinical use. Treatment protocols for Temoporfin-mediated photodynamic therapy often rely on drug-light intervals of several days in order for the photosensitizer to accumulate within the target tissue, though tumor selectivity is limited. Here, the mTHPC localization was studied at 2-8 h following systemic administration of a liposomal Temoporfin formulation (0.15 mg kg(-1) b.w.) in HT29 human colon adenocarcinoma in NMRI nu/nu mice. Photosensitizer distribution within tumor and internal organs was investigated by means of high performance liquid chromatography following chemical extraction, as well as in situ fluorescence imaging and point-monitoring fluorescence spectroscopy. For tumor tissue, the Temoporfin concentrations at 4 h (0.16+/-0.024 ng mg(-1)) and 8 h (0.18+/-0.064 ng mg(-1)) were significantly higher than at 2 h (0.08+/-0.026 ng mg(-1)). The average tumor-to-muscle and the tumor-to-skin selectivity were 6.6 and 2, respectively, and did not vary significantly with time after photosensitizer injection. In plasma, the Temoporfin concentration was low (0.07+/-0.07 ng mg(-1)) and showed no significant variation with time. Our results indicate a rapid biodistribution and clearance from the bloodstream. Within the same type of organ, data from both fluorescence methods generally exhibited a significant correlation with the extraction results.     

Photodetection with 5-Aminolevulinic acid-induced protoporphyrin IX in the rat abdominal cavity: drug-dose-dependent fluorescence kinetics

In 75% of cases, ovarian carcinoma has already metastasized in the abdominal cavity at the time of diagnosis. For determination of the necessity for a supplementary therapy, in addition to surgical resection, it is important to localize and stage microscopical intraperitoneal metastases of the tumor. Intraperitoneal photodetection of tumor metastases is based on preferential tumor distribution of a fluorescent tumor marker. The time-dependent differences in drug concentration between tumor and normal (T/N) tissues can be used to visualize small tumors. We performed fluorescence measurements on abdominal organs and tumor in the peritoneal cavity of rats. 5-Aminolevulinic acid (ALA)-induced protoporphyrin IX (PpIX) was used as the fluorescent marker. Three different drug doses (100, 25 and 5 mg/kg) were used and PpIX fluorescence profiles were followed up to 24 h after intravenous administration. Maximum T/N ratios were found 2-3 h after administration of ALA with all drug doses. A significant T/N tissue contrast was obtained for all abdominal organs tested after administration of 5 mg/kg.     

An evaluation of exogenous application of protoporphyrin IX and its dimethyl ester as a photodynamic diagnostic agent in poorly differentiated human nasopharyngeal carcinoma

5-Aminolevulinic acid and its esterified analogues have been under much investigation to enhance the endogenous production of protoporphyrin IX (PpIX) in tumor cells. However, in this work, we studied the in vitro and in vivo efficacy of exogenously administered PpIX and its esterified analogue, PpIX dimethyl ester (PME), in poorly differentiated human nasopharyngeal carcinoma (NPC/CNE-2) as a photodynamic diagnostic (PDD) agent. NPC/CNE-2 at its earliest time, 1 h after incubation with PME in in vitro studies, has exhibited 64% (P <0.01) higher tumor to normal cell (T/N) fluorescence ratio than with PpIX. In an in vivo mouse xenograft model, comparable photosensitizer concentration in tumor after intravenous administration was observed at 1-3 h time points, but at 9 h, PME had 31% (P=0.05) greater concentration in tumor compared with PpIX. In addition, by constituting PME and PpIX in different topical gel composites, of which, PME gel composition of 8:2 Plasdone and Gantrez resulted in the highest T/N ratio at 6 h after application (34%; P <0.05) in comparison with other gel composites. Evaluation of PME and PpIX constituted in the delivery vehicles investigated showed comparable selectivity for tumor at 1-3 h, thus neither photosensitizer is more efficient than the other for PDD at the early time points; however, beyond 6 h, PME had higher selectivity for tumor compared with PpIX. Thus, further investigation is warranted to improve the drug delivery vehicle for greater tumor selectivity at a shorter incubation time.     

Pharmacokinetics and pharmacodynamics of tetra(m-hydroxyphenyl)chlorin in the hamster cheek pouch tumor model: comparison with clinical measurements

The pharmacokinetics (PK) of the photosensitizer tetra(m-hydroxyphenyl)chlorin (mTHPC) was measured by optical fiber-based light-induced fluorescence spectroscopy (LIFS) in the normal and tumoral cheek pouch mucosa of 29 Golden Syrian hamsters with chemically induced squamous cell carcinoma. Similar measurements were carried out on the normal oral cavity mucosa of five patients up to 30 days after injection. The drug doses were between 0.15 and 0.3 mg per kg of body weight (mg/kg), and the mTHPC fluorescence in the tissue was excited at 420 nm. The PK in both human and hamster exhibited similar behavior although the PK in the hamster mucosa was slightly delayed in comparison with that of its human counterpart. The mTHPC fluorescence signal of the hamster mucosa was smaller than that of the human mucosa by a factor of about 3 for the same injected drug dose. A linear correlation was found between the fluorescence signal and the mTHPC dose in the range from 0.075 to 0.5 mg/kg at times between 8 and 96 h after injection. No significant selectivity in mTHPC fluorescence between the tumoral and normal mucosa of the hamsters was found at any of the applied conditions. The sensitivity of the normal and tumoral hamster cheek pouch mucosa to mTHPC photodynamic therapy as a function of the light dose was determined by light irradiation at 650 nm and 150 mW/cm2, 4 days after the injection of a drug dose of 0.15 mg/kg. These results were compared with irradiations of the normal oral and normal and tumoral bronchial mucosa of 37 patients under the same conditions. The reaction to PDT of both types of human mucosae was considerably stronger than that of the hamster cheek pouch mucosa. The sensitivity to PDT became comparable between hamster and human mucosa when the drug dose for the hamster was increased to 0.5 mg/kg. A significant therapeutic selectivity between the normal and neoplastic hamster cheek pouch was observed. Less selectivity was found following irradiations of normal mucosa and early carcinomas in the human bronchi. The pharmacodynamic behavior of mTHPC was determined by test irradiations of the normal mucosa of hamsters and patients between 6 h and 8 days after injection of 0.5 and 0.15 mg/kg in the hamsters and the patients, respectively. The normal hamster cheek pouch showed a maximum response to irradiation 6 h after injection and then decreased continuously to no observable reaction at 8 days after injection. The reaction of the normal human oral mucosa, however, showed an increasing sensitivity to the applied light between 6 h and 4 days after mTHPC injection and then decreased again at 8 days. The hamster model with the chemically induced early squamous cell cancer in the cheek pouch thus showed some similarity to the early squamous cell cancer of the human oral mucosa considering the PK. However, a quantitative difference in fluorescence signal for identical mTHPC doses as well as a significant difference in pharmacodynamic behavior were also observed. The suitability of this animal model for the optimization of PDT parameters in the clinic is therefore limited. Hence great care must be taken in screening new dyes for PDT of early squamous cell cancer of the upper aerodigestive tract based upon observables in the hamster cheek pouch model.     

光敏剂在癌症诊断和治疗中的研究新进展

光敏剂在特定波长的光照射下,产生荧光和单线态氧,已广泛应用于癌症的诊断和治疗.当前的研究热点是如何提高光敏剂的肿瘤选择性,尤其是光敏剂的靶向输送和特异性激活两方面.本文系统评述了提高光敏剂肿瘤选择性的方法及其在癌症诊断和治疗中的应用.引用文献56篇.     

A Cyanine-based Liposomal Nanophotosensitizer for Enhanced Cancer Chemo-Photodynamic Therapy

Currently, chemotherapy is one of the most important treatment modalities for malignant tumors in the clinic, however, it exhibits some shortcomings, such as poor selectivity, limited efficacy and serious adverse effects. Therefore, synergistic therapy and accurate drug delivery at tumor sites become a promising strategy for achieving tumor eradication. Herein, a smart NIR fluorescence imaging-guided nanoliposome was fabricated by encapsulating a chemotherapeutic drug(doxorubicin, DOX), liposomes(L) and a near-infrared(NIR) photosensitizer(CY) to form L@CY@DOX, which could realize enhanced therapeutic efficacy of chemo-PDT in cancer therapy(PDT=photodynamic therapy). L@CY@DOX can induce mitochondrial apoptosis and produce severe toxicity at the cellular level, and L@CY@DOX can enrich in the tumor site, which significantly induces tumor death. In vitro and in vivo studies demonstrated that L@CY@DOX exhibited great antitumor efficacy compared with each one of these monotherapies, indicating that the combination of chemotherapy and PDT possessed potential development prospects and is anticipated in clinical application.     

Fluorescence pharmacokinetics of Lutetium Texaphyrin (PCI-0123, Lu-Tex) in the skin and in healthy and tumoral hamster cheek-pouch mucosa

We have investigated the pharmacokinetics (PK) of Lutetium Texaphyrin (Lu-Tex), a second-generation photosensitizer, in the Syrian hamster cheek pouch early cancer model. Ten male hamsters, five with chemically induced early squamous cell cancer of the left cheek pouch, received an intracardiac injection of a 10 mg/ml Lu-Tex solution, resulting in a dose of 12 mg Lu-Tex per kg of bodyweight. The PK of the dye have been measured during the 24 h following the injection with an optical-fiber-based spectrofluorometer on the ventral skin, the healthy and the tumoral cheek-pouch mucosa. The Lu-Tex fluorescence is excited at 460 nm and detected around 740 nm. All the measurements yield very similar pharmacokinetic curves. The fluorescence intensity reaches a maximum between two and three hours after the injection and, at its maximum, it is consistently higher (up to 1.5 times) on the tumor than on the healthy mucosa. It remains smaller on the skin than on cheek-pouch mucosa. After 24 h, the Lu-Tex fluorescence is no longer detectable either on the skin, on the lesion or on the healthy mucosa. Moreover, Lu-Tex clearly displays a significant fluorescence selectivity between early carcinoma and healthy mucosa in this model. Furthermore, the inter-animal fluctuations of the fluorescence signal are small (+/-16% on the tumor-bearing mucosa). Eight-minute-long skin-irradiation tests have been performed 24 h after the injection of the Lu-Tex on the ventral skin of 16 additional animals with a solar simulator. No reaction is observed, either macroscopically or microscopically, which further demonstrates, as suggested by the fluorescence measurements, that this photosensitizer is significantly cleared from the skin after 24 h.     

Biodistribution of Photofrin II® and 5-Aminolevulinic Acid-Induced Protoporphyrin IX in Normal Rat Bladder and Bladder Tumor Models: Implications for Photodynamic Therapy

Photodynamic therapy (PDT) has been considered as a potential therapy for superficial bladder carcinomas. Cutaneous photosensitivity and reduction of bladder capacity are the two well-known complications following systemic administration of the commonly used photosensitizer, Photofrin II® (PII). The objective of the present study was to evaluate whether intravesical. (i.b.) instillation of photosensitizers for PDT of bladder cancer might be a more suitable treatment method. Female Fischer rats were utilized to develop orthotopic and heterotopic bladder tumor models. Rats bearing orthotopic bladder tumors were treated either intravesically or intravenously with graded doses of 5-aminolevulinic acid (ALA) or PII. Normal rats received the same doses of ALA or PII. As well, rats bearing heterotopic tumor were studied for comparison. The biodistribution times (times allowed for tissue uptake and bioconversion following drug administration) were 2, 4 or 6 h. Porphyrin fluorescence intensities within tumor, urothelium, submucosa, bladder muscularis and abdominal muscle were quantitated by confocal laser scanning microscopy. Following intravenous (i.v.) injection of ALA, tumor protoporphyrin IX (PpIX) levels peaked at 4 h and diminished by 6 h. The PpIX ratios of tumor-to-bladder mucosa, submucosa and muscle layers were 3:1, 5:1 and 8:1, respectively, 4 h following 1000 mg/kg ALA injection. After ALA instillation, the optimal biodistribution time appeared to be 4 h. Bladder instillation provided comparable tumor labeling with the i.v. route, but lost selectivity of PpIX accumulation between tumor and normal urothelium. The PpIX ratio of tumor-to-bladder muscularis was 5:1. After i.b. instillation of PII, porphyrin fluorescence was detected only within tumor and urothelium, while porphyrin fluorescence was mainly located in bladder submucosa following i.v. injection. Intravesical administration of ALA or PII might be feasible for PDT of superficial bladder cancers.     

Systemic application of photosensitizers in the chick chorioallantoic membrane (CAM) model: photodynamic response of CAM vessels and 5-aminolevulinic acid uptake kinetics by transplantable tumors.

The aim of this study is to modify the chick chorioallantoic membrane (CAM) model into a whole-animal tumor model for photodynamic therapy (PDT). By using intraperitoneal (i.p.) photosensitizer injection of the chick embryo, use of the CAM for PDT has been extended to include systemic delivery as well as topical application of photosensitizers. The model has been tested for its capability to mimic an animal tumor model and to serve for PDT studies by measuring drug fluorescence and PDT-induced effects. Three second-generation photosensitizers have been tested for their ability to produce photodynamic response in the chick embryo/CAM system when delivered by i.p. injection: 5-aminolevulinic acid (ALA), benzoporphyrin derivative monoacid ring A (BPD-MA), and Lutetium-texaphyrin (Lu-Tex). Exposure of the CAM vasculature to the appropriate laser light results in light-dose-dependent vascular damage with all three compounds. Localization of ALA following i.p. injections in embryos, whose CAMs have been implanted with rat ovarian cancer cells to produce nodules, is determined in real time by fluorescence of the photoactive metabolite protoporphyrin IX (PpIX). Dose-dependent fluorescence in the normal CAM vasculature and the tumor implants confirms the uptake of ALA from the peritoneum, systemic circulation of the drug, and its conversion to PpIX.     

Distribution and pharmacokinetics of Photofrin in human bile duct cancer

Prognosis of patients with bile duct tumors is mostly poor due to late diagnosis and a lack of adequate curative and palliative treatment modalities. To evaluate the potential of photodynamic therapy (PDT) as a novel and alternative treatment approach, we have investigated the uptake and tumor-specific localization of the photosensitizer Photofrin in human biliary tract neoplasms. We have quantified the distribution and the pharmacokinetics of Photofrin in normal and tumor tissue biopsies of the human bile duct by quantitative fluorescence microscopy and digital image analysis of cryosections. Fluorescence intensities (expressed as a percentage of a standard) are 19.0 +/- 11.4% and 25.2 +/- 12.7% for tumors and 10.9 +/- 2.9% and 13.2 +/- 9.1% (mean +/- SD) for normal bile duct tissue at 24 h (n = 5) and 48 h (n = 8) after Photofrin administration (2 mg kg-1 i.v.), respectively, and decrease afterwards in normal bile duct tissue over the period of investigation (4-35 days). The ratios of fluorescence in tumor versus normal tissue are found to be 1.7 +/- 0.7 and 2.3 +/- 1.2 (mean +/- SD) at days one and two after Photofrin administration, respectively. Thus, Photofrin preferentially accumulates in bile duct neoplasms, reaching peak values during the first two days. These data suggest that laser irradiation should be performed within this period after Photofrin injection to achieve tumor selectivity of PDT for effective treatment of bile duct carcinoma.     

Long-Circulating Prostate-Specific Membrane Antigen-Targeted NIR Phototheranostic Agent

Targeted photodynamic therapy (PDT) combined with image-guided surgical resection is a promising strategy for precision cancer treatment. Prostate-specific membrane antigen (PSMA) is an attractive target due to its pronounced overexpression in a variety of tumors, most notably in prostate cancer. Recently, we reported a pyropheophorbide-based PSMA-targeted agent, which exhibited long plasma circulation time and effective tumor accumulation. To further advance PSMA-targeted photodynamic therapy by harvesting tissue-penetrating properties of the NIR light, we developed a bacteriochlorophyll-based PSMA-targeted photosensitizer (BPP), consisting of three building blocks: (1) a PSMA-affinity ligand, (2) a peptide linker to prolong plasma circulation time and (3) a bacteriochlorophyll photosensitizer for NIR fluorescence imaging and photodynamic therapy (Qy absorption maximum at 750 nm). BPP exhibited excellent PSMA-targeting selectivity in both subcutaneous and orthotopic mouse models. The nine D-peptide linker in BPP structure prolonged its plasma circulation time (12.65 h). Favorable pharmacokinetic properties combined with excellent targeting selectivity enabled effective BPP tumor accumulation, which led to effective PDT in a subcutaneous prostate adenocarcinoma mouse model. Overall, bright NIR fluorescence of BPP enables effective image guidance for surgical resection, while the combination of its targeting capabilities and PDT activity allows for potent and precise image-guided photodynamic treatment of PSMA-expressing tumors.     

Mechanisms and Advances in Anti-Ovarian Cancer with Natural Plants Component

Ovarian cancer ranks seventh in the most common malignant tumors among female disease, which seriously threatens female reproductive health. It is characterized by hidden pathogenesis, missed diagnosis, high reoccurrence rate, and poor prognosis. In clinic, the first-line treatment prioritized debulking surgery with paclitaxel-based chemotherapy. The harsh truth is that female patients are prone to relapse due to the dissemination of tumor cells and drug resistance. In these circumstances, the development of new therapy strategies combined with traditional approaches is conductive to improving the quality of treatment. Among numerous drug resources, botanical compounds have unique advantages due to their potentials in multitarget functions, long application history, and wide availability. Previous studies have revealed the therapeutic effects of bioactive plant components in ovarian cancer. These natural ingredients act as part of the initial treatment or an auxiliary option for maintenance therapy, further reducing the tumor and metastatic burden. In this review, we summarized the functions and mechanisms of natural botanical components applied in human ovarian cancer. We focused on the molecular mechanisms of cell apoptosis, autophagy, RNA and DNA lesion, ROS damage, and the multiple-drug resistance. We aim to provide a theoretical reference for in-depth drug research so as to manage ovarian cancer better in clinic.     

Enzyme-Triggered Disassembly of Perylene Monoimide-based Nanoclusters for Activatable and Deep Photodynamic Therapy

Photodynamic therapy (PDT) exhibits great potential for cancer therapy, but still suffers from nonspecific photosensitivity and poor penetration of photosensitizer. Herein, a smart perylene monoimide-based nanocluster capable of enzyme-triggered disassembly is reported as an activatable and deeply penetrable photosensitizer. A novel carboxylesterase (CE)-responsive tetrachloroperylene monoimide (P1) was synthesized and assembled with folate-decorated albumins into a nanocluster ( FHP ) with a diameter of circa 100 nm. Once P1 is hydrolyzed by the tumor-specific CE, FHP disassembles into ultrasmall nanoparticles (ca. 10 nm), facilitating the deep tumor penetration of FHP . Furthermore, such enzyme-triggered disassembly of FHP leads to enhanced fluorescence intensity (ca. 8-fold) and elevated singlet oxygen generation ability (ca. 4-fold), enabling in situ near-infrared fluorescence imaging and promoted PDT. FHP permits remarkable tumor inhibition in vivo with minimal side effects through imaging-guided, activatable, and deep PDT. This work confirms that this cascaded multifunctional control through enzyme-triggered molecular disassembly is an effective strategy for precise cancer theranostics.     

Enzyme‐Triggered Disassembly of Perylene Monoimide‐based Nanoclusters for Activatable and Deep Photodynamic Therapy

Photodynamic therapy (PDT) exhibits great potential for cancer therapy, but still suffers from nonspecific photosensitivity and poor penetration of photosensitizer. Herein, a smart perylene monoimide‐based nanocluster capable of enzyme‐triggered disassembly is reported as an activatable and deeply penetrable photosensitizer. A novel carboxylesterase (CE)‐responsive tetrachloroperylene monoimide (P1) was synthesized and assembled with folate‐decorated albumins into a nanocluster ( FHP ) with a diameter of circa 100 nm. Once P1 is hydrolyzed by the tumor‐specific CE, FHP disassembles into ultrasmall nanoparticles (ca. 10 nm), facilitating the deep tumor penetration of FHP . Furthermore, such enzyme‐triggered disassembly of FHP leads to enhanced fluorescence intensity (ca. 8‐fold) and elevated singlet oxygen generation ability (ca. 4‐fold), enabling in situ near‐infrared fluorescence imaging and promoted PDT. FHP permits remarkable tumor inhibition in vivo with minimal side effects through imaging‐guided, activatable, and deep PDT. This work confirms that this cascaded multifunctional control through enzyme‐triggered molecular disassembly is an effective strategy for precise cancer theranostics.     

Biodistribution assessment of a lutetium(III) texaphyrin analogue in tumor-bearing mice using NIR Fourier-transform Raman spectroscopy

The use of near-infrared (NIR)-excited Fourier-transform (FT) Raman spectroscopy as a technique for evaluating the extent of photosensitizer localization in tumor (human pancreatic adenocarcinomas)-bearing mice has been tested using lutetium(III) texaphyrin analogue Lu-T2B2Tex. The complex was injected subcutaneously in the form of three injections given during the course of 3 days. The kinetics of biodistribution were then followed over a time scale of 1-6 days. The NIR-FT-Raman spectra of tissue samples obtained from the xenographic tumor, muscle, heart, brain, liver, spleen, kidney and blood were recorded and used to identify the presence of Lu-T2B2Tex in these tissues. Five Raman sensitizer markers were used to estimate the relative content of Lu-T2B2Tex in tumor at various postinjection times. UV-Visible (Vis) absorption spectroscopic detection of this sensitizer in tissue extracts was applied as a conventional method. Both spectroscopic methods were in good agreement with each other and confirm that Lu-T2B2Tex localizes well in tumor tissue. Maximal drug content was observed 3 days after the final injection. This time delay seems to be optimal for tumor irradiation in photodynamic therapy.     

H2S‐Activable MOF Nanoparticle Photosensitizer for Effective Photodynamic Therapy against Cancer with Controllable Singlet‐Oxygen Release

Photodynamic therapy (PDT) has emerged as an important minimally invasive tumor treatment technology. The search for an effective photosensitizer to realize selective cancer treatment has become one of the major foci in recent developments of PDT technology. Controllable singlet‐oxygen release based on specific cancer‐associated events, as another major layer of selectivity mode, has attracted great attention in recent years. Here, for the first time, we demonstrated that a novel mixed‐metal metal–organic framework nanoparticle (MOF NP) photosensitizer can be activated by a hydrogen sulfide (H₂S) signaling molecule in a specific tumor microenvironment for PDT against cancer with controllable singlet‐oxygen release in living cells. The effective removal of tumors in vivo further confirmed the satisfactory treatment effect of the MOF NP photosensitizer.     

Synthesis and biological evaluation of disulfide-linked HPMA copolymer-mesochlorin e6 conjugates

Novel polymeric delivery systems for the photosensitizer mesochlorin e6 (Mce6) were synthesized to overcome problems of systemic toxicity. A disulfide bond was included to allow for quick release of Mce6 from the N-(2-hydroxypropyl)methacrylamide (HPMA) copolymer backbone once internalized in tumor tissue. The synthesized conjugates demonstrated a time-dependent reductive cleavage with an accompanying increase in the quantum yield of singlet oxygen generation on exposure to DTT. Quicker release kinetics and a higher cytotoxicity in SKOV-3 human ovarian carcinoma cells were obtained as compared to polymer conjugate with a proteolytically cleavable GFLG spacer. These novel conjugates hold promise as clinically relevant drug delivery systems for photodynamic therapy of cancer.     

meso-tetraphenylporphyrin dimer derivatives as potential photosensitizers in photodynamic therapy. Part 2

Studies on the synthesis, singlet oxygen and fluorescence yields and pharmacokinetic properties of three different dimeric porphyrins with an amide linkage (D2-D4) are described and compared with the results recently reported for a dimeric porphyrin (D1). The pharmacokinetic behavior of all dimers were examined in Balb/c mice bearing MS-2 fibrosarcomas. The maximal efficiency and selectivity of photosensitizer accumulation in each tumor tissue takes place at 24 h after drug administration of 1.0 mg kg-1 into DL-alpha-dipalmitoylphosphatidylcholine liposomes by intravenous injection. Since the dimeric porphyrins exhibit high quantum yields of singlet oxygen generation, long triplet lifetimes and high photostability, the results obtained suggest that the evaluated dimeric structures may be promising candidates for further use in PDT experiments. The results also allow the possibility to establish a correlation between the chemical structure of the dyes and the efficiency/selectivity of the tumor accumulation and can be used for building up optimal photosensitizing agents for tumors.     

In vivo pharmacokinetics of protoporphyrin IX accumulation following intracutaneous injection of 5-aminolevulinic acid

Photodynamic therapy with 5-aminolevulinic acid (ALA) derived protoporphyrin IX (PpIX) as photosensitizer is a promising treatment for basal cell carcinomas. Until now ALA has been administered topically as an oil-in-water cream in most investigations. The disadvantage of this administration route is insuffici?nt penetration in deeper, nodular tumours. Therefore we investigated intracutaneous injection of ALA as an alternative administration route. ALA was administered in 6-fold in the normal skin of three 6-week-old female Dutch pigs by intracutaneous injection of an aqueous solution of ALA (pH 5.0) in volumes of 0.1-0.5 ml and concentrations of 0.5-2% and by topical administration of a 20% ALA cream. During 8 h fluorescence of ALA derived PpIX was measured under 405 nm excitation. For the injection the measured fluorescence was shown to be dose dependent. All injected doses of 3 mg ALA or more lead to a faster initial increase rate of PpIX synthesis and significantly greater fluorescence than that measured after topical administration of ALA. Irradiation (60 Jcm(-2) for 10 min) of the spots was performed at 3.5 h after ALA administration. After 48 and 96 h visual damage scores were evaluated and biopsies were taken for histopathological examination. After injection of 2 mg ALA or more the PDT damage after illumination was shown to be significantly greater than after topical application of 20% ALA. An injected dose of 10 mg ALA (0.5 ml of a 2% solution) resulted in significantly more tissue damage after illumination than all other injected doses.