The interaction of tumour-localizing porphyrins with collagen, elastin, gelatin, fibrin and fibrinogen

Increasing cancer permeability by photodynamic priming: from microenvironment to mechanotransduction signaling

The dense cancer microenvironment is a significant barrier that limits the penetration of anticancer agents, thereby restraining the efficacy of molecular and nanoscale cancer therapeutics. Developing new strategies to enhance the permeability of cancer tissues is of major interest to overcome treatment resistance. Nonetheless, early strategies based on small molecule inhibitors or matrix-degrading enzymes have led to disappointing clinical outcomes by causing increased chemotherapy toxicity and promoting disease progression. In recent years, photodynamic therapy (PDT) has emerged as a novel approach to increase the permeability of cancer tissues. By producing excessive amounts of reactive oxygen species selectively in the cancer microenvironment, PDT increases the accumulation, penetration depth, and efficacy of chemotherapeutics. Importantly, the increased cancer permeability has not been associated to increased metastasis formation. In this review, we provide novel insights into the mechanisms by which this effect, called photodynamic priming, can increase cancer permeability without promoting cell migration and dissemination. This review demonstrates that PDT oxidizes and degrades extracellular matrix proteins, reduces the capacity of cancer cells to adhere to the altered matrix, and interferes with mechanotransduction pathways that promote cancer cell migration and differentiation. Significant knowledge gaps are identified regarding the involvement of critical signaling pathways, and to which extent these events are influenced by the complicated PDT dosimetry. Addressing these knowledge gaps will be vital to further develop PDT as an adjuvant approach to improve cancer permeability, demonstrate the safety and efficacy of this priming approach, and render more cancer patients eligible to receive life-extending treatments.

Synthesis and Anticancer Activity of Gold Porphyrin Linked to Malonate Diamine Platinum Complexes

Recently, gold(III) porphyrins have gained great interest as anticancer drugs not only for the stability of gold(III) but also for the functionalization of the porphyrin to allow bridging with another metal such as platinum(II). We report here, for the first time, the synthesis of three new bimetal compounds containing a gold(III) porphyrin conjugated to a platinum diamine moiety through malonate bridging to obtain enhanced cytotoxicity from both metals combined with the phototoxicity of the porphyrin. The three complexes differ in the type of diamine ligand around platinum(II): ammonia (NH₃), cyclohexanediamine (CyDA), and pyridylmethylamine (Py). The synthesis was carried out using the complexation of activated malonic acid derivatives with aquadiaminoplatinum(II) complexes, and the products were characterized by IR, NMR, mass spectra, and elementary analysis. The cytotoxic activity of the conjugates was screened in both healthy cell lines and cancer cell lines, human fibroblast cells (FS-68) and human breast cancer cells (MCF-7), and was compared to that of the corresponding platinum(II) complexes. The cyclohexyldiamine (CyDA) derivative exhibited the greatest cytotoxic effect among the series. The results showed that Au(III)/Pt(II) conjugates are more potent by 2-5.6-fold than the corresponding platinum complexes. Moreover, the dyad AuP-PtCyDA is 18% more potent and also more selective toward cancer cells than the parent gold porphyrin substituted with malonic acid. On the other hand, the IC₅₀ of the dyad AuP-PtCyDA is 43% lower than that of AuTPP but is more selective toward healthy cells. Singlet oxygen measurements indicated that gold(III) porphyrin derivatives are poor oxygen sensitizers and cell death occurred potentially due to generation of other reactive oxygen species (ROS) upon reductive quenching of the gold porphyrin excited state. In addition, the increase in cancer cell death obtained after light irradiation is totally absent in healthy cells, demonstrating the specificity of this PDT treatment on cancer cells. Our findings imply that the incorporation of two different cytotoxic metals in the same molecule represents a remarkable cytotoxic effect in comparison to traditional homometallic Pt(II) drugs.

Experimental use of photodynamic therapy in high grade gliomas: a review focused on 5-aminolevulinic acid

Photodynamic therapy (PDT) consists of a laser light exposure of tumor cells photosensitized by general or local administration of a pharmacological agent. Nowadays, PDT is a clinically established modality for treatment of many cancers. 5-Aminolevulinic acid (ALA) induced protoporphyrin IX (PpIX) has proven its rational in fluoro-guided resection of malignant gliomas due to a selective tumor uptake and minimal skin sensitization. Moreover, the relatively specific accumulation of photosensitizing PPIX within the tumor cells has gained interest in the PDT of malignant gliomas. Several experimental and clinical studies have then established ALA-PDT as a valuable adjuvant therapy in the management of malignant gliomas. However, the procedure still requires optimizations in the fields of tissue oxygenation status, photosensitizer concentration or scheme of laser light illumination. In this extensive review, we focused on the methods and results of ALA-PDT for treating malignant gliomas in experimental conditions. The biological mechanisms, the effects on tumor and normal brain tissue, and finally the critical issues to optimize the efficacy of ALA-PDT were discussed.

Factors implicated in the assessment of aminolevulinic acid-induced protoporphyrin IX fluorescence

BACKGROUND

Photodynamic therapy and photodiagnosis of cancer requires preferential accumulation of fluorescent photosensitizers in tumors. Clinical evidence documents feasibility of ALA-based photodiagnosis for tumor detection. However, false positive results and large variations in fluorescence intensities are also reported. Furthermore, selective accumulation of fluorescent species of photosensitizers in tumor cell lines, as compared to normal ones, when cultured in vitro, is not always observed. To understand this discrepancy we analyzed the impact of various factors on the intensity of detected PpIX fluorescence.

METHODS

Impacts of cell type, mitochondrial potential, cell-cell interactions and relocalization of PpIX among different cell types in co-cultures of different cell lines were analyzed by confocal microscopy and flow cytometry. Fluorescence spectroscopy was used to estimate absolute amounts of ALA-induced PpIX in individual cell lines. Immunofluorescence staining was applied to evaluate the ability of cell lines to produce collagen.

RESULTS

Higher ALA-induced PpIX fluorescence in cancer cell lines as compared to normal ones was not detected by all the methods used. Mitochondrial activity was heterogeneous throughout the cell monolayers and could not be clearly correlated with PpIX fluorescence. Positive collagen staining was detected in all cell lines tested.

CONCLUSIONS

Contrary to in vivo situation, ALA-induced PpIX production by cell lines in vitro may not result in higher PpIX fluorescence signals in tumor cells than in normal ones. We suggest that a combination of several properties of tumor tissue, instead of tumor cells only, is responsible for increased ALA-induced PpIX fluorescence in solid tumors.

GENERAL SIGNIFICANCE

Understanding the reasons of increased ALA-induced PpIX fluorescence in tumors is necessary for reliable ALA-based photodiagnosis, which is used in various oncological fields.

Tumor vascular microenvironment determines responsiveness to photodynamic therapy

The efficacy of photodynamic therapy (PDT) depends upon the delivery of both photosensitizing drug and oxygen. In this study, we hypothesized that local vascular microenvironment is a determinant of tumor response to PDT. Tumor vascularization and its basement membrane (collagen) were studied as a function of supplementation with basement membrane matrix (Matrigel) at the time of tumor cell inoculation. Effects on vascular composition with consequences to tumor hypoxia, photosensitizer uptake, and PDT response were measured. Matrigel-supplemented tumors developed more normalized vasculature, composed of smaller and more uniformly spaced blood vessels than their unsupplemented counterparts, but these changes did not affect tumor oxygenation or PDT-mediated direct cytotoxicity. However, PDT-induced vascular damage increased in Matrigel-supplemented tumors, following an affinity of the photosensitizer Photofrin for collagen-containing vascular basement membrane coupled with increased collagen content in these tumors. The more highly collagenated tumors showed more vascular congestion and ischemia after PDT, along with a higher probability of curative outcome that was collagen dependent. In the presence of photosensitizer-collagen localization, PDT effects on collagen were evidenced by a decrease in its association with vessels. Together, our findings show that photosensitizer localization to collagen increases vascular damage and improves treatment efficacy in tumors with greater collagen content. The vascular basement membrane is thus identified to be a determinant of therapeutic outcome in PDT of tumors.

Effects of photodynamic therapy on tumor stroma

Photodynamic therapy (PDT) is a treatment that combines a photosensitizer with light to generate oxygen-dependent photochemical destruction of diseased tissue. This modality has been approved worldwide since 1993 for the treatment of several oncological and nononcological disorders. PDT continues to be interested in both preclinical and clinical research, with more than 500 publications each year during the past 5 years. This minireview focuses on the effects of PDT on tumor stroma. A tumor consists of two fundamental elements: parenchyma (neoplastic cells) and stroma. The stroma is composed of vasculature, cellular components, and intercellular matrix and is necessary for tumor growth. All the stromal components can be targeted by PDT. Although the exact mechanism of PDT is unknown, emerging evidence has indicated that effective PDT of tumor requires destruction of both parenchyma and stroma. Further, damage to subendothelial zone of vasculature, in addition to endothelium, also appears to be a crucial factor. The PDT-generated immune response as a way of vaccination for treatment and prevention of metastatic tumors remains to be exploited.

Heme biosynthesis and porphyrin studies in chronic renal failure patients following kidney transplantation

El-Far and Sobh were the first to describe abnormalities in porphyrin metabolism in Egyptian patients with chronic renal failure (CRF). Our results were confirmed by others. The present investigation aims to study and discuss the nature of those abnormalities and changes in porphyrin metabolism in CRF patients following kidney transplantation. Blood samples and urine were collected from patients (with and without polycythaemia) as well as from normal controls. The activity of heme enzymes such as ALA-S, ALA-D, URO-S, PBGase and URO-D were assayed. Total blood porphyrins as well as enzyme activities such as ALA-S and URO-S were found to be highly significantly increased in all patients, while URO-D activity remained within normal range. The observed elevated erythrocyte porphyrins may be mainly due to increased activity of ALA-S, the rate-limiting enzyme in heme synthesis. The present study is the first of its kind which clearly demonstrates that successful kidney transplantation does not correct or rectify the abnormalities in porphyrin metabolism.

Retention of haematoporphyrin in the aorta of hypertensive rats: in-vivo and in-vitro studies

Porphyrins are known to be accumulated and retained by tumours and atherosclerotic plaques. This property has been used for a new therapeutic approach called photodynamic therapy. In this study we assessed whether the presence of arterial hypertension could modify porphyrin turnover in the vascular wall. At various times after intravenous injection, haematoporphyrin concentration was assessed by a spectrophotofluorimetric method in the aortas of normotensive and hypertensive rats. Moreover, we studied the binding of haematoporphyrin to cultured smooth muscle cells obtained from normotensive and hypertensive rats. Larger amounts of haematoporphyrin were accumulated by the aorta of hypertensive rats and cleared at a slower rate, compared with normotensive rats. As for in-vitro experiments, cultured smooth muscle cells from hypertensive rats bound larger amounts of haematoporphyrin than cells from normotensive rats.

Selective in vivo tumor localization of heptacarboxylic porphyrin isomer I in a bladder tumor model: a novel technique to modulate porphyrin localization

We were the first to report that uroporphyrin isomer I is a superior tumor localizer when compared with hematoporphyrin derivative. In the present study, we have examined the tumor localization of heptacarboxylic porphyrin isomer I (hepta-P) using a bladder tumor model. We have also compared it to that found with uroporphyrin isomer I (Uro-P). We now show, for the first time, that (hepta-P) isomer I can be selectively retained in bladder malignant cells, a novel observation which has not yet been described by other investigators. Furthermore, we have provided a novel technique to modulate and manipulate blood protein binding to porphyrin in a controlled manner, such that the tumor localization properties can be effectively utilized without prolonged retention in the skin and to produce high uptake in the tumor, i.e., a higher therapeutic ratio. The biodistribution of hepta-P in different organs is presented.

Tumor localization of newly developed hematoporphyrin (DHP) using a bladder tumor model: a novel hematoporphyrin derivative

Application of laser irradiation with porphyrin(s) or their derivatives for the destruction of tumors in humans requires preliminary studies of their localization in normal and malignant tissues. A novel derivative of hematoporphyrin (HP) was prepared. The newly developed hematoporphyrin (DHP) was administered to Fisher rats with bladder tumors and showed greater accumulation in the tumoral tissues. Comparative data on (HP) and (DHP) are presented and discussed in light of the enhanced tumor porphyrin uptake caused by these agents. The homogeneous intense fluorescence noted with DHP-treated animals suggests that total tumor kill curative therapy will be more feasible. The study paves the way to refining increased porphyrin augment phototherapy and laser application in the field of oncology.

Photodynamic therapy with phthalocyanine sensitisation: quantitative studies in a transplantable rat fibrosarcoma

Photodynamic therapy (PDT) is a promising approach to the local destruction of malignant tumours, but little work has been done to determine which factors control the extent of tissue necrosis produced. Using a new photosensitiser, a sulphonated aluminium phthalocyanine (AlSPc) and light from an argon ion pumped dye laser at 675 nm, we quantified the effects of interstitial PDT in a transplantable fibrosarcoma in rats. At 100mW laser power, thermal effects were comparable to those of PDT, so subsequent studies were carried out at 50 mW, where thermal effects were minimal. The depth of PDT necrosis increased with the logarithm of the applied energy. Tissue concentration of AlSPc was measured by alkali extraction and at all times after sensitisation, correlated well with the necrosis produced with a given light dose. Peak tumour concentration of AlSPc occurred 24-48 h after sensitisation compared with a peak at 3 h in muscle. The peak ratio tumour:muscle was 2:1 at 24 h. Apart from a different time interval to reach the peak sensitiser concentration, the extent of tumour damage varied with the light and sensitiser parameters in a similar way to that found in normal liver, although the optical penetration depth was greater in the tumour (2.5 mm vs. 1.8 mm). At doses of AlSPc below 1 mg kg-1 the diameter of necrosis increased with the logarithm of the dose of sensitiser, and doubling the dose from 0.25 to 0.5 mg kg-1 increased the depth of necrosis by 50%. However, at higher doses, the changes were smaller and increasing the dose from 2.5 to 5 mg kg-1 only increased the necrosis by 10% for the same light dose. In all dose ranges, a given percentage increase in the tissue concentration of AlSPc gave a much smaller percentage increase in the extent of necrosis for the same light dose, suggesting that selectivity of necrosis between tumour and normal tissue is likely to be much less than the selectivity of retention of the photosensitiser. From these results, the extent of PDT necrosis in this fibrosarcoma is as predictable as it is in normal liver if the light dose, tissue concentration of AlSPc and optical penetration depth of the tissue are known. Further studies are now required on different tumour models to establish how tumours respond compared with adjacent normal tissue when the tumour is growing in its organ of origin rather than the non-physiological situation using a transplantable tumour as in this study.