Tumoricidal capacities of macrophages photodynamically activated with hematoporphyrin derivative

PDT and antitumor immunity: the beginnings of the story

This mini-review reports a brief description of the first experiments conducted by Canti's group on the role of photodynamic therapy in generating immunity against cancer. It highlights for the first time the effective role of PDT in the induction of anti-tumor T lymphocytes and shows that this effect is tumor-specific. It has also been reported how this adoptive immunity can improve the efficacy of chemotherapy. These studies have helped to open an important new field of scientific research on the role of PDT-generated immunity and to stimulate today's important new pre-clinical approaches.

Retinoblastoma: might photodynamic therapy be an option?

Retinoblastoma is a tumor that mainly affects children under 5 years, all over the world. The origin of these tumors is related with mutations in the RB1 gene, which may result from genetic alterations in cells of the germ line or in retinal somatic cells. In developing countries, the number of retinoblastoma-related deaths is higher due to less access to treatment, unlike what happens in developed countries where survival rates are higher. However, treatments such as chemotherapy and radiotherapy, although quite effective in treating this type of cancer, do not avoid high indices of mortality due to secondary malignances which are quite frequent in these patients. Additionally, treatments such as cryotherapy, thermotherapy, thermochemotherapy, or brachytherapy represent other options for retinoblastoma. When all these approaches fail, enucleation is the last option. Photodynamic therapy might be considered as an alternative, particularly because of its non-mutagenic character. Photodynamic therapy is a treatment modality based on the administration of photosensitizing molecules that only upon irradiation of the tumor with a light source of appropriate wavelength are activated, triggering its antitumor action. This activity may be not only due to direct damage to tumor cells but also due to damage caused to the blood vessels responsible for the vascular supply of the tumor. Over the past decades, several in vitro and in vivo studies were conducted to assess the effectiveness of photodynamic therapy in the treatment of retinoblastoma, and very promising results were achieved.

The impact of macrophage-cancer cell interaction on the efficacy of photodynamic therapy

Macrophages are one of the principal host cell populations in solid tumors. They are capable, due to their plasticity, of acquiring phenotypes that either combat (M1 type) or promote (M2 type) neoplastic growth. These cells, known as tumor-associated macrophages (TAMs), play complex but pivotal roles in the outcome of photodynamic therapy (PDT) of malignant lesions. Among the various parenchymal and stromal cell populations found in tumors, TAMs have been shown to have the greatest capacity for the uptake of systemically administered photosensitizers. Both the tumor-localizing property of photosensitizers and their tumor-localized fluorescence could be partly attributed to the activity of TAMs. Since resident TAMs with accumulated high photosensitizer content will sustain high degrees of PDT damage, this population (predominantly M2 in most tumors) is selectively destroyed, and during the ensuing inflammatory reaction is replaced with newly invading macrophages of M1 phenotype. These macrophages are sentinels responding to DAMP signals from PDT-treated tumor cells and in turn are mobilized to generate a variety of inflammatory/immune mediators and opsonins. They have a critical role in contributing to the therapeutic effect of PDT by mediating disposal of killed cancer cells and by processing/presenting tumor antigens to T lymphocytes. However, TAMs accumulating in the later post-PDT phase can acquire the M2 (healing) phenotype, and could have a role in tumor recurrence by releasing factors that promote angiogenesis and the survival/proliferation of remaining cancer cells. Various therapeutic strategies modulating TAM activity in the PDT response have potential for clinical use for improving PDT-mediated tumor control.

Ecological photodynamic therapy: new trend to disrupt the intricate networks within tumor ecosystem

As with natural ecosystems, species within the tumor microenvironment are connected by pairwise interactions (e.g. mutualism, predation) leading to a strong interdependence of different populations on each other. In this review we have identified the ecological roles played by each non-neoplastic population (macrophages, endothelial cells, fibroblasts) and other abiotic components (oxygen, extracellular matrix) directly involved with neoplastic development. A way to alter an ecosystem is to affect other species within the environment that are supporting the growth and survival of the species of interest, here the tumor cells; thus, some features of ecological systems could be exploited for cancer therapy. We propose a well-known antitumor therapy called photodynamic therapy (PDT) as a novel modulator of ecological interactions. We refer to this as "ecological photodynamic therapy." The main goal of this new strategy is the improvement of therapeutic efficiency through the disruption of ecological networks with the aim of destroying the tumor ecosystem. It is therefore necessary to identify those interactions from which tumor cells get benefit and those by which it is impaired, and then design multitargeted combined photodynamic regimes in order to orchestrate non-neoplastic populations against their neoplastic counterpart. Thus, conceiving the tumor as an ecological system opens avenues for novel approaches on treatment strategies.

Inhibitory effect of vitamin D-binding protein-derived macrophage activating factor on DMBA-induced hamster cheek pouch carcinogenesis and its derived carcinoma cell line

This study investigated the inhibitory effect of vitamin D-binding protein-derived macrophage-activating factor (GcMAF) on carcinogenesis and tumor growth, using a 9,10-dimethyl-1,2-benzanthracene (DMBA)-induced hamster cheek pouch carcinogenesis model, as well as the cytocidal effect of activated macrophages against HCPC-1, a cell line established from DMBA-induced cheek pouch carcinoma. DMBA application induced squamous cell carcinoma in all 15 hamsters of the control group at approximately 10 weeks, and all 15 hamsters died of tumor burden within 20 weeks. By contrast, 2 out of the 14 hamsters with GcMAF administration did not develop tumors and the remaining 12 hamsters showed a significant delay of tumor development for approximately 3.5 weeks. The growth of tumors formed was significantly suppressed and none of the hamsters died within the 20 weeks during which they were observed. When GcMAF administration was stopped at the 13th week of the experiment in 4 out of the 14 hamsters in the GcMAF-treated group, tumor growth was promoted, but none of the mice died within the 20-week period. On the other hand, when GcMAF administration was commenced after the 13th week in 5 out of the 15 hamsters in the control group, tumor growth was slightly suppressed and all 15 hamsters died of tumor burden. However, the mean survival time was significantly extended. GcMAF treatment activated peritoneal macrophages in vitro and in vivo, and these activated macrophages exhibited a marked cytocidal effect on HCPC-1 cells. Furthermore, the cytocidal effect of activated macrophages was enhanced by the addition of tumor-bearing hamster serum. These findings indicated that GcMAF possesses an inhibitory effect on tumor development and growth in a DMBA-induced hamster cheek pouch carcinogenesis model.

Combination approaches to potentiate immune response after photodynamic therapy for cancer

Photodynamic therapy (PDT) has been used as a cancer therapy for forty years but has not advanced to a mainstream cancer treatment. Although it has been shown to be an efficient way to destroy local tumors by a combination of non-toxic dyes and harmless visible light, it is its additional effects in mediating the stimulation of the host immune system that gives PDT great potential to become more widely used. Although the stimulation of tumor-specific cytotoxic T-cells that can destroy distant tumor deposits after PDT has been reported in some animal models, it remains the exception rather than the rule. This realization has prompted several investigators to test various combination approaches that could potentiate the immune recognition of tumor antigens that have been released after PDT. This review will cover these combination approaches using immunostimulants including various microbial preparations that activate Toll-like receptors and other receptors for pathogen-associated molecular patterns, cytokines growth factors, and approaches that target regulatory T-cells. We believe that by understanding the methods employed by tumors to evade immune response and neutralizing them, more precise ways of potentiating PDT-induced immunity can be devised.

PDT-induced inflammatory and host responses

Photodynamic therapy (PDT) is used in the management of neoplastic and nonmalignant diseases. Its unique mechanisms of action include direct cytotoxic effects exerted towards tumor cells, destruction of tumor and peritumoral vasculature and induction of local acute inflammatory reaction. The latter develops in response to (1) damage to tumor and stromal cells that leads to the release of cell death-associated molecular patterns (CDAMs) or damage associated molecular patterns (DAMPs), (2) early vascular changes that include increased vascular permeability, vascular occlusion, and release of vasoactive and proinflammatory mediators, (3) activation of alternative pathway of complement leading to generation of potent chemotactic factors, and (4) induction of signaling cascades and transcription factors that trigger secretion of cytokines, matrix metalloproteinases, or adhesion molecules. The majority of studies indicate that induction of local inflammatory response contributes to the antitumor effects of PDT and facilitates development of systemic immunity. However, the degree of PDT-induced inflammation and its subsequent contribution to its antitumor efficacy depend on multiple parameters, such as chemical nature, concentration and subcellular localization of the photosensitizers, the spectral characteristics of the light source, light fluence and fluence rate, oxygenation level, and tumor type. Identification of detailed molecular mechanisms and development of therapeutic approaches modulating PDT-induced inflammation will be necessary to tailor this treatment to particular clinical conditions.

Combination of photodynamic therapy and immunomodulation: current status and future trends

Photodynamic therapy (PDT) has been used for the treatment of nonmalignant and malignant diseases from head to toe. Over the last decade its clinical application has gained increasing acceptance around the world. Pre-clinical studies demonstrate that, in addition to the direct local cytotoxicity and vascular effects, PDT can induce various host immune responses. Recent clinical data also show that improved clinical outcomes are obtained through the combination of PDT and immunomodulation. This review will summarize and discuss recent progress in developing innovative regimen of PDT combined with immunomodulation for the treatment of both nonmalignant and malignant diseases.

Immunotherapy of metastatic breast cancer patients with vitamin D-binding protein-derived macrophage activating factor (GcMAF)

Serum vitamin D3-binding protein (Gc protein) is the precursor for the principal macrophage activating factor (MAF). The MAF precursor activity of serum Gc protein of breast cancer patients was lost or reduced because Gc protein was deglycosylated by serum alpha-N-acetylgalactosaminidase (Nagalase) secreted from cancerous cells. Patient serum Nagalase activity is proportional to tumor burden. The deglycosylated Gc protein cannot be converted to MAF, resulting in no macrophage activation and immunosuppression. Stepwise incubation of purified Gc protein with immobilized beta-galactosidase and sialidase generated probably the most potent macrophage activating factor (termed GcMAF) ever discovered, which produces no adverse effect in humans. Macrophages treated in vitro with GcMAF (100 pg/ml) are highly tumoricidal to mammary adenocarcinomas. Efficacy of GcMAF for treatment of metastatic breast cancer was investigated with 16 nonanemic patients who received weekly administration of GcMAF (100 ng). As GcMAF therapy progresses, the MAF precursor activity of patient Gc protein increased with a concomitant decrease in serum Nagalase. Because of proportionality of serum Nagalase activity to tumor burden, the time course progress of GcMAF therapy was assessed by serum Nagalase activity as a prognostic index. These patients had the initial Nagalase activities ranging from 2.32 to 6.28 nmole/min/mg protein. After about 16-22 administrations (approximately 3.5-5 months) of GcMAF, these patients had insignificantly low serum enzyme levels equivalent to healthy control enzyme levels, ranging from 0.38 to 0.63 nmole/min/mg protein, indicating eradication of the tumors. This therapeutic procedure resulted in no recurrence for more than 4 years.

ART AND SCIENCE OF PHOTODYNAMIC THERAPY

1. Photodynamic therapy is an established modality for the treatment of solid tumours and other accessible lesions. Although the concept and practice of combining light with a photosensitizing agent for the treatment of disease states has been around for almost a century, the understanding of the art and science therein has been tremendously enhanced over the past few years. 2. Photosensitized reactions are dependent on the generation of reactive oxygen species, in particular singlet oxygen, which accounts for the damaging effects on biological macromolecules, such as membrane lipids and proteins. Therefore, compounds that give a good yield of (1)O(2) are used as photosensitizers. 3. The main photosensitizers used in the clinical setting belong to the photofrin family; however, newer and more effective sensitizers are being evaluated for their potential clinical effectiveness. 4. Light sources have moved from the use of white light with specific filters in the old days to the more recent use of monochromatic light sources, such as lasers, to more sophisticated light-emitting diodes. However, dosimetry remains a big issue mainly because of difficulties in establishing the optimum treatment conditions for an approach that requires the fine-tuning of several variables, such as sensitizer and light doses and drug-to-light interval, as well as the issues of skin photosensitivity and low selectivity. A newer development to circumvent these and provide a broader application for this concept has been the phenomenon of photo-activation, whereby photo-exposure of chromophores to generate novel, small biologically active compounds has been demonstrated successfully. 5. The aim of the present review was to provide a general overview of the art and science of photodynamic therapy and to highlight some of the issues and recent developments in further advancing this modality of treatment.

Role of the lateral parabrachial nucleus in apomorphine-induced conditioned consumption reduction: cooling lesions and relationship of c-Fos-like immunoreactivity to strength of conditioning

The following experiments were designed to determine whether the lateral parabrachial nucleus (lPBN) mediates acquisition of conditioned consumption reduction induced by apomorphine, an agent that also has reinforcing properties. Temporary cooling lesions of the PBN blocked acquisition of apomorphine-induced conditioned consumption reduction. In addition, both apomorphine and LiCl activated c-Fos-like immunoreactivity (c-FLI) in the central, external, and crescent lPBN, and there was a strong correspondence between amount of c-FLI expression and strength of conditioned consumption reduction in these subnuclei. Taken together, these results support the hypothesis that the lPBN mediates apomorphine-induced conditioned consumption reduction, as is true for LiCl. Furthermore, they raise the possibility that the specific part of the lPBN mediating this conditioning effect of apomorphine and LiCl is 1 of the 3 subnuclei.

Hyperthermic photodynamic therapy combined with topical administration of OK-432 in the mouse carcinoma

This study investigated the combined effect of photodynamic therapy (PDT) using high power laser irradiation (HPL), which generates both a hyperthermic and a photodynamic effect, and OK-432 on NR-S1 mouse squamous cell carcinoma. The photosensitizer (haematoporphyrin oligomers 20 mg/kg BW) was injected to the mice intraperitoneally 48 h before laser irradiation. OK-432 was injected into the tumour 3 h prior to laser irradiation. The experimental protocols consisted of HPL-PDT with or without OK-432, low power laser PDT with or without OK-432, HPL alone and OK-432 alone, and a control group. The tumour necrotic area was determined, and tumour sizes were measured 3, 7 and 10 days after each protocol. The anti-tumour effect of HPL-PDT was enhanced by preadministration with OK-432. Treatment with OK-432 alone or hyperthermic HPL irradiation presented little anti-tumour effect. HPL-PDT in combination with OK-432 topically administered 3 h before photo-irradiation is considered to be a promising therapeutic modality.

Vitamin D binding protein-macrophage activating factor (DBP-maf) inhibits angiogenesis and tumor growth in mice

We have isolated a selectively deglycosylated form of vitamin D binding protein (DBP-maf) generated from systemically available DBP by a human pancreatic cancer cell line. DBP-maf is antiproliferative for endothelial cells and antiangiogenic in the chorioallantoic membrane assay. DBP-maf administered daily was able to potently inhibit the growth of human pancreatic cancer in immune compromised mice (T/C=0.09). At higher doses, DBP-maf caused tumor regression. Histological examination revealed that treated tumors had a higher number of infiltrating macrophages as well as reduced microvessel density, and increased levels of apoptosis relative to untreated tumors. Taken together, these data suggest that DBP-maf is an antiangiogenic molecule that can act directly on endothelium as well as stimulate macrophages to attack both the endothelial and tumor cell compartment of a growing malignancy.

Characteristics of the Immunosuppression Induced by Cutaneous Photodynamic Therapy: Persistence, Antigen Specificity and Cell Type Involved¶

Relatively little is known about the immunosuppression induced in mice which have received cutaneous photodynamic therapy (PDT). Consequently, experiments were undertaken using mice which received dorsal PDT using Photofrin as the photosensitizer in an attempt to characterize the overall nature of the immunosuppression. Photoirradiation of mice at various times after injection indicated there was no correlation between photosensitivity and immunosuppression. The suppression was found to be adoptively transferable and antigen specific suggesting the generation of suppressor cells. Selective cell depletions prior to adoptive transfer indicated a CD4+ T cell to be responsible for the immunosuppression. Interestingly, using allogeneic spleen cells, no effect on the delayed type hypersensitivity (DTH) response was found. The results indicate that the suppression induced by cutaneous PDT, with the exception of the lack of DTH suppression, is similar to that induced by UVB irradiation but unlike that reported using laser PDT of the peritoneal cavity. This suggests that not only the type of photoirradiation but also the site of photoirradiation might determine the character of the induced immunosuppression.

Foscan (mTHPC) photosensitized macrophage activation: enhancement of phagocytosis, nitric oxide release and tumour necrosis factor-alpha-mediated cytolytic activity

Photodynamic activation of macrophage-like cells contributes to an effective outcome of photodynamic therapy (PDT) treatment. The possibility for an enhancement of macrophage activity by photosensitization with meta-tetra(hydroxyphenyl)chlorin (mTHPC) (1 microg ml(-1)) was studied in U937, monocyte cell line differentiated into macrophages (U937) cells). Phagocytic activity of U937phi cells was evaluated by flow-cytometry monitoring of ingestion of fluorescein-labelled Escherichia coli particles. Increase in irradiation fluence up to 3.45 mJ cm(-2) (corresponding irradiation time 15 s) resulted in significant increase in fluorescence signal (145%), while at higher light fluences the signal lowered down to the untreated control values. A light energy-dependent production of tumour necrosis factor-alpha (TNF-alpha) by photosensitized macrophages was further demonstrated using the L929 assay. The maximum TNF-alpha mediated cytolysis was observed at 28 mJ cm(-2) and was 1.7-fold greater than that in control. In addition, we demonstrated a fluence-dependent increase in nitric oxide (NO) production by mTHPC-photosensitized macrophages. NO release increased gradually and reached a plateau after irradiation fluence of 6.9 mJ cm(-2). Cytotoxicity measurements indicated that the observed manifestations of mTHPC-photosensitized macrophage activation took place under the sublethal light doses. The relevance of the present findings to clinical mTHPC-PDT is discussed.

Activation of macrophage tumoricidal activity by photodynamic treatment in vitro--indirect activation of macrophages by photodynamically killed tumor cells

Macrophages constitute a major part of natural tumor defense by their capacity to destroy selectively a broad range of tumor types upon specific activation. In the last couple of years, these cells have also been implicated as effector cells in the destruction of tumors by photodynamic therapy. In the present work, the potential role of macrophage-mediated tumor cytotoxicity after photodynamic treatment in vitro has been investigated with respect to photodynamic activation of macrophages for tumoricidal effector functions. Our data show that photodynamic treatment of highly pure murine bone-marrow-derived macrophages with the hematoporphyrin derivative Photosan-3 does not result in activation of these cells for cytotoxicity against YAC-1 tumor cells or secretion of tumor necrosis factor and nitric oxide, irrespective of co-stimulation with interferon-gamma, a potent priming agent for macrophage antitumoral activity. On the contrary, treatment with higher photosensitizer doses is found to reduce markedly the viability of the macrophage effector cells. Thus, these results do not lend any support to the hypothesis of direct macrophage activation by photodynamic treatment. However, macrophages are found to be activated for tumoricidal effector functions indirectly by photodynamically killed tumor cells, in a way reminiscent of phagocytosis-inducing stimuli. It is thus suggested that recognition and phagocytosis of photodynamically destroyed tumor cells constitutes the major signal for local activation of macrophages in photodynamically treated tumor tissues, which may be crucial for final, specific eradication by the immune system of tumor cells surviving photodynamic treatment.

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.

Structurally well-defined macrophage activating factor derived from vitamin D3-binding protein has a potent adjuvant activity for immunization

Freund's adjuvant produced severe inflammation that augments development of antibodies. Thus, mixed administration of antigens with adjuvant was not required as long as inflammation was induced in the hosts. Since macrophage activation for phagocytosis and antigen processing is the first step of antibody development, inflammation-primed macrophage activation plays a major role in immune development. Therefore, macrophage activating factor should act as an adjuvant for immunization. The inflammation-primed macrophage activation process is the major macrophage activating cascade that requires participation of serum vitamin D3-binding protein (DBP; human DBP is known as Gc protein) and glycosidases of B and T lymphocytes. Stepwise incubation of Gc protein with immobilized beta-galactosidase and sialidase efficiently generated the most potent macrophage activating factor (designated GcMAF) we have ever encountered. Administration of GcMAF (20 or 100 pg/mouse) resulted in stimulation of the progenitor cells for extensive mitogenesis and activation of macrophages. Administration of GcMAF (100 pg/mouse) along with immunization of mice with sheep red blood cells (SRBC) produced a large number of anti-SRBC antibody secreting splenic cells in 2-4 days. Thus, GcMAF has a potent adjuvant activity for immunization. Although malignant tumours are poorly immunogenic, 4 days after GcMAF-primed immunization of mice with heat-killed Ehrlich ascites tumour cells, the ascites tumour was no longer transplantable in these mice.

Effect of photodynamic pretreatment on the susceptibility of murine tumor cells to macrophage antitumor mechanisms

In vitro photodynamic treatment of YAC-1 murine T-lymphoma cells with the hematoporphyrin derivative Photosan 3 and red light resulted in dose-dependent phototoxicity. Photodynamic pretreatment, however, did not render these cells more susceptible to macrophage-mediated tumor cytotoxicity or the cytotoxic effects of macrophage-derived antitumor mediators like tumor necrosis factor alpha (TNF-alpha) or interferon beta (IFN-beta). Independent of the degree of photosensitization used, the cytotoxicity values obtained with macrophages or the different mediators were shifted by the respective values for phototoxicity, suggesting these effects to be additive and thus not interdependent. These data show that while higher overall tumor cytotoxicity can be achieved by a combination of photodynamic treatment and macrophage-mediated tumor destruction, this apparently is not a result of enhanced sensitivity of photodynamically treated tumor cells to macrophage antitumor mechanisms in general.

Photodynamic effect on the specific antitumor immune activity

Photofrin is a potent sensitizer which localizes, among other sites in membranes of malignant cells. To evaluate the effect of photodymanic therapy (PDT) on specific antitumoral immunological response, we used a chromium release assay to compare the specific cytolytic activity (CLA) of primed mouse spleen T lymphocytes sensitized against syngeneic mastocytoma P511 cells. P511 cells or lymphocytes or both were treated or not with Photofrin and/or light (514 nm). Photofrin alone (1 microg/ml, 2 h) reduced CLA by 59% when P511 cells were treated although this decrease was not drug dose dependent. Photofrin (1 microg/ml, 2 h) followed by light (25 J/cm2) reduced CLA by 35% in a drug dose dependent manner. Longer incubation times led to reduced CLA inhibition (10% for 3 h incubation) after Photofrin followed by light. The light dose (25, 37, 50 J/cm2) did not influence CLA for a given Photofrin concentration. Photofrin alone (0.5 microg/ml, followed by light (25 J/cm2 for 2 h) reduced CLA respectively by 8 and 45% only when lymphocytes were treated. When lymphocytes and P511 cells were treated with Photofrin alone or followed by light (25 J/cm2), CLA was also reduced (by 19 and 41% respectively). This type of damage can be evaluated in terms of antigen expression on the target cells, on the lymphocyte T receptor, on H-2 (histocompatibility major complex), or on lymphocyte activity after PDT.

Macrophage-directed immunotherapy as adjuvant to photodynamic therapy of cancer

The effect of Photofrin-based photodynamic therapy (PDT) and adjuvant treatment with serum vitamin D3-binding protein-derived macrophage-activating factor (DBPMAF) was examined using a mouse SCCVII tumour model (squamous cell carcinoma). The results show that DBPMAF can markedly enhance the curative effect of PDT. The most effective DBPMAF therapy consisted of a combination of intraperitoneal and peritumoral injections (50 and 0.5 ng kg-1 respectively) administered on days 0, 4, 8 and 12 after PDT. Used with a PDT treatment curative to 25% of the treated tumours, this DBPMAF regimen boosted the cures to 100%. The DBPMAF therapy alone showed no notable effect on the growth of SCCVII tumour. The PDT-induced immunosuppression, assessed by the evaluation of delayed-type contact hypersensitivity response in treated mice, was greatly reduced with the combined DBPMAF treatment. These observations suggest that the activation of macrophages in PDT-treated mice by adjuvant immunotherapy has a synergistic effect on tumour cures. As PDT not only reduces tumour burden but also induces inflammation, it is proposed that recruitment of the activated macrophages to the inflamed tumour lesions is the major factor for the complete eradication of tumours.

Induction of tumor immunity by photodynamic therapy

The mechanism of tumor destruction by photodynamic therapy (PDT) incorporates a variety of events leading to inactivation of tumor cells. The unique feature of PDT is the mobilization of the host to participate in the eradication of treated cancer. A critical element is the induced inflammation at the treated site associated with massive invasion of activated myeloid cells. In addition to further destruction of cancer cells, conditions are created for the presentation of tumor antigens with subsequent activation of lymphoid cells, leading to tumor-specific immunity. This inflammation-primed immune development process results in generation of tumor-specific immune memory cells that appear to be elicited against both strongly and poorly immunogenic PDT-treated cancers. Once generated by PDT, it is conceivable that these immune cells (especially if further expanded and activated by adjuvant immunotherapy) can be engaged in additional eradication of disseminated and/or metastatic lesions of the same cancer. A number of immunotherapy regimens have already been proven effective in enhancing the curative effect of PDT with various animal tumor models. Inflamed cancerous tissue at the PDT-treated site appears to exert powerful attracting signals for immune cells activated by different immunotherapy regimens.

Benzophenothiazine and benzoporphyrin derivative combination phototherapy effectively eradicates large murine sarcomas

The tumoricidal effects of photochemotherapy with two photosensitizers, 5-ethylamino-9-diethylaminobenzo[a] phenothiazinium chloride (EtNBS) and benzoporphyrin derivative monoacid ring A (BPD-MA), were evaluated separately and in combination against the EMT-6 fibrosarcoma implanted subcutaneously in BALB/c mice. Animals carrying tumors 8-10 mm in diameter were divided into eight different groups (approximately 20/group) and subjected to various photoirradiation and drug conditions. The tumor response to photodynamic therapy (PDT) was measured as the mean tumor wet weight 2 weeks post-PDT. The combination treatment with 5.25 mg/kg EtNBS and 2.5 mg/kg BPD-MA followed by photoirradiation with 100 J/cm2 at 652 nm and then by 100 J/cm2 at 690 nm resulted in a 95% reduction in the average tumor weights compared to controls (no light, no drugs) with 76% of the mice being tumor free 2 weeks post-PDT. Because treatment with EtNBS or BPD-MA at twice the light dose and drug concentration resulted in either no significant reduction in tumor weights or increased the lethality of treatment, respectively, the data suggest that the enhanced PDT effect observed with the combination of drugs is synergistic rather than additive. Histology of tumors 24 h post-PDT with the combination of drugs showed nearly complete destruction of the tumor mass with little or no damage to the vasculature and no extravasation of red blood cells. There was no damage to the normal skin adjacent to the tumor. Fluorescence microscopy of EMT-6 cells incubated in vitro with the two photosensitizers revealed that they were localized to different intracellular compartments. The fluorescence pattern from frozen tumor tissue slices following the in vivo administration of the photosensitizers indicated a greater intracellular localization for EtNBS vs BPD-MA.

Sensitivity of activated murine peritoneal macrophages to photodynamic killing with benzoporphyrin derivative

This study compared the ability of highly purified resting and activated DBA/2 mouse peritoneal macrophages to survive treatment with the photosensitizer benzoporphyrin derivative (BPD, verteporfin) and light. Culture of macrophages with recombinant murine interferon-gamma (rIFN-gamma, 100 U/mL) for 72 h imparted a phenotypic and functional activation by dramatically increasing cell surface expression of major histocompatibility complex Class II (Ia) molecules and the formation of nitric oxide. The rIFN-gamma-activated macrophages were significantly (P < 0.05) more sensitive (lethal dose to cause a 50% reduction in cell survival, LD50 = 14.4 +/- 1.1 ng/mL) to photodynamic killing with BPD and light (10 J/cm2) than cells (LD50 = 18.2 +/- 2.0 ng/mL) cultured in medium alone. In contrast, macrophages treated with different concentrations of bacterial lipopolysaccharide (LPS) were as resistant or more resistant to photodynamic killing than cells cultured in medium alone. No cytotoxic effect of BPD was detected in cultures containing the drug but protected from light. Comparable amounts of BPD were taken up in vitro by unactivated and rIFN-gamma-activated macrophages, as detected by flow cytometric analysis. However, cells cultured with LPS (10 micrograms/mL) took up more BPD than macrophages cultured in medium alone or with rIFN-gamma. The DBA/2 P815 mastocytoma cells took up greater amounts of the drug and were subsequently more vulnerable to treatment with BPD and light (LD50 = 6.9 ng/mL) than macrophages cultured under any condition. The explanation for the increased vulnerability of rIFN-gamma-activated macrophages and the greater resistance of LPS-activated macrophages, relative to medium-cultured macrophages, to photodynamic killing with BPD is uncertain.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of immune cell infiltration into murine SCCVII tumour by photofrin-based photodynamic therapy

Cellular populations in the squamous cell carcinoma SCCVII, growing in C3H/HeN mice given Photofrin, were examined at various time intervals during the photodynamic light treatment and up to 8 h later. Cell populations present within excised tumours were identified by monoclonal antibodies directed against cell type-specific membrane markers using a combination of the indirect immunoperoxidase and Wright staining or by flow cytometry. Photofrin-based photodynamic therapy (PDT) induced dramatic changes in the level of different cellular populations contained in the treated tumour. The most pronounced was a rapid increase in the content of neutrophils, which increased 200-fold within 5 min after the initiation of light treatment. This was followed immediately by an increase in the levels of mast cells, while another type of myeloid cells, most likely monocytes, invaded the tumour between 0 and 2 h after PDT. The examination of cytolysis of in vitro cultured SCCVII tumour cells mediated by macrophages harvested from the SCCVII tumour revealed a pronounced increase in the tumoricidal activity of tumour-associated macrophages isolated at 2 h post PDT. It seems, therefore, that the PDT-induced acute inflammatory infiltration of myeloid cells into the treated tumour is associated with functional activation of immune cells.

Enhanced macrophage cytotoxicity against tumor cells treated with photodynamic therapy

In vitro treatment of human lung adenocarcinoma cells A549 with photofrin-based photodynamic therapy (PDT) resulted in the potentiation of macrophage-mediated killing of these cells assayed either by measuring 3H-thymidine release from the prelabeled target cells, or by determining the survival of A549 cells based on colony formation. The effector cells in these experiments were human promyelocytic leukemia cells HL60 induced to differentiate into macrophages. Very similar results were obtained with the murine squamous carcinoma SCCVII cells treated with PDT and subsequently admixed with mouse peritoneal macrophages. This effect increased with PDT dose and reached its maximum (i.e. complete or nearly complete release of the radioactive label) with the photodynamic treatment that was lethal to 40-50% of cells. In contrast, the PDT treatment of normal mouse kidney cells resulted in only a very limited enhancement of their cytolysis by mouse peritoneal macrophages. The exposure of A549 cells to X-ray irradiation had not affected the macrophage-mediated killing of these cells. The PDT survival curves of A549 cells cultured either alone or with the effector cells showed that the presence of macrophages even at very low effector: target cells ratios enhanced the PDT response of tumor cells. The enhancement ratio of 3.6 (at S = 0.01) was achieved with the effector: target cell ratio 2.5:1, which was the highest ratio tested with this assay. It is suggested that macrophages may recognize potentially repairable damage induced by PDT in tumor cells (presumably lipid fragments exposed in damaged cellular membranes), which helps them to identify the affected cells as their targets.

Effectiveness of photofrin II in activation of macrophages and in vitro killing of retinoblastoma cells

Administration of a small dose (300 ng/mouse) of photofrin II (PII) to mice, followed by 4 days of exposure to only ambient fluorescent light in animal quarters, induced Fc-receptor-mediated phagocytic and superoxide-generating capacities of peritoneal macrophages by five- and seven-fold, respectively. When these mice were kept in the dark for 4 days, no activation of macrophages was observed. These results suggest that macrophage activation is a consequence of photodynamic activation. Much higher doses (> 3000 ng/mouse) suppressed macrophage activity. However, 2 months after administration of 3000 ng PII/mouse, greatly enhanced phagocytic and superoxide-generating capacities of peritoneal macrophages were observed. In vitro photodynamic activation of macrophages was analyzed after white or red fluorescent light exposure of mouse peritoneal cells (mixture of macrophages and B and T lymphocytes) in media containing PII. A short (10 s) white fluorescent light treatment of peritoneal cells in a medium containing 0.03 ng PII/mL produced the maximal level of phagocytic activity of macrophages. Illumination with the same total fluence of red fluorescent light requires a three-fold higher concentration of PII to achieve the same extent of enhanced phagocytic activity of macrophages. Thus, photodynamic activation of macrophages with PII by white fluorescent light was more efficient than by red fluorescent light. Similarly, photodynamic killing of retinoblastoma cells was more efficient with white than red fluorescent light. The concentration of hematoporphyrin (HP) or PII required for direct photodynamic killing of retinoblastoma cells was roughly four orders of magnitude greater than that required for activation of macrophages.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo and in vitro activation of macrophages with a cyanine photosensitizing dye, platonin

A cyanine photosensitizing dye, platonin, is a potent macrophage-activating agent. Four days after the administration to mice of small amounts of platonin (20-40 ng/mouse), peritoneal macrophages exhibited greatly enhanced Fc-receptor-mediated phagocytic and superoxide-generating capacities. Much higher doses (more than 3000 ng/mouse) did not have this effect. Photodynamic experiments for macrophage activation were performed by exposing mouse peritoneal cells (mixture of macrophages and B and T lymphocytes) to white fluorenscent light (3 J m-2s-1) in media containing various low concentrations of platonin. A short exposure to white fluorescent light (5 s, 15 J m-2) of peritoneal cells in a medium containing 3 ng platonin/ml produced a maximal level of phagocytic capacity of macrophages. Although platonin absorbs light poorly at wavelengths longer than 630 nm, the region of the spectrum in which the tissues are transparent allows reasonable penetration of light. Thus, we designed experiments in which peritoneal cells were exposed to a red fluorescent light (0.5 J m-2s-1). In a medium containing 10 ng platonin/ml with 15 J m-2 red light, a markedly enhanced ingestion activity of macrophages was observed. Photodynamic treatment of peritoneal macrophages alone did not activate macrophages. Thus, participation of nonadherent cells is required for photodynamic activation of macrophages, implying that a macrophage-activating factor is generated within the nonadherent cells and transmitted to macrophages.