Malignant neoplasms are a global medical and social problem with a tendency to a steadily increasing morbidity and mortality rates (primarily due to malignant gliomas (MG)) [ 1 ]. Treatment of malignant brain gliomas remains a great challenge on a global scale, despite intensive research into the causes and mechanisms of their progression.

Gliomas are conditionally divided into two broad groups [ 2 ]: circumscribed gliomas, which have relatively well-defined margins and can be completely removed surgically, and difuse gliomas, which have no clear borders and cannot be totally removed during surgery.

In 2021, the classification of central nervous system (CNS) tumors was revised taking into account molecular biological markers (5th edition) [ 3 ]. According to the new edition, difuse gliomas in adults are classified into three groups: astrocytomas (IDH mutation, CNS WHO grade 2, 3, 4), oligodendrogliomas (IDH mutation and 1p19q codeletion, CNS WHO grade 2, 3), glioblastomas (IDH-wildtype, CNS WHO grade 4), in children into low-grade and high-grade with corresponding subtypes. Circumscribed astrocytic gliomas include The resistance of GB in response to curative pilocytic astrocytomas, high-grade astrocytomas with measures is widely known and can be explained by piloid features, pleomorphic xanthoastrocytomas, several features: GB is a heterogeneous population subependymal giant cell astrocytomas, chordoid with a large number of signaling pathways even within gliomas, astroblastomas (MN1-altered) [ 3 ]. a single tumor, which limits the possibilities of targeted

According to CBTRUS statistical report of for therapy; the microenvironment of GB enhances their 2014‒2018 (the previous edition of the CNS tumor resistance to radiation and chemotherapy; the low classification of 2016 was applied), the average annual immunogenicity of GB cells prevents an adequate incidence rate of malignant brain tumors and other CNS immunological response; invasion of the perifocal tumors was 7.06 per 100,000 population, the average zone of the brain by glioma cells (including stem cells) annual death rate was 4.43 [ 2, 4 ]. The most common significantly complicates efective treatment by surgical malignancy among brain tumors and other CNS tumors resection alone; the blood-brain barrier prevents the is glioblastoma (GB) (14.3% of all tumors and 49.1% of achievement of a suficient concentration in the brain of malignant brain tumors). The five-year relative survival systemically administered chemotherapy drugs without rate after morphological diagnosis of a malignant brain serious side efects [ 9 ]. There is an active search for tumor and other CNS tumors was 66.9%, whereas for alternative ways of diagnosis and treatment of GB in non-malignant variants of brain tumors and other CNS the following areas: new technologies of cellular and tumors it was 92.1%. Difuse gliomas had a significantly molecular diagnostics, nanotechnology, the use of worse prognosis than circumscribed/demarcated stem cells as carriers of ligands and vectors, modern gliomas, and differed significantly in the duration approaches to immunotherapy, technologies of targeted of overall and recurrence-free survival of patients and personalized therapy, etc. depending on the histological variant [ 2 ]. Among the most recent approaches are innovative

The incidence of malignant variants of primary intraoperative techniques and various methods of brain tumors in Ukraine, according to the latest data of treating the "tumor" surgical site. In particular, the the National Cancer Registry (2020), is 5.0 per 100,000 following options for the introduction of pharmacological population, the mortality rate is 3.5 per 100,000 population agents are ofered: stereotaxic injections of various [ 5 ]. Among primary CNS tumors, malignant forms of brain compounds directly into the tumor using neuronavigation, gliomas (WHO grade 3-4) predominate, most of them as well as in combination with intraoperative computed are GB (WHO grade 4). The survival analysis of patients tomography or magnetic resonance imaging (MRI) with oligoastrocytomas (163 cases for the period from (chemotherapeutic agents, radioactive iodine, iron 2005 to 2015) showed that the median overall survival oxide nanoparticles); convection-enhanced delivery of was (49.9±2.4) months and difered depending on the compounds using pressure gradient to improve their histostructure of the tumor: in patients with predominance distribution (chemotherapeutic agents, viral vectors, of the oligodendroglial pool, the average overall survival of cytotoxins, radioactive nanoliposomes); implantation of patients who underwent surgery was (100.5±4.6) months, Ommaya or Rickham reservoirs for periodic therapeutic with predominance of the progression of the astrocytic injections over a long period (for chemotherapy, component of the proliferate - (48.2±4.5) months, with administration of neural stem cells, cell therapy of approximately equal distribution of the oligodendroglial CAR (chimaeric antigen receptor) T-cells; intra-arterial and astrocytic components - (76.6± 4.9) months [ 6 ]. The delivery of high doses of therapeutic agents (antibodies, survival analysis of patients with primary GB in Ukraine chemotherapeutic agents, viral vectors) using catheters (3763 cases for the period from 2008 to 2016) showed inserted directly in the arteries involved in the blood that the median overall survival was (12.2±0.2) months, supply of the tumor focus [ 9 ]. the average overall survival of operated patients was The treatment of MG by alternating electric fields, (7.5±0 ,3) months, when using combined therapy (surgical methods of laser-induced interstitial thermotherapy, removal, radiation and chemotherapy) – (16.3±0.5) magnetic hyperthermic therapy, focused ultrasound, months (p<0.001) [ 7 ]. radiofrequency microwave and photodynamic therapy

Consequently, the results of complex treatment of (PDT) are suggested [ 9, 10 ].

GB remain unsatisfactory due to the invasive nature of Photodynamic methods, such as photodynamic their spread and multiresistance to adjuvant treatment diagnosis, f luorescence-guided tumor resec tion methods and require the development of new and (fluorescence-guided surgery (FGS)), and PDT, are improvement of existing methods for the management being intensively developed in clinical trials as adjuvant of this pathology. The modern standard of treatment methods of therapy for MG [ 11, 12 ]. for GB involves surgical treatment with maximum Invasive glial tumor spread and the degree of functionally possible resection radiochemotherapy and surgical resection are dificult to definitively assess adjuvant chemotherapy [ 8 ]. However, despite advances during surgery, and areas of tumor cell invasion may be in neurosurgery, chemotherapy, and radiotherapy, overlooked when using traditional surgical approaches GB remains one of the most treatment-resistant and imaging techniques. In addition, the functional load CNS malignant neoplasms and the tumor inevitably of certain anatomical areas limits the neurosurgeon progresses. Most cases of continued growth/recurrence in the radicality of the removal, therefore, MG often occur in or near the resection area, namely the area that progressively occur near the marginal area of the surgical received the highest dose of postoperative radiation [ 9 ]. cavity as a result of residual glioma cells. A method Many new therapies are designed to combat these local that enables visual identification of tumor tissue while recurrences by administering therapeutic agents directly selectively destroying it will contribute to better surgical into or near the tumor bed. removal of MG. Such method is PDT - a two-stage treatment involving the administration (intravenously, intraperitoneally, locally or orally) of a light-sensitive agent (photosensitizer (PS)) followed by its activation by light rays of a certain wavelength for target lesion of tumor cells.

The beginning of using the energy of photochemical reactions is associated with Ancient Egypt, when in the 6th millennium BC vitiligo skin disease was treated with a powder of leaves of parsnip, parsley and St.-John'swort, which was spread on the afected skin areas, and when exposed to sunlight, light-sensitive components contained in these plants caused a photochemical reaction in tissues, resulting in the appearance of skin pigmentation [ 13 ]. Photodynamic procedures are described in ancient books - the Ebers papyrus and the sacred Indian book "Atharvaveda", similar methods (oxygen-free photochemical reactions) were also practiced in ancient China, Thailand, Arab countries (in particular, the use of Aatrillal seed powder (later name - Ammi majus, Chinese cumin)) [ 14 ].

Over the past 100 years, the role of photosensitizing agents in the implementation of the antitumor response to photoirradiation has been investigated. In 1900, O. Raab in the laboratory of H. von Tappeiner at the University of Munich established an oxygen-dependent photodynamic efect of a number of natural dyes (in particular, acridine orange) during the solar irradiation of simple unicellular organisms Paramecium [ 14, 15 ]. H. Jesionek et al. observed an improvement in the skin condition of patients with tuberculosis and syphilis after using an aqueous eosin solution and solar rays or an arc lamp irradiation. H. von Tappeiner and H. Jesionek (1903) first performed PDT in a skin cancer patient using eosin solution as a PS. Afected areas were irradiated with sunlight or an arc lamp. A total of 6 patients were treated, 4 of them achieved complete resorption of lesions with no recurrence within 1 year (1905). It was H. von Tappeiner (1904) who proposed the term "photodynamic reaction" to describe a specific photochemical reaction when irradiation with light and the use of oxygen and a radiation-absorbing dye, resulting in the death of biological systems [ 15 ]. Since the discovery of W.H. Hausmann new PS hematoporphyrin (1908), the sensational experiment of F. Meyer-Betz (1912) with a test of its efect on himself, as well as after the works of A. Policard (1924), who suggested the use of PDT in oncology, focusing on the diagnostic value of fluorescence of tumor-transformed tissues (using hematoporphyrin) [ 14, 15 ], the issue of search and synthesis of new PS is relevant. Currently, more than 100 drugs with photosensitizing activity have been synthesized.

A new stage in the development of PDT began with the medical use of lasers (1960s). Since then, PDT is considered an intervention consisting in photochemical destruction under combined exposure to PS and low-intensity laser radiation with an optimal wavelength corresponding to the absorption spectrum of the sensitizer, which significantly increases the intensity of photochemical reactions.

PDT has been developing as a direction of tumor treatment for several decades. In one of the first reports on PDT of glioma tissue (1980), it was assumed that further improvement of the technique would promote better penetration into tumor tissue and more radical destruction of glioma cells [ 16 ]. The use of PDT in neurooncology significantly increased the duration of overall and relapse-free survival in patients, reduced the risk of severe neurological complications [ 17 ]. In 1996, the results of open phase I/II clinical trials involving more than 310 patients who received PDT after resection of a malignant tumor (primary or recurrent) were published. A clear tendency to increase the average survival rate of patients after surgical removal and single PDT was revealed [ 18, 19 ].

In Ukraine, PDT as a new technology for the treatment of oncological diseases began to be developed in the 1970s [ 20 ]. Prof. M.F. Gamaliia and Prof. R.E. Kavetsky substantiated the therapeutic effect of laser irradiation by the presence of endogenous porphyrins and molecular oxygen in the peripheral blood as the main photoacceptors, formulating the concept of "photodynamic blood modification" - optimized, mathematically verified low-intensity efect on the blood based on light parameters and doses, the consequences of which are morphological changes of blood elements, local and systemic efects. The developers were awarded the Ukrainian SSR State Prize in the field of science and technology [ 21 ].

The problem of using PDT in neuro-oncology began to be addressed in the 1990s at the Institute of Neurosurgery named after acad. A. P. Romodanov, National Academy of Medical Sciences of Ukraine, under the leadership of Prof. V.D. Rozumenko (neuro-oncology department) with the involvement of the tissue culture laboratory (head - Prof. V.M. Semenova). A number of experimental studies [ 22‒28 ] formed the basis of the clinical development of PDT regimens in neuro-oncology patients [ 29 ]. Currently, PDT is a clinically acceptable method of treating various types of cancer, which is constantly being improved [ 30, 31 ].

Photodynamic therapy was introduced as an option for topical (local) surgical therapy based on cytotoxic efects caused by a chemical photosensitizing agent that selectively accumulates in malignant tumor tissue and is activated by light rays of the appropriate wavelength [ 32, 33 ], generating singlet oxygen and free radicals, which trigger photochemical reactions in tumor cells with subsequent destruction of their protein structures. Photodynamic therapy implies photoactivation of PS molecule, which is selectively incorporated into neoplastic cells [ 34 ].

Exposure to light rays of a certain wavelength (photoirradiation) activates PS, exciting molecular oxygen to the singlet or triplet state [ 12 ]. In the singlet state, energy is converted into heat (internal conversion) or emitted as light (fluorescence). Singlet oxygen has a record long lifetime in the discharged state — 4600 s, or 1.27 h [ 36 ]. In the triplet state, reactive oxygen species (ROS) are generated, which react rapidly with macromolecules containing unsaturated double bonds (proteins, unsaturated fatty acids, cholesterols), damaging the membranes of intracellular organelles (mitochondria, lysosomes, endoplasmic reticulum), reacting with DNA, proteins, lipids and other macromolecules, disrupt multiple cell signaling pathways, extensively destroy DNA, which eventually leads to tumor cells death (through necrosis, apoptosis, autophagy), destruction of the tumor microvascular system, local ischemia, as well as to activation of antitumor immune responses [ 10, 12, 34, 37‒39 ]. One of PDT targets is macrophages, which produce inflammatory mediators and cytokines (lymphokines, thromboxanes, prostaglandins, tumor necrosis factor, etc.) after photoirradiation, thus significantly afecting the tumor stroma degradation [ 40 ]. Moreover, PDT damages endothelial cells, which leads to local thrombosis, vasoconstric tion and ultimately to the destruction of the microcirculatory channel. The combination of these efects induces a strong immune response against glioma in the experiment [ 41 ]. Therefore, PDT engages the mechanisms of not only direct cytodestructive, but also mediated immunomodulatory antitumor efects, activating the links of innate and acquired immunity.

Both PSs and photosensitizing precursors are used for PDT [ 10 ]. Ideal PSs should be purified from impurities in order to selectively accumulate in tumor tissue and be able to cross the blood-brain barrier. Photosensitizers should also be localized in the tumor tissue without simultaneous accumulation in significant concentrations in healthy tissue and have maximum cytotoxic activity against tumor cells due to absorption of light photons in the 650‒700 nm spectral range. It is important that PSs do not cause systemic toxicity and are quickly eliminated from the body [ 42, 43 ]. The selectivity of PSs accumulation in the brain is one of the key issues in the problem of PDT efectiveness increase. After administration, PSs accumulate in all body organs, but tumor tissue has a greater afinity for them [ 35 ]. The blood-brain barrier, which prevents the penetration of most drugs, does not interfere with PSs. The selectivity of PSs accumulation in brain tissues varies from 3:1 to 50:1 compared to normal tissues [ 42 ].

Photosensitizers are divided into 1st, 2nd and 3rd generation molecules.

The 1st generation PSs molecules are porphyrins, namely por f imer sodium and hematoporphyrin derivatives (HpD, a patented combination of monomers, dimers and oligomers derived from hematoporphyrin) [ 10 ]. In 1984, T.J. Dougherty et al. [ 44 ] conducted a study on the isolation of the active fraction of HpD. The purified mixture of HpD monomers, dimers and oligomers was commercially named Photofrin (USA). In Germany, the analogue is Photosun. These compounds are characterized by strong absorption in the ~400 nm range, but have limited excitation absorption at longer light wavelengths [ 45 ]. HpD is an ineficient producer of singlet oxygen, requiring prolonged photostimulation to achieve an adequate therapeutic efect [ 46 ]. For PDT with drugs based on HpD derivatives, laser radiation with a wavelength of 628‒632 nm is used, while the depth of photoinduced necrosis does not exceed 1 cm. Doses of light energy vary significantly (from 50 to 500 J/cm²) and depend on the size and localization of the tumor lesion.

The second generation photosensitizers such as chlorins (thalaporfin sodium and temoporfin (metatetra(hydroxyphenyl)chlorin (mTHPC)), pheophorbides, bacteriopheophorbides, metalloporphyrins, purpurins, phthalocyanines, and 5-aminolevulinic acid (5-ALA) have been developed to overcome the limitations inherent to 1st generation sensitizers. They are usually activated at wavelengths >600 nm and are more efective in singlet oxygen production [ 10 ]. Thalaporfin sodium is activated by light with a wavelength of 664 nm [ 46, 47 ]. Temoporfin (mTHPC) is the most potent of the clinically available PSs (activated by 652 nm photostimulation), is well tolerated, but has photosensitivity that persists up to 6 weeks after administration. Another mTHPC drug is Foscan (Germany). PDT requires minimal doses (0.1–0.15 mg /kg of body weight) and light energy (10–20 J/cm²) at a wavelength of 652 nm. However, its use is associated with side efects (development of tracheal and bronchial stenosis, esophagotracheal fistulas, esophageal perforations). The drug is rapidly excreted from the body, skin toxicity is observed within 1 week [ 48, 49 ]. Purlitin (selenium etiopurpurin) (USA) [ 50 ] and Lutex (USA) belong to this group of PSs, the feature of which is high selectivity of accumulation in tumors [ 51 ]. Photosensitizers based on zinc and aluminum porphyrazines and phthalocyanines are being studied for their cytotoxic activity as new antitumor drugs [ 52 ].

5-ALA [ 53 ], which is physiologically an intermediate product of heme synthesis, is used and commercially available PSs of the 2nd generation. Clinical use is due to oral bioavailability and a favorable safety profile. 5-ALA is highly selective, mainly accumulating in the MG tissue [ 10 ]. It is approved by the FDA for PDT of keratosis and lfuorescence-guided visualization of tumor tissue during surgical removal of MG [ 10 ]. Photodynamic therapy based on 5-ALA is an efective method of adjuvant treatment of MG. 5-ALA induces protoporphyrin IX (PpIX) formation, what is rational to use during FGS of MG due to the selective capture of photosensitizing PpIX by the tumor and minimal skin sensitization [ 54 ]. However, insuficient accumulation of PpIX may limit the possibility of using FGS and PDT in the marginal areas of gliomas [ 55 ].

Photosensitizer s of the 3rd generation are characterized by increased selectivity to tumor cells, which is achieved due to conjugation with modifiers (nanoparticles and antibodies) [ 10, 46 ]. When developing the 3rd generation PSs, the focus was on creating prodrugs that are activated only inside tumor cells. The goal of the rational design of the 3rd generation PSs is to reduce side efects while optimizing pharmacokinetics and excitation absorption properties to maximize the efective PDT window. New PSs from the groups of polymethine and tricarbocyanine dyes, which have some advantages over compounds of the porphyrin series, are being studied. They are characterized by a light absorption band with a high molar coeficient in the spectrum range of 700‒900 nm. Currently, 3rd generation PSs have not yet been approved for clinical use for PDT in patients.

In vitro and in vivo experimental studies confirmed the eficacy of PDT of brain tumors using 1st and 2nd generation PSs (HpD, mTHPC, sinoporphyrin sodium, ZnPc and Zn (II) phthalocyanines, tetraminephthalocyanine (TAZnPc), 5-AL A, chlorin E6) either alone or in combination with fractionated radiation therapy [ 56 ], cells), which matured, ac tivated and produced sonodynamic therapy [ 57 ], temozolomide (TMZ) interleukin-6, which may be potentially used in cancer chemotherapy (synergistic efect) [ 58 ] or EGFR inhibitors immunotherapy [ 66 ]. [ 59, 60 ]. In particular, the antitumor efect of PDT with PSs accumulation and PDT eficacy were evaluated 5-ALA in SU-DIPG-XIII MG cell cultures in combination in vitro in various glioma lines, primary neurons and with fractionated radiation therapy was shown in vitro astrocytes of rats and in vivo in the healthy brain and [ 56 ]. Phthalocyanines ZnPc and TAZnPc in vitro caused RG2 glioma of Fischer rats [ 67 ]. In vitro studies on the death of GB cells of T98G, MO59, LN229 and rats showed a significant improvement in the survival U87-MG lines by apoptosis, which was accompanied by of primary rat neuronal cells after PDT, in vivo studies caspase-3 activation, loss of morphology and functions showed a decrease in the volume of edema/inaflmmation of mitochondria, integrity of lysosomes, externalization on day 10 after PpIX-mediated PDT, confirming the of phosphatidylserine and DNA fragmentation of tumor neuroprotective efect. Moderate hypothermia increased cells [ 61 ]. Antitumor efects of combining PDT with PpIX fluorescence in the tumor by 5 times and the sinoporphyrin sodium and sonodynamic therapy in average survival time of rats after PDT without afecting vitro in U118 glioma cells were revealed [ 57 ]. Promising normal brain structures [ 67 ]. results were obtained for PDT with chlorin E6 of rat In an in vivo study, fox1 rnu/rnu rats with U87 GB gliomas C6 and 101.8 in vivo [ 62 ]. after intraperitoneal injection of 5-ALA (100 mg/kg) were

Experimental study of PDT in vitro using 2nd interstitially irradiated to the tumor in two regimens: generation PS - photosens (sulfonated aluminum with high (30 mW) or low (4.8 mW) radiation intensity. phthalocyanine) was carried out at the Institute of Higher intensity and fractionation of irradiation caused Neurosurgery in the tissue culture laboratory (Prof. a greater degree of tumor necrosis [ 54 ]. V.D. Rozumenko and Prof. V.M. Semenova). The method of tissue culture was used to obtain the optimal efect Experimental approaches to enhancing the of photodestruction of tumor cells in cultures of the efectiveness of photodynamic therapy transplanted rat brain MG 101.8 and primary human Various preconditioning regimens are used to MG cultures. Simultaneously, in a comparative aspect, enhance the fluorescence of PSs. Thus, selective the reaction of cultured neural cells of the brain of enhancement of PpIX fluorescence and PDT with 5-ALA experimental animals to the efect of PS and laser was achieved by pre-conditioning glioma cells and control irradiation according to diferent schemes was studied. astrocytes with calcitriol for 48 h before incubation with It was shown that laser irradiation with a wavelength 5-ALA. The authors suggest that the combined treatment of 675 nm of cultures of experimental glioma 101.8 of glioma tumor cells with calcitriol using 5-ALA may be pre-incubated in nutrient medium with the addition an efective and selective therapeutic method to improve of photosens (5 μg/ml) causes photodestruction of the quality of PpIX fluorescence induced by 5-ALA [ 55 ]. most tumor cells, which rises with increasing exposure A combination of diferent treatment methods is from 120 to 240‒300 s (subtotal tumor cell damage being investigated to increase the efectiveness of PDT. and pronounced cell loss). Assessment of 24-h efect The synergistic efect of PDT and chemotherapy has of PS on cultures of the normal brain of newborn rats been proved. It has been shown that the drug gefitinib, demonstrated the resistance of neurocytes to PS EGFR inhibitor developed for treatment of breast and accumulation and only weak incorporation of it into lung cancer, can enhance the photodynamic efect in the cytoplasm of some glial cells, which confirms the brain tumor cells through gefitinib-mediated inhibition absence of neurotoxicity when using it [ 26, 27, 63 ]. The of the ATP-binding cassette transporter ABCG2, which results of these studies formed the basis of the clinical prevents the eflux of PS from brain tumor cells and development of PDT regimens in neuro-oncological enhances efect of PDT [ 59 ]. The combined efect of patients [ 29, 64 ]. another EGFR inhibitor, lapatinib, has been also studied.

In the study of the efect of PDT on gliosarcoma cells Its administration 24 h before PDT and for 3‒5 days of the 9L/lacZ line in vitro using photodithazine (PDZ) and after PDT significantly increased PpIX accumulation Biopdi/IRRAD-LED 660 LED light source at a wavelength and the decrease in LD50 after PpIX-mediated PDT in of 660 nm showed 100% tumor cells death at diferent U87 and U87vIII MG cell lines in vitro and increased concentrations of PS, which accumulated mainly in the the survival of U87 and GSC-30 glioma-grafted rats area of nucleus and cytoplasm [ 65 ]. compared with therapy with lapatinib or PDT alone [ 60 ].

Photosens and PDZ at a light dose of 20 J/cm² The combination of TMZ with PDT significantly increased (λex 615‒635 nm) efectively induced cell death of TMZ concentration in glioma tissues, enhanced tumor glioma GL261 and fibrosarcoma MCA205 cells [ 66 ]. cell apoptosis, and increased the average survival rate Photosens was predominantly localized in lysosomes, of rats with transplanted glioma [ 58 ]. and photoirradiation-induced cell death was inhibited One of the markers of tumor vessels in glioma is an by apoptosis inhibitor (zVAD-fmk), ferostatin-1, and extra fibronectin domain A (ED A). The use of antibodies ferroptosis inhibitors (DFO), but not by the necroptosis against ED A fibronectin promoted the accumulation inhibitor necrostatin-1. Instead, PDZ accumulated of PS (F8-SIP) in the microvascular bed of the grafted in the endoplasmic reticulum and Golgi apparatus, glioma SF126 in nude mice [ 68 ]. Subsequent PDT induced and photochemical cell death was inhibited only microvascular stasis and thrombosis with decreased by z-VAD-fmk. Tumor cells dying due to photosens functional density and decreased glioma growth with or PDZ-induced photochemical reaction released restoration of microcirculation 4 days after treatment. calreticulin, HMGB1 and ATP and were effectively Repeated use of PDT prevented microvascular recovery absorbed by BMDCs (bone-marrow derived dendritic and resulted in a prolonged antiglioma efect [ 68 ].

The nature and role of ROS-mediated damage [ 11 ] involving 27 patients with newly diagnosed or to tumor cells as a result of PDT have not been fully recurrent primary parenchymal brain tumors, among elucidated. In this regard, the response of nitric oxide the 22 patients who were subsequently involved in the (NO) signaling pathways in tumor cells is worth attention, study cohort, the 12-month total survival and 6-month since the growth and proliferation of MG stem cells progression-free survival after surgery and PDT were depend on the activation of inducible NO synthase (iNOS) 95.5 and 91.0%, respectively, in 13 patients with newly [ 69 ], and iNOS inhibitors can play a role in increasing diagnosed GB - 100%. Side efects on the skin that can PDT eficiency [ 70 ]. Thus, iNOS/NO of U87 glioblastoma be associated with the use of talaporfin sodium were cells counteracts the cytotoxic efects of non-ionizing reported in 7.4% of patients. Skin photosensitivity test PDT and stimulates the growth and migration activity results were relatively mild and completely disappeared of surviving tumor cells [ 71 ], and iNOS-derived NO in within 15 days after administration of photosensitizer in GB cells causes resistance to 5-ALA-based PDT [ 72 ]. all patients [ 11 ].

It is also known that tight intercellular junctions Two photosensitizing agents have been studied (GJIC), formed by connexin (Cx) 43, can improve pr imar ily in MG: p or f imer s o dium (Photof r in, "death signal" transmission between cells, increasing FDA-approved for the treatment of esophageal cancer) the cytotoxic efect of chemotherapeutic agents, gene [ 75 ] and 5-ALA (FDA-approved for imaging of GB cells therapy, and PDT [ 73 ]. Photodynamic therapy was more during surgery) [ 13 ]. In clinical trials, PDT was usually efective in Cx43-transfected HeLa cells and Cx43- combined with other therapeutic interventions or expressing U87 glioma cells at high cell density. This manipulations. efect was significantly suppressed in the absence of Simultaneous use of fluorescence-guided surgery Cx43 expression or Cx43-GJIC blockage. In addition, (FGS) and PDT allows both imaging of tumor cells and in the presence of Cx43-GJIC, photofrin-PDT reduced selectively destruction of them [ 34 ]. For intraoperative the mass of tumor xenografts in vivo. Increased PDT and postoperative PDT, special devices based on fibereficiency associated with Cx43-GJIC was correlated with optic guided technique have been developed. Regardless ROS-mediated stress signaling pathways, Ca2+ and lipid of PDT, PSs are used for auxiliary detection of the tumor peroxidation [ 73 ]. Therefore, strategies to enhance Cx43 boundaries in order to maximize its removal during FGS expression or Cx43-GJIC function may increase tumor (5-ALA, fluorescein, indocyanine green, endogenous cell sensitivity to PDT and treatment eficacy. lfuorophores) [ 76 ].

One of the main caveats of PDT is that the laser Clinical studies of photodynamic therapy beam must reach the cells containing the sensitizing As mentioned above, PDT as a direction of tumor agent. Commonly used lasers have a wavelength range treatment has been evolving for several decades. One of 630–690 nm, and the penetration depth rarely of the first reports on PDT of glioma tissue in 1980 exceeds 5.0 mm in most tissues [ 77 ]. However, the predicted that further improvement of the technique efects of PDT may be greater, as MRI data show the would facilitate better penetration into tumor tissue and mean penetration depth of 9.1 mm [ 78 ] and postmortem more radical destruction of glioma cells [ 16 ]. Although histopathological analysis revealed penetration up to a large number of PDT trials have been conducted for 12.7 mm [ 79 ]. However, deeply located malignant cells the treatment of malignant brain tumors, most of them remain completely unafected. In addition, according are uncontrolled phase I or II studies, which difer to [ 78 ], 75% of cases of continued tumor growth/ greatly in their design (choice and dose of PS, choice recurrence were observed in the PDT area, which casts and dose of photoirradiation, method of irradiation and doubt on the long-term efect even in the resection use of additional techniques, choice and the formation of cavity. However, given the clinical availability of PSs and groups of patients according to diagnoses, indicators and the low risk level of this therapy, further studies of their interpretation of fndings, etc.), which makes the overall use in GB are needed [ 80 ]. analysis and assessment of treatment efectiveness A small number of clinical trials of PDT (porfimer extremely dificult. sodium, 5-ALA) in the treatment of MG have been

In 1996, the results of open phase I and II clinical conducted, of which several have been discontinued or trials, which involved more than 310 patients with withdrawn (n=3) or their status is unknown (n=3), 4 are primary or recurrent malignant tumors, were published. ongoing [ 81 ].

Patients received PDT after tumor resection. A clear In a phase III trial using porfimer sodium for the tendency was found to increase the average survival treatment of GB (n=27) [ 82 ], patients who received rate of patients after surgical removal and single PDT ifve daily PDT sessions with an implanted laser in the [ 18 ]. Based on the clinical experience of PDT for the resection cavity had better survival compared to those treatment of gliomas in more than 350 patients using who did not receive PDT, but patients who received PDT HpD (since 1987) and borated porphyrin (since 2001), a underwent resection with the help of FGS, which in itself group of researchers from the Royal Melbourne Hospital improves treatment outcomes [ 13 ]. In addition, 15% of reported an overall survival of patients with rediagnosed patients in both groups received TMZ, which limited the and recurrent GB 28.0 and 40.0% after 2 years and 22.0 generalizability of the study results. and 34.0% after 5 years. A meta-analysis of data from Another trial (phase I) used 5-ALA for FGS and more than 1,000 patients with MG showed that median intraoperative PDT in 20 patients with recurrent GB survival after PDT for rediagnosed and recurrent MG [ 78 ]. After 5-ALA FGS, 1‒4 cylindrical laser difusers was 16.1 and 10.3 months, respectively [ 74 ]. According were inserted into the resection cavity and PDT was to the results of a phase II clinical trial (JMA-IIA00026, performed under general anesthesia for 60 min (635 Japan) of intraoperative PDT with talaporfin sodium nm, difuser 200 mW/cm) with continuous irrigation to maintain optical clarity and ventilation with 100% after the first relapse, 9 (20.5%) after the second, oxygen. According to MRI performed after 24 hours, and another 9 (20.5%) after the third or subsequent 14 days and every 3 months thereafter, infection at the relapse. The mean iPDT target volume was 3.34 cm3 surgical site was noted in 1 patient was after 6 months (0.50–22.8 cm3). Severe neurological deterioration as the only side efect. In 16 (80%) of 20 cases, cytotoxic lasted more than 6 weeks in only one patient. Median edema along the resection margin was detected, which time-to-treatment-failure (TTF) was 7.1 months (95% regressed or disappeared after 4–5 months. The median CI 4.4–9.8 months), median post-relapse survival progression-free survival was 6 months (95% confidence 13.0 months (95% CI ‒ 9.2–16.8 months). The 2-year interval (CI) – 4.8–7.2 months), which is comparable and 5-year post-relapse survival rates were 25.0 and to the standard treatment for recurrent GB [ 83 ] and 4.5%, respectively. Response to treatment was not confirms the innovativeness and safety of FGS and PDT significantly associated with patient characteristics, combination with the use of 5 -ALA as a method of local treatment-related factors, or molecular markers. The tumor control promising for tumor progression-free promising result and acceptable risk profile deserve survival [ 78 ]. further prospective evaluation, particularly to determine

Preliminary results of a clinical study (phase I) the mechanisms and prognostic factors of a favorable Intraoperative Photodynamic Therapy of GBM (INDYGO) response to the treatment of MG [ 85 ]. clinical trial (NCT03048240) involving 10 patients with In the study [ 86 ] the efectiveness of PDT with primary GB, started in 2017 at the University Hospital talaporfin sodium in patients operated on for recurrent of Lille (France), proved the safety and feasibility of GB was retrospectively evaluated. The average relapseusing PDT based on 5-ALA in primary GB [ 80 ]. The free survival in patients with PDT (n=72) and the control standardized treatment approach involved maximal group (n=38) after the second surgery was 5.7 and 2.2 resection (close to total or gross total tumor resection) months, respectively (p=0.0043), the average overall under 5-ALA FGS control followed by intraoperative PDT. survival after the second surgery was 16, 0 and 12.8 In the postoperative period, patients received adjuvant months, respectively (p=0.031). In the PDT group, there therapy (according to the Stupp protocol). Further was no significant diference in relapse-free and overall follow-up included clinical examinations and brain MRI survival between patients previously diagnosed with GB every 3 months until tumor progression and/or death. and those with malignant transformation to GB from less No unacceptable or unexpected toxic or serious side malignant glioma variants. Therefore, the use of PDT efects were reported. At the time of the interim analysis, in the progression of GB may have potential survival the 12-month recurrence-free survival rate was 60% advantages, and its efectiveness is independent on (median 17.1 months), the 12-month overall survival pre-recurrence pathology [ 86 ]. rate was 80% (median 23.1 months) [ 80 ]. Therefore, In another study [ 87 ] the clinical and surgical data intraoperative administered PDT with 5-ALA immediately of the treatment of patients with primary GB, divided after maximal resection as adjunctive therapy in primary into three groups were compared: operated on with the GB is safe and may help reduce the risk of recurrence use of 5-ALA FGS followed by BCNU plates implantation by targeting residual tumor cells in the resection cavity. (n=20, group I), those operated on with implantation

Other ongoing studies are using stereotactic PDT in of BCNU plates (n=42, group II), operated on with the primary (NCT03897491) and recurrent (NCT04469699) use of 5-ALA FGS (n=59 patients, group III). In group GB, as well as intraoperative and interstitial PDT (iPDT) I patients, life expectancy exceeded 3 years in 15% in primary GB (NCT04391062, NCT03897491). of cases, the median relapse-free and overall survival

In the study [ 84 ], MRI results were analyzed in was 11 and 22 months, respectively. Patients implanted 11 patients with primary GB after iPDT. The procedure with BCNU plates had a significantly higher survival rate implied the use of 5-ALA for selective metabolism of after tumor removal with 5-ALA FGS (22 months with protoporphyrin IX (PpIX) in tumor cells and irradiation 5-ALA (Group I) vs. 18 months without 5-ALA (Group II), using interstitially located optical cylindrical difuser p<0.0001). Patients in group I had an increased survival ifbers (2‒10 fibers, difuser length 2-3 cm, 200 mW/cm, compared to group III (22 months with BCNU plates vs. 635 nm, 60 min irradiation), as well as intraoperative 21 months without BCNU plates, p=0.0025). Plate-related spectral online monitoring. MRI results indicated adverse events were not significantly increased with PDT-induced hemoglobin deoxygenation, methemoglobin 5-ALA FGS (20% with 5-ALA and 19% without 5-ALA) and formation and were consistent with in vitro experiments. did not afect survival outcome. This study confirms the

The results of a retrospective study of the Medical synergistic efect in patients with primary GB of 5-ALA Clinic of the University of Munich (Germany) on the FGS technology and BCNU plates implantation without analysis of the risk profile of iPDT using induced 5-ALA increasing the incidence of adverse efects [ 87 ]. PpIX as a cytotoxic PS in a large monocentric cohort of patients with local tumor recurrence after standard Therefore, PDT as a treatment method has a clearly therapy (who were consecutively treated between 2006 focused efect aimed at selectively increasing the tumor and 2018) proved its promise in local recurrences of destruction area during surgery, which improves the MG [ 85 ]. 47 patients were treated, 44 of them were survival time and quality of life of patients with MG. evaluated retrospectively. Recurrent gliomas included The main advantage of the PDT method is its high 37 GB (WHO grade 4) and 7 anaplastic astrocytomas eficiency, organ-sparing technique and low systemic (WHO grade 3). Methylated O-6-methylguanine-DNA toxicity. In published studies of PDT efectiveness, there methyltransferase (MGMT) was detected in 30 (68.2%) is no information on the development of resistance to tumors, and wild-type isocitrate dehydrogenase (IDH) multiple PDT sessions, which suggests the possibility in 29 (65.9%). 26 (59.1%) patients received treatment of re-treatment of tumor cells not removed during surgery. The accumulated experience of PDT application in oncological diseases suggests that PDT is one of the most effective methods of stopping the local spread of tumor cells, but it is necessary to optimize radiation doses, the number of treatment procedures and the intervals between them. The efectiveness of photodynamic damage to a sensitized cell is determined by the intracellular concentration of the sensitizer, its localization in the cell, photochemical activity, and the dose of laser irradiation. It is necessary to carry out fundamental research with the development of new experimental models of PDT, in which multiple efects on the tumor will be applied.

Information disclosure Conflict of interest The authors declare no conflict of interest.

Ethical approval

This article is a literature review, therefore no ethics committee approval was required.

Funding The study was conducted without sponsorship.