## 1 Introduction  
The blood-brain barrier (BBB) is a major hindrance for the effective delivery of therapeutic compounds to the brain [1]. Various strategies to overcome the BBB have been investigated, includingdirect intranasal drug delivery [2], focused ultrasound [3], intra-arterial infusion of mannitol [4], or direct intracranial infusion [5]. Nowadays the photodynamic effect on the BBB is actively discussed as a new strategy for drug brain delivery, especially for post-surgery therapy of glioblastoma multiforme (GBM) [6]. Photodynamic therapy (PDT) is a widely used tool for therapy of GBM [7; 8]. The PDT is based on a laser excitation of photosensizers (porphyrins, chlorins, and many other photosensitive dyes) that is accompanied by producing singlet oxygen (\({}^{1}\)O\({}_{2}\)) which oxidizes biomolecules causing cancer cell apoptosis and/or necrosis through plasma and mitochondrial membrane rupture. Recently, it has been revealed that PDT can also effectively and site-specifically open the BBB [9; 10; 11; 12; 13; 14]. For the first time a targeted disruption of the BBB following a 5-aminolevulenic acid (5-ALA) mediated PDT via the opened skull was shown by [PERSON] et al. in 2008 [9]. Later [PERSON] et al. demonstrated a non-invasive PDT-opening of the BBB for macrophages using a 670 nm laser and aluminum phthalocyanine disulfonate (AlPcS) [10]. In a series of our experimental studies of PDT-5-ALA-opening of the BBB we have analyzed the optimal dose of 635 nm irradiation and 5-ALA, the time window for PDT-opening/closing of the BBB, mechanisms underlying this phenomenon and age differences in PDT-related increase in the BBB permeability, which is consistent with other data [11; 12; 13; 14; 15]. In this work we attempt to answer the question of what kind of photosensitizer might be most effective for PDT-opening of the BBB. Therefore, we analyzed the BBB permeability to high molecular weight molecules using two types of photosensizers (PS) such as 5-ALA and phthalocyanines (PCs) since their application for drug delivery systems has been shown in other studies [16; 17]. Phthalocyanines (PCs) are synthetic dyes that were obtained and described already in 1907 by [PERSON] and [PERSON] [18]. PCs consist of four units of isoinodes bridged by nitrogen atoms and which form one aromatic heterocyclic structure. Main photophysical characteristics of PCs are: absorption spectrum with two important bands--the weak Soret-band located in the UV zone of the spectrum with maximum at 350-360 nm and the Q-band in the red zone of the visible spectrum at around 670-680 nm. The high intensity of the latter band, due to values of the molar extinction coefficient \(1\times 10^{5}\) M\({}^{-1}\) cm\({}^{-1}\) (two orders of magnitude higher than that at most of porphyrins) is one of the main characteristics of these dyes [19]. Photochemical properties of PCs are strongly influenced by the nature of the coordinated central metal ion. Thus, the presence of diamagnetic elements in the central cavity, such as zinc (II), aluminum (III), gallium (III) or silicon, gives them a high triplet quantum yield (\(\Phi_{\text{T}}>0.4\)) with long triplet lifetimes (\(\tau_{\text{T}}>100\) us). Triplet energy states with energy of about 1.2 eV, make them efficient generators of singlet oxygen with values of singlet oxygen quantum yields (SOQY) more than 0.4 [20; 21]. We hypothesize that functionalization of PCs by galactose might be more effective for the PDT-mediated BBB opening due to enhancing the trans-endothelial permeability by galactose via activation of protein kinase C (PKC), a family of kinases vital to intracellular signaling that is a common effect of monosaccharides on vascular endothelium [22; 23]. Our previous results indicate that functionalization of PCs by galactose is more favorable than zinc only due to their chemical properties [24; 25].