As expected, the best NP-associated radioactivity was contained in the vagina and the lower a part of cervicovaginal tract. excess weight) we observed a remarkable improvement MPEP HCl of EC50 of EFV by 20 occasions in the case of A17 strain. imaging and biodistribution showed presence of NP components at 24 and 48h after administration, respectively. Conclusions. Insoluble orthogonal inhibitors of HIV-1 life cycle may be formulated into the non-aggregating ultrasmall NP which are highly efficient against NNRTI-resistant HIV-1 variant. Introduction. Both HIV-1 reverse transcriptase and MPEP HCl integrase are in the beginning present in retroviral particles and play essential functions in the initiation of retroviral life cycle via reverse transcription of viral RNA and integration of double stranded DNA into the host genome MPEP HCl (1, 2). Therefore, both reverse transcriptase and integrase represent the most immediate and feasible drug targets for pre-and post-exposure interventions (3C6). Regrettably, many first- and second- generation non-nucleoside reverse transcriptase (NNRTI) inhibitors of HIV replication machinery as well as inhibitors of HIV integration are insoluble in water. Improving bioavailability and efficacy of these insoluble anti-retroviral drugs presents important technical difficulties. In particular, Efavirenz (EFV), a World Health Business essential medicine and a highly efficient NNRTI, is practically insoluble in water (solubility in water – 10 mg/L) (7). Elvitegravir (ELV), an FDA approved integrase strand transfer inhibitor (INSTI), is usually water insoluble (solubility <0.3 mg/L) (8). One of potential strategies of improving the bioavailability of these hydrophobic drugs is usually a co-delivery in NP. Nanoparticles (e.g. polymeric mixed micelles) dramatically increase the surface area of insoluble drug cargo and promote potential uptake of the contents of the NP by the cells (9C11). Recent evidence suggests that IFI6 after a HIV-1 challenge tenofovir/ELV NP combinations were 100% efficient in protecting humanized animals for 4 days post subcutaneous administration of the NP (12). The design of the above pre-exposure strategy is based on poly(lactic-co-glycolic acid), PLGA-mediated entrapment of NNRTI mixtures into 200 nm nanoparticles. Another recently reported approach for delivering antiretroviral drugs to mucosal surfaces also included PLGA-based NP, which were stearylamine-stabilized and then incorporated into polymer films for local application onto the mucosal surfaces (13). Poly(lactic-co-glycolic acid) copolymer has a definite advantage over other NP components since it has gained FDA acceptance and nanoformulations made up of PLGA are commonly used (14, 15). These NP benefit from PLGA matrix biodegradability, however, hydrolytic biodegradation with the breakdown of ester bonds eventually results in development of unfavorable charge in these particles (16), which may require additional polymer coatings, incorporation of PEG blocks and other polymer blends or some other option techniques resulting in masking of unfavorable charge (13, 17C21). It has been exhibited that strongly charged NP, which are mucoadhesive (22), have limited distribution and are retained mainly at the epithelial surfaces without penetration through the mucus. In contrast, PEGylated NP (i.e. mucus-penetrating particles), which do not exhibit mucoadhesiveness were found to interact with the entire epithelial lining of intestine and rectum (23). Comparable improved penetration through mucosal barriers was observed when PEGylated NP were tested for intravaginal delivery (23C25). It should be noted that to obtain PLGA NP loaded with a combination of several antiretroviral drugs one has to use multiple time-consuming procedures, such as MPEP HCl sonication for generating water-in-oil emulsions required for interfacial polymer deposition, sequential evaporations and extractions, dialysis and/or centrifugation as well as the use of additional stabilizing di-block surfactants such as.