Antimicrobial photodynamic inactivation (aPDI) and antimicrobial blue light (aBL) are considered low-risk treatments for the development of bacterial resistance and/or tolerance due to their multitargeted modes of action. In this study, we assessed the development of Staphylococcus aureus tolerance to these phototreatments. Reference S . aureus USA300 JE2 was subjected to 15 cycles of both sub-lethal aPDI (employing an exogenously administered photosensitizer (PS), i.e., rose Bengal (RB)) and sub-lethal aBL (employing endogenously produced photosensitizing compounds, i.e., porphyrins). We demonstrate substantial aPDI/aBL tolerance development and tolerance stability after 5 cycles of subculturing without aPDI/aBL exposure (the development of aPDI/aBL tolerance was also confirmed with the employment of clinical MRSA and MSSA strain as well as other representatives of Gram-positive microbes, i.e. Enterococcus faecium and Streptococcus agalactiae ). In addition, a rifampicin-resistant (RIF R ) mutant selection assay showed an increased mutation rate in S . aureus upon sub-lethal phototreatments, indicating that the increased aPDI/aBL tolerance may result from accumulated mutations. Moreover, qRT-PCR analysis following sub-lethal phototreatments demonstrated increased expression of umuC , which encodes stress-responsive error-prone DNA polymerase V, an enzyme that increases the rate of mutation. Employment of recA and umuC transposon S . aureus mutants confirmed SOS-induction dependence of the tolerance development. Interestingly, aPDI/aBL-tolerant S . aureus exhibited increased susceptibility to gentamicin (GEN) and doxycycline (DOX), supporting the hypothesis of genetic alterations induced by sub-lethal phototreatments. The obtained results indicate that S . aureus may develop stable tolerance to studied phototreatments upon sub-lethal aPDI/aBL exposure; thus, the risk of tolerance development should be considered significant when designing aPDI/aBL protocols for infection treatments in vitro and in clinical settings.

The aim of this paper was to provide the physico-chemical characterization of a key process leading to amplification of the antitumor effect of antibiotic Doxorubicin (Dox) in vivo and in vitro and occurring at the molecular level through complexation with C60 fullerene. A wide range of physico-chemical tools was used such as UV/Vis and NMR spectroscopies, atomic force microscopy, isothermal titration calorimetry and zeta-potential methods. The unusual thermodynamic behavior of the complexation process was reported, featuring unexpected and, to a certain extent, contradictory experimental observations. The explanation of the obtained results was proposed resulting in creation of a general view on aromatic drug binding with C60 fullerene. Based on these results some important practical outcomes for anticancer therapy were formulated.

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A novel nano-formulation of the anticancer drug cisplatin (Cis) with C 60 fullerene (C 60 +Cis complex) was developed, demonstrating enhanced cytotoxic activity towards tumor cell lines in vitro n comparison to Cis alone. The enhanced proapoptotic activity of the novel complexes was found to be tightly connected with their unique capability to circumvent cancer drug resistance in vitro, as revealed by investigation of human leukemia cells HL-60 together with their sublines resistant towards doxorubicin (HL-60/adr, multidrug resistance protein-1=MRP-1=ABCC1 overexpressing) and vincristine (HL-60/vinc, P-glycoprotein=P-gp=ABCB1 overexpressing). The enhanced anticancer activity of the developed С 60 +Cis complexes was also confirmed in vivo on male C57BL/6J mice bearing Lewis lung carcinoma, effectively inhibiting tumor growth and formation of metastases in comparison to free single Cis. For better understanding of molecular mechanisms underlying the potential ability of the С 60 +Cis complexes to circumvent cancer drug resistance, a molecular docking study was conducted. This analysis demonstrated the potential capability of C 60 fullerene to form van der Waals interactions with potential binding sites of P-gp, MRP-1and MRP-2 (ABCC2) molecules, with maximum affinity to MRP-2. The observed phenomenon might indicate the mechanism how the C 60 +Cis complex bypasses drug resistance of cancer cells by direct binding to ABC transporter proteins. Additionally, the results of Ames mutagenicity test demonstrated that immobilization of Cis on С 60 fullerene significantly diminishes mutagenic activity of Cis and may reduce the probability of secondary neoplasms induction. Concluding, the synthesized C 60 +Cis complex effectively induces cancer cell death in vitro and inhibits tumor growth in vivo, circumventing cancer cell resistance to chemotherapy due to the specific affinity of C 60 fullerene towards ABC-transporter proteins. The obtained results indicate the C 60 +Cis complex as a promising novel chemotherapeutic agentespecially for treatment of drug-resistant tumors.

Caffeine (CAF) is capable of interacting directly with several genotoxic aromatic ligands by stacking aggregation. Formation of such hetero-complexes may diminish pharmacological activity of these ligands, which is often related to its direct interaction with DNA. To check these interactions we performed three independent series of spectroscopic titrations for each ligand (ethidium bromide, EB, and propidium iodine, PI) according to the following setup: DNA with ligand, ligand with CAF and DNA-ligand mixture with CAF. We analyzed DNA-ligand and ligand-CAF mixtures numerically using well known models: McGhee-von Hippel model for ligand-DNA interactions and thermodynamic-statistical model of mixed association of caffeine with aromatic ligands developed by Zdunek et al. (2000).Based on these models we calculated association constants and concentrations of mixture components using a novel method developed here. Results are in good agreement with parameters calculated in separate experiments and demonstrate de-intercalation of EB and PI molecules from DNA caused by CAF.

The specific features of structural self-organization of C60 fullerene and antitumor drug cisplatin (Cis) in physiological solution (0.9% NaCl) have been investigated by means of small-angle neutron scattering, scanning electron and atomic force microscopies, as well as isothermal titration calorimetry, dynamic light scattering and UV-Vis spectroscopy. The formation of C60 + Cis complexes, has been reported, unveiling the mechanism of medico-biological synergy observed during administration of the mixture of these drugs.

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Food-borne heterocyclic aromatic amines (HCAs) are known mutagens and carcinogens present especially in Western population diet, which contains large amount of meat and its products. HCAs are capable of interacting with DNA directly through the formation of covalent adducts, however this process requires biological activation in liver, mainly by cytochrome P450 enzymes. This process may produce mutations and in consequence may contribute to the development of cancer. However, there are many studies showing that several biologically active aromatic compounds (BACs) may protect against genotoxic effects of HCAs. Direct interactions and noncovalent heterocomplexes formation may be one of the most important mechanisms of such protection. This work describes several BACs present in human diet, which are capable of molecular complexes formation with HCAs and protect cells as well as whole organisms against HCAs action.