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The global spread of bacterial resistance to antibiotics promotes a search for alternative approaches to eradication of pathogenic bacteria. One alternative is using photosensitizers for inhibition of Gram-positive and Gram-negative bacteria under illumination. Due to low penetration of visible light into tissues, applications of photosensitizers are currently limited to treatment of superficial local infections. Excitation of photosensitizers in the dark can be applied to overcome this problem. In the present work, dark antibacterial activity of the photosensitizer Rose Bengal alone and in combination with antibiotics was studied. The minimum inhibitory concentrations (MIC) value of Rose Bengal against S. aureus dropped in the presence of sub-MIC concentrations of ciprofloxacin, levofloxacin, methicillin, and gentamicin. Free Rose Bengal at sub-MIC concentrations can be excited in the dark by ultrasound at 38 kHz. Rose Bengal immobilized onto silicon showed good antibacterial activity in the dark under ultrasonic activation, probably because of Rose Bengal leaching from the polymer during the treatment. Exposure of bacteria to Rose Bengal in the dark under irradiation by electromagnetic radio frequency waves in the 9 to 12 GHz range caused a decrease in the bacterial concentration, presumably due to resonant absorption of electromagnetic energy, its transformation into heat and subsequent excitation of Rose Bengal.

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Peptide conjugates containing somatostatin (SST) cyclic analogs as a targeting moiety are able to deliver chemotherapeutic agents specifically to cancer cells expressing SST receptors (SSTRs), and hence increasing their local efficacy while limiting the peripheral toxicity. Here, we report on the synthesis and biochemical characterization of new SSTR-specific anticancer peptide conjugates, with different anticancer payloads acting through different oncogenic mechanisms to evaluate their biological activities and to provide a comparative study of their drug release profiles. The SSTR2-specific backbone cyclic peptide 3207-86 was chosen for the synthesis of a variety of novel anticancer drug conjugates with a broad drug release capabilities. The N-terminus of 3207-86 was equipped with GABA to generate free amino group available for the conjugation of chlorambucil, Camptothecin (CPT), Combretastatin 4A, ABT-751, and Amonafide through the formation of various biodegradable bonds. The chemo- and biostability/drug release of all the synthetic compounds was investigated at various pHs and in the presence of mouse liver homogenate, respectively. Their selective cytotoxic effect was evaluated on several human cancer cell lines that overexpress SSTR2. Compared with the free drugs, our peptide-drug conjugates exhibited considerable cytotoxic effect on cancer cell lines versus low SSTR2-expressed human embryonic kidney cells. Functional versatility of the conjugates was reflected in the variability of their drug release profiles, whereas the conserved sequence of a selective binding to the SSTR2 likely preserved their binding to the receptor and consequently their favorable toxicity toward targeted cancer cells.

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