Neal administration in disease-bearing mice, whereas activation of the PIC is not observed in the “no tumor” control mice (scale bars are 100 m). B. Peritoneal distribution of BPD fluorescence in mice with disseminated ovarian tumors administered with free BPD (top) or the activatable Cetuximab-BPD PIC. The PIC (bottom) demonstrates selectivity and little activation at disease-free organs, such as the colon (white dotted line), as compared to the non-specific binding of free BPD (top). Figure adapted from Spring et al [146].http://www.thno.orgTheranostics 2016, Vol. 6, IssueZheng very recently published a study presenting the compelling efficacy of a multi-MMP PMB with proven in vivo efficacy against vertebral metastases [150]. Treatment selectivity at such critical physiological sites is of the utmost importance, where preservation of the nervous system is a considerable challenge. The multi-MMP peptidic substrate GPLGLARK was flanked as before by the NIR PS pyropheophorbide and BQH3. PDT treatment using the MMP molecular beacon reduced tumor growth in vertebrate metastasis rat model by approximately 2-fold, significantly reduced numbers of tumor cells and osteoclasts, and increased the number of apoptotic cells, as compared to the respective controls.zo[a]phenothiazinium chloride (EtNBS-COOH). Conjugation of two EtNBS molecules each to cephalosporin resulted in a 5-fold quenching of the PS. When cleaved by -lactamase expressed by methicillin-resistant Staphylococcus Aureus (MRSA), the PSs were spatially separated and the fluorescence was dequenched. The EtNBS cleavage products were also capable of exerting a 76-96 photodynamic reduction in viability of multiple AZD3759 web clinical MRSA strains following irradiation. A major limitation of cleavable probes is their off-target non-specific cleavage or hydrolysis, which renders them ineffective and reduces the signal-to-noise ratio. Furthermore, in the context of deep tissue-PDT for cancer, sufficient intratumoral concentrations of small molecular weight probes can be limited by suboptimal pharmacokinetics, which may necessitate their improved delivery by multiple means, such as PEGylation [153]. Without altering the probe to promote cellular internalization, photodynamic molecular beacons are also restricted to extracellular activation, given that the cleavage product with PS is cell-permeable. Alternatively, intracellular cytosolic targets required for the activation of molecular probes can be reached through the conjugation of the probe to a cell penetrating peptide, or by internalization using nano-sized delivery vehicles, all of which are hindered their own limitations [154]. Stacking of hydrophobic macrocyclic photosensitizers with each other or with their respective FRET pairs can also limit the extent of dequenching following target-specific cleavage, and therefore requires the careful selection of PSs with appropriate opto-chemical properties.Non-cleavable probesAlthough not cleavable, an elegant alternative system is the more conventional oligonucleotidebased molecular beacon platform, typically utilized as genetic biosensors. More recently, the oligonucleotide molecular beacon technology was described in a photodynamic system, where complimentary nucleic acid binding to target-specific DNA sequences activates the photoactivity of the probe [151]. A 3′ pyropheophorbide PS and 5′ BlackBerry quencher phosphoramidite molecules, either as a CEP-37440 solubility monomer, duplex or triplex, flanked the nucleic acid.Neal administration in disease-bearing mice, whereas activation of the PIC is not observed in the “no tumor” control mice (scale bars are 100 m). B. Peritoneal distribution of BPD fluorescence in mice with disseminated ovarian tumors administered with free BPD (top) or the activatable Cetuximab-BPD PIC. The PIC (bottom) demonstrates selectivity and little activation at disease-free organs, such as the colon (white dotted line), as compared to the non-specific binding of free BPD (top). Figure adapted from Spring et al [146].http://www.thno.orgTheranostics 2016, Vol. 6, IssueZheng very recently published a study presenting the compelling efficacy of a multi-MMP PMB with proven in vivo efficacy against vertebral metastases [150]. Treatment selectivity at such critical physiological sites is of the utmost importance, where preservation of the nervous system is a considerable challenge. The multi-MMP peptidic substrate GPLGLARK was flanked as before by the NIR PS pyropheophorbide and BQH3. PDT treatment using the MMP molecular beacon reduced tumor growth in vertebrate metastasis rat model by approximately 2-fold, significantly reduced numbers of tumor cells and osteoclasts, and increased the number of apoptotic cells, as compared to the respective controls.zo[a]phenothiazinium chloride (EtNBS-COOH). Conjugation of two EtNBS molecules each to cephalosporin resulted in a 5-fold quenching of the PS. When cleaved by -lactamase expressed by methicillin-resistant Staphylococcus Aureus (MRSA), the PSs were spatially separated and the fluorescence was dequenched. The EtNBS cleavage products were also capable of exerting a 76-96 photodynamic reduction in viability of multiple clinical MRSA strains following irradiation. A major limitation of cleavable probes is their off-target non-specific cleavage or hydrolysis, which renders them ineffective and reduces the signal-to-noise ratio. Furthermore, in the context of deep tissue-PDT for cancer, sufficient intratumoral concentrations of small molecular weight probes can be limited by suboptimal pharmacokinetics, which may necessitate their improved delivery by multiple means, such as PEGylation [153]. Without altering the probe to promote cellular internalization, photodynamic molecular beacons are also restricted to extracellular activation, given that the cleavage product with PS is cell-permeable. Alternatively, intracellular cytosolic targets required for the activation of molecular probes can be reached through the conjugation of the probe to a cell penetrating peptide, or by internalization using nano-sized delivery vehicles, all of which are hindered their own limitations [154]. Stacking of hydrophobic macrocyclic photosensitizers with each other or with their respective FRET pairs can also limit the extent of dequenching following target-specific cleavage, and therefore requires the careful selection of PSs with appropriate opto-chemical properties.Non-cleavable probesAlthough not cleavable, an elegant alternative system is the more conventional oligonucleotidebased molecular beacon platform, typically utilized as genetic biosensors. More recently, the oligonucleotide molecular beacon technology was described in a photodynamic system, where complimentary nucleic acid binding to target-specific DNA sequences activates the photoactivity of the probe [151]. A 3′ pyropheophorbide PS and 5′ BlackBerry quencher phosphoramidite molecules, either as a monomer, duplex or triplex, flanked the nucleic acid.
