Urokinase-plasminogen-activator sensitive polymeric photosensitizer prodrugs: design, synthesis and in vitro evaluation

Double-PEGylated Cyclopeptidic Photosensitizer Prodrug Improves Drug Uptake from In Vitro to Hen's Egg Chorioallantoic Membrane Model

Cyclopeptidic photosensitizer prodrugs (cPPPs) are compounds designed to specifically target overexpressed hydrolases such as serine proteases, resulting in their specific activation in close proximity to tumor cells. In this study, we explored a series of conjugates that can be selectively activated by the urokinase plasminogen activator (uPA). They differ from each other by their pheophorbide a (Pha) loading, their number of PEG chains and the eventual presence of black hole quenchers (BHQ3). The involvement of a peptidic linker between the drugs and the cyclopeptidic carrier allows specific cleavage by uPA. Restoration of the photophysical activity was observed in vitro on A549 lung and MCF7 breast cancer cells that exhibited an increase in red fluorescence emission up to 5.1-fold and 7.8-fold, respectively for uPA-cPPQ_2+2/5. While these cPPP conjugates do not show dark toxicity, they revealed their phototoxic potential in both cell lines at 5 µM of Pha_eq and a blue light fluence of 12.7 J/cm² that resulted in complete cell death with almost all conjugates. This suggests, in addition to the promising use for cancer diagnosis, a use as a PDT agent. Intravenous injection of tetrasubstituted conjugates in fertilized hen eggs bearing a lung cancer nodule (A549) showed that a double PEGylation was favorable for the selective accumulation of the unquenched Pha moieties in the tumor nodules. Indeed, the diPEGylated uPA-cPPP_4/5² induced a 5.2-fold increase in fluorescence, while the monoPEGylated uPA-cPPP_4/5 or uPA-cPPQ_2+2/5 led to a 0.4-fold increase only.

Catch and Release Photosensitizers: Combining Dual-Action Ruthenium Complexes with Protease Inactivation for Targeting Invasive Cancers

Dual action agents containing a cysteine protease inhibitor and Ru-based photosensitizer for photodynamic therapy (PDT) were designed, synthesized, and validated in 2D culture and 3D functional imaging assays of triple-negative human breast cancer (TNBC). These combination agents deliver and release Ru-based PDT agents to tumor cells and cause cancer cell death upon irradiation with visible light, while at the same time inactivating cathespin B (CTSB), a cysteine protease strongly associated with invasive and metastatic behavior. In total five Ru-based complexes were synthesized with the formula [Ru(bpy)₂(1)](O₂CCF₃)₂ (3), where bpy = 2,2'-bipyridine and 1 = a bipyridine-based epoxysuccinyl inhibitor; [Ru(tpy)(NN)(2)](PF₆)₂, where tpy = terpiridine, 2 = a pyridine-based epoxysuccinyl inhibitor and NN = 2,2'-bipyridine (4); 6,6'-dimethyl-2,2'-bipyridine (5); benzo[ i]dipyrido[3,2- a:2',3'- c]phenazine (6); and 3,6-dimethylbenzo[ i]dipyrido[3,2- a:2',3'- c]phenazine (7). Compound 3 contains a [Ru(bpy)₃]²⁺ fluorophore and was designed to track the subcellular localization of the conjugates, whereas compounds 4-7 were designed to undergo either photoactivated ligand dissociation and/or singlet oxygen generation. Photochemical studies confirmed that complexes 5 and 7 undergo photoactivated ligand dissociation, whereas 6 and 7 generate singlet oxygen. Inhibitors 1-7 all potently and irreversibly inhibit CTSB. Compounds 4-7 were evaluated against MDA-MB-231 TNBC and MCF-10A breast epithelial cells in 2D and 3D culture for effects on proteolysis and cell viability under dark and light conditions. Collectively, these data reveal that 4-7 potently inhibit dye-quenched (DQ) collagen degradation, whereas only compound 7 causes efficient cell death under light conditions, consistent with its ability to release a Ru(II)-based photosensitizer and to also generate ¹O₂.

Enhanced prostate cancer targeting by modified protease sensitive photosensitizer prodrugs

Prodrugs combining macromolecular delivery systems with site-selective drug release represent a powerful strategy to increase selectivity of anticancer agents. We have adapted this strategy to develop new polymeric photosensitizer prodrugs (PPP) sensitive to urokinase-like plasminogen activator (uPA). In these compounds (to be referred to as uPA-PPPs) multiple copies of pheophorbide a are attached to a polymeric carrier via peptide linkers that can be cleaved by uPA, a protease overexpressed in prostate cancer (PCa). uPA-PPPs are non-phototoxic in their native state but become fluorescent and produce singlet oxygen after uPA-mediated activation. In the present work, we studied the influence of side-chain modifications, molecular weight, and overall charge on the photoactivity and pharmacokinetics of uPA-PPPs. An in vitro promising candidate with convertible phototoxicity was then further investigated in vivo. Systemic administration resulted in a selective accumulation and activation of the prodrug in luciferase transfected PC-3 xenografts, resulting in a 4-fold increase in fluorescence emission over time. Irradiation of fluorescent tumors induced immediate tumor cell eradication as shown by whole animal bioluminescence imaging. PDT with uPA-PPP could therefore provide a more selective treatment of localized PCa and reduce side effects associated with current radical treatments.

Long-distance energy transfer photosensitizers arising in hybrid nanoparticles leading to fluorescence emission and singlet oxygen luminescence quenching

This paper presents energy transfer occurring in small organically modified core-shell nanoparticles (core lanthanide oxide, shell polysiloxane) (diameter < 10 nm) conjugated with photosensitizers designed for photodynamic therapy applications. These nanoparticles covalently encapsulate a photosensitizing PDT drug in different concentrations. Stable dispersions of the nanoparticles were prepared and the photophysical properties of the photosensitizers were studied and compared to those of the photosensitizers in solution. Increasing the photosensitizer concentration in the nanoparticles was not found to cause any changes in the absorption properties while fluorescence and singlet oxygen quantum yields decreased. As a possible explanation, we have suggested that both long distance energy transfer such as FRET and self-quenching could occur into the nanoparticles. A simple "trend" model of this kind of energy transfer complies with results of experiments on steady state fluorescence and singlet oxygen luminescence.

Thrombin-sensitive photodynamic agents: a novel strategy for selective synovectomy in rheumatoid arthritis

Protease-sensitive macromolecular prodrugs have attracted interest for bio-responsive drug delivery to sites with up-regulated proteolytic activities such as inflammatory or cancerous lesions. Here we report the development of a novel polymeric photosensitizer prodrug (T-PS) to target thrombin, a protease up-regulated in synovial tissues of rheumatoid arthritis (RA) patients, for minimally invasive photodynamic synovectomy. In T-PS, multiple photosensitizer units are tethered to a polymeric backbone via short, thrombin-cleavable peptide linkers. Photoactivity of the prodrug is efficiently impaired due to energy transfer between neighbouring photosensitizer units. T-PS activation by exogenous and endogenous thrombin induced an increase in fluorescence emission by a factor of 16 after in vitro digestion and a selective fluorescence enhancement in arthritic lesions in vivo, in a collagen-induced arthritis mouse model. In vitro studies on primary human synoviocytes showed a phototoxic effect only after enzymatic digestion of the prodrug and light irradiation, thus demonstrating the functionality of T-PS induced PDT. The developed photosensitizer prodrugs combine the passive targeting capacity of macromolecular drug delivery systems with site-selective photosensitizer release and activation. They illuminate lesions with pathologically enhanced proteolytic activity and induce cell death, subsequent to irradiation.