Relative to non-treated control, over 70% of the cells showed a loss of viability 72 h after PDT with TuBB-9 PICELs. a photoactivatable agent followed by encapsulation in non-cationic liposomes. Nucleolar localization of the PICELs was confirmed by confocal imaging. Photodynamic activation with PICELs specifically killed pKi-67 positive cancer cells both in monolayer and in 3D cultures of OVCAR-5 cells with the antibody TuBB-9 targeting a physiologically active form of pKi-67 but not with MIB-1, directed to a different epitope. This is the first demonstration of: – 1. the exploitation of Ki-67 as a GSK5182 molecular target for therapy and – 2. specific delivery of an antibody to the nucleolus in monolayer cancer cells and in an 3D model system. In view of the ubiquity of pKi-67 in proliferating cells in cancer and the specificity of targeting in 3D multicellular acini, these findings are promising and the approach merits further investigation. INTRODUCTION Targeted brokers that block or interrupt specific pathways intricately involved in tumor growth and cancer cell proliferation, hold promise for effective, patient customized treatment. The choice of the molecular target around which to design molecularly targeted therapies then becomes a key factor. In that context, the nuclear protein Ki-67 (pKi-67) is usually a compelling candidate. It is strongly expressed in proliferating cells (1, 2) and is an established prognostic indicator for the assessment of cell proliferation in biopsies from cancer patients (3). Despite the important role of pKi-67 as a diagnostic marker, three challenges have limited its suitability as a target for cancer therapy: 1.) Lack of targeting moieties that specifically recognize the physiologically active form of pKi-67; 2.) Lack of effective vehicles for intracellular delivery that effectively transport the targeting moiety to the appropriate sub cellular site. 3.) The inability to link the targeting mechanism with an externally activatable intervention strategy for additional specificity that neutralizes the active state of pKi-67. We address these challenges using a multifunctional (fluorescence and therapy) nanotechnology platform for intracellular delivery of TuBB-9, a recently developed monoclonal antibody (4) (Mab) that specifically recognizes a physiologically active form of pKi-67, in combination with a photoactivatable agent in a photochemistry-based approach called photodynamic therapy (PDT). PDT involves the excitation of light activatable chemicals to trigger site-specific photochemistry for localized GSK5182 damage via active molecular species because of which very specific target damage can be achieved (5, 6, 7). In this study we show the first antibody-targeted inactivation of a nuclear protein in large cell populations. This was made feasible through nanotechnology derived liposomal delivery of an antibody. We subsequently present the first evidence that inactivation of the proliferation marker pKi-67 leads to cell death in proliferating cells only. Figure 1 shows the schema of the targeting strategy. TuBB-9 antibody is usually conjugated to a PDT agent to yield a photoimmunoconjugate (PIC), which is usually then encapsulated into non-cationic PEGylated liposomes to provide PIC encapsulating liposomes (PICELs). These are taken up by ovarian cancer cells upon incubation by a combination of endocytic and liposome fusion processes. A fraction of the liposomes release the Mab into the cytoplasm of the cancer cell. Within 24 h the Mab relocalizes into the nucleus consistent with earlier reports using single cell injections (8). The putative relocalization mechanism involves the cotransport of the Mab with newly synthesized Ki-67 protein, or binding GSK5182 to pKi-67 during mitosis after breakdown of the nuclear envelope. Light irradiation triggers inactivation of the Ki-67 protein and cell death of the ovarian cancer cells. Open in a separate window Physique 1 Schema showing proposed mechanism of nanotechnology mediated sub-cellular antibody delivery and subsequent light inactivation of pKi-67 leading to ovarian cancer cell death. TuBB-9 antibody is usually conjugated to FITC to yield a photoimmunoconjugate (PIC), which is usually then encapsulated into non-cationic PEGylated liposomes to provide PIC encapsulating liposomes (PICELs). (MIB-1-FITC conjugates are also encapsulated in liposomes and used as control GSK5182 but are not shown in the scheme). These PICELs are internalized by OVCAR-5 cells and a fraction of the TuBB-9-FITC conjugates are released into the cytoplasm. Within 24 h the conjugates relocalize into the nucleus. Proposed mechanisms for this relocalization are the cotransport of the antibody-FITC-conjugates with the Ki-67 protein, after its synthesis in the cytoplasm, or binding to pKi-67 during mitosis after breakdown of the nuclear envelope. Light irradiation inactivates the Ki-67 protein and is followed by cell death of the ovarian cancer cells. Liposomes are self-assembling spherical vesicles made of lipids and have been extensively investigated for drug delivery in cancer as well as non-cancer applications (9). Several CCDC122 GSK5182 liposomal drugs have already been approved for clinical use. The drugs.