Development Of Cancer Targeted Multifunctional Nanoprobes For Optical Theranostics

Despite rapid advances in diagnostic and therapeutic techniques, cancer remains one of the most deadly diseases in the world today. There is a strong need to develop new theranostic agents and novel approaches for the accurate cancer detection and targeted therapy. Optics-based fluorescence imaging and photodynamic therapy (PDT) offer excellent prospects for cancer theranostics because of the advantages such as noninvasive features, nonionizing radiation and in-situ diagnosis and treatment. However, some shortcomings of cancer fluorescence imaging and PDT, including the poor targeting, low signal-to-background (SBR) of imaging and tissue penetration of PDT, stepwise and separate imaging and therapy, and lack of self-feedback of therapeutic efficacy, still need to be overcomed for the widespread application in clinic. Recently, the development and integration of chemistry, biology, optics, molecular recognition and nanotechnology hold great promise in cancer theranostics. First, using a "top-down" strategy, various kinds of functional molecules can be designed and synthesized based on cancer-specific biological characteristics to over the disadvantages. Then, using a "bottom-up" strategy, multifunctional nanoprobes constructed from the functional molecules can be synthesized by virtue of the unique physicochemical properties of nonmaterials. Therefore, the strategies of utilizing molecular recognition to enhance the active targeting, "off-on" cancer imaging to increase the SBR, near-infrared (NIR) photosensitizer to increase the tissue penetration of PDT, multifunctional assembly to achieve theranostics, and lysosome as the target to monitor the therapeutic efficacy has been carried out to solve the problems. In this thesis, several cancer targeted multifunctional nanoprobes have been developed for optical theranostics and the works of thesis includes the following sections:1. A Folate and pH-Activatable Rubyrin-Based Cancer Targeted Nanoprobe for Photodynamic TherapySpatiotemporal control of singlet oxygen (1O2) release is a major challenge for PDT against cancer with high therapeutic efficacy and minimum side effects. Here a selenium-rubyrin (NMe2Se4N2)-loaded nanoparticle functionalized with folate (FA) was designed and synthesized as an acidic pH-activatable targeted photosensitizer. The nanoparticles could specifically recognize cancer cells via the FA-FA receptor binding and were selectively taken up by cancer cells via receptor-mediated endocytosis to enter lysosomes, in which NMe2Se4N2 was activated to produce 1O2. The pH-controllable release of 1O2 specially damaged the lysosomes and thus killed cancer cells in a lysosome-associated pathway. The introduction of selenium into the rubyrin core enhanced the 1O2 generation efficiency due to the heavy atom effect, and the substitution of dimethylaminophenyl moiety at meso-position led to the pH-controllable activation of NMe2Se4N2. Under NIR irradiation, NMe2Se4N2 possessed high singlet oxygen quantum yield (ΦΔ) at an acidic pH (ΦΔ= 0.69 at pH 5.0 at 635 nm) and could be deactivated at physiological pH (ΦΔ= 0.06 at pH 7.4 at 635 nm). The subcellular location-confined pH-activatable photosensitization at NIR region and the cancer cell-targeting feature led to excellent capability to selectively kill cancer cells and prevent the damage to normal cells, which greatly lowered the side effects. Through intravenous injection of FA-NMe2Se4N2 nanoparticles in tumor-bearing mice, tumor elimination was observed after NIR irradiation. This work presents a new paradigm for specific PDT against cancer, and provides a new avenue for preparation of highly efficient photosensitizers.2. A Graphene oxide, Photosensitizer and Cathepsin B-Activatable Peptide-Based Cancer Targeted Nanoprobe for Optical Theranostics and Therapeutic MonitoringCathepsin B (EC 3.4.22.1), a lysosomal cysteine protease, is overexpressed in many human cancer cells and is responsible for cancer growth, migration, invasion, and metastasis. Therefore, Cathepsin B can be used as a target for cancer imaging and therapy. Herein, a cathepsin B-activatable nanoprobe has been designed by non-covalent assembling phospholipid and poly(ethylene oxide) modified folate and photosensitizer-labeled peptide on the surface of graphene oxide. After selective uptake of the nanoprobe into lysosome of cancer cells via folate receptor-mediated endocytosis, the peptide can be cleaved to release the photosensitizer in the presence of cancer-associated cathepsin B, which leads to bright fluorescence for cancer discrimination and specific detection of intracellular cathepsin B. Under 660-nm irradiation, the released photosensitizer induces the formation of cytotoxic 1O2 for triggering photosensitive lysosomal cell death. After lysosomal destruction, the lighted photosensitizer diffuses from lysosome into cytoplasm, which can be used for in situ monitoring of therapeutic efficacy. Unlike cancer cells, the normal cells that produce low-level both folate receptor and cathepsin B are unaffected. This work provides a simple but powerful protocol to integrate precise cancer imaging, therapy and therapeutic monitoring.3. An Aptamer, pH-Activatable BODIPY and Porphyrin-Based Cancer Targeted Nanoprobe for Near-Infrared Optical Theranostics and Real-Time Therapeutic MonitoringLysosomes with interior pH of 4.5-5.0 are cellular organelles containing protein-degrading cathepsins that can trigger cell self-destruction after released into cytosol. Herein, using lysosome as the target for cancer imaging and therapy, this work designs a multifunctional nanomicelle that encapsulates a new pH-activatable fluorescent probe, BDP-688, and a robust photosensitizer, R16FP, and functionalized with a screened cancer-specific aptamer, Apt S1. Apt S1 is selected against MDA-MB-231 cells after a 15-round selection through a cell-SELEX process. It possesses high affinity and excellent specificity to MDA-MB-231 cells. The nanomicelle can recognize viable MDA-MB-231 cancer cells by Apt S1 and light up their lysosomes with BDP-688 due to the low pH environment for cancer imaging with high SBR. Upon near-infrared irradiation, R16FP-mediated generation of 1O2 causes lysosomal destruction and subsequent leakage of cathepsins into cytosol to trigger cell death. Meanwhile, the fluorescent probe can reflect the cellular status and in situ visualize the treatment process because of the proton release, thus could prevent undertreatment or overtreatment. Through intravenous injection of the nanomicelle in tumor-bearing mice, the tumor site can be distinguished from normal tissues by fluorescence imaging with high SBR. After NIR irradiation, tumor is eliminated and the fluorescence at tumor site has been dramatically reduced, thus providing a convenient mehod for therapeutic monitoring. This protocol achieves precise NIR cancer therapy, molecular therapeutic monitoring and contributes to the acquirement of deep insight into the complex molecular mechanisms of lysosome-related life processes.