Tumor Therapy And Diagnosis Based On Chimeric Peptides

During the last decades, tumor has severely threatened human health. And scientists paid much attention to developing ingenious nanoparticles for tumor therapy and diagnosis. Compared with nanoparticles based on gold, carbon and polymers, peptide-based nanoparticles presented prominent advantages due to their better biocompatibility, biodegradability and more flexibility. Importantly, the advanced biology has facilitated the identification of specific bioactive and functional peptides, and peptide-based nanoparticles can transport the bioactive substances to the tumor with ease.In light of recent development of regarding peptide-based nanoparticles for tumor therapy and diagnosis, the work of this thesis is mainly focused on the following issues:In chapter 1, the very recent progress of peptides was reviewed, including the bioactive peptides as well as the application in drug and gene delivery, tumor diagnosis.In chapter 2, an amphiphilic chimeric peptide (Fmoc)2KH7-TAT with pH-responsibility for gene and drug delivery was designed and fabricated. As a drug carrier, the micelles self-assembled from the peptide exhibited a much faster doxorubicin (DOX) release rate at pH 5.0 than that at pH 7.4. As a non-viral gene vector, (Fmoc)2KH7-TAT peptide with well endosomal escape capability could satisfactorily mediate transfection of pGL-3 reporter plasmid with or without the existence of serum in both 293T and HeLa cell-lines. Besides, p53 plasmid and DOX were simultaneously loaded in the peptide micelles to form micelleplexes during the self-assembly of the peptide. These micelleplexes could be internalized by HeLa cells and mediated satisfactory p53 protein expression. Results suggested that the co-delivery of gene and drug from peptide micelles resulted in effective cell growth inhibition in vitro and significant tumor growth restraining in vivo.In chapter 3, we developed a tumor-targetd chimeric peptide to codeliver a photosensitizer, protoporphyrin IX (PpIX), and plasmid DNA simultaneously. In the presence of matrix metalloproteinase-2 (MMP-2), the chimeric peptide underwent the process of hydrolysis of PLGVR peptide sequence, exfoliation of PEG, and increased of positive charges. As a result, the chimeric peptide could be preferentially uptaken by MMP-2 rich tumor cells. Importantly, for the first time, we proposed a dual-stage light irradiation strategy, i.e., the short time light irradiation could efficiently enhance the endosomal escape of the chimeric peptide/PpIX/DNA complexes by the formation of reactive oxygen species (ROS), resulting in synergistic endosomal escape and improved DNA expression. In addition, due to the screened phototoxicity of PpIX, short time light irradiation did not lead to detectable changes in the cell viability. After the gene transfection, the screened phototoxicity of PpIX was subsequently stimulated by long time irradiation to achieve high synergistic efficacy of photodynamic and gene therapies.In chapter 4, a self-delivery system PpIX-PEG-(KLAKLAK)2 (designated as PPK) was fabricated to realize mitochondria-targeted photodynamic tumor therapy. This PPK self-delivery system exhibited high drug loading efficacy as well as novel capacity in generation of intracellular ROS. Besides, photochemical internalization (PCI) effect of the photosensitizer protoporphyrin IX (PpIX) under a short time light irradiation improved the cellular internalization of PPK. On the other hand, PPK could target to the subcellular organelle mitochondria due to the presence of proapoptosis (KLAKLAK)2 peptide. Importantly, the in situ generation of ROS in mitochondria enhanced the photodynamic therapy (PDT) efficacy under another long time irradiation, leading to significant cell death with decreased mitochondrial membrane potential. Furthermore, in vivo antitumor study via subcutaneous injection and intravenous injection was investigated by using a murine model.In chapter 5, for the first time, we proposed a new concept to construct a chimeric peptide as a theranostic agent based on fluorescence resonance energy transfer (FRET) with introduction of therapeutic function. This chimeric peptide was fluorescence quenched (OFF). Once the apoptosis was initiated and propagated, green fluorescence was lighted up rapidly (ON), achieving simultaneous tumor therapy and real-time apoptosis monitoring.