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Previously, we successfully developed the c(phg-isoDGRk) peptide as a novel integrin α5β1-targeted SPECT imaging probe 99mTc-HisoDGR for Glioma imaging. However, the fast clearance of 99mTc-HisoDGR in blood reduced its tumor accumulation and retention, which would be the obstacles for further clinical application. Dimerization and albumin-binding strategies have been proven as effective approaches to improve tumor targeting capability and blood circulation time of radiotracers. In this study, the novel PEGylated dimeric isoDGR peptides (termed 3PisoDGR2) and its analogue with an albumin binder (termed AB-3PisoDGR2) were designed, and the corresponding radiotracers 99mTc-3PisoDGR2 and 99mTc-AB-3PisoDGR2 were fabricated and assessed for tumor-targeting and in vivo pharmacokinetics properties in subcutaneous and orthotopic tumor models. The dimerization of isoDGR peptide provided higher binding affinity to tumor cells and longer blood circulation time than the original monomeric isoDGR peptide, resulting in twice increased tumor uptake (99mTc-3PisoDGR2 2.51 ± 0.17 %ID/g vs 99mTc-PisoDGR 1.17 ± 0.21 %ID/g, P < 0.01) at 0.5 h post-injection (p.i.) and enhanced tumor to nontargeting tissue ratios (T/NT) in most normal organs. The blocking study indicated that the tumor uptake was receptor-mediated specifically. NanoScanSPECT/CT imaging of 99mTc-3PisoDGR2 in glioma tumor-bearing model showed clear visions of tumors with low background, except high uptake in excretion system including kidneys and bladder at all detected time points (0.5, 1, and 2 h p.i.). The orthotopic glioma tumor could also be clearly visualized by nanoScanSPECT/CT imaging with 99mTc-3PisoDGR2. The addition of albumin-binding entity further prolonged blood circulation time and reached higher tumor uptake for 99mTc-AB-3PisoDGR2. However, since 99mTc-AB-3PisoDGR2 is less capable of passing BBB than 99mTc-3PisoDGR2, 99mTc-3PisoDGR2 is preferable for the in situ glioma imaging. In conclusion, 99mTc-3PisoDGR2 represents an improved molecular probe for integrin α5β1-targeted tumor imaging, showing more potential for further clinical application.

Colorectal cancer is a common malignant tumour with a low 5-year survival rate. A combination therapy with high selectivity and easy controllability is a pressing need for the effective treatment of such cancer. In this study, an indocyanine green derivative (Cy7)-conjugated lipid with a terminal carboxyl group was synthesized, which could self-assemble with a cerasome-forming lipid (CFL) into nanoparticles (NPs) by encapsulating doxorubicin (DOX) to achieve combined photothermal chemotherapy. The resulting Gly@Cy7-Si-DOX NPs with a surface covalent silicate framework showed excellent morphological stability and colloidal stability. Specifically, the conjugated Cy7 was covalently conjugated in the liposomal bilayer, resulting in high drug loading content, high photostability, and high photothermal conversion efficiency, which enabled the resulting nanoparticles to be an effective platform for photothermal therapy. Meanwhile, the encapsulated DOX leaked only slightly under physiological conditions due to the silicate surface of Gly@Cy7-Si-DOX NPs and exhibited controlled release in a weakly acidic environment or under near-infrared (NIR) light irradiation for chemotherapy. Gly@Cy7-Si-DOX NPs were efficiently taken up by tumour cells. Upon light irradiation, the released DOX entered the nuclei of tumour cells, as observed by confocal microscopy and flow cytometry. In vitro cell experiments indicated that both healthy cells and tumour cells were viable under treatment with only Gly@Cy7-Si-DOX NPs, indicating the encapsulated DOX was stably confined to the NPs, and cells were significantly killed when treated with both Gly@Cy7-Si-DOX NPs and NIR laser irradiation. After i.v. administration, Gly@Cy7-Si-DOX NPs accumulated at the tumour site, as monitored by near-infrared fluorescence imaging. A significant tumour inhibition rate (95.8%) was also achieved in a HT-29 colorectal cancer model when treated with Gly@Cy7-Si-DOX NPs plus irradiation. Therefore, the Gly@Cy7-Si-DOX NPs hold great promise for controllable combined colorectal cancer photothermal chemotherapy.

Doxorubicin (DOX) has been clinically used as a broad-spectrum chemotherapeutic agent for decades, but its clinical application is hindered by the lack of tumour specificity, severe cardiotoxicity and haematotoxicity. Pre-targeted strategies are highly tumour-specific, therapeutic approaches. Herein, a novel pre-targeted system was constructed, aiming to enhance anticancer efficacy of DOX and maximally reduce its side effects. Methods: The DOX prodrug (bDOX) was first synthesized by conjugating DOX with mini-PEGylated (mPEGylated) biotin through a pH-sensitive bond. During the pre-targeted treatment, avidin was first administrated. After an optimized interval, bDOX was second administrated. The nontoxic prodrug bDOX was eventually transformed into the toxic anticancer form (DOX) by a pH-triggered cleavage specifically in tumour cells. The drug efficacy and side effect of the two-step, pre-targeted treatment were fully compared with free DOX in vitro and in vivo. Results: The prodrug bDOX was quite stable under neutral conditions and nearly nontoxic, but was immediately transformed into the toxic anticancer form (DOX) under acidic conditions. Compared to free DOX, the pre-targeted bDOX exhibited a higher cellular uptake by human colorectal tumour cells (LS180 and HT-29 cells). In vivo evaluation performed on LS180 xenograft animal model demonstrated that the pre-targeted bDOX achieved a much more significant tumour inhibition than free DOX. The largely decreased, unwanted bystander toxicity was demonstrated by changes in body weight, cardiomyocyte apoptosis, blood routine examination and splenic pathological changes. Conclusion: The high therapeutic efficacy, together with the minimal side effects, of this easily synthesized, pre-targeted system exhibited immense potentiality for the clinical application of DOX delivery.

Keywords: avidin; biotin; chemotherapy; doxorubicin prodrug; pre-targeted strategy.

Antiangiogenic therapies have been demonstrated to improve the efficacy of immune checkpoint inhibition by overcoming the immunosuppressive status of the tumor microenvironment. However, most of the current antiangiogenic agents cannot discriminate tumor angiogenesis from physiological angiogenesis. The aim of this study was to investigate whether a photodynamic therapy (PDT) agent that targets CD276, a receptor overexpressed in various tumor cells and tumor vasculature but with limited expression in normal tissue vasculature, could improve the tumor inhibitory efficacy of a PD-1/PD-L1 blockade. A CD276-targeting agent (IRD-αCD276/Fab) was synthesized by conjugating the Fab fragment of an anti-CD276 antibody with a photosensitizer IRDye700. The in vivo tumor-targeting efficacy and therapeutic effects of IRD-αCD276/Fab with or without an anti-PD-1/PD-L1 blockade were tested in subcutaneous and lung metastatic tumor models. PDT using IRD-αCD276/Fab significantly suppressed the growth of subcutaneous 4T1 tumor and inhibited its lung metastasis. Moreover, it triggered in vivo antitumor immunity by increasing the activation and maturation of dendritic cells. Tumor PD-L1 levels were also markedly increased after PDT using IRD-αCD276/Fab, as evidenced by noninvasive PD-L1-targeted small-animal PET imaging. In combination with an anti-PD-1/PD-L1 blockade, IRD-αCD276/Fab PDT markedly suppressed the growth of tumors and prevented their metastasis to the lung by recruiting the tumor infiltration of CD8+ T cells. Our data provide evidence for the role of CD276-targeted PDT for local immune modulation, and its combination with PD-L1/PD-1 axis inhibition is a promising strategy for eliminating primary tumors as well as disseminated metastases, by generating local and systemic antitumor responses.

Keywords: PET imaging; angiogenesis; checkpoint inhibition; molecular imaging; photo-immunotherapy.