Delivery of siRNAs for the treatment of tumors critically depends on the development of efficient nucleic acid carrier systems. The complexation of dendritic polymers (dendrimers) results in nanoparticles, called dendriplexes, that protect siRNA from degradation and mediate non-specific cellular uptake of siRNA. However, large siRNA doses are required for in vivo use due to accumulation of the nanoparticles in sinks such as the lung, liver, and spleen. This suggests the exploration of targeted nanoparticles for enhancing tumor cell specificity and achieving higher siRNA levels in tumors. In this work, we report on the targeted delivery of a therapeutic siRNA specific for BIRC5/Survivin in vitro and in vivo to tumor cells expressing the surface marker prostate stem cell antigen (PSCA). For this, polyplexes consisting of single-chain antibody fragments specific for PSCA conjugated to siRNA/maltose-modified poly(propylene imine) dendriplexes were used. These polyplexes were endocytosed by PSCA-positive 293T^PSCA/ffLuc and PC3^PSCA cells and caused knockdown of reporter gene firefly luciferase and Survivin expression, respectively. In a therapeutic study in PC3^PSCA xenograft-bearing mice, significant anti-tumor effects were observed upon systemic administration of the targeted polyplexes. This indicates superior anti-tumor efficacy when employing targeted delivery of Survivin-specific siRNA, based on the additive effects of siRNA-mediated Survivin knockdown in combination with scFv-mediated PSCA inhibition.

Introduction: In human glioblastomas, glioma pathogenesis-related protein1 (GliPR1) is overexpressed and appears to be an oncoprotein. We investigated whether GliPR1 knockdown in glioma cells by RNA interference exerts anti-glioma effects. Methods: Experiments used human glioblastoma cell lines transduced with GliPR1 shRNA (sh#301, sh#258). Transduction produced stringent doxycycline-dependent GliPR1 knockdown in clones (via lentiviral “all-in-one” TetOn-shRNA vector) or stable GliPR1 knockdown in polyclonal cells (via constitutive retroviral-shRNA vector). In vitro assessments included cellular proliferation and clonogenic survival. In vivo assessments in tumor-bearing nude mice included tumor growth and survival. Results: Using doxycycline-dependent GliPR1 knockdown, shGliPR1-transduced U87-MG clones demonstrated reductions in cellular proliferation in the presence versus absence of doxycycline. Using stable GliPR1 knockdown, polyclonal shGliPR1-transduced U87-MG, A172, and U343-MG cells consistently showed decreased clonogenic survival and induced apoptosis (higher proportion of early apoptotic cells) compared to control shLuc-transduced cells. In tumor-bearing nude mice, using doxycycline-dependent GliPR1 knockdown, subcutaneous and cranial transplantation of the U87-MG clone 980-5 (transduced with GliPR1 sh#301) resulted in reduced subcutaneous tumor volume and cerebral tumor area in doxycycline-treated mice versus those left untreated. Using stable GliPR1 knockdown, nude mice cranially transplanted with polyclonal U87-MG cells transduced with GliPR1 sh#258 had significantly prolonged survival compared to mice cranially transplanted with control shLuc-transduced cells (41 versus 26 days; P < 0.001). Conclusion: GliPR1 knockdown in glioma cells decreased cellular proliferation, decreased clonogenic survival, and induced apoptosis in vitro, and reduced glioblastoma tumor growth and prolonged survival in vivo. These findings support that GliPR1 may have potential value as a therapeutic target.

Among non-viral vectors, cationic polymers, such as poly(propylene imine) (PPI), play a prominent role in nucleic acid delivery. However, limitations of polycationic polymer-based DNA delivery systems are (i) insufficient target specificity, (ii) unsatisfactory transgene expression, and (iii) undesired transfer of therapeutic DNA into non-target cells. We developed single-chain antibody fragment (scFv)-directed hybrid polyplexes for targeted gene therapy of prostate stem cell antigen (PSCA)-positive tumors. Besides mono-biotinylated PSCA-specific single-chain antibodies (scFv(AM1-P-BAP)) conjugated to neutravidin, the hybrid polyplexes comprise β-cyclodextrin-modified PPI as well as biotin/maltose-modified PPI as carriers for minicircle DNAs encoding for Sleeping Beauty transposase and a transposon encoding the gene of interest. The PSCA-specific hybrid polyplexes efficiently delivered a GFP gene in PSCA-positive tumor cells, whereas control hybrid polyplexes showed low gene transfer efficiency. In an experimental gene therapy approach, targeted transposition of a codon-optimized p53 into p53-deficient HCT116^{p53−/−/PSCA} cells demonstrated decreased clonogenic survival when compared to mock controls. Noteworthily, p53 transposition in PTEN-deficient H4^PSCA glioma cells caused nearly complete loss of clonogenic survival. These results demonstrate the feasibility of combining tumor-targeting hybrid polyplexes and Sleeping Beauty gene transposition, which, due to the modular design, can be extended to other target genes and tumor entities.

Glioblastoma multiforme (GBM) is the most prevalent primary brain tumor endowed with a dismal prognosis. Nowadays, immunotherapy in a particular immune checkpoint blockade and therapeutic vaccines are being extensively pursued. Yet, several characteristics of GBM may impact such immunotherapeutic approaches. This includes tumor heterogeneity, the relatively low mutational load of primary GBM, insufficient delivery of antibodies to tumor parenchyma and the unique immunosuppressive microenvironment of GBM. Moreover, standard treatment of GBM, comprising temozolomide chemotherapy, radiotherapy and in most instances the application of glucocorticoids for management of brain edema, results in a further increased immunosuppression. This review will provide a brief introduction to the principles of vaccine-based immunotherapy and give an overview of the current clinical studies, which employed immune checkpoint inhibitors, oncolytic viruses-based vaccination, cell-based and peptide-based vaccines. Recent experiences as well as the latest developments are reviewed. Overcoming obstacles, which limit the induction and long-term immune response against GBM when using vaccination approaches, are necessary for the implementation of effective immunotherapy of GBM.