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  • The specificity for human primary brain cancer

    2020-08-28

    The specificity for human primary brain cancer cells over human
    Fig. 6. PBAE nanoparticle co-delivery of five siRNAs reduced tumor growth in an orthotopic model of human GBM. Hemotoxylin- and eosin-stained histological slides of siRNA treated tumors (A) show reduced tumor burden versus (B) scRNA treated tumors. (C) IVIS tracking of luciferase-positive GBM tumors shows inhibited tumor growth in siRNA-treated tumors. (D) Quantification of siRNA-mediated reduction in tumor burden (n = 3 per group). Scale bar = 2 mm.
    primary healthy neural cells highlights one of the advantages of PBAE nanoparticles and could greatly improve nanotherapeutics for cancer by minimizing adverse side effects to off-target cells. This is in agreement with recent results showing that PBAE/nucleic PF06700841 nanoparticles ty-pically exhibit high specificity for cancer cells over healthy cells [15,44,45] and makes this technology attractive for in vivo cancer treatment.
    Polymer-based synthetic delivery systems are also advantageous versus traditional nucleic acid delivery vectors like viruses, which can generally carry only one nucleic acid sequence per particle. As we showed here, approximately 1500 siRNA molecules are estimated to be packaged into a single PBAE/siRNA nanoparticle, and thus, many co-pies of different types of siRNA can be complexed together within a single particle. This opens the possibility of combination siRNA therapy, which may be crucial for effective cancer treatment, and overcoming tumor resistances, allowing this technology to target mul-tiple different pathways relevant to tumor cell proliferation and ma-lignancy. Even within a single patient, tumors often comprise a highly heterogeneous population of malignant cells with a range of different mutations. Thus, knocking down multiple genes or pathways at the same time can help ensure that few or no GBM cells would evade the therapeutic effect of the nanoparticles.
    Multimodal agent delivery is a particularly attractive approach to treat diseases like GBM, which have heterogeneous characteristics be-tween patients and even within the same tumor [46]. Our results showing codelivery of siRNAs targeting GBM-promoting genes such as YAP1, NKCC1, survivin, Robo1 and EGFR suggest that while some se-quences are effective in causing cell death and others decrease tumor cell migration, all five sequences in combination are effective at dis-rupting multiple pathways in parallel. This is particularly relevant to target the “go or grow” aspect of cancer that describes how the pro-liferation and migration behaviors of cancer cells are inversely pro-portional, and when one of the two is targeted individually, the other 
    one is enhanced [47]. This also broadens the potential utility of com-bination siRNA delivery, as different patients' tumors may have dif-ferent sensitivities to knockdown of specific genes and drug resistances. In this study, we chose five gene targets known to promote GBM pro-liferation and migration to show that combination delivery enables multi-gene knockdown and yields simulataneous reduction in both of these behaviors. Our results suggest that this codelivery system could work with theoretically any combination of siRNAs. A combination of multiple siRNA sequences can therefore be delivered to each patient to hit multiple targets simultaneously without significantly lessening the effect of each sequence and working effectively in a wide array of heterogeneous tumors. This would allow for the delivery of patient-specific siRNA combinations that are tuned to the gene expression profile of individual GBMs. As GBM is often heterogeneous even within single tumors, this also would allow us to use a single formulation to deliver siRNAs that would target aberrant behavior within differing tumor subpopulations. Additionally, while 120 nM of siRNA was de-livered under the optimized transfection conditions, our dose-response experiment showed that up to 90% of the total siRNA could be replaced with scrambled control scRNA without affecting the extent of protein knockdown (Supplementary Fig. S3), suggesting that potentially 10 siRNA sequences can be mixed and formulated into the same particles without compromising the effect of any individual sequence.
    Combination siRNA delivery via bioreducible PBAE nanoparticles is a promising strategy for the treatment of glioblastoma. This advanced therapeutic strategy of delivering YAP1, NKCC1, survivin, Robo1, and EGFR siRNA together for intracellular delivery is complementary to recent advancements in the field. For example, delivery of lipopoly-meric nanoparticles have recently been shown encapsulating siRNAs against the four transcription factors SOX2, OLIG2, SALL2, and POU3F2 to stop the growth of brain tumor-initiating cells [48]. In contrast, we demonstrate the potential of bioreducible non-lipid nanoparticles that may be safer due to their quick environmentally-triggered