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Targeted RNAi of BIRC5/Survivin Using Antibody-Conjugated Poly(Propylene Imine)-Based Polyplexes Inhibits Growth of PSCA-Positive Tumors
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 293TPSCA/ffLuc and PC3PSCA cells and caused knockdown of reporter gene firefly luciferase and Survivin expression, respectively. In a therapeutic study in PC3PSCA 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.
Targeted delivery of TLR3 agonist to tumor cells with single chain antibody fragment-conjugated nanoparticles induces type I-interferon response and apoptosis
Application of Toll-like receptor (TLR) agonists is a promising approach to treat cancer. In particular, nucleic acid-based TLR agonists such as short ssRNA and dsRNA molecules, which activate endosomal TLRs, can be delivered to tumors by use of nanoparticle delivery systems. However, such delivery systems bear unspecific side effects and poor pharmacokinetics. To overcome these limitations we developed a system for targeted delivery of a 50 bp dsRNA TLR3 agonist (Riboxxol) to treat PSCA-positive tumor cells, which consists of neutravidin conjugated to mono-biotinylated dsRNA and to humanized mono-biotinylated anti-PSCA single chain antibody derivative scFv(h-AM1)-BAP. The assembly of the components resulted in the formation of nanoparticle-like immunoconjugates designated Rapid Inducer of Cellular Inflammation and Apoptosis (RICIA). Anti-PSCA-RICIA exclusively delivered Riboxxol to PSCA-positive tumor cells as well as subcutaneous tumors. Uptake of anti-PSCA-RICIA induced a type I-interferon response and apoptosis in HEK-Blue hTLR3/PSCA reporter cells and PSCA-positive HT1376 bladder cancer cells in vitro. No such effects were observed when using RICIA coupled to an unspecific control antibody or when using Riboxxol alone. Treatment of HT1376 xenografts in immune-deficient hosts with targeted delivery of TLR3 agonist did not induce adverse effects and only modestly inhibited tumor growth when compared to controls. These results suggest promising activation of innate immune response and apoptosis upon selective delivery of TLR3 agonists in tumor cells. Yet, further studies using syngeneic and orthotopic tumor models are needed to fully exploit the potential of RICIA immunoconjugates. © 2019, The Author(s).