Securing the Payload, Finding the Cell, and Avoiding the Endosome: Peptide‐Targeted, Fusogenic Porous Silicon Nanoparticles for Delivery of siRNA

Abstract

in the development of siRNA-based therapeutics over more than 15 years, substantial challenges have limited their clinical translation. The first siRNA-based drug was approved only in the last year, and that only for treatment of a rare hereditary disease; [2] there is currently no approved cancer therapeutic based on siRNA. A primary obstacle in this endeavor has been the lack of delivery vehicles that can overcome in vivo clearance and cellular degradation via endocytosis. [3,4] One of the early proposed solutions to the problem of endocytotic sequestration and subsequent lysosomal degradation of siRNA was delivery via fusogenic liposomes. [5] Fusogenic liposomes directly fuse with the cell membrane, bypassing endocytotic uptake pathways. [6] While they have shown promise as delivery vehicles for ribonucleic acid interference (RNAi) therapeutics, [7] liposomes suffer from a generally low carrying capacity for nucleic acid therapeutics [8] and leakage of their payloads either during storage or in vivo. [9] We recently demonstrated a delivery system that harnessed together a fusogenic lipid and a solid porous silicon nanoparticle (pSiNP) core. The system capitalized on the relatively high loading of Despite the promise of ribonucleic acid interference therapeutics, the delivery of oligonucleotides selectively to diseased tissues in the body, and specifically to the cellular location in the tissues needed to provide optimal therapeutic outcome, remains a significant challenge. Here, key material properties and biological mechanisms for delivery of short interfering RNAs (siRNAs) to effectively silence target-specific cells in vivo are identified. Using porous silicon nanoparticles as the siRNA host, tumor-targeting peptides for selective tissue homing, and fusogenic lipid coatings to induce fusion with the plasma membrane, it is shown that the uptake mechanism can be engineered to be independent of common receptor-mediated endocytosis pathways. Two examples of the potential broad clinical applicability of this concept in a mouse xenograft model of ovarian cancer peritoneal carcinomatosis are provided: silencing the Rev3l subunit of polymerase Pol ζ to impair DNA repair in combination with cisplatin; and reprogramming tumor-associated macrophages into a proinflammatory state. RNAi TherapyOf the ≈100 FDA-approved anticancer drugs, about 40% are cytotoxic agents and 60% are inhibitors of oncogenic pathways. [1] As the discovery of key oncogenic markers and pathways has progressed, short interfering RNAs (siRNAs) have emerged as a promising class of drugs to transiently silence oncogenic mutations. Despite the worldwide effort expended

Rekindling RNAi Therapy: Materials Design Requirements for In Vivo siRNA Delivery

“…A most recent development for pSi‐based siRNA therapeutics is fusogenic lipid‐coated pSi nanoparticles (FNPs; Figure ) . Using the above calcium silicate condenser chemistry, the FNPs were able to obtain loading capacity up to 25 wt% of siRNA, a significantly higher loading capacity compared with other materials of similar size and structure .…”

“…Using the above calcium silicate condenser chemistry, the FNPs were able to obtain loading capacity up to 25 wt% of siRNA, a significantly higher loading capacity compared with other materials of similar size and structure . Like Brinker's MSN‐based Protocell, the inorganic pSi core prevents premature leakage of siRNA payloads from the liposomal shell, and inversely, the liposomal shell is able to protect the pSi core from dissolution . Currently, the FNP system represents the most thoroughly investigated pSi‐based siRNA delivery technology, as its material properties, biological mechanism of action, and its in vitro and in vivo behavior and therapeutic effects have been delineated .…”

“…Like Brinker's MSN‐based Protocell, the inorganic pSi core prevents premature leakage of siRNA payloads from the liposomal shell, and inversely, the liposomal shell is able to protect the pSi core from dissolution . Currently, the FNP system represents the most thoroughly investigated pSi‐based siRNA delivery technology, as its material properties, biological mechanism of action, and its in vitro and in vivo behavior and therapeutic effects have been delineated . Overall, the FNPs are able to undergo a plasma membrane fusion to directly deposit the siRNA‐loaded pSi core particles in the cytoplasm, where the pSi quickly degrades to release the siRNA for RNAi.…”

“…Moreover, FNPs represent a modular therapeutic platform; by exchanging the siRNA sequence and the homing peptide, the FNPs have been be configured for three different disease targets (anti‐inflammatory, chemo‐sensitizing, and tumor‐associated macrophage reprogramming). This system has demonstrated remarkable therapeutic effects in bacterial infection models (Gram positive Staphylococcus aureus , Gram negative Pseudomonas aeruginosa , and Methicilin‐resistant S. aureus (MRSA)), as well as in ovarian peritoneal carcinomatosis …”

“…With regard to in vivo siRNA delivery, the fusogenic porous silicon nanoparticles (FNPs) demonstrated effective use of targeting peptides to induce siRNA‐mediated gene silencing in multiple cell targets within a single mouse model . Figure shows a significant example of the versatility of the approach, where three different targeting peptides were used to bring FNPs to their three respective targets with high selectivity.…”