RNA aptamer-mediated gene therapy of prostate cancer: lessons from the past and future directions

ABSTRACTIntroduction Prostate cancer (PCa) is one of the most prevalent cancers in the world, and the fifth cause of death from cancer in men. Among the non-surgical treatments for PCa, gene therapy strategies are in the early stages of development and recent clinical trials have provided new insights suggesting promising future.Areas covered Recently, the creation of targeted gene delivery systems, based on specific PCa cell surface markers, has been viewed as a viable therapeutic approach. Prostate-specific membrane antigen (PSMA) is vastly expressed in nearly all prostate malignancies, and the intensity of expression increases with tumor aggressiveness, androgen independence, and metastasis. RNA aptamers are short and single-stranded oligonucleotides, which selectively binds to a specific ligand on the surface of the cells, which makes them fascinating small molecules for target delivery of therapeutics. PSMA-selective RNA aptamers represented great potential for developing targeted-gene delivery tools for PCa.Expert opinion This review provides a thorough horizon for the researchers interested in developing targeted gene delivery systems for PCa via PSMA RNA aptamers. In addition, we provided general information about different prospects of RNA aptamers including discovery approaches, stability, safety, and pharmacokinetics.KEYWORDS: PSMARNA aptamersgene therapyProstate cancerDisclaimerAs a service to authors and researchers we are providing this version of an accepted manuscript (AM). Copyediting, typesetting, and review of the resulting proofs will be undertaken on this manuscript before final publication of the Version of Record (VoR). During production and pre-press, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal relate to these versions also. Declaration of interestThe authors have no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.Reviewer disclosuresPeer reviewers on this manuscript have no relevant financial or other relationships to disclose.Article highlightsProstate-specific membrane antigen (PSMA) is vastly expresses in nearly all prostate malignancies, and the intensity of expression increases with tumor aggressiveness, androgen independence, and metastasis.Aptamers are short and single-stranded oligonucleotides (ssRNA or ssDNA) with excellent selective affinity to a variety of target molecules on the surface of the cell membrane.While PSMA RNA-aptamers truncation provides the possibility of a faster and cheaper chemical synthesis, this process may cause the loss of their ability to inhibit PSMA enzymatic activity.PSMA RNA aptamer acts as a smart drug for PCa by blocking the enzymatic activity of PSMA.PSMA RNA aptamer chimeras showed great potential for RNA interference therapy in PCa.Figure 1. A schematic for the impact of PSMA RNA aptamers; A10-3.2, A9g, and A9g.6 (control non-binding aptamer) on; the inhibition of PSMA enzymatic activity (a); in vitro cell proliferation (b), cell migration (c), and cell invasion (d); and in vivo ati-metastatic treatment efficacy (e). Doxorubicin: antiproliferative chemotherapeutic drug; 2-PMPA: small molecule inhibitor of PSMA enzymatic activity (This figure is adapted from figures 2 and 3 of the ref. [Citation4] with permission).Display full sizeFigure 2. An illustration of how siRNA can be delivered intracellularly using aptamer-siRNA chimeras and siRNA-loaded nanocarriers that are taken up by the target cells via endocytosis. The siRNA portion of aptamer-siRNA chimeras is separated from chimeras by the Dicer enzyme. Finally, the cytoplasmic siRNA is detected by the RNAi machinery after endosomal escape.The target messenger RNA (mRNA) is specifically degraded by complementary base pairing by the RNA-inducing silencing complex (RISC), which incorporates the siRNA.Display full sizeFigure 3. An illustrative summary for the PSMA RNA aptamers from discovery to the future direction.Display full sizeFigure 4. PLK 1 gene silencing ability of the truncated A10 aptamer (A10-3.2)-siRNA chimeras compared with the A10-siRNA chimera. In the A10-3.2 aptamer-siRNA chimeras, the longer RNA strand is replaced with 2′-fluoropyrimidines while the shorter RNA strand is left unmodified. The stem loop chimera, which has undergone full modification, is an exception. OVH is a blunt-like chimera with an overhang of a two nucleotides of U-U at the 3′ end of the siRNA duplex. The G-U, G-U wobble chimeras are similar to OVH but with a wobble base pair at the 5′ end of the antisense siRNA strand (silencing/guide strand). The sense and antisense strands of the siRNA duplex are reversed for swap chimera. The aptamer (loop) and siRNA duplex (stem) are interconnected in stem loop chimera (This figure is adapted from figures 1 and 3 of the ref.[Citation58] with permission).Display full sizeAdditional informationFundingThis work was supported by University of Torino grant AREM_RILO_19_01 - Bando Ricerca Locale 2019 – to M Arese, AIRC IG grants # 22910, #12182 # 18652 to F Bussolino; Regione Piemonte (grant A1907A, Deflect) to F.B., Fondazione CRT, Ministero dell'Università e della Ricerca (PRIN 2017, grant 2017237P5X to F.B.), FPRC 5xmille 2016 MIUR (Biofilm) to F Bussolino.