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Small interfering RNAs (siRNAs) represent a novel class of drugs capable of potent and sustained modulation of genes across various tissues. Preclinical development of siRNAs necessitates assessing efficacy and toxicity in animal models. While identifying therapeutic leads with cross-species activity can expedite development, it may compromise efficacy and be infeasible for certain gene targets. Here, we investigate whether deriving species-active siRNAs from potent human-targeting leads-an approach termed mismatch conversion-can yield potent compounds. We systematically altered potent siRNAs targeting human genes associated with diseases- SOD1 (ALS), JAK1 (inflammation), and HTT (HD)-to generate species-matching variants with full complementarity to their target in NHPs, mice, rats, sheep, and dogs. Variants potency and efficacy were measured in corresponding cell lines. We demonstrate that sequence, position, and number of mismatches significantly influence the ability to generate potent species-active compounds via mismatch conversion. Across tested sequences, mismatch conversion strategy ability to identify a species-active lead varied from 0% to 70%. For SOD1 , lead compounds identified from species-focus screening in mouse and dog cells were more potent than leads obtained from mismatch conversion. Thus, a focused screening of therapeutic lead and model compounds may represent a more reliable strategy for the clinical advancement of siRNAs.

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative condition, with 20% of familial and 2-3% of sporadic cases linked to mutations in the cytosolic superoxide dismutase (SOD1) gene. Mutant SOD1 protein is toxic to motor neurons, making SOD1 gene lowering a promising approach, supported by preclinical data and the 2023 FDA approval of the GapmeR ASO targeting SOD1, tofersen. Despite the approval of an ASO and the optimism it brings to the field, the pharmacodynamics and pharmacokinetics of therapeutic SOD1 modulation can be improved. Here, we developed a chemically stabilized divalent siRNA scaffold (di-siRNA) that effectively suppresses SOD1 expression in vitro and in vivo . With optimized chemical modification, it achieves remarkable CNS tissue permeation and SOD1 silencing in vivo . Administered intraventricularly, di-siRNA SOD1 extended survival in SOD1-G93A ALS mice, surpassing survival previously seen in these mice by ASO modalities, slowed disease progression, and prevented ALS neuropathology. These properties offer an improved therapeutic strategy for SOD1-mediated ALS and may extend to other dominantly inherited neurological disorders., Competing Interests: Competing interests: AK is a co-founder, on the scientific advisory board, and holds equities of Atalanta Therapeutics; AK is a founder of Comanche Pharmaceuticals, and on the scientific advisory board of Aldena Therapeutics, AlltRNA, Prime Medicine, and EVOX Therapeutics; Select authors hold patents or on patent applications relating to the divalent siRNA, SOD1-targeting oligonucleotides, and the methods described in this report. NH received compensation for other services from Myrobalan Inc. and General Dynamics during the conduct of this study, unrelated to the present work.

Identifying therapeutic oligonucleotides that are cross-reactive to experimental animal species can dramatically accelerate the process of preclinical development and clinical translation. Here, we identify fully chemically-modified small interfering RNAs (siRNAs) that are cross-reactive to Janus kinase 1 (JAK1) in humans and a large variety of other species. We validated the identified siRNAs in silencing JAK1 in cell lines and skin tissues of multiple species. JAK1 is one of the four members of the JAK family of tyrosine kinases that mediate the signaling transduction of many inflammatory cytokine pathways. Dysregulation of these pathways is often involved in the pathogenesis of various immune disorders, and modulation of JAK family enzymes is an effective strategy in the clinic. Thus, this work may open up unprecedented opportunities for evaluating the modulation of JAK1 in many animal models of human inflammatory skin diseases. Further chemical engineering of the optimized JAK1 siRNAs may expand the utility of these compounds for treating immune disorders in additional tissues., Competing Interests: A.K. is a founder of Atalanta Therapeutics and Comanche Biopharma; serves on the Scientific Advisory Board of Aldena Therapeutics, Prime Medicine, Alltrna, and Evox Therapeutics; and owns equities in RXi Pharmaceuticals and Advirna. J.E.H. owns equities in Rheos Medicines, and is a founder of Villaris Therapeutics, Aldena Therapeutics, NIRA Biosciences, Vimela Therapeutics, and Klirna Therapeutics. Q.T., H.H.F., K.Y.G., M.Z.U.I.A., K.R.M., J.E.H., A.K., and J.F.A. are listed as inventors of RNAi technology patents and patent applications. C.B., C.B.-P., and T.P. are executives of Aldena Therapeutics.