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Targeting structured RNA elements in the SARS-CoV-2 viral genome with small molecules is an attractive strategy for pharmacological control over viral replication. In this work, we report the discovery of small molecules that target the frameshifting element (FSE) in the SARS-CoV-2 RNA genome using high-throughput small-molecule microarray (SMM) screening. A new class of aminoquinazoline ligands for the SARS-CoV-2 FSE are synthesized and characterized using multiple orthogonal biophysical assays and structure−activity relationship (SAR) studies. This work reveals compounds with mid-micromolar binding affinity (K D = 60 ± 6 μM) to the FSE RNA and supports a binding mode distinct from previously reported FSE binders MTDB and merafloxacin. In addition, compounds are active in in vitro dual-luciferase and in-cell dual-fluorescent-reporter frameshifting assays, highlighting the promise of targeting structured elements of RNAs with druglike compounds to alter expression of viral proteins.

New targeted chemotherapeutics are urgently needed to minimize off-target toxicity and reduce the high mortality rate associated with metastatic prostate cancer (PCa). We report on the modular synthesis, pharmacokinetics, and efficacy of two small-molecule drug-conjugates (SMDCs) targeted to prostate-specific membrane antigen (PSMA) incorporating either: (1) a cathepsin-B cleavable valine-citrulline, or (2) an acid-responsive phosphoramidate linker. Key to the selectivity of these conjugates is CTT1298, a nanomolar affinity ligand that binds irreversibly to PSMA and has been shown to rapidly internalize payloads into PSMA-expressing PCa cells. Other crucial components in the design of the conjugates include: (1) MMAE, a known potent cytotoxic payload, and (2) an albumin-binder, proven to improve residence time of drug conjugates. At a dose of 0.8 mg/kg (~250 nmol/kg), both SMDCs showed significant efficacy in a PSMA(+) PC3-PIP mouse model of human PCa compared to controls, without inducing systemic toxicity. Though localization of the SMDCs was observed in tissues apart from the tumor, release of MMAE was observed predominantly in tumor tissue, at levels 2-3 orders of magnitude higher than non-target tissues. Furthermore, SMDC 2, which incorporated a novel pH-responsive phosporamidate linker, demonstrated improved efficacy over SMDC 1 that has a valine-citrulline linker, with a 100% survival over 90 days and 4 out of 8 mice showing complete tumor growth inhibition after 6 weekly doses of 0.8 mg/kg (244 nmol/kg). Our findings demonstrate the potential of irreversible PSMA inhibitors combined with pH-responsive linkers as a way to specifically deliver chemotherapeutic drugs to PCa tumors with minimal toxicity.