Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is the causative agent of the coronavirus disease 2019 (COVID-19) pandemic. The virus still spreads globally through human-to-human transmission. Nevertheless, there are no specific treatments clinically approved. This study aimed to compare antiviral activity of gemcitabine and its analogue 2′-fluoro-2′-deoxycytidine (2FdC) against SARS-CoV-2 as well as cytotoxicity in vitro. Fluorescent image-based antiviral assays revealed that gemcitabine was highly potent, with a 50% effective concentration (EC₅₀) of 1.2 μM, more active than the well-known nucleoside monophosphate remdesivir (EC₅₀ = 35.4 μM). In contrast, 2FdC was marginally active (EC₅₀ = 175.2 μM). For all three compounds, the 50% cytotoxic concentration (CC₅₀) values were over 300 μM toward Vero CCL-81 cells. Western blot and quantitative reverse-transcription polymerase chain reaction analyses verified that gemcitabine blocked viral protein expression in virus-infected cells, not only Vero CCL-81 cells but also Calu-3 human lung epithelial cells in a dose-dependent manner. It was found that gemcitabine has a synergistic effect when combined with remdesivir. This report suggests that the difluoro group of gemcitabine is critical for the antiviral activity and that its combination with other evaluated antiviral drugs, such as remdesivir, could be a desirable option to treat SARS-CoV-2 infection.

Purpose: The pathogenesis of colorectal cancer is largely driven by mutations of the tumor suppressor gene APC (adenomatous polyposis coli) that lead to aberrant activation of the β-catenin–dependent (canonical) Wnt signaling pathway. We evaluated basroparib, a tankyrase-selective inhibitor targeting the Wnt/β-catenin signaling pathway, in a first-in-human phase I clinical study for safety, tolerability, pharmacokinetics, and efficacy in patients with advance-stage solid tumors. Patients and Methods: Patients enrolled to this open-label, multicenter study (NCT04505839) were treated with basroparib capsules orally once daily in 28-day cycles (21-day on and 7-day off) in dose escalation at seven dose levels (30–360 mg) following the classic “3 + 3” design. Results: Twenty-five patients (colorectal cancer, 23 patients; male sex, 48%, and median age, 58 years) were treated with basroparib. Dose-limiting toxicities and fatal treatment-related adverse events were not observed. The most commonly reported treatment-related adverse events were fatigue and nausea with mild/moderate severity. Basroparib pharmacokinetics increased less than proportionally with dose increase up to 300 mg. Among 17 patients evaluated for response, four (23.5%) had stable disease with a duration of up to 2.5 months and relative higher drug exposure compared with others. The dose of 360 mg was determined to be the maximum tolerated dose and recommended phase II dose. Conclusions: Basroparib was shown to be a safe and well-tolerated tankyrase-selective inhibitor with preliminary antitumor activity warranting further investigation. Significance: Tankyrase in the active β-catenin–dependent (canonical) Wnt signaling pathway has been a desirable but difficult target because of safety concerns. We developed a tankyrase-selective inhibitor, basroparib, and successfully introduced it in a first-in-human study. This study demonstrated a favorable safety profile and modest antitumor activity for basroparib and suggests that basroparib may play a role when combined with other rational targeted therapies.

Patient demographic and baseline characteristics (N = 25).

Best change (%) in target lesion from baseline. Note: “▲” marks patients with RCC; SD, stable disease in overall evaluation following Response Evaluation Criteria in Solid Tumours 1.1.

Supplementary Table S4. Summary of Progression-free Survival for Stable Disease Patients