Background: The first generation irreversible BTK inhibitor ibrutinib has been approved for the treatment of B cell-related diseases, including chronic lymphocytic leukemia (CLL), for several years. However, CLL patients who used ibrutinib may develop drug resistance due to acquired mutations, in particular BTK C481S that directly impacts the binding of ibrutinib. In recent years, efforts have been made to develop the second generation reversible BTK inhibitors that are effective against both wild-type and C481S mutated B-cell malignancies. LOXO-305 and ARQ-531 are two examples of the second generation reversible BTK inhibitors in advanced clinical trials for ibrutinib-resistant CLL. Methods: New reversible BTK inhibitors were designed, synthesized and tested for enzymatic activities against wild-type and C481S-mutated BTK. Highly active compounds were confirmed for growth effects in diffuse large B-cell lymphoma derived TMD8 cells. Their microsomal stability and ADME properties were also assessed. Potent and bioavailable compounds were further evaluated in vivo efficacy using a TMD8 xenograft tumor model in mice. A 14-day toxicity study in rats was performed correspondingly. Results: As shown in the table, HBW-3-10 has greater potency and pharmacokinetic profile (rats, 10mg/kg PO) than ARQ-531. In a TMD8 mouse xenograft study, HBW-3-10, ARQ-531 and ibrutinib were compared directly, all dosed at 10mg/kg QD, and the resulting tumor growth inhibition rates (TGI) are 38.3%, 9.3% and 22.5%, respectively. Based on our data, HBW-3-10 is more efficacious than ARQ-531 and ibrutinib. In a 14-day preliminary toxicity experiment in rats, both HBW-3-10 and ARQ-531 were dosed 100mg/kg QD. Animals in ARQ531 group started showing signs of sickness on day 3, and all died on day 6 due toxicity; in contrast, no animal in HBW-3-10 group showed any sign of sickness or died during the entire course of study. Conclusions: We have discovered a novel second generation reversible BTK inhibitors HBW-3-10, that has a superior preclinical profile, efficacy and safety than other known ones. HBW-3-10 provides a valuable clinical candidate for treating Ibrutinib resistant CLL and beyond!