The discovery and characterization of K-563, a novel inhibitor of the Keap1/Nrf2 pathway produced by Streptomyces sp.

Keap1/Nrf2 pathway regulates the antioxidant stress response, detoxification response, and energy metabolism. Previous reports found that aberrant Keap1/Nrf2 pathway activation due to Kelch-like ECH-associated protein 1 (Keap1) mutations or Nuclear factor E2-related factor 2 (Nrf2) mutations induced resistance of cancer cells to chemotherapy and accelerated cell growth via the supply of nutrients. Therefore, Keap1/Nrf2 pathway activation is associated with a poor prognosis in many cancers. These previous findings suggested that inhibition of Keap1/Nrf2 pathway could be a target for anti-cancer therapies. To discover a small-molecule Keap1/Nrf2 pathway inhibitor, we conducted high-throughput screening in Keap1 mutant human lung cancer A549 cells using a transcriptional reporter assay. Through this screening, we identified the novel Keap1/Nrf2 pathway inhibitor K-563, which was isolated from actinomycete Streptomyces sp. K-563 suppressed the expression of Keap1/Nrf2 pathway downstream target genes or the downstream target protein, which induced suppression of GSH production, and activated reactive oxygen species production in A549 cells. K-563 also inhibited the expression of downstream target genes in other Keap1- or Nrf2-mutated cancer cells. Furthermore, K-563 exerted anti-proliferative activities in these mutated cancer cells. These in vitro analyses showed that K-563 was able to inhibit cell growth in Keap1- or Nrf2-mutated cancer cells by Keap1/Nrf2 pathway inhibition. K-563 also exerted synergistic combinational effects with lung cancer chemotherapeutic agents. An in vivo study in mice xenotransplanted with A549 cells to further explore the therapeutic potential of K-563 revealed that it also inhibited Keap1/Nrf2 pathway in lung cancer tumors. K-563, a novel Keap1/Nrf2 pathway inhibitor, may be a lead compound for development as an anti-cancer agent.