Identification of PI3K/HDAC Dual-targeted inhibitors with subtype selectivity as potential therapeutic agents against solid Tumors: Building HDAC6 potency in a Quinazolinone-based PI3Kδ-selective template

Pharmacological inhibition of PI3Kδ for battling solid tumors is relatively unexplored. Given the potential synergism of concurrent PI3Kδ/HDAC6 inhibition, and the drawbacks of pioneering PI3K/HDAC dual inhibitors, we discovered a novel series of dual-targeted inhibitors via building HDAC6 potency in a PI3Kδ-selective template. SAR study culminated in the discovery of compound 59, which exhibited remarkable inhibitory activity against both PI3Kδ (IC₅₀ = 2.3 nM) and HDAC6 (IC₅₀ = 13 nM), along with acceptable subtype specificity. In addition to the attractive anti-proliferative activities, especially against T47D cell line (IC₅₀ = 0.042 μM), 59 treatment dramatically ablated the tumor immune escape-related STAT3 signaling and lowered PD-L1 expression at two-digit nanomolar level, reflecting the immunomodulatory properties. Due to its subtype selectivity, it demonstrated low cytotoxicity against normal cells. This research validated the therapeutic potential of PI3Kδ/HDAC6 dual inhibitors against solid tumors, attributed to their dual roles in anti-proliferation and anticancer immunomodulation.