Development of PI3K/mTOR-HSP90 ligand conjugates for improved colorectal cancer therapy

Dysregulation of the PI3K/Akt/mTOR signaling pathway is a hallmark in colorectal cancer (CRC) development, making it an important target for anticancer drug discovery. However, limited efficacy and poor selectivity have significantly hindered the clinical application of PI3K/mTOR inhibitors. To overcome these limitations, we designed a series of novel small-molecule drug conjugates (SMDCs) by linking potent PI3K/mTOR inhibitors to extracellular heat shock protein 90 (eHSP90)-targeting ligands via cleavable linkers. This strategy exploits the overexpression of eHSP90 in tumors to facilitate receptor-mediated endocytosis and selective intracellular release of the active payload within the tumor microenvironment. Among the synthesized conjugates, CC-11 emerged as a lead compound with potent HSP90 binding activity (IC₅₀ = 15 nM) and inhibition of PI3Kα kinase (IC₅₀ = 0.54 nM). CC-11 demonstrated superior in vitro anti-proliferative activity against CRC cell lines (HCT-116 IC₅₀ = 0.20 μM; HT-29 IC₅₀ = 0.89 μM) while exhibiting enhanced selectivity (50-fold) over normal liver cells compared to its monomeric PI3K inhibitor counterpart (CC-M-1). Gene knockdown experiments confirmed that CC-11's activity is dependent on the presence of HSP90. Importantly, CC-11 achieved significantly improved in vivo efficacy in HCT-116 xenograft models (62.12 % tumor growth inhibition) compared to CC-M-1 (32.95 %), without observable toxicity. Mechanistic studies validated target engagement through suppression of the PI3K/mTOR signaling pathway. Although further optimization of plasma stability is required, this work highlights the potential of SMDCs utilizing HSP90 ligands to enhance both the selectivity and efficacy of PI3K/mTOR inhibitors, positioning CC-11 as a promising candidate for targeted CRC therapy.