HSP90 inhibitors can target many oncoproteins simultaneously, but none have made it through clinical trials due to dose-limiting toxicity and induction of heat shock response, leading to clinical resistance. We identified diptoindonesin G (dip G) as an HSP90 modulator that can promote degradation of HSP90 clients by binding to the middle domain of HSP90 (K_d =0.13 ± 0.02 μM) without inducing heat shock response. This is likely because dip G does not interfere with the HSP90-HSF1 interaction like N-terminal inhibitors, maintaining HSF1 in a transcriptionally silent state. We found that binding of dip G to HSP90 promotes degradation of HSP90 client protein estrogen receptor α (ER), a major oncogenic driver protein in most breast cancers. Mutations in the ER ligand-binding domain (LBD) are an established mechanism of endocrine resistance, and decrease the binding affinity of mainstay endocrine therapies targeting ER, reducing their ability to promote ER degradation or transcriptionally silence ER. Because dip G binds to HSP90 and does not bind to the LBD of ER, unlike endocrine therapies, it is insensitive to ER LBD mutations that drive endocrine resistance. Additionally, we determined that dip G promoted degradation of wild type and mutant ER with similar efficacy, downregulated ER- and mutant ER-regulated gene expression, and inhibited WT and mutant cell proliferation. Our data suggest that dip G is not only a molecular probe to study HSP90 biology and the HSP90 conformation cycle, but also a new therapeutic avenue for various cancers, particularly endocrine-resistant breast cancer harboring ER LBD mutations.

HSP90 抑制剂可以同时靶向多种癌蛋白，但由于剂量限制毒性和诱导热休克反应导致临床耐药性，因此没有一种通过临床试验。我们将二氢吲哚酮 G (dip G) 鉴定为 HSP90 调节剂，它可以通过与 HSP90 (K _{d ) 的中间结构域结合来促进 HSP90 客户的降解}=0.13 ± 0.02 μM)，不会引起热休克反应。这可能是因为 dip G 不会像 N 末端抑制剂那样干扰 HSP90-HSF1 相互作用，从而使 HSF1 保持转录沉默状态。我们发现 dip G 与 HSP90 的结合促进了 HSP90 客户蛋白雌激素受体 α (ER) 的降解，ER 是大多数乳腺癌中的主要致癌驱动蛋白。ER 配体结合域 (LBD) 中的突变是内分泌耐药的既定机制，并降低靶向 ER 的主要内分泌疗法的结合亲和力，从而降低它们促进 ER 降解或转录沉默 ER 的能力。因为 dip G 与 HSP90 结合而不与 ER 的 LBD 结合，与内分泌治疗不同，它对驱动内分泌抵抗的 ER LBD 突变不敏感。此外，我们确定 dip G 以相似的功效促进野生型和突变体 ER 的降解，下调 ER 和突变体 ER 调节的基因表达，并抑制 WT 和突变体细胞增殖。我们的数据表明，dip G 不仅是研究 HSP90 生物学和 HSP90 构象周期的分子探针，而且还是各种癌症的新治疗途径，尤其是具有 ER LBD 突变的内分泌耐药性乳腺癌。