Targeting Hsp90beta potentiates nab-paclitaxel-based chemotherapy response in pancreatic cancer models

Objective: Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive malignancy with an extremely poor prognosis. Standard treatment with nab-paclitaxel and gemcitabine (NPT+GEM) yields a median survival of only 8.5 months. Heat shock protein 90 (Hsp90) client proteins-including EGFR, IGF-1R, Raf, PI3K, AKT, CXCR4, and MMP2/9-are implicated in proliferation, survival, angiogenesis, metastasis, and chemoresistance in multiple tumor types, including PDAC. Traditional Hsp90 inhibitors that bind to the N-terminal ATP-binding site exhibit pan-inhibitory activity against all four Hsp90 isoforms, leading to induction of the heat shock response, which causes chemoresistance and dose-limiting toxicities. Here, we evaluated the antitumor efficacy of novel Hsp90beta-selective inhibitors in preclinical PDAC models. Methods: In vitro cell proliferation assays were performed using the colorimetric WST-1 method. Protein expression levels were analyzed by immunoblotting. Tumor growth studies were conducted using NOD/SCID mice bearing subcutaneous xenografts, and survival studies were carried out in PDAC peritoneal dissemination xenograft models. Results: Overexpression of Hsp90beta and its client proteins-including EGFR, IGF-1Rbeta, CXCR4, and AKT-was observed across PDAC-associated epithelial, endothelial, and stromal cells, whereas normal human pancreatic tissue showed negligible expression. The Hsp90beta-selective inhibitors NDNB-25 and NDNB-21, synthesized through a structure-based approach, demonstrated dose-dependent antiproliferative activity and synergistic effects when combined with standard chemotherapy in Hsp90beta-expressing PDAC epithelial and stromal cell lines. NDNB-25 reduced expression of key Hsp90 client proteins (EGFR, IGF-1R, HER2, p-MEK, p-ERK, p-S6, and c-Myc) without inducing HSP90 expression. Treatment also induced expression of apoptosis markers (cleaved caspase-3 and cleaved PARP-1) and the epithelial differentiation marker E-cadherin. In subcutaneous xenograft models using Hsp90beta-overexpressing PDAC cell lines (AsPC-1 and Panc-1), NDNB-25 and NDNB-21 significantly inhibited tumor growth, with synergistic effects in combination with chemotherapy. In AsPC-1 xenografts, tumor growth inhibition ranged from 47-61% with NPT+GEM, 58-72% with NDNB-25 or NDNB-21 monotherapy, and 79-85% with combination treatment. In AsPC-1 peritoneal dissemination models, Hsp90beta inhibitors provided limited survival benefit. In Capan-2 PDAC xenografts with low Hsp90beta expression, the antitumor effects of NDNB-25 and NDNB-21 were less pronounced. Conclusion: Our preclinical data support the continued development of Hsp90beta-selective inhibitors as next-generation agents capable of improving treatment outcomes in PDAC, particularly in tumors with high Hsp90beta expression.