Abstract 3035: Effects of novel isoform selective HSP90 beta inhibitors alone and in combinations against experimental esophageal adenocarcinoma

Abstract Background: Inhibition of the heat shock protein 90 (HSP90) chaperone activity with small molecules is an attractive therapeutic approach for cancer treatment because more than 300 client proteins are involved in aggressive cancer growth and metastasis. To date, ∼20 inhibitors have undergone clinical trials, however, all have failed due to pan-inhibitory activities and insufficient isoform selectivity. In this study, we have investigated isoform selective HSP90β inhibitors, NDNB21, NDNB25 and NDNB11.82 on esophageal adenocarcinoma (EAC), which is one of the most aggressive human cancers with increasing incidence in the United States. A major target for EAC therapies is the human epidermal growth factor receptor 2 (HER2), which is a well-known client protein of HSP90. In this research, we tested the effect of NDNB21 and NDNB25 on HER2 overexpressing EAC cell lines, including one cell line that acquired lapatinib resistance either alone or in combination with HER2/MET targeting by lapatinib/capmatinib. Methods: We first evaluated HER2/pHER2 and MET/pMET expression status by Western blot analysis in a panel of EAC cell lines (Flo-1, ESO26, OE19, OE33, SK-GT-2, ESO51, OACM5.1C, and LPR-OE19). Lapatinib-resistant OE19 (LPR-OE19) cell line was established from OE19 cells by intermittent exposure to increasing concentrations of lapatinib for a period over six months. Lapatinib is a potent EGFR/HER2 inhibitor and capmatinib is a potent c-MET inhibitor. Antiproliferative activities were measured by WST-1 assay and Western blot analyses were performed to evaluate apoptosis. Results: NDNB21 and NDNB25 dose-dependently inhibited in-vitro cell proliferation of HER2 overexpressing EAC cell lines with NDNB11.82 maintaining much lower potency. All three HER2 overexpressing EAC cell lines showed significant sensitivity to NDNB21 and NDNB25 mediated inhibition of cell proliferation with IC50 values between 16 nM to 2 µM and degree of sensitivities are OE19>LPR-OE19>OE33. NDNB21 and NDNB25 dose-dependently induced apoptosis as measured by the expression of cleavage of poly ADP-ribose polymerase (cleaved PARP). Treatment with increasing doses of NDNB21/NDNB25 resulted in a dose-dependent decrease in HER2, p-HER2, AKT, and p-AKT. Coadministration of NDNB21 or NDNB25 with lapatinib effectively inhibited HER2 phosphorylation and significantly enhanced inhibition of cell proliferation in OE19/LPR-OE19 but not in OE33. The OE33 cells with the strongest expression of phosphorylated MET showed reduced sensitivity to HER2 targeted NDNB21/NDNB25/lapatinib induced cell death compared to that of OE19/LPR-OE19. OE33 showed enhanced cell death when HER2 targeted NDNB25 were combined with MET inhibitor capmatinib. Conclusions: In conclusion, our data shows that NDNB21/NDNB25 exhibited potent apoptotic activity against HER2-positive EAC cells either alone or in combination. Citation Format: Md Sazzad Hassan, Erin Garzella, Annie Ritter, Elizabeth Heffernan, Aktar Ali, Brian Blagg, Urs von Holzen. Effects of novel isoform selective HSP90 beta inhibitors alone and in combinations against experimental esophageal adenocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 3035.