Complex crystal structure determination and anti-non-small-cell lung cancer activity of the Hsp90N inhibitor Debio0932

Debio0932 is a promising lead compound in phase I clinical trials targeting the N-terminal ATP-binding pocket of the molecular chaperone heat-shock protein 90 (Hsp90^N). The absence of a crystal structure of the Hsp90^N-Debio0932 complex, however, has impeded further structural optimization of Debio0932 and understanding of the molecular-interaction mechanism. Here, a high-resolution crystal structure of the Hsp90^N-Debio0932 complex was successfully determined (resolution limit 2.20 Å; PDB entry 6lr9) by X-ray diffraction and the molecular-interaction mechanism was analysed in detail, which suggested that Debio0932 suppresses cancer cells by accommodating itself in the ATP-binding pocket of Hsp90^N, disabling its molecular-chaperone capability. The results of a thermal shift assay (ΔT_m = 8.83 ± 0.90°C) and isothermal titration calorimetry (K_d = 15.50 ± 1.30 nM) indicated strong binding and favourable thermodynamic changes in the binding of Hsp90^N and Debio0932. Based on the crystal structure of the complex and on molecular-interaction analysis, 30 new Debio0932 derivatives were designed and nine new derivatives exhibited increased binding to Hsp90^N, as determined by molecular-docking evaluation. Additionally, Debio0932 suppressed cell proliferation (IC₅₀ values of 3.26 ± 2.82 µM for A549, 20.33 ± 5.39 µM for H1299 and 3.16 ± 1.04 µM for H1975), induced cell-cycle arrest and promoted apoptosis in three non-small-cell lung cancer (NSCLC) cell lines. These results provide novel perspectives and guidance for the development of new anti-NSCLC drugs based on the lead compound Debio0932.

Debio0932, a second-generation oral heat shock protein (HSP) inhibitor, in patients with advanced cancer-results of a first-in-man dose-escalation study with a fixed-dose extension phase

BACKGROUND

Objective was to determine maximum tolerated dose (MTD), recommended dose (RD) and schedule, safety, pharmacokinetic (PK) profile, pharmacodynamic (PD) effects, and antitumor activity of Debio0932, a new second-generation oral heat shock protein (HSP) inhibitor.

PATIENTS AND METHODS

This was a multicenter, uncontrolled, open-label, nonrandomized, dose-escalation study in adults with treatment-resistant advanced cancer. Groups of three patients received oral Debio0932 either daily or every other day. The starting dose of 50 mg was escalated until the MTD was reached, i.e. dose-limiting toxicity (DLT) occurred in ≥2 patients. Further 9 patients and an extension cohort of 30 patients were treated at the next lower dose (=RD). Adverse events (AEs), tumor response, PK, and HSP70 levels in peripheral blood mononuclear cells were recorded over 30 days.

RESULTS

Fifty patients were treated with doses up to 1600 mg, at which level three DLT occurred (febrile neutropenia, diarrhea, asthenia). In total, 39 patients were then treated at the RD of 1000 mg daily. Most common drug-related AEs were asthenia and gastrointestinal events. No ocular toxicities were observed. Debio0932 was rapidly absorbed and metabolized. Plasma steady state was reached within 9 days. Volume of distribution was high and elimination half-life was 9-11 h. Food had no effect on PK. PD showed large interpatient variability, but no dose-effect relationship. Partial tumor response was observed in 2 patients (NSCLC and breast cancer), stable disease (SD) in 12 patients (5 of 8 NSCLC patients). In the extension cohort, 9 patients had SD, and 1 patient a partial metabolic tumor response.

CONCLUSION

Debio0932 has limited clinical activity, together with manageable toxicity. Further development as adjunct treatment of NSCLC at daily doses of 1000 mg is warranted.

CLINICAL TRIAL

NCT01168752.