A Novel Class of Sulfonanilides Entering Clinical Trials for Targeted Treatment of Multiple Myeloma: Dual-Mechanism Compounds Inhibiting HIF1A-Signaling and Inducing Apoptosis
Authors: Hose Dirk , Seckinger Anja , Goldschmidt Hartmut , Meißner Tobias , Leber Blanka , Neben Kai , Hillengass Jens , Bertsch Uta , Janssen Bernd , Klein Bernard , Lewis Joe , Vanderkerken Karin , Schultes Christoph 
Published: October 2019

Abstract
Abstract 2987

Background.
We have recently shown HIF1A to be expressed in 95.4% of CD138-purified myeloma cell samples from previously untreated patients (n= 329), with significantly higher [lower] expression in case of presence of t(4,14) [hyperdiploidy] vs. patients without the respective aberration. This makes HIF1A an interesting target in myeloma treatment. Additionally, we have shown about 40% of myeloma cell samples to have a proliferation-index above the median plus three standard-deviations of normal bone-marrow plasma cells, and we and others have proven proliferation to be associated with adverse prognosis in myeloma. Here, we report on 2 members of a novel class of sulfonanilides, their preclinical activity and pharmacology, and their dual mechanism of action, targeting HIF1A-signaling and inducing apoptosis via cell cycle arrest and tubulin depolymerization.

Patients and Methods.
The effect of the novel sulfonanilides ELR510444 and ELR510552 on the proliferation of 20 human myeloma cell lines and the survival of 5 primary myeloma cell-samples cultured within their microenvironment were tested. The results of efficacy studies in in two murine models (RPMI8226-xenograft-model and 5T33-model) are also presented. The mechanism of action was investigated using a variety of in-vitro assays (see below).

Results.
Preclinical activity in Myeloma. i) The sulfonanilides ELR510444 and ELR510552 completely inhibit proliferation of 20/20 tested myeloma cell lines at low nM concentrations and ii) induce apoptosis in 5/5 primary myeloma cell-samples at 6.4 – 32 nM concentration, without major effect on the bone marrow microenvironment. iii) They significantly inhibit tumor growth (xenograft; RPMI8226 mouse model, 6 mg p.o. bid for ELR510444, 15 mg p.o. bid for ELR510552) and bone marrow infiltration (5T33-model; ELR510444, 6 mg/kg p.o. bid × 4d, rest 3d (cycle)). Mechanism of action. Apoptosis induction and G2/M-block. i) Both compounds lead to caspase-3/7 activation and subsequent apoptosis with cellular EC50 values of 50–100 nM. ii) The compounds induce an initial cellular arrest in G2/M and a significant tubulin depolymerizing effect, followed by an increase in a sub-G1 (apoptotic) population after 24h. HIF1A-inhibition. i) Both compounds show a potent inhibition of HIF1A signaling in a cell based reporter assay (HRE-bla HCT-116) at EC50s of 1–25nM, whereas ii) at concentrations of 1 μ M, neither of the compounds shows an effect in assay systems monitoring the JAK/STAT, NFκB, PI3K/AKT/FOXO or Wnt/β-catenin-signaling pathways. iii) Kinase inhibition profiling showed no significant inhibition at 1μ M in two assays assessing 100 (Invitrogen) and 442 (Ambit) kinases, respectively. Pre-clinical pharmacology. Single dose exposure of 25 mg p.o. yields a maximum concentration of 1.1 μ M with a half life time of 3.6 hours (ELR510444) and 2.7 μ M and 6.6 h (ELR510552) in mice, respectively. The compounds are well-tolerated at levels that are significantly above the in vitro EC50 in all myeloma cell lines and primary samples tested.

Conclusion.
ELR510444 and ELR510552 are very active on all tested myeloma cell lines and primary myeloma cells without major impact on the bone marrow microenvironment, and show activity in two different mouse models. The compounds inhibit HIF1A-signaling and induce apoptosis via cell cycle arrest and tubulin depolymerization. Preclinical pharmacology data show favorable in vivo profiles with exposure levels in mice significantly higher than concentrations required for in vitro activity. Therefore, this novel class of compounds represents a promising weapon in the therapeutic arsenal against multiple myeloma entering a phase I/II trial within the next year.

Disclosures:
Leber: ELARA Pharmaceuticals GmbH: Employment. Janssen:ELARA Pharmaceuticals GmbH: Employment. Lewis:ELARA Pharmaceuticals GmbH: Employment. Schultes:ELARA Pharmaceuticals GmbH: Employment.