The ubiquitin-proteasome system is crucial in tumorigenesis. The division rate of cancer cells, thus protein synthesis, is increased in comparison to normal ones, what sensitizes tumors for any protein changes. Proteasome inhibitor - bortezomib was the first inhibitor registered in treatment of blood cancers. However, drugs beneficial for solid tumors are still missing. Therefore targeting of E1 enzyme as a start of UPS pathway may serve as a promising anticancer therapy.
We have designed a novel E1 small molecule inhibitor, CPL-410-005. The inhibitory potency of compound was assessed on purified E1 enzyme, using biochemical assay. Assays to measure cellular poliubiquitylation or ubiquitin-like modifications level were developed. The compound’s biological activity and selectivity was evaluated in a number of cancer cells using cell viability assays, Western Blot and flow cytometry, analyzing programmed cell death, unfolded protein response or cell cycle inhibition.
CPL-410-005 inhibits E1 enzyme with greater potency than MLN7243. This results in cellular polyubiquitylation inhibition, while the impact on other ubiquitin-like modifications (neddylation, sumoilation) is minor. Tumor proliferation rate inhibition was pronounced in reference to the non-malignant cells [IC50 values of 20 nM for HCT-116 cells vs IC50 values of 400 nM for HEK293 cells]. Moreover, a higher level of unfolded protein response or programmed cell death was observed in cells treated with CPL-410-005 in reference to MLN7243 (5% apoptotic cells vs 30% for MLN7243 vs CPL-410-005, respectively). In case of CPL-410-005, apoptosis rate was higher in tumor than in normal cells (80% apoptotic cells vs 20%, respectively). A high throughput study was performed, to determine the activity of CPL-410-005 on 120 human tumor cell lines, showing that >85% tested cell lines responded with IC50 value below 100nM. The initial in vivo studies on tumor human xenografts are ongoing.
We have designed and evaluated in vitro a potent E1 inhibitor - CPL-410-005, which shows promising in vitro activity. Further preclinical studies are necessary to develop this compound as a novel anticancer therapy.
Clinical trial identification
Legal entity responsible for the study
A. Stanczak, A. Górnicka, B. Stypik, M. Mroczkiewicz, J. Pieczykolan, K. Dubiel: Full-time employee of Celon Pharma S.A., Lomianki, Poland. M. Wieczorek: Chief Executive Officer of Celon Pharma S.A., Lomianki, Poland.