AUTHORS: R. Pal1, R. Berlin1, M.Y. Mapara1, S. Cameron1, D. Stirling2, G.D. Roodman1, and S. Lentzsch1
1 University of Pittsburgh Cancer Institute, Pittsburgh, PA, USA; 2 Celgene Corporation, Summit, NJ, USA
Introduction: Despite impressive response rates induced by IMiDs in patients with multiple myeloma, one of the major side effects of this therapy is the increased risk of thromboembolic events (TEE). Cathepsin G is a serine proteinase present in the azurophilic granules of polymorphonuclear neutrophils (PMNs) and is a potent platelet activator with potency similar to thrombin. In the current study we investigated the effect of IMiDs (CC-4047, CC-5013) on cathepsin G. Methods and Results: CD34+ hematopoietic progenitors were cultured under conditions (IL-3, IL-6 and SCF) supporting the development of granulocytes and treated with CC-4047 or DMSO (control). RNA and protein were extracted for the analysis of cathepsin G. A significant up-regulation of cathepsin G (7.7 fold) was detected in oligonucleotide gene array analysis after 3 days of treatment with CC-4047 as compared to control group. These results were confirmed by RT-PCR, which showed a 3.7 and 7.6 fold mRNA-increase on day 6 and day 10 of culture compared to vehicle control. Measuring cathepsin G in supernatant by ELISA revealed a 1.5 and 1.6 fold up-regulation on day 6 and 10, respectively. Next we analyzed the cathepsin G levels of patients (n=10) treated with CC-5013 before treatment and on day 15 of each cycle. We observed a continuous significant increase of the mRNA levels over the course of treatment (baseline: 1, cycle 2: 1.7 fold, cycle 3: 4.8 fold, cycle 4: 20.7 fold). These data were confirmed by measuring cathepsin G levels in patient serum by ELISA. Cathepsin G significantly increased from a baseline mean of 53 ng/ml to 77.5 ng/ml (cycle 2), 129.2 ng/ml (cycle 3) and 145.5 ng/ml (cycle 4). Conclusions: These results show that IMiDs up-regulate the potent platelet activator cathepsin G in hematopoietic cells and thereby might contribute to the development of thromboembolic events in patients receiving IMiD treatment. These results might explain why aspirin is effective in preventing TEE in patients receiving IMiDs. Further studies are needed to determine if cathepsin G helps to predict thromboembolic events. Inhibition of cathepsin G might be a potential therapeutic target for preventing the hypercoagulable state induced by IMiD treatment.