Pharmacogenomic Study of Carfilzomib in Relapsed/Refractory Multiple Myeloma Suggests That Carfilzomib Is a More Potent Proteasome Inhibitor Than Bortezomib

The introduction of bortezomib (BOZ) – the first FDA-approved proteasome inhibitor (PI) – as a therapeutic option for multiple myeloma (MM) has significantly improved patient outcomes in the last decade. However, relapsing patients often have BOZ-resistant disease. Carfilzomib (CFZ), a next-generation PI, recently received FDA approval for the treatment of patients with relapsed and/or refractory MM with prior history of BOZ treatment. The present study is the first post-CFZ phamacogenomic study in patients with relapsed/refractory MM, and was performed as part of the previously reported UARK Phase II CFZ compassionate use trial (registered with ClinicalTrials. gov as NCT00999414).

Gene expression profiling (GEP) analyses were performed on samples from 20 patients, all of whom had received prior treatment with BOZ and at least 1 immunomodulatory agent. CD138-purified plasma cells were collected from patients prior to and 24 hours after the second dose of CFZ. Ten patients received 20 mg/m²/day, and 10 patients received 27 mg/m²/day CFZ. Similar GEP analyses were done on pre- and 48-hr post a BOZ test dose (1. 0mg/m²) paired samples available on 25 previously treated patients on Total Therapy 6 (TT6) trial (received >1 cycle of prior treatment, 14 with previous BOZ treatment), and 142 newly diagnosed patients on Total Therapy 3A (TT3A) clinical trial. All samples were hybridized to Affymetrix U133Plus2. 0 arrays according to the manufacturer's recommendations.

Eight patients (40%; 4 patients in each dosing group) achieved responses of PR or better after 1 cycle of CFZ. At the false discovery rate (FDR) of 0. 05 by paired significance analysis of microarrays (SAM), expression levels of 113 probesets (104 genes) significantly changed in response to CFZ treatment, with higher expression values observed post CFZ. Among these 104 genes, 22 (21%) were proteasome-related genes (PSMA1, PSMA4, PSMA5, PSMA7, PSMB2, PSMB3, PSMB4, PSMB5, PSMB6, PSMB7, PSMC1, PSMC3, PSMC4, PSMC5, PSMD1, PSMD2, PSMD3, PSMD4, PSMD6, PSMD11, PSMD13, PSMD14). Additionally, expression-based proliferation indices (Zhan, Blood 2006) were significantly lower (p<0. 05) for the post CFZ samples. Using the same statistical analysis, no probesets were significantly changed in response to the BOZ test dose in the 25 patients treated on TT6. Additionally, the GEP-based proliferation indices in response to BOZ were also unchanged. The same results were obtained when comparison was limited to the 14 TT6 patients with prior BOZ treatment. In a similar analysis of samples from 142 TT3A patients (newly diagnosed patients with no prior BOZ exposure), expression of 51 probesets (40 genes) significantly changed (FDR=0. 05) in response to BOZ treatment. Among those 40 genes, only 3 (7. 5%) were proteasome-related (PSMA6, PSMC2, PSMD14). PSMD14 is the only proteasome-related gene overlapping between the CFZ and the BOZ studies at FDR=0. 05. PSMB2, PSMD4, and PSMA7 were also changed when a higher FDR threshold (FDR=0. 15) was used for TT3A. Above results suggest that the proteasome subunits targeted by these 2 PIs could be different. Higher expression of proteasome genes following test doses of proteasome inhibitors may reflect a cellular response to the inhibition of a critical pathway. Alternatively, it may reflect selection of cells less sensitive to the inhibitor.

This is the first-in-human pharmacogenomic study comparing CFZ with BOZ and reporting on their differential GEP features. We have compared CFZ GEP effects (all patients with prior BOZ exposure) to BOZ GEP effects on patients with prior BOZ exposure or without prior BOZ exposure. The study results indicate that CFZ leads to a more global effect on the proteasomal degradation pathway compared with BOZ, and likely has more potent proteasome inhibitory activity than BOZ. This effect may in part reflect CFZ's irreversible inhibitory activity, whereas BOZ is a reversible inhibitor.

Barlogie:Onyx: Research Funding. Usmani:Onyx: Consultancy, Research Funding.