Proteomic Signature Predicting Achievement of Very Good Partial Response In Patients with Multiple Myeloma Based On Complementary Label-Free and iTRAQ Quantitative Proteome Analysis

Multiple myeloma (MM) remains mostly incurable. Novel therapies have improved response rates, which are now reaching 100%. More importantly, number of recent studies showed that the depth of response, e.g. achievement of at least 90% reduction of the disease (≥VGPR) is associated with longer disease control. Therefore, improving VGPR rates and establishing predictors of VGPR to a given regimen may be an important clinical goal. High throughput quantitative proteomics may offer greater insight into the actual biology of the malignant cell than genome analysis and therefore, may be more useful in the development of personalized therapy. The objective of this study is to establish a proteomic signature predicting achievement of at least VGPR to initial treatment with bortezomib (Velcade®), pegylated liposomal doxorubicin, and dexamethasone (VDD). We previously reported preliminary proteomic profile of malignant plasma cells (PCs) obtained from a set of naïve MM pts enrolled in the VDD trial (Dytfeld et al., ASH 2009). Here we present the results of differential proteomic analysis of MM PCs of all available samples from the frontline VDD study (≥VGPR vs. <VGPR) using two independent and complementary quantitative proteomic platforms. We also compared the proteomic profile with gene expression data. Preliminary validation of the biomarkers of response prediction is presented.

PCs were acquired from pre-treatment bone marrow specimens after obtaining informed consent from patients (pts), and were thereafter enriched with a RosetteSep^® negative selection kit. Quantitative proteomic analysis of PCs from 17 naïve pts with MM from the VDD study was performed using iTRAQ approach in 8-plex variant. To increase confidence of analysis, label-free quantitative proteomics (LF) based on spectra counting was conducted on PCs from 12 pts. In iTRAQ experiments, proteins were processed with reagents according to the manufacturer's protocol followed by SCX fractionation and LC-MS/MS analysis (4800 Plus MALDI TOF/TOF). Peptides from the MM1S cell line were used as a reference. The data were analyzed using ProteinPilot™. For LF analysis, proteins were fractionated before trypsin digestion on Bis-Tris-Gel and subsequently run on LC-ESI-MS/MS on a linear trap mass spectrometer (LTQ Orbitrap). A database search was carried out using X!Tandem followed by Trans-proteomic Pipeline. At least 1.5-fold difference in expression in both platforms was used as a cut-off value. To correlate proteomics with gene expression of dysregulated proteins of interest, mRNA levels were analyzed by quantitative real time PCR (RT-PCR). Validation of proteomic findings on proteins of interest was performed using Western Blot.

We identified a total of 894 proteins in 3 iTRAQ experiments with high confidence (FDR<1%) and 1058 proteins by LF approach. Based on iTRAQ analysis, 20 proteins were found up-regulated in samples from pts with ≥VGPR (8 out of 17 pts) while 14 were down- regulated. Using LF approach, 284 proteins were elevated in the ≥VGPR group (6 out of 12 pts) while 315 proteins were down-regulated. Both iTRAQ and LF methods showed 15 differentially expressed proteins in common and 14 of them showed identical up or down trends. Interestingly, among differentially expressed proteins, there were proteins involved in proteasome activation (PSME1 and TXNL1), protection against oxidative stress (TXN and TXNDC5), glucose and cholesterol metabolism (TP1, APOA1 and ACAT1) and apoptosis (MX1). RT-PCR performed on a subset of genes confirmed the trend in differential expression between pts with ≥VGPR and <VGPR for TXNDC5 and PSME1. No change in mRNA expression levels was observed in TXN, APOA1, TPI1 and MX1while the trend in expression was reversed for ACAT1. Western blot analysis performed to date validated differential expression of PSME1.

We present patient-derived proteomic characteristics of MM cells using two independent proteomic platforms. As a proof of concept, analysis of PCs obtained from pts enrolled in the frontline VDD study shows differential expression of 34 proteins in pts who achieved ≥VGPR vs. pts with <VGPR. Correlation with gene expression and further validation and functional analysis are in progress.

This study was supported by a grant from the Multiple Myeloma Research Foundation.

Jakubowiak:Millennium, Celgene, Bristol-Myers Squibb, Johnson & Johnson Ortho-Centocor: Honoraria; Millennium, Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Millennium, Celgene, Centocor-Ortho Biotech: Speakers Bureau.