High Number of Copy Number Alterations and Over-Expression of Genes Involved in the Response Mechanisms to Genotoxic Stress Both Characterize Newly Diagnosed Multiple Myeloma (MM) Patients Carrying Amplified MDM4 and/or Deleted p53,

The p53 tumor suppressor pathway is tightly kept in check, or completely silenced in cancer cells. A potent inhibitor of p53 is represented by MDM4, which is critical for the control of p53 activity during the response to stress and is often amplified in several types of cancer. TP53 mutations are rare in newly diagnosed MM, while occur more frequently as late event in the course of the disease and are related to survival. Recently, the adverse prognostic impact of chr. 1q amplification, described in almost 40% of newly diagnosed MM pts, has been reported. The minimal amplified region on chr. 1q harbors MDM4. Since both del(17p) and amp(1q) identify a subgroup of high-risk MM pts, even when the novel agents are part of up-front treatment strategy, we molecularly analyzed a subgroup of MM patients treated with bortezomib-thalidomide-dexamethasone (VTD) incorporated into autologous stem cell transplantation, in order to investigate mechanisms which might be activated in myeloma plasma cells to direct and/or indirect limit the p53 function.

Thirty eight pts treated with VTD incorporated into autologous stem cell transplantation were analysed by means of gene expression profile (Affymetrix U133 Plus2.0 array) and unpaired analysis of copy number alterations (CNA) (Affymetrix 6.0 SNP array). Both GEP and SNP arrays experiments were performed on highly purified CD138+ bone marrow plasma cells obtained at diagnosis from each pts. The presence of CNAs in chr.1 and 17 was evaluated to identify pts carrying amp(1q) and del(17p).

Eighteen out of 38 pts (42%) carried a minimal amplification region of 1,1 Mb on chr.1q, which harbors MDM4. Five out of 38 pts (13%) carried a minimal deletion region of 482 Kb on chr.17, which harbors TP53. To explore the involvement of the p53 pathway in MM, pts were stratified according to the presence of amplified MDM4 and/or deleted p53 (group A, 18 pts) or the absence of both these abnormalities (group B, 20 pts). Baseline clinical characteristics were homogeneous, except for a higher rate of ≥ 3 bone lesions in pts carrying amplified MDM4 and/or deleted p53. The rate of best complete or near complete response was 89% in group A and 75% in group B. With a median follow-up of 36 months, the risk of relapse or progression was 50% for pts in group A and 25% for those in group B. The average number of aberrations per group was overall higher in group A as compared to group B (165 vs. 103 CNAs, p =0.03); indeed, the presence of amplified MDM4 and/or deleted p53 was significantly associated with a list of 95 CNAs (clustered on chr. 1, 2, 6, 8, 11, 13, 16 and 18), which included del16q (with a minimal area of deletion including WWOX), observed in 39% vs. 5% cases from group A and B, respectively (p<0.05) and chr.8 aberrations (with amplifications and or deletions, both including TRPS1) observed in 61% vs. 15% cases from group A and B, respectively (p<0.05). A comparison of expression profiles of patients carrying or not amplified MDM4 and/or deleted p53 confirmed the over-expression of MDM4 in the former group of pts and highlighted in these pts an overall activation of genes involved in the response mechanisms to genotoxic stress: indeed a significant over-expression of damage sensor genes (ATM, RAD9, RAD 50, ATRip), of damage signal mediator genes (H2AFX, 14-3-3), of genes involved in regulation of cell proliferation (CDK6, CDC25, CCND2) and of anti-apoptotic genes (BCL2, p73) was observed in pts with amplified MDM4 and/or deleted p53 (one-way ANOVA plus multiple-test correction with FDR <0,05). Finally, this group of pts significantly over-express the transcription factor YY1, which is known to interact with p53, thus inhibiting its transcriptional activity.

Pts carrying amplified MDM4 and/or deleted p53 showed a significantly higher number of CNAs and the significant over-expression of genes involved in the response mechanisms to genotoxic stress, as compared to pts lacking these chromosomal aberrations. This might account for the worse outcome of patients harboring del(17p) and/or amp(1q). The amplification of MDM4 locus and the over-expression of YY1 might contribute to maintain p53 in an OFF state by an indirect mechanism. Additional data on the role of both direct and indirect control of p53 pathway on VTD-treated MM pts prognosis, extended to an higher number of pts, will be presented during the meeting.

Supported by: Fondazione Del Monte di Bo e Ra, Ateneo RFO grants (M.C.) BolognAIL.

Cavo:Genzyme: Honoraria.