Quantification of MDM2 Gene Expression Level by RQ-PCR Is Predictive of the First Complete Remission in Adulte Acute Myeloid Leukaemia.

The overall survival of patients with p 53 mutated gene acute myeloid leukaemia (AML) is significantly shorter than those of patients without mutations. The frequency of p53 gene mutations in AML ranges from 4 to 15% in populations from USA and Europe, thus this is not a useful criteria in the vast majority of patients with a poor prognosis. Mdm2 is the natural functional inhibitor of p53, but very few studies have assessed its prognosis value in AML, and this was done only at the protein level, suffering major lacking of precision.

In this study, we have quantified gene expression levels of both MDM2 and p53 by RQ-PCR in a series of 18 patients with more that 50% blast cell in the bone marrow: 4 AML1, 6 AML2 (one with multilineage dysplasia), 4 AML4 (one AML4 Eos), 4 AML5. Median age was 57 years, ranging 39–84. Eight patients had a white cell blood count over 30 G/L. Eleven patients had a normal karyotype, 3 had a complex caryotype, 2 had an inv(16). FLT3 amplification was found in 2 cases. Two patients died immediately following the diagnosis because of an immediate massive global failure of vital functions. Three patients were treated with low doses of Aracytine because of the performance status. Thirteen patients were treated with intensive chemotherapy according classical scheme, and complete remission was obtained in 6 cases.

After total RNA extraction of bone marrow mononuclear cells, assessment of MDM2 and p53 gene expression levels was done in duplicate on an ABI PRISM 7000 automat using the TaqMan^R Assay on demand^TM gene expression reference system. The Abl1 gene was used as a reference gene for the control of amplification. The relative expression levels of the genes were calculated as follow: briefly, for each gene, the cycle threshold (CT) was defined for a delta Rn of 10⁻¹. Then, the delta CT (DCT) was calculated as the CT of the gene minus the CT of Abl1 (expected CT for Abl1 ranged from 22 to 24). For each experimental condition, the delta delta CT (DDCT) was calculated as the DCT of the given condition minus the DCT of the RNA pool. For each gene and in each experimental condition, the calculated relative gene expression level was equal to 2^−DDCT.

No correlation was found between p53 gene expression levels and any of the other clinical, biological or genetic prognosis marker. By contrast, complete remission was obtained for all patients with low levels MDM2 expression and MDM2 expression was markedly increased in 5 out the 7 patient without remission (t-test, p=0,01). It is noteworthy that, among the 3 patients treated with low doses of Aracytine, the patient with the shortest survival was the only one with increased levels of MDM2. No correlation was found between MDM2 gene expression levels and other biological prognosis markers. This suggests that quantification of MDM2 mRNA by RQ-PCR could be an interesting prognosis factor in AML.