Polymorphisms in the Promoter Region of the Mcl-1 Gene Are Associated with Ex Vivo Cytotoxicity but Not with Response to Treatment in Advanced Chronic Lymphocytic Leukemia (CLL).

High levels of Mcl-1 have been related to a poor response to therapy in patients with CLL. Genetic polymorphisms in the promoter region of the Mcl-1 gene consisting in insertions of 6 (+6) or 18 (+18) bp have been described in 30% to 60% of patients with CLL. The biological and clinical translation of such polymorphisms is controversial. We have analysed this issue in a cohort of newly diagnosed patients with CLL (14 F/ 46 M; 80% in B or C Binet’s stage), treated with a combination of fludarabine (F), cyclophospamide (C) and mitoxantrone (M). Polymorphisms were correlated with:

• Mcl-1 RNA expression as assessed by quantitative PCR,

• ex vivo cytotoxicity against F, C, and M, alone or in combination, using the MTT assay, and

• clinical response to treatment.

The frequency of the wild type (wt), +6, and +18 allel was 56%, 12%, and 32 %, respectively (table). Twenty-one of 60 (35%) patients were homozygous for wt allel. Quantification of Mcl-1 RNA expression was performed in 18 patients. Wt/wt patients (n=6) tended to have lower Mcl-1 gene expression than the remaining patients (1.0 AU ±0.4 vs 2.2 AU ±2.8). Ex vivo cytotoxicity was different according to the Mcl-1 genotypes for F, M, F+M, and C+F, but not for FCM. The highest cytotoxicity was observed in patients with +18/+18 genotype (n=7) while those with wt/wt (n=11) presented intermediate cytotoxicity and those with other genotypes (n=17) had the lowest cytotoxicity. Twenty-eight patients achieved CR, 22 PR, and 5 failed to respond. No relationship was found between Mcl-1 polymorphisms and response to therapy (table). Interestingly, however, the ex vivo response to F (58.2% ±16 vs 45.7% ±16, p=0.05) and F+M (87% ±9 vs 76% ±15.5, p=0.04) was greater in the 13 patients who achieved MRD-negative CR. After a median follow up of 28 months (range: 6–53), 16 of 38 patients have progressed. No relationship was found between Mcl-1 polymorphism and progression after treatment. In summary, in this series of patients with advanced CLL homogeneously treated the frequency of insertions in the promoter region of Mcl-1 gene was high. Although Mcl-1 polymorphisms were associated with the ex vivo response to antileukemic drugs, they did not correlate with response to treatment and disease progression.