Rituximab and 2-Cda Activity in CLL/SLL Patients: An Update of Pharmacogenomic and Clinical Results

In CLL/SLL pts the combination of purine analogue and rituximab represents a well known effective therapy. Human concentrative nucleotide transporter (hCNT1) and human equilibrative nucleotide transporter (hENT1) are proteins involved in uptake of nucleoside analogues into the tumour cells. The aim of this study was to investigate R-2CDA as first line therapy and in pre-treated pts with active CLL and SLL, and to identify, by pharmacogenomic approaches, genetic factors that may predict clinical response to such treatment. 45 pts with active CLL (27 pts) or SLL (18 pts) were treated. The median age was 59 years (31–76). Patients received 4 cycles of rituximab 375 mg/m² on day 1 and 2-CDA 0.1 mg/kg (subcutaneously) on days 2 to 6. The treatment was repeated every 4 weeks. A CT scan of the abdomen was performed at baseline and at the end of treatment in all pts; CT scan before treatment was abnormal in 42 pts. Minimal residual disease was evaluated by 6-colour flow-cytometry and PCR methods. Treatment outcome was evaluated according to NCI-WG updating guidelines: to confirm a CR the marrow should be free of clonal B-CLL cells by flow-cytometry and a CTscan should be negative. At baseline we investigated, on bone marrow for SLL and on peripheral blood for CLL, the expression of human concentrative nucleotide transporter (hCNT1) and human equilibrative nucleotide transporter (hENT1) using ABI PRISM 7000 Real Time RT-PCR platform in 24 pts. 42 pts (26 untreated) were fully evaluable for response.LDH and beta2microglobulins were abnormal in 14% and 30% of pts respectively. The percentage of neoplastic cells in the bone marrow was more than 70% in 17% of pts. The overall response rate was 88% (26% CR and 62% PR), with 21% of untreated pts and 5% of pre-treated pts achieving a CR. Severe neutropenia (grade 4) developed in 7% of pts. 4 pts developed pneumonia, 1 with neutropenia. 1 pt had reactivation of herpes zoster virus and 1 pt experienced febrile neutropenia of unknown origin. The median TTP was 41 months. There was not statistically significant difference in terms of duration of response between untreated and pre-treated pts (TTP: 44 vs 35 months, p=0.1814). Pts achieving a CR had a longer response duration than pts with PR (p=0.0047). Low serum lactate dehydrogenase levels, a lower (< 70%) neoplastic marrow infiltration at baseline and a normal CT scan at the end of therapy (independent of response) predicted a longer response duration (p=0.0145, p=0.0164 and p=0.008 respectevely). The pharmacogenomic analysis showed a difference (p=0.8345) in terms of hCNT1 expression levels between patients achieving a CR and pts with PR or NR. Pts in CR had higher levels of hCNT1 expression and the increase of 1 unit of the expression level of hCNT1 is associated with a reduced risk of PD by 33%. The refractory pts had lower levels of hCNT1 than non refractory pts but the difference was not statistically significant. There was no statistically significant difference in terms of hCNT1 expression between CLL and SLL pts. The combination of 2-CDA and rituximab induces a high response rate, including CR in pre-treated pts. The treatment is well tolerated with acceptable toxicity also in pts over 70 years. The achievement of a CR is important to obtain durable response. The correlation between the levels of expression of hCNT1 and the response to therapy needs to be confirmed in larger studies.