Cenersen, An Antisense Inhibitor of p53, in Combination with Fludarabine, Cyclophosphamide, and Rituximab Shows Clinical Activity in High Risk CLL.

Chronic lymphocytic leukemia (CLL) is a malignant B cell lymphoproliferative disorder characterized by the clonal expansion and accumulation of CD5+ B cells. CLL is quite heterogeneous in clinical behavior, where some patients remain asymptomatic and require no therapy for many years, whereas other patients follow an aggressive clinical course with early need for therapy and short overall survival. Those patients with somatic deletions and / or mutations of p53, a central mediator of cell cycle control, apoptosis, and a potent tumor suppressor, follow the most aggressive clinical courses of all patients with CLL. Furthermore, these patients tend to be refractory to conventional CLL chemotherapy regimens, and therefore novel therapeutic approaches are needed. Cenersen (Eleos Inc.) is a 20-mer antisense molecule and binds to a coding region of exon 10 in p53 mRNA and has been shown in vitro to increase apoptosis in lymphoma cell lines. We hypothesize that the addition of cenersen to chemo-immunotherapy will enhance leukemic cell apoptosis and thus increase chemotherapy sensitivity in vivo for patients with aggressive CLL. Here we report early clinical responses to cenersen in combination with FCR chemo-immunotherapy at a planned interim analysis for efficacy and safety after enrollment of 17 patients.

We have undertaken a clinical trial at Duke University Medical Center of cenersen in combination with chemo-immunotherapy for patients with CLL or SLL (ClinicalTrials.gov identifier: NCT00636155). Patients with relapsed CLL or previously untreated patients with a deletion or mutation of p53 requiring therapy were enrolled. Cenersen was administered at 2.4 mg/kg/day as a continuous infusion over 24 hours starting on day 1 and ending on day 4. Fludarabine was administered daily at 25 mg/m² on days 2 through 4, cyclophosphamide was administered daily at 250 mg/m² on days 2 through 4, and rituximab was administered at 375 mg/m² on day 2. Cycles were repeated every 28 days for a maximum of 6 cycles. The primary outcome measure was the overall response rate (complete and partial responses by iwCLL response criteria), and secondary outcome measures included progression free survival, event free survival and overall survival. All patients received growth factor support as well as prophylaxis with acyclovir and trimethoprim / sulfamethoxazole. Interphase cytogenetics and sequencing analysis for somatic mutations of p53 was performed in all patients.

To date, 17 patients have been enrolled to a protocol-defined interim analysis of efficacy and safety. Of the enrolled patients, 1 was previously untreated, and the remaining 16 were relapsed (median number of prior therapies 4, range 1 - 8). Among previously treated patients, the mean response duration of the most recent prior regimen was 2 months. 15 of 16 had previously received fludarabine and 14 of 16 patients had previously received rituximab. 10 of 16 patients tested showed 17p deletions by FISH. Among the 14 patients tested to date, 8 showed somatic mutations in p53 by sequence analysis, of these, 6 showed both deletion of 17p as well as somatic mutation of p53. Of the 17 patients enrolled, 14 are evaluable for response: 1 patient has not yet received 3 cycles of therapy and 2 patients voluntarily discontinued trial participation. To date, 5 patients show a partial response by iwCLL criteria, including 2 patients who have concluded all therapy and show a partial response with incomplete hematologic recovery (PRi) with no detectable CLL B cells by flow cytometry analysis of bone marrow aspirate. One of these patients has subsequently undergone allogeneic stem cell transplantation. The remainder of the patients had stable disease (SD), though 3 were removed from study prior to the completion of 3 cycles for inadequate response as determined by the treating physician. There have been 4 episodes of febrile neutropenia, and there have been no toxicities specifically attributed to cenersen.

We have observed encouraging clinical responses to the combination of cenersen with FCR chemo-immunotherapy among a group of extensively pretreated patients with high risk genetic features. There does not appear to be any excess toxicity associated with the investigational agent. The results to date suggest that there may be therapeutic benefit to p53-targeted therapies in high risk CLL. This study will be continued to full accrual.

Lanasa:Genentech: Membership on an entity's Board of Directors or advisory committees. Off Label Use: Rituximab, in combination with fludarabine and cyclophosphamide, for the treatment of CLL. Cook:Eleos: Employment. Rizzieri:Eleos: Research Funding.