Targeted therapy and outcome in chronic lymphocytic leukemia

Abstract

Despite major advances, chronic lymphocytic leukemia (CLL) is still considered incurable. Fludarabine refractory patients and those with TP53disruptions have a particularly poor prognosis. Alemtuzumab is an established treatment option for these patients. However, its use is complicated by immunosuppressive side effects. New drugs targeting cellular pathways are currently developed but there are few manufacturer-independent comparative experiments. The aim of this thesis is to gain an insight into the outcome of patients with advanced CLL and to explore new emerging drugs.

In the first study, the natural history of advanced CLL in a well-defined region without external referrals was retrospectively investigated. All patients diagnosed with CLL 1991-2010 were screened and those with bulky fludarabine refractory (BFR) and double (i.e. fludarabine and alemtuzumab) refractory (DR) CLL were identified. Subjects were primary referrals within the Stockholm region. The ORR to salvage therapy was 20% and the median time to treatment failure was 6 months, both significantly lower in BFR/DR patients than in non-BFR/DR patients. Median overall-survival (OS) was 18 months; 29 months in BFR vs 13 months in DR. Our results on consecutive patients in routine clinical practice may facilitate interpretation of non-randomized trials on novel drugs in advanced-stage CLL.

In the second study, the safety and efficacy of alemtuzumab, when used in routine health care in relapsed/refractory patients at experienced medical centres in a defined region, was evaluated. Records from patients diagnosed within the Stockholm region year 2000-2010 were retrospectively screened. Files from alemtuzumab treated patients were analysed in detail. Patients were heavily pretreated and the majority had fludarabine refractory disease. The median cumulative dose of alemtuzumab was 930 mg and median duration of therapy was 12 weeks. The ORR was 43% and a higher dose was associated with higher response rate. Median OS was 22.5 months. Compared with the results from previous reports, we observed a higher cumulative dose/longer duration of therapy, numerically higher response rates as well as longer survival in our regional, consecutive patients. Our results suggest that optimal patient management and patient identification may result in avoidance of early discontinuation of planned therapy and possibly better treatment outcomes.

In the third study, the safety and efficacy of lenalidomide in combination with alemtuzumab was explored in a phase I study and additionally, the capacity of low-dose lenalidomide in maintaining immune functions in advanced-stage CLL patients prior and during alemtuzumab was evaluated. Tumor flare reaction occurred in some patients but there was no evidence of tumor lysis syndrome. The combination showed an acceptable safetyprofile as well as clinical activity with an overall response rate of 42%. Median progression free survival was 5 months, exceeding 12 months in 3 patients. T-cell stimulation as well as a decreased number of regulatory T cells was evident on low dose lenalidomide. Our results provide the basis for an extended phase 2 trial on this combination of drugs as well as further studies on lenalidomide as an immune-enhancing agent.

In the fourth study, we provide a manufacturer independent, head-to-head comparison on sensitivity of CLL cells to a panel of emerging small targeted therapeutic molecules using highthroughput screening based on an automated fluorescence digital scanning system. Fresh CLL cells from patients with indolent or progressive disease were cultured in a unique primary cell-culture medium and the in vitro anti-tumor effects of 31 small therapeutic molecules were compared. The sensitivity to each drug showed considerable inter-patient variability. Highest mean direct killing was observed with one survivin inhibitor (YM-155), 2 BCL-2 inhibitors (ABT-199, ABT 737) and one selective CDK inhibitor (dinaciclib). Their killing capacity was similarly high in refractory and untreated patients and was significantly higher in cells with TP53disruptions. Sensitivity in bone marrow showed a high correlation to that in blood. Our results may help to identify drugs of particular interest for further clinical development.