Imatinib therapy for chronic myeloid leukemia: where do we go now?

Nilotinib for the treatment of chronic myeloid leukemia

The introduction of targeted therapy has revolutionized the treatment of chronic myeloid leukemia (CML). The pivotal role of the Philadelphia chromosome, resulting from the breakpoint cluster region-Abelson (BCR-ABL) translocation, led to the development of imatinib mesylate, a tyrosine kinase inhibitor with significant activity against the BCR-ABL oncoprotein. Unprecedented clinical activity in CML led to rapid approval and established first-line therapy with imatinib mesylate as the standard of care in most patients. However, the occurrence of imatinib resistance or intolerance has sparked the development of newer drugs with increased activity or specificity. Nilotinib is a second-generation tyrosine kinase inhibitor that has been rationally designed on the basis of imatinib. An overview is given on clinical results in imatinib-resistant or -intolerant patients that led to its current approval as second-line therapy for the chronic and accelerated phases of CML. Future studies will address the role of nilotinib as first-line therapy, in combination strategies and in the context of specific BCR-ABL mutations.

Hematopathologic and cytogenetic findings in imatinib mesylate treated chronic myelogenous leukemia patients: 2.5 years' experience

BACKGROUND/AIM

Imatinib mesylate, a tyrosine kinase inhibitor with specific activity against the breakpoint cluster region--Abelson murine leukemia (BCR-ABL) tyrosine kinase has been developed for treatment of chronic myelogenous leukemia (CML). Its hematologic and cytogenetic effects have been evaluated in a series of clinical trials. The aim of this study was to report hematologic and cytogenetic response in CML patients during the treatment with imatinib mesylate.

METHODS

A total of 21 patients were treated and observed from July 2006 to December 2008. The median time from CML diagnosis was no more than 12 months, so all the patients received previous treatment with hydroxyurea for which the median time was 3 months. The patients received imatinib mesylate in an effective oral dose of 400 to 800 mg daily, which was followed with peripheral blood counts, bone marrow examination, and cytogenetic studies at 6, 12, 18 and 24 months.

RESULTS

Complete hematologic responses were reported for 19 (90.48%) of 21 patients studied. Among 19 patients who had a response, 16 (86%) did so within 3 months. The best cytogenetic response rate at any time during the study treatment with imatinib mesylate, among 14 patients in which cytogenetic response evaluated was: complete cytogenetic response in 7 (50%) patients, partial cytogenetic response in 6 (42.9%) patients and minor cytogenetic response in 1 (7.1%) patient. No patients had progressed to accelerated or blastic phase. The most frequent adverse effects that seemed to be related to treatment with imatinib mesylate were edema and musculoskeletal pain; overall, most were mild. Only one patient discontinued treatment because of hematologic toxic effects.

CONCLUSION

The results obtained in this study confirm that imatinib mesylate induces a complete hematological and cytogenetic response in a high percentage of patients with chronic-phase CML.

Are chronic myeloid leukemia patients more at risk for second malignancies? A population-based study

The authors used cancer registry data to assess the incidence rate of second primary cancers among chronic myeloid leukemia (CML) patients and the long-term survival of CML patients before the introduction of tyrosine kinase inhibitors. In the Swedish Cancer Registry, the authors identified 2,753 adult CML patients diagnosed between 1970 and 1995 who were followed through December 2007. Standardized incidence ratios (SIRs) and relative survival ratios were computed. With a total of 145 subsequent primary malignancies, an increased incidence rate of second malignancy was found for stomach cancer (SIR = 2.76, 95% confidence interval (CI): 1.33, 5.08), skin cancer (SIR = 5.36, 95% CI: 3.18, 8.47), urogenital tract cancer (SIR = 1.61, 95% CI: 1.15, 2.21), and lymphoid leukemia (SIR = 5.53, 95% CI: 1.79, 12.89). Long-term relative survival figures showed that CML was related, in the era prior to the introduction of imatinib, to a very steep decline in survival (2 years from diagnosis, relative survival = 51%, 95% CI: 49, 53). This was in spite of a marginal improvement after 1985, possibly related to the introduction of interferon-α for treatment. These estimates constitute a relevant reference for future studies and a benchmark for comparisons with prognosis in CML patients after chronic use of tyrosine kinase inhibitors.

Prognostic factors associated with complete cytogenetic response in patients with chronic myelogenous leukemia on imatinib mesylate therapy

Introduction Imatinib mesylate, a selective Bcr-Abl tyrosine kinase inhibitor, has proved to be most effective therapy of Philadelphia chromosome-positive chronic myelogenous leukemia. Imatinib induces complete haematological and cytogenetic response in high percentage of patients. Objective The aim of this study was to identify potential prognostic factors before beginning treatment with imatinib associated with complete cytogenetic response. Methods We analyzed 20 patients with newly diagnosed Philadelphia positive chronic myelogenous leukemia treated at our institution from June 2006 until May 2009. These patients were treated with imatinib mesylate in oral dose of 400 to 800 mg daily. Complete blood counts were performed every month, while serum chemistry evaluations and bone marrow evaluations including morphology and cytogenetics were performed every 6 months. Results Of the 20 patients analyzed in this study, 19 (95%) achieved complete haematologic response within three months. In all patients cytogenetic analyses were done and all have achieved absolute cytogenetic response. The best cytogenetic response rate at any time during study treatment among 20 patients was: complete cytogenetic response in 15, partial cytogenetic response in three and minor cytogenetic response in two patients. Among 11 observed base-line patients' characteristics five were independent predictors of a high rate of complete cytogenetic response; the absence of blasts and basophils in peripheral blood, the presence of less than 5 percent of bone marrow blasts, white blood cell count less than 10x109/L and the absence of splenomegaly (p<0.01). Conclusion Our results showed that some pre-treatment characteristics of patients might be the cause of differences in treatment outcome. On the basis of this analysis, we identified several pre-treatment patients' characteristics to be independent prognostic factors for achievement of complete cytogenetic response. .

Class effects of tyrosine kinase inhibitors in the treatment of chronic myeloid leukemia

Tyrosine kinase inhibitors have revolutionized the treatment of chronic myeloid leukemia (CML), offering patients several targeted therapeutic options that provide the possibility of sustained remissions and prolonged survival. With the availability of imatinib, nilotinib and dasatinib, physicians must weigh the efficacy and safety profile of each agent when choosing the best therapeutic option for individual patients. Each agent targets tyrosine kinases within the cell uniquely to cause the desired antiproliferative effect. In addition to inhibiting the BCR-ABL kinase, imatinib and nilotinib target the same array of other tyrosine kinases, including c-KIT and platelet-derived growth factor receptor (PDGFR), albeit with differing potencies. While targeting BCR-ABL with the highest potency among approved agents in CML, dasatinib also targets a broad array of off-target kinases, including SRC family members, PDGFR and EPHB4. The differences in kinase inhibition profiles among these agents in vitro probably account for the differing clinical safety profiles of these agents. This paper reviews the various kinases inhibited by imatinib, nilotinib and dasatinib, and describes the potential impact of kinase inhibition on the efficacy and safety of each agent.

First-line therapy for chronic myeloid leukemia: Past, present, and future

The development of Bcr-Abl tyrosine kinase inhibitors has dramatically changed the prognosis of patients with newly diagnosed chronic myeloid leukemia (CML). Standard-dose imatinib (400 mg/day in chronic phase, 600 mg/day in advanced CML) now dominates the management of this disease, producing considerably higher hematologic, cytogenetic, and molecular response rates than seen with previous drug therapies. However, although many patients respond well to standard-dose imatinib initially, some patients do not achieve adequate levels of response or discontinue therapy because of resistance. One approach to improving treatment response with first-line imatinib may be to increase the imatinib dose (800 mg/day), although recent trial data indicate that overall increases in response rates may be modest. Newer Bcr-Abl tyrosine kinase inhibitors can induce responses in patients with all phases of imatinib-resistant CML, even those with imatinib-resistant mutations in the BCR-ABL gene. Furthermore, in initial studies, first-line dasatinib or nilotinib treatment has produced response rates that compare favorably with historical controls treated with imatinib, although confirmation is required from head-to-head clinical trials. Future clinical approaches may include drug combinations, which may allow quiescent leukemia stem cells to be eradicated. Further improvements in drug treatment for first-line CML are expected during the next few years.