Progress in the treatment of acute myeloid leukemia

Trends in adult leukemia incidence and survival in Denmark, 1943-2003

The etiology of leukemia is largely unknown. Ecological data indicating trends in incidence and survival can provide information about changes in risk factors, can reflect underlying changes in diagnostic classification, and can measure therapeutic advances. From the records of the Danish Cancer Registry with registration starting from 1943, we calculated age-specific, period-specific, and age-standardized (world standard) incidence rates of chronic lymphoid leukemia (CLL), acute lymphoid leukemia (ALL), chronic myeloid leukemia (CML), and acute myeloid leukemia (AML) for persons above the age of 18. Kaplan-Meier survival curves and median survival times were calculated. Between 1943 and 2003, there were 26,036 cases of leukemia reported. The age-specific incidence rates of CLL, CML, and AML were higher for older men and women, while the incidence rates of ALL by age were more homogeneous. The age-standardized incidence rates during the study period increased for CLL and AML, increased less strongly for ALL, and decreased for CML in both men and women, although the incidence rates for women were almost always lower. Patients with CLL had the longest survival time in all age groups. The median survival time increased for all leukemia subtypes throughout the period of study most pronounced for CLL since 1950 and CML since 1990.

Targeting C-type lectin-like molecule-1 for antibody-mediated immunotherapy in acute myeloid leukemia

BACKGROUND

C-type lectin-like molecule-1 is a transmembrane receptor expressed on myeloid cells, acute myeloid leukemia blasts and leukemic stem cells. To validate the potential of this receptor as a therapeutic target in acute myeloid leukemia, we generated a series of monoclonal antibodies against the extracellular domain of C-type lectin-like molecule-1 and used them to extend the expression profile analysis of acute myeloid leukemia cells and to select cytotoxic monoclonal antibodies against acute myeloid leukemia cells in preclinical models.

DESIGN AND METHODS

C-type lectin-like molecule-1 expression was analyzed in acute myeloid leukemia cell lines, and in myeloid derived cells from patients with acute myeloid leukemia and healthy donors. Anti-C-type lectin-like molecule-1 antibody-mediated in vitro cytotoxic activity against acute myeloid leukemia blasts/cell lines and in vivo anti-cancer activity in a mouse xenograft model were assessed. Internalization of C-type lectin-like molecule-1 monoclonal antibodies upon receptor ligation was also investigated.

RESULTS

C-type lectin-like molecule-1 was expressed in 86.5% (45/52) of cases of acute myeloid leukemia, in 54.5% (12/22) of acute myeloid leukemia CD34(+)/CD38(-) stem cells, but not in acute lymphoblastic leukemia blasts (n=5). Selected anti-C-type lectin-like molecule-1 monoclonal antibodies mediated dose-dependent complement-dependent cytotoxicity and antibody-dependent cellular cytotoxicity specifically against acute myeloid leukemia-derived cell lines. Exogenous expression of the transmembrane receptor in HEK293 cells rendered the cells susceptible to antibody-mediated killing by monoclonal antibodies to the receptor. Furthermore, these monoclonal antibodies demonstrated strong complement-dependent cytotoxicity against freshly isolated acute myeloid leukemia blasts (15/16 cases; 94%). The monoclonal antibodies were efficiently internalized upon binding to C-type lectin-like molecule-1 in HL-60 cells. Moreover, a lead chimeric C-type lectin-like molecule-1 monoclonal antibody reduced the tumor size in xenograft mice implanted with HL-60 cells. Conclusions Our results demonstrate that targeting C-type lectin-like molecule-1 with specific cytotoxic monoclonal antibodies is an attractive approach which could lead to novel therapies for acute myeloid leukemia.

Protein synthesis is resistant to rapamycin and constitutes a promising therapeutic target in acute myeloid leukemia

The deregulation of translation markedly contributes to the malignant phenotype in cancers, and the assembly of the translation initiating complex eIF4F is the limiting step of this process. The mammalian Target of Rapamycin Complex 1 (mTORC1) is thought to positively regulate eIF4F assembly and subsequent oncogenic protein synthesis through 4E-BP1 phosphorylation. We showed here that the translation inhibitor 4EGI-1 decreased the clonogenic growth of leukemic progenitors and induced apoptosis of blast cells, with limited toxicity against normal hematopoiesis, which emphasize the importance of translation deregulation in acute myeloid leukemia (AML) biology. However, the mTORC1 inhibitor RAD001 (a rapamycin derivate) did not induce AML blast cell apoptosis. We herein demonstrated that mTORC1 disruption using raptor siRNA or RAD001 failed to inhibit 4E-BP1 phosphorylation in AML. Moreover, RAD001 failed to inhibit eIF4F assembly, to decrease the proportion of polysome-bound c-Myc mRNA, and to reduce the translation-dependent accumulation of oncogenic proteins. We identified the Pim-2 serine/threonine kinase as mainly responsible for 4E-BP1 phosphorylation on the S(65) residue and subsequent translation control in AML. Our results strongly implicate an mTORC1-independent deregulation of oncogenic proteins synthesis in human myeloid leukemogenesis. Direct inhibition of the translation initiating complex thus represents an attractive option for the development of new therapies in AML.

Autologous stem cell transplantation for elderly patients with acute myeloid leukaemia conditioned with continuous infusion idarubicin and busulphan

Different studies have suggested the potential utility of autologous stem cell transplantation (ASCT) in acute myeloid leukaemia (AML) of the elderly with encouraging results in selected patients. However, while the introduction of peripheral blood stem cells (PBSC) has consistently reduced morbidity and mortality of the procedure, relapse still represents the major cause of ASCT failure. One possibility to ameliorate therapeutic results could rely on the adoption of conditioning regimens specifically designed for AML. We report therapeutic results from a series of 40 AML patients older than 60 years (median age 67 years) autografted in first complete remission (CR), after conditioning with continuous infusion (c.i.) high dose idarubicin and busulphan. Fourty patients (median age: 67 years) received 2 days c.i. idarubicin at 20 mg/m(2)/day, followed by 3 days oral or intravenous busulphan (4 mg/kg/day) as conditioning. No case of transplant-related mortality occurred. Cardiac toxicity was absent, while 31 patients (77%) had grade 3-4 mucositis. After a median follow-up of 25 months, median disease free and overall survival (OS) for the whole patient population were 13 and 22 months, respectively. Three patients died while in CR from causes unrelated to AML. Better results were achieved in patients with intermediate karyotype as opposed to those with adverse cytogenetics. Our data confirm the feasibility of a conditioning regimen based on high-dose idarubicin plus busulphan in older selected AML patients and suggest clinical improvement in patients with normal cytogenetics.

Expansion of highly cytotoxic human natural killer cells for cancer cell therapy

Infusions of natural killer (NK) cells are an emerging tool for cancer immunotherapy. The development of clinically applicable methods to produce large numbers of fully functional NK cells is a critical step to maximize the potential of this approach. We determined the capacity of the leukemia cell line K562 modified to express a membrane-bound form of interleukin (IL)-15 and 41BB ligand (K562-mb15-41BBL) to generate human NK cells with enhanced cytotoxicity. Seven-day coculture with irradiated K562-mb15-41BBL induced a median 21.6-fold expansion of CD56(+)CD3(-) NK cells from peripheral blood (range, 5.1- to 86.6-fold; n = 50), which was considerably superior to that produced by stimulation with IL-2, IL-12, IL-15, and/or IL-21 and caused no proliferation of CD3(+) lymphocytes. Similar expansions could also be obtained from the peripheral blood of patients with acute leukemia undergoing therapy (n = 11). Comparisons of the gene expression profiles of the expanded NK cells and their unstimulated or IL-2-stimulated counterparts showed marked differences. The expanded NK cells were significantly more potent than unstimulated or IL-2-stimulated NK cells against acute myeloid leukemia cells in vitro. They could be detected for >1 month when injected into immunodeficient mice and could eradicate leukemia in murine models of acute myeloid leukemia. We therefore adapted the K562-mb15-41BBL stimulation method to large-scale clinical-grade conditions, generating large numbers of highly cytotoxic NK cells. The results that we report here provide rationale and practical platform for clinical testing of expanded and activated NK cells for cell therapy of cancer.

Therapeutic advances in leukemia and myelodysplastic syndrome over the past 40 years

Major therapeutic progress has been accomplished in leukemia and myelodysplastic syndrome (MDS) over the past 40 years, which may not be fully appreciated by the larger medical community. The objective of this review was to briefly highlight the treatment breakthroughs in leukemia and MDS. Therapeutic progress happened through better understanding of disease pathophysiologies and rational development of targeted agents, like imatinib mesylate in chronic myeloid leukemia (CML), and through astute, empirical discoveries in the clinic, like all-trans retinoic acid and arsenic trioxide in acute promyelocytic leukemia (APL) and chlorodeoxyadenosine in hairy cell leukemia (HCL). Today, the 5- to 10-year survival rates in patients with APL and HCL exceed 80%. In patients with CML, imatinib therapy has been associated with estimated 5- to 7-year survival rates from 85% to 90%. In patients with adult acute lymphocytic leukemia, modern intensive regimens have improved the 5-year survival rates from 20% up to 40%. In patients with chronic lymphocytic leukemia, chemoimmunotherapy recently produced high rates of quality responses and improved long-term outcome. In younger patients with acute myeloid leukemia (AML), the 5-year survival rates range from 40% to 50%, although elderly AML remains a therapeutic challenge. In patients with MDS, it was recently demonstrated that epigenetic therapy with hypomethylating agents improved survival. Much therapeutic progress has been witnessed in leukemia and MDS, and much more is expected to occur soon.

Single-agent lenalidomide induces complete remission of acute myeloid leukemia in patients with isolated trisomy 13

Patients with acute myeloid leukemia (AML) frequently fail chemotherapy due to refractory disease, relapse, or toxicity. Among older AML patients (age > 60 years), there are few long-term survivors. Lenalidomide is a candidate for study in AML based on its clinical activity in a related disorder, myelodysplastic syndrome (MDS), with the 5q- chromosomal abnormality. We report induction of sustained morphologic and cytogenetic complete remission in 2 older AML patients treated with high-dose, single-agent lenalidomide; each patient had trisomy 13 as the sole cytogenetic abnormality. We show for the first time that lenalidomide has clinical activity in this poor-risk cytogenetic subset of AML. The clinical trials described in this paper have been registered with www.clinicaltrials.gov under identifiers NCT00466895 and NCT00546897.