Expression of the chemokine receptor CCR1 promotes the dissemination of multiple myeloma plasma cells in vivo

Multiple myeloma (MM) disease progression is dependent on the ability of MM plasma cells (PCs) to egress from the bone marrow (BM), enter the circulation and disseminate to distal BM sites. Expression of the chemokine CXCL12 by BM stromal cells is crucial for MM PC retention within the BM. However, the mechanisms which overcome CXCL12-mediated retention to enable dissemination are poorly understood. We have previously identified that treatment with the CCR1 ligand CCL3 inhibits the response to CXCL12 in MM cell lines, suggesting that CCL3/CCR1 signalling may enable egress of MM PC from the BM. Here, we demonstrated that CCR1 expression was an independent prognostic indicator in newly diagnosed MM patients. Furthermore, we showed that CCR1 is a crucial driver of dissemination in vivo, with CCR1 expression in the murine MM cell line 5TGM1 being associated with an increased incidence of bone and splenic disseminated tumours in C57BL/KaLwRij mice. Furthermore, we demonstrated that CCR1 knockout in the human myeloma cell line OPM2 resulted in a >95% reduction in circulating MM PC numbers and BM and splenic tumour dissemination following intratibial injection in NSG mice. Therapeutic targeting of CCR1 with the inhibitor CCX9588 significantly reduced OPM2 or RPMI-8226 dissemination in intratibial xenograft models. Collectively, our findings suggest a novel role for CCR1 as a critical driver of BM egress of MM PCs during tumour dissemination. Furthermore, these data suggest that CCR1 may represent a potential therapeutic target for the prevention of MM tumour dissemination.

Genomic subtyping and therapeutic targeting of acute erythroleukemia.

Acute erythroid leukemia (AEL) is a high-risk leukemia of poorly understood genetic basis, with controversy regarding diagnosis in the spectrum of myelodysplasia and myeloid leukemia. We compared genomic features of 159 childhood and adult AEL cases with non-AEL myeloid disorders and defined five age-related subgroups with distinct transcriptional profiles: adult, TP53 mutated; NPM1 mutated; KMT2A mutated/rearranged; adult, DDX41 mutated; and pediatric, NUP98 rearranged. Genomic features influenced outcome, with NPM1 mutations and HOXB9 overexpression being associated with a favorable prognosis and TP53, FLT3 or RB1 alterations associated with poor survival. Targetable signaling mutations were present in 45% of cases and included recurrent mutations of ALK and NTRK1, the latter of which drives erythroid leukemogenesis sensitive to TRK inhibition. This genomic landscape of AEL provides the framework for accurate diagnosis and risk stratification of this disease, and the rationale for testing targeted therapies in this high-risk leukemia.

HIF-2α Promotes Dissemination of Plasma Cells in Multiple Myeloma by Regulating CXCL12/CXCR4 and CCR1.

Disease progression and relapse in multiple myeloma is dependent on the ability of the multiple myeloma plasma cells (PC) to reenter the circulation and disseminate throughout the bone marrow. Increased bone marrow hypoxia is associated with increased recirculation of multiple myeloma PCs. Accordingly, we hypothesized that during chronic hypoxia, activation of HIF-2α may overcome the bone marrow retention signal provided by stromal-derived CXCL12, thereby enabling dissemination of multiple myeloma PCs. Here we demonstrate that HIF-2α upregulates multiple myeloma PC CXCL12 expression, decreasing migration toward CXCL12 and reducing adhesion to mesenchymal stromal cells in vitro We also found that HIF-2α strongly induced expression of the chemokine receptor CCR1 in multiple myeloma PCs. CCR1 activation potently induces multiple myeloma PC migration toward CCL3 while abrogating the multiple myeloma PC migratory response to CXCL12. In addition, increased CCR1 expression by multiple myeloma PCs conferred poor prognosis in newly diagnosed multiple myeloma patients and was associated with an increase in circulating multiple myeloma PCs in these patients. Taken together, our results suggest a role for hypoxia-mediated CCR1 upregulation in driving the egress of multiple myeloma PCs from the bone marrow. Targeting CCR1 may represent a novel strategy to prevent dissemination and overt relapse in multiple myeloma. Cancer Res; 77(20); 5452-63. ©2017 AACR.

Dynamic assessment of RBC-transfusion dependency improves the prognostic value of the revised-IPSS in MDS patients.

RBC-transfusion dependency (RBC-TD) is an independent prognostic factor for poor overall survival (OS) in the WHO classification-based prognostic scoring system (WPSS) for MDS patients. However, WPSS did not include cytopenia, whereas revised International Prognostic Scoring System (IPSS-R) did not include RBC-TD. Thus, neither of these prognostic scoring systems incorporates both cytopenia and RBC-TD. We aimed to test whether RBC-TD adds prognostic value to the IPSS-R. We analyzed MDS patients not treated with disease-modifying therapy, and enrolled in SA-MDS Registry (derivation cohort; n = 295) and Dusseldorf registry (Germany; validation cohort; n = 113) using time-dependent Cox proportional regression and serial landmark analyses. In the derivation cohort, RBC-TD patients had inferior OS compared to RBC transfusion-independent (RBC-TI) patients (P < 0.0001) at 6- (18 vs. 64 months), 12- (24 vs. 71 months), and 24-months (40 vs. 87 months). In a Cox proportional regression analysis, RBC-TD was an independent adverse prognostic marker in addition to age, sex, and IPSS-R variables (P < 0.0001). A prognostic index (PI) was derived using these Cox-proportional regression model variables. In the validation cohort, this PI classified patients into four prognostic groups with significantly different OS (P < 0.001) as in the derivation cohort. In conclusion, multivariate analysis by Cox proportional hazards regression and serial landmark analyses clearly demonstrates that development of RBC-TD at any time during the course of MDS is associated with poor OS, independent of IPSS-R. This study demonstrates that dynamic assessment of RBC-TD provides additional prognostic value to IPSS-R and should be included in treatment decision algorithms for MDS patients.

Results of a phase 2 study of pacritinib (SB1518), a JAK2/JAK2(V617F) inhibitor, in patients with myelofibrosis.

Pacritinib (SB1518) is a Janus kinase 2 (JAK2), JAK2(V617F), and Fms-like tyrosine kinase 3 inhibitor that does not inhibit JAK1. It demonstrated a favorable safety profile with promising efficacy in phase 1 studies in patients with primary and secondary myelofibrosis (MF). This multicenter phase 2 study further characterized the safety and efficacy of pacritinib in the treatment of patients with MF. Eligible patients had clinical splenomegaly poorly controlled with standard therapies or were newly diagnosed with intermediate- or high-risk Lille score. Patients with any degree of cytopenia were eligible. Thirty-five patients were enrolled. At entry, 40% had hemoglobin <10 g/dL and 43% had platelets <100 000× 10(9)/L. Up to week 24, 8 of 26 evaluable patients (31%) achieved a ≥35% decrease in spleen volume determined by magnetic resonance imaging and 14 of 33 (42%) attained a ≥50% reduction in spleen size by physical examination. Median MF symptom improvement was ≥50% for all symptoms except fatigue. Grade 1 or 2 diarrhea (69%) and nausea (49%) were the most common treatment-emergent adverse events. The study drug was discontinued in 9 patients (26%) due to adverse events (4 severe). Pacritinib is an active agent in patients with MF, offering a potential treatment option for patients with preexisting anemia and thrombocytopenia. This trial was registered at www.clinicaltrials.gov as #NCT00745550.

Tetraspanin 7 (TSPAN7) expression is upregulated in multiple myeloma patients and inhibits myeloma tumour development in vivo.

BACKGROUND: Increased expression of the tetraspanin TSPAN7 has been observed in a number of cancers; however, it is unclear how TSPAN7 plays a role in cancer progression. METHODS: We investigated the expression of TSPAN7 in the haematological malignancy multiple myleoma (MM) and assessed the consequences of TSPAN7 expression in the adhesion, migration and growth of MM plasma cells (PC) in vitro and in bone marrow (BM) homing and tumour growth in vivo. Finally, we characterised the association of TSPAN7 with cell surface partner molecules in vitro. RESULTS: TSPAN7 was found to be highly expressed at the RNA and protein level in CD138(+) MM PC from approximately 50% of MM patients. TSPAN7 overexpression in the murine myeloma cell line 5TGM1 significantly reduced tumour burden in 5TGM1/KaLwRij mice 4 weeks after intravenous adminstration of 5TGM1 cells. While TSPAN7 overexpression did not affect cell proliferation in vitro, TSPAN7 increased 5TGM1 cell adhesion to BM stromal cells and transendothelial migration. In addition, TSPAN7 was found to associate with the molecular chaperone calnexin on the cell surface. CONCLUSION: These results suggest that elevated TSPAN7 may be associated with better outcomes for up to 50% of MM patients.

Salvage second hematopoietic cell transplantation in myeloma.

Autologous hematopoietic cell transplantation (AHCT) as initial therapy of patients with multiple myeloma (MM) improves survival. However, data to support this approach for relapsed/progressive disease after initial AHCT (AHCT1) are limited. Using Center for International Blood and Marrow Transplant Research data, we report the outcomes of 187 patients who underwent a second AHCT (AHCT2) for the treatment of relapsed/progressive MM. Planned tandem AHCT was excluded. Median age at AHCT2 was 59 years (range, 28 to 72), and median patient follow-up was 47 months (range, 3 to 97). Nonrelapse mortality after AHCT2 was 2% at 1 year and 4% at 3 years. Median interval from AHCT1 to relapse/progression was 18 months, and median interval between transplantations was 32 months. After AHCT2, the incidence of relapse/progression at 1 and 3 years was 51% and 82%, respectively. At 3 years after AHCT2, progression-free survival was 13%, and overall survival was 46%. In multivariate analyses, those relapsing ≥36 months after AHCT1 had superior progression-free (P = .045) and overall survival (P = .019). Patients who underwent AHCT2 after 2004 had superior survival (P = .026). AHCT2 is safe and feasible for disease progression after AHCT1. In this retrospective study, individuals relapsing ≥36 months from AHCT1 derived greater benefit from AHCT2 compared with those with a shorter disease-free interval. Storage of an adequate graft before AHCT1 will ensure that the option of a second autologous transplantation is retained for patients with relapsed/progressive MM.

The genomic landscape of hypodiploid acute lymphoblastic leukemia.

The genetic basis of hypodiploid acute lymphoblastic leukemia (ALL), a subtype of ALL characterized by aneuploidy and poor outcome, is unknown. Genomic profiling of 124 hypodiploid ALL cases, including whole-genome and exome sequencing of 40 cases, identified two subtypes that differ in the severity of aneuploidy, transcriptional profiles and submicroscopic genetic alterations. Near-haploid ALL with 24-31 chromosomes harbor alterations targeting receptor tyrosine kinase signaling and Ras signaling (71%) and the lymphoid transcription factor gene IKZF3 (encoding AIOLOS; 13%). In contrast, low-hypodiploid ALL with 32-39 chromosomes are characterized by alterations in TP53 (91.2%) that are commonly present in nontumor cells, IKZF2 (encoding HELIOS; 53%) and RB1 (41%). Both near-haploid and low-hypodiploid leukemic cells show activation of Ras-signaling and phosphoinositide 3-kinase (PI3K)-signaling pathways and are sensitive to PI3K inhibitors, indicating that these drugs should be explored as a new therapeutic strategy for this aggressive form of leukemia.

The granulocyte-associated transcription factor Krüppel-like factor 5 is silenced by hypermethylation in acute myeloid leukemia.

Krüppel-like factor 5 (KLF5) has been implicated as a tumor suppressor in various solid tumors such as breast and prostate, and recent studies have demonstrated a role for this protein in neutrophil differentiation of acute promyelocytic leukemia cells in response to ATRA. Here, we show that KLF5 expression increases during primary granulocyte differentiation and that expression of KLF5 is a requirement for granulocyte differentiation of 32D cells. In AML, we show that KLF5 mRNA expression levels are reduced in multiple French-American-British subtypes compared to normal controls, and also in leukemic stem cells relative to normal hematopoietic stem cells. We demonstrate that in selected AML cases, reduced expression is associated with hypermethylation of the KLF5 locus in the proximal promoter and/or intron 1, suggesting that this may represent a Class II genetic lesion in the development of AML.

Hematopoietic cell transplantation for primary plasma cell leukemia: results from the Center for International Blood and Marrow Transplant Research.

There are limited data on hematopoietic cell transplantation (HCT) in primary plasma cell leukemia (pPCL), an aggressive plasma cell disorder. We report outcomes of 147 patients with pPCL receiving autologous (n=97) or allogeneic (n=50) HCT within 18 months after diagnosis between 1995 and 2006. Median age was 56 years and 48 years for autologous HCT and allogeneic HCT, respectively. Progression-free survival (PFS) at 3 years was 34% (95% confidence interval (CI), 23-46%) in the autologous group and 20% (95% CI, 10-34%) in the allogeneic group. Cumulative incidence of relapse at 3 years was 61% (95% CI, 48-72%) in the autologous group and 38% (95% CI, 25-53%) in the allogeneic group. Overall survival (OS) at 3 years was 64% (95% CI, 52-75%) in the autologous group and 39% (95% CI, 26-54%) in the allogeneic group. Non-relapse mortality (NRM) at 3 years was 5% (95% CI, 1-11%) in the autologous group and 41% (95% CI, 28-56%) in the allogeneic group. The encouraging OS after autologous HCT, establishes the safety and feasibility of this consolidative treatment option after initial induction therapy for pPCL. Allogeneic HCT, although associated with a significantly lower relapse rate, carries a much higher risk of NRM and no OS benefit.

Mobilisation strategies for normal and malignant cells.

This review evaluates the latest information on the mobilisation of haemopoietic stem cells for transplantation, with the focus on what is the current best practice and how new understanding of the bone marrow stem cell niche provides new insights into optimising mobilisation regimens. The review then looks at the mobilisation of mesenchymal stromal cells, immune cells as well as malignant cells and what clinical implications there are.

Heritable GATA2 mutations associated with familial myelodysplastic syndrome and acute myeloid leukemia.

We report the discovery of GATA2 as a new myelodysplastic syndrome (MDS)-acute myeloid leukemia (AML) predisposition gene. We found the same, previously unidentified heterozygous c.1061C>T (p.Thr354Met) missense mutation in the GATA2 transcription factor gene segregating with the multigenerational transmission of MDS-AML in three families and a GATA2 c.1063_1065delACA (p.Thr355del) mutation at an adjacent codon in a fourth MDS family. The resulting alterations reside within the second zinc finger of GATA2, which mediates DNA-binding and protein-protein interactions. We show differential effects of the mutations on the transactivation of target genes, cellular differentiation, apoptosis and global gene expression. Identification of such predisposing genes to familial forms of MDS and AML is critical for more effective diagnosis and prognosis, counseling, selection of related bone marrow transplant donors and development of therapies.

How I treat patients who mobilize hematopoietic stem cells poorly.

Transplantation with 2-5 × 10(6) mobilized CD34(+)cells/kg body weight lowers transplantation costs and mortality. Mobilization is most commonly performed with recombinant human G-CSF with or without chemotherapy, but a proportion of patients/donors fail to mobilize sufficient cells. BM disease, prior treatment, and age are factors influencing mobilization, but genetics also contributes. Mobilization may fail because of the changes affecting the HSC/progenitor cell/BM niche integrity and chemotaxis. Poor mobilization affects patient outcome and increases resource use. Until recently increasing G-CSF dose and adding SCF have been used in poor mobilizers with limited success. However, plerixafor through its rapid direct blockage of the CXCR4/CXCL12 chemotaxis pathway and synergy with G-CSF and chemotherapy has become a new and important agent for mobilization. Its efficacy in upfront and failed mobilizers is well established. To maximize HSC harvest in poor mobilizers the clinician needs to optimize current mobilization protocols and to integrate novel agents such as plerixafor. These include when to mobilize in relation to chemotherapy, how to schedule and perform apheresis, how to identify poor mobilizers, and what are the criteria for preemptive and immediate salvage use of plerixafor.

Expression profiling of a hemopoietic cell survival transcriptome implicates osteopontin as a functional prognostic factor in AML.

Deregulated cell survival programs are a classic hallmark of cancer. We have previously identified a serine residue (Ser585) in the betac subunit of the granulocyte-macrophage colony-stimulating factor receptor that selectively and independently promotes cell survival. We now show that Ser585 phosphorylation is constitutive in 20 (87%) of 23 acute myeloid leukemia (AML) patient samples, indicating that this survival-only pathway is frequently deregulated in leukemia. We performed a global expression screen to identify gene targets of this survival pathway and report a 138-gene betac Ser585-regulated transcriptome. Pathway analysis defines a gene network enriched for PI3-kinase target genes and a cluster of genes involved in cancer and cell survival. We show that one such gene, osteopontin (OPN), is a functionally relevant target of the Ser585-survival pathway as shown by siRNA-mediated knockdown of OPN expression that induces cell death in both AML blasts and CD34(+)CD38(-)CD123(+) leukemic progenitors. Increased expression of OPN at diagnosis is associated with poor prognosis with multivariate analysis indicating that it is an independent predictor of overall patient survival in normal karyotype AML (n = 60; HR = 2.2; P = .01). These results delineate a novel cytokine-regulated Ser585/PI3-kinase signaling network that is deregulated in AML and identify OPN as a potential prognostic and therapeutic target.

Cotransplantation of placental mesenchymal stromal cells enhances single and double cord blood engraftment in nonobese diabetic/severe combined immune deficient mice.

Limited cell numbers in a unit restricts cord blood transplantation (CBT) in adults. We evaluated whether cotransplantation of placental mesenchymal stromal cells (MSCs) would enhance engraftment. Plastic adherent cells from placenta demonstrated typical characteristics of MSCs. In six individual experiments, 4 cohorts of 24 nonobese diabetic/severe combined immune deficient (NOD/SCID) mice were evaluated. Cohort 1 received 5 x 10(4) CD34+ cells from unit (U) one (SCBT); cohort 2 received 5 x 10(4) CD34+ cells from U1 + 4 x 10(4) MSCs (SCBT+MSCs); cohort 3 received 2.5 x 10(4) CD34+ cells from U1 + 2.5 x 10(4) CD34+ cells from U2 (double cord blood transplant [DCBT]); cohort 4 received 2.5 x 10(4) CD34+ cells from U1 + 2.5 x 10(4) CD34+ cells from U2 + 4 x 10(4) MSCs (DCBT+MSCs). Hematopoietic engraftment evaluated after 6 to 8 weeks, was similar in recipients of SCBT and DCBT. MSC cotransplantation demonstrated enhanced engraftment in DCBT (51.8 +/- 6.8% versus 14.9 +/- 6.5%; p = .04) with an increased trend in SCBT (48.7 +/- 7.7% versus 17.5 +/- 6.1%; p = .07). In DCBT, cotransplantation of placental MSCs reduced single cord dominance. Self-renewal capacity was assessed by serial transplantation in secondary recipients infused with engrafted human cells from primary mice transplanted with or without MSCs. In secondary transplant experiments, 13 of 17 evaluable mice engrafted at levels of 1% to 6.5%. Despite enhanced engraftment in primary mice, long-term engraftment capacity was unaltered with MSC cotransplantation. Imaging studies showed MSCs migrated to pelvic region and improved cord blood (CB) CD34+ homing. Cotransplantation of placental MSCs enhanced cord blood engraftment and may act by improving homing of CD34+ cells.

Targeted disruption of the CXCL12/CXCR4 axis inhibits osteolysis in a murine model of myeloma-associated bone loss.

The plasma cell (PC) malignancy, multiple myeloma (MM), is unique among hematological malignancies in its capacity to cause osteoclast (OC)-mediated skeletal destruction. We have previously shown that elevated plasma levels of PC-derived CXCL12 are associated with presence of X-ray detectable osteolytic lesions in MM patients. To further investigate this relationship, plasma levels of CXCL12 and betaCrossLaps, a marker of bone loss, were measured. A strong correlation between levels of CXCL12 and OC-mediated bone resorption was identified. To confirm the OC-activating potential of MM PC-derived CXCL12 in vivo, we established a model of MM-mediated focal osteolysis, wherein MM PC lines, such as RPMI-8226, were injected into the tibias of nude mice. Implanting RPMI-8226 gave rise to osteolytic lesions proximal to the tumor, resulting in a 5% decrease in bone volume (BV) compared with vehicle control. Importantly, bone loss was significantly inhibited with systemic administration of the CXCL12/CXCR4 antagonist T140. Furthermore, implanting CXCL12-overexpressing RPMI-8226 cells resulted in a 13% decrease in BV and was associated with increased OC recruitment proximal to the tumor, increased serum matrix metalloproteinase activity, and increased levels of collagen I degradation products. These findings confirm our hypothesis that MM PC-derived CXCL12 stimulates the recruitment and activity of OC, thereby contributing to the formation of MM osteolytic lesions.

Comparison of twin and autologous transplants for multiple myeloma.

Relapse is the overwhelming cause of treatment failure after autologous transplantation for multiple myeloma (MM). For patients with a syngeneic donor, twin transplants provide a healthy graft that is free of myeloma. The relative impact of the graft on posttransplant relapse can be estimated by comparing risk of relapse after hematopoietic cell transplantation from genetically identical twins versus autotransplants because confounding differences in minor or major histocompatibility antigens are absent in the syngeneic transplant setting. Outcomes of 43 subjects who received twin transplants for MM were compared to 170 matched autotransplant recipients reported to the Center for International Blood and Marrow Transplant Research (CIBMTR). Multivariate analysis was performed by fitting a Cox model stratified on matched pairs. The matched transplant patients studied were similar with respect to subject-, disease-, and transplant-related characteristics. Cumulative incidence of relapse/progression was significantly lower, and progression-free survival (PFS) was significantly higher following twin transplants. In multivariate analysis, the probability of relapse/progression was lower in twins (relative risk [RR] = 0.49, 95% confidence interval [CI] 0.28-0.86, P = .011). Twin transplants have a significantly lower relapse risk than autotransplants in MM, suggesting that graft composition may impact outcomes following high-dose chemotherapy.

Comparable outcomes in nonsecretory and secretory multiple myeloma after autologous stem cell transplantation.

Nonsecretory myeloma (NSM) accounts for <5% of cases of multiple myeloma (MM). The outcome of these patients following autologous stem cell transplantation (ASCT) has not been evaluated in clinical trials. We compared the outcomes after ASCT for patients with NSM reported to the Center for International Blood and Marrow Transplant Research (CIBMTR) between 1989 and 2003, to a matched group of 438 patients (4 controls for each patient) with secretory myeloma (SM). The patients were matched using propensity scores calculated using age, Durie-Salmon stage, sensitivity to pretransplant therapy, time from diagnosis to transplant, and year of transplant. Disease characteristics were similar in both groups at diagnosis and at transplant except higher risk of anemia, hypoalbuminemia, and marrow plasmacytosis (in SM) and plasmacytoma (more in NSM). Cumulative incidence of treatment-related mortality (TRM), relapse, progression-free survival (PFS), and overall survival (OS) were similar between the groups. In multivariate analysis, based on a Cox model stratified on matched pairs and adjusted for covariates not considered in the propensity score, we found no difference in outcome between the NSM and SM groups. In this large cohort of patients undergoing ASCT, we found no difference in outcomes of patients with NSM compared to those with SM.

Dasatinib cellular uptake and efflux in chronic myeloid leukemia cells: therapeutic implications.

PURPOSE: The organic cation transporter OCT-1 mediates active transport of imatinib. We recently showed that low OCT-1 activity is a major contributor to suboptimal response in chronic myeloid leukemia (CML) patients treated with imatinib. The relevance of OCT-1 activity and efflux pumps in determining intracellular uptake and retention (IUR) of dasatinib was assessed. EXPERIMENTAL DESIGN: The effect of OCT inhibitors on [14C]dasatinib and [14C]imatinib IUR was compared using peripheral blood mononuclear cells from newly diagnosed CML patients. The role of efflux transporters was studied using ABCB1- and ABCG2-overexpressing cell lines and relevant inhibitors. RESULTS: Unlike imatinib, there was no significant difference in the dasatinib IUR at 37 degrees C and 4 degrees C (P = 0.8), and OCT-1 inhibitors including prazosin did not reduce dasatinib IUR significantly. In CML mononuclear cells, prazosin inhibitable IUR was significantly higher for imatinib than dasatinib (6.38 versus 1.48 ng/200,000 cells; P = 0.002; n = 11). Patients with high OCT-1 activity based on their imatinib uptake had IC50(dasatinib) values equivalent to patients with low OCT-1 activity. Dasatinib IUR was significantly lower in ABCB1-overexpressing cell lines compared with parental cell lines (P < 0.05). PSC833 (ABCB1 inhibitor) significantly increased the dasatinib IUR (P < 0.05) and reduced IC50(dasatinib) (from 100 to 8 nmol/L) in K562-DOX cell line. The ABCG2 inhibitor Ko143 significantly increased dasatinib IUR in ABCG2-overexpressing cell lines and reduced IC(50)(dasatinib). CONCLUSION: Unlike imatinib, dasatinib cellular uptake is not significantly affected by OCT-1 activity, so that expression and function of OCT-1 is unlikely to affect response to dasatinib. Dasatinib is a substrate of both efflux proteins, ABCB1 and ABCG2.

Long-term imatinib therapy promotes bone formation in CML patients.

Imatinib inhibits tyrosine kinases important in osteoclast (c-Fms) and osteoblast (platelet-derived growth factor receptor [PDGF-R], c-Abl) function, suggesting that long-term therapy may alter bone homeostasis. To investigate this question, we measured the trabecular bone volume (TBV) in iliac crest bone biopsies taken from chronic myeloid leukemia (CML) patients at diagnosis and again after 2 to 4 years of imatinib therapy. Half the patients (8 of 17) showed a substantive increase in TBV (> 2-fold), after imatinib therapy, with the TBV in the posttreatment biopsy typically surpassing the normal upper limit for the patient's age group. Imatinib-treated patients exhibited reduced serum calcium and phosphate levels with hypophosphatemia evident in 53% (9 of 17) of patients. In vitro, imatinib suppressed osteoblast proliferation and stimulated osteogenic gene expression and mineralized-matrix production by inhibiting PDGF receptor function. In PDGF-stimulated cultures, imatinib dose-dependently inhibited activation of Akt and Crk-L. Using pharmacologic inhibitors, inhibition of PI3-kinase/Akt activation promoted mineral formation, suggesting a possible molecular mechanism for the imatinib-mediated increase in TBV in vivo. Further investigation is required to determine whether the increase in TBV associated with imatinib therapy may represent a novel therapeutic avenue for the treatment of diseases that are characterized by generalized bone loss.