Imatinib mesylate and nilotinib decrease synthesis of bone matrix in vitro.

Tyrosine kinase inhibitors (TKIs), such as imatinib (IMA) and nilotinib (NIL), are the cornerstone of chronic myeloid leukemia (CML) treatment via the blockade of the oncogenic BCR-ABL1 fusion protein. However, skeletal side effects are commonly observed in pediatric patients receiving long-term treatment with IMA. Additionally, in vitro studies have shown that IMA and NIL alter vitamin D metabolism, which may further impair bone metabolism. To determine whether TKIs directly affect bone cell function, the present study treated the human osteoblastic cell line SaOS-2 with IMA or NIL and assessed effects on their mineralization capacity as well as mRNA expression of receptor activator of nuclear factor κB ligand (RANKL) and osteoprotegerin (OPG), two cytokines that regulate osteoclastogenesis. Both TKIs significantly inhibited mineralization and downregulated osteoblast marker genes, including alkaline phosphatase, osteocalcin, osterix, as well as genes associated with the pro-osteogenic Wnt signaling pathway; NIL was more potent than IMA. In addition, both TKIs increased the RANKL/OPG ratio, which is known to stimulate osteoclastogenesis. The present results suggested that the TKIs IMA and NIL directly inhibited osteoblast differentiation and directly promoted a pro-osteoclastogenic environment through the RANKL-OPG signaling axis. Thus, we propose that future work is required to determine whether the bone health of CML patients undergoing TKI-treatment should be routinely monitored.

Off­target effect of imatinib and nilotinib on human vitamin D3 metabolism.

Prolonged treatment with tyrosine kinase inhibitors (TKI) including imatinib (IMA) or nilotinib (NIL), induces severe disturbances of bone metabolism in patients with chronic myeloid leukaemia. As vitamin D3 (VD3) is involved in the complex cycle of bone remodelling, the present study investigated in vitro, the influence of IMA and NIL on VD3 metabolism i) in HaCaT cells and ii) in cultured outer root sheath keratinocytes (ORS­KC) from hair follicles of IMA treated children. Cells were incubated in the presence of IMA or NIL. Concomitantly, specific inhibitors were applied to analyze the inhibition of the VD3 processing cytochrome P450 isoenzyme family by TKIs. In vitro, IMA and NIL significantly impaired the production of calcitriol in HaCaT and cultured ORS­KC cells from hair follicles of IMA treated children. For NIL, this inhibitory effect demonstrated a 4­fold increase. In HaCaT and ORS­KC, application of specific CYP450 inhibitors revealed that CYP27B1 was impaired by IMA and NIL leading to an intracellular accumulation of calcidiol. However, during TKI treatment, KC of IMA treated children revealed no differences in calcidiol and calcitriol levels. In conclusion, IMA and NIL interfere with the vitamin D3 cascade due to their metabolism by CYP27B1.

Inhibitory effects of imatinib on vitamin D3 synthesis in human keratinocytes.

Chronic myeloid leukemia (CML) is a myeloproliferative disease characterized by the presence of the BCR­ABL1 fusion gene, a constitutively active, oncogenic tyrosine kinase that is responsible for the clinical features of CML. Tyrosine kinase inhibitors, such as imatinib, have markedly altered the treatment of CML. However, tyrosine kinase inhibitors are associated with side effects on bone metabolism, in adult and pediatric patients. Vitamin D3 is involved in the complex cycle of bone remodeling, therefore the present study aimed to investigate the influence of imatinib on vitamin D3 metabolism in the HaCaT human keratinocyte cell line, using commercially available enzyme assays. Imatinib was shown to significantly reduce the production of calcidiol and calcitriol. Based on interaction studies of imatinib with the cytochrome P450 (CYP450) inhibitors VID400 and ketoconazole, it is proposed that imatinib may interfere with the vitamin D3 cascade due to its metabolism by CYP27B1, which is involved in vitamin D3 metabolism.

Micro-osmotic pumps for continuous release of the tyrosine kinase inhibitor bosutinib in juvenile rats and its impact on bone growth.

BACKGROUND: Bosutinib is a third-generation dual tyrosine kinase inhibitor (TKI) inhibiting Abl and Src kinases. It was developed to act on up-regulated tyrosine kinases (TKs) like BCR-ABL in Philadelphia chromosome positive (Ph+) chronic myeloid leukemia (CML) when resistance to first- and second-generation TKIs developed. However, first- and second-generation TKIs show off-target effects on bone metabolism, whereas studies on skeletal adverse effects of bosutinib are still lacking. Therefore, it was the aim of this study to continuously expose juvenile rats to bosutinib and to analyze its influence on the growing bone. MATERIAL/METHODS: Starting after weaning, 4-week-old Wistar rats were chronically exposed over a 28-day period to varying concentrations of bosutinib, which were continuously administered subcutaneously via implanted Alzet® micro-osmotic pumps. After necropsy, the length of the femora and tibiae were analyzed. RESULTS: Continuous administration of bosutinib by micro-osmotic pumps led to serum drug levels in the lower therapeutic range, was well tolerated, and exhibited only minor adverse effects on the growing skeleton. CONCLUSIONS: Micro-osmotic pumps represent a convenient system for continuous TKI release in young growing rats. Compared to first- and second-generation TKIs, bosutinib seems to exert fewer adverse effects on the growing bone.

Changes in bone metabolic parameters in children with chronic myeloid leukemia on imatinib treatment.

BACKGROUND: Imatinib is a highly effective drug in up-front treatment of chronic myeloid leukemia (CML). In children impaired longitudinal growth has been reported as side effect exerted by this drug under prolonged therapy. We therefore prospectively evaluated alterations of bone biochemical markers in pediatric patients with CML under ongoing imatinib exposure. MATERIAL/METHODS: Bone metabolic markers (calcium, phosphate, magnesium, parathyroid hormone, vitamin D, procollagen type l N propeptide [PINP], and C-terminal cross-linking telopeptide of collagen [CTX-I], osteocalcin [OC]; pyridinoline [PYD], and desoxypyridinoline [DPD]) were determined in 17 patients with CML aged 4-17 years under imatinib treatment in three-month intervals over a 2.5 year period. RESULTS: Hyperparathyroidism developed in 8/17 patients and low 25-hydroxyvitamin-D3 levels were found in 15/17 patients. Increased OC levels were detected in 58% of all specimen showing a linear significant decline of -0.30 µg OC per l per week (p=0.04). Serum PINP was lowered in 25% and serum CTX-I was above the normal range in 57% of the specimen originating exclusively from prepupertal patients. Urine PYD and Urine DPD levels were above the normal range in 10% and 9%, respectively, of all specimen collected and a statistically significant linear decline of -0.16 nmol DPD/mg creatinine/week was calculated (p=0.01). CONCLUSIONS: Bone remodeling may be dysregulated by imatinib. Data suggest that impaired bone formation exceeds that of decreased bone resorption. Regular evaluation of the skeletal actions during long-term imatinib treatment in childhood CML is warranted.

Management of chronic myeloid leukemia in childhood.

Childhood chronic myelogenous leukemia (CML) is a rare malignancy, and experience with optimal treatment is very limited. Traditionally, allogeneic hematopoietic stem cell transplantation was considered the only curative treatment. Imatinib, a small-molecule inhibitor of the BCR-ABL tyrosine kinase (TKI), has been proven highly successful in adults with CML, resulting in prolonged molecular response with limited drug toxicity. This drug is now included as front-line therapy for CML in pediatrics as well, though valid concerns about serious late sequelae remain unresolved. Specific pediatric treatment guidelines have not yet been formulated, and most algorithms are derived from experience in adult CML. This overview attempts to summarize pediatric studies on issues such as dose, duration, adverse effects, and steering criteria for TKI treatment, adapting guidelines developed in adult medicine to pediatrics. Most importantly, pediatric patients with CML receiving TKI treatment should be enrolled into formal trials.

Investigations of Platelet Function in Whole Blood with BAPA as Anticoagulant.

BACKGROUND: Citrate anticoagulation of blood results in non-physiologically low calcium concentration and rapid deterioration of platelet viability. Benzylsulfonyl-D-Arg-Pro-4-amidinobenzylamide (BAPA) as anticoagulant maintains the physiological calcium level and seems to retain platelet function (PF) over a time period of at least 24 h. We evaluated PF in BAPA-anticoagulated peripheral whole blood (WB) between 0.5 and 30 h after blood collection. METHODS: In WB from 21 healthy volunteers (15 women, 6 men, age range 19-57 years) platelet aggregation (PA) was determined by impedance method and ATP release by luminometry. Platelet response was tested by ADP (10 and 20 µmol/l) and collagen (1 and 2 µg/ml) between 0.5 and 30 h after blood collection. RESULTS: Parameters of ADP-induced PA showed stable values until 6.5 h after blood collection followed by a significant decline. PA in response to collagen was stable up to 25 h of storage. ATP release induced by collagen displayed a continuous, significant decrease over time. CONCLUSION: Preservation of platelet response in BAPA-anticoagulated blood depends on the applied agonist showing that collagen-induced PA is more stable compared to ADP known as a weak agonist in WB.