Imatinib is a Bcr-Abl inhibitor used as first-line therapy of chronic myeloid leukemia (CML). p21(Cip1), initially described as a cell cycle inhibitor, also protects from apoptosis in some models. We describe that imatinib down-regulates p21(Cip1) expression in CML cells. Using K562 cells with inducible p21 expression and transient transfections we found that p21 confers partial resistance to imatinib-induced apoptosis. This protection is not related to the G2-arrest provoked by p21, a decrease in the imatinib activity against Bcr-Abl or a cytoplasmic localization of p21. The results suggest an involvement of p21(Cip1) in the response to imatinib in CML. less...

Vascular endothelial growth factor (VEGF), which is a key regulator of angiogenesis, often induces formation of immature vessels with increased permeability and reduced vessel functionality. Here, we demonstrate that de novo expression of murine (m)VEGF-164 induces malignant and invasive tumor growth of HaCaT keratinocytes. However, the mVEGF-164-induced tumors are ulcerated with a disorganized epithelium that is interrupted by lacunae with limited basement membrane and endothelial cell coverage. Vessel maturation is strongly impaired. Tumor and vessel micromorphology are markedly improved by the combined expression of human platelet-derived growth factor (hPDGF)-B and mVEGF-164. Although tumor size and malignancy are comparable with either mVEGF-164 alone or combined human PDGF-B and mVEGF-164 expression, combined hPDGF-B and mVEGF-164 expression leads to a more solid and compact tumor tissue with a mature functional tumor vasculature and a higher microvessel density, as demonstrated histologically and by dynamic contrast-enhanced magnetic resonance imaging. Treatment of the hPDGF-B- and mVEGF-164-expressing tumors with imatinib mesylate to block PDGF-B signaling reverses this effect. In addition, tumor cell invasion of mVEGF-164 transfectants and mVEGF-164 plus hPDGF-B transfectants in vivo is associated with a marked induction of tumor-derived matrix metalloproteinase-1 and stromal matrix metalloproteinase-9 and -13, as was confirmed in three-dimensional organotypic co-cultures with fibroblasts in vitro. These data clearly demonstrate the need for a concerted action of different growth factors in the establishment of solid tumors with functional vasculature and emphasize the need for a multifactorial therapy. less...

AIMS AND BACKGROUND: Most gastrointestinal stromal tumor (GIST) patients respond to KIT inhibition therapy of imatinib, but eventually become resistant with a median time to progression of 2 years. The mechanism of acquired resistance to imatinib and oncogenic KIT signal transduction in GISTs has not been well defined. We sought to investigate the spectrum of molecular and genomic changes in imatinib-resistant GIST patients. METHODS: KIT and PDGFRA mutations were evaluated in 48 samples obtained from 32 GIST patients who underwent surgery after imatinib treatment. KIT downstream signaling profiles were also investigated in eight specimens of five patients who were clinically responsive or resistant to imatinib therapy. Biochemical inhibition of KIT, mitogen-activated protein kinase (MAPK), mammalian target of rapamycin (MTOR), AKT, proliferating cell nuclear antigen (PCNA) and BCL-2 were determined by western blotting for protein activation. RESULTS: In all 32 GIST patients, activating mutations in the KIT gene were seen in 26 (81.3%) patients, PDGFRA gene mutations were seen in 2 (6.2%) patients and no primary mutations were found in 4 (12.5%) patients. Secondary KIT mutations were identified in 11/14 (78.6%) imatinib-acquired-resistance patients, with nine patients in KIT gene exon17, and the other two in exon 13. The expressions of p-KIT, p-AKT, PCNA and BCL-2 were higher in the samples of imatinib-resistant GISTs than those of imatinib-responsive ones. P-KIT, p-AKT expressions were higher in imatinib acquired-resistance GISTs with secondary KIT mutations than imatinib-responsive ones with primary mutation. Total KIT, MAPK, p-MAPK, p-MTOR expressions were comparable in all varied GISTs. CONCLUSIONS: Novel additional mutations of KIT gene exon 13 or exon 17 indicate the likely mechanism of secondary resistance to imatinib. The PI3-K/AKT pathway might be more relevant than MEK/MAPK for therapeutic targeting in imatinib-resistant GIST patients with secondary mutation. less...

Radiation-induced midbrain fibrosarcoma is a rare, highly aggressive tumor, which is associated with poor prognosis. We present the case of a 48-year old man with brainstem fibrosarcoma 20 years following radiation therapy received for a pituitary tumor. We discuss this case in the context of the diagnostic criteria for these tumors, and previous reports of secondary and primary sarcomas of the central nervous system. less...

ABSTRACT: BACKGROUND: Access to medicines in developing countries continues to be a significant problem due to lack of insurance and lack of affordability. Chronic Myeloid Leukemia (CML), a rare disease, can be treated effectively, but the pharmaceutical treatment available (imatinib) is costly and unaffordable by most patients. GIPAP, is a programme set up between a manufacturer and an NGO to provide free treatment to eligible CML patients in 80 countries worldwide. Objectives: To discuss the socio-economic and demographic characteristics of patients participating in GIPAP; to research the impact GIPAP is having on health outcomes (survival) of assistance-eligible CML patients; and to discuss the determinants of such outcomes and whether there are any variations according to socio-economic, demographic, or geographical criteria. METHODS: Data for 13,568 patients across 15 countries, available quarterly, were analysed over the 2005-2007 period. Ordered Probit panel data analysis was used to analyze the determinants of a patient's progress in terms of participation in the programme. Four waves of patients entering quarterly in 2005 were used to evaluate patient survival over the sample period. RESULTS: All patients in the sample are eligible to receive treatment provided they report to a facility quarterly. 62.3% of patients were male and 37.7% female. The majority (84.4%) entered during the chronic phase of the disease and their average age was 38.4 years. Having controlled for age, location and occupation, the analysis showed that patients were significantly much more likely to move towards a better health state after receiving treatment irrespective of their disease stage at the point of entry to the program (OR=30.5, alpha=1%); and that the larger the gap between diagnosis and approval for participation in the program, the more likely it is that patients' condition deteriorates (OR=0.995, alpha=1%), due to absence of treatment. Regressions to account for the effect of large countries (India, China, Pakistan) did not show any important differences when compared to the remaining countries in the sample. Survival analysis shows that at least 66 percent of all patients that entered the program in 2005 were alive and active by the end of 2007. CONCLUSIONS: GIPAP has a significant positive effect on patient access to important medicines for a life threatening condition such as CML. It impacts both the progress and phase of the disease and leads to a high survival rate. Overall, it sets a good example for access to treatment in developing countries, where such programmes can substitute or complement local efforts to provide care to eligible patients. less...

The importance of H(2)O(2) as a cellular signaling molecule has been demonstrated in a number of cell types and pathways. Here we explore a positive feedback mechanism of H(2)O(2)-mediated regulation of the phagocyte respiratory burst NADPH oxidase (NOX2). H(2)O(2) induced a dose-dependent stimulation of superoxide production in human neutrophils, as well as in K562 leukemia cells over-expressing NOX2 system components. Stimulation was abrogated by addition of catalase, the extracellular Ca(2+) chelator BAPTA, the T-type Ca(2+) channel inhibitor mibefradil, the PKCdelta inhibitor rottlerin, or the c-Abl non-receptor tyrosine kinase inhibitor imatinib mesylate, or by over-expression of a dominant-negative form of c-Abl. H(2)O(2) induced phosphorylation of tyrosine(311) on PKCdelta and this activating phosphorylation was blocked by treatment with rottlerin, imatinib mesylate, or BAPTA. Rac GTPase activation in response to H(2)O(2) was abrogated by BAPTA, imatinib mesylate, or rottlerin. In conclusion, H(2)O(2) stimulates NOX2-mediated superoxide generation in neutrophils and K562/NOX2 cells via a signaling pathway involving Ca(2+) influx and c-Abl tyrosine kinase acting upstream of PKCdelta. This positive feedback regulatory pathway has important implications for amplifying the innate immune response and contributing to oxidative stress in inflammatory disorders. less...

BACKGROUND: The tyrosine kinase inhibitors (TKI) sunitinib and imatinib were shown to induce macrocytosis in patients with renal cell cancer (RCC) and gastrointestinal stromal tumors (GIST), presumably through inhibition of the c-KIT dependent signaling pathway of erythroid progenitor cells of the bone marrow. PATIENTS AND METHODS: Hematology charts of patients with RCC, breast cancer (BC), GIST, non-small cell lung cancer (NSCLC) and hepatocellular cancer (HCC), receiving single-agent sunitinib, imatinib, sorafenib, erlotinib and BI 2992 (Tovok) at the recommended dose for at least 3 months were reviewed retrospectively for the occurrence of macrocytosis. RESULTS: Macrocytosis occurred in all patients with RCC and BC treated with sunitinib and in all patients with GIST treated with imatinib. The percentage increase of the mean corpuscular volume (MCV) of peripheral red blood cells (RBC) compared with baseline at 3, 6, 9 and 12 months was 12.4%, 16.8%, 16.6%, 12.7% and 0.7%, 5.6%, 5.9%, 5% with sunitinib and imatinib respectively. The values at 3, 6 and 9 months between both groups were significantly different. Sorafenib, erlotinib and BI 2992 did not induce macrocytosis. CONCLUSION: Sunitinib-induced macrocytosis was not confined to patients with RCC alone but also occurred in patients with BC. Imatinib also induced macrocytosis in patients with GIST but to a significantly lower degree. Because both drugs were used at an effective pharmacodynamic dose inhibiting c-KIT, these data strongly suggest that pathways in addition to c-KIT and not common to both agents are involved in the TKI-induced macrocytosis. less...

The co-occurrence of JAK2 V617F mutation with BCR-ABL reciprocal translocation is uncommon. We report a 60-year-old man who initially presented with phenotype of polycythemia vera (PV), which evolved into chronic myeloid leukemia and back to PV once treatment with imatinib was commenced. JAK2 V617F mutation and BCR-ABL fusion transcripts were detected in the initial sample. However, JAK2 V617F alleles diminished when BCR-ABL mRNA burden increased and reappeared once the patient was commenced on imatinib. The dynamic interaction between JAK2 V617F and BCR-ABL implies that two independent clones exist with the JAK2 V617F clone only achieving clonal dominance when BCR-ABL positive clones are suppressed by imatinib. less...

We report a case of imatinib- and nilotinib-resistant Ph-positive chronic myeloid leukemia (CML) in blast crisis in which successful pretreatment with dasatinib with cord blood transplantation resulted in molecular remission. Before dasatinib therapy, the patient was found to have a F359V BCR-ABL mutation. He was treated with dasatinib for just 16, 19 days before allogeneic stem cell transplantation. This successful case indicates that reduction of tumor burden by second-generation tyrosine kinase inhibitors, in combination with stem cell transplantation, might be effective to treat CML, even in the advanced phase. less...

Gastrointestinal stromal tumor (GIST) is considered to be driven by a gain-of-function mutation in the KIT or PDGFRA gene. Cure can be obtained only by complete surgical removal of the GIST; however, imatinib, an inhibitor of KIT and PDGFRA, is indicated for advanced, recurrent, and/or metastatic GISTs. Imatinib exhibited remarkable clinical effects on advanced GISTs, with substantial tolerability. Its efficacy greatly depends on the genotype of GIST. The drug, however, met intrinsic or acquired resistance during the treatment, of which the molecular mechanisms were mostly dependent on the genotype of GIST, including primary mutations or secondary mutations in the kinase domains of the corresponding target genes, respectively. Although sunitinib had substantial effects on imatinib-resistant GIST, this drug also encountered primary or secondary resistance depending on the genotype. Thus, advanced GIST may require multidisciplinary treatment. Because resistance mechanisms show some regularity, it is hoped that, in the near future, we may be able to develop a new drug to which resistance does not occur easily, based on scientific evidence. less...