Midostaurin: a magic bullet that blocks mast cell expansion and activation.

Clinically relevant features in patients with systemic mastocytosis (SM) include the cosmetic burden of lesional skin, mediator-related symptoms, and organ damage resulting from mast cell (MC) infiltration in advanced forms of SM. Regardless of the SM variant, expansion of neoplastic MC in the skin and other organs is triggered by mutant forms of KIT, the most prevalent being D816V. Activation of MC with subsequent release of chemical mediators is often caused by IgE-dependent mechanisms in these patients. Midostaurin, also known as PKC412, blocks the kinase activity of wild-type KIT and KIT D816V, counteracts KIT-dependent growth of neoplastic MC, and inhibits IgE-dependent mediator secretion. Based on this activity-profile, the drug has been used for treatment of patients with advanced SM. Indeed, encouraging results have been obtained with the drug in a recent multi-center phase II trial in patients with advanced SM, with an overall response rate of 60% and a substantial decrease in the burden of neoplastic MC in various organs. Moreover, midostaurin improved the overall survival and relapse-free survival in patients with advanced SM compared with historical controls. In addition, midostaurin was found to improve mediator-related symptoms and quality of life, suggesting that the drug may also be useful in patients with indolent SM suffering from mediator-related symptoms resistant to conventional therapies or those with MC activation syndromes. Ongoing and future studies will determine the actual value of midostaurin-induced MC depletion and MC deactivation in these additional indications.

The KIT D816V allele burden predicts survival in patients with mastocytosis and correlates with the WHO type of the disease.

KIT D816V is present in a majority of patients with systemic mastocytosis (SM). We determined the KIT D816V allele burden by quantitative real-time PCR in bone marrow and peripheral blood of 105 patients with mastocytosis. KIT D816V was detected in 92/105 patients (88%). Significant differences in the median allele burden were observed between disease subgroups: cutaneous mastocytosis (0.042%), indolent SM (0.285%), smoldering SM (5.991%), aggressive SM (9.346%), and SM with associated hematologic non-mast cell lineage disease (3.761%) (P < 0.001). The KIT D816V burden also correlated with serum tryptase (R = 0.5, P < 0.005) but not with mast cell infiltration in bone marrow or mediator symptoms. Moreover, the allele burden was of prognostic significance regarding survival (P < 0.01). Patients responding to cytoreductive therapy showed a significant decrease in KIT D816V (P < 0.05). To conclude, the KIT D816V burden correlates with the variant of mastocytosis, predicts survival, and is a valuable follow-up parameter in SM.

The Hsp32 inhibitors SMA-ZnPP and PEG-ZnPP exert major growth-inhibitory effects on D34+/CD38+ and CD34+/CD38- AML progenitor cells.

Heat shock protein 32 (Hsp32), also known as heme oxygenase 1 (HO-1), has recently been identified as a potential target in various hematologic malignancies. We provide evidence that Hsp32 is constitutively expressed in primary leukemic cells in patients with acute myeloid leukemia (AML) and in various AML cell lines (HL60, U937, KG1). Expression of Hsp32 mRNA was demonstrable by qPCR, and expression of the Hsp32 protein by immunocytochemistry and Western blotting. The stem cell-enriched CD34+/CD38+ and CD34+/CD38- fractions of AML cells were found to express Hsp32 mRNA in excess over normal CD34+ progenitor cells. Two Hsp32-targeting drugs, pegylated zinc-protoporphyrin (PEG-ZnPP) and styrene-maleic-acid-copolymer-micelle-encapsulated ZnPP (SMAZnPP), were found to inhibit cytokine-dependent and spontaneous proliferation in all 3 AML cell lines as well as in primary AML cells. Growth inhibitory effects of SMA-ZnPP and PEG-ZnPP were dose-dependent with IC50 values ranging between 1 and 20 µM, and were accompanied by apoptosis as evidenced by light- and electron microscopy, Tunel assay, and caspase-3 activation. Finally, we were able to demonstrate that SMA-ZnPP inhibits cytokine-dependent proliferation of CD34+/CD38+ and CD34+/CD38- AML progenitor cells in vitro in all patients as well as leukemiainitiation of AML stem cells in NOD-SCID IL-2Rγ(-/-) (NSG) mice in vivo. Together, our data suggest that Hsp32 plays an important role as a survival factor in leukemic stem cells and as a potential new target in AML.

Targeting of Hsp32 in solid tumors and leukemias: a novel approach to optimize anticancer therapy.

Heat shock protein 32 (Hsp32), also known as heme oxygenase-1 (HO-1), is a stress-related anti-apoptotic molecule, that has been implicated in enhanced survival of neoplastic cells and in drug-resistance. We here show that Hsp32 is expressed in most solid tumors and hematopoietic neoplasms and may be employed as a new therapeutic target as evidenced by experiments using specific siRNA and a Hsp32-targeting pharmacologic inhibitor. This Hsp-32 targeting drug, SMA-ZnPP, was found to inhibit the proliferation of neoplastic cells with IC(50) values ranging between 1 and 50 microM. In addition, SMA-ZnPP induced apoptosis in all neoplastic cells examined. Furthermore, SMA-ZnPP was found to synergize with other targeted and conventional drugs in producing growth-inhibition. Resulting synergistic effects were observed in all tumor and leukemia cells examined. Interestingly, several of the drug partners, when applied as single agents, induced the expression of Hsp32 in neoplastic cells, suggesting that synergistic effects resulted from SMA-ZnPP-induced ablation of a Hsp32-mediated survival-pathway that is otherwise used by tumor cells to escape drug-induced apoptosis. Together, Hsp32 is an important survival factor and target in solid tumors and hematopoietic neoplasms, and may be used to optimize anticancer therapy by combining conventional or targeted drugs with Hsp32-inhibitors. Based on these data, it seems desirable to explore the value of Hsp32-targeting drugs as anti-cancer agents in clinical trials.

Targeting of mTOR is associated with decreased growth and decreased VEGF expression in acute myeloid leukaemia cells.

BACKGROUND: The mammalian target of rapamycin (mTOR) has recently been implicated in leukaemic cell growth, tumour-associated angiogenesis and expression of vascular endothelial growth factor (VEGF). We examined whether mTOR plays a role as regulator of growth and VEGF-expression in acute myeloid leukaemia (AML). Three mTOR-targeting drugs, rapamycin, everolimus (RAD001) and CCI-779, were applied. The effects of these drugs on growth, survival, apoptosis and VEGF expression in primary AML cells and various AML cell lines were examined. MATERIALS AND METHODS: Growth of AML cells and AML-derived cell lines was assessed by (3)H-thymidine incorporation, survival was examined by light- and electron microscopy, by Tunel assay and by AnnexinV-staining, and the expression of VEGF by Northern blotting, RT-PCR and ELISA. RESULTS: Rapamycin was found to counteract growth in the AML cell lines U937 and KG1a as well as in primary AML cells in 14/18 patients examined. The effects of rapamycin and its derivatives were dose-dependent (IC(50): 10 pM-100 nM). It was also found that exposure to mTOR-targeting drugs resulted in apoptosis and in decreased expression of VEGF in leukaemic cells. CONCLUSIONS: mTOR-targeting drugs exert antileukaemic effects on AML cells in vitro through multiple actions, including direct inhibition of proliferation, induction of apoptosis and suppression of VEGF. Based on this study and other studies, mTOR can be regarded as a potential drug target in AML.

Treatment responses to cladribine and dasatinib in rapidly progressing aggressive mastocytosis.

BACKGROUND: Systemic mastocytosis (SM) is a mast cell neoplasm in which neoplastic cells usually display the D816V-mutated variant of KIT. Cladribine (2CdA) and dasatinib are two drugs that counteract the in vitro growth of neoplastic mast cells in SM. However, only little is known about the in vivo effects of these drugs in SM. PATIENT AND METHODS: We report on a patient with highly aggressive interferon-alpha-resistant SM who was treated with 2CdA and dasatinib. In vitro pretesting revealed a response of neoplastic mast cells to both compounds with reasonable IC(50) values. RESULTS: The patient was treated with six cycles of 2CdA (0.13 mg kg(-1) intravenously daily on 5 consecutive days). Despite a short-lived major clinical response and a decrease in serum tryptase, the patient progressed to mast cell leukaemia after the sixth cycle of 2CdA. The patient then received two further courses of 2CdA followed by treatment with dasatinib (100 mg per os daily). However, no major response was obtained and the patient died from disease progression after 2 months. CONCLUSIONS: In a patient with rapidly progressing aggressive SM, neither 2CdA nor dasatinib produced a long-lasting response in vivo, despite encouraging in vitro results. For such patients, alternative treatment strategies have to be developed.