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DCC-2618: a new drug against mastocytosis
cacy, midostaurin is unable to produce long-lasting com- plete remission in all patients.28 Therefore, new drugs and drug-combinations are currently being tested in the con- text of advanced SM. DCC-2618 might be a promising candidate for several reasons. First, DCC-2618 exhibits a broad target profile and is able to block growth of various neoplastic cells.36 In the current study, DCC-2618 was found to block growth of neoplastic cells obtained from patients with ASM and MCL. In addition, the drug pro- duced growth inhibition in all MCL-like cell lines tested, including KIT-mutated cells and cell lines in which other oncogenic pathways (such as the RAS pathway) trigger malignant cell growth. Moreover, unlike other KIT-target- ing drugs, DCC-2618 is able to suppress the growth and survival of other cell types relevant to advanced SM and AHN, including monocytes, blast cells, neoplastic eosinophils and endothelial cells. The concentrations required to mediate these cellular inhibitory effects are readily achievable based on the recent report of clinical exposure of 5 μM or higher in patients with gastrointesti- nal stroma tumors.43
After intake, DCC-2618 is considered to be converted to one active metabolite, DP-5439. We therefore investi- gated whether DP-5439 is also able to counteract growth and survival of neoplastic cells. In these experiments, we were able to show that DP-5439 is able to suppress growth and survival of neoplastic MC and of other leukemic (non-MC-lineage) cells in the same way (and with comparable IC50 values) as DCC-2618. These data suggest that DCC-2618 treatment should be effective even if the DP-5439 metabolite may accumulate over time.
It is well known that about one-third of all patients with advanced SM have an AHN at diagnosis. Of these patients, most have a myeloid neoplasm, often in the form of CMML or AML.2-8,13,32 The treatment of these SM- AHN patients is a clinical challenge because the AHN is often drug-resistant. In fact patients with SM-AHN still have a poor prognosis with an overall survival time of about 24 months.13,32 Because of its broad activity profile, we asked whether DCC-2618 might be a promising agent for patients with SM-AHN. In a first step, we found that DCC-2618 is a potent inhibitor of proliferation and sur- vival of the FLT3-mutated AML cell lines MOLM-13 and MV4-11. DCC-2618 also inhibits the growth of other AML cell lines examined (KG-1 and U937), but at IC50 val- ues considerably higher than those for MOLM-13 or MV4-11 cells. We also found that DCC-2618 counteracts proliferation of primary leukemic cells obtained from patients with SM-AHN, AML or CMML (Table 1 and Online Supplementary Table S1). These findings suggest that DCC-2618 may be a promising agent for SM-AHN.
In SM patients, disease progression is often accompa- nied by expansion of neoplastic eosinophils, sometimes even resembling (chronic) eosinophilic leukemia. In most cases the eosinophils are of clonal origin as they express KIT D816V.33 In rare cases, neoplastic eosinophils display the FIP1L1/PDGFRA fusion gene.34 However, this fusion gene is usually detectable only in eosinophilic neoplasms, such as CEL. Since DCC-2618 is known to exert inhibito- ry effects against PDGFRA35 we examined its effects on EOL-1 cells harboring FIP1L1-PDGFRA. DCC-2618 was found to exert strong anti-proliferative and apoptosis- inducing effects in EOL-1 cells, with IC50 values in the low nanomolar range. In addition, DCC-2618 was found to
inhibit growth of primary eosinophils obtained from patients with KIT D816V-positive SM or reactive hypere- osinophilia. Together, these data suggest that DCC-2618 inhibits multiple AHN-related cell types, which may be relevant clinically as progression of SM is often accompa- nied by multilineage expansion of various sub-clones, including cells harboring or lacking KIT D816V.15,28,29
A number of different pro-oncogenic pathways and tar- gets may be involved in KIT D816V-dependent expansion and accumulation of MC in advanced SM.25,40,44-50 Several of these target pathways may be sensitive to therapy with tyrosine kinase inhibitors. We studied whether key target pathways in neoplastic MC can be disrupted by DCC-2618. As assessed by Western blotting, DCC-2618 was found to block the phosphorylation and thus activa- tion of wild-type KIT and KIT D816V. In addition, we were able to show that DCC-2618 blocks the activation of AKT, ERK and STAT5, suggesting that multiple target pathways are accessible to this drug. By contrast, howev- er, the drug did not disrupt activation of BTK, another important target displayed by neoplastic MC.46
Since the target spectrum of midostaurin (PKC412) and DCC-2618 is not identical, we were also interested to learn whether DCC-2618 and midostaurin can produce synergistic antineoplastic effects on neoplastic MC. Indeed, we found that both drugs induce cooperative or even synergistic growth-inhibitory effects on HMC-1.1 and HMC-1.2 cells.
Specific alterations in the microenvironment, including increased angiogenesis, are frequently detectable in advanced bone marrow neoplasms and are often consid- ered to play an important role in disease progression. A typical finding in the affected bone marrow of patients with advanced SM is increased microvessel density.41 We found that DCC-2618 inhibits the proliferation of human endothelial cells, including HUVEC and a microvascular endothelial cell line, HMEC-1. These data suggest that DCC-2618 also acts as an anti-angiogenic agent. Interestingly, the IC50 values obtained for HMEC-1 cells were higher than those for HUVEC, which may be explained by the fact that HMEC-1 is a cell line, whereas HUVEC are primary cells. An alternative explanation would be the lack of key targets in HMEC-1 cells. Indeed, it is well known, that KDR, a key target of DCC- 2618, is only expressed in HUVEC but not in HMEC-1 cells.
Patients with SM frequently suffer from symptoms produced by MC-derived mediators.4-6,16 These mediators are released on IgE-dependent activation of MC and may cause severe problems or even lead to life-threatening anaphylaxis. Concomitant (IgE-dependent) allergies are, therefore, relevant comorbidities in the context of SM. We found that DCC-2618 counteracts IgE-dependent secretion of histamine from basophils obtained from healthy donors. In addition, we were able to show that DCC-2618 blocks IgE-independent, spontaneous release of tryptase from HMC-1.1 and HMC-1.2 cells in vitro. These results suggest that, apart from its antineoplastic effects, DCC-2618 might also have an impact on media- tor release (and probably on the resulting symptoms) in patients with SM with concomitant allergies. Whether these data can be reproduced in vivo and whether the drug is able to suppress mediator symptoms in patients with advanced SM or SM with concomitant allergies remains to be determined. In fact, whereas the concentrations of
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