Imatinib Therapy in Clonal Eosinophilic Disorders, Including Systemic Mastocytosis

The Molecular Analysis for Therapy Choice (NCI-MATCH) Trial: Lessons for Genomic Trial Design

Background

The proportion of tumors of various histologies that may respond to drugs targeted to molecular alterations is unknown. NCI-MATCH, a collaboration between ECOG-ACRIN Cancer Research Group and the National Cancer Institute, was initiated to find efficacy signals by matching patients with refractory malignancies to treatment targeted to potential tumor molecular drivers regardless of cancer histology.

Methods

Trial development required assumptions about molecular target prevalence, accrual rates, treatment eligibility, and enrollment rates as well as consideration of logistical requirements. Central tumor profiling was performed with an investigational next-generation DNA–targeted sequencing assay of alterations in 143 genes, and protein expression of protein expression of phosphatase and tensin homolog, mutL homolog 1, mutS homolog 2, and RB transcriptional corepressor 1. Treatments were allocated with a validated computational platform (MATCHBOX). A preplanned interim analysis evaluated assumptions and feasibility in this novel trial.

Results

At interim analysis, accrual was robust, tumor biopsies were safe (<1% severe events), and profiling success was 87.3%. Actionable molecular alteration frequency met expectations, but assignment and enrollment lagged due to histology exclusions and mismatch of resources to demand. To address this lag, we revised estimates of mutation frequencies, increased screening sample size, added treatments, and improved assay throughput and efficiency (93.9% completion and 14-day turnaround).

Conclusions

The experiences in the design and implementation of the NCI-MATCH trial suggest that profiling from fresh tumor biopsies and assigning treatment can be performed efficiently in a large national network trial. The success of such trials necessitates a broad screening approach and many treatment options easily accessible to patients.

New sources of drugs for hematologic malignancies

Advancing novel therapeutic agents for the treatment of malignancy into the marketplace is an increasingly costly and lengthy process. As such, new strategies for drug discovery are needed. Drug repurposing represents an opportunity to rapidly advance new therapeutic strategies into clinical trials at a relatively low cost. Known on-patent or off-patent drugs with unrecognized anticancer activity can be rapidly advanced into clinical testing for this new indication by leveraging their known pharmacology, pharmacokinetics, and toxicology. Using this approach, academic groups can participate in the drug discovery field and smaller biotechnology companies can "de-risk" early-stage drug discovery projects. Here, several scientific approaches used to identify drug repurposing opportunities are highlighted, with a focus on hematologic malignancies. In addition, a discussion of the regulatory issues that are unique to drug repurposing and how they impact developing old drugs for new indications is included. Finally, the mechanisms to enhance drug repurposing through increased collaborations between academia, industry, and nonprofit charitable organizations are discussed.

Imatinib mesylate reduces rituximab-induced tumor-growth inhibition in vivo on Epstein-Barr virus-associated human B-cell lymphoma

We have reported earlier an increase of tumor-growth inhibition following chemotherapy combined with concomitant administration of imatinib mesylate. Conversely, the combination of imatinib and rituximab has been reported in very few cases of patients and remains controversial. To explore this particular combination of targeted therapies, we therefore investigated the in-vivo impact of rituximab plus imatinib on B-cell lymphoproliferation. Combination of the tyrosine kinase inhibitor imatinib mesylate (STI571) and the anti-CD20 monoclonal antibody rituximab was evaluated on an Epstein-Barr virus-associated B-cell lymphoproliferative disorder xenografted into severe combined immunodeficient or Rag2/gammac-/- (B-, T- and NK-) mice. Using severe combined immunodeficient mice, we found that STI571 diminished the efficacy of rituximab to inhibit tumor growth in vivo. Using alymphoid Rag2/gammac-/- mice, we showed that the effect of STI571 was not dependent on the presence of natural killer cells. In contrast, serum complement administered after STI571 treatment reversed this inhibitory effect. Finally, using nonimmunodeficient mice, we observed an in-vivo decrease of CD4-positive T-cells and mature B-cell lymphocytes after imatinib administration. We found that STI571 decreased the in-vivo efficacy of rituximab via serum protein components that could influence complement-dependent cytotoxicity. In contrast, this effect was not dependent on the presence of natural killer cells.

Targeting immunosupportive cancer therapies: accentuate the positive, eliminate the negative

In this Commentary we aim to provide an overview of some specific examples of cancer therapeutics, including targeted approaches using monoclonal antibodies and kinase inhibitors, as well as highlight novel approaches for enhancing immunological responses against tumors. We point out that a fundamental property of the cancer cell, genomic instability, confounds the targeted therapies that aim to induce cell death directly while simultaneously enhancing the potential for immunological attack by creating a large number of neoantigens. We argue for combinatorial strategies with agents that target tumor cells to release these antigens together with innovative therapies that enhance immunological responses by interfering with inhibitory checkpoints.

Diagnostic evaluation and classification of mastocytosis

During the past few years, mastocytosis research has reached important milestones, including the formulation of diagnostic criteria, definition of markers, and targeting of mutated KIT. Important aims for the future are to standardize diagnostic assays and techniques, and to achieve harmonization among centers as a basis for the design of multicenter clinical trials in SM, including the rare ASM and MCL subvariants.

Pathogenesis, clinical features, and treatment advances in mastocytosis

Systemic mastocytosis (SM) is characterized by the abnormal growth and accumulation of mast cells (MC) in one or more organs. The interaction between the cytokine stem cell factor (SCF) and its cognate receptor, the c-kit receptor tyrosine kinase (KIT), plays a central role in regulating MC growth and differentiation. Whereas germline and somatically acquired activating mutations of KIT have been identified in SM, the issue as to whether individual KIT mutation(s) are necessary and sufficient to cause MC transformation remains unclear based on currently available data. Activating mutations of platelet-derived growth factor receptor-alpha (FIP1 L1-PDGFRA) are identified in a significant number of SM cases that have associated eosinophilia. To date, as with gastrointestinal stromal tumors, activating mutations of KIT and PDGFRA appear to be alternative and mutually exclusive genetic events in SM. The World Health Organization has specified criteria for classification of SM into six major subtypes: cutaneous mastocytosis, indolent systemic mastocytosis (ISM), systemic mastocytosis with an associated clonal hematological non-mast-cell disorder (SM-AHNMD), aggressive systemic mastocytosis (ASM), mast cell leukemia, and mast cell sarcoma. The ability to molecularly classify individual SM cases based on the presence or absence of specific mutations allows for molecularly targeted therapy in a growing number of cases. Imatinib mesylate therapy might result in complete remission of SM cases with wild-type KIT, certain KIT mutations, such as F522C, or the FIP1L1-PDGFRA fusion gene, but not of D816V-KIT-bearing SM. For the latter, interferon-alpha and 2-CdA are potential first- and second-line therapeutic options. Other drugs under investigation include novel tyrosine kinase inhibitors, as well as NF-kappaB inhibitors, which might display greater selectivity towards D816V-KIT as compared to wild type KIT. The pathogenesis of mastocytosis, its major clinical subtypes, and recent treatment advances are discussed in this chapter.

Ph-Chromosome-positive chronic myeloid leukemia with associated bone marrow mastocytosis

The concurrent development of chronic myeloid (CML) or myelomonocytic (CMML) leukemia in patients with systemic mastocytosis (SM) is a well recognized phenomenon. Although the leukemia often resembles CML in morphological and in clinical terms, a Ph-Chromosome-positive variant has not been reported in SM so far. We here describe a 43-year-old female patient with typical Ph-Chromosome-positive CML in whom a co-existing bone marrow mastocytosis, a special subvariant of SM, was diagnosed. RT-PCR analysis revealed the typical p210 kDa form of BCR/ABL in leukemic cells. The diagnosis SM was based on the typical focal aggregates of spindle-shaped mast cells (MC) in the bone marrow, expression of CD25 in MC, and the c-kit mutation D816V, which was detectable in microdissected bone marrow MC, but not in microdissected leukemic cells, suggesting the presence of two different (sub)clones of neoplastic cells. Therapy with the BCR/ABL-targeting drug Imatinib (STI571) resulted in complete cytogenetic remission of CML. Together, our case provides further evidence for the biologic diversity of leukemias that may occur in patients with SM. The exact knowledge of the pathology and target-profile of the associated leukemias in SM have important therapeutic implications.

Mastocytosis: pathology, genetics, and current options for therapy

Mast cell disorders are defined by an abnormal accumulation of tissue mast cells (MCs) in one or more organ systems. Symptoms in mastocytosis result from MC-derived mediators and, less frequently, from destructive infiltration of MCs. Cutaneous mastocytosis (CM) is a benign disease of the skin and may regress spontaneously. Systemic mastocytosis (SM) is a persistent disease in which a somatic c-kit mutation at codon 816 is usually detectable in MCs and their progenitors. The clinical course in these patients is variable ranging from asymptomatic for years to highly aggressive and rapidly devastating. The WHO discriminates five categories of SM: indolent SM (ISM), aggressive SM (ASM), SM with associated clonal hematological non-MC-lineage disease (AHNMD), and mast cell leukemia (MCL). The c-kit mutation D816V is quite common and may be found in all SM-categories. In SM-AHNMD, additional genetic abnormalities have been reported, whereas no additional defects are yet known for ASM or MCL. Patients with ISM and CM are treated with "mediator-targeting" drugs, whereas patients with ASM or MCL are candidates for cytoreductive therapy. The use of "Kit-targeting" tyrosine kinase inhibitors such as STI571 (Imatinib, Gleevec), has also been suggested. However, the D816V mutation of c-kit is associated with relative resistance against STI571. Therefore, these patients require alternative targeted drugs or new drug-combinations. In patients with SM-AHNMD, separate treatment plans for the SM-component and the AHNMD should be established. Examples include the use of STI571 in patients with SM plus hypereosinophilic syndrome (SM-HES) and the FIPL1/PDGFRA fusion gene target, or chemotherapy for eradication of AML in patients with SM-AML.

Systemic mastocytosis: bone marrow pathology, classification, and current therapies

Mast cell disease (MCD) is characterized by the abnormal growth and accumulation of neoplastic mast cells (MC) in one or more organs. The diagnosis of systemic MCD is most commonly established by a thorough histological and immunohistochemical examination of a bone marrow (BM) trephine specimen. In cases with pathognomonic perivascular and -trabecular aggregates of morphologically atypical MC and significant BM involvement, the diagnosis may be relatively straightforward. In contrast, when a sparse, loose pattern of MC infiltration predominates, or when MCs are obscured by an associated non-MC hematological neoplasm, a high index of suspicion and use of adjunctive tests, including special stains, such as tryptase and CD25, may be necessary to reach a diagnosis. The updated classification for MCD clarifies the clinical and pathological criteria for categorizing patients into relatively discrete subgroups. Some cases, however, such those with Fip1-like-1-platelet-derived growth factor receptor alpha (FIP1L1-PDGFRA)(+) clonal eosinophilia associated with elevated serum tryptase levels, with features that overlap MCD and chronic eosinophilic leukemia, may not be easy to categorize on the basis of this classification. There is no standard therapy for MCD and treatment has to be tailored to the needs of the individual patient. MC-cytoreductive therapies, such as interferon-alpha and chemotherapy, are generally reserved for patients with progressive disease and organopathy. A subset of MCD patients with associated eosinophilia who carry the FIP1L1-PDGFRA oncogene will achieve complete clinical, histological, and molecular remissions with imatinib mesylate therapy, in contrast to those with c-kit D816V mutations. The BM pathology, consensus classification, and current therapies for MCD are further discussed in this article.