George Ansstas

Mobilization of Hematopoietic Stem and Progenitor Cells Using Inhibitors of CXCR4 and VLA-4

Successful hematopoietic stem cell transplant requires the infusion of a sufficient number of hematopoietic stem/progenitor cells (HSPCs) that are capable of homing to the bone marrow cavity and regenerating durable trilineage hematopoiesis in a timely manner. Stem cells harvested from peripheral blood are the most commonly used graft source in HSCT. Although granulocyte colony-stimulating factor (G-CSF) is the most frequently used agent for stem cell mobilization, the use of G-CSF alone results in suboptimal stem cell yields in a significant proportion of patients. Both the chemokine receptor CXCR4 and the integrin α4β1 (very late antigen 4 (VLA-4)) have important roles in the homing and retention of HSPCs within the bone marrow microenvironment. Preclinical and/or clinical studies have shown that targeted disruption of the interaction of CXCR4 or VLA-4 with their ligands results in the rapid and reversible mobilization of hematopoietic stem cells into the peripheral circulation and is synergistic when combined with G-CSF. In this review, we discuss the development of small-molecule CXCR4 and VLA-4 inhibitors and how they may improve the utility and convenience of peripheral blood stem cell transplantation.

Immunogenomics of Hypermutated Glioblastoma: A Patient with Germline POLE Deficiency Treated with Checkpoint Blockade Immunotherapy

We present the case of a patient with a left frontal glioblastoma with primitive neuroectodermal tumor features and hypermutated genotype in the setting of a POLE germline alteration. During standard-of-care chemoradiation, the patient developed a cervical spine metastasis and was subsequently treated with pembrolizumab. Shortly thereafter, the patient developed an additional metastatic spinal lesion. Using whole-exome DNA sequencing and clonal analysis, we report changes in the subclonal architecture throughout treatment. Furthermore, a persistently high neoantigen load was observed within all tumors. Interestingly, following initiation of pembrolizumab, brisk lymphocyte infiltration was observed in the subsequently resected metastatic spinal lesion and an objective radiographic response was noted in a progressive intracranial lesion, suggestive of active central nervous system (CNS) immunosurveillance following checkpoint blockade therapy. SIGNIFICANCE It is unclear whether hypermutated glioblastomas are susceptible to checkpoint blockade in adults. Herein, we provide proof of principle that glioblastomas with DNA-repair defects treated with checkpoint blockade may result in CNS immune activation, leading to clinically and immunologically significant responses. These patients may represent a genomically stratified group for whom immunotherapy could be considered. Cancer Discov; 6(11); 1230-6. ©2016 AACR.See related commentary by Snyder and Wolchok, p. 1210This article is highlighted in the In This Issue feature, p. 1197.

Efficacy and tolerability of PTK787/ZK 222584 in a phase II study of post-transplant maintenance therapy in patients with multiple myeloma following high-dose chemotherapy and autologous stem cell transplant.

Elevated serum levels of vascular endothelial growth factor (VEGF) have been reported in patients with multiple myeloma (MM) [1] and correlate with both increased angiogenesis in MM bone marrow [2–5] and a higher plasma cell labeling index [3,4]. Binding of MM cells to bone marrow stromal cells markedly up-regulates VEGF secretion [6]. Moreover, VEGF secreted by MM cells triggers interleukin-6 (IL-6) production from bone marrow stromal cells [7], thereby augmenting paracrine MM cell growth. Importantly, VEGF acts directly on MM cells. Specifically, VEGF receptor-1 protein (Flt-1), but not the VEGF receptor-2 (Flk-1, or KDR), is expressed on MM cell lines and patient cells. Exogenous VEGF has been shown to stimulate in vitro proliferation and migration of MM cells through an extracellular matrix [8,9]. Recent reports have demonstrated that bone marrow angiogenesis and microvessel density (MVD) are significantly increased in MM, and may play an important role in the pathophysiology and prognosis of MM [10] and hematological malignancies in general [11]. This provides the framework for targeting VEGF and Flt1 as a novel therapeutic target in MM. PTK787/ZK 222584 is a tyrosine kinase inhibitor initially designed to inhibit VEGF signal transduction by binding directly to the adenosine triphosphate (ATP)-binding sites of VEGFRs. The drug is most specific for KDR (half maximal inhibitory concentration [IC50], 37 nM), but can also inhibit Flt-1 (77 nM) and Flt-4 (660 nM) [12]. It also has activity against other type III tyrosine kinase receptors, including c-Kit (730 nM), platelet-derived growth factor receptor-b (580 nM), and c-Fms (1.4 mM). MM cells have been found to express c-Kit [13]. In preclinical studies in MM, PTK/ZK was shown to inhibit VEGF-induced tyrosine phosphorylation of Flt-1 in MM cells. PTK/ZK (1–5 mM) also inhibited proliferation in MM cell lines (MM.1S, MM.1R, RPMI 8226, ARP1), and this decrease in proliferation was correlated with a reduction in downstream extracellular signal-regulated kinase (ERK) phosphorylation. Interestingly, the one cell line that lacked Flt-1 (RPMI-Dox40) had a higher IC50 (410 mM) than Flt-1-expressing MM cell lines. In addition, PTK/ZK inhibits MM cell migration, assayed via transwell cell migration. PTK/ZK can interrupt the paracrine interaction between MM cells and bone marrow stromal cells through down-regulation of both IL-6 and VEGF secretion. Reduced levels of IL-6 result in reduced proliferation of MM cells and an increased susceptibility to dexamethasone-induced apoptosis. A reduction in VEGF levels coupled with VEGF blockade, decreased MM cell migration, and bone marrow angiogenesis may potentially abrogate the progression of disease [13]. Taken together, these observations show that PTK/ZK acts directly on MM cells and in the bone marrow milieu, providing the framework for clinical trials of PTK/ZK to improve patient outcome in

Rapid Clinical and Radiographic Response With Combined Dabrafenib and Trametinib in Adults With BRAF-Mutated High-Grade Glioma

BRAF V600E mutations have been successfully treated with targeted therapy in melanoma, non-small cell lung cancer, and thyroid cancer. Interestingly, these mutations have also been identified in a subset of pediatric and adult brain tumors, with several cases reportedly responding to targeted therapy. However, these reports have been limited to single-agent BRAF inhibitor therapy and recurrent disease. Herein, we report dramatic clinical and radiographic responses to combination dabrafenib (BRAF inhibitor) and trametinib (MEK inhibitor) in 2 adults with high-grade gliomas (HGGs), with 1 patient treated in the first-line setting. These observations, together with prior case reports, advocate for routine screening of BRAF point mutations in adult HGGs, and suggest that treatment with dual-targeted therapy, even in newly diagnosed cases, is safe and effective.

Use of extracranial radiation therapy in metastatic melanoma patients receiving immunotherapy

PURPOSE Explore the patterns of use of extracranial radiation therapy (RT) in metastatic melanoma patients receiving immunotherapy, its potential association with OS, the impact of the site and timing of RT on clinical outcomes when combined with immunotherapy. MATERIALS AND METHODS Patients with extracranial metastatic melanoma who received immunotherapy with or without extracranial RT from 2004 to 2013 were obtained from the National Cancer Database. Multivariable Cox regression analysis was used to evaluate factors associated with overall survival (OS). Subset analyses comparing outcomes in patients receiving RT to bone metastases versus soft tissue metastases were also performed. OS was compared using the Kaplan-Meier and log-rank statistics. RESULTS A total of 1675 patients were identified: 1387 received immunotherapy alone and 288 received immunotherapy plus RT. An increase in the utilization of RT as well as SBRT was noted over time. The rate of RT use was 11.5% (0% with SBRT) in 2004 and gradually rose to 19.8% (27.0% with SBRT) in 2013 (P = 0.04). The median OS was 15.4 vs. 19.4 months in the immunotherapy plus RT and immunotherapy alone groups, respectively (P = 0.02). However, on multivariable analysis, RT was not associated with worse OS. The poor OS in the RT group was confined to the patients who received RT to bone metastases, but not in patients who received RT to soft tissue metastases. In subset analyses of patients irradiated to soft tissue, RT administered at least 30 days before immunotherapy was associated with a higher OS than RT administered within 30 days or 30 days after immunotherapy: median 26.1 months vs. 16.0 months (P = 0.009) vs. 15.4 months (P = 0.004), respectively. CONCLUSIONS This study demonstrates that extracranial RT plays an increasing role in the management of metastatic melanoma patients in the era of immunotherapy. The site and the timing of RT may have important interaction with immunotherapy, and need to be carefully considered in future clinical trials.

BRAF-Targeted Therapy in the Treatment of BRAF-Mutant High-Grade Gliomas in Adults

Use of small molecule inhibitors specific to activating BRAF V600 mutations first demonstrated efficacy in metastatic melanoma.1 Recently, similar results were observed in patients with BRAF-mutated non–small cell lung cancer, leading to FDA approval in June 2017.2,3 Furthermore, the observation that combining BRAF inhibition (BRAFi) with MEK inhibition (MEKi) leads to improved efficacy and reduced resistance without increased toxicity has set the bar for any future multidrug combination.4,5 These observations, along with encouraging early-phase data in other histologies, such as papillary thyroid cancer6 and hairy cell leukemia,7 which both have high frequencies of BRAF V600E mutations, have led to increasing interest in exploring the role of BRAFi and MEKi in all BRAF-mutated cancers, regardless of histology.8 However, the lack of efficacy in BRAF-mutated colorectal cancer cautions against the agnostic generalization of results with these agents. For primary central nervous system (CNS) tumors, increasing evidence has suggested that BRAFi therapy may be effective. Preliminary results from a phase I/II study of dabrafenib in relapsed or progressive pediatric BRAF V600E–mutated low-grade gliomas reported an 82% clinical benefit rate (stable disease or better at 6 months) among 32 evaluable subjects.9 A subsequent phase II study is underway evaluating the efficacy of combined BRAFi/MEKi in a similar patient population (ClinicalTrials.gov identifier: NCT02684058). Conversely, the efficacy of these agents in adult patients, particularly those with high-grade gliomas (HGGs; WHO grade III) or glioblastoma (GBM; WHO grade IV), which are more common in adults, remains undefined. Two recent publications in JNCCN—an earlier work by Johanns et al10 and an article by Schreck et al found elsewhere in this issue describing the successful use of combined BRAFi/MEKi therapy in adults with HGG or GBM—contribute to this growing body of literature, suggesting a therapeutic role for these agents in primary CNS disease, and raise several important clinical considerations.

Analysis of point mutations and copy number variation in Grade II and III meningioma

Meningiomas are among the most common tumors of the adult central nervous system (CNS). They are classified by the World Health Organization into three pathologic grades with increasing severity: grade I are benign with favorable treatment outcomes and low recurrence rates while grade III display malignant behavior and poor progression-free survival. Previous studies have shown that inactivation of NF-2 is the most common genetic event in high-grade meningioma; however, there is dearth of molecular data to distinguish grade II (AM-II) from the even more aggressive grade III (AM-III). As part of a routine diagnostic workup, 19 AM-II and 5 AM-III were submitted for targeted sequencing on a panel of twenty-four genes relevant to CNS tumors. The data generated during the course of clinical care was collected and re-analyzed with the aim of identifying molecular features to distinguish AM-II and AM-III. Our cases contained several well-characterized, potentially actionable mutations, but we did not find any novel, recurrent sequence variants. Copy number variations were common in both AM-II and AM-III; chr22q loss was the most prevalent followed in decreasing frequency by losses of chr1p, chr14q, and chr10. In particular, chr10 loss was noted in 4 of 5 AM-III cases but none of the AM-II cases. This suggests that chr10 loss may serve as a diagnostic and perhaps a prognostic marker to differentiate AM-II from AM-III. If confirmed in larger studies, our finding could further aid the classification of meningioma.

Application of CXCR4 Inhibitors in Leukemia

Hematopoietic and cancer cells express the CXCR4 receptor, which in conjunction with its SDF-1/CXCL12 ligand mediates leukemia cell trafficking and homing to the marrow microenvironment. This interaction brings CXCR4-bearing cells within close proximity to marrow stromal cells, thus providing a niche for leukemic cell growth and contributing to drug resistance. Historically, CXCR4 antagonists were developed for the treatment of human immunodeficiency virus (HIV), but were also found to induce leukocytosis upon administration. This led to their use in hematopoietic stem cell mobilization. However, since CXCR4 plays a key role in homing and retention of normal and leukemic stem cells as well as other cancer cells to their microenvironments, the use of CXCR4 antagonists may provide for a novel therapeutic approach to interrupt these protective interactions and thus sensitize AML blasts to chemotherapy in vivo. Preclinical and/or clinical studies have shown that these novel drugs mobilize both normal hematopoietic progenitors and AML blasts into the peripheral circulation and that they are synergistic with G-CSF. In this chapter we will discuss CXCR4 inhibitors and their effects on mobilizing normal and leukemic cells when given alone or with G-CSF in preclinical models and in the clinic.

Evolution of definitions of response, progression-free survival and event-free survival in front-line studies of chronic myeloid leukemia

Abstract Standardized definitions of response and outcome are useful to evaluate study data, facilitate treatment guideline adherence and aid clinical decision-making. Although definitions of response in chronic myeloid leukemia (CML) have been standardized, definitions of disease progression have not been standardized, despite widespread adoption of the term to reflect development of advanced disease. This article reviews definitions of response and disease progression used for progression-free survival and event-free survival in key CML studies and implications for interpreting patient response. It is proposed that adherence to definitions of progression from the European LeukmiaNet may aid future research and therapeutic decision-making.