Amide proton transfer weighted imaging in pediatric neuro-oncology: initial experience

Amide proton transfer weighted (APTw) imaging enables in vivo assessment of tissue-bound mobile proteins and peptides through the detection of chemical exchange saturation transfer. Promising applications of APTw imaging have been shown in adult brain tumors. As pediatric brain tumors differ from their adult counterparts, we investigate the radiological appearance of pediatric brain tumors on APTw imaging. APTw imaging was conducted at 3 T. APTw maps were calculated using magnetization transfer ratio asymmetry at 3.5 ppm. First, the repeatability of APTw imaging was assessed in a phantom and in five healthy volunteers by calculating the within-subject coefficient of variation (wCV). APTw images of pediatric brain tumor patients were analyzed retrospectively. APTw levels were compared between solid tumor tissue and normal-appearing white matter (NAWM) and between pediatric high-grade glioma (pHGG) and pediatric low-grade glioma (pLGG) using t-tests. APTw maps were repeatable in supratentorial and infratentorial brain regions (wCV ranged from 11% to 39%), except those from the pontine region (wCV between 39% and 50%). APTw images of 23 children with brain tumor were analyzed (mean age 12 years ± 5, 12 male). Significantly higher APTw values are present in tumor compared with NAWM for both pHGG and pLGG (p < 0.05). APTw values were higher in pLGG subtype pilocytic astrocytoma compared with other pLGG subtypes (p < 0.05). Non-invasive characterization of pediatric brain tumor biology with APTw imaging could aid the radiologist in clinical decision-making.

Rational combination platform trial design for children and young adults with diffuse midline glioma: A report from PNOC

Background Diffuse midline glioma (DMG) is a devastating pediatric brain tumor unresponsive to hundreds of clinical trials. Approximately 80% of DMGs harbor H3K27M oncohistones, which reprogram the epigenome to increase the metabolic profile of the tumor cells. Methods We have previously shown preclinical efficacy of targeting both oxidative phosphorylation and glycolysis through treatment with ONC201, which activates the mitochondrial protease ClpP, and paxalisib, which inhibits PI3K/mTOR, respectively. Results ONC201 and paxalisib combination treatment aimed at inducing metabolic distress led to the design of the first DMG-specific platform trial PNOC022 (NCT05009992). Conclusions Here, we expand on the PNOC022 rationale and discuss various considerations, including liquid biome, microbiome, and genomic biomarkers, quality-of-life endpoints, and novel imaging modalities, such that we offer direction on future clinical trials in DMG.

Theranostics in Neurooncology: Heading Toward New Horizons

Therapeutic approaches to brain tumors remain a challenge, with considerable limitations regarding delivery of drugs. There has been renewed and increasing interest in translating the popular theranostic approach well known from prostate and neuroendocrine cancer to neurooncology. Although far from perfect, some of these approaches show encouraging preliminary results, such as for meningioma and leptomeningeal spread of certain pediatric brain tumors. In brain metastases and gliomas, clinical results have failed to impress. Perspectives on these theranostic approaches regarding meningiomas, brain metastases, gliomas, and common pediatric brain tumors will be discussed. For each tumor entity, the general context, an overview of the literature, and future perspectives will be provided. Ongoing studies will be discussed in the supplemental materials. As most theranostic agents are unlikely to cross the blood-brain barrier, the delivery of these agents will be dependent on the successful development and clinical implementation of techniques enhancing permeability and retention. Moreover, the international community should strive toward sufficiently large and randomized studies to generate high-level evidence on theranostic approaches with radioligand therapies for central nervous system tumors.

Relapsed Medulloblastoma in Pre-Irradiated Patients: Current Practice for Diagnostics and Treatment

Relapsed medulloblastoma (rMB) accounts for a considerable, and disproportionate amount of childhood cancer deaths. Recent advances have gone someway to characterising disease biology at relapse including second malignancies that often cannot be distinguished from relapse on imaging alone. Furthermore, there are now multiple international early-phase trials exploring drug-target matches across a range of high-risk/relapsed paediatric tumours. Despite these advances, treatment at relapse in pre-irradiated patients is typically non-curative and focuses on providing life-prolonging and symptom-modifying care that is tailored to the needs and wishes of the individual and their family. Here, we describe the current understanding of prognostic factors at disease relapse such as principal molecular group, adverse molecular biology, and timing of relapse. We provide an overview of the clinical diagnostic process including signs and symptoms, staging investigations, and molecular pathology, followed by a summary of treatment modalities and considerations. Finally, we summarise future directions to progress understanding of treatment resistance and the biological mechanisms underpinning early therapy-refractory and relapsed disease. These initiatives include development of comprehensive and collaborative molecular profiling approaches at relapse, liquid biopsies such as cerebrospinal fluid (CSF) as a biomarker of minimal residual disease (MRD), modelling strategies, and the use of primary tumour material for real-time drug screening approaches.

Identification of Two Protein-Signaling States Delineating Transcriptionally Heterogeneous Human Medulloblastoma

The brain cancer medulloblastoma consists of different transcriptional subgroups. To characterize medulloblastoma at the phosphoprotein-signaling level, we performed high-throughput peptide phosphorylation profiling on a large cohort of SHH (Sonic Hedgehog), group 3, and group 4 medulloblastomas. We identified two major protein-signaling profiles. One profile was associated with rapid death post-recurrence and resembled MYC-like signaling for which MYC lesions are sufficient but not necessary. The second profile showed enrichment for DNA damage, as well as apoptotic and neuronal signaling. Integrative analysis demonstrated that heterogeneous transcriptional input converges on these protein-signaling profiles: all SHH and a subset of group 3 patients exhibited the MYC-like protein-signaling profile; the majority of the other group 3 subset and group 4 patients displayed the DNA damage/apoptotic/neuronal signaling profile. Functional analysis of enriched pathways highlighted cell-cycle progression and protein synthesis as therapeutic targets for MYC-like medulloblastoma.

Exogenous HGF Bypasses the Effects of ErbB Inhibition on Tumor Cell Viability in Medulloblastoma Cell Lines

Recent clinical trials investigating receptor tyrosine kinase (RTK) inhibitors showed a limited clinical response in medulloblastoma. The present study investigated the role of micro-environmental growth factors expressed in the brain, such as HGF and EGF, in relation to the effects of hepatocyte growth factor receptor (MET) and epidermal growth factor receptor family (ErbB1-4) inhibition in medulloblastoma cell lines. Medulloblastoma cell lines were treated with tyrosine kinase inhibitors crizotinib or canertinib, targeting MET and ErbB1-4, respectively. Upon treatment, cells were stimulated with VEGF-A, PDGF-AB, HGF, FGF-2 or EGF. Subsequently, we measured cell viability and expression levels of growth factors and downstream signaling proteins. Addition of HGF or EGF phosphorylated MET or EGFR, respectively, and demonstrated phosphorylation of Akt and ERK1/2 as well as increased tumor cell viability. Crizotinib and canertinib both inhibited cell viability and phosphorylation of Akt and ERK1/2. Specifically targeting MET using shRNA’s resulted in decreased cell viability. Interestingly, addition of HGF to canertinib significantly enhanced cell viability as well as phosphorylation of Akt and ERK1/2. The HGF-induced bypass of canertinib was reversed by addition of crizotinib. HGF protein was hardly released by medulloblastoma cells itself. Addition of canertinib did not affect RTK cell surface or growth factor expression levels. This manuscript points to the bypassing capacity of exogenous HGF in medulloblastoma cell lines. It might be of great interest to anticipate on these results in developing novel clinical trials with a combination of MET and EGFR inhibitors in medulloblastoma.

Breast Cancer Resistance Protein (BCRP) in Acute Leukaemia

Multidrug resistance, cross-resistance to structurally and functionally unrelated drugs, is an important cause of treatment failure in acute leukemia. Multidrug resistance can result from the overexpression of ATP-dependent efflux pumps, such as P-glycoprotein and members of the multidrug resistance associated protein (MRP) family. Recently a novel transporter has been identified, which is called breast cancer resistance protein (BCRP), ABCG2 or mitoxantrone resistance protein. BCRP confers resistance to chemotherapeutic agents, such as mitoxantrone, doxorubicin and daunorubicin. This review describes BCRP detection techniques and the normal physiology of BCRP. The role of BCRP in the physiology of hematopoietic stem cells is addressed as well as the involvement of BCRP in multidrug resistance in acute leukemia. In AML and ALL, several studies showed that BCRP is expressed and functionally active at low, but variable levels. However, further studies are warranted to investigate its effect on clinical outcome, and explore whether patients could benefit from the combination of BCRP inhibitors and chemotherapy.

Expression of Multidrug Resistance–Associated Proteins Predicts Prognosis in Childhood and Adult Acute Lymphoblastic Leukemia

PURPOSE

Patients with acute lymphoblastic leukemia (ALL) are treated with a variety of chemotherapeutic drugs, which can be transported by six multidrug resistance-associated proteins (MRP). These MRPs have strongly overlapping functional activities. The aim of this study was to investigate the expression levels of MRP1 to MRP6 and study their effect on prognosis.

EXPERIMENTAL DESIGN

The mRNA expression levels of MRP1 to MRP6 were analyzed by quantitative real-time PCR in leukemic blasts of 105 de novo ALL patients (adults, n=49; children, n=56) including 70% B-lineage and 30% T-lineage ALL patients.

RESULTS

Adults showed a higher expressions of MRP1 (P=0.008), MRP2 (P=0.026), and MRP3 (P=0.039) than children. Interestingly, this difference disappeared when patients were categorized based on clinical outcome. Relapsed patients showed a higher expression of all MRP genes, except MRP4. For the total group of ALL patients, the expressions of MRP1, MRP2, MRP3, MRP5, and MRP6 predicted relapse. Moreover, high expression of all MRP genes, except MRP4, was associated with a reduced relapse-free survival in children and adults (MRP1, P=0.005; MRP2, P=0.008; MRP3, P=0.001; MRP5, P=0.016; MRP6, P=0.037).

CONCLUSIONS

The present study shows that a subset of ALL patients with high MRP expression has an unfavorable prognosis independently of age.

Influence of functional polymorphisms of the gene on vincristine pharmacokinetics in childhood acute lymphoblastic leukemia

OBJECTIVE

Our objective was to investigate the effect of single nucleotide polymorphisms (SNPs) in the P-glycoprotein MDR1 gene on vincristine pharmacokinetics and side effects in childhood acute lymphoblastic leukemia.

METHODS

From 52 of 70 children who participated in a previous study on vincristine pharmacokinetics, patient material was available for investigation of the MDR1 genetic variants. The SNPs C3435T and G2677T were determined by use of polymerase chain reaction-restriction fragment length polymorphism. Vincristine side effects were scored retrospectively from patient records.

RESULTS

No association was observed between C3435T or G2677T and vincristine pharmacokinetic variables. When haplotypes were assigned, haplotype 1/1 carriers (3435C/2677G) showed a longer elimination half-life than noncarriers (1156 versus 805 minutes, P =.038). In contrast, haplotype 1/2 carriers (3435T/2677G) had a shorter elimination half-life than noncarriers (805 versus 1180 minutes, P =.044). However, this significance was lost after Bonferroni correction for multiple testing. The haplotypes did not affect the other pharmacokinetic parameters, such as clearance and area under the concentration-time curve, suggesting that the observed effect on elimination half-life is of very limited relevance. Moreover, SNPs in the MDR1 gene did not identify patients with an increased risk for vincristine-induced constipation.

CONCLUSION

The genetic variants in the MDR1 gene alone cannot explain the large variability in vincristine pharmacokinetics.

Prognosis in childhood and adult acute lymphoblastic leukaemia: a question of maturation?

Acute lymphoblastic leukaemia (ALL) is a disease diagnosed in children as well as adults. Progress in the treatment of ALL has led to better survival rates, however, children have benefited more from improved treatment modalities than adults. Recent evidence has underscored that the difference in characteristics and biology of adult versus childhood ALL might be the result of a different origin. According to the two-hit paradigm of Knudson, to develop cancer two genetic events are necessary. It has been suggested, that in childhood ALL the first genetic event happens in the more mature lymphoid committed progenitor cells, whereas in adult ALL the first hit occurs in multipotent stem cells. This review compares patient characteristics, the extent of the disease, leukaemic cell characteristics and treatment between childhood and adult ALL. This is discussed in relation to the hypothesis that the maturation stage of the cells, from which the leukaemia arises, is responsible for the differential behaviour of adult and childhood ALL.

The role of breast cancer resistance protein in acute lymphoblastic leukemia

PURPOSE

Overexpression of the transporter ABCG2, also known as breast cancer resistance protein and mitoxantrone resistance protein, can confer resistance to a variety of cytostatic drugs, such as mitoxantrone, topotecan, doxorubicin, and daunorubicin. This study analyzes the ABCG2 expression and activity in 46 human de novo acute lymphoblastic leukemia B- and T-lineage (ALL) samples.

EXPERIMENTAL DESIGN

ABCG2 expression was measured flow cytometrically with the BXP-34 monoclonal antibody. ABCG2 functional activity was determined flow cytometrically by measuring mitoxantrone accumulation in combination with the ABCG2 inhibitor fumitremorgin C (FTC). To determine a possible effect of the transporters P-glycoprotein and multidrug resistance-associated protein (MRP1 and MRP2) on mitoxantrone accumulation, the accumulation was investigated in the presence of the P-glycoprotein inhibitor PSC 833 and MRP inhibitor MK-571. The ABCG2 gene was sequenced to investigate the amino acid at position 482.

RESULTS

In B-lineage ALL (n = 23), the median BXP-34:IgG1 ratio was higher, namely 2.4 (range, 1.7-3.7), than in T-lineage ALL (n = 23; 1.9; range, 1.2-6.6; P = 0.003). The addition of FTC to mitoxantrone treatment caused a median increase in mitoxantrone accumulation of 21% (range, 0-140%) in B-lineage ALL. In T-lineage ALL, this FTC effect was less pronounced (5%; range, 0-256%; P = 0.013). The influence of FTC on mitoxantrone accumulation correlated with ABCG2 protein expression (r = 0.52; P < 0.001; n = 43). The increase in mitoxantrone accumulation, when FTC was added to cells treated with both PSC 833 and MK-571, correlated with the ABCG2 expression in B-lineage ALL but not in T-lineage ALL. Sequencing the ABCG2 gene revealed no ABCG2 mutation at position 482 in patients who accumulated more rhodamine after FTC.

CONCLUSIONS

This study shows that ABCG2 is expressed higher and functionally more active in B-lineage than in T-lineage ALL.

High functional P-glycoprotein activity is more often present in T-cell acute lymphoblastic leukaemic cells in adults than in children

There is a distinct difference in prognosis between childhood versus adult acute lymphoblastic leukaemia (ALL). To define whether multidrug resistance (MDR) genes might contribute to this distinction, the expression and functional activity of P-glycoprotein (P-gp) and MDR associated proteins (MRP) were determined with RT-PCR (MDR-1, MRP1, MRP2, MRP3) and flow cytometry (P-gp and MRP). Patient samples were obtained from 36 children and 35 adults with de novo ALL. Of these patients, 38 showed a T-lineage and 33 showed a B-lineage immunophenotype. In the samples, large variability in P-gp activity (0.8-4.9) and MRP activity (1.1-13.9) was observed. Most T-ALL patients with high P-gp activity were adults (89%). The mRNA expression of MDR-1 correlated weakly with P-gp activity. In contrast, MRP activity did not correlate with the mRNA expression of MRP1, MRP2 and MRP3. In T-ALL, a worse overall survival and event-free survival was observed with increasing P-gp activity. P-gp activity had no prognostic impact in B-lineage ALL. In addition, high MRP activity did not influence treatment outcome in either T- or B-lineage ALL. Multivariate Cox regression analysis, showed P-gp activity to be the only unfavourable prognostic factor for overall survival in T-ALL. In conclusion, this study demonstrates the prognostic relevance of P-gp activity in T-ALL. Since the majority of the patients with high P-gp activity were adults, P-gp might contribute to the poor prognosis of adult T-ALL.