Hulleman group

Group leader: Dr. Esther Hulleman

 
(Combinational) Drug screens: 

To identify compounds that can be incorporated into new treatment schemes, we perform (semi) high-throughput drug screens on primary cell cultures, either as monotherapy or in combination with other (epigenetic) drugs or gamma-irradiation. Radiotherapy is an important component of the current treatment schedules for most types of high-grade brain tumor in children, and – as such – should be considered when screening for novel agents. Drug screen libraries consist of both ‘classical chemotherapeutics’, and targeted agents: epigenetic-, kinase- or pathway inhibitors, depending on the methylation- and gene expression data of the primary tumor. In addition, we use gene expression profiling and protein phosphorylation arrays that enable us to identify signal transduction routes that are essential for the growth of tumor cells, as well as pathways that are involved in escape mechanisms leading to drug resistance. This allows a rational design of combinational therapies, in which the drugs act with an additive or synergistic effect. Preferably, we test compounds that pass the blood-brain barrier (BBB) and have been proven safe in children and approved for the European market, to enable a quick translation to the clinic.

Tumor Biology:

Besides the abovementioned drug screens, we aim to develop novel therapies based on the biology/immunology of pediatric brain tumor (sub)types, with a special focus on crosstalk with healthy brain- or immune cells and therapy resistance. In recent years, an increasing number of publications has shown that brain tumors closely interact with neighboring healthy cells and infiltrating immune cells to support their growth and survival.

To determine the feasibility of immunotherapy in, we investigate the role of the tumor immune microenvironment (TIME) in various pediatric brain tumor (sub)types and explore the possibility to alter their immunophenotype using co-cultures and immunocompetent in vivo models, such as the murine syngeneic grafts. Therefore, we map changes in TIME upon treatment with immunomodulating agents and perform synthetic lethality screens using CRISPR (clustered regularly interspaced short palindromic repeats)/Cas9 screening methods. This technique can also be applied to identify pathways involved in therapy resistance, both in in vitro and in in vivo experiments where we can consider the role of the tumor microenvironment, BBB integrity and tumor heterogeneity. Again, we use different approaches to identify therapeutic targets: unbiased screens in which drug and/or irradiation treatment is combined with (inducible) CRISPR/Cas9 knock-outs, or a more rationalized approach in which we compare the gene expression profiles and pathway activation before-, and after treatment in resected patient material (provided that a second biopsy or debulking of the tumor is performed upon recurrence), or by exposing cell cultures to low drug concentrations for an extended period of time.

Drug delivery:

The minimal progress in the treatment of pediatric brain tumors in the past decades may be attributed to a limited drug distribution in the brain. Most chemotherapeutics – and small molecules in particular – are good substrates of drug efflux transporters, as they have historically been selected for their inability to pass the BBB to minimalize neurological damage and treatment related side effects. However, good brain penetration and subsequent drug accumulation will be essential for the treatment of (pediatric) brain tumors. Thus, novel treatment strategies (both invasive- and non-invasive) need to be developed, such as convection enhanced-, intra-arterial-, or intranasal delivery, sonoporation, implanted therapies, the use of nanocarriers, chemical modification of parent drugs with vectors that help crossing the BBB, or co-administration of chemotherapeutic agents with compounds that open up the BBB.

Novel research models:

Since the focus or our laboratory experiments is on translational projects, we need robust in vitro and in vivo models that mimic the molecular and histological phenotype of the tumors, to evaluate novel treatment modalities. Currently, such models are scarce, and most exhibit relatively slow tumor growth, making them unsuitable to test new therapies. Therefore, we routinely establish novel patient-derived xenograft (PDX) models for various forms of high-grade pediatric brain tumors from primary patient material. These models are extensively characterized on different levels (gene-expression profiles, genomic characteristics, and histology) and compared to the original tumor, to ensure their reliability. Besides drug testing, the PDX models can be used to study the blood-brain barrier, tumor biology, tumor-stroma interactions, or novel neurosurgical- and diagnostic techniques.