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A beautiful little girl with cancer takes a break from treatment. She is standing near a large bay of windows in the hospital's corridor. The girl is wearing a headscarf and is holding a stuffed rabbit toy. She is looking out the window with a peaceful expression.

Drug combination could overcome tumour resistance in paediatric cancers

Children with some solid tumours may benefit from receiving a combination of inhibitor drugs, according to interim results of research presented at the American Association of Cancer Research’s Annual Meeting 2023, held April 14-19.

The ongoing research being conducted by an international team including the University of Birmingham suggests that a combination of the PARP inhibitor olaparib (Lynparza) and the investigational ATR inhibitor ceralasertib showed clinical benefit in paediatric patients with solid tumours exhibiting DNA replication stress and/or DNA repair deficiencies.

Dr Susanne Gatz, associate clinical professor in pediatric oncology at the Institute of Cancer and Genomic Sciences of the University of Birmingham presented the study.

Dr Gatz said: “To our knowledge, the combination of PARP inhibitors and ATR inhibitors has not been widely investigated in adult tumour types. This is the first proof of principle that the combination is well tolerated and can lead to clinically relevant responses in paediatric cancers.”

AcSé-ESMART is an international European proof-of-concept platform trial intended to match paediatric, adolescent, and young adult patients with relapsed or treatment-refractory cancers with a treatment regimen targeted to their cancer’s mutational profile. Gatz and colleagues, including Birgit Geoerger, MD, PhD, head of the AcSé-ESMART trial, have so far evaluated 15 different treatments, mostly combination strategies, in more than 220 children following mandatory high-throughput genomic profiling of their tumours.

Arm N of AcSé-ESMART is tailored toward patients with malignancies that exhibit defects in DNA replication and damage repair. Impairments in homologous recombination (HR), a type of DNA repair, can sensitize cells to drugs called PARP inhibitors. PARP inhibitors have proven effective against specific adult cancers with HR deficiencies—most notably, mutations in BRCA1 or BRCA2. How to best use PARP inhibitors in paediatric patients where BRCA1/2 mutations are rarely found remains unclear.

Dr Gatz said: “Paediatric cancer cells proliferate rapidly and have some element of replication stress and a dependency on ATR. We think there might be a kind of primary resistance of paediatric cancers to PARP inhibitors and that combination with an ATR inhibitor could potentially overcome that.”

Gatz also explained that paediatric cancers are often driven by complex mechanisms, making it difficult to identify an effective treatment regimen. Single-agent therapies targeting one mutated protein are often insufficient in paediatric patients, necessitating additional research into combination therapies and mechanisms of response.

“So far, it is unclear if the molecular alterations based on which the patients were enrolled in this trial are the sole reasons for response,” Gatz said.

“Further, it may be difficult to identify patterns of response in specific tumour types due to the tumour-agnostic nature of the study. Nevertheless, this study design can give preliminary indications of signals in specific alterations and tumour types and can provide the basis for future clinical trials.”

Gatz and colleagues plan to evaluate biomarkers of response from the raw sequencing data of the enrolled patients, from the expression of key target proteins such as ATM, and from RNA sequencing data.

Gatz noted that these analyses may identify “molecular constellations” indicative of response to olaparib plus ceralasertib.

“There are enormously valuable drugs currently in development and, provided there is a good clinical or preclinical rationale, we need to apply them more creatively to diseases for which the drug is not currently indicated,” Gatz said.

Limitations of this study include a small, non-randomized sample intended primarily as a proof of concept and to determine the optimal dose for study expansion.

The study is as yet unpublished.