Pediatric low-grade gliomas (pLGG) are the most common pediatric central nervous system tumors, with driving alterations typically occurring in the MAPK pathway. The ERK1/2 inhibitor ulixertinib (BVD-523) has shown promising responses in adult patients with mitogen-activated protein kinase (MAPK)-driven solid tumors. We investigated the antitumoral activity of ulixertinib monotherapy as well as in combination with MEK inhibitors (MEKi), BH3-mimetics, or chemotherapy in pLGG. Patient-derived pLGG models reflecting the two most common alterations in the disease, KIAA1549:BRAF-fusion and BRAF^V600E mutation (DKFZ-BT66 and BT40, respectively) were used for in vitro and in vivo (zebrafish embryos and mice) efficacy testing. Ulixertinib inhibited MAPK pathway activity in both models, and reduced cell viability in BT40 with clinically achievable concentrations in the low nanomolar range. Combination treatment of ulixertinib with MEKi or BH3-mimetics showed strong evidence of antiproliferative synergy in vitro. Ulixertinib showed on-target activity in all tested combinations. In vivo, sufficient penetrance of the drug into brain tumor tissue in concentrations above the in vitro IC₅₀ and reduction of MAPK pathway activity was achieved. In a preclinical mouse trial, ulixertinib mono- and combined therapies slowed tumor growth and increased survival. These data indicate a high clinical potential of ulixertinib for the treatment of pLGG and strongly support its first clinical evaluation in pLGG as single agent and in combination therapy in a currently planned international phase I/II umbrella trial.

The survival rate among children with relapsed tumors remains poor, due to tumor heterogeneity, lack of directly actionable tumor drivers and multidrug resistance. Novel personalized medicine approaches tailored to each tumor are urgently needed to improve cancer treatment. Current pediatric precision oncology platforms, such as the INFORM (INdividualized Therapy FOr Relapsed Malignancies in Childhood) study, reveal that molecular profiling of tumor tissue identifies targets associated with clinical benefit in a subgroup of patients only and should be complemented with functional drug testing. In such an approach, patient-derived tumor cells are exposed to a library of approved oncological drugs in a physiological setting, e.g., in the form of animal avatars injected with patient tumor cells. We used molecularly fully characterized tumor samples from the INFORM study to compare drug screen results of individual patient-derived cell models in functional assays: (i) patient-derived spheroid cultures within a few days after tumor dissociation; (ii) tumor cells reisolated from the corresponding mouse PDX; (iii) corresponding long-term organoid-like cultures and (iv) drug evaluation with the corresponding zebrafish PDX (zPDX) model. Each model had its advantage and complemented the others for drug hit and drug combination selection. Our results provide evidence that in vivo zPDX drug screening is a promising add-on to current functional drug screening in precision medicine platforms.

The survival rate among children with relapsed neuroblastomas continues to be poor, and thus new therapeutic approaches identified by reliable preclinical drug testing models are urgently needed. Zebrafish are a powerful vertebrate model in preclinical cancer research. Here, we describe a zebrafish neuroblastoma yolk sac model to evaluate efficacy and toxicity of histone deacetylase (HDAC) inhibitor treatments. Larvae were engrafted with fluorescently labeled, genetically diverse, established cell lines and short-term cultures of patient-derived primary cells. Engrafted tumors progressed locally and disseminated remotely in an intact environment. Combination treatments involving the standard chemotherapy doxorubicin and HDAC inhibitors substantially reduced tumor volume, induced tumor cell death, and inhibited tumor cell dissemination to the tail region. Hence, this model allows for fast, cost-efficient, and reliable in vivo evaluation of toxicity and response of the primary and metastatic tumor sites to drug combinations.

Ulixertinib (BVD-523) is a well-tolerated, orally delivered, catalytic ERK1/2 inhibitor, which has shown promising responses in adult patients with mitogen-activated protein kinase (MAPK)-driven solid tumors. Pediatric low grade gliomas (pLGGs) are the most common pediatric brain tumors, with the most frequent driving alterations (KIAA:BRAF fusion, BRAF V600E mutation) occurring in the MAPK pathway. To investigate the anti-tumoral activity of ulixertinib in pLGG, cell lines recapitulating both main MAPK alterations were used: DKFZ-BT66 (pilocytic astrocytoma; KIAA:BRAF fusion) and BT40 (pleomorphic xanthoastrocytoma; BRAF V600E mutation and CDKN2A/B deletion). The potential synergism of combinations with MEK inhibitors, senolytics, and chemotherapy was investigated in vitro using metabolic activity and MAPK activity assays. The most promising combinations were validated in vitro by analysis of viable, dead, and apoptotic cells through high-content microscopy. The most clinically relevant combinations were further validated in vivo: 1) in two zebrafish embryo models (respectively, BT40 and DKFZ-BT66 yolk sac injection) and 2) in NSG mice (BT40 orthotopic PDX) including in vivo pharmacokinetic and -dynamic analyses. Our data demonstrate ulixertinib’s ability to inhibit MAPK pathway activity in all used models. Ulixertinib treatment reduced cell viability in the BRAF V600E mutated cell line at a remarkably low concentration of 62.7 nM (compared to other cell lines’ IC50 from the Genomics of Drug Sensitivity in Cancer database). In vivo pharmacokinetic and -dynamic analyses showed good penetrance of the drug into mouse brain tissue, with concentrations above the in vitro IC50 and reduction of MAPK activity as assessed by Western blot. Furthermore, ulixertinib treatment slowed tumor growth and significantly increased survival in NSG mice with orthotopic BT40 xenografts. Ulixertinib showed indications for anti-proliferative synergy in vitro, according to the Loewe and Bliss independence models, in combination with MEK inhibitors (trametinib, binimetinib) or senolytics (navitoclax, A1331852). Combinations with chemotherapy (carboplatin, vinblastine) were at most additive. Indications for synergy with binimetinib and navitoclax were confirmed in the zebrafish embryo xenograft models for both MAPK-altered backgrounds. The combination of ulixertinib with navitoclax was further investigated in the BT40 PDX mouse model, where tumor growth and survival were comparable to ulixertinib monotherapy. In conclusion, our data indicate a strong potential for ulixertinib as a clinically relevant therapeutic option for the treatment of pLGG to be further investigated in upcoming clinical trials. Potential synergism with MEK inhibitors and senolytics was noted and warrants further investigation. Citation Format: Romain Sigaud, Lisa Rösch, Charlotte Gatzweiler, Julia Benzel, Laura von Soosten, Heike Peterziel, Sara Najafi, Simay Ayhan, Nina Hofmann, Kathrin I. Förster, Jürgen Burhenne, Rémi Longuespée, Cornelis M. van Tilburg, David T. Jones, Stefan M. Pfister, Deborah Knoerzer, Brent Kreider, Max Sauter, Kristian W. Pajtler, Marc Zuckermann, Ina Oehme, Olaf Witt, Till Milde. The first-in-class ERK inhibitor ulixertinib (BVD-523) shows activity in MAPK-driven pediatric low-grade glioma models as single agent and in combination with MEK inhibitors or senolytics [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5221.