Introduction:Diffuse intrinsic pontine glioma (DIPG) is a rare pediatric brain tumor with a critical unmet need due to the lack of approved, curative interventions available. The interweaving of malignant cells with normal tissue makes surgical extraction essentially impossible, and radiation provides only transient benefit. The recent ONC201 FDA approval, however, suggests DIPG therapy is tractable. Having identified overexpression of IL13Rα2 in DIPG tumor tissue versus normal brain tissue, we investigated binding of commercially available IL13Rα2 monoclonal antibodies. The top candidate antibody was used to generate a chimeric antibody, to which we conjugated deruxtecan to create a preclinical therapeutic candidate. Methods:We validated the novel antibody-drug conjugate (ADC) in vitro, demonstrating dose-dependent, IL13Rα2 expression-dependent cell death. We further validated the novel ADC ex ovo in quail xenograft models of DIPG and in vivo in a mouse xenograft model. Results:The ADC showed tumor reduction in the ex ovo quail embryo model for both IL13Rα2-high and IL13Rα2-low DIPG cell models. A proof-of-concept in vivo mouse xenograft experiment demonstrated a reduction in tumor volume beyond antibody treatment alone. Discussion:The work here represents an important milestone in preclinical development of a novel deruxtecan-based ADC agent for an intractable pediatric brain cancer, concurrent with other ADC agents demonstrating real-world clinical efficacy and gaining approvals in multiple disease indications.
The third in a series of Paediatric Therapeutic Development Workshops focused on rhabdomyosarcoma. Rhabdomyosarcoma is the most common soft tissue sarcoma in children, with 90% survival for those with the lowest risk disease, but just 20-30% in children with metastatic disease. An urgent unmet need exists to develop targeted therapeutics for high-risk disease and to reduce the toxicity of treatment. The results of trials of CAR T-cells and ADCs against FGFR4 are awaited with great interest, and developing a FGFR4 degrader is a priority. Directly targeting PAX3::FOXO1 and PAX7::FOXO1 fusion proteins is a high priority. An in vivo study of a MYOD1 degrader approach is required prior to clinical development. Degraders of P300/CBP should be evaluated preclinically with a view to clinical investigation. ROR2 is an interesting target for the L122R mutant MYOD1 rhabdomyosarcoma. Development of a TEAD degrader is a high priority, and this should be evaluated in combination with a Notch inhibitor. Considering targets with existing clinical agents, antibody-drug conjugates targeting cell-surface antigen B7-H3/CD276 are showing preclinical promise in other paediatric cancers and are also deemed a high priority for evaluation in rhabdomyosarcoma. Based on currently available evidence, MEK inhibitors should be evaluated, potentially with BRAF or PI3K inhibitors, in combination with chemotherapy in the maintenance setting. Understanding the mechanism of action underpinning drug combinations, gaining access to therapeutics and optimising clinical trial design will be essential to enable combinatorial testing in patients.
OBJECTIVE(S):Myoepithelial Carcinoma (MECA) is an ultra-rare soft tissue cancer with a rare EWSR1::KLF15 fusion reported in some cases. However, fusion positive MECA has been classified as a carcinoma, despite sharing qualities with sarcomas in terms of fusion protein rearrangement. An exploration of MECA in the context of a sarcoma versus an adenocarcinoma could be crucial to the understanding of MECA with respect to other cancers. Beyond gene fusions, MECA can also be difficult to characterize, but functional genomics could reveal distinctions. SUBJECT(S) (OR MATERIALS) AND METHODS:We performed next generation DNA exome and RNA deep sequencing for a 27 patient cohort for this ultra-rare cancer. RESULTS:Our Principal Component Analysis that categorized MECA tumors among other sarcomas vs. salivary carcinomas, with closest relatedness to salivary Adenoid Cystic Carcinoma. Both fusion positive and fusion negative MECA over-express IGF1R. CONCLUSION(S):Despite sharing a chromosomal translocation partner (the EWSR1 gene) with sarcomas, MECA are most related to other salivary carcinomas. Further exploration of IGF1R as a therapeutic target in MECA is warranted. We also make available the 27 patients' next generation DNA exome and RNA sequencing through the EGA Repository.
Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma found in children, with distinct biological subtypes. We found that the protein Osteopontin (Ostp) is highly expressed in our genetically engineered mouse models (GEMM) of RMS alveolar and embryonal subtypes. Through GEMM studies and allograft mouse studies we explored how Ostp expression affects the onset and growth of tumors in vivo. Ostp loss in alveolar RMS tumors and the tumor microenvironment of genetically-engineered mice changed the character of the tumors (decreasing multiplicity, decreasing limb predominance, and decreasing tumor stage) without changing tumor-free survival or histological appearance. Similarly, tumor growth rates and metastasis were not different for Ostp expressing and Ostp null tumors in orthotopic allograft studies. Conversely, loss of Ostp expression increased tumor incidence in embryonal RMS GEMMs animals compared to mice on an Ostp wildtype background, although the sample size was small. When combined with the clinical correlation of human Osteopontin gene expression and altered patient survival, Ostp in embryonal RMS may be a topic of further interest and investigation.
TrkB (NTRK2) overexpression in neuroblastoma is reported to be associated with poor prognostic features, including MYCN amplification and advanced tumor stages. In this study, TrkB expression in available cell lines was characterized, and allosteric inhibitors of ligand-activated TrkB were designed, characterized, and tested. The designed compounds commonly bear a triazole group at their center, which bridges three aromatic components. Based on the chemical design, 25 compounds were synthesized for the cell-based assay to examine the neuroblastoma cell growth inhibition. Several cell lines were used in the assay based on TrkB expression levels. TrkB non-enhanced and TrkA overexpressing cell cultures were also tested for comparison. Many of the synthesized compounds suppressed the phosphorylation of the TrkB (cytoplasmic side) induced by brain-derived neurotrophic factor (BDNF) binding to the extracellular domain of TrkB. Several compounds showed effective suppression of phosphorylation to a similar degree as larotrectinib, an approved TrkB inhibitor targeting the cytoplasmic tyrosine kinase domain. The compounds’ potency to suppress neuroblastoma cell growth was evaluated using a basal high TrkB-expressing culture. Select compounds showed strong cell growth suppression, with 50% inhibitory activities below 30 nM. Two potent compounds were also tested to determine their inhibitory activities on other cell lines. Cell growth inhibition was observed for three cell cultures, but moderate for one. Neither the approved TrkB inhibitor, larotrectinib, nor our allosteric compounds could completely inhibit the growth of all neuroblastoma cell lines natively expressing TrkB.
