Karlyne M. Reilly

Gastrointestinal stromal tumors (GIST) are rare sarcomas arising predominantly in the stomach and small intestine, with limited incidence in other gastrointestinal sites. GIST originates from c-KIT–/DOG1-positive interstitial cells of Cajal (ICC) most commonly driven by activating gain-of-function mutations in the c-KIT and PDGFRA genes. However, a subset of these malignancies, defined as wild-type GIST (WT-GIST), has mutations in the RAS pathway genes (e.g., NF1, KRAS, and BRAF), succinate dehydrogenase subunit genes, and rare gene fusions. A major obstacle in understanding WT-GIST pathogenesis and treatment resistance has been the lack of robust in vivo models. In this study, we report the development of a fully penetrant mouse model of BRAF-driven GIST by inducing BRAFV600E expression in c-Kit+ ICC. Unlike previous models which targeted only subsets of ICC leading to hyperplasia, the use of c-KitCreERT2 enables broader targeting, including ICC progenitors, resulting in rapid, multifocal tumor formation primarily in the pyloric region. These tumors express diagnostic GIST markers (c-Kit and DOG1) and show significant response to the BRAF inhibitor dabrafenib. This model recapitulates key histopathologic and molecular features of human BRAF-mutant GIST and provides a valuable platform for studying tumor initiation, progression, and therapeutic resistance. Importantly, it allows for preclinical testing of targeted therapies in BRAF GIST, offering new insights into treatment strategies. Significance: This is the first fully penetrant mouse model of BRAF-driven GIST by inducing BRAFV600E in c-Kit+ ICC. This model faithfully recapitulates human BRAF-mutant GIST, enabling mechanistic studies and preclinical testing of targeted therapies, including response to BRAF inhibition with dabrafenib.

Purpose Neuroendocrine neoplasms (NEN) are rare but increasingly recognized malignancies. Fatigue is common among individuals with NEN, but factors associated with fatigue in this population are not well described. Understanding these factors is essential for optimizing supportive care and quality of life. This study aimed to investigate factors associated with fatigue in patients with NEN using a biopsychosocial model. Methods Participants enrolled on a rare tumor natural history study (NCT03739827) were included in this analysis if they had NEN, were ≥ 18 years old, and completed at least one evaluation of patient-reported outcome measures. Fatigue was assessed using the Patient-Reported Outcome Measurement Information System (PROMIS). Results Sixty-four adult participants with NEN (mean age = 59 years; SD = 12.0) completed PROMIS measures. Over half (53%) had PROMIS Fatigue T-scores > 55, indicating fatigue, including 31% in the moderate-to-severe range. Fatigue was highly correlated with pain, functional status, and psychosocial factors including depression, anxiety, and emotional support. There were no significant differences in fatigue based on identified sociodemographic or disease-related factors, although a significant association between fatigue and serotonin, a neuroactive peptide secreted by some NENs, was found in a subset of patients. Conclusion Fatigue is common in patients with NEN, with one-third having moderate to severe fatigue impacting daily functioning. Pain, anxiety, and depression were significantly associated with fatigue, suggesting that interventions targeting these symptoms also may improve fatigue in these patients. Further work is needed to investigate additional NEN-specific factors to optimize management of fatigue in individuals living with this long-term disease.

While immunotherapeutic targeting of cell surface proteins is an increasingly effective cancer therapy, identification of new surface proteins, particularly those with biological importance, is critical. Here, we uncover delta-like non-canonical Notch ligand 1 (DLK1) as a cell surface protein with limited normal tissue expression and high expression in multiple refractory adult metastatic cancers including small cell lung cancer (SCLC) and adrenocortical carcinoma (ACC), a rare cancer with few effective therapies. In ACC, ADCT-701, a DLK1 targeting antibody-drug conjugate (ADC), shows in vitro and in vivo activity but is overall limited due to high expression and activity of the drug efflux protein ABCB1 (MDR1, P-glycoprotein). In contrast, ADCT-701 induces complete responses in DLK1⁺ ACC and SCLC in vivo models with low or no ABCB1 expression. Genetic deletion of DLK1 in ACC dramatically downregulates ABCB1 and increases ADC payload and chemotherapy sensitivity through NOTCH1-mediated transdifferentiation. This work identifies DLK1 as an immunotherapeutic target that regulates tumor cell plasticity and chemoresistance in ACC and supports an active phase I clinical trial targeting DLK1 with an ADC in ACC and neuroendocrine neoplasms (NCT06041516).

Understanding of tumor biology and identification of effective therapies is lacking for many rare tumors. My Pediatric and Adult Rare Tumor (MyPART) network was established to engage patients, advocates, and researchers and conduct a comprehensive longitudinal Natural History Study of Rare Solid Tumors. Through remote or in-person enrollment at the NIH Clinical Center, participants with rare solid tumors ≥4 weeks old complete standardized medical and family history forms, patient reported outcomes, and provide tumor, blood and/or saliva samples. Medical records are extracted for clinical status and treatment history, and tumors undergo genomic analysis. A total of 200 participants (65% female, 35% male, median age at diagnosis 43 years, range = 2–77) enrolled from 46 U.S. states and nine other countries (46% remote, 55% in-person). Frequent diagnoses were neuroendocrine neoplasms (NEN), adrenocortical carcinomas (ACC), medullary thyroid carcinomas (MTC), succinate dehydrogenase (SDH)-deficient gastrointestinal stromal tumors (sdGIST), and chordomas. At enrollment, median years since diagnosis was 3.5 (range = 0–36.6), 63% participants had metastatic disease and 20% had no evidence of disease. Pathogenic germline and tumor mutations included SDHA/B/C (sdGIST), RET (MTC), TP53 and CTNNB1 (ACC), MEN1 (NEN), and SMARCB1 (poorly-differentiated chordoma). Clinically significant anxiety was observed in 20%–35% of adults. Enrollment of participants and comprehensive data collection were feasible. Remote enrollment was critical during the COVID-19 pandemic. Over 30 patients were enrolled with ACC, NEN, and sdGIST, allowing for clinical/genomic analyses across tumors. Longitudinal follow-up and expansion of cohorts are ongoing to advance understanding of disease course and establish external controls for interventional trials. Significance: This study demonstrates that comprehensive, tumor-agnostic data and biospecimen collection is feasible to characterize different rare tumors, and speed progress in research. The findings will be foundational to developing external controls groups for single-arm interventional trials, where randomized control trials cannot be conducted because of small patient populations.

Malignant peripheral nerve sheath tumors (MPNST) are soft-tissue sarcomas that are the leading cause of mortality in patients with Neurofibromatosis type 1 (NF1). Single chemotherapeutic agents have shown response rates ranging from 18% to 44% in clinical trials, so there is still a high medical need to identify chemotherapeutic combination treatments that improve clinical prognosis and outcome. We screened a collection of compounds from the NCATS Mechanism Interrogation PlatE (MIPE) library in three MPNST cell lines, using cell viability and apoptosis assays. We then tested whether compounds that were active as single agents were synergistic when screened as pairwise combinations. Synergistic combinations in vitro were further evaluated in patient-derived orthotopic xenograft/orthoxenograft (PDOX) athymic models engrafted with primary MPNST matching with their paired primary-derived cell line where synergism was observed. The high-throughput screening identified 21 synergistic combinations, from which four exhibited potent synergies in a broad panel of MPNST cell lines. One of the combinations, MK-1775 with Doxorubicin, significantly reduced tumor growth in a sporadic PDOX model (MPNST-SP-01; sevenfold) and in an NF1-PDOX model (MPNST-NF1–09; fourfold) and presented greater effects in TP53 mutated MPNST cell lines. The other three combinations, all involving Panobinostat (combined with NVP-BGT226, Torin 2, or Carfilzomib), did not reduce the tumor volume in vivo at noncytotoxic doses. Our results support the utility of our screening platform of in vitro and in vivo models to explore new therapeutic approaches for MPNSTs and identified that combination MK-1775 with Doxorubicin could be a good pharmacologic option for the treatment of these tumors.

Supplementary Figure from A High-Throughput Screening Platform Identifies Novel Combination Treatments for Malignant Peripheral Nerve Sheath Tumors

Supplementary Table from A High-Throughput Screening Platform Identifies Novel Combination Treatments for Malignant Peripheral Nerve Sheath Tumors

Supplementary Figure from A High-Throughput Screening Platform Identifies Novel Combination Treatments for Malignant Peripheral Nerve Sheath Tumors

Malignant peripheral nerve sheath tumors (MPNST) are soft-tissue sarcomas that are the leading cause of mortality in patients with Neurofibromatosis type 1 (NF1). Single chemotherapeutic agents have shown response rates ranging from 18% to 44% in clinical trials, so there is still a high medical need to identify chemotherapeutic combination treatments that improve clinical prognosis and outcome. We screened a collection of compounds from the NCATS Mechanism Interrogation PlatE (MIPE) library in three MPNST cell lines, using cell viability and apoptosis assays. We then tested whether compounds that were active as single agents were synergistic when screened as pairwise combinations. Synergistic combinations in vitro were further evaluated in patient-derived orthotopic xenograft/orthoxenograft (PDOX) athymic models engrafted with primary MPNST matching with their paired primary-derived cell line where synergism was observed. The high-throughput screening identified 21 synergistic combinations, from which four exhibited potent synergies in a broad panel of MPNST cell lines. One of the combinations, MK-1775 with Doxorubicin, significantly reduced tumor growth in a sporadic PDOX model (MPNST-SP-01; sevenfold) and in an NF1-PDOX model (MPNST-NF1–09; fourfold) and presented greater effects in TP53 mutated MPNST cell lines. The other three combinations, all involving Panobinostat (combined with NVP-BGT226, Torin 2, or Carfilzomib), did not reduce the tumor volume in vivo at noncytotoxic doses. Our results support the utility of our screening platform of in vitro and in vivo models to explore new therapeutic approaches for MPNSTs and identified that combination MK-1775 with Doxorubicin could be a good pharmacologic option for the treatment of these tumors.

Supplementary Table from A High-Throughput Screening Platform Identifies Novel Combination Treatments for Malignant Peripheral Nerve Sheath Tumors