In vivo CRISPR screening identifies NF1/RASA1/TP53 co-mutations and downstream MEK signaling as a common key mechanism of sinonasal tumorigenesis

Sinonasal malignancies represent a heterogeneous group of rare cancers with poorly understood molecular origins that frequently present at advanced stages. It was already known that the anatomical complexity of the nasal cavity complicates early diagnosis and effective treatment strategies, often leading to poor patient prognosis. Existing clinical approaches often rely on broad-spectrum therapies due to a lack of identified genetic drivers, which limits the potential for personalized medicine in this patient population. Genomic landscapes of these tumors remain largely uncharacterized compared to more common head and neck cancers, leaving a significant void in our understanding of their biological progression. Understanding the specific loss-of-function mutations that initiate these diverse histologies is essential for developing targeted interventions that can bypass the limitations of conventional chemotherapy and radiation. This gap motivated the development of high-throughput functional screens to pinpoint essential oncogenic regulators in vivo, providing a more accurate representation of the tumor microenvironment.

This research identifies critical cancer driver genes across diverse sinonasal malignancies using a systematic loss-of-function approach to elucidate the underlying genetic architecture of these rare diseases. The investigators sought to determine whether distinct histological subtypes share common genetic vulnerabilities or possess unique mutational profiles that dictate their aggressive behavior. Mapping the functional consequences of specific gene deletions within the sinonasal cavity provided a framework for therapeutic discovery by highlighting pathways that are essential for tumor maintenance. The study aimed to validate the requirement of specific tumor suppressors, such as Nf1 and Trp53, in maintaining the malignant phenotype across different cellular contexts. Evaluating the efficacy of small molecule inhibitors against identified pathways offered a path toward clinical translation for patients who currently have limited treatment options. Establishing a robust mouse model for sinonasal cancer allowed for the exploration of tumor biology in a native microenvironment, ensuring that the findings are physiologically relevant.

Researchers deployed an adeno-associated virus (AAV) vector to deliver a pooled custom single-guide RNA (sgRNA) library directly into the sinonasal cavity of mice to initiate localized genetic modifications. This in vivo CRISPR-Cas9 system facilitated the targeted disruption of candidate genes to observe spontaneous tumor formation within the complex architecture of the nasal passages. Histological analysis categorized the resulting growths into squamous cell carcinoma, adenocarcinoma, and neuroendocrine variants, allowing for a comprehensive assessment of phenotypic diversity. Orthogonal validation experiments utilized specific gene knockouts to confirm the necessity of Nf1 and Trp53 in driving oncogenesis, ensuring the reliability of the initial screening results. The team established primary cell lines and organoid models from both murine and human sinonasal tumor samples to create a versatile platform for drug testing. Pharmacological assays measured the sensitivity of these models to MEK inhibition using standardized in vitro culture techniques that simulate the metabolic conditions of the tumor.

The CRISPR screen revealed that Nf1, Rasa1, and Trp53 mutations occurred in 79%, 74%, and 68% of tumors, respectively, indicating a high degree of mutational convergence. These recurrent alterations appeared consistently across diverse histological subtypes, including olfactory neuroblastoma and poorly differentiated carcinoma, suggesting a universal mechanism of transformation. Loss of NF1 and RASA1-mediated Ras-GAP activity significantly elevated Ras activation and downstream MEK signaling, which served as a central node for oncogenic signaling. Functional assays confirmed that the combined deletion of Nf1 and Trp53 was sufficient to initiate sinonasal tumorigenesis in vivo, replicating the findings from the pooled library screen. Both murine-derived cell lines and human sinonasal malignancy samples exhibited high sensitivity to MEK inhibitors, demonstrating the therapeutic potential of targeting this pathway. Organoid models demonstrated a significant reduction in viability when treated with small molecules targeting the RAS-MAPK pathway, further validating the importance of MEK signaling in tumor survival.

These findings establish that a common genetic axis involving the loss of Ras-GAP activity drives the development of multiple sinonasal tumor subtypes. The identification of the NF1/RASA1/TP53 co-mutation signature provides a new diagnostic marker for these rare malignancies, potentially improving patient stratification in clinical settings. Targeting the MEK signaling pathway emerges as a promising therapeutic strategy for patients with diverse sinonasal histologies, offering a more precise alternative to traditional treatments. Future research should focus on refining these targeted therapies and exploring potential resistance mechanisms to improve long-term clinical outcomes in refractory cases. The study highlights the utility of in vivo CRISPR screening for uncovering universal mechanisms in heterogeneous cancer types, paving the way for similar studies in other rare diseases. Clinical trials investigating MEK inhibition in sinonasal cancer patients may be warranted based on these preclinical results, which demonstrate a clear link between genotype and drug response.