Singapore Researchers Develop CRISPR-Cas9 BAP1 Knockout Melanoma Model Recapitulating Human Tumorigenesis

Singaporean scientists have made a significant advance in melanoma research with the development of a novel preclinical tumor model using CRISPR-Cas9 technology to knock out the BAP1 gene. This innovative model, detailed in a recent publication in Communications Biology, faithfully recapitulates the complex processes of human melanoma development and immune system interactions. Led by researchers from the Singapore Eye Research Institute (SERI), Singapore National Eye Centre, and Duke-NUS Medical School, the study addresses a critical gap in cancer modeling by providing an immune-competent platform to explore aggressive BAP1-deficient melanomas.

Melanoma, the deadliest form of skin cancer, poses unique challenges in Asian populations like Singapore's, where incidence rates have been steadily rising. While less common than in Caucasians, melanoma here often presents as acral lentiginous or mucosal types, which are more aggressive and harder to treat. According to data from the Singapore Cancer Registry, skin cancer rates, including melanoma, increased from 2.9 per 100,000 in the late 1960s to around 7.4 per 100,000 by the mid-2000s, with ongoing trends highlighting the need for better models to study local disease biology.

The BAP1 gene, or BRCA1-associated protein 1, is a tumor suppressor frequently mutated in melanomas, particularly uveal melanoma (a subtype originating in the eye) and cutaneous forms. Loss of BAP1 leads to DNA repair defects, metabolic shifts, and immune evasion, contributing to poor prognosis. Prior models failed to capture these dynamics in an immune-intact setting, limiting immunotherapy testing.

🧬 The CRISPR-Cas9 Breakthrough: Engineering a Faithful Melanoma Model

The research team employed CRISPR-Cas9, a precise gene-editing tool consisting of a guide RNA and Cas9 nuclease, to target and disrupt the BAP1 gene in a murine melanocyte cell line. This created a syngeneic model—meaning the cells are genetically matched to the host mouse strain—allowing tumors to grow in immune-competent animals without rejection.

Step-by-step, the process involved:

• Designing specific guide RNAs to cleave the BAP1 locus.
• Transfecting cells and selecting knockout clones via single-cell sorting.
• Validating knockouts with sequencing and western blots, confirming no functional BAP1 protein.
• Implanting cells subcutaneously and orthotopically to assess tumor formation.

The chosen clone (#2) displayed epithelioid morphology, rapid proliferation, and high tumorigenicity, hallmarks of human BAP1-deficient melanomas. In mice, tumors grew aggressively, mimicking clinical progression.

Recapitulating Human Tumorigenesis: From Cells to Tumors

One of the model's standout features is its ability to mirror human melanoma development. Single-cell RNA sequencing revealed upregulated pathways in lipid metabolism, transmembrane signaling, and epithelial-mesenchymal transition—key drivers in high-risk, class 2 uveal melanomas. Gene Set Enrichment Analysis (GSEA) confirmed lipid reprogramming, a metabolic vulnerability previously noted in patient samples.

In vivo, tumors showed vascularization, necrosis, and invasion, akin to advanced human disease. Histology matched epithelioid subtypes prevalent in Asian patients, where acral melanomas dominate over sun-exposed types.

Immune Landscape: Unveiling Suppressive Microenvironments

BAP1 loss fosters an immunosuppressive tumor microenvironment (TME), a major barrier to immunotherapy. The model replicated this with increased myeloid-derived suppressor cells (MDSCs), regulatory T cells (Tregs), and M2 macrophages, while exhausted CD8+ T cells dominated. Pro-tumorigenic cytokines like IL-10 and TGF-β were elevated, suppressing anti-tumor immunity.

Cross-species comparisons with human datasets showed 80-90% overlap in immune signatures, validating the model's relevance. This setup allows testing checkpoint inhibitors or combination therapies in a realistic immune context.

Singapore's Research Powerhouses: Duke-NUS and SERI Lead the Way

Duke-NUS Medical School, a collaboration between Duke University and the National University of Singapore, spearheaded this work alongside SERI and Singapore National Eye Centre. Key contributors include Dr. Anita S.Y. Chan, a clinician-scientist bridging ophthalmology and oncology, and Mona M. Wang, whose dual affiliations highlight international ties with the University of Turku.

Funded by Singapore's National Medical Research Council (NMRC), this reflects the nation's S$25 billion investment in biomedical sciences since 2000, positioning Duke-NUS as Asia's top medical research institution per recent rankings. SERI's focus on ocular oncology aligns perfectly, given uveal melanoma's prominence.

Such collaborations exemplify Singapore's higher education ecosystem, where graduate programs at Duke-NUS train PhD students in CRISPR and immuno-oncology, fostering a pipeline of talent.

🔬 Methodological Innovations and Validation

Beyond knockout generation, the study integrated multi-omics: bulk and single-cell transcriptomics, flow cytometry, and immunohistochemistry. Tumors were profiled at multiple timepoints, capturing evolution from initiation to progression.

Comparisons:

Access the full study for detailed datasets: Communications Biology paper.

Challenges in Melanoma Research and Model Advantages

• Patient-derived xenografts (PDXs): Immunodeficient hosts limit immune studies.
• GEMMs (genetically engineered mouse models): Slow development, not BAP1-specific.
• Syngeneic models: This one adds BAP1 knockout for precision.

Benefits include rapid tumor formation (weeks vs. months), cost-effectiveness, and syngeneicity for immunotherapy screens.

Therapeutic Horizons: Paving the Way for Immunotherapies

The model's immunosuppressive TME enables screening of PD-1 inhibitors, CAR-T cells, or novel combos. Early data suggest vulnerabilities in lipid pathways, targetable by metabolic drugs. In Singapore, where immunotherapy access is high but response rates low (20-30% in advanced melanoma), this could optimize regimens.

Related work at Duke-NUS/NCCS on BAP1 mechanisms (Science Translational Medicine) identifies LSD1/PARP1 inhibitors, synergizing with immune approaches.

Singapore's Biomedical Ecosystem and Higher Education Impact

Singapore invests heavily in R&D, with Duke-NUS ranking top in Asia for clinical medicine. PhD programs in Cancer & Stem Cell Biology train researchers in CRISPR, attracting global talent. SERI's ocular focus complements, with facilities like the Genome Institute of Singapore aiding multi-omics.

This positions Singapore as a hub for precision oncology, benefiting from A*STAR and NMRC funding. Students gain hands-on experience, boosting careers in biotech.

Future Directions: From Bench to Bedside

Next steps: orthotopic eye implants for uveal melanoma, drug screens, and human trials. Collaborations with pharma could accelerate translation. Challenges include validating in diverse ethnicities and scaling for high-throughput.

Outlook: Enhanced immunotherapies could improve survival from 50% 5-year for metastatic melanoma.

Photo by Timothy Chambers on Unsplash

This model not only advances science but underscores Singapore higher education's global role in tackling cancers like melanoma, offering hope through innovation.