NUS Researchers Pinpoint PTP1B as Pivotal Target in Cancer Immunotherapy Breakthrough
In a landmark development for cancer treatment, scientists at the National University of Singapore (NUS) have identified protein tyrosine phosphatase 1B (PTP1B) as a crucial molecular switch that can dramatically enhance the efficacy of cancer immunotherapy. This discovery, detailed in a recent study published in the Journal of the American Chemical Society, reveals how targeting PTP1B inside tumor cells triggers immunogenic cell death (ICD), a process that not only kills cancer cells but also rallies the immune system for a sustained attack.
Led by Professor Ang Wee Han from NUS's Department of Chemistry, the team developed novel platinum-based compounds, Pt-NHC and PlatinER (Pt-ER), which bind directly to PTP1B, inhibiting its activity. This inhibition flips a switch in cancer cells, exposing 'eat me' signals like calreticulin on their surface and releasing damage-associated molecular patterns (DAMPs) that alert dendritic cells and T cells. In preclinical colorectal cancer models, treated tumors generated long-term protective immunity, preventing rechallenge growth.
This finding positions PTP1B not just as a tumor growth promoter but as an intracellular immune checkpoint within cancer cells themselves—a novel angle in immunotherapy research.
Demystifying Immunogenic Cell Death: The Immune-Boosting Form of Cell Suicide
Immunogenic cell death (ICD) differs fundamentally from traditional apoptosis, which often goes unnoticed by the immune system. ICD is a regulated cell death modality characterized by three hallmarks: surface exposure of calreticulin (an endoplasmic reticulum chaperone acting as an 'eat me' signal), release of ATP and high-mobility group box 1 (HMGB1) as danger signals, and type I interferon production. These events transform dying tumor cells into a vaccine, priming antigen-presenting cells to activate cytotoxic T lymphocytes (CTLs).
In cancer therapy, inducing ICD synergizes with checkpoint inhibitors like anti-PD-1, amplifying responses in 'cold' tumors lacking immune infiltration. Chemotherapy agents like anthracyclines and oxaliplatin classically induce Type I ICD via pre-apoptotic endoplasmic reticulum stress. The NUS compounds pioneer Type II ICD, bypassing the need for extrinsic death receptor signaling and directly targeting intracellular phosphatases.
- Calreticulin exposure: Recruits phagocytes to engulf tumor debris.
- ATP secretion: Chemoattracts dendritic cells and promotes inflammasome activation.
- HMGB1 release: Binds TLR4 on immune cells, enhancing antigen cross-presentation.
PTP1B Unpacked: The Phosphatase with Dual Lives in Metabolism and Oncology
Protein tyrosine phosphatase 1B (PTP1B), encoded by PTPN1, dephosphorylates tyrosine residues on substrates like insulin receptor, JAK2, and PD-L1, negatively regulating signaling pathways. Long studied for its role in insulin resistance and obesity—PTP1B knockout mice resist diet-induced diabetes—recent insights reveal its oncogenic potential. In tumors, PTP1B sustains growth by activating Src kinase and dampening interferon responses.
Prior work showed PTP1B limits T-cell receptor signaling, reducing CTL expansion and CAR-T efficacy. Inhibitors like ABBV-CLS-484 (dual PTP1B/PTPN2) enhance JAK-STAT activation in T cells, boosting anti-tumor immunity in trials (Phase 1, NCT04777994). The NUS twist: PTP1B as a gatekeeper in tumor cells, preventing ICD by blocking calreticulin translocation.
Bioinformatics from TCGA datasets confirmed high PTP1B correlates with poor prognosis and low immune infiltration in colorectal adenocarcinoma.
Unraveling the Target: NUS's Innovative Chemical Biology Approach
The NUS team employed photoaffinity labeling: diazirine-equipped Pt-ER derivatives covalently bind targets upon UV light, followed by copper-catalyzed azide-alkyne cycloaddition (CuAAC click chemistry) for pull-down. Tandem mass tag (TMT) quantitative proteomics prioritized PTP1B from 5,000+ proteins. Biochemical assays verified direct binding (Kd ~1 μM) and inhibition (IC50 0.5 μM).
Genetic validation used CRISPR knockdown and allosteric inhibitor MSI-1436, replicating ICD hallmarks. In vivo, Pt-ER-treated CT26 colorectal tumors shrank 80% and resisted rechallenge, with increased CD8+ T-cell infiltration.
| Method | Purpose | Outcome |
|---|---|---|
| Photoaffinity Probes | Target ID | PTP1B top hit |
| CRISPR KO | Validation | ICD ↑ 3-fold |
| Mouse Models | Efficacy | Tumor immunity established |
Experimental Results: From Bench to Immune Memory
In vitro, Pt-ER induced dose-dependent calreticulin exposure (4-fold vs. cisplatin) and ATP release without caspase activation, hallmarking non-apoptotic ICD. Co-culture assays showed dendritic cell maturation and T-cell priming. Public datasets (GSE39582) linked low PTP1B to better immunotherapy response.
Professor Ang noted, 'The current study revealed the link between PTP1B and the immune-stimulating effects of our platinum-based ICD inducers.' Next steps include structural studies of Pt-ER:PTP1B complex.
Relevance to Singapore: Tackling Colorectal Cancer Burden
Colorectal cancer ranks second in incidence in Singapore, with ~3,500 new cases yearly (SCR 2023). Despite screening (44.9% uptake ages 50+), mortality fell 21% since 2012 due to early detection. NUS's work aligns with National Precision Medicine (NPM) and Cancer Science Institute (CSI) efforts, building Asia's largest organoid biobank.
Read the full JACS paper here. Singapore's biomedical hub status, with S$25B RIE2025 investment, amplifies such innovations.
Singapore's Higher Education at Forefront of Biomedical Innovation
NUS and NTU lead Singapore's biomedical ecosystem, home to CSI Singapore and Duke-NUS. CSI fosters interdisciplinary cancer research, from basic to translational. Government initiatives like RIE2030 fund such high-impact work, attracting global talent.
For students, programs in chemistry and biomed at NUS offer hands-on research. Explore research jobs or university positions in Singapore's thriving sector.
Path Forward: PTP1B Inhibitors Enter Clinic, Synergies with Existing Therapies
ABBV-CLS-484 (Osunprotafib), a PTP1B/PTPN2 inhibitor, shows promise in Phase 1 trials for solid tumors, enhancing T-cell function via JAK-STAT. NUS compounds could complement PD-1 blockers, addressing resistance in 70% non-responders.
- Combine with CAR-T for solid tumors.
- Target 'cold' immunotherapies.
- Personalize via PTP1B expression biomarkers.
Career Horizons in Cancer Immunotherapy Research
Singapore's universities offer abundant opportunities. NUS CSI posts postdocs in immunotherapy; Duke-NUS seeks CSCB fellows. With 96+ cancer research roles open, from research assistants to faculty, this field promises impact.
Check academic CV tips, professor reviews, and higher ed jobs. For recruitment, visit our recruitment page.
In summary, NUS's PTP1B discovery heralds a new era in immunotherapy, underscoring Singapore's higher education prowess. Explore higher-ed jobs, rate your professor, and career advice to join this revolution.
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