Negative effects of tumor cell nitric oxide on anti-glioblastoma photodynamic therapy
Albert W Girotti1, Jonathan M Fahey1, Witold Korytowski2
1Department of Biochemistry, Medical College of Wisconsin, Milwaukee, WI 53226, United States.
Abstract:
Glioblastomas are highly aggressive brain tumors that can persist after exposure to conventional chemotherapy or radiotherapy. Nitric oxide (NO) produced by inducible NO synthase (iNOS/NOS2) in these tumors is known to foster malignant cell proliferation, migration, and invasion as well as resistance to chemo- and radiotherapy. Minimally invasive photodynamic therapy (PDT) sensitized by 5-aminolevulinic acid (ALA)-induced protoporphyrin IX (PpIX) is a highly effective anti-glioblastoma modality, but it is also subject to NO-mediated resistance. Studies by the authors have revealed that glioblastoma U87 and U251 cells use endogenous iNOS/NO to not only resist photokilling after an ALA/light challenge, but also to promote proliferation and migration/invasion of surviving cells. Stress-upregulated iNOS/NO was found to play a major role in these negative responses to PDT-like treatment. Our studies have revealed a tight network of upstream signaling events leading to iNOS induction in photostressed cells and transition to a more aggressive phenotype. These events include activation or upregulation of pro-survival/ pro-expansion effector proteins such as NF-κB, phosphoinositide-3-kinase (PI3K), protein kinase-B (Akt), p300, Survivin, and Brd4. In addition to this upstream signaling and its regulation, pharmacologic approaches for directly suppressing iNOS at its activity vs. transcriptional level are discussed. One highly effective agent in the latter category is bromodomain and extra-terminal (BET) inhibitor, JQ1, which was found to minimize iNOS upregulation in photostressed U87 cells. By acting similarly at the clinical level, a BET inhibitor such as JQ1 should markedly improve the efficacy of anti-glioblastoma PDT.
Insights
Glioblastoma cells resist photodynamic therapy (PDT) via nitric oxide (NO) produced by inducible NO synthase (iNOS/NOS2). Targeting iNOS with agents like JQ1 can overcome this resistance, improving PDT efficacy against aggressive brain tumors.
Area of Science:
- Oncology
- Biochemistry
- Molecular Biology
Background:
- Glioblastomas are aggressive brain tumors resistant to standard treatments.
- Nitric oxide (NO), produced by inducible NO synthase (iNOS/NOS2), promotes glioblastoma growth and treatment resistance.
- Photodynamic therapy (PDT) using 5-aminolevulinic acid (ALA) is effective but can be hindered by NO-mediated resistance.
Purpose of the Study:
- To investigate the role of endogenous iNOS/NO in glioblastoma cell resistance to ALA-induced PDT.
- To identify signaling pathways involved in iNOS induction and glioblastoma cell aggression post-PDT.
- To explore pharmacologic strategies for overcoming NO-mediated PDT resistance.
Main Methods:
- Utilized glioblastoma cell lines (U87, U251) to study responses to ALA/light treatment.
- Analyzed the role of inducible NO synthase (iNOS/NOS2) and nitric oxide (NO) in cell survival, proliferation, and invasion.
- Investigated upstream signaling pathways including NF-κB, PI3K/Akt, p300, Survivin, and Brd4.
- Evaluated the efficacy of bromodomain and extra-terminal (BET) inhibitor JQ1 in suppressing iNOS.
Main Results:
- Endogenous iNOS/NO production in glioblastoma cells confers resistance to photokilling by ALA-PDT.
- Surviving cells exhibit increased proliferation and invasion, driven by stress-upregulated iNOS/NO.
- A signaling network involving NF-κB, PI3K/Akt, p300, Survivin, and Brd4 mediates iNOS induction and aggressive phenotype.
- The BET inhibitor JQ1 effectively reduced iNOS upregulation in photostressed glioblastoma cells.
Conclusions:
- Inducible NO synthase (iNOS) and its product nitric oxide (NO) are critical mediators of glioblastoma resistance to photodynamic therapy (PDT).
- Targeting the upstream signaling network that induces iNOS, particularly using BET inhibitors like JQ1, holds promise for enhancing PDT efficacy.
- Pharmacologic inhibition of iNOS transcription represents a viable strategy to improve outcomes for glioblastoma patients undergoing PDT.
