Introduction: Pyruvate kinase M2 (PKM2) is an enzyme that catalyzes the final step in glycolysis, a key step in tumor metabolism and growth, making PKM2 an important marker of cancer glycolytic reprogramming. The 1-((2-fluoro-6-[18F]fluorophenyl)sulfonyl)-4-((4-methoxyphenyl)sulfonyl)piperazine ([18F]DASA-23) radiotracer has been developed to measure the expression of PKM2. Glioblastoma (GBM) is traditionally treated with surgical resection, temozolomide (TMZ) chemotherapy, and radiation therapy. Tumor treating fields (TTFields), the application of alternating electric fields (100-500 kHz, 1-4 V/cm) to tumors, is emerging as the fourth therapeutic modality in GBM. There is an important need to assess early on whether a patient’s GBM is responding to a given standard-of-care or experimental therapy. In this study we evaluated the ability of [18F]DASA-23 to detect changes in metabolism in response to standard-of-care (TMZ) and emerging (TTFields) therapies, in cell culture and an orthotopic murine model of human GBM.
Methods: Human U87-MG GBM cells were subjected to either 200 kHz TTFields or the IC50 of TMZ for three or six days (n≥3/condition), followed by evaluation of 30-minute cellular uptake of [18F]DASA-23. In parallel experiments, immunofluorescence for PKM2 was performed to confirm the [18F]DASA-23 uptake results. Finally, U87-MG human GBM cells were orthotopically implanted in nude mice (N=5), and evaluated with 7T small animal magnetic resonance imaging (MRI) and [18F]DASA-23 microPET/CT before and one week post-initiation of vehicle or TMZ therapy.
Results: There was a significant interaction between the treatment (vehicle, TMZ, or TTFields) and treatment duration (3 or 6 days) on PKM2 expression as measured by cellular uptake of [18F]DASA-23 (p=0.005, 2-way ANOVA). Immunofluorescence for PKM2 in TTFields-exposed and unexposed U87-MG cells revealed reduced cell count and less intense PKM2 staining due to TTFields. In the orthotopic mouse model, the tumor/normal brain (T/N) [18F]DASA-23 uptake ratio (unitless) at one week post-treatment was divided by the pre-treatment T/N ratio. The resulting ratio of ratios was significantly smaller in the TMZ cohort (1.0±0.4) compared to in the vehicle cohort (2.2±0.2), p=0.004.
Conclusion: Together, these data suggest the potential for non-invasive assessment of GBM’s response to various therapies using [18F]DASA-23, a radiotracer that measures PKM2 expression. Clinical studies are currently being completed to evaluate the diagnostic ability of [18F]DASA-23 in patients with intracranial malignancies and future studies will evaluate the ability of [18F]DASA-23 to predict responders vs. non-responders to therapy in recurrent GBM.
Citation Format: Chirag B. Patel, Corinne Beinat, Yuanyang Xie, Edwin Chang, Sanjiv S. Gambhir. Molecular imaging of pyruvate kinase M2 (PKM2) with [18F]DASA-23 detects temozolomide- and tumor treating fields (TTFields)-induced changes in glycolysis in glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5271.