Research And Grants

Exploring Novel Targets In DIPG

Diffuse intrinsic pontine glioma (DIPG) that represents up to 85% of brainstem tumors is a rare, infiltrative, and incurable brainstem malignancy in children resulting in death within one year from diagnosis (1-5). To find new drug targets for DIPG, we recently performed the first analysis of the metabolic pathways dysregulated in DIPG.  Our metabolomics analysis revealed many dysregulated pathways including the mitochondrial electron transport chain (mETC).   The mETC contains five protein complexes. Inhibitors of complex I such as the common anti-diabetic drug metformin is in many oncology clinical trials.   We observed that several DIPG lines including a new biopsy-derived line (RTS3798) in our laboratory  are exquisitely sensitive to metformin and IACS-010759.   IACS-010759 is a similar inhibitor that crosses the blood brain barrier and is in clinical trial for other cancers.   We will test if IACS (as a naked drug or delivered through nano particles) shrinks DIPG tumors and cooperates with radiation therapy in our preclinical mouse model of DIPG.  In the second part of our grant, we propose to perform a medium throughput screening of a library of blood brain barrier penetrating compounds to test if any of these compounds are therapeutic in cell culture and in our mouse model.

Many cancers with active glycolysis, such as adult glioblastoma (GBM), still depend on mitochondrial oxidative phosphorylation for growth and dissemination despite their metabolic plasticity.   Accordingly, mitochondrial inhibitors are in clinical development.  The biguanide metformin that inhibits mitochondrial complex I (MCI) is in over 200 cancer trials, including adult GBM (NCT02780024, NCT03243851).   However, there is limited knowledge about molecular markers that can be leveraged to tailor MCI inhibitor (MCI-i) therapy specifically to responders.  For example, in some cancers, mutations in MCI genes sensitize tumors to MCI-i therapy.   However, such mutations are currently unknown in either adult or pediatric brain tumors. By examining human adult GBM data that is publicly available, and through experimental analysis, we have identified that a mitochondrial gene called pyruvate dehydrogenase A1 (PDHA1) is a predictive molecular marker for MCI-i sensitivity in adult GBM. This means that cell lines that present high levels of this gene are sensitive while cell lines with low level expression are resistant to MCI-i. We extrapolated our findings to DIPG lines and found that the majority of DIPG lines express high amounts of this gene and are even more sensitive to MCI-i that adult GBM lines. However, cellular transport proteins that import metformin (called OCT1 and OCT2) are not well expressed in the brain and therefore metformin does not accumulate in brain tumors at therapeutic doses.  We will therefore use another similar MCI-i called IACS-010759 that crosses into the brain and test its efficacy in our mouse models of DIPG.  As an alternative method of IACS delivery, we are collaborating with Dr. Marina Sokolsky-Papkov, Director, Center for Nanotechnology in Drug Delivery at University of North Carolina.  She has recently published brain delivery of CDK4 and mTOR inhibitors complexed with poly(2-oxazoline)-based nanoparticles in medulloblastoma.

While the first aim of the project is defined, the second aim of the project is exploratory, nonetheless no less important. The blood-brain barrier (BBB) is one of the greatest impediments to brain drug delivery. Although BBB I soften disrupted in brain tumors, delivery of drugs is still not optimal in most cases. This physiological hurdle of the BBB stops 95% of compounds for drug development. Therefore, we will screen compound libraries with confirmed penetration of the BBB. Such a unique library of 767 compounds is available with MedChemExpress with confirmed CNS penetration property. We will first use this library to test which of these compounds exert in vitro toxicity specifically to DIPG cells leaving normal neural stem cells and astrocytes unharmed. Once we complete this test, we expect to identify one or more compounds with desirable properties. In the future, we plan to test some of these compounds in vivo in our mouse models of DIPG (these mouse studies beyond the scope of this grant). Another such BBB penetrating library is also available with Otava Chemicals that has a library of 1,735 compounds with physicochemical properties preferable for BBB penetration and simultaneously suitable for oral administration. We also plan to screen this library in in the future.