Targeting BCAT1 Combined with α-Ketoglutarate Triggers Metabolic Synthetic Lethality in Glioblastoma.

Branched-chain amino acid transaminase 1 (BCAT1) is upregulated selectively in human isocitrate dehydrogenase (IDH) wildtype (WT) but not mutant glioblastoma multiforme (GBM) and promotes IDHWT GBM growth. Through a metabolic synthetic lethal screen, we report here that α-ketoglutarate (AKG) kills IDHWT GBM cells when BCAT1 protein is lost, which is reversed by reexpression of BCAT1 or supplementation with branched-chain α-ketoacids (BCKA), downstream metabolic products of BCAT1. In patient-derived IDHWT GBM tumors in vitro and in vivo, cotreatment of BCAT1 inhibitor gabapentin and AKG resulted in synthetic lethality. However, AKG failed to evoke a synthetic lethal effect with loss of BCAT2, BCKDHA, or GPT2 in IDHWT GBM cells. Mechanistically, loss of BCAT1 increased the NAD+/NADH ratio but impaired oxidative phosphorylation, mTORC1 activity, and nucleotide biosynthesis. These metabolic alterations were synergistically augmented by AKG treatment, thereby causing mitochondrial dysfunction and depletion of cellular building blocks, including ATP, nucleotides, and proteins. Partial restoration of ATP, nucleotides, proteins, and mTORC1 activity by BCKA supplementation prevented IDHWT GBM cell death conferred by the combination of BCAT1 loss and AKG. These findings define a targetable metabolic vulnerability in the most common subset of GBM that is currently incurable. SIGNIFICANCE: Metabolic synthetic lethal screening in IDHWT glioblastoma defines a vulnerability to ΑΚG following BCAT1 loss, uncovering a therapeutic strategy to improve glioblastoma treatment. See related commentary by Meurs and Nagrath, p. 2354.

Patient-derived tumor xenograft models for melanoma drug discovery.

INTRODUCTION: Cutaneous metastatic melanoma (MM) is an aggressive form of skin cancer, with treatment providing cures to a minority of patients. The multiple risk factors that contribute to MM development suggest that cutaneous melanomas embody a repertoire of altered genetic events requiring studies to better understand its biology in order to develop novel therapies. AREAS COVERED: Patient-derived tumor xenograft (PDTX) mouse models are noted to be superior for novel drug discovery and tumor biology studies due to their ability to maintain tumor heterogeneity and their use as real-time individualized patient models. In this review, the authors highlight the utility of PDTX models in advancing treatment options for patients with MM by creating invaluable preclinical models that exhibit patient-relevant treatment outcomes. EXPERT OPINION: There is a strong necessity to reassess current approaches in which preclinical experiments are designed and executed in order to minimize unwarranted clinical trials. With rigorously performed preclinical studies, PDTX models have the capability to effectively confirm or deny drug effective outcomes. The ability to do this, however, will demand better aids to guide experimental design, the redefining of preclinical efficacy, and the understanding that these models should be viewed as complementary to other drug prediction and efficacy tools.

Pomalidomide shows significant therapeutic activity against CNS lymphoma with a major impact on the tumor microenvironment in murine models.

Primary CNS lymphoma carries a poor prognosis. Novel therapeutic agents are urgently needed. Pomalidomide (POM) is a novel immunomodulatory drug with anti-lymphoma activity. CNS pharmacokinetic analysis was performed in rats to assess the CNS penetration of POM. Preclinical evaluation of POM was performed in two murine models to assess its therapeutic activity against CNS lymphoma. The impact of POM on the CNS lymphoma immune microenvironment was evaluated by immunohistochemistry and immunofluorescence. In vitro cell culture experiments were carried out to further investigate the impact of POM on the biology of macrophages. POM crosses the blood brain barrier with CNS penetration of ~ 39%. Preclinical evaluations showed that it had significant therapeutic activity against CNS lymphoma with significant reduction in tumor growth rate and prolongation of survival, that it had a major impact on the tumor microenvironment with an increase in macrophages and natural killer cells, and that it decreased M2-polarized tumor-associated macrophages and increased M1-polarized macrophages when macrophages were evaluated based on polarization status. In vitro studies using various macrophage models showed that POM converted the polarization status of IL4-stimulated macrophages from M2 to M1, that M2 to M1 conversion by POM in the polarization status of lymphoma-associated macrophages is dependent on the presence of NK cells, that POM induced M2 to M1 conversion in the polarization of macrophages by inactivating STAT6 signaling and activating STAT1 signaling, and that POM functionally increased the phagocytic activity of macrophages. Based on our findings, POM is a promising therapeutic agent for CNS lymphoma with excellent CNS penetration, significant preclinical therapeutic activity, and a major impact on the tumor microenvironment. It can induce significant biological changes in tumor-associated macrophages, which likely play a major role in its therapeutic activity against CNS lymphoma. POM should be further evaluated in clinical trials.

C-lysine conjugates: pH-controlled light-activated reagents for efficient double-stranded DNA cleavage with implications for cancer therapy.

Double-stranded DNA cleavage of light-activated lysine conjugates is strongly enhanced at the slightly acidic pH (<7) suitable for selective targeting of cancer cells. This enhancement stems from the presence of two amino groups of different basicities. The first amino group plays an auxiliary role by enhancing solubility and affinity to DNA, whereas the second amino group, which is positioned next to the light-activated DNA cleaver, undergoes protonation at the desired pH threshold. This protonation results in two synergetic effects which account for the increased DNA-cleaving ability at the lower pH. First, lysine conjugates show tighter binding to DNA at the lower pH, which is consistent with the anticipated higher degree of interaction between two positively charged ammonium groups with the negatively charged phosphate backbone of DNA. Second, the unproductive pathway which quenches the excited state of the photocleaver through intramolecular electron transfer is eliminated once the donor amino group next to the chromophore is protonated. Experiments in the presence of traps for diffusing radicals show that reactive oxygen species do not contribute significantly to the mechanism of DNA cleavage at the lower pH, which is indicative of tighter binding to DNA under these conditions. This feature is valuable not only because many solid tumors are hypoxic but also because cleavage which does not depend on diffusing species is more localized and efficient. Sequence-selectivity experiments suggest combination of PET and base alkylation as the chemical basis for the observed DNA damage. The utility of these molecules for phototherapy of cancer is confirmed by the drastic increase in toxicity of five conjugates against cancer cell lines upon photoactivation.