Medium-chain acyl CoA dehydrogenase protects mitochondria from lipid peroxidation in glioblastoma

Glioblastoma (GBM) is highly resistant to chemo- and immune-based therapies and targeted inhibitors. To identify novel drug targets, we screened orthotopically implanted, patient-derived glioblastoma sphere-forming cells (GSCs) using an RNAi library to probe essential tumor cell metabolic programs. This identified high dependence on mitochondrial fatty acid metabolism. We focused on medium-chain acyl-CoA dehydrogenase (MCAD), which oxidizes medium-chain fatty acids (MCFAs), due to its consistently high score and high expression among models and upregulation in GBM compared to normal brain. Beyond the expected energetics impairment, MCAD depletion in primary GBM models induced an irreversible cascade of detrimental metabolic effects characterized by accumulation of unmetabolized MCFAs, which induced lipid peroxidation and oxidative stress, irreversible mitochondrial damage, and apoptosis. Our data uncover a novel protective role for MCAD to clear lipid molecules that may cause lethal cell damage, suggesting that therapeutic targeting of MCFA catabolism could exploit a key metabolic feature of GBM.

Cysteine depletion induces pancreatic tumor ferroptosis in mice

Ferroptosis is a form of cell death that results from the catastrophic accumulation of lipid reactive oxygen species (ROS). Oncogenic signaling elevates lipid ROS production in many tumor types and is counteracted by metabolites that are derived from the amino acid cysteine. In this work, we show that the import of oxidized cysteine (cystine) via system x_C ^- is a critical dependency of pancreatic ductal adenocarcinoma (PDAC), which is a leading cause of cancer mortality. PDAC cells used cysteine to synthesize glutathione and coenzyme A, which, together, down-regulated ferroptosis. Studying genetically engineered mice, we found that the deletion of a system x_C ^- subunit, Slc7a11, induced tumor-selective ferroptosis and inhibited PDAC growth. This was replicated through the administration of cyst(e)inase, a drug that depletes cysteine and cystine, demonstrating a translatable means to induce ferroptosis in PDAC.

Tissue of origin dictates GOT1 dependence and confers synthetic lethality to radiotherapy

BACKGROUND

Metabolic programs in cancer cells are influenced by genotype and the tissue of origin. We have previously shown that central carbon metabolism is rewired in pancreatic ductal adenocarcinoma (PDA) to support proliferation through a glutamate oxaloacetate transaminase 1 (GOT1)-dependent pathway.

METHODS

We utilized a doxycycline-inducible shRNA-mediated strategy to knockdown GOT1 in PDA and colorectal cancer (CRC) cell lines and tumor models of similar genotype. These cells were analyzed for the ability to form colonies and tumors to test if tissue type impacted GOT1 dependence. Additionally, the ability of GOT1 to impact the response to chemo- and radiotherapy was assessed. Mechanistically, the associated specimens were examined using a combination of steady-state and stable isotope tracing metabolomics strategies and computational modeling. Statistics were calculated using GraphPad Prism 7. One-way ANOVA was performed for experiments comparing multiple groups with one changing variable. Student's t test (unpaired, two-tailed) was performed when comparing two groups to each other. Metabolomics data comparing three PDA and three CRC cell lines were analyzed by performing Student's t test (unpaired, two-tailed) between all PDA metabolites and CRC metabolites.

RESULTS

While PDA exhibits profound growth inhibition upon GOT1 knockdown, we found CRC to be insensitive. In PDA, but not CRC, GOT1 inhibition disrupted glycolysis, nucleotide metabolism, and redox homeostasis. These insights were leveraged in PDA, where we demonstrate that radiotherapy potently enhanced the effect of GOT1 inhibition on tumor growth.

CONCLUSIONS

Taken together, these results illustrate the role of tissue type in dictating metabolic dependencies and provide new insights for targeting metabolism to treat PDA.

High-Throughput Excipient Discovery Enables Oral Delivery of Poorly Soluble Pharmaceuticals

Polymeric excipients are crucial ingredients in modern pills, increasing the therapeutic bioavailability, safety, stability, and accessibility of lifesaving products to combat diseases in developed and developing countries worldwide. Because many early-pipeline drugs are clinically intractable due to hydrophobicity and crystallinity, new solubilizing excipients can reposition successful and even failed compounds to more effective and inexpensive oral formulations. With assistance from high-throughput controlled polymerization and screening tools, we employed a strategic, molecular evolution approach to systematically modulate designer excipients based on the cyclic imide chemical groups of an important (yet relatively insoluble) drug phenytoin. In these acrylamide- and methacrylate-containing polymers, a synthon approach was employed: one monomer served as a precipitation inhibitor for phenytoin recrystallization, while the comonomer provided hydrophilicity. Systems that maintained drug supersaturation in amorphous solid dispersions were identified with molecular-level understanding of noncovalent interactions using NOESY and DOSY NMR spectroscopy. Poly(N-isopropylacrylamide-co-N,N-dimethylacrylamide) (poly(NIPAm-co-DMA)) at 70 mol % NIPAm exhibited the highest drug solubilization, in which phenytoin associated with inhibiting NIPAm units only with lowered diffusivity in solution. In vitro dissolution tests of select spray-dried dispersions corroborated the screening trends between polymer chemical composition and solubilization performance, where the best NIPAm/DMA polymer elevated the mean area-under-the-dissolution-curve by 21 times its crystalline state at 10 wt % drug loading. When administered to rats for pharmacokinetic evaluation, the same leading poly(NIPAm-co-DMA) formulation tripled the oral bioavailability compared to a leading commercial excipient, HPMCAS, and translated to a remarkable 23-fold improvement over crystalline phenytoin.

Chemoselective immobilization of proteins by microcontact printing and bio-orthogonal click reactions

Herein, a combination of microcontact printing of functionalized alkanethiols and site-specific modification of proteins is utilized to chemoselectively immobilize proteins onto gold surfaces, either by oxime- or copper-catalyzed alkyne-azide click chemistry. Two molecules capable of click reactions were synthesized, an aminooxy-functionalized alkanethiol and an azide-functionalized alkanethiol, and self-assembled monolayer (SAM) formation on gold was confirmed by IR spectroscopy. The alkanethiols were then individually patterned onto gold surfaces by microcontact printing. Site-specifically modified proteins-horse heart myoglobin (HHMb) containing an N-terminal α-oxoamide and a red fluorescent protein (mCherry-CVIA) with a C-terminal alkyne-were immobilized by incubation onto respective stamped functionalized alkanethiol patterns. Pattern formation was confirmed by fluorescence microscopy.

Poly(trehalose): sugar-coated nanocomplexes promote stabilization and effective polyplex-mediated siRNA delivery

When nanoparticles interact with their environment, the nature of that interaction is governed largely by the properties of its outermost surface layer. Here, we exploit the exceptional properties of a common disaccharide, trehalose, which is well-known for its unique biological stabilization effects. To this end, we have developed a synthetic procedure that readily affords a polymer of this disaccharide, poly(methacrylamidotrehalose) or "poly(trehalose)" and diblock copolycations containing this polymer with 51 repeat units chain extended with aminoethylmethacrylamide (AEMA) at three degrees of polymerization (n = 34, 65, and 84). Two series of experiments were conducted to study these diblock copolymers in detail and to compare their properties to two control polymers [PEG-P(AEMA) and P(AEMA)]. First, we demonstrate that the poly(trehalose) coating ensures colloidal stability of polyplexes containing siRNA in the presence of high salt concentrations and serum proteins. Poly(trehalose) retains the ability of trehalose to lower the phase transition energy associated with water freezing and can protect siRNA polyplexes during freeze-drying, allowing complete nanoparticle resuspension without loss of biological function. Second, we show that siRNA polyplexes coated with poly(trehalose) have exceptional cellular internalization into glioblastoma cells that proceeds with zero-order kinetics. Moreover, the amount of siRNA delivered by poly(trehalose) block copolycations can be controlled by the siRNA concentration in cell culture media. Using confocal microscopy we show that trehalose-coated polyplexes undergo active trafficking in cytoplasm upon internalization and significant siRNA-induced target gene down-regulation was achieved with an IC50 of 19 nM. These findings coupled with a negligible cytotoxicity suggests that poly(trehalose) has the potential to serve as an important component of therapeutic nanoparticle formulations of nucleic acids and has great promise to be extended as a new coating for other nanobased technologies and macromolecules, in particular, those related to nanomedicine applications.

Synthesis of a photo-caged aminooxy alkane thiol

A photo-caged aminooxy alkane thiol synthesized in 7 steps and 15% overall yield was used to form a self-assembled monolayer (SAM). Photo-deprotection on the surface was confirmed by FT-IR spectroscopy and contact angle goniometry. Conjugation of a small molecule ketone, ethyl levulinate, further confirmed the presence of aminooxy groups on the surface.

Synthesis of a pyridyl disulfide end-functionalized glycopolymer for conjugation to biomolecules and patterning on gold surfaces

A pyridyl disulfide end-functionalized polymer with N-acetyl-d-glucosamine pendant side-chains was synthesized by atom transfer radical polymerization (ATRP). The glycopolymer was prepared from a pyridyl disulfide initiator catalyzed by a Cu(I)/Cu(II)/2,2'-bipyridine system in a mixture of methanol and water at 30 degrees C. The final polymer had a number-average molecular weight (M(n)) of 13.0 kDa determined by (1)H NMR spectroscopy and a narrow polydispersity index (1.12) determined by gel permeation chromatography (GPC). The pyridyl disulfide end-group was then utilized to conjugate the glycopolymer to a double-stranded short interfering RNA (siRNA). Characterization of the glycopolymer-siRNA by polyacrylamide gel electrophoresis (PAGE) showed 97% conjugation. The activated disulfide polymer was also patterned on gold via microcontact printing. The pyridyl disulfide allowed for ready immobilization of the glycopolymer into 200 microm sized features on the surface.

Synthesis of Aminooxy End-functionalized pNIPAAm by RAFT Polymerization for Protein and Polysaccharide Conjugation

A Boc-protected aminooxy end-functionalized poly(N-isopropylacrylamide) (pNIPAAm) was synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. The monomer was polymerized in the presence of a Boc-protected aminooxy trithiocarbonate chain transfer agent (CTA) utilizing 2,2'-azobis(2-isobutyronitrile) (AIBN) as the initiator in DMF at 70 °C. The final polymer had a number-average molecular weight (M(n)) of 4,200 Da as determined by (1)H NMR spectroscopy and a narrow polydispersity index (1.14) by gel permeation chromatography (GPC). The Boc group was removed, and the polymer was then incubated with N(ε)-levulinyl lysine-modified bovine serum albumin (BSA). Gel electrophoresis confirmed that the conjugation was successful. The aminooxy end-functionalized pNIPAAm was also immobilized on a gold surface after reduction of the trithiocarbonate end-group. The pNIPAAm surface was then incubated with an aldehyde-modified heparin to yield the polysaccharide-functionalized surface. All surface modifications were monitored by FT-IR spectroscopy.

Investigation of a Privileged Polymorphic Motif: a Dimeric ROY Derivative

Bis(5-methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrilyl)acetylene, a derivative of the highly polymorphic compound 5-methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile (ROY) that possesses two chromophores electronically coupled through a triple bond, was found to be trimorphic. Structural data for two of these forms indicates that symmetry is maintained in one structure and broken in the other leading to spontaneous differentiation of the methyl-thiophenecarbonitrile units. This study contributes to the mounting evidence that ROY and its derivatives are particularly prone to polymorphism.