Acetylcarnitine shuttling links mitochondrial metabolism to histone acetylation and lipogenesis

The metabolite acetyl-CoA is necessary for both lipid synthesis in the cytosol and histone acetylation in the nucleus. The two canonical precursors to acetyl-CoA in the nuclear-cytoplasmic compartment are citrate and acetate, which are processed to acetyl-CoA by ATP-citrate lyase (ACLY) and acyl-CoA synthetase short-chain 2 (ACSS2), respectively. It is unclear whether other substantial routes to nuclear-cytosolic acetyl-CoA exist. To investigate this, we generated cancer cell lines lacking both ACLY and ACSS2 [double knockout (DKO) cells]. Using stable isotope tracing, we show that both glucose and fatty acids contribute to acetyl-CoA pools and histone acetylation in DKO cells and that acetylcarnitine shuttling can transfer two-carbon units from mitochondria to cytosol. Further, in the absence of ACLY, glucose can feed fatty acid synthesis in a carnitine responsive and carnitine acetyltransferase (CrAT)-dependent manner. The data define acetylcarnitine as an ACLY- and ACSS2-independent precursor to nuclear-cytosolic acetyl-CoA that can support acetylation, fatty acid synthesis, and cell growth.

Glutamine deprivation triggers NAGK-dependent hexosamine salvage

Tumors frequently exhibit aberrant glycosylation, which can impact cancer progression and therapeutic responses. The hexosamine biosynthesis pathway (HBP) produces uridine diphosphate N-acetylglucosamine (UDP-GlcNAc), a major substrate for glycosylation in the cell. Prior studies have identified the HBP as a promising therapeutic target in pancreatic ductal adenocarcinoma (PDA). The HBP requires both glucose and glutamine for its initiation. The PDA tumor microenvironment is nutrient poor, however, prompting us to investigate how nutrient limitation impacts hexosamine synthesis. Here, we identify that glutamine limitation in PDA cells suppresses de novo hexosamine synthesis but results in increased free GlcNAc abundance. GlcNAc salvage via N-acetylglucosamine kinase (NAGK) is engaged to feed UDP-GlcNAc pools. NAGK expression is elevated in human PDA, and NAGK deletion from PDA cells impairs tumor growth in mice. Together, these data identify an important role for NAGK-dependent hexosamine salvage in supporting PDA tumor growth.

Dietary Protein Restriction Reprograms Tumor-Associated Macrophages and Enhances Immunotherapy

PURPOSE

Diet and healthy weight are established means of reducing cancer incidence and mortality. However, the impact of diet modifications on the tumor microenvironment and antitumor immunity is not well defined. Immunosuppressive tumor-associated macrophages (TAMs) are associated with poor clinical outcomes and are potentially modifiable through dietary interventions. We tested the hypothesis that dietary protein restriction modifies macrophage function toward antitumor phenotypes.

EXPERIMENTAL DESIGN

Macrophage functional status under different tissue culture conditions and in vivo was assessed by Western blot, immunofluorescence, qRT-PCR, and cytokine array analyses. Tumor growth in the context of protein or amino acid (AA) restriction and immunotherapy, namely, a survivin peptide-based vaccine or a PD-1 inhibitor, was examined in animal models of prostate (RP-B6Myc) and renal (RENCA) cell carcinoma. All tests were two-sided.

RESULTS

Protein or AA-restricted macrophages exhibited enhanced tumoricidal, proinflammatory phenotypes, and in two syngeneic tumor models, protein or AA-restricted diets elicited reduced TAM infiltration, tumor growth, and increased response to immunotherapies. Further, we identified a distinct molecular mechanism by which AA-restriction reprograms macrophage function via a ROS/mTOR-centric cascade.

CONCLUSIONS

Dietary protein restriction alters TAM activity and enhances the tumoricidal capacity of this critical innate immune cell type, providing the rationale for clinical testing of this supportive tool in patients receiving cancer immunotherapies.

Genetic susceptibility to toxicity of chemotherapy in mice as pharmacokinetics-independent and drug-specific

e13549

Background: Adverse drug reactions (ADRs) are a significant obstacle in cancer chemotherapy. In spite of the advances in the development of drugs for cancer therapy, ADRs compromise their potential beneficial effects in many patients by imposing reduction of dose or cessation of treatment. Prediction of susceptibility to ADRs in individual patients could significantly improve treatment outcomes by more effectively choosing which drugs to treat with and which dose is appropriate. The pharmacokinetics (PK) of many drugs has been extensively studied and numerous enzymes and transporters that are involved in their activation and processing have been identified. However, when their role in individual susceptibility to ADRs has been tested in numerous studies, the variants of these proteins have not been able to consistently predict specific ADRs. Therefore, additional studies are required for a reliable prediction of toxicity. Methods: We used mouse strains with precisely defined limited genomic differences to evaluate genetic control of ADRs to three drugs commonly used in cancer chemotherapy - irinotecan, gemcitabine, and doxorubicin. We compared strain distribution of susceptibility to ADRs caused by each of these drugs and tested whether there is a correlation with genotypes at the major processing/transport (PK) genes that were reported in humans to affect toxicity of these drugs. Results: The major genetic differences in toxic reactions caused by these drugs do not correlate with the major PK loci and that the strain distribution pattern of susceptibility vs. resistance for each drug is different. Conclusions: This data suggests that a significant part of genetic susceptibility to ADRs is controlled by genes other than the presently known PK-related genes, and that many responsible genes are drug specific, with some possible overlaps. We hypothesize that these genes are likely involved in downstream pharmacodynamic (PD) processes and have remained largely unknown, because most studies in humans have been limited to known PK-related genes. We are proceeding towards identification of these novel genes, as they could help to optimize the selection of therapy for individual patients.