Fatty acid synthase (FASN), the sole cytosolic mammalian enzyme for de novo lipid synthesis, is crucial for cancer cell survival and associates with poor prognosis. FASN overexpression has been found to cause resistance to genotoxic insults. Here we tested the hypothesis that FASN regulates DNA repair to facilitate survival against genotoxic insults and found that FASN suppresses NF-κB but increases specificity protein 1 (SP1) expression. NF-κB and SP1 bind to a composite element in the poly(ADP-ribose) polymerase 1 (PARP-1) promoter in a mutually exclusive manner and regulate PARP-1 expression. Up-regulation of PARP-1 by FASN in turn increases Ku protein recruitment and DNA repair. Furthermore, lipid deprivation suppresses SP1 expression, which is able to be rescued by palmitate supplementation. However, lipid deprivation or palmitate supplementation has no effect on NF-κB expression. Thus, FASN may regulate NF-κB and SP1 expression using different mechanisms. Altogether, we conclude that FASN regulates cellular response against genotoxic insults by up-regulating PARP-1 and DNA repair via NF-κB and SP1.fatty acid synthase | transcription regulation | DNA repair | drug resistance | radiation resistance F atty acid synthase (FASN) is the key mammalian enzyme required for de novo synthesis of palmitate. FASN expression and activity are largely suppressed by sufficient dietary fat in most normal nonadipose tissues but are abnormally elevated in many human cancers and associated with poor prognosis (1). FASN association with poor prognosis may derive in part from FASN function in drug resistance during chemotherapy. Indeed, it has been found that FASN expression and/or activity was increased in drug-selected and -resistant breast (2) and pancreatic (3) cancer cells. It was also found that FASN overexpression causes cellular resistance to DNA-damaging drugs such as doxorubicin and mitoxantrone but not to microtubule modulators such as vinblastine and paclitaxel (4). Decreased ceramide production following doxorubicin treatment via suppression of tumor necrosis factor (TNF)-α production is believed to be one of the mechanisms of FASN-induced resistance to doxorubicin (4).The observation that FASN increases resistance to genotoxic drugs prompted us to hypothesize that FASN overexpression may up-regulate DNA damage response/repair pathways. In this study, we tested this hypothesis with a focus on the repair of DNA double-strand breaks (DSBs), which are commonly induced by the anticancer drugs doxorubicin and mitoxantrone and ionizing radiation. In mammalian cells, DSBs are repaired mainly via homologous recombination (HR) and nonhomologous end-joining (NHEJ) pathways. NHEJ is the predominant form of DSB repair because it occurs during all phases of the cell cycle whereas HR only initiates at late G1 and S phases (5). Hence, we examined NHEJ repair of DSBs and found that FASN up-regulates NHEJ activity and repair of DSBs by increasing poly(ADP-ribose) polymerase 1 (PARP-1) expression via increasing the expression of spec...

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Translation initiation in protein synthesis regulated by eukaryotic initiation factors (eIFs) is a crucial step in controlling gene expression. eIF3a has been shown to regulate protein synthesis and cellular response to treatments by anticancer agents including cisplatin by regulating nucleotide excision repair. In this study, we tested the hypothesis that eIF3a regulates the synthesis of proteins important for the repair of double-strand DNA breaks induced by ionizing radiation (IR). We found that eIF3a upregulation sensitized cellular response to IR while its downregulation caused resistance to IR. eIF3a increases IR-induced DNA damages and decreases non-homologous end joining (NHEJ) activity by suppressing the synthesis of NHEJ repair proteins. Furthermore, analysis of existing patient database shows that eIF3a expression associates with better overall survival of breast, gastric, lung, and ovarian cancer patients. These findings together suggest that eIF3a plays an important role in cellular response to DNA-damaging treatments by regulating the synthesis of DNA repair proteins and, thus, eIIF3a likely contributes to the outcome of cancer patients treated with DNA-damaging strategies including IR.

Purpose: The PI3K pathway is dysregulated in the majority of triple-negative breast cancer(TNBCs), yet single agent inhibition of PI3K has been ineffective in TNBC. PI3K inhibition leads to an immediate compensatory up-regulation of the Wnt pathway. Dual targeting of both pathways is highly synergistic against TNBC models in vitro and in vivo. We initiated a Phase I clinical trial combining gedatolisib, a pan-class I isoform PI3K/mTOR inhibitor, and cofetuzumab pelidotin, an antibody-drug conjugate against the cell-surface PTK7 protein (Wnt pathway co-receptor) with an auristatin payload. Experimental Design: Participants(pts) had metastatic TNBC or ER low (ER and PgR<5%, HER2-negative) breast cancer, and had received at least one prior chemotherapy for advanced disease. The primary objective was safety. Secondary endpoints included objective response(ORR), clinical benefit at 18 weeks(CB18), progression-free survival(PFS), and correlative analyses. Results: 18 pts were enrolled in 3 dose cohorts: gedatolisib 110 mg weekly + cofetuzumab pelidotin 1.4mg/kg every 3 weeks (n=4), 180mg + 1.4mg/kg (n=3), and 180mg + 2.8mg/kg (n=11). Nausea, anorexia, fatigue, and mucositis were common but rarely reached {greater than or equal to} Grade 3 severity. Myelosuppression was uncommon. ORR was 16.7% (3/18). An additional 3 pts had stable disease, of these 2 had stable disease for >18 weeks; CB18 was 27.8%. Median PFS was 2.0 months (95%CI for PFS:1.2-6.2). Pts with clinical benefit were enriched with genomic alterations in the PI3K and PTK7 pathways. Conclusions: The combination of gedatolisib + cofetuzumab pelidotin was well tolerated and demonstrated promising clinical activity. Further investigation of this drug combination in metastatic TNBC is warranted.

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