Loss of PHF8 induces a viral mimicry response by activating endogenous retrotransposons.

Immunotherapy has become established as major treatment modality for multiple types of solid tumors, including colorectal cancer. Identifying novel immunotherapeutic targets to enhance anti-tumor immunity and sensitize current immune checkpoint blockade (ICB) in colorectal cancer is needed. Here we report the histone demethylase PHD finger protein 8 (PHF8, KDM7B), a Jumonji C domain-containing protein that erases repressive histone methyl marks, as an essential mediator of immune escape. Ablation the function of PHF8 abrogates tumor growth, activates anti-tumor immune memory, and augments sensitivity to ICB therapy in mouse models of colorectal cancer. Strikingly, tumor PHF8 deletion stimulates a viral mimicry response in colorectal cancer cells, where the depletion of key components of endogenous nucleic acid sensing diminishes PHF8 loss-meditated antiviral immune responses and anti-tumor effects in vivo. Mechanistically, PHF8 inhibition elicits H3K9me3-dependent retrotransposon activation by promoting proteasomal degradation of the H3K9 methyltransferase SETDB1 in a demethylase-independent manner. Moreover, PHF8 expression is anti-correlated with canonical immune signatures and antiviral immune responses in human colorectal adenocarcinoma. Overall, our study establishes PHF8 as an epigenetic checkpoint, and targeting PHF8 is a promising viral mimicry-inducing approach to enhance intrinsic anti-tumor immunity or to conquer immune resistance.

Targeting metabolic vulnerability in mitochondria conquers MEK inhibitor resistance in KRAS-mutant lung cancer.

MEK is a canonical effector of mutant KRAS; however, MEK inhibitors fail to yield satisfactory clinical outcomes in KRAS-mutant cancers. Here, we identified mitochondrial oxidative phosphorylation (OXPHOS) induction as a profound metabolic alteration to confer KRAS-mutant non-small cell lung cancer (NSCLC) resistance to the clinical MEK inhibitor trametinib. Metabolic flux analysis demonstrated that pyruvate metabolism and fatty acid oxidation were markedly enhanced and coordinately powered the OXPHOS system in resistant cells after trametinib treatment, satisfying their energy demand and protecting them from apoptosis. As molecular events in this process, the pyruvate dehydrogenase complex (PDHc) and carnitine palmitoyl transferase IA (CPTIA), two rate-limiting enzymes that control the metabolic flux of pyruvate and palmitic acid to mitochondrial respiration were activated through phosphorylation and transcriptional regulation. Importantly, the co-administration of trametinib and IACS-010759, a clinical mitochondrial complex I inhibitor that blocks OXPHOS, significantly impeded tumor growth and prolonged mouse survival. Overall, our findings reveal that MEK inhibitor therapy creates a metabolic vulnerability in the mitochondria and further develop an effective combinatorial strategy to circumvent MEK inhibitors resistance in KRAS-driven NSCLC.

The oncoprotein BCL6 enables solid tumor cells to evade genotoxic stress.

Genotoxic agents remain the mainstay of cancer treatment. Unfortunately, the clinical benefits are often countered by a rapid tumor adaptive response. Here, we report that the oncoprotein B cell lymphoma 6 (BCL6) is a core component that confers solid tumor adaptive resistance to genotoxic stress. Multiple genotoxic agents promoted BCL6 transactivation, which was positively correlated with a weakened therapeutic efficacy and a worse clinical outcome. Mechanistically, we discovered that treatment with the genotoxic agent etoposide led to the transcriptional reprogramming of multiple pro-inflammatory cytokines, among which the interferon-α and interferon-γ responses were substantially enriched in resistant cells. Our results further revealed that the activation of interferon/signal transducer and activator of transcription 1 axis directly upregulated BCL6 expression. The increased expression of BCL6 further repressed the tumor suppressor PTEN and consequently enabled resistant cancer cell survival. Accordingly, targeted inhibition of BCL6 remarkably enhanced etoposide-triggered DNA damage and apoptosis both in vitro and in vivo. Our findings highlight the importance of BCL6 signaling in conquering solid tumor tolerance to genotoxic stress, further establishing a rationale for a combined approach with genotoxic agents and BCL6-targeted therapy.

Glycochenodeoxycholic acid induces stemness and chemoresistance via the STAT3 signaling pathway in hepatocellular carcinoma cells.

The poor prognosis of hepatocellular carcinoma (HCC) is primarily attributed to its high frequency of recurrence and resistance to chemotherapy. Epithelial-to-mesenchymal transition (EMT) and the acquisition of cancer stem cells (CSCs) are the fundamental drivers of chemoresistance in HCC. Glycochenodeoxycholic acid (GCDC), a component of bile acid (BA), has been reported to induce necrosis in primary human hepatocytes. In the present work, we investigated the function of GCDC in HCC chemoresistance. We found that GCDC promoted chemoresistance in HCC cells by down-regulating and up-regulating the expression of apoptotic and anti-apoptotic genes, respectively. Furthermore, GCDC induced the EMT phenotype and stemness in HCC cells and activated the STAT3 signaling pathway. These findings reveal that GCDC promotes chemoresistance in HCC by inducing stemness via the STAT3 pathway and could be a potential target in HCC chemotherapy.

The Bcr-Abl inhibitor GNF-7 inhibits necroptosis and ameliorates acute kidney injury by targeting RIPK1 and RIPK3 kinases.

Necroptosis is a form of programmed, caspase-independent cell death that is involved in various pathologic disorders such as ischemia/reperfusion injury, acute kidney injury and inflammatory bowel diseases. Identification of necroptosis inhibitors has great therapeutic potential for the treatment of necroptosis-associated diseases. In this study, we identified that the Bcr-Abl inhibitor GNF-7 was a potent inhibitor of necroptosis. GNF-7 inhibited necroptosis in both human and mouse cells, while not protecting cells from apoptosis. Drug affinity responsive target stability assay (DARTS) demonstrated that it binded with RIPK1 and RIPK3. GNF-7 inhibited RIPK1 and RIPK3 kinase activities and thus disrupted RIPK1-RIPK3 necrosome complex formation. In vivo, GNF-7 ameliorated both cisplatin- and ischemia/reperfusion-induced AKI. Orally administration of GNF-7 attenuated renal cell necrosis and reduced pro-inflammatory responses in mouse models of AKI. Taken together, our study shows that GNF-7 is a novel necroptosis inhibitor and has great potential for the treatment of acute renal inflammatory disorders by targeting both RIPK1 and RIPK3 kinases.

N-(7-Cyano-6-(4-fluoro-3-(2-(3-(trifluoromethyl)phenyl)acetamido)phenoxy)benzo[d]thiazol-2-yl)cyclopropanecarboxamide (TAK-632) Analogues as Novel Necroptosis Inhibitors by Targeting Receptor-Interacting Protein Kinase 3 (RIPK3): Synthesis, Structure-Activity Relationships, and in Vivo Efficacy.

Necroptosis, a form of programmed cell death, plays a critical role in various diseases, including inflammatory, infectious, and degenerative diseases. We previously identified N-(7-cyano-6-(4-fluoro-3-(2-(3-(trifluoromethyl)phenyl)acetamido)phenoxy)benzo[d]thiazol-2-yl)cyclopropanecarboxamide (TAK-632) (6) as a potent inhibitor of necroptosis by targeting both receptor-interacting protein kinase 1 (RIPK1) and 3 (RIPK3) kinases. Herein, we performed three rounds of structural optimizations of TAK-632 and elucidated structure-activity relationships to generate more potent inhibitors by targeting RIPK3. The analogues with carbamide groups exhibited great antinecroptotic activities, and compound 42 showed >60-fold selectivity for RIPK3 than RIPK1. It blocked necrosome formation by specifically inhibiting the phosphorylation of RIPK3 in necroptotic cells. In a tumor necrosis factor-induced systemic inflammatory response syndrome model, it significantly protected mice from hypothermia and death at a dose of 5 mg/kg, which was much more effective than TAK-632. Moreover, it showed favorable and druglike pharmacokinetic properties in rats with an oral bioavailability of 25.2%. Thus, these RIPK3-targeting small molecules represent promising lead structures for further development.

Identification of the Raf kinase inhibitor TAK-632 and its analogues as potent inhibitors of necroptosis by targeting RIPK1 and RIPK3.

BACKGROUND AND PURPOSE: Necroptosis is a form of programmed, caspase-independent, cell death, mediated by receptor-interacting protein kinases, RIPK1 and RIPK3, and the mixed lineage kinase domain-like (MLKL). Necroptosis contributes to the pathophysiology of various inflammatory, infectious, and degenerative diseases. Thus, identification of low MW inhibitors for necroptosis has broad therapeutic relevance. Here, we identified that the pan-Raf inhibitor TAK-632 was also an inhibitor of necroptosis. We have further generated a more selective, highly potent analogue of TAK-632 by targeting RIPK1 and RIPK3. EXPERIMENTAL APPROACH: Cell viability was measured by MTT, propidium staining, or CellTiter-Glo luminescent assays. Effects of TAK-632 on necroptosis signalling pathways were investigated by western blotting, immunoprecipitation, and in vitro kinase assays. Downstream targets of TAK-632 were identified by a drug affinity responsive target stability assay and a pull-down assay with biotinylated TAK-632. A mouse model of TNF-α-induced systemic inflammatory response syndrome (SIRS) was further used to explore the role of TAK-632 in protecting against necroptosis-associated inflammation in vivo. KEY RESULTS: TAK-632 protected against necroptosis in human and mouse cells but did not protect cells from apoptosis. TAK-632 directly bound with RIPK1 and RIPK3 to inhibit kinase activities of both enzymes. In vivo, TAK-632 alleviated TNF-induced SIRS. Furthermore, we performed a structure-activity relationship analysis of TAK-632 analogues and generated SZM594, a highly potent inhibitor of RIPK1/3. CONCLUSIONS AND IMPLICATIONS: TAK-632 is an inhibitor of necroptosis and represents a new lead compound in the development of highly potent inhibitors of RIPK1 and RIPK3.