Perfluorooctanesulfonic Acid and Perfluorooctanoic Acid Promote Migration of Three-Dimensional Colorectal Cancer Spheroids

Perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA) are persistent environmental contaminants that are of increasing public concern worldwide. However, their relationship with colorectal cancer (CRC) is poorly understood. This study aims to comprehensively investigate the effect of PFOS and PFOA on the development and progression of CRC in vitro using a series of biological techniques and metabolic profiling. Herein, the migration of three-dimensional (3D) spheroids of two CRC cell lines, SW48 KRAS wide-type (WT) and SW48 KRAS G12A, were observed after exposure to PFOS and PFOA at 2 μM and 10 μM for 7 days. The time and dose-dependent migration phenotype induced by 10 μM PFOS and PFOA was further confirmed by wound healing and trans-well migration assays. To investigate the mechanism of action, derivatization-mass spectrometry-based metabolic profiles were examined from 3D spheroids of SW48 cell lines exposed to PFOS and PFOA (2 μM and 10 μM). Our findings revealed this exposure altered epithelial-mesenchymal transition related metabolic pathways, including fatty acid β-oxidation and synthesis of proteins, nucleotides, and lipids. Furthermore, this phenotype was confirmed by the downregulation of E-cadherin and upregulation of N-cadherin and vimentin. These findings show novel insight into the relationship between PFOS, PFOA, and CRC.

Abstract 6030: Asparagine metabolism is linked to sex differences in colorectal cancer growth

Colorectal cancer (CRC) is the third leading cause of cancer-related deaths in men and women in the United States. We have shown that tumors from female CRC patients have increased asparagine (Asn) which is positively associated with poorer overall survival for female patients only (n=196, stage I-III). Furthermore, analysis of asparagine synthetase (ASNS) expression shows that ASNS is similarly associated with poorer survival for females with CRC only. Currently it is not understood why there are sex-specific differences in tumor metabolism of Asn, or the roles of ASNS in CRC progression. Therefore, we hypothesize that limiting ASNS-driven Asn production is a viable target to suppress CRC development in a sex-specific manner. Therefore, we used a combination of in vitro and in vivo models with human CRC ASNS knock out (KO) cells to generate additional hypotheses that may reveal mechanisms that underlie this finding. Using a 3D spheroid model, we cultured HCT116 ASNS KO and isogenic HCT116 ASNS WT cell lines and modulated Asn supply. During 7 days of growth, depletion of Asn slowed the growth of ASNS KO cells compared to WT, whereas Asn supplementation (400 μM) recovered growth in both cell lines; however, spheroid growth was less in the KO cells. Subcutaneous xenograft of these cell lines in male and female mice (n=10/genotype/sex) showed that loss of ASNS reduced tumor burden in both male and female mice, and improved survival in female mice alone. Pathological assessment of tumors indicated poorly differentiated carcinoma and presence of viable tumor mass in both groups. However, the mitotic activity index, and cellular proliferation (measured by Ki67 staining) was significantly reduced in female ASNS KO mice compared to ASNS WT, showing that the tumor cells with ASNS KO are growing slower than those of ASNS WT counterparts. A multi-omics approach was then used to investigate metabolic pathways and signaling networks altered between the tumor genotypes. Tumor tissue metabolomics revealed significant decreases in nucleotides, amino acids, fatty acids within the ASNS KO compared to WT tumors. Using RNA-Seq, gene set enrichment and Ingenuity Pathway Analysis (IPA), data were integrated revealing disruption to Wnt/B-catenin signaling and immune responses associated with ASNS KO in female mice. Serum metabolomics also revealed a higher ratio of circulating glutamine to glutamate in the female mice with ASNS KO xenografts compared to WT, and a decreased expression of the tumor aspartate-glutamate transporter SLC1A3, therefore tumors with ASNS KO could have decreased ability to transport metabolites needed for Asn generation. In summary we identified that lack of ASNS suppresses tumor progression in a pre-clinical CRC model, and significantly improves survival in female mice only. Validation and further mechanistic experiments will reveal the robustness of this finding.

Citation Format: Caroline Johnson, Oladimeji Aladelokun, Sajid Khan. Asparagine metabolism is linked to sex differences in colorectal cancer growth [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6030.

Ferroptosis in colorectal cancer: a future target?

Colorectal cancer (CRC) is the third leading cause of cancer deaths worldwide and is characterised by frequently mutated genes, such as APC, TP53, KRAS and BRAF. The current treatment options of chemotherapy, radiation therapy and surgery are met with challenges such as cancer recurrence, drug resistance, and overt toxicity. CRC therapies exert their efficacy against cancer cells by activating biological pathways that contribute to various forms of regulated cell death (RCD). In 2012, ferroptosis was discovered as an iron-dependent and lipid peroxide-driven form of RCD. Recent studies suggest that therapies which target ferroptosis are promising treatment strategies for CRC. However, a greater understanding of the mechanisms of ferroptosis initiation, propagation, and resistance in CRC is needed. This review provides an overview of recent research in ferroptosis and its potential role as a therapeutic target in CRC. We also propose future research directions that could help to enhance our understanding of ferroptosis in CRC.

Asparagine, colorectal cancer, and the role of sex, genes, microbes, and diet: A narrative review

Asparagine (Asn) and enzymes that catalyze the metabolism of Asn have been linked to the regulation and propagation of colorectal cancer (CRC). Increased Asn and asparagine synthetase (ASNS) expression, both contribute to CRC progression and metastasis. In contradistinction, L-asparaginase (ASNase) which breaks down Asn, exhibits an anti-tumor effect. Metabolic pathways such as KRAS/PI3K/AKT/mTORC1 signaling and high SOX12 expression can positively regulate endogenous Asn production. Conversely, the tumor suppressor, TP53, negatively impacts ASNS, thus limiting Asn synthesis and reducing tumor burden. Asn abundance can be altered by factors extrinsic to the cancer cell such as diet, the microbiome, and therapeutic use of ASNase. Recent studies have shown that sex-related factors can also influence the regulation of Asn, and high Asn production results in poorer prognosis for female CRC patients but not males. In this narrative review, we critically review studies that have examined endogenous and exogenous modulators of Asn bioavailability and summarize the key metabolic networks that regulate Asn metabolism. We also provide new hypotheses regarding sex-related influences on Asn, including the involvement of the sex-steroid hormone estrogen and estrogen receptors. Further, we hypothesize that sex-specific factors that influence Asn metabolism can influence clinical outcomes in CRC patients.

Fatty acid metabolism and colon cancer protection by dietary methyl donor restriction

INTRODUCTION

A methyl donor depleted (MDD) diet dramatically suppresses intestinal tumor development in Apc-mutant mice, but the mechanism of this prevention is not entirely clear.

OBJECTIVES

We sought to gain insight into the mechanisms of cancer suppression by the MDD diet and to identify biomarkers of cancer risk reduction.

METHODS

A plasma metabolomic analysis was performed on Apc^Δ14/+ mice maintained on either a methyl donor sufficient (MDS) diet or the protective MDD diet. A group of MDS animals was also pair-fed with the MDD mice to normalize caloric intake, and another group was shifted from an MDD to MDS diet to determine the durability of the metabolic changes.

RESULTS

In addition to the anticipated changes in folate one-carbon metabolites, plasma metabolites related to fatty acid metabolism were generally decreased by the MDD diet, including carnitine, acylcarnitines, and fatty acids. Some fatty acid selectivity was observed; the levels of cancer-promoting arachidonic acid and 2-hydroxyglutarate were decreased by the MDD diet, whereas eicosapentaenoic acid (EPA) levels were increased. Machine-learning elastic net analysis revealed a positive association between the fatty acid-related compounds azelate and 7-hydroxycholesterol and tumor development, and a negative correlation with succinate and β-sitosterol.

CONCLUSION

Methyl donor restriction causes dramatic changes in systemic fatty acid metabolism. Regulating fatty acid metabolism through methyl donor restriction favorably effects fatty acid profiles to achieve cancer protection.

Lack of Multidrug Resistance-associated Protein 4 Prolongs Partial Hepatectomy-induced Hepatic Steatosis

Multidrug resistance-associated protein 4 (Mrp4) is an efflux transporter involved in the active transport of several endogenous and exogenous chemicals. Previously, we have shown that hepatic Mrp4 expression increases following acetaminophen overdose. In mice, these increases in Mrp4 expression are observed specifically in hepatocytes undergoing active proliferation. From this, we hypothesized that Mrp4 plays a key role in hepatocyte proliferation and that lack of Mrp4 impedes liver regeneration following liver injury and/or tissue loss. To evaluate the role of Mrp4 in these processes, we employed two-third partial hepatectomy (PH) as an experimental liver regeneration model. In this study, we performed PH-surgery on male wildtype (C57BL/6J) and Mrp4 knockout mice. Plasma and liver tissues were collected at 24, 48, and 72 h postsurgery and evaluated for liver injury and liver regeneration endpoints, and for PH-induced hepatic lipid accumulation. Our results show that lack of Mrp4 did not alter hepatocyte proliferation and liver injury following PH as evaluated by Ki-67 antigen staining and plasma alanine aminotransferase levels. To our surprise, Mrp4 knockout mice exhibited increased hepatic lipid content, in particular, di- and triglyceride levels. Gene expression analysis showed that lack of Mrp4 upregulated hepatic lipin1 and diacylglycerol O-acyltransferase 1 and 2 gene expression, which are involved in the synthesis of di- and triglycerides. Our observations indicate that lack of Mrp4 prolonged PH-induced hepatic steatosis in mice and suggest that Mrp4 may be a novel genetic factor in the development of hepatic steatosis.

Methyl Donor Deficiency Blocks Colorectal Cancer Development by Affecting Key Metabolic Pathways

Our understanding of the role of folate one-carbon metabolism in colon carcinogenesis remains incomplete. Previous studies indicate that a methyl donor-deficient (MDD) diet lacking folic acid, choline, methionine, and vitamin B12 is associated with long-lasting changes to the intestinal epithelium and sustained tumor protection in Apc-mutant mice. However, the metabolic pathways by which the MDD diet affects these changes are unknown. Colon samples harvested from Apc^Δ14/+ mice fed the MDD diet for 18 weeks were profiled using a GC-MS and LC-MS/MS metabolomics platform. Random forest and pathway analyses were used to identify altered metabolic pathways, and associated gene expression changes were analyzed by RT-PCR. Approximately 100 metabolites affected by the MDD diet were identified. As expected, metabolites within the methionine cycle, including methionine (-2.9-fold, P < 0.001) and betaine (-3.3-fold, P < 0.001), were reduced. Elevated homocysteine (110-fold, P < 0.001) was associated with increased flux through the transsulfuration pathway. Unexpectedly, levels of deoxycholic acid (-4.5-fold, P < 0.05) and several other secondary bile acids were reduced. There were also unexpected reductions in the levels of carnitine (-2.0-fold, P < 0.01) and a panel of acylcarnitines involved in fatty acid β-oxidation. Finally, metabolites involved in redox balance, including ascorbate and hypotaurine, were found to be persistently elevated. These findings provide clues to the molecular changes underlying MDD-mediated tumor protection and identify regulatable metabolic pathways that may provide new targets for colon cancer prevention and treatment. IMPLICATIONS: Metabolomic profiling reveals molecular changes underlying MDD-induced tumor protection and may provide new targets for colorectal cancer prevention and treatment.

Inhibition of PGE2/EP4 receptor signaling enhances oxaliplatin efficacy in resistant colon cancer cells through modulation of oxidative stress

The platinum-based chemotherapeutic agent, oxaliplatin, is used to treat advanced colorectal cancer (CRC). Unfortunately, nearly all patients acquire resistance to oxaliplatin after long-term use, limiting its therapeutic efficacy. Since COX-2 and PGE₂ signaling can impact colon cancer cell proliferation and survival, we examined how this pathway was affected in an oxaliplatin resistant colon cancer cell line. PGE₂ levels were significantly elevated in oxaliplatin-resistant HT29 cells (OXR) compared to naïve parental HT29 cells (PAR). This increase was associated with elevated COX-2 (17.9-fold; P = 0.008) and reduced 15-hydroxyprostaglandin dehydrogenase (2.9-fold; P < 0.0001) expression. RNAi knockdown of microsomal prostaglandin E synthase-1, the rate-limiting enzyme in PGE₂ synthesis, sensitized OXR cells to oxaliplatin. Downstream effects of PGE₂ in OXR cells were also examined. Selective inhibition of the EP4 PGE₂ receptor by the small molecule inhibitor, L-161,982 enhanced oxaliplatin-induced apoptosis in OXR cells. L-161,982 also reduced expression of the colonic stem cell markers, CD133 and CD44, and inhibited tumor sphere formation. The accumulation of intracellular reactive oxygen species (ROS), a key component of oxaliplatin cytotoxicity, was significantly increased by EP4 inhibition (2.4 -fold; P < 0.0001). Overall, our findings uncover an important role for the COX-2/PGE₂/EP4 signaling axis in oxaliplatin resistance via regulation of oxidative stress.

The Role of Cyclic Nucleotides in Compensatory Hepatocyte Proliferation

BACKGROUND

The study of the mechanisms of liver regeneration is quite an intriguing field that has been extensively modeled. Through the process of compensatory proliferation of the hepatocytes, the liver mass is restored after loss of up to two-thirds of the entire mass. Cyclic nucleotides are intracellular second messengers which are involved in the transduction of a diverse array of stimuli, mediating metabolic and growth regulation. The relationship between cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) signaling and liver regeneration has somehow been elusive to pioneer researchers in the field of liver regeneration. In this review, we will highlight the mechanistic approach involving cyclic nucleotide signaling and its regulation of cell cycle progression in proliferating hepatocytes, highlighting its usefulness to devising therapeutic tools for managing liver diseases.

METHOD

A structured search and review of relevant papers was conducted by the authors.

RESULTS

Authors included forty-two peer-reviewed literature in the review which identified possible roles of cyclic nucleotides in hepatocyte proliferation.

CONCLUSION

This review article confirms the biological importance of cyclic nucleotides and the mediatory growth signaling events that could bring about compensatory proliferation of the liver tissues.