Preferential attachment of peritoneal tumor metastases to omental immune aggregates and possible role of a unique vascular microenvironment in metastatic survival and growth

Pathophysiology of Peritoneal Metastasis

Peritoneal metastasis is the result of a complex, stepwise process that involves multiple, spatially and temporally distinct interactions between the primary cancer, disseminated cancer cells or clusters, and the mesothelial lining of the peritoneal cavity and intraperitoneal organs. The biology of peritoneal metastasis, long a neglected field of research, is now increasingly being unraveled. Here, we provide an update on the mechanisms that drive the journey that eventually leads to widespread peritoneal metastatic disease.

Ablation of hematopoietic stem cell derived adipocytes reduces tumor burden in syngeneic mouse models of high-grade serous carcinoma

In this study we examined the influence of hematopoietic stem cell-derived adipocytes (HSCDAs) on the proliferation and metastasis of high-grade serous carcinoma (HGSC) - the most common type of ovarian cancer. HSCDAs are a subtype of adipocytes that differentiate from myeloid precursors that traffic from bone marrow to adipose tissue and accumulate therein. These are distinct from conventional mesenchymal adipocytes (CMAs), which are derived from mesenchymal precursors. We hypothesized that HSCDAs promote HGSC progression and establish a pro-tumoral niche within peritoneal adipose tissues such as the omentum. Primary human white adipose tissue samples were obtained via biopsy and then sorted into myeloid and mesenchymal populations through flow cytometry. These adipose precursors were then differentiated in vitro into mature HSCDAs and CMAs, respectively. Transcriptomic analysis showed that HSCDAs have a distinct transcriptional profile from CMAs, including downregulation of cell cycle and upregulation of multiple metabolic and adipogenic pathways. Using ELISA, we found that HSCDAs secreted greater amounts of inflammatory cytokines IL-6 and IL-8 than CMAs. Next, we incubated HGSC cells in conditioned media from HSCDAs and CMAs and performed proliferation and protein expression profiling. HGSC cells in HSCDA media, compared to those in CMA media, had elevated expression of protein markers related to epithelial to mesenchymal plasticity, including fibronectin, as well as increased serine phosphorylation of pro-survival AKT1/2. Conversely, HGSC cells in HSCDA media exhibited comparably downregulated expression of tumor suppressors including the Wnt regulator GSK3β. Depending on the cell line and adipose donor, HGSC cells also showed altered growth rates in conditioned media. We next investigated the role of HSCDAs in HGSC progression and metastasis in vivo . We generated immunocompetent mice that were either HSCDA Proficient (can make both adipocyte subtypes) or Deficient (can only make CMAs). Using these models, we conducted two independent tumor studies using the ID8 ( Tp53-/- , Brca2-/- ) and SO ( Tp53-/- , Brca1/2 wild-type, Hras and Myc amplified) syngeneic models. Overall tumor burden was lower in HSCDA Deficient mice in both models. In the ID8 model, omental tumors from HSCDA Deficient mice showed reduced proliferation (Ki67) and apoptosis (cleaved caspase 3) relative to those from Proficient mice. Transcriptionally, omental ID8 tumors from HSCDA Deficient downregulated oxidative phosphorylation, adipogenesis, and fatty acid metabolism relative to tumors from HSCDA Proficient mice. These pathways were enriched in HSCDA cells in vitro , suggesting that ablation of HSCDAs had a significant influence on the tumor metabolic environment. Reduced inflammatory pathways in ID8 tumors from HSCDA Deficient mice were also observed leading us to interrogate immune cell infiltration into omental tumors. Compared to HSCDA Proficient mice, tumors from HSCDA Deficient mice showed reduced densities of dendritic cells (DC) and natural killer (NK) cells, as well as fewer DCs, NKs, and B-cells in proximity to tumor cells, as determined by spatial analysis. Overall, our data suggest that HSCDAs promote HGSC survival and plasticity while downregulating expression of tumor suppressors and altering the peritoneal immune and metabolic environment to promote HGSC progression.

Pathologic Outcomes and Survival in Patients with Rectal Cancer and Increased Body Mass Index

INTRODUCTION

We assessed the association between increased body mass index (BMI) and rectal cancer outcomes.

METHODS

We included patients who underwent surgery for stage I-III rectal adenocarcinoma who were divided according to BMI at diagnosis: ideal BMI (18.5-24.9 kg/m2) and increased BMI (≥25 kg/m2). Groups were compared using univariate association analyses relative to baseline characteristics, pathologic outcomes, overall survival (OS), and disease-free survival (DFS). Main outcome measures involved circumferential resection margin (CRM), pathologic TNM stage, total mesorectal incision (TME) grade, OS, and DFS.

RESULTS

243 patients (64.6% male; median age 59 years) with a median BMI of 26.3 kg/m2 were included. 62.1% had BMI ≥25 kg/m2. Increased BMI patients had similar proportions of males (66.9% vs. 60.9%; p = 0.407) and comorbidities (ASA III: 47% vs. 37.4%; p = 0.24) to ideal BMI patients. There were no significant differences in cN1-2 stage (p = 0.279) or positive CRM (p = 0.062) rates. The groups had similar complete/near-complete TME, pathologic TN stage, and survival rates. Pathologic and survival outcomes were also similar with a BMI cutoff of 30.

CONCLUSIONS

There was a trend toward more nodal involvement in preoperative assessment and less CRM involvement in the final pathology of patients with increased BMI. Complete/near-complete TME and survival rates were comparable between the groups.

Proteobacteria impair anti-tumor immunity in the omentum by consuming arginine

Gut microbiota influence anti-tumor immunity, often by producing immune-modulating metabolites. However, microbes consume a variety of metabolites that may also impact host immune responses. We show that tumors grow unchecked in the omenta of microbe-replete mice due to immunosuppressive Tregs. By contrast, omental tumors in germ-free, neomycin-treated mice or mice colonized with altered Schaedler's flora (ASF) are spontaneously eliminated by CD8+ T cells. These mice lack Proteobacteria capable of arginine catabolism, causing increases in serum arginine that activate the mammalian target of the rapamycin (mTOR) pathway in Tregs to reduce their suppressive capacity. Transfer of the Proteobacteria, Escherichia coli (E. coli), but not a mutant unable to catabolize arginine, to ASF mice reduces arginine levels, restores Treg suppression, and prevents tumor clearance. Supplementary arginine similarly decreases Treg suppressive capacity, increases CD8+ T cell effectiveness, and reduces tumor burden. Thus, microbial consumption of arginine alters anti-tumor immunity, offering potential therapeutic strategies for tumors in visceral adipose tissue.

Development and organization of omental milky spots

The milky spots in omentum are atypical lymphoid tissues that play a pivotal role in regulating immune responses in the peritoneal cavity. The milky spots act as central hubs for collecting antigens and particles from the peritoneal cavity, regulating lymphocyte trafficking, promoting the differentiation and self-renewal of immune cells, and supporting the local germinal centre response. In addition, the milky spots exhibit unique developmental characteristics that combine the features of secondary and tertiary lymphoid tissues. These structures are innately programmed to form during foetal development; however, they can also be formed postnatally in response to peritoneal irritation such as inflammation, infection, obesity, or tumour metastasis. In this review, I discuss emerging perspectives on homeostatic development and organization of the milky spots.

Vagus nerve signal has an inhibitory influence on the development of peritoneal metastasis in murine gastric cancer

The vagus nerve is the only pathway for transmitting parasympathetic signals between the brain and thoracoabdominal organs, thereby exhibiting anti-inflammatory functions through the cholinergic anti-inflammatory pathway. Despite often being resected during lymph node dissection in upper gastrointestinal cancer surgery, the impact of vagotomy on postoperative outcomes in gastric cancer patients remains unclear. Sub-diaphragmatic vagotomy was performed on C57BL/6 mice. Three weeks later, syngeneic murine gastric cancer cell line YTN16P was injected into the peritoneal cavity, and the number of peritoneal metastases (PM) on the mesentery and omentum compared with control mice. The phenotypes of immune cells in peritoneal lavage and omental milky spots one day after tumor inoculation were analyzed using flow cytometry and immunohistochemistry. Intraperitoneal transfer of 3 × 105 YTN16P significantly increased the number of metastatic nodules on the mesentery in the vagotomy group compared to the control group. The omental metastasis grade was also significantly higher in the vagotomy group. Phenotypic analysis of immune cells in peritoneal lavage did not reveal significant differences after vagotomy. However, vagotomized mice exhibited a notable increase in milky spot area, with a higher presence of cytokeratin(+) tumor cells, F4/80(+) macrophages, and CD3(+) T cells. Vagus nerve signaling appears to regulate the immune response dynamics within milky spots against disseminated tumor cells and inhibits the development of PM. Preserving the vagus nerve may offer advantages in advanced gastric cancer surgery to reduce peritoneal recurrence.

Reciprocal crosstalk between Th17 and mesothelial cells promotes metastasis-associated adhesion of ovarian cancer cells

BACKGROUND

IL-17A and TNF synergistically promote inflammation and tumorigenesis. Their interplay and impact on ovarian carcinoma (OC) progression are, however, poorly understood. We addressed this question focusing on mesothelial cells, whose interaction with tumor cells is known to play a pivotal role in transcoelomic metastasis formation.

METHODS

Flow-cytometry and immunohistochemistry experiments were employed to identify cellular sources of IL-17A and TNF. Changes in transcriptomes and secretomes were determined by bulk and single cell RNA sequencing as well as affinity proteomics. Functional consequences were investigated by microscopic analyses and tumor cell adhesion assays. Potential clinical implications were assessed by immunohistochemistry and survival analyses.

RESULTS

We identified Th17 cells as the main population of IL-17A- and TNF producers in ascites and detected their accumulation in early omental metastases. Both IL-17A and its receptor subunit IL-17RC were associated with short survival of OC patients, pointing to a role in clinical progression. IL-17A and TNF synergistically induced the reprogramming of mesothelial cells towards a pro-inflammatory mesenchymal phenotype, concomitantly with a loss of tight junctions and an impairment of mesothelial monolayer integrity, thereby promoting cancer cell adhesion. IL-17A and TNF synergistically induced the Th17-promoting cytokines IL-6 and IL-1β as well as the Th17-attracting chemokine CCL20 in mesothelial cells, indicating a reciprocal crosstalk that potentiates the tumor-promoting role of Th17 cells in OC.

CONCLUSIONS

Our findings reveal a novel function for Th17 cells in the OC microenvironment, which entails the IL-17A/TNF-mediated induction of mesothelial-mesenchymal transition, disruption of mesothelial layer integrity and consequently promotion of OC cell adhesion. These effects are potentiated by a positive feedback loop between mesothelial and Th17 cells. Together with the observed clinical associations and accumulation of Th17 cells in omental micrometastases, our observations point to a potential role in early metastases formation and thus to new therapeutic options.

Greater Omentum: Multifaceted Interactions in Neurological Recovery and Disease Progression

The greater omentum, a unique anatomical structure composed of adipocytes, loose connective tissue, and a dense vascular network. Plays a pivotal role beyond its traditional understanding. It houses specialized immunological units known as 'Milky spots,' making it a key player in immune response. Moreover, the omentum's capacity to enhance tissue perfusion, absorb edema fluid, boost acetylcholine synthesis, and foster neuron repair have rendered it a topic of interest in the context of various diseases, especially neurological disorders. This review provides a comprehensive overview of the intricate anatomy and histology of the greater omentum, casting light on its multifaceted functions and its associations with a spectrum of diseases. With a specific focus on neurological ailments, we delineate the intricate relationship that the omentum shares with other pathologies like stroke and we underly its contribution to serving as a therapeutic agent in neurological disorders. By deciphering the underlying mechanisms and emphasizing areas that demand further investigation. This review aims to spark renewed interest and pave the way for comprehensive studies exploring the greater omentum's potential in neurology and broader medicine overall. Given these diverse interactions that yet remain elusive, we must investigate and understand the nuanced relationship between the greater omentum and pathologies, especially its role in stroke's pathophysiology and therapeutic interventions so as to enhance patient care.

Omental coating attenuates implant-induced foreign body reaction in rats

The objective of this study is to clarify whether the omental coating can effectively attenuate foreign body reaction (FBR) induced by implanted materials. Male Sprague-Dawley rats were injected with polydextran particle slurry intraperitoneally to activate the omentum. 7 days later, polyether polyurethane sponge discs were implanted subcutaneously on each side of the rat's back as the foreign implants to induce FBR. The next day, omental transposition were performed. The disc on the left side of each rat's back was wrapped with omental flap (omental group); the disc on the right side was untreated (control group). All discs were removed 21 days after implantation and assessed by determining the components of the fibrovascular tissue (angiogenesis, inflammation, foreign body giant cells (FBGCs) aggregation and fibrogenesis). In implants in omental group, micro vessel density (MVD), Hemoglobin (Hb) content and VEGF levels (pro-angiogenic cytokine) were increased when compared with implants from control group. Inflammatory parameters (IL-1β; macrophage accumulation-NAG activity; neutrophil accumulation- MPO levels) were decreased in implants after omental coating. Also, collagen deposition, fibrous capsule thickness, and FBGCs decreased in implants from omental group. However, intra-implant levels of TNF-α and TGF-β1 were not different after omental coating. Our findings showed for the first time that the omental coating around the implants attenuate the adverse FBR, it may be critical in developing new strategies to control FBR and improve the function and performance of the implanted materials.

Obesity, Dietary Fats, and Gastrointestinal Cancer Risk-Potential Mechanisms Relating to Lipid Metabolism and Inflammation

Obesity is a major driving factor in the incidence, progression, and poor treatment response in gastrointestinal cancers. Herein, we conducted a comprehensive analysis of the impact of obesity and its resulting metabolic perturbations across four gastrointestinal cancer types, namely, oesophageal, gastric, liver, and colorectal cancer. Importantly, not all obese phenotypes are equal. Obese adipose tissue heterogeneity depends on the location, structure, cellular profile (including resident immune cell populations), and dietary fatty acid intake. We discuss whether adipose heterogeneity impacts the tumorigenic environment. Dietary fat quality, in particular saturated fatty acids, promotes a hypertrophic, pro-inflammatory adipose profile, in contrast to monounsaturated fatty acids, resulting in a hyperplastic, less inflammatory adipose phenotype. The purpose of this review is to examine the impact of obesity, including dietary fat quality, on adipose tissue biology and oncogenesis, specifically focusing on lipid metabolism and inflammatory mechanisms. This is achieved with a particular focus on gastrointestinal cancers as exemplar models of obesity-associated cancers.

Obesity modulates the cellular and molecular microenvironment in the peritoneal cavity: implication for ovarian cancer risk

Introduction

Abdominal obesity increases the risk of developing ovarian cancer but the molecular mechanisms of how obesity supports ovarian cancer development remain unknown. Here we investigated the impact of obesity on the immune cell and gene expression profiles of distinct abdominal tissues, focusing on the peritoneal serous fluid (PSF) and the omental fat band (OFB) as critical determinants for the dissemination of ovarian metastases and early metastatic events within the peritoneal cavity.

Methods

Female C57BL/6 mice were fed a low-fat (LFD) or a high-fat diet (HFD) for 12 weeks until the body weights in the HFD group were significantly higher and the mice displayed an impaired glucose tolerance. Then the mice were injected with the murine ovarian cancer cells (MOSE-LTICv) while remaining on their diets. After 21 days, the mice were sacrificed, tumor burden was evaluated and tissues were harvested. The immune cell composition of abdominal tissues and changes in gene expression in the PSF and OFB were evaluated by flow cytometry and qPCR RT2-profiler PCR arrays and confirmed by qRT-PCR, respectively. Other peritoneal adipose tissues including parametrial and retroperitoneal white adipose tissues as well as blood were also investigated.

Results

While limited effects were observed in the other peritoneal adipose tissues, feeding mice the HFD led to distinct changes in the immune cell composition in the PSF and the OFB: a depletion of B cells but an increase in myeloid-derived suppressor cells (MDSC) and mono/granulocytes, generating pro-inflammatory environments with increased expression of cyto- and chemokines, and genes supporting adhesion, survival, and growth, as well as suppression of apoptosis. This was associated with a higher peritoneal tumor burden compared to mice fed a LFD. Changes in cellular and genetic profiles were often exacerbated by the HFD. There was a large overlap in genes that were modulated by both the HFD and the cancer cells, suggesting that this 'genetic fingerprint' is important for ovarian metastases to the OFB.

Discussion

In accordance with the 'seed and soil' theory, our studies show that obesity contributes to the generation of a pro-inflammatory peritoneal environment that supports the survival of disseminating ovarian cancer cells in the PSF and the OFB and enhances the early metastatic adhesion events in the OFB through an increase in extracellular matrix proteins and modulators such as fibronectin 1 and collagen I expression as well as in genes supporting growth and invasion such as Tenacin C. The identified genes could potentially be used as targets for prevention strategies to lower the ovarian cancer risk in women with obesity.

Loss of B1 and marginal zone B cells during ovarian cancer

Recent advances in immunotherapy have not addressed the challenge presented by ovarian cancer. Although the peritoneum is an "accessible" locus for this disease there has been limited characterization of the immunobiology therein. We investigated the ID8-C57BL/6J ovarian cancer model and found marked depletion of B1 cells from the ascites of the peritoneal cavity. There was also selective loss of the B1 and marginal zone B cell subsets from the spleen. Immunity to antigens that activate these subsets validated their loss rather than relocation. A marked influx of myeloid-derived suppressor cells correlated with B cell subset depletion. These observations are discussed in the context of the housekeeping burden placed on innate B cells during ovarian cancer and to foster consideration of B cell biology in therapeutic strategies to address this challenge.

The impact of body weight on the development of peritoneal metastases in colorectal cancer patients: results from a nationwide cohort study

BACKGROUND

Obesity is a major global health problem and an important risk factor for colorectal cancer (CRC) is increased body weight. Obesity plays a role in the peritoneal dissemination of cancer; however, it is unclear whether this also applies for peritoneal dissemination of CRC. The purpose of this study was to provide insight in the role of obesity on the peritoneal dissemination of colorectal cancer.

METHODS

Of all patients diagnosed with CRC in the Netherlands in the first half of 2015, follow-up data was completed in 2019. Weight at time of primary diagnosis was categorized as underweight, normal weight, overweight, or obese. Logistic regression modelling was used to assess the association between weight and the presence of synchronous colorectal peritoneal metastases (CPM), and Cox regression modelling was used to assess the association between weight and metachronous CPM. Patient and tumor characteristics were taken into account. The analyses were adjusted for tumor stage, nodal stage, tumor location, and tumor histology.

RESULTS

In total, 6436 patients were included in this study. Two-hundred ninety-three (4.6%) patients presented with synchronous CPM at the time of primary diagnosis, while another 278 (5.1%) patients developed metachronous CPM after a median time of 16.5 months. Univariable and multivariable logistic regression modelling did not identify an effect of weight on the presence of synchronous CPM. Neither underweight (odds ratio [OR] 1.10, 95% CI 0.48-2.54), nor overweight (OR 0.96, 95% CI 0.71-1.29), or obesity (OR 0.84, 95% CI 0.56-1.26) was either positively or negatively associated with the presence of synchronous peritoneal metastases as compared to normal weight. Univariable and multivariable Cox regression modelling did not identify an effect of weight on the development of metachronous CPM. Neither underweight (HR 0.162, 95% CI 0.02-1.16), nor overweight (HR 1.07, 95% CI 0.82-1.39), or obesity (HR 1.02, 95% CI 0.73-1.16) was either positively or negatively associated with the presence of synchronous peritoneal metastases as compared to normal weight.

CONCLUSION

CRC patients who are overweight or obese are not more at risk for the presence of synchronous CPM nor development of metachronous CPM than their normal-weight counterparts.

Robotic omentectomy in gynecologic oncology: surgical anatomy, indications, and a technical approach

An omentectomy is a standard component care of gynecological cancers, particularly for surgical staging and treatment for malignant ovarian neoplasms, borderline tumors, fallopian tube cancers, primary peritoneal cancers as well as certain histological subtypes of endometrial cancer. Traditionally, an omentectomy is performed by an open laparotomy approach, however, use of a robotic approach has gained popularity and has been proven to be both safe and effective. In spite of the advantages of robotic surgery compared to laparotomy, the inherent technical challenges of a robotic omentectomy may limit its uptake. In this article, we review (1) the physiology and surgical anatomy of the omentum, (2) the role of the omentum in immune regulation and oncogenesis, (3) indications for an omentectomy in the setting of gynecological malignancy, and (4) describe a step-by-step 3-arm technique for performing both a infracolic and gastrocolic omentectomy procedure using a robotic approach.

Mouse Tissue-Resident Peritoneal Macrophages in Homeostasis, Repair, Infection, and Tumor Metastasis

Large peritoneal macrophages (LPMs) are long-lived, tissue-resident macrophages, formed during embryonic life, developmentally and functionally confined to the peritoneal cavity. LPMs provide the first line of defense against life-threatening pathologies of the peritoneal cavity, such as abdominal sepsis, peritoneal metastatic tumor growth, or peritoneal injuries caused by trauma, or abdominal surgery. Apart from their primary phagocytic function, reminiscent of primitive defense mechanisms sustained by coelomocytes in the coelomic cavity of invertebrates, LPMs fulfill an essential homeostatic function by achieving an efficient clearance of apoptotic, that is crucial for the maintenance of self-tolerance. Research performed over the last few years, in mice, has unveiled the mechanisms by which LPMs fulfill a crucial role in repairing peritoneal injuries and controlling microbial and parasitic infections, reflecting that the GATA6-driven LPM transcriptional program can be modulated by extracellular signals associated with pathological conditions. In contrast, recent experimental evidence supports that peritoneal tumors can subvert LPM metabolism and function, leading to the acquisition of a tumor-promoting potential. The remarkable functional plasticity of LPMs can be nevertheless exploited to revert tumor-induced LPM protumor potential, providing the basis for the development of novel immunotherapeutic approaches against peritoneal tumor metastasis based on macrophage reprogramming.

The molecular biology of peritoneal metastatic disease

Peritoneal metastases are a common form of tumor cell dissemination in gastrointestinal malignancies. Peritoneal metastatic disease (PMD) is associated with severe morbidity and resistance to currently employed therapies. Given the distinct route of dissemination compared with distant organ metastases, and the unique microenvironment of the peritoneal cavity, specific tumor cell characteristics are needed for the development of PMD. In this review, we provide an overview of the known histopathological, genomic, and transcriptomic features of PMD. We find that cancers representing the mesenchymal subtype are strongly associated with PMD in various malignancies. Furthermore, we discuss the peritoneal niche in which the metastatic cancer cells reside, including the critical role of the peritoneal immune system. Altogether, we show that PMD should be regarded as a distinct disease entity, that requires tailored treatment strategies.

Is Routine Omentectomy a Necessary Component of Cytoreductive Surgery and HIPEC?

BACKGROUND

Cytoreductive surgery (CRS) with or without hyperthermic intraperitoneal chemotherapy (HIPEC) for peritoneal metastases traditionally includes omentectomy, even in the absence of visible omental metastases. We sought to determine the rate of occult histologic omental metastasis (OHOM), evaluate morbidity with omentectomy, and examine the rate of omental recurrence among patients undergoing CRS-HIPEC.

METHODS

All CRS-HIPEC procedures from August 2007 to August 2020 were included in this single-center, retrospective, cohort study. Procedures were divided into those that included greater omentectomy (OM) and those that did not (NOM). The incidence of OHOM was evaluated specifically among the OM group with a grossly normal omentum. Multivariate regression analyses were performed to evaluate return of bowel function, ileus, and morbidity in the OM and NOM groups.

RESULTS

Among 683 CRS-HIPEC procedures, 578 (84.6%) included omentectomy and 105 (15.4%) did not. The OM group had higher operative time, blood loss, peritoneal cancer index, number of visceral resections, and length of stay. In the OM group, 72 (12.5%) patients had a grossly normal omentum, and 23 (31.9%) of these had OHOM. Risk-adjusted return of bowel function, ileus, and 60-day complications were no different in the OM and NOM groups. Among 43 patients with residual omentum, 24 (55.8%) recurred, including 9 (20.9%) with omental recurrence.

CONCLUSIONS

Histologically occult metastasis was present in one-third of patients undergoing omentectomy during CRS-HIPEC. Omentectomy did not increase the rate of overall morbidity, and one-fifth of patients with residual omentum later developed omental recurrence. Thus, omentectomy is warranted in the absence of gross metastases during CRS-HIPEC.

Basal cell adhesion molecule promotes metastasis-associated processes in ovarian cancer

BACKGROUND

Basal cell adhesion molecule (BCAM) is a laminin α5 (LAMA5) binding membrane-bound protein with a putative role in cancer. Besides full-length BCAM1, an isoform lacking most of the cytoplasmic domain (BCAM2), and a soluble form (sBCAM) of unknown function are known. In ovarian carcinoma (OC), all BCAM forms are abundant and associated with poor survival, yet BCAM's contribution to peritoneal metastatic spread remains enigmatic.

METHODS

Biochemical, omics-based and real-time cell assays were employed to identify the source of sBCAM and metastasis-related functions of different BCAM forms. OC cells, explanted omentum and a mouse model of peritoneal colonisation were used in loss- and gain-of-function experiments.

RESULTS

We identified ADAM10 as a major BCAM sheddase produced by OC cells and identified proteolytic cleavage sites proximal to the transmembrane domain. Recombinant soluble BCAM inhibited single-cell adhesion and migration identically to membrane-bound isoforms, confirming its biological activity in OC. Intriguingly, this seemingly anti-tumorigenic potential of BCAM contrasts with a novel pro-metastatic function discovered in the present study. Thus, all queried BCAM forms decreased the compactness of tumour cell spheroids by inhibiting LAMA5 - integrin β1 interactions, promoted spheroid dispersion in a three-dimensional collagen matrix, induced clearance of mesothelial cells at spheroid attachment sites in vitro and enhanced invasion of spheroids into omental tissue both ex vivo and in vivo.

CONCLUSIONS

Membrane-bound BCAM as well as sBCAM shed by ADAM10 act as decoys rather than signalling receptors to modulate metastasis-related functions. While BCAM appears to have tumour-suppressive effects on single cells, it promotes the dispersion of OC cell spheroids by regulating LAMA5-integrin-β1-dependent compaction and thereby facilitating invasion of metastatic target sites. As peritoneal dissemination is majorly mediated by spheroids, these findings offer an explanation for the association of BCAM with a poor clinical outcome of OC, suggesting novel therapeutic options.

Intracavitary adoptive transfer of IL-12 mRNA-engineered tumor-specific CD8+ T cells eradicates peritoneal metastases in mouse models

Previous studies have shown that local delivery of tumor antigen-specific CD8⁺ T lymphocytes engineered to transiently express single-chain IL-12 mRNA is highly efficacious. Peritoneal dissemination of cancer is a frequent and often fatal patient condition usually diagnosed when the tumor burden is too large and hence uncontrollable with current treatment options. In this study, we have modeled intracavitary adoptive T cell therapy with OVA-specific OT-I T cells electroporated with IL-12 mRNA to treat B16-OVA and PANC02-OVA tumor spread in the peritoneal cavity. Tumor localization in the omentum and the effects of local T-cell encounter with the tumor antigens were monitored, the gene expression profile evaluated, and the phenotypic reprogramming of several immune subsets was characterized. Intraperitoneal administration of T cells promoted homing to the omentum more effectively than intravenous administration. Transient IL-12 expression was responsible for a favorable reprogramming of the tumor immune microenvironment, longer persistence of transferred T lymphocytes in vivo, and the development of immunity to endogenous antigens following primary tumor eradication. The efficacy of the strategy was at least in part recapitulated with the adoptive transfer of lower affinity transgenic TCR-bearing PMEL-1 T lymphocytes to treat the aggressive intraperitoneally disseminated B16-F10 tumor. Locoregional adoptive transfer of transiently IL-12-armored T cells appears to offer promising therapeutic advantages in terms of anti-tumor efficacy to treat peritoneal carcinomatosis.

Laminins in tumor-derived exosomes upregulated by ETS1 reprogram omental macrophages to promote omental metastasis of ovarian cancer

Tumor-derived exosomes participate in omental metastatic colonization of ovarian cancer by inducing an adaptive response in the tumor microenvironment. However, cell-cell communication via exosomes between primary tumor cells and the microenvironment of distant omentum and the mechanism of pre-metastatic niche formation are poorly understood. Here, we demonstrated that ETS1-overexpressing ovarian cancer cells secreted larger exosomes with higher laminin levels. In addition, ovarian cancer exosomes could be taken up by omental macrophages through integrin and laminin interaction. Compared with control exosomes, exosomes derived from ETS1-overexpressing ovarian cancer cells (LV-ETS1 Exos) stimulated the polarization of more macrophages toward the M2 phenotype (CD163 marker), as well as the production of more CXCL5 and CCL2 in macrophages, via integrin αvβ5/AKT/Sp1 signaling. In vivo experiments showed that LV-ETS1 Exos promoted omental metastasis of ovarian cancer by mediating the tumor-promoting effect of macrophages, which could be neutralized by integrin ανβ5 inhibitor cilengitide. These results indicated that ETS1 could drive ovarian cancer cells to release exosomes with higher laminin levels, thereby accelerating the exosome-mediated pro-metastatic effects of omental macrophages via the integrin αvβ5/AKT/Sp1 signaling pathway, and the integrin ανβ5 inhibitor cilengitide could inhibit omental metastasis of ovarian cancer driven by tumor-derived exosomes.

New Insights into Ferroptosis Initiating Therapies (FIT) by Targeting the Rewired Lipid Metabolism in Ovarian Cancer Peritoneal Metastases

Ovarian cancer is one of the most lethal gynecological cancers worldwide. The poor prognosis of this malignancy is substantially attributed to the inadequate symptomatic biomarkers for early diagnosis and effective remedies to cure the disease against chemoresistance and metastasis. Ovarian cancer metastasis is often relatively passive, and the single clusters of ovarian cancer cells detached from the primary ovarian tumor are transcoelomic spread by the peritoneal fluid throughout the peritoneum cavity and omentum. Our earlier studies revealed that lipid-enriched ascitic/omental microenvironment enforced metastatic ovarian cancer cells to undertake metabolic reprogramming and utilize free fatty acids as the main energy source for tumor progression and aggression. Intriguingly, cell susceptibility to ferroptosis has been tightly correlated with the dysregulated fatty acid metabolism (FAM), and enhanced iron uptake as the prominent features of ferroptosis are attributed to the strengthened lipid peroxidation and aberrant iron accumulation, suggesting that ferroptosis induction is a targetable vulnerability to prevent cancer metastasis. Therefore, the standpoints about tackling altered FAM in combination with ferroptosis initiation as a dual-targeted therapy against advanced ovarian cancer were highlighted herein. Furthermore, a discussion on the prospect and challenge of inducing ferroptosis as an innovative therapeutic approach for reversing remedial resistance in cancer interventions was included. It is hoped this proof-of-concept review will indicate appropriate directions for speeding up the translational application of ferroptosis-inducing compounds (FINs) to improve the efficacy of ovarian cancer treatment.

Integration of Genomic Biology Into Therapeutic Strategies of Gastric Cancer Peritoneal Metastasis

The peritoneum is a common site of metastasis in advanced gastric cancer (GC). Diagnostic laparoscopy is now routinely performed as part of disease staging, leading to an earlier diagnosis of synchronous peritoneal metastasis (PM). The biology of GCPM is unique and aggressive, leading to a dismal prognosis. These tumors tend to be resistant to traditional systemic therapy, and yet, this remains the current standard-of-care recommended by most international clinical guidelines. As this is an area of unmet clinical need, several translational studies and clinical trials have focused on addressing this specific disease state. Advances in genomic sequencing and molecular profiling have revealed several promising therapeutic targets and elucidated novel biology, particularly on the role of the surrounding tumor microenvironment in GCPM. Peritoneal-specific clinical trials are being designed with a combination of locoregional therapeutic strategies with systemic therapy. In this review, we summarize the new knowledge of cancer biology, advances in surgical techniques, and emergence of novel therapies as an integrated strategy emerges to address GCPM as a distinct clinical entity.

Cell origin and niche availability dictate the capacity of peritoneal macrophages to colonize the cavity and omentum

The relationship between macrophages of the peritoneal cavity and the adjacent omentum remains poorly understood. Here, we describe two populations of omental macrophages distinguished by CD102 expression and use an adoptive cell transfer approach to investigate whether these arise from peritoneal macrophages, and whether this depends upon inflammatory status, the origin of peritoneal macrophages and availability of the omental niches. We show that whereas established resident peritoneal macrophages largely fail to migrate to the omentum, monocyte-derived resident cells readily migrate and form a substantial component of omental CD102⁺ macrophages in the months following resolution of peritoneal inflammation. In contrast, both populations had the capacity to migrate to the omentum in the absence of endogenous peritoneal and omental macrophages. However, inflammatory macrophages expanded more effectively and more efficiently repopulated both CD102⁺ and CD102^- omental populations, whereas established resident macrophages partially reconstituted the omental niche via recruitment of monocytes. Hence, cell origin determines the migration of peritoneal macrophages to the omentum and predisposes established resident macrophages to drive infiltration of monocyte-derived cells.

Fat-associated lymphoid clusters as expandable niches for ectopic liver development

BACKGROUND AND AIMS

Hepatocyte transplantation holds great promise as an alternative approach to whole-organ transplantation. Intraportal and intrasplenic cell infusions are primary hepatocyte transplantation delivery routes for this procedure. However, patients with severe liver diseases often have disrupted liver and spleen architectures, which introduce risks in the engraftment process. We previously demonstrated i.p. injection of hepatocytes as an alternative route of delivery that could benefit this subpopulation of patients, particularly if less invasive and low-risk procedures are required; and we have established that lymph nodes may serve as extrahepatic sites for hepatocyte engraftment. However, whether other niches in the abdominal cavity support the survival and proliferation of the transplanted hepatocytes remains unclear.

APPROACH AND RESULTS

Here, we showed that hepatocytes transplanted by i.p. injection engraft and generate ectopic liver tissues in fat-associated lymphoid clusters (FALCs), which are adipose tissue-embedded, tertiary lymphoid structures localized throughout the peritoneal cavity. The FALC-engrafted hepatocytes formed functional ectopic livers that rescued tyrosinemic mice from liver failure. Consistently, analyses of ectopic and native liver transcriptomes revealed a selective ectopic compensatory gene expression of hepatic function-controlling genes in ectopic livers, implying a regulated functional integration between the two livers. The lack of FALCs in the abdominal cavity of immunodeficient tyrosinemic mice hindered ectopic liver development, whereas the restoration of FALC formation through bone marrow transplantation restored ectopic liver development in these mice. Accordingly, induced abdominal inflammation increased FALC numbers, which improved hepatocyte engraftment and accelerated the recovery of tyrosinemic mice from liver failure.

CONCLUSIONS

Abdominal FALCs are essential extrahepatic sites for hepatocyte engraftment after i.p. transplantation and, as such, represent an easy-to-access and expandable niche for ectopic liver regeneration when adequate growth stimulus is present.

Omentum: Friend or foe in ovarian cancer immunotherapy?

Ovarian cancer often spreads out of the ovary before a patient is diagnosed and is the deadliest gynecological malignancy. The aggressiveness of ovarian cancer is determined by the progression in the form of peritoneal carcinomatosis, a stage with a poor prognosis and an untreatable condition in most patients. One of the first tumor nests or the origin of metastasis in the peritoneal cavity is the omentum. The omentum contains immune aggregates, called milky spots, embedded in adipose tissue, which support tumor growth by various mechanisms, including immunosuppressive immune cells and metabolic functions. In this sense, the abundance of blood vessels, omental resident macrophages, and chemokines, among other factors, are known to promote invasiveness, proliferation and resistance to cancer therapies. As a result, surgical practice employed in advanced-stage ovarian cancer almost constantly includes omentectomy. Paradoxically, the omentum is considered the "abdominal policeman" that contributes to peritoneal immunity by capturing antigens and pathogens from the peritoneal cavity and promoting effective immune responses against microbes. Why immunosurveillance against the metastatic tumor does not take place in the omentum? Could omental immune responses be activated with immunotherapeutic interventions? The omentum has largely been ignored in cancer immunology and immunotherapy, and the potential translational implications of this in ovarian cancer are still unclear. Here, we focus on the dual role of the omentum in ovarian cancer: its role in antitumor immune responses versus its activities fostering cancer progression.

Fibrosis of Peritoneal Membrane as Target of New Therapies in Peritoneal Dialysis

Peritoneal dialysis (PD) is an efficient renal replacement therapy for patients with end-stage renal disease. Even if it ensures an outcome equivalent to hemodialysis and a better quality of life, in the long-term, PD is associated with the development of peritoneal fibrosis and the consequents patient morbidity and PD technique failure. This unfavorable effect is mostly due to the bio-incompatibility of PD solution (mainly based on high glucose concentration). In the present review, we described the mechanisms and the signaling pathway that governs peritoneal fibrosis, epithelial to mesenchymal transition of mesothelial cells, and angiogenesis. Lastly, we summarize the present and future strategies for developing more biocompatible PD solutions.

The functional multipotency of transforming growth factor β signaling at the intersection of senescence and cancer

The transforming growth factor β (TGF-β) family of cytokines comprises a group of proteins, their receptors, and effector molecules that, in a coordinated manner, modulate a plethora of physiological and pathophysiological processes. TGF-β1 is the best known and plausibly most active representative of this group. It acts as an immunosuppressant, contributes to extracellular matrix remodeling, and stimulates tissue fibrosis, differentiation, angiogenesis, and epithelial-mesenchymal transition. In recent years, this cytokine has been established as a vital regulator of organismal aging and cellular senescence. Finally, the role of TGF-β1 in cancer progression is no longer in question. Because this protein is involved in so many, often overlapping phenomena, the question arises whether it can be considered a molecular bridge linking some of these phenomena together and governing their reciprocal interactions. In this study, we reviewed the literature from the perspective of the role of various TGF-β family members as regulators of a complex mutual interplay between senescence and cancer. These aspects are then considered in a broader context of remaining TGF-β-related functions and coexisting processes. The main narrative axis in this work is centered around the interaction between the senescence of normal peritoneal cells and ovarian cancer cells. The discussion also includes examples of TGF-β activity at the interface of other normal and cancer cell types.

Angiogenic Role of Mesothelium-Derived Chemokine CXCL1 During Unfavorable Peritoneal Tissue Remodeling in Patients Receiving Peritoneal Dialysis as Renal Replacement Therapy

Peritoneal dialysis (PD) is a valuable ‘home treatment’ option, even more so during the ongoing Coronavirus pandemic. However, the long-term use of PD is limited by unfavourable tissue remodelling in the peritoneal membrane, which is associated with inflammation-induced angiogenesis. This appears to be driven primarily through vascular endothelial growth factor (VEGF), while the involvement of other angiogenic signaling pathways is still poorly understood. Here, we have identified the crucial contribution of mesothelial cell-derived angiogenic CXC chemokine ligand 1 (CXCL1) to peritoneal angiogenesis in PD. CXCL1 expression and peritoneal microvessel density were analysed in biopsies obtained by the International Peritoneal Biobank (NCT01893710 at www.clinicaltrials.gov), comparing 13 children with end-stage kidney disease before initiating PD to 43 children on chronic PD. The angiogenic potential of mesothelial cell-derived CXCL1 was assessed in vitro by measuring endothelial tube formation of human microvascular endothelial cells (HMECs) treated with conditioned medium from human peritoneal mesothelial cells (HPMCs) stimulated to release CXCL1 by treatment with either recombinant IL-17 or PD effluent. We found that the capillary density in the human peritoneum correlated with local CXCL1 expression. Both CXCL1 expression and microvessel density were higher in PD patients than in the age-matched patients prior to initiation of PD. Exposure of HMECs to recombinant CXCL1 or conditioned medium from IL-17-stimulated HPMCs resulted in increased endothelial tube formation, while selective inhibition of mesothelial CXCL1 production by specific antibodies or through silencing of relevant transcription factors abolished the proangiogenic effect of HPMC-conditioned medium. In conclusion, peritoneal mesothelium-derived CXCL1 promotes endothelial tube formation in vitro and associates with peritoneal microvessel density in uremic patients undergoing PD, thus providing novel targets for therapeutic intervention to prolong PD therapy.

Peritoneal Metastasis: Current Status and Treatment Options

Simple Summary

Surgical and locoregional treatments of peritoneal metastasis, e.g., from colorectal cancer, has gained increasing acceptance after the publication of excellent patient outcomes from many groups around the world. Apart from systemic chemotherapy and surgical removal of the tumor, locoregional therapies such as HIPEC or PIPAC may improve tumor control. Understanding the molecular characteristics of peritoneal metastasis is crucial to evolve future therapeutic strategies for peritoneal metastasis. This includes the genetic background of PM, which is often different from other sites of metastasis, and promotes peritoneal dissemination and the growth of tumor cells. Growing knowledge and insight into the physiology of the peritoneal tumor microenvironment and the specific role of the immune system in this compartment may provide a critical step to move locoregional therapy to the next level. This review summarizes the current knowledge and highlights the molecular characteristics of peritoneal metastasis.

Abstract

Peritoneal metastasis (PM) originating from gastrointestinal cancer was considered a terminal disease until recently. The advent of better systemic treatment, a better understanding of prognostic factors, and finally, the advent of novel loco-regional therapies, has opened the door for the multimodal treatment of PM. These strategies, including radical surgery and hyperthermic intraperitoneal chemotherapy (HIPEC) showed surprisingly good results, leading to the prolonged survival of patients with peritoneal metastasis. This has triggered a significant body of research, leading to the molecular characterization of PM, which may further help in the development of novel treatments. This review summarizes current evidence on peritoneal metastasis and explores potential novel mechanisms and therapeutic approaches to treat patients with peritoneal metastasis.

Primary and metastatic peritoneal surface malignancies

Peritoneal surface malignancies comprise a heterogeneous group of primary tumours, including peritoneal mesothelioma, and peritoneal metastases of other tumours, including ovarian, gastric, colorectal, appendicular or pancreatic cancers. The pathophysiology of peritoneal malignancy is complex and not fully understood. The two main hypotheses are the transformation of mesothelial cells (peritoneal primary tumour) and shedding of cells from a primary tumour with implantation of cells in the peritoneal cavity (peritoneal metastasis). Diagnosis is challenging and often requires modern imaging and interventional techniques, including surgical exploration. In the past decade, new treatments and multimodal strategies helped to improve patient survival and quality of life and the premise that peritoneal malignancies are fatal diseases has been dismissed as management strategies, including complete cytoreductive surgery embedded in perioperative systemic chemotherapy, can provide cure in selected patients. Furthermore, intraperitoneal chemotherapy has become an important part of combination treatments. Improving locoregional treatment delivery to enhance penetration to tumour nodules and reduce systemic uptake is one of the most active research areas. The current main challenges involve not only offering the best treatment option and developing intraperitoneal therapies that are equivalent to current systemic therapies but also defining the optimal treatment sequence according to primary tumour, disease extent and patient preferences. New imaging modalities, less invasive surgery, nanomedicines and targeted therapies are the basis for a new era of intraperitoneal therapy and are beginning to show encouraging outcomes.

Immune Niche Within the Peritoneal Cavity

There are numbers of leukocytes present in peritoneal cavity, not only protecting body cavity from infection but also contributing to peripheral immunity including natural antibody production in circulation. The peritoneal leukocytes compose unique immune compartment, the functions of which cannot be replaced by other lymphoid organs. Atypical lymphoid clusters, called "milky spots", that are located in visceral adipose tissue omentum have the privilege of immune niche in terms of differentiation, recruitment, and activation of peritoneal immunity, yet mechanisms underlying the regulation are underexplored. In this review, I discuss the emerging views of peritoneal immune system in the contexts of its development, organization, and functions.

The multicellular signalling network of ovarian cancer metastases

BACKGROUND

Transcoelomic spread is the major route of metastasis of ovarian high-grade serous carcinoma (HGSC) with the omentum as the major metastatic site. Its unique tumour microenvironment with its large populations of adipocytes, mesothelial cells and immune cells establishes an intercellular signaling network that is instrumental for metastatic growth yet poorly understood.

METHODS

Based on transcriptomic analysis of tumour cells, tumour-associated immune and stroma cells we defined intercellular signaling pathways for 284 cytokines and growth factors and their cognate receptors after bioinformatic adjustment for contaminating cell types. The significance of individual components of this network was validated by analysing clinical correlations and potentially pro-metastatic functions, including tumour cell migration, pro-inflammatory signal transduction and TAM expansion.

RESULTS

The data show an unexpected prominent role of host cells, and in particular of omental adipocytes, mesothelial cells and fibroblasts (CAF), in sustaining this signaling network. These cells, rather than tumour cells, are the major source of most cytokines and growth factors in the omental microenvironment (n = 176 vs. n = 13). Many of these factors target tumour cells, are linked to metastasis and are associated with a short survival. Likewise, tumour stroma cells play a major role in extracellular-matrix-triggered signaling. We have verified the functional significance of our observations for three exemplary instances. We show that the omental microenvironment (i) stimulates tumour cell migration and adhesion via WNT4 which is highly expressed by CAF; (ii) induces pro-tumourigenic TAM proliferation in conjunction with high CSF1 expression by omental stroma cells and (iii) triggers pro-inflammatory signaling, at least in part via a HSP70-NF-κB pathway.

CONCLUSIONS

The intercellular signaling network of omental metastases is majorly dependent on factors secreted by immune and stroma cells to provide an environment that supports ovarian HGSC progression. Clinically relevant pathways within this network represent novel options for therapeutic intervention.

Communication, construction, and fluid control: lymphoid organ fibroblastic reticular cell and conduit networks

Fibroblastic reticular cells (FRCs) are a crucial part of the stromal cell infrastructure of secondary lymphoid organs (SLOs). Lymphoid organ fibroblasts form specialized niches for immune cell interactions and thereby govern lymphocyte activation and differentiation. Moreover, FRCs produce and ensheath a network of extracellular matrix (ECM) microfibers called the conduit system. FRC-generated conduits contribute to fluid and immune cell control by funneling fluids containing antigens and inflammatory mediators through the SLOs. We review recent progress in FRC biology that has advanced our understanding of immune cell functions and interactions. We discuss the intricate relationships between the cellular FRC and the fibrillar conduit networks, which together form the basis for efficient communication between immune cells and the tissues they survey.

Potential Role of Diabetes Mellitus-Associated T Cell Senescence in Epithelial Ovarian Cancer Omental Metastasis

Epithelial ovarian cancer (EOC) is one of the most common causes of cancer-related deaths among women and is associated with age and age-related diseases. With increasing evidence of risks associated with metabolic inflammatory conditions, such as obesity and type 2 diabetes mellitus (T2DM), it is important to understand the complex pathophysiological mechanisms underlying cancer progression and metastasis. Age-related conditions can lead to both genotypic and phenotypic immune function alterations, such as induction of senescence, which can contribute to disease progression. Immune senescence is a common phenomenon in the ageing population, which is now known to play a role in multiple diseases, often detrimentally. EOC progression and metastasis, with the highest rates in the 75-79 age group in women, have been shown to be influenced by immune cells within the "milky spots" or immune clusters of the omentum. As T2DM has been reported to cause T cell senescence in both prediabetic and diabetic patients, there is a possibility that poor prognosis in EOC patients with T2DM is partly due to the accumulation of senescent T cells in the omentum. In this review, we explore this hypothesis with recent findings, potential therapeutic approaches, and future directions.

FOXM1: A Multifunctional Oncoprotein and Emerging Therapeutic Target in Ovarian Cancer

Forkhead box M1 (FOXM1) is a member of the conserved forkhead box (FOX) transcription factor family. Over the last two decades, FOXM1 has emerged as a multifunctional oncoprotein and a robust biomarker of poor prognosis in many human malignancies. In this review article, we address the current knowledge regarding the mechanisms of regulation and oncogenic functions of FOXM1, particularly in the context of ovarian cancer. FOXM1 and its associated oncogenic transcriptional signature are enriched in >85% of ovarian cancer cases and FOXM1 expression and activity can be enhanced by a plethora of genomic, transcriptional, post-transcriptional, and post-translational mechanisms. As a master transcriptional regulator, FOXM1 promotes critical oncogenic phenotypes in ovarian cancer, including: (1) cell proliferation, (2) invasion and metastasis, (3) chemotherapy resistance, (4) cancer stem cell (CSC) properties, (5) genomic instability, and (6) altered cellular metabolism. We additionally discuss the evidence for FOXM1 as a cancer biomarker, describe the rationale for FOXM1 as a cancer therapeutic target, and provide an overview of therapeutic strategies used to target FOXM1 for cancer treatment.

Intraperitoneal Glucose Transport to Micrometastasis: A Multimodal In Vivo Imaging Investigation in a Mouse Lymphoma Model

Bc-DLFL.1 is a novel spontaneous, high-grade transplantable mouse B-cell lymphoma model for selective serosal propagation. These cells attach to the omentum and mesentery and show dissemination in mesenteric lymph nodes. We aimed to investigate its early stage spread at one day post-intraperitoneal inoculation of lymphoma cells (n = 18 mice), and its advanced stage at seven days post-inoculation with in vivo [18F]FDG-PET and [18F]PET/MRI, and ex vivo by autoradiography and Cherenkov luminescence imaging (CLI). Of the early stage group, nine animals received intraperitoneal injections, and nine received intravenous [18F]FDG injections. The advanced stage group (n = 3) received intravenous FDG injections. In the early stage, using autoradiography we observed a marked accumulation in the mesentery after intraperitoneal FDG injection. Using other imaging methods and autoradiography, following the intravenous injection of FDG no accumulations were detected. At the advanced stage, tracer accumulation was clearly detected in mesenteric lymph nodes and in the peritoneum after intravenous administration using PET. We confirmed the results with immunohistochemistry. Our results in this model highlight the importance of local FDG administration during diagnostic imaging to precisely assess early peritoneal manifestations of other malignancies (colon, stomach, ovary). These findings also support the importance of applying topical therapies, in addition to systemic treatments in peritoneal cancer spread.

Roles and mechanisms of adipokines in drug resistance of tumor cells

The drug resistance of cancer cells has become one of the biggest obstacles of effective anticancer treatments. Adipocytes produce plenty of cytokines (also known as adipokines), which remarkably affect the drug resistance exhibited by cancer cells. Different adipokines (leptin, visfatin, resistin, adiponectin, Interleukin 6, and tumor necrosis factor α) can induce drug resistance in different cancer cells by various functional mechanisms. This phenomenon is of great interest in pharmacological anti-cancer studies since it indicates that in the cancers with adipocyte-rich microenvironment, all adipokines join together to assist cancer cells to survive by facilitating drug resistance. Studies on adipokines contribute to the development of novel pharmacological strategies for cancer therapy if their roles and molecular targets are better understood. The review will elucidate the roles and the underlying mechanisms of adipokines in drug resistance, which may be of great significance for revealing new strategies for cancer treatment.

Conventional peritoneal cytology lacks the prognostic significance of detecting local or peritoneal recurrence in colorectal cancer: An Egyptian experience

Background and Aim

Colorectal cancer (CRC) accounts for over 8% of all deaths each year, with 1.2 million new cases diagnosed annually worldwide. It represents the seventh most common cancer in Egypt. Early detection of peritoneal metastasis is a major challenge in such cases. It helps with the decision of the immediate application of intraperitoneal chemotherapy after resection. Meta-analysis studies reported contrast evidence for a possible prognostic role of intraperitoneal free cancer cells (IPCCs) in peritoneal recurrence and survival after curative resection. In this work, we aim to evaluate the prevalence and impact of detecting free malignant cells in peritoneal fluid on survival and local recurrence and to estimate the incidence of peritoneal carcinomatosis (PC) during follow up.

Methods

Design: This was a prospective cohort study. Settings: From June 2016 to December 2018, samples were collected from 104 patients who underwent abdominal surgery for colorectal cancer in the Egyptian National Cancer Institute. A total of 96 Egyptian CRC patients who underwent curative resection were enrolled. Intraoperative peritoneal lavage was performed to detect IPCC by conventional cytology. Patients with no residual tumor after surgery and no evidence of PC were followed up for a median 14 months. The cumulative 12-month overall survival rate for patients with IPCC was 100% versus 86% for patients with negative cytology.

Results

Our results demonstrated that the prevalence of IPCC in the peritoneal lavage was 11.5%. Peritoneal and local recurrence occurred at a higher rate in patients with cytology positive lavage (9.1% vs 6.3% and 9.1% vs 3.8%, respectively), although this was statistically insignificant. Distant metastasis occurred significantly in patients with positive cytology (45.5% vs 8.9%) with P-value <0.001.The conventional cytology technique has a high specificity but less sensitivity.

Conclusions

The presence of IPCC using conventional cytology was not an independent prognostic factor for the development of PC or survival.

Obesity and Cancer Metastasis: Molecular and Translational Perspectives

Obesity is a modern health problem that has reached pandemic proportions. It is an established risk factor for carcinogenesis, however, evidence for the contribution of adipose tissue to the metastatic behavior of tumors is also mounting. Over 90% of cancer mortality is attributed to metastasis and metastatic tumor cells must communicate with their microenvironment for survival. Many of the characteristics observed in obese adipose tissue strongly mirror the tumor microenvironment. Thus in the case of prostate, pancreatic and breast cancer and esophageal adenocarcinoma, which are all located in close anatomical proximity to an adipose tissue depot, the adjacent fat provides an ideal microenvironment to enhance tumor growth, progression and metastasis. Adipocytes provide adipokines, fatty acids and other soluble factors to tumor cells whilst immune cells infiltrate the tumor microenvironment. In addition, there are emerging studies on the role of the extracellular vesicles secreted from adipose tissue, and the extracellular matrix itself, as drivers of obesity-induced metastasis. In the present review, we discuss the major mechanisms responsible for the obesity-metastatic link. Furthermore, understanding these complex mechanisms will provide novel therapies to halt the tumor-adipose tissue crosstalk with the ultimate aim of inhibiting tumor progression and metastatic growth.

Where does cellular senescence belong in the pathophysiology of ovarian cancer?

Although ovarian cancer is the leading cause of death from gynecological malignancies, there are still some issues that hamper accurate interpretation of the complexity of cellular and molecular events underlying the pathophysiology of this disease. One of these is cellular senescence, which is the process whereby cells irreversibly lose their ability to divide and develop a phenotype that fuels a variety of age-related diseases, including cancer. In this review, various aspects of cellular senescence associated with intraperitoneal ovarian cancer metastasis are presented and discussed, including mechanisms of senescence in normal peritoneal mesothelial cells; the role of senescent mesothelium in ovarian cancer progression; the effect of drugs commonly used as first-line therapy in ovarian cancer patients on senescence of normal cells; mechanisms of spontaneous senescence in ovarian cancer cells; and, last but not least, other pharmacologic strategies to induce senescence in ovarian malignancies. Collectively, this study shows that cellular senescence is involved in several aspects of ovarian cancer pathobiology. Proper understanding of this phenomenon, particularly its clinical relevance, seems to be critical for oncology patients from both therapeutic and prognostic perspectives.

Lipid Regulatory Proteins as Potential Therapeutic Targets for Ovarian Cancer in Obese Women

Obesity has become a recognized global epidemic that is associated with numerous comorbidities including type II diabetes, cardiovascular disease, hypertension, and cancer incidence and progression. Ovarian cancer (OvCa) has a unique mechanism of intra-peritoneal metastasis, already present in 80% of women at the time of diagnosis, making it the fifth leading cause of death from gynecological malignancy. Meta-analyses showed that obesity increases the risk of OvCa progression, leads to enhanced overall and organ-specific tumor burden, and adversely effects survival of women with OvCa. Recent data discovered that tumors grown in mice fed on a western diet (40% fat) have elevated lipid levels and a highly increased expression level of sterol regulatory element binding protein 1 (SREBP1). SREBP1 is a master transcription factor that regulates de novo lipogenesis and lipid homeostasis, and induces lipogenic reprogramming of tumor cells. Elevated SREBP1 levels are linked to cancer cell proliferation and metastasis. This review will summarize recent findings to provide a current understanding of lipid regulatory proteins in the ovarian tumor microenvironment with emphasis on SREBP1 expression in the obese host, the role of SREBP1 in cancer progression and metastasis, and potential therapeutic targeting of SREBPs and SREBP-pathway genes in treating cancers, particularly in the context of host obesity.

Role of adipose-associated lymphoid tissues in the immunological homeostasis of the serosal surface

Although not typical lymphoid organs, analysis of the visceral adipose-associated lymphoid tissues has recently substantially expanded our knowledge about the immunological features of these elusive compartments. Recent data have highlighted their considerable complexity in cellular organization and interactions in several biological processes, including adaptive immune responses, tissue plasticity to accommodate mesenchymal stem cells and progenitors, and providing a suitable microenvironment for serosal tumor propagation. This review aims to present a comprehensive view of the adipose-associated lymphoid tissues in local and systemic immune responsiveness, with particular emphasis on the omental and mesenteric lymphoid tissues in the serosal defense of abdominal organs.

Adipocytes: active facilitators in epithelial ovarian cancer progression?

There is growing evidence that adipocytes play important roles in the progression of multiple cancers. Moreover, in obesity, adipocytes alter their original functions and contribute to the metabolic and inflammatory changes of adipose tissue microenvironment, which can further enhance tumor development. At present, the roles of adipocytes in the pathogenesis of epithelial ovarian cancer (EOC) are far from being fully elucidated. Herein, we summarized the recent advances in understanding the roles of adipocytes in EOC progression. Adipocytes, close neighbors of EOC tissue, promote EOC growth, invasion, metastasis and angiogenesis through adipokine secretion, metabolic remodeling and immune microenvironment modulation. Moreover, adipocytes are important therapeutic targets and may work as useful anticancer drug delivery depot for EOC treatment. Furthermore, adipocytes also act as a therapeutic obstacle for their involvement in EOC treatment resistance. Hence, better characterization of the adipocytes in EOC microenvironment and the crosstalk between adipocytes and EOC cells may provide insights into EOC progression and suggest novel therapeutic opportunities.

Omental macrophages secrete chemokine ligands that promote ovarian cancer colonization of the omentum via CCR1

The omentum is the most common site of ovarian cancer metastasis. Immune cell clusters called milky spots are found throughout the omentum. It is however unknown if these immune cells contribute to ovarian cancer metastasis. Here we report that omental macrophages promote the migration and colonization of ovarian cancer cells to the omentum through the secretion of chemokine ligands that interact with chemokine receptor 1 (CCR1). We found that depletion of macrophages reduces ovarian cancer colonization of the omentum. RNA-sequencing of macrophages isolated from mouse omentum and mesenteric adipose tissue revealed a specific enrichment of chemokine ligand CCL6 in omental macrophages. CCL6 and the human homolog CCL23 were both necessary and sufficient to promote ovarian cancer migration by activating ERK1/2 and PI3K pathways. Importantly, inhibition of CCR1 reduced ovarian cancer colonization. These findings demonstrate a critical mechanism of omental macrophage induced colonization by ovarian cancer cells via CCR1 signaling.

Krishnan et al. find that CCR1 ligands CCL6 and CCL23 secreted by murine and human macrophages, respectively, enhance metastatic colonization of ovarian cancer cells to the omentum in manner dependent on chemokine receptor 1 (CCR1). This study suggests that targeting CCR1 or CCL23 in ovarian cancer may be a therapeutic strategy.

Specialized immune responses in the peritoneal cavity and omentum

The peritoneal cavity is a fluid filled space that holds most of the abdominal organs, including the omentum, a visceral adipose tissue that contains milky spots or clusters of leukocytes that are organized similar to those in conventional lymphoid tissues. A unique assortment of leukocytes patrol the peritoneal cavity and migrate in and out of the milky spots, where they encounter Ags or pathogens from the peritoneal fluid and respond accordingly. The principal role of leukocytes in the peritoneal cavity is to preserve tissue homeostasis and secure tissue repair. However, when peritoneal homeostasis is disturbed by inflammation, infection, obesity, or tumor metastasis, specialized fibroblastic stromal cells and mesothelial cells in the omentum regulate the recruitment of peritoneal leukocytes and steer their activation in unique ways. In this review, the types of cells that reside in the peritoneal cavity, the role of the omentum in their maintenance and activation, and how these processes function in response to pathogens and malignancy will be discussed.

The influence of secreted factors and extracellular vesicles in ovarian cancer metastasis

Ovarian cancer cells mainly metastasise within the peritoneal cavity, the lethal consequence of tumour progression in this cancer type. Classically, changes in tumour cells, such as epithelial to mesenchymal transition, involve the down-regulatinon of E-cadherin, activation of extracellular proteases and integrin-mediated adhesion. However, our current understanding of ovarian tumour progression suggests the implication of both intrinsic and extrinsic factors. It has been proposed that ovarian cancer metastases are a consequence of the crosstalk between cancer cells and the tumour microenvironment by soluble factors and extracellular vesicles. Characterisation of the alterations in both the tumour cells and the surrounding microenvironment has emerged as a new research field to understand ovarian cancer metastasis. In this mini review, we will summarise the most recent findings, focusing our attention on the role of secreted factors and extracellular vesicles in ovarian cancer metastasis.

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During ovarian cancer metastasis, tumour cells metastasise in the mesothelium as primarily ‘soil’ for ovarian cancer ‘seeds’.

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Soluble factors and extracellular vesicles secreted by tumor cells are involved in the generation of the pre-metastatic niche.

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Cancer-associated fibroblasts (CAFs) represent the majority of stromal cells in various types of human carcinoma, including ovarian cancer.

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Analysis of early metastasis to the omentum indicates that ovarian cancer cells rely on the interaction with immune cells such as macrophages.

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Liquid biopsy analyses in ovarian cancer may help to define novel biomarkers improving patient survival and reduce lethality.

Molecular mediators of peritoneal metastasis in pancreatic cancer

Pancreatic cancer is the third leading cause of cancer death in the USA, and pancreatic ductal adenocarcinoma (PDA) constitutes 85% of pancreatic cancer diagnoses. PDA frequently metastasizes to the peritoneum, but effective treatment of peritoneal metastasis remains a clinical challenge. Despite this unmet need, understanding of the biological mechanisms that contribute to development and progression of PDA peritoneal metastasis is sparse. By contrast, a vast number of studies have investigated mechanisms of peritoneal metastasis in ovarian and gastric cancers. Here, we contrast similarities and differences between peritoneal metastasis in PDA as compared with those in gastric and ovarian cancer by outlining molecular mediators involved in each step of the peritoneal metastasis cascade. This review aims to provide mechanistic insights that could be translated into effective targeted therapies for patients with peritoneal metastasis from PDA.

Spectral photon-counting CT imaging of colorectal peritoneal metastases: initial experience in rats

Computed tomography imaging plays a major role in the preoperative assessment of tumor burden by providing an accurate mapping of the distribution of peritoneal metastases (PM). Spectral Photon Counting Computed Tomography (SPCCT) is an innovative imaging modality that could overcome the current limitations of conventional CT, offering not only better spatial resolution but also better contrast resolution by allowing the discrimination of multiple contrast agents. Based on this capability, we tested the feasibility of SPCCT in the detection of PM at different time of tumor growth in 16 rats inoculated with CC531 cells using dual-contrast injection protocols in two compartments (i.e. intravenous iodine and intraperitoneal gadolinium or the reverse protocol), compared to surgery. For all peritoneal regions and for both protocols, sensitivity was 69%, specificity was 100% and accuracy was 80%, and the correlation with surgical exploration was strong (p = 0.97; p = 0.0001). No significant difference was found in terms of diagnostic performance, quality of peritoneal opacification or diagnostic quality between the 2 injection protocols. We also showed poor vascularization of peritoneal metastases by measuring low concentrations of contrast agent in the largest lesions using SPCCT, which was confirmed by immunohistochemical analyses. In conclusion, SPCCT using dual-contrast agent injection protocols in 2 compartments is a promising imaging modality to assess the extent of PM in a rat model.