The PPARγ Agonist Rosiglitazone Suppresses Syngeneic Mouse SCC (Squamous Cell Carcinoma) Tumor Growth through an Immune-Mediated Mechanism

The Loss of PPARγ Expression and Signaling Is a Key Feature of Cutaneous Actinic Disease and Squamous Cell Carcinoma: Association with Tumor Stromal Inflammation

Given the importance of peroxisome proliferator-activated receptor (PPAR)-gamma in epidermal inflammation and carcinogenesis, we analyzed the transcriptomic changes observed in epidermal PPARγ-deficient mice (Pparg-/-epi). A gene set enrichment analysis revealed a close association with epithelial malignancy, inflammatory cell chemotaxis, and cell survival. Single-cell sequencing of Pparg-/-epi mice verified changes to the stromal compartment, including increased inflammatory cell infiltrates, particularly neutrophils, and an increase in fibroblasts expressing myofibroblast marker genes. A comparison of transcriptomic data from Pparg-/-epi and publicly available human and/or mouse actinic keratoses (AKs) and cutaneous squamous cell carcinomas (SCCs) revealed a strong correlation between the datasets. Importantly, PPAR signaling was the top common inhibited canonical pathway in AKs and SCCs. Both AKs and SCCs also had significantly reduced PPARG expression and PPARγ activity z-scores. Smaller reductions in PPARA expression and PPARα activity and increased PPARD expression but reduced PPARδ activation were also observed. Reduced PPAR activity was also associated with reduced PPARα/RXRα activity, while LPS/IL1-mediated inhibition of RXR activity was significantly activated in the tumor datasets. Notably, these changes were not observed in normal sun-exposed skin relative to non-exposed skin. Finally, Ppara and Pparg were heavily expressed in sebocytes, while Ppard was highly expressed in myofibroblasts, suggesting that PPARδ has a role in myofibroblast differentiation. In conclusion, these data provide strong evidence that PPARγ and possibly PPARα represent key tumor suppressors by acting as master inhibitors of the inflammatory changes found in AKs and SCCs.

Peroxisome proliferator-activated receptors: A key link between lipid metabolism and cancer progression

Lipids represent the essential components of membranes, serve as fuels for high-energy processes, and play crucial roles in signaling and cellular function. One of the key hallmarks of cancer is the reprogramming of metabolic pathways, especially abnormal lipid metabolism. Alterations in lipid uptake, lipid desaturation, de novo lipogenesis, lipid droplets, and fatty acid oxidation in cancer cells all contribute to cell survival in a changing microenvironment by regulating feedforward oncogenic signals, key oncogenic functions, oxidative and other stresses, immune responses, or intercellular communication. Peroxisome proliferator-activated receptors (PPARs) are transcription factors activated by fatty acids and act as core lipid sensors involved in the regulation of lipid homeostasis and cell fate. In addition to regulating whole-body energy homeostasis in physiological states, PPARs play a key role in lipid metabolism in cancer, which is receiving increasing research attention, especially the fundamental molecular mechanisms and cancer therapies targeting PPARs. In this review, we discuss how cancer cells alter metabolic patterns and regulate lipid metabolism to promote their own survival and progression through PPARs. Finally, we discuss potential therapeutic strategies for targeting PPARs in cancer based on recent studies from the last five years.

T-box transcription factor 2 mediates antitumor immune response in cutaneous squamous cell carcinoma by regulating the expression of programmed death ligand 1

BACKGROUND

Cutaneous squamous cell carcinoma (CSCC) is the second largest nonmelanoma skin cancer in humans; effective treatment options for metastatic CSCC are still in short. In this study, we aimed to explore the function of T-box transcription factor 2 (TBX2) in CSCC.

METHODS

The expression level of TBX2 was determined in CSCC samples and cell lines. Programmed death ligand 1 (PD-L1) expression was also analyzed in human CSCC samples. Furthermore, SCC13 cells were transfected with TBX2-DN (loss of function) or normal TBX2 to check its role in regulating PD-L1.

RESULTS

The expression level of TBX2 was positively correlated with the stage of CSCC. CSCC tumor cell lines have significantly higher expression levels of TBX2 than normal skin cell lines, and SCC13 cells showed the highest expression. PD-L1 expressions were upregulated during the progression of CSCC, and positively correlated with TBX2. Furthermore, PD-L1 expression increased in SCC13 cells overexpressing TBX2. However, TBX2 did not regulate the activation of IFNγ signal, but mediated the expression of interferon regulatory factor 1 (IRF1) and PD-L1 in both SCC13 and PDV cells.

CONCLUSION

TBX2 could mediate antitumor immune response in CSCC by regulating the expression of PD-L1 through IRF1. It might be a prognostic marker in CSCC and synergistic target for PD-1 immunotherapy.

Investigating Cutaneous Squamous Cell Carcinoma in vitro and in vivo: Novel 3D Tools and Animal Models

Cutaneous Squamous Cell Carcinoma (cSCC) represents the second most common type of skin cancer, which incidence is continuously increasing worldwide. Given its high frequency, cSCC represents a major public health problem. Therefore, to provide the best patients’ care, it is necessary having a detailed understanding of the molecular processes underlying cSCC development, progression, and invasion. Extensive efforts have been made in developing new models allowing to study the molecular pathogenesis of solid tumors, including cSCC tumors. Traditionally, in vitro studies were performed with cells grown in a two-dimensional context, which, however, does not represent the complexity of tumor in vivo. In the recent years, new in vitro models have been developed aiming to mimic the three-dimensionality (3D) of the tumor, allowing the evaluation of tumor cell-cell and tumor-microenvironment interaction in an in vivo-like setting. These models include spheroids, organotypic cultures, skin reconstructs and organoids. Although 3D models demonstrate high potential to enhance the overall knowledge in cancer research, they lack systemic components which may be solved only by using animal models. Zebrafish is emerging as an alternative xenotransplant model in cancer research, offering a high-throughput approach for drug screening and real-time in vivo imaging to study cell invasion. Moreover, several categories of mouse models were developed for pre-clinical purpose, including xeno- and syngeneic transplantation models, autochthonous models of chemically or UV-induced skin squamous carcinogenesis, and genetically engineered mouse models (GEMMs) of cSCC. These models have been instrumental in examining the molecular mechanisms of cSCC and drug response in an in vivo setting. The present review proposes an overview of in vitro, particularly 3D, and in vivo models and their application in cutaneous SCC research.

Epidermal PPARγ Is a Key Homeostatic Regulator of Cutaneous Inflammation and Barrier Function in Mouse Skin

Both agonist studies and loss-of-function models indicate that PPARγ plays an important role in cutaneous biology. Since PPARγ has a high level of basal activity, we hypothesized that epidermal PPARγ would regulate normal homeostatic processes within the epidermis. In this current study, we performed mRNA sequencing and differential expression analysis of epidermal scrapings from knockout mice and wildtype littermates. Pparg-/-^epi mice exhibited a 1.5-fold or greater change in the expression of 11.8% of 14,482 identified transcripts. Up-regulated transcripts included those for a large number of cytokines/chemokines and their receptors, as well as genes associated with inflammasome activation and keratinization. Several of the most dramatically up-regulated pro-inflammatory genes in Pparg-/-^epi mouse skin included Igfl3, 2610528A11Rik, and Il1f6. RT-PCR was performed from RNA obtained from non-lesional full-thickness skin and verified a marked increase in these transcripts, as well as transcripts for Igflr1, which encodes the receptor for Igfl3, and the 2610528A11Rik receptor (Gpr15). Transcripts for Il4 were detected in Pparg-/-^epi mouse skin, but transcripts for Il17 and Il22 were not detected. Down-regulated transcripts included sebaceous gland markers and a number of genes associated with lipid barrier formation. The change in these transcripts correlates with an asebia phenotype, increased transepidermal water loss, alopecia, dandruff, and the appearance of spontaneous inflammatory skin lesions. Histologically, non-lesional skin showed hyperkeratosis, while inflammatory lesions were characterized by dermal inflammation and epidermal acanthosis, spongiosis, and parakeratosis. In conclusion, loss of epidermal Pparg alters a substantial set of genes that are associated with cutaneous inflammation, keratinization, and sebaceous gland function. The data indicate that epidermal PPARγ plays an important role in homeostatic epidermal function, particularly epidermal differentiation, barrier function, sebaceous gland development and function, and inflammatory signaling.

Metabolic regulation of T cells in the tumor microenvironment by nutrient availability and diet

Recent advances in immunotherapies such as immune checkpoint blockade (ICB) and chimeric antigen receptor T cells (CAR-T) for the treatment of cancer have generated excitement over their ability to yield durable, and potentially curative, responses in a multitude of cancers. These findings have established that the immune system is capable of eliminating tumors and led us to a better, albeit still incomplete, understanding of the mechanisms by which tumors interact with and evade destruction by the immune system. Given the central role of T cells in immunotherapy, elucidating the cell intrinsic and extrinsic factors that govern T cell function in tumors will facilitate the development of immunotherapies that establish durable responses in a greater number of patients. One such factor is metabolism, a set of fundamental cellular processes that not only sustains cell survival and proliferation, but also serves as a means for cells to interpret their local environment. Nutrient sensing is critical for T cells that must infiltrate into a metabolically challenging tumor microenvironment and expand under these harsh conditions to eliminate cancerous cells. Here we introduce T cell exhaustion with respect to cellular metabolism, followed by a discussion of nutrient availability at the tumor and organismal level in relation to T cell metabolism and function to provide rationale for the study and targeting of metabolism in anti-tumor immune responses.

Cancer-associated adipocytes as immunomodulators in cancer

Cancer-associated adipocytes (CAAs), as a main component of the tumor-adipose microenvironment (TAME), have various functions, including remodeling the extracellular matrix and interacting with tumor cells or infiltrated leukocytes through a variety of mutual signals. Here, we summarize the primary interplay among CAAs, the immune response and cancer with a focus on the mechanistic aspects of these relationships. Finally, unifying our understanding of CAAs with the immune cell function may be an effective method to enhance the efficacy of immunotherapeutic and conventional treatments.

Evidence for a non-stochastic two-field hypothesis for persistent skin cancer risk

With recurring carcinogen exposures, individual tumors develop in a field of genetic mutations through a stepwise process of clonal expansion and evolution. Once established, this “cancer field” persists in the absence of continued carcinogen exposures, resulting in a sustained risk for cancer development. Using a bioimaging approach, we previously demonstrated that a dermal premalignant field characterized by inflammatory angiogenesis persists following the cessation of ultraviolet light exposures and accurately predicts future overlying epidermal tumor formation. Following ultraviolet light treatments, others have observed that patches of p53 immunopositive cells persist stochastically throughout the epidermal stem cell population. However, these studies were done by random biopsies, introducing sampling bias. We now show that, rather than being randomly distributed, p53⁺ epidermal cells are enriched only in areas overlying this multi-focal dermal field. Moreover, we also show that the dermal field is characterized by a senescent phenotype. We propose that persistence of the overlying epithelial cancerization field in the absence of exogenous carcinogens or promoters requires a two-field composite consisting of a dermal senescent field driving the persistence of the overlying epidermal cancer field. These observations challenge current models that suggest that persistence of cancer risk in the absence of continued carcinogen exposures is simply a function of stochastically arranged, long-lived but dormant epithelial clonal stem cells mutants. The model proposed here could provide new insights into how cancer risk persists following cessation of carcinogenic exposures.

Lipid-mediated regulation of the cancer-immune crosstalk

Besides acting as principle cellular building blocks and energy reservoirs, lipids also carry important signals associated with many fundamental cell biological processes, such as proliferation, differentiation, migration, stress responses and cell demise. Hyperactive lipid metabolism is closely associated with cancer progression and unfavorable outcomes. The underlying mechanisms are being gradually deciphered. In this review, we aim to summarize recent advances on how reprogrammed lipid metabolism and accompanying signaling cascades directly modulate cancer cells, as well as influencing stromal cells and immune cells within the tumor microenvironment. For future studies, special attention should be paid to lipid-mediated crosstalk among cancer cells, their neighboring stromal cells, and immune cells, plus how these multi-level communications determine anti-tumor immunity and bring novel immunotherapeutic opportunities.

FGF2 alters macrophage polarization, tumour immunity and growth and can be targeted during radiotherapy

Regulation of the programming of tumour-associated macrophages (TAMs) controls tumour growth and anti-tumour immunity. We examined the role of FGF2 in that regulation. Tumours in mice genetically deficient in low-molecular weight FGF2 (FGF2^LMW) regress dependent on T cells. Yet, TAMS not T cells express FGF receptors. Bone marrow derived-macrophages from Fgf2^LMW−/− mice co-injected with cancer cells reduce tumour growth and express more inflammatory cytokines. FGF2 is induced in the tumour microenvironment following fractionated radiation in murine tumours consistent with clinical reports. Combination treatment of in vivo tumours with fractionated radiation and a blocking antibody to FGF2 prolongs tumour growth delay, increases long-term survival and leads to a higher iNOS⁺/CD206⁺ TAM ratio compared to irradiation alone. These studies show for the first time that FGF2 affects macrophage programming and is a critical regulator of immunity in the tumour microenvironment.

Macrophages contribute to tumour progression and response to therapy. Here, the authors show that absence of FGF2 in the tumour microenvironment reduces tumour growth and enhances the anti-tumour immune response by altering macrophage polarization. As a result, disruption of this macrophage programming by anti-FGF2 blocking antibodies enhances the outcome from radiotherapy. 

Important players in carcinogenesis as potential targets in cancer therapy: an update

The development of cancer is a problem that has accompanied mankind for years. The growing number of cases, emerging drug resistance, and the need to reduce the serious side effects of pharmacotherapy are forcing scientists to better understand the complex mechanisms responsible for the initiation, promotion, and progression of the disease. This paper discusses the modulation of the particular stages of carcinogenesis by selected physiological factors, including: acetylcholine (ACh), peroxisome proliferator-activated receptors (PPAR), fatty acid-binding proteins (FABPs), Bruton's tyrosine kinase (Btk), aquaporins (AQPs), insulin-like growth factor-2 (IGF-2), and exosomes. Understanding their role may contribute to the development of more effective and safer therapies based on new binding sites.

Association between pioglitazone use and head and neck cancer: Population-based case-control study

BACKGROUND

This study aimed to evaluate the association between pioglitazone use and the occurrence of head and neck cancer.

METHODS

Data for this case-control study were retrieved from the Taiwan National Health Insurance Research Database. A total of 21 464 diabetic patients newly diagnosed with head and neck cancers were identified. We used propensity score matching to select 64 392 comparison patients (3:1 ratio). Multiple logistic regression modeling was used to examine the association of head and neck cancer with pioglitazone use in the 5 years preceding the cancer diagnosis.

RESULTS

Bivariate analysis showed a significant difference in the prevalence of prior using pioglitazone between cases and controls (19.3% vs 18.5%, P < .001) was observed. Multiple regression analysis showed adjusted odds of pioglitazone use of 1.06 (95% CI: 1.02-1.10) among cases relative to controls.

CONCLUSIONS

Prior pioglitazone use was associated with oral cavity cancer.

Myeloid-Derived Suppressor Cells and Pancreatic Cancer: Implications in Novel Therapeutic Approaches

Pancreatic ductal adenocarcinoma (PDAC) remains a devastating human malignancy with poor prognosis and low survival rates. Several cellular mechanisms have been linked with pancreatic carcinogenesis and also implicated in inducing tumor resistance to known therapeutic regimens. Of various factors, immune evasion mechanisms play critical roles in tumor progression and impeding the efficacy of cancer therapies including PDAC. Among immunosuppressive cell types, myeloid-derived suppressor cells (MDSCs) have been extensively studied and demonstrated to not only support PDAC development but also hamper the anti-tumor immune responses elicited by therapeutic agents. Notably, recent efforts have been directed in devising novel approaches to target MDSCs to limit their effects. Multiple strategies including immune-based approaches have been explored either alone or in combination with therapeutic agents to target MDSCs in preclinical and clinical settings of PDAC. The current review highlights the roles and mechanisms of MDSCs as well as the implications of this immunomodulatory cell type as a potential target to improve the efficacy of therapeutic regimens for PDAC.