GREM1 signaling in cancer: tumor promotor and suppressor?

GREMLIN1 (GREM1) is member of a family of structurally and functionally related secreted cysteine knot proteins, which act to sequester and inhibit the action of multifunctional bone morphogenetic proteins (BMPs). GREM1 binds directly to BMP dimers, thereby preventing BMP-mediated activation of BMP type I and type II receptors. Multiple reports identify the overexpression of GREM1 as a contributing factor in a broad range of cancers. Additionally, the GREM1 gene is amplified in a rare autosomal dominant inherited form of colorectal cancer. The inhibitory effects of GREM1 on BMP signaling have been linked to these tumor-promoting effects, including facilitating cancer cell stemness and the activation of cancer-associated fibroblasts. Moreover, GREM1 has been described to bind and signal to vascular endothelial growth factor receptor (VEGFR) and stimulate angiogenesis, as well as epidermal and fibroblast growth factor receptor (EGFR and FGFR) to elicit tumor-promoting effects in breast and prostate cancer, respectively. In contrast, a 2022 report revealed that GREM1 can promote an epithelial state in pancreatic cancers, thereby inhibiting pancreatic tumor growth and metastasis. In this commentary, we will review these disparate findings and attempt to provide clarity around the role of GREM1 signaling in cancer.

CD26-negative and CD26-positive tissue-resident fibroblasts contribute to functionally distinct CAF subpopulations in breast cancer.

Cancer-associated fibroblasts (CAFs) are abundantly present in the microenvironment of virtually all tumors and strongly impact tumor progression. Despite increasing insight into their function and heterogeneity, little is known regarding the origin of CAFs. Understanding the origin of CAF heterogeneity is needed to develop successful CAF-based targeted therapies. Through various transplantation studies in mice, we show that CAFs in both invasive lobular breast cancer and triple-negative breast cancer originate from mammary tissue-resident normal fibroblasts (NFs). Single-cell transcriptomics, in vivo and in vitro studies reveal the transition of CD26+ and CD26- NF populations into inflammatory CAFs (iCAFs) and myofibroblastic CAFs (myCAFs), respectively. Functional co-culture experiments show that CD26+ NFs transition into pro-tumorigenic iCAFs which recruit myeloid cells in a CXCL12-dependent manner and enhance tumor cell invasion via matrix-metalloproteinase (MMP) activity. Together, our data suggest that CD26+ and CD26- NFs transform into distinct CAF subpopulations in mouse models of breast cancer.

The lung fibroblast as "soil fertilizer" in breast cancer metastasis.

Fibroblasts strongly impact tumor progression, but whether they prime the pre-metastatic niche is poorly understood. In this issue of Immunity, Gong and Li et al. identify lung-specific immunosuppressive fibroblasts, which are hijacked by breast cancer cells to facilitate metastasis.

Detection of endogenously circulating mesenchymal stem cells in human cancer patients.

Mesenchymal stem cells (MSCs) can play a vital role in tumor progression and anticancer therapy response, as demonstrated by various in vitro and in vivo model systems. Their ability to home to developing tumors and modulate the tumor microenvironment, by suppressing T-cell responses and contributing to the tumor stroma, is suggested to have a significant impact on disease progression, metastasis formation, and therapy response. Most evidence, however, is derived from artificial models using exogenously administered MSCs. The contribution of endogenous MSCs to tumor progression is currently unclear. Furthermore, few studies have been conducted in humans. A prospective biomarker study was therefore undertaken in 40 human cancer patients and 10 healthy controls of similar age, aimed at (i) exploring and quantifying circulating MSC levels in healthy volunteers and patients with advanced malignancies, (ii) determining the variability of MSC levels between healthy volunteers and cancer patients with different histologic tumor types, and (iii) exploring biomarkers associated with MSC levels. Significantly increased levels of circulating MSC-like cells were observed in cancer patients when compared to healthy individuals (1.72 fold difference, 95% CI 1.03-2.81%, p = 0.03). In addition, prior systemic therapy was associated with a significant increase in MSC-like cells (1.73 fold difference, 95% CI 1.02-2.95, p = 0.04). These results indicate that the amount of endogenously circulating MSCs in humans is increased in response to cancer, and that systemic anticancer treatment can influence MSC levels. Further research is needed to determine whether MSCs have a predictive value.

Phase I study of combined indomethacin and platinum-based chemotherapy to reduce platinum-induced fatty acids.

PURPOSE: Chemotherapy-resistance remains a major obstacle to effective anti-cancer treatment. We previously showed that platinum analogs cause the release of two fatty acids. These platinum-induced fatty acids (PIFAs) induced complete chemoresistance in mice, whereas co-administration of a COX-1 inhibitor, indomethacin, prevented PIFA release and significantly enhanced chemosensitivity. To assess the safety of combining indomethacin with platinum-based chemotherapy, and to explore its efficacy and associated PIFA levels, a multi-center phase I trial was conducted. METHODS: The study was comprised of two arms: oxaliplatin plus capecitabine (CAPOX, arm I) and cisplatin plus gemcitabine, capecitabine or 5FU (arm II) in patients for whom these regimens were indicated as standard care. Indomethacin was escalated from 25 to 75 mg TID, using a standard 3 × 3 design per arm, and was administered orally 8 days around chemo-infusion from cycle two onwards. PIFA levels were measured before and after treatment initiation, with and without indomethacin. RESULTS: Thirteen patients were enrolled, of which ten were evaluable for safety analyses. In arm I, no dose-limiting toxicities were observed, and all indomethacin dose levels were well-tolerated. Partial responses were observed in three patients (30%). Indomethacin lowered plasma levels of 12-S-hydroxy-5,8,10-heptadecatrienoic acid (12-S-HHT), whereas 4,7,10,13-hexadecatetraenoic acid (16:4(n-3)) levels were not affected. Only one patient was included in arm II; renal toxicity led to closure of this cohort. CONCLUSIONS: Combined indomethacin and CAPOX treatment is safe and reduces the concentrations of 12-S-HHT, which may be associated with improved chemosensitivity. The recommended phase II dose is 75 mg indomethacin TID given 8 days surrounding standard dosed CAPOX.

BRCA-deficient mouse mammary tumor organoids to study cancer-drug resistance.

Poly(ADP-ribose) polymerase inhibition (PARPi) is a promising new therapeutic approach for the treatment of cancers that show homologous recombination deficiency (HRD). Despite the success of PARPi in targeting HRD in tumors that lack the tumor suppressor function of BRCA1 or BRCA2, drug resistance poses a major obstacle. We developed three-dimensional cancer organoids derived from genetically engineered mouse models (GEMMs) for BRCA1- and BRCA2-deficient cancers. Unlike conventional cell lines or mammospheres, organoid cultures can be efficiently derived and rapidly expanded in vitro. Orthotopically transplanted organoids give rise to mammary tumors that recapitulate the epithelial morphology and preserve the drug response of the original tumor. Notably, GEMM-tumor-derived organoids can be easily genetically modified, making them a powerful tool for genetic studies of tumor biology and drug resistance.

Fatty acid 16:4(n-3) stimulates a GPR120-induced signaling cascade in splenic macrophages to promote chemotherapy resistance.

Although chemotherapy is designed to eradicate tumor cells, it also has significant effects on normal tissues. The platinum-induced fatty acid 16:4(n-3) (hexadeca-4,7,10,13-tetraenoic acid) induces systemic resistance to a broad range of DNA-damaging chemotherapeutics. We show that 16:4(n-3) exerts its effect by activating splenic F4/80+/CD11blow macrophages, which results in production of chemoprotective lysophosphatidylcholines (LPCs). Pharmacologic studies, together with analysis of expression patterns, identified GPR120 on F4/80+/CD11blow macrophages as the relevant receptor for 16:4(n-3). Studies that used splenocytes from GPR120-deficient mice have confirmed this conclusion. Activation of the 16:4(n-3)-GPR120 axis led to enhanced cPLA2 activity in these splenic macrophages and secretion of the resistance-inducing lipid mediator, lysophosphatidylcholine(24:1). These studies identify a novel and unexpected function for GPR120 and suggest that antagonists of this receptor might be effective agents to limit development of chemotherapy resistance.-Houthuijzen, J. M., Oosterom, I., Hudson, B. D., Hirasawa, A., Daenen, L. G. M., McLean, C. M., Hansen, S. V. F., van Jaarsveld, M. T. M., Peeper, D. S., Jafari Sadatmand, S., Roodhart, J. M. L., van de Lest, C. H. A., Ulven, T., Ishihara, K., Milligan, G., Voest, E. E. Fatty acid 16:4(n-3) stimulates a GPR120-induced signaling cascade in splenic macrophages to promote chemotherapy resistance.

Increased Plasma Levels of Chemoresistance-Inducing Fatty Acid 16:4(n-3) After Consumption of Fish and Fish Oil.

IMPORTANCE: Our research group previously identified specific endogenous platinum-induced fatty acids (PIFAs) that, in picomolar quantities, activate splenic macrophages leading to resistance to chemotherapy in mouse models. Fish oil was shown to contain the PIFA 16:4(n-3) (hexadeca-4,7,10,13-tetraenoic acid) and when administered to mice neutralized chemotherapy activity. OBJECTIVE: Because patients with cancer frequently use fish oil supplements, we set out to determine exposure to 16:4(n-3) after intake of fish or fish oil. DESIGN, SETTING, AND PARTICIPANTS: (1) In November 2011, 400 patients with cancer undergoing treatment at the University Medical Center Utrecht were surveyed to determine their use of fish oil supplements; 118 patients responded to the questionnaire (30%); (2) pharmacokinetic analysis of the 16:4(n-3) content of 6 fish oils and 4 fishes was carried out; (3) from April through November 2012, a healthy volunteer study was performed to determine 16:4(n-3) plasma levels after intake of 3 different brands of fish oil or 4 different fish species. Thirty healthy volunteers were randomly selected for the fish oil study; 20 were randomly selected for the fish study. These studies were supported by preclinical tumor experiments in mice to determine chemoresistance conducted between September 2011 and December 2012. MAIN OUTCOMES AND MEASURES: (1) Rate of use of fish oil supplements among patients undergoing cancer treatment at our institution; (2) levels of 16:4(n-3) present in 3 brands of fish oil and 4 species of fish; and (3) plasma levels of 16:4(n-3) present in healthy volunteers after consuming fish oil or fish. RESULTS: Eleven percent of respondents reported using omega-3 supplements. All fish oils tested contained relevant amounts of 16:4(n-3), from 0.2 to 5.7 µM. Mouse experiments showed that addition of 1 µL of fish oil to cisplatin was sufficient to induce chemoresistance, treatment having no impact on the growth rate of tumors compared with vehicle-treated controls (estimated tumor volume difference, 44.1 mm3; P > .99). When the recommended daily amount of 10 mL of fish oil was administered to healthy volunteers, rises in plasma 16:4(n-3) levels were observed, reaching up to 20 times the baseline levels. Herring and mackerel contained high levels of 16:4(n-3) in contrast to salmon and tuna. Consumption of fish with high levels of 16:4(n-3) also resulted in elevated plasma levels of 16:4(n-3). CONCLUSIONS AND RELEVANCE: All tested fish oils and herring and mackerel fishes contained relevant levels of fatty acid 16:4(n-3), a fatty acid with chemotherapy-negating effects in preclinical models. After ingestion of these fish oils or fishes, 16:4(n-3) was rapidly taken up in the plasma of human volunteers. Until further data become available, fish oil and fish containing high levels of 16:4(n-3) may best be avoided on the days surrounding chemotherapy.

Lysophospholipids secreted by splenic macrophages induce chemotherapy resistance via interference with the DNA damage response.

Host responses to systemic anti-cancer treatment play important roles in the development of anti-cancer drug resistance. Here we show that F4/80(+)/CD11b(low) splenocytes mediate the resistance to DNA-damaging chemotherapeutics induced by two platinum-induced fatty acids (PIFAs), 12-S-keto-5,8,10-heptadecatrienoic acid and 4,7,10,13-hexadecatetraenoic acid (16:4(n-3)) in xenograft mouse models. Splenectomy or depletion of splenic macrophages by liposomal clodronate protects against PIFA-induced chemoresistance. In addition, we find that 12-S-HHT, but not 16:4(n-3), functions via leukotriene B4 receptor 2 (BLT2). Genetic loss or chemical inhibition of BLT2 prevents 12-S-HHT-mediated resistance. Mass spectrometry analysis of conditioned medium derived from PIFA-stimulated splenic macrophages identifies several lysophosphatidylcholines as the resistance-inducing molecules. When comparing cisplatin and PIFA-treated tumours with cisplatin alone treated tumours we found overall less γH2AX, a measure for DNA damage. Taken together, we have identified an intricate network of lysophospholipid signalling by splenic macrophages that induces systemic chemoresistance in vivo via an altered DNA damage response.

Amygdala 14-3-3ζ as a novel modulator of escalating alcohol intake in mice.

Alcoholism is a devastating brain disorder that affects millions of people worldwide. The development of alcoholism is caused by alcohol-induced maladaptive changes in neural circuits involved in emotions, motivation, and decision-making. Because of its involvement in these processes, the amygdala is thought to be a key neural structure involved in alcohol addiction. However, the molecular mechanisms that govern the development of alcoholism are incompletely understood. We have previously shown that in a limited access choice paradigm, C57BL/6J mice progressively escalate their alcohol intake and display important behavioral characteristic of alcohol addiction, in that they become insensitive to quinine-induced adulteration of alcohol. This study used the limited access choice paradigm to study gene expression changes in the amygdala during the escalation to high alcohol consumption in C57BL/6J mice. Microarray analysis revealed that changes in gene expression occurred predominantly after one week, i.e. during the initial escalation of alcohol intake. One gene that stood out from our analysis was the adapter protein 14-3-3ζ, which was up-regulated during the transition from low to high alcohol intake. Independent qPCR analysis confirmed the up-regulation of amygdala 14-3-3ζ during the escalation of alcohol intake. Subsequently, we found that local knockdown of 14-3-3ζ in the amygdala, using RNA interference, dramatically augmented alcohol intake. In addition, knockdown of amygdala 14-3-3ζ promoted the development of inflexible alcohol drinking, as apparent from insensitivity to quinine adulteration of alcohol. This study identifies amygdala 14-3-3ζ as a novel key modulator that is engaged during escalation of alcohol use.

Mesenchymal stem cells induce resistance to chemotherapy through the release of platinum-induced fatty acids.

The development of resistance to chemotherapy is a major obstacle for lasting effective treatment of cancer. Here, we demonstrate that endogenous mesenchymal stem cells (MSCs) become activated during treatment with platinum analogs and secrete factors that protect tumor cells against a range of chemotherapeutics. Through a metabolomics approach, we identified two distinct platinum-induced polyunsaturated fatty acids (PIFAs), 12-oxo-5,8,10-heptadecatrienoic acid (KHT) and hexadeca-4,7,10,13-tetraenoic acid (16:4(n-3)), that in minute quantities induce resistance to a broad spectrum of chemotherapeutic agents. Interestingly, blocking central enzymes involved in the production of these PIFAs (cyclooxygenase-1 and thromboxane synthase) prevents MSC-induced resistance. Our findings show that MSCs are potent mediators of resistance to chemotherapy and reveal targets to enhance chemotherapy efficacy in patients.