Growth Of Colon Cancer Xenografts Research Articles

Targeting POLRMT by IMT1 inhibits colorectal cancer cell growth

This study investigates the potential anti-colorectal cancer (CRC) activity of IMT1, a novel specific inhibitor of mitochondrial RNA polymerase (POLRMT). Single-cell RNA sequencing data reveal that POLRMT is overexpressed in CRC cells. Additionally, elevated POLRMT expression was observed in local CRC tissues and cells, while its expression remained relatively low in colon epithelial tissues and cells. IMT1 significantly inhibited colony formation, cell viability, proliferation, cell cycle progression, and migration in both primary and immortalized CRC cells. Furthermore, IMT1 induced apoptosis and cell death in CRC cells. The inhibition of POLRMT by IMT1 disrupted mitochondrial functions in CRC cells, leading to mitochondrial depolarization, oxidative damage, and decreased ATP levels. Using targeted shRNA to silence POLRMT closely mirrored the effects of IMT1, showing robust anti-CRC cell activity. Crucially, the efficacy of IMT1 was diminished in CRC cells with silenced POLRMT. Contrarily, boosting POLRMT expression externally by a lentiviral construct promoted the proliferation and migration of CRC cells. Importantly, treatment with IMT1 or silencing POLRMT in primary colon cancer cells decreased the phosphorylation of Akt1-S6K1, whereas overexpression of POLRMT had the opposite effect. In nude mice, orally administering IMT1 potently restrained primary colon cancer xenograft growth. IMT1 suppressed POLRMT activity, disrupted mitochondrial function, hindered Akt-mTOR activation, and prompted apoptosis within the xenograft tissues. In addition, IMT1 administration suppressed lung metastasis of primary colon cancer cells in nude mice. These combined results highlight the robust anti-CRC activity of IMT1 by specifically targeting POLRMT.

Integrated network pharmacology and serum metabolomics approach deciphers the anti-colon cancer mechanisms of Huangqi Guizhi Wuwu Decoction.

Huangqi Guizhi Wuwu Decoction (HGWD), as a classic Chinese herbal decoction, has been widely used in treating various diseases for hundreds of years. However, systematically elucidating its mechanisms of action remains a great challenge to the field. In this study, taking advantage of the network pharmacology approach, we discovered a potential new use of HGWD for patients with colon cancer (CC). Our in vivo result showed that orally administered HGWD markedly inhibited the growth of CC xenografts in mice. The subsequent enrichment analyses for the core therapeutic targets revealed that HGWD could affect multiple biological processes involving CC growth, such as metabolic reprogramming, apoptosis and immune regulation, through inhibiting multiple cell survival-related signalings, including MAPK and PI3K-AKT pathways. Notably, these in silico analysis results were most experimentally verified by a series of in vitro assays. Furthermore, our results based on serum metabolomics showed that the lipid metabolic pathways, including fatty acid biosynthesis and cholesterol metabolism, play key roles in delivery of the anti-CC effect of HGWD on tumor-bearing mice, and that cytochrome P450 family 2 subfamily E member 1 (CYP2E1) is a potential therapeutic target. Together, our integrated approach reveals a therapeutic effect of HGWD on CC, providing a valuable insight into developing strategies to predict and interpret the mechanisms of action for Chinese herbal decoctions.

Cyst(e)ine in nutrition formulation promotes colon cancer growth and chemoresistance by activating mTORC1 and scavenging ROS

Weight loss and cachexia are common problems in colorectal cancer patients; thus, parenteral and enteral nutrition support play important roles in cancer care. However, the impact of nonessential amino acid components of nutritional intake on cancer progression has not been fully studied. In this study, we discovered that gastrointestinal cancer patients who received cysteine as part of the parenteral nutrition had shorter overall survival (P < 0.001) than those who did not. Cystine indeed robustly promotes colon cancer cell growth in vitro and in immunodeficient mice, predominately by inhibiting SESN2 transcription via the GCN2-ATF4 axis, resulting in mTORC1 activation. mTORC1 inhibitors Rapamycin and Everolimus block cystine-induced cancer cell proliferation. In addition, cystine confers resistance to oxaliplatin and irinotecan chemotherapy by quenching chemotherapy-induced reactive oxygen species via synthesizing glutathione. We demonstrated that dietary deprivation of cystine suppressed colon cancer xenograft growth without weight loss in mice and boosted the antitumor effect of oxaliplatin. These findings indicate that cyst(e)ine, as part of supplemental nutrition, plays an important role in colorectal cancer and manipulation of cyst(e)ine content in nutritional formulations may optimize colorectal cancer patient survival.

The therapeutic effect of the BRD4-degrading PROTAC A1874 in human colon cancer cells

A1874 is a novel BRD4-degrading proteolysis targeting chimera (PROTAC). In primary colon cancer cells and established HCT116 cells, A1874 potently inhibited cell viability, proliferation, cell cycle progression, as well as cell migration and invasion. The BRD4-degrading PROTAC was able to induce caspase and apoptosis activation in colon cancer cells. Furthermore, A1874-induced degradation of BRD4 protein and downregulated BRD-dependent genes (c-Myc, Bcl-2, and cyclin D1) in colon cancer cells. Significantly, A1874-induced anti-colon cancer cell activity was more potent than the known BRD4 inhibitors (JQ1, CPI203, and I-BET151). In BRD4-knockout colon cancer cells A1874 remained cytotoxic, indicating the existence of BRD4-independent mechanisms. In addition to BRD4 degradation, A1874 cytotoxicity in colon cancer cells was also associated with p53 protein stabilization and reactive oxygen species production. Importantly, the antioxidant N-acetyl-cysteine and the p53 inhibitor pifithrin-α attenuated A1874-induced cell death and apoptosis in colon cancer cells. In vivo, A1874 oral administration potently inhibited colon cancer xenograft growth in severe combined immuno-deficient mice. BRD4 degradation and p53 protein elevation, as well as apoptosis induction and oxidative stress were detected in A1874-treated colon cancer tissues. Together, A1874 inhibits colon cancer cell growth through both BRD4-dependent and -independent mechanisms.

Abstract 1868: B-125, a novel berberine derivative, acts as a better retinoid X receptor a agonist with stronger anti-tumor activity in colon cancer

Abstract Our previous study showed that Berberine binds to RXRα to suppress colon cancer growth (Ruan et. al., Oncogene 2017, 36: 6906). To achieve better RXRα binding activity, stronger anti-tumor effect and higher bioavailability, 21 novel berberine derivatives were designed based on the binding information of berberine to RXRα. Among them B-125 performs the best solubility, RXRE luciferase activity and tumor suppressing ability. NMR and fluorescent titration results show that B-125 retain the similar binding ability to RXRα compared with Berberine. CD study suggests that B-125 has stronger allosteric effect on RXRα than berberine. The bioavailability of B-125 is 25 times higher than berberine. In KM12C colon cancer cells, B-125 performs stronger RXRα dependent inhibitory effects than berberine. In vivo results showed that B-125 inhibits the growth of colon cancer xenograft in nude mice, and the effect is stronger than that of berberine. All the above results indicate that B-125 is a better anti-cancer drug than berberine with better RXRα modulation ability, higher bioavailability and stronger tumor suppressing effect. The study promotes B-125 as a potential novel RXRα based anti-cancer drug in the treatment of colon cancer. Note: This abstract was not presented at the meeting. Citation Format: Beibei Xu, Tian hui Hu, jing Xiong. B-125, a novel berberine derivative, acts as a better retinoid X receptor a agonist with stronger anti-tumor activity in colon cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1868.

Lemongrass Extract Possesses Potent Anticancer Activity Against Human Colon Cancers, Inhibits Tumorigenesis, Enhances Efficacy of FOLFOX, and Reduces Its Adverse Effects.

Current chemotherapeutics for metastatic colorectal cancers have limited success and are extremely toxic due to nonselective targeting. Some natural extracts have been traditionally taken and have shown anticancer activity. These extracts have multiple phytochemicals that can target different pathways selectively in cancer cells. We have shown previously that lemongrass (Cymbopogon citratus) extract is effective at inducing cell death in human lymphomas. However, the efficacy of lemongrass extract on human colorectal cancer has not been investigated. Furthermore, its interactions with current chemotherapies for colon cancer is unknown. In this article, we report the anticancer effects of ethanolic lemongrass extract in colorectal cancer models, and importantly, its interactions with FOLFOX and Taxol. Lemongrass extract induced apoptosis in colon cancer cells in a time and dose-dependent manner without harming healthy cells in vitro. Oral administration of lemongrass extract was well tolerated and effective at inhibiting colon cancer xenograft growth in mice. It enhanced the anticancer efficacy of FOLFOX and, interestingly, inhibited FOLFOX-related weight loss in animals given the combination treatment. Furthermore, feeding lemongrass extract to APCmin/+ transgenic mice led to the reduction of intestinal tumors, indicating its preventative potential. Therefore, this natural extract has potential to be developed as a supplemental treatment for colorectal cancer.

A positive feedback loop between miR-181b and STAT3 that affects Warburg effect in colon cancer via regulating PIAS3 expression.

This study aimed to investigate the relationship between the expression of microRNA (miR)‐181b, protein inhibitor of activated STAT3 (PIAS3) and STAT3, and to examine the function of the miR‐181b/PIAS3/STAT3 axis on the Warburg effect and xenograft tumour growth of colon cancer. Moreover, a positive feedback loop between miR‐181b and STAT3 that regulated the Warburg effect in colon cancer was explored. A luciferase reporter assay was used to identify whether PIAS3 was a direct target of miR‐181b. The gain‐of‐function and loss‐of‐function experiments were performed on HCT 116 cells to investigate the effect of miR‐181b/PIAS3/STAT3 on the Warburg effect and xenograft tumour growth of colon cancer, as determined by commercial kits and xenograft experiments. The relationship between the expression of miR‐181b, PIAS3 and STAT3 in HCT 116 and HT‐29 cells was determined using RT‐qPCR and Western blot. We found miR‐181b was a direct regulator of PIAS3. miR‐181b promoted the Warburg effect and the growth of colon cancer xenografts; however, these effects could be reversed by PIAS3. miR‐181b expression interacted with STAT3 phosphorylation in a positive feedback loop in colon cancer cells via regulating PIAS3 expression. In conclusion, this study for the first time demonstrated that miR‐181b contributed to the Warburg effect and xenograft tumour growth of colon cancer by targeting PIAS3. Moreover, a positive feedback loop between miR‐181b and STAT3 that regulated the Warburg effect in colon cancer was also demonstrated. This study suggested miR‐181b/PIAS3/STAT3 axis as a novel target for colon cancer treatment.

MicroRNA-299-3p suppresses proliferation and invasion by targeting VEGFA in human colon carcinoma

Accumulating evidences have shown that microRNAs (miRNAs) are vital regulators and possess huge capabilities in post-transcriptional control. Although a large number of miRNAs have been identified to be dysregulated in human cancers especially in colon cancer, our understandings of the function of most miRNAs are still largely limited. In this study, we have demonstrated that miR-299-3p plays a critical role in suppressing colon carcinoma progression by targeting Vascular Endothelial Growth Factor A (VEGFA). We observed that miR-299-3p was down-regulated in colon carcinoma tissues and colon cancer cell lines. The level of miR-299-3p was significantly negatively correlated with that of VEGFA mRNA level in colon carcinoma. More importantly, the low level of miR-299-3p predicted poor prognosis of colon cancer patients. Functionally, overexpression of miR-299-3p inhibited the proliferation and invasion of colon carcinoma cells and suppressed the growth of colon cancer xenografts in nude mice. Luciferase reporter assays showed that miR-299-3p could target VEGFA 3′ UTR. In addition, up-regulation of miR-299-3p decreased VEGFA expression both in vitro and in vivo, showing that miR-299-3p plays a suppressive effect on VEGFA via post-transcriptional control. However, ectopical expression of VEGFA could abrogate this effect and also abolish miR-299-3p-induced inhibition of cell proliferation and invasion. Taken together, our study provides evidences showing that miR-299-3p functions as a suppressor in colon cancer by targeting VEGFA, suggesting that miR-299-3p might serve as a novel target for colon cancer therapy.

MicroRNA-645 is an oncogenic regulator in colon cancer

Despite advances in early diagnosis and the development of molecularly targeted therapy, curative treatment of colon cancer once it has metastasized is yet to be accomplished. This is closely associated with deregulated CRC cell proliferation and resistance to apoptosis. Here we reveal that upregulation of microRNA-645 (miR-645) through DNA copy number gain is responsible for enhanced proliferation and resistance to apoptosis in colon cancer. MiR-645 was upregulated in most colon cancer tissues related to adjacent normal mucosa. This appeared to be associated with amplification of a section of chromosome 20q13.13, where miR-645 is located. Inhibition of miR-645 reduced proliferation and enhanced sensitivity to apoptosis triggered by the chemotherapeutic drugs 5-fluorouracil and cisplatin in CRC cells, and retarded colon cancer xenograft growth. Conversely, overexpression of miR-645 in normal colon epithelial cells enhanced proliferation and triggered anchorage-independent cell growth. Although SRY-related HMG-box 30 (SOX30) was identified as a miR-645 target, its expression was only partially affected by miR-645, suggesting that miR-645 is a fine-tuning mechanism of SOX30 expression. Moreover, overexpression of SOX30 only moderately inhibited promotion of CRC cell proliferation by miR-645, indicating that miR-645 may have more targets that contribute to its pro-proliferation effect in colon cancer. Together, this study reveals that miR-645 can regulate oncogenesis in colon cancer with SOX30 being one of its targets.

Inhibition of Hematopoietic Cell Kinase Activity Suppresses Myeloid Cell-Mediated Colon Cancer Progression

Aberrant activation of the SRC family kinase hematopoietic cell kinase (HCK) triggers hematological malignancies as a tumor cell-intrinsic oncogene. Here we find that high HCK levels correlate with reduced survival of colorectal cancer patients. Likewise, increased Hck activity in mice promotes the growth of endogenous colonic malignancies and of human colorectal cancer cell xenografts. Furthermore, tumor-associated macrophages of the corresponding tumors show a pronounced alternatively activated endotype, which occurs independently of mature lymphocytes or of Stat6-dependent Th2 cytokine signaling. Accordingly, pharmacological inhibition or genetic reduction of Hck activity suppresses alternative activation of tumor-associated macrophages and the growth of colon cancer xenografts. Thus, Hck may serve as a promising therapeutic target for solid malignancies.

Colon cancer modulation by a diabetic environment: A single institutional experience.

BackgroundMultiple observational studies suggest an increased risk of colon cancer in patients with diabetes mellitus (DM). This can theoretically be the result of an influence of the diabetic environment on carcinogenesis or the tumor biologic behavior.AimTo gain insight into the influence of a diabetic environment on colon cancer characteristics and outcomes.Material and methodsRetrospective analysis of clinical records in an academic tertiary care hospital with detailed analysis of 81 diabetic patients diagnosed of colon cancer matched with 79 non-diabetic colon cancer patients. The impact of streptozotocin-induced diabetes on the growth of colon cancer xenografts was studied in mice.ResultsThe incidence of DM in 1,137 patients with colorectal cancer was 16%. The diabetic colon cancer cases and non-diabetic colon cancer controls were well matched for demographic and clinical variables. The ECOG Scale Performance Status was higher (worse) in diabetics (ECOG ≥1, 29.1% of controls vs 46.9% of diabetics, p = 0.02), but no significant differences were observed in tumor grade, adjuvant therapy, tumor site, lymphovascular invasion, stage, recurrence, death or cancer-related death. Moreover, no differences in tumor variables were observed between patients treated or not with metformin. In the xenograft model, tumor growth and histopathological characteristics did not differ between diabetic and nondiabetic animals.ConclusionOur findings point towards a mild or negligible effect of the diabetes environment on colon cancer behavior, once cancer has already developed.

FH535 Inhibits Proliferation and Motility of Colon Cancer Cells by Targeting Wnt/β-catenin Signaling Pathway.

Aberrant Wnt/β-catenin pathway activation is frequently observed in human colorectal cancer (CRC) and has become a promising target for CRC treatment. Our study aimed to evaluate the effect of FH535, a small molecule inhibitor of Wnt/β-catenin pathway, on two colon cancer cell lines, HT29 and SW480. We found FH535 significantly inhibited colon cancer cell proliferation in vitro and induced cell cycle arrest. Moreover, FH535 inhibited colon cancer xenograft growth in vivo. Wound-healing assay and Transwell assay revealed that FH535 notably suppressed migration and invasion of SW480 cells. FH535 also repressed expression of cancer stem cell markers, CD24, CD44 and CD133 in HT29 cells. Real time-quantitative PCR and Western blotting revealed that targeting Wnt/β-catenin pathway using FH535 effectively downregulated target genes including cyclin D1 and survivin at mRNA and protein level, which contributed to the FH535-induced inhibitory effect on colon cancer cell proliferation. As mechanisms for suppressing cancer cell motility, FH535 downregulated expression of matrix metalloproteinase-7 and -9, Snail and vimentin. RNA sequencing revealed that FH535 prominently altered multiple biological pathways associated with DNA replication, cell cycle and metabolism. Our study highlights the anti-cancer effect of FH535 on colon cancer and presents its potential in colon cancer treatment.

Long-Lasting WNT-TCF Response Blocking and Epigenetic Modifying Activities of Withanolide F in Human Cancer Cells.

The WNT-TCF signaling pathway participates in adult tissue homeostasis and repair, and is hyperactive in a number of human diseases including cancers of the colon. Whereas to date there are no antagonists approved for patient use, a potential problem for their sustained use is the blockade of WNT signaling in healthy tissues, thus provoking potentially serious co-lateral damage. Here we have screened a library of plant and microorganism small molecules for novel WNT signaling antagonists and describe withanolide F as a potent WNT-TCF response blocker. This steroidal lactone inhibits TCF-dependent colon cancer xenograft growth and mimics the effects of genetic blockade of TCF and of ivermectin, a previously reported WNT-TCF blocker. However, withanolide F is unique in that it imposes a long-lasting repression of tumor growth, WNT-TCF targets and cancer stem cell clonogenicity after drug treatment. These findings are paralleled by its modulation of chromatin regulators and its alteration of overall H3K4me1 levels. Our results open up the possibility to permanently repress essential signaling responses in cancer cells through limited treatments with small molecules.

Abrin P2 suppresses proliferation and induces apoptosis of colon cancer cells via mitochondrial membrane depolarization and caspase activation.

To explore the cytotoxic mechanism of abrin P2 on human colon cancer HCT-8 cells, abrin P2 was isolated from the seed of Abrus precatorius L. It was found that abrin P2 exhibited cytotoxicity toward 12 different human cancer cell lines. Our results demonstrated that abrin P2 suppressed the proliferation of human colon cancer cells (HCT-8 cells) and induced cell cycle arrest at the S and G2/M phases. The mechanism by which abrin P2 inhibited cell proliferation was via the down-regulation of cyclin B1, proliferating cell nuclear antigen and Ki67, as well as the up-regulation of P21. In addition, abrin P2 induced a dose- and time-dependent increase in the rate of HCT-8 cell apoptosis. Treatment with both Z-VAD-FMK, a broad-spectrum caspase inhibitor, and abrin P2 demonstrated that abrin P2 induced HCT-8 cell apoptosis via the activation of caspases. Together, our results revealed that abrin P2-induced apoptosis in HCT-8 cells was associated with the activation of caspases-3/-8/-9, the reduction in the Bcl-2/Bax ratio, the loss of mitochondrial membrane potential, and the increase in cytochrome c release. We further showed that abrin P2 administration effectively suppressed the growth of colon cancer xenografts in nude mice. This is the first report that abrin P2 effectively inhibits colon cancer cell growth in vivo and in vitro by suppressing proliferation and inducing apoptosis.

Novel, isoform-selective, cholecystokinin A receptor antagonist inhibits colon and pancreatic cancers in preclinical models through novel mechanism of action.

Colon and pancreatic cancers contribute to 90,000 deaths each year in the USA. These cancers lack targeted therapeutics due to heterogeneity of the disease and multiple causative factors. One important factor that contributes to increased colon and pancreatic cancer risk is gastrin. Gastrin mediates its actions through two G-protein coupled receptors (GPCRs): cholecystokinin receptor A (CCK-A) and CCK-B/gastrin receptor. Previous studies have indicated that colon cancer predominantly expresses CCK-A and responds to CCK-A isoform antagonists. However, many CCK-A antagonists have failed in the clinic due to poor pharmacokinetic properties or lack of efficacy. In the present study, we synthesized a library of CCK-A isoform-selective antagonists and tested them in various colon and pancreatic cancer preclinical models. The lead CCK-A isoform, selective antagonist PNB-028, bound to CCK-A at 12 nM with a 60-fold selectivity towards CCK-A over CCK-B. Furthermore, it inhibited the proliferation of CCK-A-expressing colon and pancreatic cancer cells without affecting the proliferation of non-cancerous cells. PNB-028 was also extremely effective in inhibiting the growth of MAC-16 and LoVo colon cancer and MIA PaCa pancreatic cancer xenografts in immune-compromised mice. Genome‑wide microarray and kinase-array studies indicate that PNB-028 inhibited oncogenic kinases and angiogenic factors to inhibit the growth of colon cancer xenografts. Safety pharmacology and toxicology studies have indicated that PNB-028 is extremely safe and has a wide safety margin. These studies suggest that targeting CCK-A selectively renders promise to treat colon and pancreatic cancers and that PNB-028 could become the next-generation treatment option.

INPP4B is an oncogenic regulator in human colon cancer.

Inositol polyphosphate 4-phosphatase type II (INPP4B) negatively regulates phosphatidylinositol 3-kinase signaling and is a tumor suppressor in some types of cancers. However, we have found that it is frequently upregulated in human colon cancer cells. Here we show that silencing of INPP4B blocks activation of Akt and serum- and glucocorticoid-regulated kinase 3 (SGK3), inhibits colon cancer cell proliferation and retards colon cancer xenograft growth. Conversely, overexpression of INPP4B increases proliferation and triggers anchorage-independent growth of normal colon epithelial cells. Moreover, we demonstrate that the effect of INPP4B on Akt and SGK3 is associated with inactivation of phosphate and tensin homolog through its protein phosphatase activity and that the increase in INPP4B is due to Ets-1-mediated transcriptional upregulation in colon cancer cells. Collectively, these results suggest that INPP4B may function as an oncogenic driver in colon cancer, with potential implications for targeting INPP4B as a novel approach to treat this disease.

The Inhibitory Efficacy of Methylseleninic Acid Against Colon Cancer Xenografts in C57BL/6 Mice

Data indicate that methylselenol is a critical selenium (Se) metabolite for anticancer activity in vivo. We tested the hypothesis that oral dosing methylseleninic acid (MSeA), a methylselenol precursor, inhibits the growth of colon cancer xenografts in C57BL/6 mice fed a Se adequate diet. In this study, MSeA supplementation was given by an oral dose (0, 1, or 3 mg/kg body weight) regimen. MSeA increased Se content of liver, kidney, muscle, stomach (w/intestine) and plasma, and elevated blood glutathione peroxidase (GPx) activities. However, MSeA did not change lean/fat body composition, food consumption, levels of plasma leptin/adiponectin, and body weight gain. MSeA (3 mg/kg body weight) inhibited tumor growth up to 61% when compared to the control group, and this inhibition was associated with a reduction of plasma tumor necrosis factor (TNFα)/interleukin 6 (IL6) level but elevated blood GPx activities. In addition, MSeA (1 mg/kg body weight) increased the activation of caspase-3, a major apoptotic enzyme, in tumor tissues. Taken together, our MSeA oral dosing regimen was at safe levels; and high blood GPx activities, caspase-3 activities in tumor tissue and a reduction of plasma TNFα/IL6 level, play critical roles in inhibiting colon tumor growth in an immune-competent C57BL/6 mouse model.

Obesity-Related Colorectal Cancer: The Role of Leptin.

Obesity is linked to increased risk of colon cancer. Consequently, rising levels of obesity worldwide are likely to have a significant impact on obesity-related colon cancers in the decades to come. Understanding the molecular mechanisms whereby obesity increases the risk of colon cancer is, thus, a focus for research on strategies to prevent the increasing trend in obesity-related cancers. The epidemiological evidence clearly indicates common factors linking obesity and colon cancer. Both are associated with consumption of high-energy diets, a sedentary lifestyle, increased age and reduced consumption of fruit, vegetables and fiber [1-3]. All these factors influence adipose tissue, now firmly established as the body’s largest endocrine organ [4]. These factors have the potential to influence the production of adipose-derived hormones and cytokines from the adipose organ [5-8]. Leptin and adiponectin are two of the most abundant and most investigated adipose-derived hormones. Friedman and Halaas [9] positionally cloned the ob gene and demonstrated that it was encoded for a hormone that they called leptin (after the Greek ‘leptos’ for thin). The proposed role of leptin was as a growth factor in the colon, stimulating proliferation of the colon epithelium and inhibiting apoptosis. That leptin increased colon tumor growth in obese patients subsequent to the initiation of colon cancer. Leptin is important for colorectal cancer (CRC) growth in obese patients and acts as a growth factor for CRC at stages subsequent to tumor initiation in colorectal carcinogenesis [10]. However, leptin failed to promote the growth of colon cancer xenografts in nude mice and did not increase intestinal tumorigenesis in ApcMin/ + mice [11]. The present study also failed to demonstrate the impact of leptin for increasing tumorigenesis and improving the prognosis. Moreover, an inverse association of nodal stage with high leptin expression was found. Therefore, the authors concluded that a higher leptin expression level was a predictor of a better oncologic outcome and that high leptin expression in colorectal-cancer tissue might be a good prognostic factor. Assessment of leptin signaling in tumor tissue needs further investigation to determine its possible impact on prognosis [12]. The complexity of this issue is confounded by various aspects associated with leptin production and signaling in human coloncancer patients. Leptin receptors are expressed by normal colon epithelial cells in human subjects [13, 14]. High expression of the long-form signaling receptor, ObRb, has been associated with increased age, proximally-located tumors, and high levels of microsatellite instability and lymphocyte infiltration [13]. The impact of plasma leptin is confounded by inconsistent and conflicting data reported from studies on patients with colon cancer [15-20]. A more recent report failed to determine significant differences in serum leptin between patients with colon cancer and controls [15]. The conflicting reports may be due, in part, to cachexia and anorexia, which are common in patients with CRC [21]. Leptin expression in colon tissue may be positively correlated with tumor features that are associated with improved survival of patients with CRC [22]. At present, the significant relationship between leptin expression and clinicopathological details, such as tumor stage and prognosis, suggests a possible role for leptin as a novel growth factor driving the development and the progression of CRC. Large clinical studies are needed to determine the mechanisms underlying the effects of leptin on the development and the progression of CRC.

Suppression of Tumor Growth in Mice by Rationally Designed Pseudopeptide Inhibitors of Fibroblast Activation Protein and Prolyl Oligopeptidase

Tumor microenvironments (TMEs) are composed of cancer cells, fibroblasts, extracellular matrix, microvessels, and endothelial cells. Two prolyl endopeptidases, fibroblast activation protein (FAP) and prolyl oligopeptidase (POP), are commonly overexpressed by epithelial-derived malignancies, with the specificity of FAP expression by cancer stromal fibroblasts suggesting FAP as a possible therapeutic target. Despite overexpression in most cancers and having a role in angiogenesis, inhibition of POP activity has received little attention as an approach to quench tumor growth. We developed two specific and highly effective pseudopeptide inhibitors, M83, which inhibits FAP and POP proteinase activities, and J94, which inhibits only POP. Both suppressed human colon cancer xenograft growth >90% in mice. By immunohistochemical stains, M83- and J94-treated tumors had fewer microvessels, and apoptotic areas were apparent in both. In response to M83, but not J94, disordered collagen accumulations were observed. Neither M83- nor J94-treated mice manifested changes in behavior, weight, or gastrointestinal function. Tumor growth suppression was more extensive than noted with recently reported efforts by others to inhibit FAP proteinase function or reduce FAP expression. Diminished angiogenesis and the accompanying profound reduction in tumor growth suggest that inhibition of either FAP or POP may offer new therapeutic approaches that directly target TMEs.

Partial inhibition of gp130-Jak-Stat3 signaling prevents Wnt-β-catenin-mediated intestinal tumor growth and regeneration.

Most colon cancers arise from somatic mutations in the tumor suppressor gene APC (adenomatous polyposis coli), and these mutations cause constitutive activation of the Wnt-to-β-catenin pathway in the intestinal epithelium. Because Wnt-β-catenin signaling is required for homeostasis and regeneration of the adult intestinal epithelium, therapeutic targeting of this pathway is challenging. We found that genetic activation of the cytokine-stimulated pathway mediated by the receptor gp130, the associated Jak (Janus kinase) kinases, and the transcription factor Stat3 (signal transducer and activator of transcription 3) was required for intestinal regeneration in response to irradiation-induced damage in wild-type mice and for tumorigenesis in Apc-mutant mice. Systemic pharmacological or partial genetic inhibition of gp130-Jak-Stat3 signaling suppressed intestinal regeneration, the growth of tumors in Apc-mutant mice, and the growth of colon cancer xenografts. The growth of Apc-mutant tumors depended on gp130-Jak-Stat3 signaling for induction of the polycomb repressor Bmi-1, and the associated repression of genes encoding the cell cycle inhibitors p16 and p21. However, suppression of gp130-Jak-Stat3 signaling did not affect Wnt-β-catenin signaling or homeostasis in the intestine. Thus, these data not only suggest a molecular mechanism for how the gp130-Jak-Stat3 pathway can promote cancer but also provide a rationale for therapeutic inhibition of Jak in colon cancer.