Crosstalk between insulin/insulin-like growth factor-1 receptors and G protein-coupled receptor signaling systems: a novel target for the antidiabetic drug metformin in pancreatic cancer

Neuroendocrine-derived peptides promote prostate cancer cell survival through activation of IGF-1R signaling

BACKGROUND

Neuroendocrine (NE) cells promote the progression of prostate cancer to a castration-resistant state through the production of paracrine growth factors. We have demonstrated this principle using in vitro and in vivo proliferative endpoints; however, the contributions of NE-derived pro-survival factors and anti-apoptosis to this phenomenon have not been thoroughly investigated.

METHODS

Here, we utilized conditioned-medium (CM) from LNCaP cells, engineered to undergo NE differentiation, and examined its effects on PC3 and LNCaP cell survival.

RESULTS

Statistically significant changes in clonogenic survival, Annexin V staining, PARP cleavage and trypan blue positivity of approximately twofold were observed in the presence of NE-derived CM relative to control-CM for both LNCaP and PC3 cells. These changes were partially abrogated by antagonists of the neuropeptides neurotensin, bombesin, and PTHrP. Selective inhibitors of IGF-1R, EGFR or Src caused significant and nearly complete blockade of prostate cancer cell survival due to NE secretions. Similar increases in cell survival were observed for LNCaP or PC3 cells treated with NE-derived medium in the presence of docetaxel. Increased phosphorylation of IGF-1R, following treatment with NE-derived medium, was accompanied by decreased protein tyrosine phosphatase, receptor type F (PTPRF) mRNA, and protein levels. Overexpression of PTPRF decreased cell survival, the amplitude and duration of IGF-1R phosphorylation, and enhanced PARP cleavage in the presence of NE-derived medium.

CONCLUSIONS

These data support the hypothesis that NE-derived factors act upon prostate cancer cells to stimulate pro-survival signaling and describe a novel mechanism of cross-talk between NE-derived factors and IGF-1R, mediated in part by PTPRF.

The role of insulin and IGF system in pancreatic cancer

The importance of the IGF system in carcinogenesis has been established for many solid cancers. It is well known that individuals with higher circulating levels of the IGF1 ligand present an increased risk of cancer. However, therapies with monoclonal antibodies targeting the IGF1 receptor (IGF1R) have been largely unsuccessful. One of the potential reasons for this failure is the existence of the highly homologous insulin receptor (IR), which appears to be at least equally efficient as the IGF1R in the transition of mitogenic signals to the nucleus and promotion of cell growth. Furthermore, IGF1 and insulin receptors can form hybrid receptors sensitive to stimulation of all three ligands of the system: insulin, IGF1, and IGF2. Although the connection between insulin, diabetes, and cancer has been established for years now, clear evidence that demonstrate the redundancy of insulin and insulin receptors and insulin-like growth factors and their receptors in cancer is missing. In this review, we focus on the contribution of insulin and IGFs to carcinogenesis in the insulin-producing organ, the pancreas. We give a short summary on the complexity of insulin and the IGF system in the pancreas and their potential roles in pancreatic cancer, especially pancreatic ductal adenocarcinoma. Finally, we discuss drug-targeting options of this system and the rationale of simultaneous targeting of both the insulin and the IGF systems.

Targeting TORC1/2 enhances sensitivity to EGFR inhibitors in head and neck cancer preclinical models

Head and neck squamous cell carcinoma (HNSCC) is characterized by overexpression of the epidermal growth factor receptor (EGFR) where treatments targeting EGFR have met with limited clinical success. Elucidation of the key downstream-pathways that remain activated in the setting of EGFR blockade may reveal new therapeutic targets. The present study was undertaken to test the hypothesis that inhibition of the mammalian target of rapamycin (mTOR) complex would enhance the effects of EGFR blockade in HNSCC preclinical models. Treatment of HNSCC cell lines with the newly developed TORC1/TORC2 inhibitor OSI-027/ASP4876 resulted in dose-dependent inhibition of proliferation with abrogation of phosphorylation of known downstream targets including phospho-AKT (Ser473), phospho-4E-BP1, phospho-p70s6K, and phospho-PRAS40. Furthermore, combined treatment with OSI-027 and erlotinib resulted in enhanced biochemical effects and synergistic growth inhibition in vitro. Treatment of mice bearing HNSCC xenografts with a combination of the Food and Drug Administration (FDA)-approved EGFR inhibitor cetuximab and OSI-027 demonstrated a significant reduction of tumor volumes compared with either treatment alone. These findings suggest that TORC1/TORC2 inhibition in conjunction with EGFR blockade represents a plausible therapeutic strategy for HNSCC.

Modulation of insulin-like growth factor-1 receptor and its signaling network for the treatment of cancer: current status and future perspectives

Based on over three decades of pre-clinical data, insulin-like growth factor-1 receptor (IGF-1R) signaling has gained recognition as a promoter of tumorogenesis, driving cell survival and proliferation in multiple human cancers. As a result, IGF-1R has been pursued as a target for cancer treatment. Early pioneering efforts targeting IGF-1R focused on highly selective monoclonal antibodies, with multiple agents advancing to clinical trials. However, despite some initial promising results, recent clinical disclosures have been less encouraging. Moreover, recent studies have revealed that IGF-1R participates in a dynamic and complex signaling network, interacting with additional targets and pathways thereof through various crosstalk and compensatory signaling mechanisms. Such mechanisms of bypass signaling help to shed some light on the decreased effectiveness of selective IGF-1R targeted therapies (e.g. monoclonal antibodies) and suggest that targeting multiple nodes within this signaling network might be necessary to produce a more effective therapeutic response. Additionally, such findings have led to the development of small molecule IGF-1R inhibitors which also co-inhibit additional targets such as insulin receptor and epidermal growth factor receptor. Such findings have helped to guide the design rationale of numerous drug combinations that are currently being evaluated in clinical trials.

Diabetes and cancer: placing the association in perspective

PURPOSE OF REVIEW

The association of diabetes and cancer has received increased attention as data have emerged to indicate that the type of diabetes treatment may influence the risk of cancer, and that the risk of cancer among diabetic individuals can be reduced by intervention. The association of diabetes and pancreatic cancer is particularly strong, but often misunderstood. Long-standing type 1 diabetes and type 2 diabetes increase the risk for this malignancy, but the cancer can also induce pancreatogenic, or type 3c, diabetes as well.

RECENT FINDINGS

This review covers the recent findings which help to clarify these relationships, and offers guidance for prevention, early detection, and treatment. Obesity and, separately, diabetes increase the risk of several common malignancies by about two-fold. This risk is reduced by successful treatments. Type 3c diabetes is more common than previously realized, and strategies to differentiate type 3c diabetes from type 2 diabetes, to identify those candidates who will benefit from screening studies, are discussed.

SUMMARY

The death rate because of pancreatic and other cancers can be reduced by an aggressive approach to reversing obesity and hyperinsulinemia, achieving good glycemic control in diabetic patients, and identifying at an early timepoint those patients with pancreatogenic diabetes.

Clinical outcomes of chemotherapy for diabetic and nondiabetic patients with pancreatic cancer: better prognosis with statin use in diabetic patients

OBJECTIVES

The aim of this study was to clarify the impact of diabetes mellitus (DM) as well as antidiabetic, antihypertensive, and antihyperlipidemic medications such as metformin and statins on survival in patients with advanced pancreatic cancer receiving chemotherapy.

METHODS

We retrospectively reviewed the medical records of 250 patients with advanced pancreatic cancer receiving chemotherapy. Multivariate analyses of prognostic factors for survival were performed both in overall population and in subgroups with and without DM.

RESULTS

Diabetes mellitus was diagnosed in 124 patients (50%) who had less distant metastasis and more hypertension. Thirty patients received statin for hyperlipidemia. Overall survival was 13.3 versus 10.0 months with and without DM (P = 0.084), but hazard ratio of DM was 1.05 (P = 0.758) in the multivariate analysis. Subgroup analysis of diabetic patients, but not in non-diabetic patients, demonstrated use of statins (hazard ratio, 0.40; P = 0.010) as a prognostic factor, as well as distant metastasis, performance status, combination therapy with gemcitabine and S-1, and use of angiotensin-converting enzyme inhibitors or angiotensin receptor blockers. No antidiabetic medications were prognostic factors.

CONCLUSIONS

Neither DM nor antidiabetic treatment had prognostic impact on advanced pancreatic cancer. Statin use was associated with better survival in the diabetic patients.

Inhibition of mutant GNAQ signaling in uveal melanoma induces AMPK-dependent autophagic cell death

Oncogenic mutations in GNAQ and GNA11 genes are found in 80% of uveal melanoma. These mutations result in the activation of the RAF/MEK signaling pathway culminating in the stimulation of ERK1/2 mitogen-activated protein kinases. In this study, using a siRNA strategy, we show that mutant GNAQ signals to both MEK and AKT, and that combined inhibition of these pathways with the MEK inhibitor selumetinib (AZD6244) and the AKT inhibitor MK2206 induced a synergistic decrease in cell viability. This effect was genotype dependent as autophagic markers like beclin1 and LC3 were induced in GNAQ-mutant cells, whereas apoptosis was the mechanism of cell death of BRAF-mutant cells, and cells without either mutation underwent cell-cycle arrest. The inhibition of MEK/ATK pathways induced activation of AMP-activated protein kinase (AMPK) in the GNAQ-mutant cells. The downregulation of AMPK by siRNA or its inhibition with compound C did not rescue the cells from autophagy, rather they died by apoptosis, defining AMPK as a key regulator of mutant GNAQ signaling and a switch between autophagy and apoptosis. Furthermore, this combination treatment was effective in inhibiting tumor growth in xenograft mouse models. These findings suggest that inhibition of MEK and AKT may represent a promising approach for targeted therapy of patients with uveal melanoma.

Different patterns of Akt and ERK feedback activation in response to rapamycin, active-site mTOR inhibitors and metformin in pancreatic cancer cells

The mTOR pathway is aberrantly stimulated in many cancer cells, including pancreatic ductal adenocarcinoma (PDAC), and thus it is a potential target for therapy. However, the mTORC1/S6K axis also mediates negative feedback loops that attenuate signaling via insulin/IGF receptor and other tyrosine kinase receptors. Suppression of these feed-back loops unleashes over-activation of upstream pathways that potentially counterbalance the antiproliferative effects of mTOR inhibitors. Here, we demonstrate that treatment of PANC-1 or MiaPaCa-2 pancreatic cancer cells with either rapamycin or active-site mTOR inhibitors suppressed S6K and S6 phosphorylation induced by insulin and the GPCR agonist neurotensin. Rapamycin caused a striking increase in Akt phosphorylation at Ser(473) while the active-site inhibitors of mTOR (KU63794 and PP242) completely abrogated Akt phosphorylation at this site. Conversely, active-site inhibitors of mTOR cause a marked increase in ERK activation whereas rapamycin did not have any stimulatory effect on ERK activation. The results imply that first and second generation of mTOR inhibitors promote over-activation of different pro-oncogenic pathways in PDAC cells, suggesting that suppression of feed-back loops should be a major consideration in the use of these inhibitors for PDAC therapy. In contrast, metformin abolished mTORC1 activation without over-stimulating Akt phosphorylation on Ser(473) and prevented mitogen-stimulated ERK activation in PDAC cells. Metformin induced a more pronounced inhibition of proliferation than either KU63794 or rapamycin while, the active-site mTOR inhibitor was more effective than rapamycin. Thus, the effects of metformin on Akt and ERK activation are strikingly different from allosteric or active-site mTOR inhibitors in PDAC cells, though all these agents potently inhibited the mTORC1/S6K axis.

Therapeutic strategies targeting cancer stem cells

Increasing studies have demonstrated a small proportion of cancer stem cells (CSCs) exist in the cancer cell population. CSCs have powerful self-renewal capacity and tumor-initiating ability and are resistant to chemotherapy and radiation. Conventional anticancer therapies kill the rapidly proliferating bulk cancer cells but spare the relatively quiescent CSCs, which cause cancer recurrence. So it is necessary to develop therapeutic strategies acting specifically on CSCs. In recent years, studies have shown that therapeutic agents such as metformin, salinomycin, DECA-14, rapamycin, oncostatin M (OSM), some natural compounds, oncolytic viruses, microRNAs, cell signaling pathway inhibitors, TNF-related apoptosis inducing ligand (TRAIL), interferon (IFN), telomerase inhibitors, all-trans retinoic acid (ATRA) and monoclonal antibodies can suppress the self-renewal of CSCs in vitro and in vivo. A combination of these agents and conventional chemotherapy drugs can significantly inhibit tumor growth, metastasis and recurrence. These strategies targeting CSCs may bring new hopes to cancer therapy.

Targeting LKB1 signaling in cancer

The serine/threonine kinase LKB1 is a master kinase involved in cellular responses such as energy metabolism, cell polarity and cell growth. LKB1 regulates these crucial cellular responses mainly via AMPK/mTOR signaling. Germ-line mutations in LKB1 are associated with the predisposition of the Peutz-Jeghers syndrome in which patients develop gastrointestinal hamartomas and have an enormously increased risk for developing gastrointestinal, breast and gynecological cancers. In addition, somatic inactivation of LKB1 has been associated with sporadic cancers such as lung cancer. The exact mechanisms of LKB1-mediated tumor suppression remain so far unidentified; however, the inability to activate AMPK and the resulting mTOR hyperactivation has been detected in PJS-associated lesions. Therefore, targeting LKB1 in cancer is now mainly focusing on the activation of AMPK and inactivation of mTOR. Preclinical in vitro and in vivo studies show encouraging results regarding these approaches, which have even progressed to the initiation of a few clinical trials. In this review, we describe the functions, regulation and downstream signaling of LKB1, and its role in hereditary and sporadic cancers. In addition, we provide an overview of several AMPK activators, mTOR inhibitors and additional mechanisms to target LKB1 signaling, and describe the effect of these compounds on cancer cells. Overall, we will explain the current strategies attempting to find a way of treating LKB1-associated cancer.

Metformin and prostate cancer: reduced development of castration-resistant disease and prostate cancer mortality

BACKGROUND

In vitro data and early clinical results suggest that metformin has desirable antineoplastic effects and has a theoretical benefit on castration-resistant prostate cancer (CRPC).

OBJECTIVE

To determine whether the use of metformin would be associated with improved clinical outcomes and a reduction in the development of CRPC.

DESIGN, SETTING, AND PARTICIPANTS

Data from 2901 consecutive patients (157 metformin, 162 diabetic non-metformin, and 2582 nondiabetic) with localized prostate cancer treated with external-beam radiation therapy from 1992 to 2008 were collected from a single institution in the United States.

INTERVENTION

Use of metformin in localized prostate cancer.

OUTCOME MEASUREMENTS AND STATISTICAL ANALYSIS

Univariate and multivariate regression models utilizing k-sample, Fine and Gray, Cox regression, log-rank, and Kaplan-Meier methods to assess prostate-specific antigen-recurrence-free survival (PSA-RFS), distant metastases-free survival (DMFS), prostate cancer-specific mortality (PCSM), overall survival (OS), and development of CRPC.

RESULTS AND LIMITATIONS

With a median follow-up of 8.7 yr, the 10-yr actuarial rates for metformin, diabetic non-metformin, and nondiabetic patients for PCSM were 2.7%, 21.9%, and 8.2% (log-rank p ≤ 0.001), respectively. Metformin use independently predicted (correcting for PSA, T stage, Gleason score, age, diabetic status, and androgen-deprivation therapy use) improvement in all outcomes compared with the diabetic non-metformin group; PSA-RFS (hazard ratio [HR]: 1.99 [1.24-3.18]; p=0.004), DMFS (adjusted HR: 3.68 [1.78-7.62]; p<0.001), and PCSM (HR: 5.15 [1.53-17.35]; p=0.008). Metformin use was also independently associated with a decrease in the development of CRPC in patients experiencing biochemical failure compared with diabetic non-metformin patients (odds ratio: 14.81 [1.83-119.89]; p=0.01). The retrospective study design was the primary limitation of the study.

CONCLUSIONS

To our knowledge, our results are the first clinical data to indicate that metformin use may improve PSA-RFS, DMFS, PCSM, OS, and reduce the development of CRPC in prostate cancer patients. Further validation of metformin's potential benefits is warranted.

Metformin inhibition of mTORC1 activation, DNA synthesis and proliferation in pancreatic cancer cells: dependence on glucose concentration and role of AMPK

Metformin, a widely used anti-diabetic drug, is emerging as a potential anticancer agent but the mechanisms involved remain incompletely understood. Here, we demonstrate that the potency of metformin induced AMPK activation, as shown by the phosphorylation of its substrates acetyl-CoA carboxylase (ACC) at Ser(79) and Raptor at Ser(792), was dramatically enhanced in human pancreatic ductal adenocarcinoma (PDAC) cells PANC-1 and MiaPaCa-2 cultured in medium containing physiological concentrations of glucose (5 mM), as compared with parallel cultures in medium with glucose at 25 mM. In physiological glucose, metformin inhibited mTORC1 activation, DNA synthesis and proliferation of PDAC cells stimulated by crosstalk between G protein-coupled receptors and insulin/IGF signaling systems, at concentrations (0.05-0.1 mM) that were 10-100-fold lower than those used in most previous reports. Using siRNA-mediated knockdown of the α(1) and α(2) catalytic subunits of AMPK, we demonstrated that metformin, at low concentrations, inhibited DNA synthesis through an AMPK-dependent mechanism. Our results emphasize the importance of using medium containing physiological concentrations of glucose to elucidate the anticancer mechanism of action of metformin in pancreatic cancer cells and other cancer cell types.

Diabetes and pancreatic cancer

Epidemiological studies clearly indicate that the risk of pancreatic cancer (PC) is increased in diabetic patients, but most studies focus on overall diabetes or type 2 diabetes mellitus (T2DM), and there are few studies on the risks of type 1 and type 3c (secondary) diabetes. Possible mechanisms for increased cancer risk in diabetes include cellular proliferative effects of hyperglycemia, hyperinsulinemia, and abnormalities in insulin/IGF receptor pathways. Recently, insulin and insulin secretagogues have been observed to increase the PC risk, while metformin treatment reduces the cancer risk in diabetic subjects. In addition, anticancer drugs used to treat PC may either cause diabetes or worsen coexisting diabetes. T3cDM has emerged as a major subset of diabetes and may have the highest risk of pancreatic carcinoma especially in patients with chronic pancreatitis. T3cDM is also a consequence of PC in at least 30% of patients. Distinguishing T3cDM from the more prevalent T2DM among new-onset diabetic patients can be aided by an assessment of clinical features and confirmed by finding a deficiency in postprandial pancreatic polypeptide release. In conclusion, diabetes and PC have a complex relationship that requires more clinical attention. The risk of developing PC can be reduced by aggressive prevention and treatment of T2DM and obesity and the prompt diagnosis of T3cDM may allow detection of a tumor at a potentially curable stage.

Metformin, an antidiabetic agent reduces growth of cutaneous squamous cell carcinoma by targeting mTOR signaling pathway

The biguanide metformin is widely used for the treatment of Type-II diabetes. Its antiproliferative and pro-apoptotic effects in various tumor cells suggest its potential candidacy for cancer chemoprevention. Herein, we report that metformin significantly inhibited human epidermoid A431 tumor xenograft growth in nu/nu mice, which was associated with a significant reduction in proliferative biomarkers PCNA and cyclins D1/B1. This tumor growth reduction was accompanied by the enhanced apoptotic cell death and an increase in Bax:Bcl2 ratio. The mechanism by which metformin manifests antitumor effects appears to be dependent on the inhibition of nuclear factor kappa B (NFkB) and mTOR signaling pathways. Decreased phosphorylation of NFkB inhibitory protein IKBα together with reduced enhancement of NFkB transcriptional target proteins, iNOS/COX-2 were observed. In addition, a decrease in the activation of ERK/p38-driven MAP kinase signaling was seen. Similarly, AKT signaling activation as assessed by the diminished phosphorylation at Ser473 with a concomitant decrease in mTOR signaling pathway was also noted as phosphorylation of mTOR regulatory proteins p70S6K and 4E-BP-1 was significantly reduced. Consistently, decreased phosphorylation of GSK3β, which is carried out by AKT kinases was also observed. These results suggest that metformin blocks SCC growth by dampening NFkB and mTOR signaling pathways.

The bidirectional interation between pancreatic cancer and diabetes

The bidirectional interation between pancreatic cancer (PanCa) and diabetes has been confirmed by epidemiological studies, which provide evidence-based medical support for further research into the mechanisms involved in the interaction. We reviewed the literature regarding the role of diabetes in the generation and progression of PanCa and the mechanism by which PanCa induces diabetes for its malignant progression. The effect of antidiabetic drugs on the occurrence and prognosis of PanCa was also reviewed. Diabetes may directly promote the progression of PanCa by pancreatic duct enlargement and hypertension, as well as by enabling an increased tumor volume. Hyperinsulinemia, insulin resistance, cytokines, hyperglycemia and genotype change are also important factors in the progression of PanCa with diabetes. Hyperglycemia may be the first clinical manifestation and is helpful in the early diagnosis of PanCa. Furthermore, antidiabetic drugs can have different effects on the occurrence and prognosis of PanCa. The bidirectional interation between PanCa and diabetes is involved in the occurrence, proliferation, invasion, metastasis and prognosis of PanCa with diabetes. The discovery of biomarkers for the early diagnosis of PanCa, as well as the novel usage of metformin for its antitumor effects and determining the potential mechanisms of these effects, may be the next direction for PanCa research and treatment.

Acute inflammation induces insulin-like growth factor-1 to mediate Bcl-2 and Muc5ac expression in airway epithelial cells

Generally, exposure to LPS in human airways occurs in the form of aerosols and causes an acute inflammatory response or exacerbates existing chronic inflammatory conditions by enhancing airway remodeling and associated pathologies. The present study evaluated which inflammatory mediators may be responsible for the expression of Bcl-2 and mucus cell metaplasia when mice are exposed to aerosolized LPS. At 3 days after exposure, aerosolized LPS (for 20-40 min) with the estimated lung deposited dosage of 0, 0.02, 0.2, 1.4, and 20.2 μg showed a characteristic dose-dependent increase in polymorphonuclear neutrophils. Significant increases of proinflammatory mediators, including IL-1β, TNF-α, IL-6, growth-related oncogene or keratinocyte-derived cytokine, IFN-γ-induced protein-10, monocyte chemotactic protein-1, and macrophage inflammatory protein-1α, were detected at the highest doses. In addition to increased numbers of airway epithelial cells, mucus cell numbers and mucus production were increased in a dose-dependent manner. Hyperplastic epithelial cells expressed insulin-like growth factor (IGF)-1 and, similar to previous studies, increased expression of the prosurvival protein Bcl-2 and induced expression of Muc5ac. Suppression of IGF-1 expression using retroviral shRNA blocked Bcl-2 expression in human and murine airway epithelial cells and Muc5ac in primary murine airway epithelial cells. These findings show that acute inflammation induces IGF-1 to mediate Bcl-2 and Muc5ac expression in airway epithelial cells.

Targeting metabolism for cancer treatment and prevention: metformin, an old drug with multi-faceted effects

Understanding the complexity of cancer and of the underlying regulatory networks provides a new paradigm that tackles cancer development and treatment through a system biology approach, contemporarily acting on various intersecting pathways. Cancer cell metabolism is an old pathogenetic issue that has recently gained new interest as target for therapeutic approaches. More than 70 years ago, Warburg discovered that malignant cells generally have altered metabolism with high rates of glucose uptake and increased glycolysis, even under aerobic condition. Observational studies have provided evidence that impaired metabolism, obesity, hyperglycemia and hyperinsulinemia may have a role in cancer development, progression and prognosis, and actually diabetic and obese patients have increased cancer risk. On the other hand, caloric restriction has been shown to prolong life span and reduce cancer incidence in several animal models, having an impact on different metabolic pathways. Metformin, an antidiabetic drug widely used for over 40 years, mimics caloric restriction acting on cell metabolism at multiple levels, reducing all energy-consuming processes in the cells, including cell proliferation. By overviewing molecular mechanisms of action, epidemiological evidences, experimental data in tumor models and early clinical study results, this review provides information supporting the promising use of metformin in cancer prevention and treatment.

Downregulation of the CCK-B receptor in pancreatic cancer cells blocks proliferation and promotes apoptosis

Gastrin stimulates the growth of pancreatic cancer cells through the activation of the cholecystokinin-B receptor (CCK-BR), which has been found to be overexpressed in pancreatic cancer. In this study, we proposed that the CCK-BR drives growth of pancreatic cancer; hence, interruption of CCK-BR activity could potentially be an ideal target for cancer therapeutics. The effect of CCK-BR downregulation in the human pancreatic adenocarcinoma cells was examined by utilizing specific CCK-BR-targeted RNA interference reagents. The CCK-BR receptor expression was both transiently and stably downregulated by transfection with selective CCK-BR small-interfering RNA or short-hairpin RNA, respectively, and the effects on cell growth and apoptosis were assessed. CCK-BR downregulation resulted in reduced cancer cell proliferation, decreased DNA synthesis, and cell cycle arrest as demonstrated by an inhibition of G(1) to S phase progression. Furthermore, CCK-BR downregulation increased caspase-3 activity, TUNEL-positive cells, and decreased X-linked inhibitor of apoptosis protein expression, suggesting apoptotic activity. Pancreatic cancer cell mobility was decreased when the CCK-BR was downregulated, as assessed by a migration assay. These results show the importance of the CCK-BR in regulation of growth and apoptosis in pancreatic cancer. Strategies to decrease the CCK-BR expression and activity may be beneficial for the development of new methods to improve the treatment for patients with pancreatic cancer.

Metformin use is associated with better survival of diabetic patients with pancreatic cancer

PURPOSE

Accumulating evidence suggests that metformin has antitumor activity. The aim of this study was to determine whether metformin use has a survival benefit in patients with pancreatic cancer.

EXPERIMENTAL DESIGN

We conducted a retrospective study of patients with diabetes and pancreatic cancer treated at The University of Texas MD Anderson Cancer Center (Houston, TX). Information on diabetes history, including treatment modalities and clinical outcome of pancreatic cancer, was collected using personal interviews and medical record review. Survival analysis was carried out using a Kaplan-Meier plot, log-rank test, and Cox proportional hazards regression models.

RESULTS

Among the 302 patients identified, there were no significant differences in demographic or major clinical characteristics between the patients who had received metformin (n = 117) and those who had not (n = 185). The 2-year survival rate was 30.1% for the metformin group and 15.4% for the non-metformin group (P = 0.004; χ(2) test). The median overall survival time was 15.2 months for the metformin group, and 11.1 months for the non-metformin group (P = 0.004, log-rank test). Metformin users had a 32% lower risk of death; the HR (95% confidence interval) was 0.68 (0.52-0.89) in a univariate model (P = 0.004), 0.64 (0.48-0.86) after adjusting for other clinical predictors (P = 0.003), and 0.62 (0.44-0.87) after excluding insulin users (P = 0.006). Metformin use was significantly associated with longer survival in patients with nonmetastatic disease only.

CONCLUSIONS

Our finding that metformin use was associated with improved outcome of patients with diabetes and pancreatic cancer should be confirmed in independent studies. Future research should prospectively evaluate metformin as a supplemental therapy in this population.

Insulin-like growth factor-I regulates GPER expression and function in cancer cells

Functional cross talk between insulin-like growth factor-I (IGF-I) system and estrogen signaling has been largely reported, although the underlying molecular mechanisms remain to be fully elucidated. As GPR30/GPER mediates rapid cell responses to estrogens, we evaluated the potential of IGF-I to regulate GPER expression and function in estrogen receptor (ER)α-positive breast (MCF-7) and endometrial (Ishikawa) cancer cells. We found that IGF-I transactivates the GPER promoter sequence and upregulates GPER mRNA and protein levels in both cells types. Similar data were found, at least in part, in carcinoma-associated fibroblasts. The upregulation of GPER expression by IGF-I involved the IGF-IR/PKCδ/ERK/c-fos/AP1 transduction pathway and required ERα, as ascertained by specific pharmacological inhibitors and gene-silencing. In both MCF-7 and Ishikawa cancer cells, the IGF-I-dependent cell migration required GPER and its main target gene CTGF, whereas the IGF-I-induced proliferation required both GPER and cyclin D1. Our data demonstrate that the IGF-I system regulates GPER expression and function, triggering the activation of a signaling network that leads to the migration and proliferation of cancer cells.

GPCRs and cancer

G-protein-coupled receptors (GPCRs), which represent the largest gene family in the human genome, play a crucial role in multiple physiological functions as well as in tumor growth and metastasis. For instance, various molecules like hormones, lipids, peptides and neurotransmitters exert their biological effects by binding to these seven-transmembrane receptors coupled to heterotrimeric G-proteins, which are highly specialized transducers able to modulate diverse signaling pathways. Furthermore, numerous responses mediated by GPCRs are not dependent on a single biochemical route, but result from the integration of an intricate network of transduction cascades involved in many physiological activities and tumor development. This review highlights the emerging information on the various responses mediated by a selected choice of GPCRs and the molecular mechanisms by which these receptors exert a primary action in cancer progression. These findings provide a broad overview on the biological activity elicited by GPCRs in tumor cells and contribute to the identification of novel pharmacological approaches for cancer patients.

mIGF-1/JNK1/SirT1 signaling confers protection against oxidative stress in the heart

Oxidative stress contributes to the pathogenesis of aging-associated heart failure. Among various signaling pathways mediating oxidative stress, the NAD(+) -dependent protein deacetylase SirT1 has been implicated in the protection of heart muscle. Expression of a locally acting insulin-like growth factor-1 (IGF-1) propeptide (mIGF-1) helps the heart to recover from infarct and enhances SirT1 expression in cardiomyocytes (CM) in vitro, exerting protection from hypertrophic and oxidative stresses. To study the role of mIGF-1/SirT1 signaling in vivo, we generated cardiac-specific mIGF-1 transgenic mice in which SirT1 was depleted from adult CM in a tamoxifen-inducible and conditional fashion. Analysis of these mice confirmed that mIGF-1-induced SirT1 activity is necessary to protect the heart from paraquat (PQ)-induced oxidative stress and lethality. In cultured CM, mIGF-1 increases SirT1 expression through a c-Jun NH(2)-terminal protein kinase 1 (JNK1)-dependent signaling mechanism. Thus, mIGF-1 protects the heart from oxidative stress via SirT1/JNK1 activity, suggesting new avenues for cardiac therapy during aging and heart failure.

Insulin induces production of new elastin in cultures of human aortic smooth muscle cells

Diabetes mellitus accelerates atherosclerotic progression, peripheral angiopathy development, and arterial hypertension, all of which are associated with elastic fiber disease. However, the potential mechanistic links between insulin deficiency and impaired elastogenesis in diabetes have not been explored. Results of the present study reveal that insulin administered in therapeutically relevant concentrations (0.5 to 10 nmol/L) selectively stimulates formation of new elastic fibers in cultures of human aortic smooth muscle cells. These concentrations of insulin neither up-regulate collagen type I and fibronectin deposition nor stimulate cellular proliferation. Further, the elastogenic effect of insulin occurs after insulin receptor activation, which triggers the PI3K downstream signaling pathway and activates elastin gene transcription. In addition, the promoter region of the human elastin gene contains the CAAATAA sequence, consistent with the FoxO-recognized element, and the genomic effects of insulin occur after removal of the FoxO1 transcriptional inhibitor from the FoxO-recognized element in the elastin gene promoter. In addition, insulin signaling facilitates the association of tropoelastin with its specific 67-kDa elastin-binding protein/spliced form of β-galactosidase chaperone, enhancing secretion. These results are crucial to understanding of the molecular and cellular mechanisms of diabetes-associated vascular disease, and, in particular, endorse use of insulin therapy for treatment of atherosclerotic lesions in patients with type 1 diabetes, in which induction of new elastic fibers would mechanically stabilize the developing plaques and prevent arterial occlusions.

Insulin-like growth factor: current concepts and new developments in cancer therapy

The insulin-like growth factor (IGF) family and the IGF-1 receptor (IGF-1R) play an important role in cancer. This intricate and complex signaling pathway provides many opportunities for therapeutic intervention, and several novel therapeutics aimed at the IGF-1R, particularly monoclonal antibodies and small molecule tyrosine kinase inhibitors, are under clinical investigation. This article provides a patent overview of the IGF signaling pathway and its complexity, addresses the justification for the use of IGF-1R-targeted therapy, and reviews the results of in vivo and in vitro novel therapeutics. Over the past year, the completion of several phase I, II, and III trials have provided interesting new information about the clinical activity of these novel compounds, particularly CP-751,871, IMC-A12, R1507, AMG-479, AVE-1642, MK-0646, XL-228, OSI-906, and BMS-754807. We review the important preliminary results from clinical trials with these compounds and conclude with a discussion about future therapeutic efforts.

Personalized therapy in endometrial cancer: challenges and opportunities

Early stage endometrial cancer is generally curable. However, progress in the treatment of advanced and recurrent endometrial cancer has been limited. This has led to a shift from the use of traditional chemotherapeutic agents and radiotherapy regimens to the promising area of targeted therapy, given the large number of druggable molecular alterations found in endometrial cancer. To maximize the effects of directed targeted therapy, careful molecular characterization of the endometrial tumor is necessary. This represents an important difference in the use of targeted therapy vs. traditional chemotherapy or radiation treatment. This review will discuss relevant pathways to target in endometrial cancer as well as the challenges that arise during development of a personalized oncology approach.

Acquired resistance to drugs targeting receptor tyrosine kinases

Development of resistance to chemotherapeutic drugs represents a significant hindrance to the effective treatment of cancer patients. The molecular mechanisms responsible have been investigated for over half a century and have revealed the lack of a single cause. Rather, a multitude of mechanisms have been delineated ranging from induction and expression of membrane transporters that pump drugs out of cells (multidrug resistance (MDR) phenotype), changes in the glutathione system and altered metabolism to name a few. Treatment of cancer patients/cancer cells with chemotherapeutic agents and/or molecularly targeted drugs is accompanied by acquisition of resistance to the treatment administered. Chemotherapeutic agent resistance was initially assumed to be due to induction of mutations leading to a resistant phenotype. This has also been true for molecularly targeted drugs. Considerable experience has been gained from the study of agents targeting the Bcr-Abl tyrosine kinase including imatinib, dasatinib and sunitinib. It is clear that mutations alone are not responsible for the many resistance mechanisms in play. Rather, additional mechanisms are involved, ranging from epigenetic changes, alternative splicing and the induction of alternative/compensatory signaling pathways. In this review, resistance to receptor tyrosine kinase inhibitors (RTKIs), RTK-directed antibodies and antibodies that inactivate ligands for RTKs are discussed. New approaches and concepts aimed at avoiding the generation of drug resistance will be examined. The recent observation that many RTKs, including the IGF-1R, are dependence receptors that induce apoptosis in a ligand-independent manner will be discussed and the implications this signaling paradigm has on therapeutic strategies will be considered.

Metformin as an antitumor agent in cancer prevention and treatment

Recent epidemiological investigations conducted in diabetic cohorts and cancer patients have found that metformin users have lower risks for cancer than those using insulin or insulin secretagogues. Studies conducted in various animal tumor models and cancer cell lines have demonstrated that metformin prevents tumor development or inhibits cell proliferation. In addition, a recent clinical trial has shown that short-term use of metformin reduces aberrant crypt foci (ACF) formation in non-diabetic patients with ACF. The antitumor activity of metformin may be mediated through its regulatory effect on hormonal, metabolic, and immune functions. Metformin achieves glycemic control by reducing hepatic glucose production and increasing the muscle intake of glucose, thus lowering levels of circulating glucose and, consequently, insulin. The major molecular targets of metformin are the liver kinase B1 (LKB1)-AMP-activated protein kinase (AMPK) signaling and mammalian target of rapamycin (mTOR) pathways, which are central in the regulation of cellular energy homeostasis and play a crucial role in the control of cell division and cell proliferation. Metformin has been shown to improve endothelial function, decrease inflammatory activity, and regulate immune function. Increasing experimental evidence provides a strong biological rationale for metformin as an antitumor and chemopreventive agent. Metformin is being tested as an adjuvant cancer therapy in clinical settings, and metformin is recommended for all cases of Type 2 diabetes without contraindications. As described in this review, the chemopreventive value of metformin is not restricted to diabetic or obese individuals.

Metformin represses self-renewal of the human breast carcinoma stem cells via inhibition of estrogen receptor-mediated OCT4 expression

Metformin, a Type II diabetic treatment drug, which inhibits transcription of gluconeogenesis genes, has recently been shown to lower the risk of some diabetes-related tumors, including breast cancer. Recently, “cancer stem cells” have been demonstrated to sustain the growth of tumors and are resistant to therapy. To test the hypothesis that metformin might be reducing the risk to breast cancers, the human breast carcinoma cell line, MCF-7, grown in 3-dimensional mammospheres which represent human breast cancer stem cell population, were treated with various known and suspected breast cancer chemicals with and without non-cytotoxic concentrations of metformin. Using OCT4 expression as a marker for the cancer stem cells, the number and size were measured in these cells. Results demonstrated that TCDD (100 nM) and bisphenol A (10 µM) increased the number and size of the mammospheres, as did estrogen (10 nM E2). By monitoring a cancer stem cell marker, OCT4, the stimulation by these chemicals was correlated with the increased expression of OCT4. On the other hand, metformin at 1 and 10 mM concentration dramatically reduced the size and number of mammospheres. Results also demonstrated the metformin reduced the expression of OCT4 in E2 & TCDD mammospheres but not in the bisphenol A mammospheres, suggesting different mechanisms of action of the bisphenol A on human breast carcinoma cells. In addition, these results support the use of 3-dimensional human breast cancer stem cells as a means to screen for potential human breast tumor promoters and breast chemopreventive and chemotherapeutic agents.

The effects of metformin on the survival of colorectal cancer patients with diabetes mellitus

Metformin use has been associated with decreased cancer risk and mortality. However, the effects of metformin on clinical outcomes of colorectal cancer (CRC) are not defined. This study aimed to evaluate the association between metformin use and mortality of CRC in diabetic patients. We identified 595 patients who were diagnosed both CRC and diabetes mellitus. Patients were compared by two groups; 258 diabetic patients taking metformin and 337 diabetic patients not taking metformin. Patient's demographics, clinical characteristics, overall mortality and CRC-specific mortality were analyzed. After a median follow-up of 41 months, there were 71 total deaths (27.5%) and 55 CRC-specific deaths (21.3%) among 258 patients who used metformin, compared with 136 total deaths (40.4%) and 104 CRC-specific deaths (30.9%) among 337 patients who did not use metformin. Metformin use was associated with decreased overall mortality (p = 0.018) and CRC-specific mortality (p = 0.042) by univariate analysis. After adjustment for clinically relevant factors, metformin use showed lower risk of overall mortality (HR, 0.66; 95% CI 0.476-0.923; p = 0.015) and CRC-specific mortality (HR, 0.66; 95% CI 0.45-0.975; p = 0.037) in CRC patients with diabetes. Metformin use in CRC patients with diabetes is associated with lower risk of CRC-specific and overall mortality.

Inhibition of p42 MAPK using a nonviral vector-delivered siRNA potentiates the anti-tumor effect of metformin in prostate cancer cells

AIMS

The aim of this work was to study if a G1-polyamidoamine dendrimer/siRNA dendriplex can remove the p42 MAPK protein in prostate cancer cells and to potentiate the anti-tumoral effect of the antidiabetic drug metformin and taxane docetaxel.

MATERIAL & METHODS

The dendriplex uptake was studied using flow cytometry analysis. Transfection efficiency was determined by measuring p42 MAPK mRNA and protein levels. Anti-tumoral effects were determined by measuring cellular proliferation and damage.

RESULTS

The dendriplex siRNA/G1-polyamidoamine dendrimer decreased both p42 MAPK mRNA and protein levels by more than 80%, which potentiates the anti-tumoral effects of metformin.

CONCLUSION

Blockade of the MAPK pathway using a dendrimer-vehiculized siRNA to block the MAPK signaling pathway in prostate cancer cells can potentiate the anti-tumoral activity of anticancer drugs, indicating that the combination of siRNA-mediated blockade of survival signals plus anti-tumoral therapy might be a useful approach for cancer therapy.

Plasma and tissue insulin-like growth factor-I receptor (IGF-IR) as a prognostic marker for prostate cancer and anti-IGF-IR agents as novel therapeutic strategy for refractory cases: a review

Cancer database analysis indicates that prostate cancer is one of the most seen cancers in men meanwhile composing the leading cause of morbidity and mortality among developed countries. Current available therapies are surgery, radiotherapy and androgene ablation for prostate carcinoma. The response rate is as high nearly 90% however, most of these recur or become refractory and androgene independent (AI). Therefore recent studies intensified on molecular factors playing role on development of prostate carcinoma and novel treatment strategies targetting these factors and their receptors. Insulin-like growth factor-I (IGF-I) and its primary receptor insulin-like growth factor receptor-I (IGF-IR) are among these factors. Biologic functions and role in malign progression are primarily achieved via IGF-IR which is a type 2 tyrosine kinase receptor. IGF-IR plays an important role in mitogenesis, angiogenesis, transformation, apoptosis and cell motility. It also generates intensive proliferative signals leading to carcinogenesis in prostate tissue. So IGF-IR and its associated signalling system have provoked considerable interest over recent years as a novel therapeutic target in cancer. In this paper it is aimed to sum up the lately published literature searching the relation of IGF-IR and prostate cancer in terms of incidence, pathologic features, and prognosis. This is followed by a discussion of the different possible targets within the IGF-1R system, and drugs developed to interact at each target. A systems-based approach is then used to review the in vitro and in vivo data in the published literature of the following compounds targeting IGF-1R components using specific examples: growth hormone releasing hormone antagonists (e.g. JV-1-38), growth hormone receptor antagonists (e.g. pegvisomant), IGF-1R antibodies (e.g. CP-751,871, AVE1642/EM164, IMC-A12, SCH-717454, BIIB022, AMG 479, MK-0646/h7C10), and IGF-1R tyrosine kinase inhibitors (e.g. BMS-536942, BMS-554417, NVP-AEW541, NVP-ADW742, AG1024, potent quinolinyl-derived imidazo (1,5-a)pyrazine PQIP, picropodophyllin PPP, nordihydroguaiaretic acid Insm-18/NDGA). And the other end point is to yield an overview on the recent progress about usage of this receptor as a novel anticancer agent of targeted therapies in treatment of prostate carcinoma.

Pancreatogenic diabetes: special considerations for management

BACKGROUND/AIMS

Pancreatogenic, or type 3c, diabetes (T3cDM) occurs due to inherited or acquired pancreatic disease or resection. Although similar to the more prevalent type 1 and type 2 diabetes, pancreatogenic diabetes has a unique pattern of hormonal and metabolic characteristics and a high incidence of pancreatic carcinoma in the majority of patients with T3cDM. Despite these differences, no guidelines for therapy have been described.

METHODS

Published studies on the prevalence, pathophysiology, and cancer associations of T3cDM were reviewed. The recent studies on the protective role and mechanism of metformin therapy as both an anti-diabetic and anti-neoplastic agent were reviewed, and studies on the cancer risk of other anti-diabetic drugs were surveyed.

RESULTS

T3cDM accounts for 5-10% of Western diabetic populations and is associated with mild to severe disease. Hepatic insulin resistance is characteristic of T3cDM and is caused by deficiencies of both insulin and pancreatic polypeptide. 75% of T3cDM is due to chronic pancreatitis, which carries a high risk for pancreatic carcinoma. Insulin and insulin secretagogue treatment increases the risk of malignancy, whereas metformin therapy reduces it. Pancreatic exocrine insufficiency associated with T3cDM contributes to nutritional deficiencies and the development of metabolic bone disease.

CONCLUSIONS

Until consensus recommendations are reached, the glycemic treatment of T3cDM should avoid insulin and insulin secretagogues if possible. Metformin should be the first line of therapy, and continued if insulin treatment must be added for adequate glucose control. Pancreatic enzyme therapy should be added to prevent secondary nutritional and metabolic complications. and IAP.

Does metformin influence the insulin-, IGF I- and IGF II-receptor gene expression and Akt phosphorylation in human decidualized endometrial stromal cells?

OBJECTIVE

To assess the effects of metformin on insulin-, IGF I-, and IGF II-receptor gene expression and Akt phosphorylation in decidualized human endometrial stromal cells (ESC) after stimulation with insulin, IGF I and II.

STUDY DESIGN

ESC were isolated from healthy, regularly cycling women and after two passages decidualized with estrogen/progesterone±metformin. Cells were incubated with insulin, IGF I or IGF II for 1, 5, and 10 min to assess Akt phosphorylation by Western blot. To investigate the insulin-, IGF I- and IGF II-receptor gene expression ESC were incubated with insulin, IGF I or IGF II for 6 and 24h.

RESULTS

Insulin- and IGF I-receptor gene expression in ESC changed significantly after incubation with insulin, IGF I or IGF II. This was further augmented in metformin pretreated cells, while IGF II-receptor gene expression changed particularly after pretreatment with metformin. Akt phosphorylation peaked after 5 min insulin, IGF I and IGF II stimulation in ESC in both control (control 0.08 ± 0.03 vs. insulin 0.74 ± 0.19, IGF I 0.68 ± 0.22, IGF II 0.53 ± 0.13, p<0.05) and metformin pretreated cells (control 0.03 ± 0.01 vs. insulin 0.75 ± 0.11, IGF I 0.74 ± 0.15, IGF II 0.67 ± 0.09, p<0.005). However, there was no significant difference between the control and metformin pretreated group.

CONCLUSION

Insulin, IGF I and IGF II lead to changes in their receptor gene expression and induced Akt phosphorylation in ESC. These effects were further highlighted in the presence of metformin.

Anticancer effects of metformin and its potential use as a therapeutic agent for breast cancer

Metformin is an orally available, biguanide derivative that is widely used in the treatment of Type 2 diabetes. Recent preclinical data have demonstrated that it can also act as an anticancer agent by activation of AMPK and subsequent inhibition of mTOR. Metformin is currently being investigated in several Phase II/III clinical trials. This article will review the current evidence for its mechanism of action, efficacy in preclinical and clinical models, and toxicity. Ongoing and planned studies evaluating the impact of metformin on breast cancer outcomes are also discussed.

Cancer risk in type 2 diabetes mellitus: metabolic links and therapeutic considerations

Type 2 diabetes mellitus (DM2) is increasing in incidence, creating worldwide public health concerns and impacting morbidity and mortality rates. An increasing number of studies have demonstrated shared associations between DM2 and malignancy, including key clinical, biochemical, and metabolic commonalities. This paper will attempt to explore the relationship between the various types of cancer and diabetes, the common metabolic pathways underlying cancer development, and the potential impact of various antidiabetes therapies on cancer risk.

Emerging therapies in pancreas cancer

Pancreas cancer has a grave prognosis and treatment options remain limited despite advancement in anti-cancer chemotherapeutics. This review provides an overview of the emerging therapies for pancreas cancer, focusing on novel signal transduction inhibitors (insulin-like growth factor receptor, hedgehog/Smo, PI3k/Akt/mTOR) and cytotoxics (nab-paclitaxel) that are currently in clinical development. Despite the impact molecularly targeted agents have on other tumor types, their application without cytotoxics in pancreas cancer remains limited. In addition, recent report of the superiority of an intensive cytotoxic regimen using fluorouracil, irinotecan and oxaliplatin (FOLFIRINOX) over gemcitabine reminded us of the importance of cytotoxics in this disease. As such, the future of pancreas cancer therapy may be combination regimens consisting of cytotoxics and molecularly targeted agents.

The complexities of obesity and diabetes with the development and progression of pancreatic cancer

Pancreatic cancer (PC) is one of the most lethal malignant diseases with the worst prognosis. It is ranked as the fourth leading cause of cancer-related deaths in the United States. Many risk factors have been associated with PC. Interestingly, large numbers of epidemiological studies suggest that obesity and diabetes, especially type-2 diabetes, are positively associated with increased risk of PC. Similarly, these chronic diseases (obesity, diabetes, and cancer) are also a major public health concern. In the U.S. population, 50 percent are overweight, 30 percent are medically obese, and 10 percent have diabetes mellitus (DM). Therefore, obesity and DM have been considered as potential risk factors for cancers; however, the focus of this article is restricted to PC. Although the mechanisms responsible for the development of these chronic diseases leading to the development of PC are not fully understood, the biological importance of the activation of insulin, insulin like growth factor-1 (IGF-1) and its receptor (IGF-1R) signaling pathways in insulin resistance mechanism and subsequent induction of compensatory hyperinsulinemia has been proposed. Therefore, targeting insulin/IGF-1 signaling with anti-diabetic drugs for lowering blood insulin levels and reversal of insulin resistance could be useful strategy for the prevention and/or treatment of PC. A large number of studies have demonstrated that the administration of anti-diabetic drugs such as metformin and thiazolidinediones (TZD) class of PPAR-γ agonists decreases the risk of cancers, suggesting that these agents might be useful anti-tumor agents for the treatment of PC. In this review article, we will discuss the potential roles of metformin and TZD anti-diabetic drugs as anti-tumor agents in the context of PC and will further discuss the complexities and the possible roles of microRNAs (miRNAs) in the pathogenesis of obesity, diabetes, and PC.

Diabetes and pancreatic cancer: chicken or egg?

OBJECTIVES

Although half of all patients with pancreatic cancer are diabetic at the time of diagnosis, it remains unclear whether the diabetes associated with pancreatic cancer is a cause or an effect of the malignancy.

METHODS

Epidemiologic studies were reviewed, the geographic prevalence of diabetes and the incidence of pancreatic cancer were examined, and clinical and laboratory studies were reviewed.

RESULTS

Long-standing diabetes increases the risk of pancreatic cancer by 40% to 100%, and recent-onset diabetes is associated with a 4- to 7-fold increase in risk, such that 1% to 2% of patients with recent-onset diabetes will develop pancreatic cancer within 3 years. Treatment of diabetes or morbid obesity decreases the risk of pancreatic cancer, and metformin therapy decreases the risk due to both its antidiabetic and antineoplastic effects. Recent-onset diabetes associated with pancreatic cancer likely represents secondary or type 3 diabetes. The discrimination of type 3 diabetes from the more prevalent type 2 diabetes may identify the high-risk subgroup of diabetic patients in whom potentially curable pancreatic cancer may be found.

CONCLUSIONS

Type 2 and type 1 diabetes mellitus increase the risk of pancreatic cancer with a latency period of more than 5 years. Type 3 diabetes mellitus is an effect, and therefore a harbinger, of pancreatic cancer in at least 30% of patients.

Glucose metabolism disorders and the risk of cancer

Diabetes and cancer are diseases which take the size of an epidemic spread across the globe. Those diseases are influenced by many factors, both genetic and environmental. Precise knowledge of the complex relationships and interactions between these two conditions is of great importance for their prevention and treatment. Many epidemiological studies have shown that certain types of cancer, especially gastrointestinal cancers (pancreas, liver, colon) and also the urinary and reproductive system cancers in women are more common in patients with diabetes or related metabolic disorders. There are also studies showing the inverse relationship between diabetes and cancer, or the lack of it, but they are less numerous and relate mainly to prostate cancer or squamous cell carcinoma of the esophagus. Epidemiological studies, however, do not say anything about the mechanisms of these dependencies. For this purpose, molecular research is needed on the metabolism of cells (including tumor cells) and on metabolic dysfunctions that arise due to changes in the cell environment taking place in the sick, as well as in the intensely treated human organism.

G protein-coupled receptors: novel targets for drug discovery in cancer

G protein-coupled receptors (GPCRs) belong to a superfamily of cell surface signalling proteins that have a pivotal role in many physiological functions and in multiple diseases, including the development of cancer and cancer metastasis. Current drugs that target GPCRs - many of which have excellent therapeutic benefits - are directed towards only a few GPCR members. Therefore, huge efforts are currently underway to develop new GPCR-based drugs, particularly for cancer. We review recent findings that present unexpected opportunities to interfere with major tumorigenic signals by manipulating GPCR-mediated pathways. We also discuss current data regarding novel GPCR targets that may provide promising opportunities for drug discovery in cancer prevention and treatment.

Metabolic disorder, inflammation, and deregulated molecular pathways converging in pancreatic cancer development: implications for new therapeutic strategies

Pancreatic cancer develops and progresses through complex, cumulative biological processes involving metabolic disorder, local inflammation, and deregulated molecular pathways. The resulting tumor aggressiveness hampers surgical intervention and renders pancreatic cancer resistant to standard chemotherapy and radiation therapy. Based on these pathologic properties, several therapeutic strategies are being developed to reverse refractory pancreatic cancer. Here, we outline molecular targeting therapies, which are primarily directed against growth factor receptor-type tyrosine kinases deregulated in tumors, but have failed to improve the survival of pancreatic cancer patients. Glycogen synthase kinase-3β (GSK3β) is a member of a serine/threonine protein kinase family that plays a critical role in various cellular pathways. GSK3β has also emerged as a mediator of pathological states, including glucose intolerance, inflammation, and various cancers (e.g., pancreatic cancer). We review recent studies that demonstrate the anti-tumor effects of GSK3β inhibition alone or in combination with chemotherapy and radiation. GSK3β inhibition may exert indirect anti-tumor actions in pancreatic cancer by modulating metabolic disorder and inflammation.

Molecular targeted approaches for treatment of pancreatic cancer

Human pancreatic cancer remains a highly malignant disease with almost similar incidence and mortality despite extensive research. Many targeted therapies are under development. However, clinical investigation showed that single targeted therapies and most combined therapies were not able to improve the prognosis of this disease, even though some of these therapies had excellent anti-tumor effects in pre-clinical models. Cross-talk between cell proliferation signaling pathways may be an important phenomenon in pancreatic cancer, which may result in cancer cell survival even though some pathways are blocked by targeted therapy. Pancreatic cancer may possess different characteristics and targets in different stages of pathogenesis, maintenance and metastasis. Sensitivity to therapy may also vary for cancer cells at different stages. The unique pancreatic cancer structure with abundant stroma creates a tumor microenvironment with hypoxia and low blood perfusion rate, which prevents drug delivery to cancer cells. In this review, the most commonly investigated targeted therapies in pancreatic cancer treatment are discussed. However, how to combine these targeted therapies and/or combine them with chemotherapy to improve the survival rate of pancreatic cancer is still a challenge. Genomic and proteomic studies using pancreatic cancer samples obtained from either biopsy or surgery are recommended to individualize tumor characters and to perform drug sensitivity study in order to design a tailored therapy with minimal side effects. These studies may help to further investigate tumor pathogenesis, maintenance and metastasis to create cellular expression profiles at different stages. Integration of the information obtained needs to be performed from multiple levels and dimensions in order to develop a successful targeted therapy.

Role of protein kinase D signaling in pancreatic cancer

Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal cancers with dismal survival rates. Its intransigence to conventional therapy renders PDAC an aggressive disease with early metastatic potential. Thus, novel targets for PDAC therapy are urgently needed. Multiple signal transduction pathways are implicated in progression of PDAC. These pathways stimulate production of intracellular messengers in their target cells to modify their behavior, including the lipid-derived diacylglycerol (DAG). One of the prominent intracellular targets of DAG is the protein kinase C (PKC) family. However, the mechanisms by which PKC-mediated signals are decoded by the cell remain incompletely understood. Protein kinase D1 (PKD or PKD1, initially called atypical PKCμ), is the founding member of a novel protein kinase family that includes two additional protein kinases that share extensive overall homology with PKD, termed PKD2, and PKD3. The PKD family occupies a unique position in the signal transduction pathways initiated by DAG and PKC. PKD lies downstream of PKCs in a novel signal transduction pathway implicated in the regulation of multiple fundamental biological processes. We and others have shown that PKD-mediated signaling pathways promote mitogenesis and angiogenesis in PDAC. Our recent observations demonstrate that PKD also potentiates chemoresistance and invasive potential of PDAC cells. This review will briefly highlight diverse biological roles of PKD family in multiple neoplasias including PDAC. Further, this review will underscore our latest advancement with the development of a potent PKD family inhibitor and its effect both in vitro and in vivo in PDAC.

Crosstalk between VEGFR2 and muscarinic receptors regulates the mTOR pathway in serum starved SK-N-SH human neuroblastoma cells

Muscarinic acetylcholine receptors (mAchRs) are guanosine nucleotide-binding protein (G protein) coupled receptors that crosstalk with receptor tyrosine kinases (RTKs) to signal mitogenic pathways. In particular, mAchRs are known to couple with RTKs for several growth factors to activate the mammalian target of rapamycin (mTOR)/Akt pathway, a regulator of protein synthesis. The RTK for the vascular endothelial growth factor (VEGF), VEGFR2, can signal protein synthesis but whether it cooperates with mAchRs to mediate mTOR activation has not been demonstrated. Using serum starved SK-N-SH neuroblastoma cells, we show that the muscarinic receptor agonists carbachol and pilocarpine enhance the activation of the mTOR substrate p70 S6 Kinase (S6K) and its target ribosomal protein S6 (S6) in a VEGFR2 dependent manner. Treatments with carbachol increased VEGFR2 phosphorylation, suggesting that mAchRs stimulate VEGFR2 transactivation to enhance mTOR signaling. Inhibitor studies revealed that phosphatidylinositol 3 kinase resides upstream from S6K, S6 and Akt phosphorylation while protein kinase C (PKC) functions in an opposing fashion by positively regulating S6K and S6 phosphorylation and suppressing Akt activation. Treatments with the phosphatase inhibitors sodium orthovanadate and okadaic acid increase S6, Akt and to a lesser extent S6K phosphorylation, indicating that tyrosine and serine/threonine dephosphorylation also regulates their activity. However, okadaic acid elicited a far greater increase in phosphorylation, implicating phosphatase 2A as a critical determinant of their function. Finally, pilocarpine but not carbachol induced a time and dose dependent cell death that was associated with caspase activation and oxidative stress but independent of S6K and S6 activation through VEGFR2. Accordingly, our findings suggest that mAchRs crosstalk with VEGFR2 to enhance mTOR activity but signal divergent effects on survival through alternate mechanisms.

Crosstalk between insulin receptor and G protein-coupled receptor signaling systems leads to Ca²+ oscillations in pancreatic cancer PANC-1 cells

We examined crosstalk between the insulin receptor and G protein-coupled receptor (GPCR) signaling pathways in individual human pancreatic cancer PANC-1 cells. Treatment of cells with insulin (10 ng/ml) for 5 min markedly enhanced the proportion of cells that display an increase in intracellular [Ca²+] induced by picomolar concentrations of the GPCR agonist neurotensin. Interestingly, insulin increased the proportion of a subpopulation of cells that exhibit intracellular [Ca²+] oscillations in response to neurotensin at concentrations as low as 50-200 pM. Insulin enhanced GPCR-induced Ca²+ signaling in a time- and dose-dependent manner; a marked potentiation was obtained after an exposure to a concentration of 10 ng/ml for 5 min. Treatment with the mTORC1 inhibitor rapamycin abrogated the increase in GPCR-induced [Ca²+](i) oscillations produced by insulin. Our results identify a novel aspect in the crosstalk between insulin receptor and GPCR signaling systems in pancreatic cancer cells, namely that insulin increases the number of [Ca²+](i) oscillating cells induced by physiological concentrations of GPCR agonists through an mTORC1-dependent pathway.

Metformin: taking away the candy for cancer?

Metformin is widely used in the treatment of diabetes mellitus type 2 where it reduces insulin resistance and diabetes-related morbidity and mortality. Population-based studies show that metformin treatment is associated with a dose-dependent reduction in cancer risk. The metformin treatment also increases complete pathological tumour response rates following neoadjuvant chemotherapy for breast cancer, suggesting a potential role as an anti-cancer drug. Diabetes mellitus type 2 is associated with insulin resistance, elevated insulin levels and an increased risk of cancer and cancer-related mortality. This increased risk may be explained by activation of the insulin- and insulin-like growth factor (IGF) signalling pathways and increased signalling through the oestrogen receptor. Reversal of these processes through reduction of insulin resistance by the oral anti-diabetic drug metformin is an attractive anti-cancer strategy. Metformin is an activator of AMP-activated protein kinase (AMPK) which inhibits protein synthesis and gluconeogenesis during cellular stress. The main downstream effect of AMPK activation is the inhibition of mammalian target of rapamycin (mTOR), a downstream effector of growth factor signalling. mTOR is frequently activated in malignant cells and is associated with resistance to anticancer drugs. Furthermore, metformin can induce cell cycle arrest and apoptosis and can reduce growth factor signalling. This review discusses the role of diabetes mellitus type 2 and insulin resistance in carcinogenesis, the preclinical rationale and potential mechanisms of metformin's anti-cancer effect and the current and future clinical developments of metformin as a novel anti-cancer drug.

Defining the pathway to insulin-like growth factor system targeting in cancer

The insulin-like growth factors (IGFs; IGF-1 and IGF-2) play central roles in cell growth, differentiation, survival, transformation and metastasis. The biologic effects of the IGFs are mediated by the IGF-1 receptor (IGF-1R), a receptor tyrosine kinase with homology to the insulin receptor (IR). Dysregulation of the IGF system is well recognized as a key contributor to the progression of multiple cancers, with IGF-1R activation increasing the tumorigenic potential of breast, prostate, lung, colon and head and neck squamous cell carcinoma (HNSCC). Despite this relationship, targeting the IGF-1R has only recently undergone development as a molecular cancer therapeutic. As it has taken hold, we are witnessing a robust increase and interest in targeting the inhibition of IGF-1R signaling. This is accentuated by the list of over 30 drugs, including monoclonal antibodies (mAbs) and tyrosine kinase inhibitors (TKIs) that are under evaluation as single agents or in combination therapies. The IGF-binding proteins (IGFBPs) represent the third component of the IGF system consisting of a class of six soluble secretory proteins. They represent a unique class of naturally occurring IGF-antagonists that bind to and sequester IGF-1 and IGF-2, inhibiting their access to the IGF-1R. Due to their dual targeting of the IGFs without affecting insulin action, the IGFBPs are an untapped "third" class of IGF-1R inhibitors. In this commentary, we highlight some of the significant aspects of and prospects for targeting the IGF-1R and describe what the future may hold.