Combined Inhibition of IGF-1R/IR and Src Family Kinases Enhances Antitumor Effects in Prostate Cancer by Decreasing Activated Survival Pathways

Background

Treatment of metastatic prostate cancer (PCa) with single agents has shown only modest efficacy. We hypothesized dual inhibition of different pathways in PCa results in improved tumor inhibition. The Src family kinases (SFK) and insulin-like growth factor-1 (IGF-1) signaling axes are aberrantly activated in both primary PCa and bone metastases and regulate distinct and overlapping functions in PCa progression. We examined the antitumor effects of combined inhibition of these pathways.

Materials and Methods

Src andIGF-1 receptor (IGF-1R) inhibition was achieved in vitro by short hairpin (sh)RNA and in vitro and in vivo by small molecule inhibitors (dasatinib and BMS-754807, against SFK and IGF-1R/Insulin Receptor(IR), respectively).

Results

In vitro, inhibition of IGF-1 signaling affected cell survival and proliferation. SFK blockade alone had modest effects on proliferation, but significantly enhanced the IGF-1R blockade. These findings correlated with a robust inhibition of IGF-1-induced Akt1 phophorylation by dasatinib, whereas Akt2 phosphorylation was SFK independent and only inhibited by BMS-754807. Thus, complete inhibition of both Akt genes, not seen by either drug alone, is likely a major mechanism for the decreased survival of PCa cells. Furthermore, dasatinib and BMS-754807 inhibited in vivo growth of the primary human xenograft MDA PCa 133, with corresponding inhibition of Akt in tumors. Also, both orthotopic and intratibial tumor growth of PC-3 cells were more potently inhibited by dual SFK and IGF-1R/IR blockade compared to either pathway alone, with a corresponding decrease in bone turnover markers.

Conclusions

Dual IGF-1R/IR and SFK inhibition may be a rational therapeutic approach in PCa by blocking both independent and complementary processes critical to tumor growth.     

肿瘤相关成纤维细胞促进肿瘤侵袭转移的作用机制

肿瘤相关成纤维细胞(cancer-associated fibroblasts,CAFs)是肿瘤微环境中最主要的成分之一,在肿瘤的发生发展中发挥着必不可少的作用。骨髓和脂肪的局部组织固有成纤维细胞及间充质干细胞是CAFs来源的主要前体细胞。大量研究表明,CAFs并不作为单独细胞在肿瘤周围存在,而是和肿瘤细胞相互作用,促进肿瘤的生长与存活并维持其恶性倾向。肿瘤细胞可以影响CAFs前体的招募,并诱导正常成纤维细胞活化为CAFs;同时,CAFs可以分泌多种细胞因子、生长因子和细胞外基质蛋白质,促进肿瘤细胞的增殖、耐药及侵袭转移,从而影响肿瘤的预后。CAFs还参与血管淋巴管的生成、细胞外基质重塑、免疫抑制以及肿瘤细胞上皮间质转化等有利于肿瘤发生发展的外源性途径,为肿瘤细胞提供了一个良好的微环境。大量研究显示,研发靶向CAFs的药物可以中断其与肿瘤细胞之间的联系,从而抑制肿瘤的生长和转移。因此,深入了解CAFs促肿瘤的作用机制将有利于肿瘤治疗新靶点的发现。本文将对CAFs促进肿瘤侵袭转移的作用机制加以综述。     

牛肠道病毒（MZ—468株）对P615移植瘤及人癌细胞增殖的影响

本文进行了牛牛肠道病毒(MZ—468株)对P_(615)移植瘤和体内、外对人癌细胞增殖影响的实验研究,结果表明,MZ—468株病毒可以明显抑制P_(615)移植瘤的生长(P<0.01),明显延长荷瘤小鼠的生存时间(P<0.05);同时该病毒不仅可以在体外杀伤人癌(HeLa、AGZY-83—a和LTEP-a-2)干细胞,抑制其细胞集落形成,而且可以在体内抑制人癌细胞(HeLa和AGZY-83—a)异种移植瘤的生长。这充分提示MZ—468株病毒对动物和人的固体瘤具有比较明显的抗肿瘤作用。     

A comparison of the biological activity of the recombinant intact and truncated insulin-like growth factor 1 (IGF-1)

A truncated form of insulin-like growth factor 1 (IGF-1), which lacked the aminoterminal tripeptide Gly-Pro-Glu has been isolated from human fetal and adult brain. This truncated IGF-1 displayed more potent cross-reactivity and biological action on brain cells than IGF-1 isolated from human serum. We now present data on a recombinant DNA-derived truncated IGF-1 lacking the aminoterminal tripeptide. Recombinant truncated IGF-1 was 1.4-5-times more potent than recombinant and natural IGF-1 in displacing [125 I]IGF-1 from human fetal and adult brain and placenta membranes. These differences were slightly enhanced when truncated IGF-1 was used as radioligand. The relative potencies compared to insulin-like growth factor 2 (IGF-2) in displacing [125I]IGF-2 from rat liver membranes were recombinant truncated IGF-1, 0.3% and recombinant IGF-1, 0.2%. Recombinant truncated IGF-1 displayed 100-fold reduced affinity for the low molecular weight binding protein (IGF-BP) isolated from human amniotic fluid when compared to recombinant IGF-1. Likewise, the IGF-BP was 100-fold less potent in inhibiting the receptor binding of recombinant truncated IGF-1 than that of recombinant IGF-1. Recombinant truncated IGF-1 was 4-times more potent than recombinant and natural IGF-1 in stimulating DNA synthesis in fetal rat brain cells. This biological activity of recombinant truncated IGF-1 was not affected by the IGF-BP at concentrations which abolished the biological activity of recombinant IGF-1. The hypothesis that IGF-BP bound intact IGF-1 represents the endocrine form of IGF-1, whereas truncated IGF-1 represents the paracrine or autocrine form of IGF-1, is proposed.     

Insulin-like growth factor-1 (IGF-1) and leucine activate pig myogenic satellite cells through mammalian target of rapamycin (mTOR) pathway

Myogenic satellite cells are adult stem cells and have important roles in skeletal muscle growth, repair, and regeneration. Both insulin-like growth factor-1 (IGF-1) and leucine stimulate skeletal muscle growth, which link to the activation and proliferation of myogenic satellite cells in skeletal muscle. Mammalian target of rapamycin (mTOR) signaling is one of the main signaling pathways controlling protein synthesis and cell proliferation. Thus, IGF-1 and leucine may stimulate activation of myogenic satellite cells through mTOR signaling. In this study, myogenic satellite cells were isolated from 6-month-old pigs and subjected to IGF-1 and leucine treatments. Both IGF-1 and leucine upregulated mTOR signaling in myogenic satellite cells. The phosphorylation of mTOR at Ser(2448) increased 83.8 +/- 7.7% by IGF-1 (P < 0.05) and 83.4 +/- 5.7% by leucine (P < 0.05). The downstream targets of mTOR, S6 kinase, and 4E-binding protein 1 (4EBP1) were also phosphorylated due to IGF-1 and leucine treatments. Treatment with IGF-1 and leucine induced the phosphorylation of tuburin (TSC2), a key mediator upstream of mTOR signaling, by 272.8 +/- 26.4% and 94.2 +/- 28.7%, respectively. Treatment of cells with both IGF-1 and leucine did not show synergistic effect on mTOR signaling. Inhibition of mTOR by rapamycin abolished the protein synthesis and cell proliferation stimulated by both IGF-1 and leucine. In summary, our data showed that in preliminary cultured myogenic satellite cells mTOR signaling was activated due to IGF-1 and leucine treatments, and this mTOR activation is necessary for the activation of myogenic satellite cells.     

Silencing of the type 1 insulin-like growth factor receptor increases the sensitivity to apoptosis and inhibits invasion in human lung adenocarcinoma A549 cells

The type 1 insulin-like growth factor receptor (IGF-1R), which is over-expressed or activated in many human cancers, including lung cancer, mediates cancer cell proliferation and metastasis. Several studies indicate that blocking IGF-1R expression can inhibit tumor cell proliferation and metastasis. In this study, inhibition of the endogenous IGF-1R by recombinant adenoviruses encoding short hairpin RNAs against IGF-1R was found to significantly suppress IGF-1R expression, arrest the cell cycle, enhance the apoptotic response, and inhibit proliferation, adhesion, invasion and migration in A549 cells. Moreover, silencing IGF-1R decreases the expression of invasive-related genes including matrix metalloproteinase-2 (MMP-2), MMP-9, and urokinase-plasminogen activator (u-PA), and the phosphorylation of Akt and ERK1/2. These results suggest that the silencing of IGF-1R has the potential to be an effective cancer gene therapy strategy for human lung cancer.     

Reduction of TGF-beta activity abrogates growth promoting tumor cell-cell interactions in vivo.

We have shown in previous studies that metastatically-competent variant subpopulations (B5, C1) derived from a non-metastatic murine mammary adenocarcinoma (SP1) have a pronounced growth advantage over their non-metastatic tumor cell counterparts in primary tumors. As a result, primary tumors can be progressively overgrown by cells having the competence to spread elsewhere in the body. This occurs despite any evidence to indicate an intrinsic in vivo growth rate advantage of the metastatic cells when grown as isolated populations. This suggested that cell-cell interactions between metastatic and non-metastatic tumor populations may be involved in the metastatic cell growth dominance process. Evidence was therefore sought for growth factors released by SP1 cells which could preferentially stimulate the B5 or C1 variants and thereby mediate this cell-cell interaction process. We found that cocultures of SP1 and C1 or B5 cells with irradiated C1, B5, or SP1 "feeder" cells showed significant stimulation of C1 and B5 by SP1 "feeder" cells. Cell growth stimulation in response to EGF, TGF-alpha, TGF-beta 1, bFGF, PDGF, NGF, IGF-1, or IGF-2 demonstrated that only TGF-beta 1 could duplicate this effect. A repeat of the coculture experiment in the presence of specific neutralizing anti-TGF-beta antibodies was therefore undertaken and this was found to markedly reduce the stimulation of C1 or B5 cells by irradiated SP1 cells. Conditioned media from the SP1 and C1 cell lines was quantitated for TGF-beta activity and contained 4.5 ng/ml and 2.0 ng/ml, respectively. However, the majority of the TGF-beta released by SP1 cells was found to be spontaneously active, whereas 70% of the TGF-beta released by C1 cells was in its latent form. Scatchard analysis revealed approximately four times the number of TGF-beta receptors, of similar type and affinity, present on C1 as compared with SP1 cells. The in vitro results support the hypothesis that active TGF-beta released by SP1 cells may stimulate the proliferation of metastatic variant cells in a paracrine like fashion. In vivo evidence for this was obtained by showing that coinjection of irradiated SP1 cells could selectively stimulate tumor growth of viable C1 cells and this effect was markedly diminished by neutralizing polyclonal anti-TGF-beta antibodies. Taken together, the results suggest a novel role for TGF-beta in clonal evolution of malignant tumor growth and as a molecular mediator of tumor cell-tumor cell interactions involved in facilitating tumor progression.     

Insulin-like growth factor-1 receptor and ErbB kinase inhibitor combinations block proliferation and induce apoptosis through cyclin D1 reduction and Bax activation

The insulin-like growth factor-1 receptor (IGF-1R) and ErbB family of receptors are receptor tyrosine kinases that play important roles in cancer. Lack of response and resistance to therapies targeting ErbB receptors occur and are often associated with activation of the IGF-1R pathway. Combinations of agents that inhibit IGF-1R and ErbB receptors have been shown to synergistically block cancer cell proliferation and xenograft tumor growth. To determine the mechanism by which targeting both IGF-1R and ErbB receptors causes synergistic effects on cell growth and survival, we investigated the effects of combinations of selective IGF-1R and ErbB kinase inhibitors on proliferative and apoptotic signaling. We identified A431 squamous cell carcinoma cells as most sensitive to combinations of ErbB and IGF-1R inhibitors. The inhibitor combinations resulted in not only blockade of A431 cell proliferation, but also induced apoptosis, which was not seen with either agent alone. Upon examining phosphorylation states and expression levels of proteins in the IGF-1R and ErbB signaling pathways, we found a correlation between the ability of combinations to inhibit proliferation and to decrease levels of phosphorylated Akt and cyclin D1. In addition, the massive cell death induced by combined IGF-1R/ErbB inhibition was associated with Mcl-1 reduction and Bax activation. Thus, targeting both IGF-1R and ErbB receptors simultaneously results in cell cycle arrest and apoptosis through combined effects on Akt, cyclin D1, and Bax activation.     

Extracellular signal-regulated kinase and phosphoinositol-3 kinase mediate IGF-1 induced proliferation of fetal sheep cardiomyocytes

Growth of the fetal heart involves cardiomyocyte enlargement, division, and maturation. Insulin-like growth factor-1 (IGF-1) is implicated in many aspects of growth and is likely to be important in developmental heart growth. IGF-1 stimulates the IGF-1 receptor (IGF1R) and downstream signaling pathways, including extracellular signal-regulated kinase (ERK) and phosphoinositol-3 kinase (PI3K). We hypothesized that IGF-1 stimulates cardiomyocyte proliferation and enlargement through stimulation of the ERK cascade and stimulates cardiomyocyte differentiation through the PI3K cascade. In vivo administration of Long R3 IGF-1 (LR3 IGF-1) did not stimulate cardiomyocyte hypertrophy but led to a decreased percentage of cells that were binucleated in vivo. In culture, LR3 IGF-1 increased myocyte bromodeoxyuridine (BrdU) uptake by three- to five-fold. The blockade of either ERK or PI3K signaling (by UO-126 or LY-294002, respectively) completely abolished BrdU uptake stimulated by LR3 IGF-1. LR3 IGF-1 did not increase footprint area, but as expected, phenylephrine stimulated an increase in binucleated cardiomyocyte size. We conclude that 1) IGF-1 through IGF1R stimulates cardiomyocyte division in vivo; hyperplastic growth is the most likely explanation of IGF-1 stimulated heart growth in vivo; 2) IGF-1 through IGF1R does not stimulate binucleation in vitro or in vivo; 3) IGF-1 through IGF1R does not stimulate hypertrophy either in vivo or in vitro; and 4) IGF-1 through IGF1R requires both ERK and PI3K signaling for proliferation of near-term fetal sheep cardiomyocytes in vitro.     

外源NF-IL6(C/EBPβ)对肝癌细胞系BEL-7404的肿瘤抑制效应

目的:探讨核转录因子NFIL6对肝癌细胞系BEL7404恶性度的影响。方法:用磷酸钙介导转染技术,将NFIL6表达载体(pCN)和空载体质粒(pCN空)分别导入肝癌细胞系BEL7404,并借助细胞生长曲线,软琼脂集落形成试验,裸鼠成瘤试验对转染细胞的恶性度进行了检测。结果:与原细胞系BEL7404和空载体转染的该细胞系相比较,转染了NFIL6基因的BEL7404的各细胞克隆生长速度减慢,在软琼脂中集落形成率恶性度下降,裸鼠成瘤试验显示成瘤性明显降低。结论:表明外源转染的NFIL6对肝癌细胞系BEL7404具有明显的肿瘤抑制作用 。     

Comprehensive Suppression of All Apoptosis-Induced Proliferation Pathways as a Proposed Approach to Colorectal Cancer Prevention and Therapy

Mutations in the WNT/beta-catenin pathway are present in the majority of all sporadic colorectal cancers (CRCs), and histone deacetylase inhibitors induce apoptosis in CRC cells with such mutations. This apoptosis is counteracted by (1) the signaling heterogeneity of CRC cell populations, and (2) the survival pathways induced by mitogens secreted from apoptotic cells. The phenomena of signaling heterogeneity and apoptosis-induced survival constitute the immediate mechanisms of resistance to histone deacetylase inhibitors, and probably other chemotherapeutic agents. We explored the strategy of augmenting CRC cell death by inhibiting all survival pathways induced by the pro-apoptotic agent LBH589, a histone deacetylase inhibitor: AKT, JAK/STAT, and ERK signaling. The apoptosis-enhancing ability of a cocktail of synthetic inhibitors of proliferation was compared to the effects of the natural product propolis. We utilized colorectal adenoma, drug-sensitive and drug-resistant colorectal carcinoma cells to evaluate the apoptotic potential of the combination treatments. The results suggest that an effective approach to CRC combination therapy is to combine apoptosis-inducing drugs (e.g., histone deacetylase inhibitors, such as LBH589) with agents that suppress all compensatory survival pathways induced during apoptosis (such as the cocktail of inhibitors of apoptosis-associated proliferation). The same paradigm can be applied to a CRC prevention approach, as the apoptotic effect of butyrate, a diet-derived histone deacetylase inhibitor, is augmented by other dietary agents that modulate survival pathways (e.g., propolis and coffee extract). Thus, dietary supplements composed by fermentable fiber, propolis, and coffee extract may effectively counteract neoplastic growth in the colon.     

Muscle-specific overexpression of the type 1 IGF receptor results in myoblast-independent muscle hypertrophy via PI3K, and not calcineurin, signaling

The insulin-like growth factors (IGF-I and IGF-II), working through the type 1 IGF receptor (IGF-1R), are key mediators of skeletal muscle fiber growth and hypertrophy. These processes are largely dependent on stimulation of proliferation and differentiation of muscle precursor cells, termed myoblasts. It has not been rigorously determined whether the IGFs can also mediate skeletal muscle hypertrophy in a myoblast-independent fashion. Similarly, although the phosphatidylinositol 3-kinase (PI3K) and calcineurin signaling pathways have been implicated in skeletal muscle hypertrophy, these pathways are also involved in skeletal myoblast differentiation. To determine whether the IGFs can stimulate skeletal muscle hypertrophy in a myoblast-independent fashion, we developed and validated a retroviral expression vector that mediated overexpression of the human IGF-1R in rat L6 skeletal myotubes (immature muscle fibers), but not in myoblasts. L6 myotubes transduced with this vector accumulated significantly higher amounts of myofibrillar proteins, in a ligand- and receptor-dependent manner, than controls and demonstrated significantly increased rates of protein synthesis. Stimulation of myotube hypertrophy was independent of myoblast contributions, inasmuch as these cultures did not exhibit increased levels of myoblast proliferation or differentiation. Experiments with PI3K and calcineurin inhibitors indicated that myoblast-independent myotube hypertrophy was mediated by PI3K, but not calcineurin, signaling. This study demonstrates that IGF can mediate skeletal muscle hypertrophy in a myoblast-independent fashion and suggests that muscle-specific overexpression of the IGF-1R or stimulation of its signaling pathways could be used to develop strategies to ameliorate muscle wasting without stimulating proliferative pathways leading to carcinogenesis or other pathological sequelae.     

Dynamic roles of angiopoietin-like proteins 1, 2, 3, 4, 6 and 7 in the survival and enhancement of ex vivo expansion of bone-marrow hematopoietic stem cells

Recent advances in hematopoietic stem cells (HSCs) expansion by growth factors including angiopoietin-like proteins (Angptls) have opened up the possibility to use HSCs in regenerative medicine. However, the unavailability of true in vitro HSCs expansion by these growth factors has limited the understanding of the cellular and molecular mechanism of HSCs expansion. Here, we report the functional role of mouse Angptls 1, 2, 3, 4, 6 and 7 and growth factors SCF, TPO, IGF-2 and FGF-1 on purified mouse bone-marrow (BM) Lineage^-Sca-1⁺(Lin^-Sca-1⁺) HSCs. The recombinant retroviral transduced- CHO-S cells that secrete Angptls in serum-free medium were used alone or in combination with growth factors (SCF, TPO, IGF-2 and FGF-1). None of the Angptls stimulated HSC proliferation, enhanced or inhibited HSCs colony formation, but they did support the survival of HSCs. By contrast, any of the six Angptls together with saturating levels of growth factors dramatically stimulated a 3- to 4.5-fold net expansion of HSCs compared to stimulation with a combination of those growth factors alone. These findings lead to an understanding of the basic function of Angptls on signaling pathways for the survival as well as expansion of HSCs in the bone marrow niche.     

Growth factors sustain primordial germ cell survival, proliferation and entering into meiosis in the absence of somatic cells

It is known that mammalian primordial germ cells (PGCs), the precursors of oocytes and prospermatogonia, depend for survival and proliferation on specific growth factors and other undetermined compounds. Adhesion to neighboring somatic cells is also believed to be crucial for preventing PGC apoptosis occurring when they lose appropriate cell to cell contacts. This explains the current impossibility to maintain isolated mouse PGCs in culture for periods longer than a few hours in the absence of suitable cell feeder layers producing soluble factors and expressing surface molecules necessary for preventing PGTC apoptosis and stimulating their proliferation. In the present paper, we identified a cocktail of soluble growth factors, namely KL, LIF, BMP-4, SDF-1, bFGF and compounds (N-acetyl-L-cysteine, forskolin, retinoic acid) able to sustain the survival and self-renewal of mouse PGCs in the absence of somatic cell support. We show that under culture conditions allowing PGC adhesion to an acellular substrate, such growth factors and compounds were able to prevent the occurrence of significant levels of apoptosis in PGCs for two days, stimulate their proliferation and, when LIF was omitted from the cocktail, allow most of them to enter into and progress through meiotic prophase I. These results consent for the first time to establish culture conditions for purified mammalian PGCs in the absence of somatic cell support and should make easier the molecular dissection of the processes governing the development of such cells crucial for early gametogenesis.     

Multiple mechanisms are responsible for transactivation of the epidermal growth factor receptor in mammary epithelial cells

The number of distinct signaling pathways that can transactivate the epidermal growth factor receptor (EGFR) in a single cell type is unclear. Using a single strain of human mammary epithelial cells, we found that a wide variety of agonists, such as lysophosphatidic acid (LPA), uridine triphosphate, growth hormone, vascular endothelial growth factor, insulin-like growth factor-1 (IGF-1), and tumor necrosis factor-alpha, require EGFR activity to induce ERK phosphorylation. In contrast, hepatocyte growth factor can stimulate ERK phosphorylation independent of the EGFR. EGFR transactivation also correlated with an increase in cell proliferation and could be inhibited with metalloprotease inhibitors. However, there were significant differences with respect to transactivation kinetics and sensitivity to different inhibitors. In particular, IGF-1 displayed relatively slow transactivation kinetics and was resistant to inhibition by the selective ADAM-17 inhibitor WAY-022 compared with LPA-induced transactivation. Studies using anti-ligand antibodies showed that IGF-1 transactivation required amphiregulin production, whereas LPA was dependent on multiple ligands. Direct measurement of ligand shedding confirmed that LPA treatment stimulated shedding of multiple EGFR ligands, but paradoxically, IGF-1 had little effect on the shedding rate of any ligand, including amphiregulin. Instead, IGF-1 appeared to work by enhancing EGFR activation of Ras in response to constitutively produced amphiregulin. This enhancement of EGFR signaling was independent of both receptor phosphorylation and PI-3-kinase activity, suggestive of a novel mechanism. Our studies demonstrate that within a single cell type, the EGFR autocrine system can couple multiple signaling pathways to ERK activation and that this modulation of EGFR autocrine signaling can be accomplished at multiple regulatory steps.     

Novel Agents Targeting the IGF-1R/PI3K Pathway Impair Cell Proliferation and Survival in Subsets of Medulloblastoma and Neuroblastoma

The receptor tyrosine kinase (RTK)/phosphoinositide 3-kinase (PI3K) pathway is fundamental for cancer cell proliferation and is known to be frequently altered and activated in neoplasia, including embryonal tumors. Based on the high frequency of alterations, targeting components of the PI3K signaling pathway is considered to be a promising therapeutic approach for cancer treatment. Here, we have investigated the potential of targeting the axis of the insulin-like growth factor-1 receptor (IGF-1R) and PI3K signaling in two common cancers of childhood: neuroblastoma, the most common extracranial tumor in children and medulloblastoma, the most frequent malignant childhood brain tumor. By treating neuroblastoma and medulloblastoma cells with R1507, a specific humanized monoclonal antibody against the IGF-1R, we could observe cell line-specific responses and in some cases a strong decrease in cell proliferation. In contrast, targeting the PI3K p110α with the specific inhibitor PIK75 resulted in broad anti-proliferative effects in a panel of neuro- and medulloblastoma cell lines. Additionally, sensitization to commonly used chemotherapeutic agents occurred in neuroblastoma cells upon treatment with R1507 or PIK75. Furthermore, by studying the expression and phosphorylation state of IGF-1R/PI3K downstream signaling targets we found down-regulated signaling pathway activation. In addition, apoptosis occurred in embryonal tumor cells after treatment with PIK75 or R1507. Together, our studies demonstrate the potential of targeting the IGF-1R/PI3K signaling axis in embryonal tumors. Hopefully, this knowledge will contribute to the development of urgently required new targeted therapies for embryonal tumors.     

Tumor necrosis factor stimulates proliferation of human osteosarcoma cells and accumulation of c-myc messenger RNA

The objective of this study was to establish whether human recombinant tumor necrosis factor (TNF) can significantly stimulate the proliferation of some tumor cells. Treatment with TNF had little or no effect on the growth of human tumor cells and murine NIH/3T3 cells cultured in medium with high serum concentration. Two tumor lines, SK-MEL-109 melanoma and HOS osteosarcoma cells, were adapted to grow in medium supplemented with 0.5% serum. The growth of these SK-MEL-109 cells was inhibited by TNF, but that of the HOS cells was greatly stimulated by TNF in a dose-dependent way. Treatment with 10 ng/ml of TNF resulted in a two-fold increase in the rate of cell division. This effect of TNF was also shown by measuring DNA and protein synthesis. The continuous presence of TNF was not required for its mitogenic activity on HOS cells cultured with 0.5% serum, since treatment for only one day with TNF resulted in prolonged growth stimulation. The failure of TNF to promote division of cells cultured in medium with 10% serum may possibly be explained by the presence of saturating amounts of growth factors in serum. Interferons abolished the mitogenic activity of TNF on HOS cells. Furthermore, TNF did not show synergism with insulin or epidermal growth factor in stimulating growth of these cells. The level of c-myc mRNA was increased five-fold after 30 minutes of treatment with TNF. This shows that TNF is a growth factor for HOS cells and that it induces accumulation of c-myc mRNA.     

Let-7e enhances the radiosensitivity of colorectal cancer cells by directly targeting insulin-like growth factor 1 receptor

Abnormal expression of various microRNAs (miRNAs), as regulators of biological signaling pathways, has a strong association with cancer resistance to chemotherapy and radiotherapy. The let-7 family of miRNAs as tumor suppressors have shown to be downregulated in different types of human malignancies including colorectal cancer (CRC). However, the biological function of let-7 members in the processes of resistance to radiation in CRC has not yet been completely elucidated. Insulin-like growth factor 1 receptor (IGF-1R) signaling pathway is amplified in CRC and leads to its progression, development, and also radiation resistance. So, it seems like an attractive target for anticancer therapy. In this study, by using bioinformatics analysis, it has been revealed that IGF-1R is a direct target of the let-7e member. Consistent with this, we identified that increased levels of let-7e in CRC cells reduced IGF-1R protein level and subsequently its downstream signaling pathways, which resulted in the G1 cell cycle arrest and a significant reduction in the proliferation, survival and also resistance to radiation of CRC cells. Altogether, these results suggested that let-7e by targeting the IGF-1R signaling pathway might serve as therapeutics in anticancer therapy.