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Transforming growth factor-b1 (TGF-b1) induces stromal fibroblast-to-myofibroblast transdifferentiation in the tumor-stroma interactive microenvironment via modulation of multiple phenotypic and functional genes, which plays a critical role in tumor progression. Up to now, the involvement of micro-RNAs (miRNAs) and their roles in TGF-b1-induced myofibroblast differentiation in tumor-stroma interaction are unclear. Using quantitative real-time RT-PCR, we demonstrated that the expression of micro-RNA-21 (miR-21) was upregulated in activated fibroblasts after treatment with TGF-b1 or conditioned medium from cancer cells. To determine the potential roles of miR-21 in TGF-b1-mediated gene regulation during myofibroblast conversion, we showed that miR-21 expression was downregulated by miR-21 inhibitor and upregulated by miR-21 mimic. Interestingly, downregulation of miR-21 with the inhibitor effectively inhibited TGF-b1-induced myofibroblast differentiation while upregulation of miR-21 with a mimic significantly promoted myofibroblast differentiation. We further demonstrated that MiR-21 directly targeted and downregulated programmed cell death 4 (PDCD4) gene, which in turn acted as a negative regulator of several phenotypic and functional genes of myofibroblasts. Taken together, these results suggested that miR-21 participated in TGF-b1-induced myofibroblast transdifferentiation in cancer stroma by targeting PDCD4.Increasing evidence has indicated that cancer development is facilitated by continuing interaction between tumor cells and activated stromal cells. 1 Fibroblasts and myofibroblasts are the major cell types in various human tumor stroma. These cells are receiving increasing attention because of their participation in tumor progression, including invasion, 2,3 metastasis, 2 angiogenesis 4,5 and the response to therapy. 6,7 Myofibroblasts modulate the stroma in physiology and pathology via direct cell-cell contacts and/or secretion of a range of phenotypic and functional proteins. In general, stromal fibroblasts that are adjacent to cancer cell nests express various differentiation markers, such as the well-known differentiated marker a-smooth muscle actin (a-SMA), and thus are termed as myofibroblasts. 8,9 a-SMA positive myofibroblasts do stimulate tumor invasion and angiogenesis whereas a-SMA negative fibroblasts do not promote such activities. 2,5 Although the origin of stromal myofibroblasts remains controversial, fibroblasts and bone marrow progenitor cells are considered to be the main precursor cells, 5,10,11 which are transdifferentiated into myofibroblasts by paracrine signals generated by cancer cells. Among these signals, transforming growth factor-b (TGF-b) is thought to be the most potent. TGF-b induced myofibroblast differentiation constitutes an important niche for tumor development through proinvasion and proangiogenesis. [2][3][4] In a three dimensional coculture model of human fibroblasts with human colon cancer cells HCT-8/E11, TGF-b is the dominant factor to mediate

The unique properties of the tumour microenvironment can be exploited by using recombinant anaerobic clostridial spores as highly selective gene delivery vectors. Although several recombinant Clostridium species have been generated during the past decade, their efficacy has been limited. Our goal was to substantially improve the prospects of clostridia as a gene delivery vector. Therefore, we have assessed a series of nitroreductase (NTR) enzymes for their capacity to convert the innocuous CB1954 prodrug to its toxic derivative. Among the enzymes tested, one showed superior prodrug turnover characteristics. In addition, we established an efficient gene transfer procedure, based on conjugation, which allows for the first time genetic engineering of Clostridium strains with superior tumour colonisation properties with high success rates. This conjugation procedure was subsequently used to create a recombinant C. sporogenes overexpressing the isolated NTR enzyme. Finally, analogous to a clinical setting situation, we have tested the effect of multiple consecutive treatment cycles, with antibiotic bacterial clearance between cycles. Importantly, this regimen demonstrated that intravenously administered spores of NTR-recombinant C. sporogenes produced significant antitumour efficacy when combined with prodrug administration.

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Bacterial-based tumor-targeted therapy is an area of growing interest and holds promise for the treatment of solid tumors. Upon systemic administration, various types of non-pathogenic obligate anaerobes and facultative anaerobes have been shown to infiltrate and selectively replicate within solid tumors. The tumor specificity is based upon the unique physiology of solid tumors, which is often characterized by regions of hypoxia and necrosis. Prokaryotic vectors can be safely administered and their potential to deliver therapeutic proteins has been demonstrated in a variety of preclinical models. Although the amount of clinical experience with bacterial vectors is limited to date, the available data clearly demonstrated the feasibility of bacterial-mediated therapy in humans. There are several issues however that are still unknown and remain major challenges. In this review, using Clostridium and modified Salmonella as prototypical agents, we will discuss the major advantages, challenges and shortcomings of bacterial systems for tumor-specific therapy. In addition, we will highlight the requirements needed to advance the approach into clinical trials.