Marilena Loizidou

Liposomes and nanoparticles: nanosized vehicles for drug delivery in cancer

Nanoscale drug delivery systems using liposomes and nanoparticles are emerging technologies for the rational delivery of chemotherapeutic drugs in the treatment of cancer. Their use offers improved pharmacokinetic properties, controlled and sustained release of drugs and, more importantly, lower systemic toxicity. The commercial availability of liposomal Doxil and albumin-nanoparticle-based Abraxane has focused attention on this innovative and exciting field. Recent advances in liposome technology offer better treatment of multidrug-resistant cancers and lower cardiotoxicity. Nanoparticles offer increased precision in chemotherapeutic targeting of prostate cancer and new avenues for the treatment of breast cancer. Here we review current knowledge on the two technologies and their potential applications to cancer treatment.

3D tumour models: novel in vitro approaches to cancer studies

Abstract3D in vitro models have been used in cancer research as a compromise between 2-dimensional cultures of isolated cancer cells and the manufactured complexity of xenografts of human cancers in immunocompromised animal hosts. 3D models can be tailored to be biomimetic and accurately recapitulate the native in vivo scenario in which they are found. These 3D in vitro models provide an important alternative to both complex in vivo whole organism approaches, and 2D culture with its spatial limitations. Approaches to create more biomimetic 3D models of cancer include, but are not limited to, (i) providing the appropriate matrix components in a 3D configuration found in vivo, (ii) co-culturing cancer cells, endothelial cells and other associated cells in a spatially relevant manner, (iii) monitoring and controlling hypoxia- to mimic levels found in native tumours and (iv) monitoring the release of angiogenic factors by cancer cells in response to hypoxia. This article aims to overview current 3D in vitro models of cancer and review strategies employed by researchers to tackle these aspects with special reference to recent promising developments, as well as the current limitations of 2D cultures and in vivo models. 3D in vitro models provide an important alternative to both complex in vivo whole organism approaches, and 2D culture with its spatial limitations. Here we review current strategies in the field of modelling cancer, with special reference to advances in complex 3D in vitro models.

Endothelin-1: a multifunctional molecule in cancer

Endothelin-1 is a small vasoconstrictor peptide that was first identified in 1988. Here we review the evidence implicating ET-1 in tumorigenesis. In particular, we concentrate on the role of ET-1 in mitogenesis, apoptosis, angiogenesis, tumour invasion and metastasis, and discuss the potential for endothelin-system modulation as an adjuvant therapeutic strategy.

Increased endothelin-1 in colorectal cancer and reduction of tumour growth by ET A receptor antagonism

Endothelin-1 (ET-1) is a vasoconstrictor peptide which stimulates proliferation in vitro in different cell types, including colorectal cancer cells. Raised ET-1 levels have been detected both on tissue specimens and in the plasma of patients with cancers. To investigate the role of ET-1 in colorectal cancer: (i) ET-1 plasma levels in patients with colorectal cancer were measured by radioimmunoassay: group 1 = controls (n = 22), group 2 = primary colorectal cancer only (n = 39), group 3 = liver metastases only (n = 26); (ii) ET-1 expression in primary colorectal cancer specimens (n=10) was determined immunohistochemically and (iii) the effect of intraportally infused antagonists to the two ET-1 receptors, ETA and ETB, on the growth of liver metastases in a rat model was assessed. ET-1 plasma levels were significantly increased in both patients with primary tumour and patients with metastases, compared to controls (P<0.01, 3.9±1.4, 4.5±1.5, vs. 2.75±1.37pg/ml, respectively). Immunohistochemically, strong expression of ET-1 was found in the cytoplasm, stroma and blood vessels of cancers, unlike the normal colon where only the apical layer of the epithelium, vascular endothelial cells and surrounding stroma were positively stained. In the rat model, there was significant reduction in liver tumour weights compared to controls, following treatment with the ETA antagonist (BQ123) 30min after the intraportal inoculation of tumour cells (P < 0.05). These results suggest ET-1 is produced by colorectal cancers and may play a role in the growth of colorectal cancer acting through ETA receptors. ETA antagonists are indicated as potential anti-cancer agents.

Improved in vivo delivery of m-THPC via pegylated liposomes for use in photodynamic therapy

Pegylated liposomal nanocarriers have been developed with the aim of achieving improved uptake of the clinical PDT photosensitiser, m-THPC, into target tissues through increased circulation time and bioavailability. This study investigates the biodistribution and PDT efficacy of m-THPC in its standard formulation (Foscan®) compared to m-THPC incorporated in liposomes with different degrees of pegylation (FosPEG 2% and FosPEG 8%), following i.v. administration to normal and tumour bearing rats. The plasma pharmacokinetics were described using a three compartmental analysis and gave elimination half lives of 90 h, 99 h and 138 h for Foscan®, FosPEG 2% and 8% respectively. The accumulation of m-THPC in tumour and normal tissues, including skin, showed that maximal tumour to skin ratios were observed at ≤ 24 h with FosPEG 2% and 8%, whilst skin photosensitivity studies showed Foscan® induces more damage compared to the liposomes at drug-light intervals of 96 and 168 h. PDT treatment at 24h post-administration (0.05 mg kg⁻¹) showed higher tumour necrosis using pegylated liposomal formulations in comparison to Foscan®, which is attributed to the higher tumour uptake and blood plasma concentrations. Clinically, this improved selectivity has the potential to reduce not only normal tissue damage, but the drug dose required and cutaneous photosensitivity.

Endothelin-1 and Angiogenesis in Cancer

Tumours require oxygenation, nutrition and a route for dissemination. This necessitates the development of new vessels or angiogenesis. High levels of new vessel development are indicators of poor prognosis in cancer; they also provide new avenues of anti-tumour therapy. Angiogenesis in cancer produces structurally different vessels from angiogenesis in wound healing and inflammation. This article reviews the differences between vessels in tumour angiogenesis and normal angiogenesis. The main focus of the article is the role of the vasoactive peptide endothelin-1 (ET-1) in tumour angiogenesis. The role of ET-1 in tumour development is reviewed, before the direct and indirect effects of ET-1 in angiogenesis are examined. ET-1 has a direct angiogenic effect on endothelial and peri-vascular cells. It also has an indirect action through the increased release of the potent pro-angiogenic substance vascular endothelial growth factor (VEGF), via hypoxia inducible factor-1. ET-1 also indirectly stimulates angiogenesis by stimulating fibroblasts and cancer cells to produce pro-angiogenic proteases. ET-1 is a novel stimulator of tumour angiogenesis and warrants further examination as an anti-angiogenic treatment target.

A novel tissue engineered three-dimensional in vitro colorectal cancer model.

The interactions of cancer cells within a solid mass with the surrounding reactive stroma are critical for growth and progression. The surrounding vasculature is recruited into the periphery of the growing tumour to supply cancer cells with nutrients and O2. This study focuses on developing a novel three-dimensional (3-D) in vitro biomimetic colorectal cancer model using colorectal cancer cells and connective tissue cells. The 3-D model comprises a dense artificial cancer mass, created by partial plastic compression of collagen type I containing HT29 colorectal cancer cells, nested in a non-dense collagen type I gel populated by fibroblasts and/or endothelial cells. HT29 cells within the dense mass proliferate slower than when cultured in a two-dimensional system. These cells form tumour spheroids which invade the surrounding matrix, away from the hypoxic conditions in the core of the construct, measured using real time O2 probes. This model is also characterized by the release of vascular endothelial growth factor (VEGF) by HT29 cells, mainly at the invading edge of the artificial cancer mass. This characterization is fundamental in establishing a reproducible, complex model that could be used to advance our understanding of cancer pathology and will facilitate therapeutic drug testing.

Mechanisms of endothelin 1-stimulated proliferation in colorectal cancer cell lines†

The peptide endothelin (ET) 1 promotes proliferation in a number of epithelial cancers. The aim of this study was to identify the mechanism of ET‐1‐stimulated proliferation in colorectal cancer cells in vitro.

Endothelin-1 and tumour development

There has been a growing conviction amongst oncologists that cancer is a disease characterized by changes in specific molecules. These changes include alteration in the structure, regulation or quantity of growth factors and their receptors, signal transducers and the proteins encoded by dominant or suppressor/recessive oncogenes. The role of endothelin (vasoactive peptide) in tumour cell signal transduction and mitogenesis and induction of endothelial cell growth and angiogenesis in tumour growth is discussed in this article.

Endothelin receptor antagonism and cancer

The endothelin peptides have an important role in the cancer‐stromal interactions that promote tumour growth. Endothelin‐1 (ET‐1), clinically the most investigated endothelin, is a vital agent in the growth and progression of several tumours including prostate, ovarian, colorectal, bladder, breast and lung carcinomas. ET‐1 exerts its effects through the activation of two distinct receptors, ETA and ETB. Once activated, these receptors transmit signals via numerous intracellular signalling pathways. The effects of ET receptor stimulation in cancer cells or cancer‐associated cells include proliferation, resistance to apoptosis, angiogenesis, migration and subsequent invasion. At present, the manipulation of the endothelin axis within the pre‐clinical setting is the subject of intense investigation. Recent studies into ET receptor antagonism have produced interesting results highlighting the fact that these receptors may provide novel targets for a new generation of chemotherapeutic agents in a variety of cancers.