Cellular basis of cancer metastasis: A review of fundamentals and new advances

This review provides an introduction to fundamentals and new advances in cancer metastasis for general readers. The first segment includes topics such as cell adhesion, cell migration, proteases, inflammation, coagulation and site selection in metastasis. Then follows a discussion of an interesting report by Kaplan et al. [VEGFR1-positive haematopoietic bone marrow progenitors initiate the pre-metastatic niche. Nature 2005;438:820-7] that provides evidence for a role of VEGFR1+bone marrow cells in preparing pre-metastatic niches in specific organs that host the arrival and growth of metastatic cancer cells. The therapeutic implications of this study are explored.     

Targeting podocyte-associated diseases

Injury to the podocytes is the initiating cause of many renal diseases, leading to proteinuria with possible progression to end-stage renal disease. Podocytes are highly specialized cells, with an important role in maintaining the glomerular filtration barrier and producing growth factors for both mesangial cells and endothelial cells. With their foot processes they cover the glomerular basement membrane, and form slit diaphragms with neighboring podocytes.Human podocytopathies include focal and segmental glomerulosclerosis, minimal change disease, membranous nephropathy, collapsing glomerulopathy and diabetic nephropathy. Research in the last two decades has demonstrated great progress in understanding the molecular mechanisms leading to podocytopathies. These include single gene defects in slit diaphragm proteins, but also discovery of apoptotic, enzymatic and other pathways involved in podocyte injury. With this progress, a great number of animal models is now available to study either specific podocytopathies, e.g. in mouse models with single gene mutations, or more general podocyte injury patterns, such as the lipopolysaccharide or protamine sulfate model of foot process effacement.In this review, the morphology of the glomerulus will be discussed, with a focus on the podocyte, its interactions with surrounding cells, and the highly differentiated slit diaphragm separating the apical from the basal membrane. We also provide an overview of human podocytopathies and animal models to study these diseases. In the last part we discuss targeted therapies addressing pathways and proteins affected in podocyte injury.     

Malignant pleural mesothelioma: current treatments and emerging drugs

Background: Malignant pleural mesothelioma (MPM) is an uncommon disease whose incidence is increasing worldwide over the past 30 years. Surgical resection and radiotherapy represent the standard treatment in patient with resectable MPM. Chemotherapy is also necessary to reduce incidence of distant metastases, but the optimal setting of treatment (neoadjuvant, adjuvant and intrapleural) is not clarified. For the patients with unresectable MPM, the combination cisplatin and pemetrexed or ralitrexed is the standard treatment as supported by a Phase III study. Better understanding of molecular pathways involved in MPM has enabled inclusion of new drugs targeted against pathways responsible for proliferation, cell survival and angiogenesis. Objective: This review discusses the current treatment option, the specific signal pathways activated in MPM and the novel agents under evaluation in clinical trials. Methods: We use for this article abstracts, papers, oral presentations from ASCO and the website http://www.clinical-trials.gov. Results/ conclusion: This review summarizes the activity of chemotherapy and of new agents under evaluation in clinical trials. The better understanding of molecular pathways activated in MPM will hopefully provide new therapeutic options for these patients in the future.     

Targeting signaling pathways in ovarian cancer

Background: Ovarian cancer is the most lethal gynecological cancer in western countries. Prognosis is poor for patients who relapse after platinum- and taxane-based therapy and additional treatment options besides second-line chemotherapy are necessary. Signaling pathways form promising novel candidates for pinpoint cancer treatment and thus much effort has been made to establish signal transduction as target for therapy. Objective: Tyrosine kinases, as crucial parts of the transduction pathways, have become important objects in successful treatment of various cancers. This review aims to examine the role of tyrosine kinase inhibition in treatment of ovarian cancer. Methods: Based on results of various clinical Phase I – III trials and preclinical basic research this review focuses on inhibition of growth factor receptors like human epidermal growth factor receptor 2 (HER2), epidermal growth factor receptor (EGFR), and vascular endothelial growth factor (VEGFR), including presentations from the American Society of Clinical Oncology (ASCO) annual meeting 2007. Conclusions: Although various agents show activity in ovarian cancer results are variable and mostly disappointing. Clinical value may be relevant only for an immunohistologically defined subgroup of patients. These questions have to be examined in larger Phase III trials.     

Neutrophil-mediated experimental metastasis is enhanced by VEGFR inhibition in a zebrafish xenograft model

Inhibition of VEGF signalling effectively suppresses localized tumour growth but accelerates tumour invasiveness and micrometastasis by unknown mechanisms. To study the dynamic and reciprocal interactions between tumour cells and their microenvironment during these processes, we established a xenograft model by injecting tumour cells into the blood circulation of transparent zebrafish embryos. This reproducibly results in rapid simultaneous formation of a localized tumour and experimental micrometastasis, allowing time-resolved imaging of both processes at single-cell resolution within 1 week. The tumour vasculature was initiated de novo by remodelling of primitive endothelial cells into a functional network. Roles of myeloid cells in critical tumourigenesis steps such as vascularization and invasion were revealed by genetic and pharmaceutical approaches. We discovered that the physiological migration of neutrophils controlled tumour invasion by conditioning the collagen matrix and forming the metastatic niche, as detected by two-photon confocal microscopy and second harmonic generation. Administration of VEGFR inhibitors blocked tumour vascularization and a localized tumour growth but enhanced migration of neutrophils, which in turn promoted tumour invasion and formation of micrometastasis. This demonstrates the in vivo cooperation between VEGF signalling and myeloid cells in metastasis and provides a new mechanism underlying the recent findings that VEGFR targeting can promote tumour invasiveness.     

Live imaging in zebrafish reveals neu(trophil) insight into the metastatic niche

Non-cancerous immune cells can significantly contribute to tumour progression and metastases. Neutrophils associated with tumours can both promote and inhibit tumour progression, but less is known about how non-associated immune cells contribute to cancer biology. In a recent issue of the Journal of Pathology, He and colleagues use non-invasive, high-resolution imaging of the whole living animal to provide a compelling glimpse at how physiological migration of neutrophils can prepare a metastatic niche and how their activities can be altered by the unintended consequences of targeted therapeutics.     

In silico repurposing the Rac1 inhibitor NSC23766 for treating PTTG1-high expressing clear cell renal carcinoma

The pituitary tumor-transforming gene 1 (PTTG1), also known as Securin, is considered an oncogene. This study aimed to investigate the role of PTTG1 in clear cell renal cell carcinoma (ccRCC) using in silico bioinformatics approaches. A pan-cancer analysis using The Cancer Genome Atlas (TCGA) data indicated that among all cancer types copy number amplification of PTTG1 gene was most frequently found in ccRCC. However, amplification of PTTG1 gene copy number did not correlate with the increase of mRNA level in ccRCC, and did not predict the patients' overall survival. Instead, ccRCC was correlated with overexpression of PTTG1 mRNA, and its expression level was stage-dependent increased in cancer patients. An outlier analysis using the Oncomine database suggested that PTTG1 mRNA expression served as a good biomarker for ccRCC. Pathway analysis for upregulated genes enriched in PTTG1-high expressing ccRCC patients found that PTTG1 overexpression was associated with mitotic defects. Mining drug sensitivity data using the Cancer Therapeutics Response Portal (CTRP) discovered that PTTG1-high expressing ccRCC cell lines were susceptible to a Rac1 (Ras-related C3 botulinum toxin substrate 1) inhibitor NSC23766. Therefore, this study provides an in silico insight into the role of PTTG1 in ccRCC, and repurposes the Rac1 inhibitor NSC23766 for treating PTTG1-high expressing ccRCC.     

Targeted therapy in gastric cancer

Gastric cancer is often diagnosed at an advanced stage. Although chemotherapy prolongs survival and improves quality of life, the survival of gastric cancer patients with advanced disease is short. Thanks to recent insights into the molecular pathways involved in gastric carcinogenesis, new targeted treatment options have become available for gastric cancer patients. Trastuzumab, an antibody targeted to HER‐2, was shown to improve survival of advanced gastric cancer patients harboring HER‐2 overexpression due to gene amplification in their tumor cells, and is currently also explored in adjuvant and neoadjuvant settings. Another agent with promising results in clinical trials is ramucirumab, an antibody targeting VEGFR‐2. No clear survival benefit, however, were experienced with agents targeting EGFR (cetuximab, panitumumab), VEGF‐A (bevacizumab), or mTOR (everolimus). Drugs targeting c‐MET/HGF are currently under investigation in biomarker‐selected cohorts, with promising results in early clinical trials. This review will summarize the current status of targeted treatment options in gastric cancer.     

Bevacizumab‐enhanced antitumor effect of 5‐fluorouracil via upregulation of thymidine phosphorylase through vascular endothelial growth factor A/vascular endothelial growth factor receptor 2‐specificity protein 1 pathway

Bevacizumab (Bv) can be used synergistically with fluoropyrimidine‐based chemotherapy to treat colorectal cancer. Whether and how it affects the delivery of fluoropyrimidine drugs is unknown. The present study aimed to explore the effect of Bv on the delivery of 5‐fluorouracil (5‐FU) to tumors and the underlying mechanism from metabolic perspective. Bv enhanced the anti‐tumor effects of 5‐FU in LoVo colon cancer xenograft mice and increased the 5‐FU concentration in tumors without affecting hepatic 5‐FU metabolism. Interestingly, Bv remarkably upregulated thymidine phosphorylase (TP) in tumors, which mediated the metabolic activation of 5‐FU. Although TP is reported to promote angiogenesis and resistance, the combination of Bv and 5‐FU resulted in anti‐angiogenesis and vessel normalization in tumors, indicating that the elevated TP mainly contributed to the enhanced response to 5‐FU. Bv also induced TP upregulation in LoVo cancer cells. Treatment with vascular endothelial growth factor receptor 2 (VEGFR2) antagonist apatinib and VEGFR2 silencing further confirmed TP upregulation. Bv and apatinib both enhanced the cytotoxicity of 5‐FU in LoVo cells, but there was no synergism with adriamycin and paclitaxel. We further demonstrated that the effect of Bv was dependent on VEGFR2 blockade and specificity protein 1 activation via MDM2 inhibition. In summary, Bv enhanced the accumulation of 5‐FU in tumors and the cytotoxicity of 5‐FU via TP upregulation. We provide data to better understand how Bv synergizes with 5‐FU from metabolic perspective, and it may give clues to the superiority of Bv in combination with fluoropyrimidine drugs compared to other chemotherapeutic drugs in colon cancer.