Patient-derived xenografts: a relevant preclinical model for drug development

Diagnosis and treatment of ALT tumors: is Trabectedin a new therapeutic option?

Telomeres are specialized nucleoprotein structures responsible for protecting chromosome ends in order to prevent the loss of genomic information. Telomere maintenance is required for achieving immortality by neoplastic cells. While most cancer cells rely on telomerase re-activation for linear chromosome maintenance and sustained proliferation, a significant population of cancers (10-15%) employs telomerase-independent strategies, collectively referred to as Alternative Lengthening of Telomeres (ALT). ALT mechanisms involve different types of homology-directed telomere recombination and synthesis. These processes are facilitated by loss of the ATRX or DAXX chromatin-remodeling factors and by abnormalities of the telomere nucleoprotein architecture. Although the functional consequences of telomerase and ALT up-regulation are similar in that they both prevent overall telomere shortening in tumors, these telomere maintenance mechanisms (TMMs) differ in several aspects which may account for their differential prognostic significance and response to therapy in various tumor types. Therefore, reliable methods for detecting telomerase activity and ALT are likely to become an important pre-requisite for the use of treatments targeting one or other of these mechanisms. However, the question whether ALT presence can confer sensitivity to rationally designed anti-cancer therapies is still open. Here we review the latest discoveries in terms of mechanisms of ALT activation and maintenance in human tumors, methods for ALT identification in cell lines and human tissues and biomarkers validation. Then, original results on sensitivity to rational based pre-clinical and clinical anti-tumor drugs in ALT vs hTERT positive cells will be presented.

Mouse models of metastasis: progress and prospects

Metastasis is the spread of cancer cells from a primary tumor to distant sites within the body to establish secondary tumors. Although this is an inefficient process, the consequences are devastating as metastatic disease accounts for >90% of cancer-related deaths. The formation of metastases is the result of a series of events that allow cancer cells to escape from the primary site, survive in the lymphatic system or blood vessels, extravasate and grow at distant sites. The metastatic capacity of a tumor is determined by genetic and epigenetic changes within the cancer cells as well as contributions from cells in the tumor microenvironment. Mouse models have proven to be an important tool for unraveling the complex interactions involved in the metastatic cascade and delineating its many stages. Here, we critically appraise the strengths and weaknesses of the current mouse models and highlight the recent advances that have been made using these models in our understanding of metastasis. We also discuss the use of these models for testing potential therapies and the challenges associated with the translation of these findings into the provision of new and effective treatments for cancer patients.

Ex vivo tumor culture systems for functional drug testing and therapy response prediction

Optimal patient stratification is of utmost importance in the era of personalized medicine. Prediction of individual treatment responses by functional ex vivo assays requires model systems derived from viable tumor samples, which should closely resemble in vivo tumor characteristics and microenvironment. This review discusses a broad spectrum of model systems, ranging from classic 2D monolayer culture techniques to more experimental ‘cancer-on-chip’ procedures. We mainly focus on organotypic tumor slices that take tumor heterogeneity and tumor–stromal interactions into account. These 3D model systems can be exploited for patient selection as well as for fundamental research. Selection of the right model system for each specific research endeavor is crucial and requires careful balancing of the pros and cons of each technology.

Selection of the right therapy for individual cancer patients is very important with the expanding number of possible treatments. How tumors respond to a therapy can be tested by treating a sample from the tumor outside the body. Various culture methods can be used to maintain this tumor sample. Each of these model systems has its own benefits and disadvantages. In this review, we discuss the advantages and drawbacks of the available model systems and how they can be used to guide personalized medicine.