The ubiquitin proteasome pathway plays a critical role in regulating many processes in the cell which are important for tumour cell growth and survival. Inhibition of proteasome function has emerged as a powerful strategy for anti-cancer therapy. Clinical validation of the proteasome as a therapeutic target was achieved with bortezomib and has prompted the development of a second generation of proteasome inhibitors with improved pharmacological properties. This review summarises the main mechanisms of action of proteasome inhibitors in cancer, the development of proteasome inhibitors as therapeutic agents and the properties and progress of next generation proteasome inhibitors in the clinic.

The 26S proteasome is a multicatalytic protease responsible for regulated intracellular protein degradation. Its function is mediated by three main catalytic activities: (a) chymotrypsinlike (CT-L), (b) trypsin-like, and (c) peptidylglutamyl peptide hydrolysing (PGPH). Proteasome inhibition is an emerging therapy for many cancers and is a novel treatment for multiple myeloma. Here, we profile the contributions of the three catalytic activities in multiple myeloma cell lines and compare the specificity and cytotoxicity of the novel proteasome inhibitor BzLLLCOCHO and inhibitors PS-341 (Velcade, bortezomib) and MG-132. Using fluorogenic substrates and an active site-directed probe specific for proteasome catalytic subunits, we show differential subunit specificity for each of the inhibitors. Addition of BzLLLCOCHO strongly inhibited all three catalytic activities, treatment with PS-341 completely inhibited CT-L and PGPH activities, and treatment with MG-132 resulted in weak inhibition of the CT-L and PGPH activities. Multiple myeloma cells were more sensitive to induction of apoptosis by PS-341 and MG-132 than BzLLLCO-CHO. This study emphasizes the need for further investigation of the effects of these compounds on gene and protein expression in the cell to allow for the development of more specific and targeted inhibitors. (Cancer Res 2006; 66(12): 6379-86)

SummaryMolecular testing for the BCR-ABL1 fusion gene by real time quantitative polymerase chain reaction (RT-qPCR) is the most sensitive routine approach for monitoring the response to therapy of patients with chronic myeloid leukaemia. In the context of tyrosine kinase inhibitor (TKI) therapy, the technique is most appropriate for patients who have achieved complete cytogenetic remission and can be used to define specific therapeutic milestones. To achieve this effectively, standardization of the laboratory procedures and the interpretation of results are essential. We present here consensus best practice guidelines for RT-qPCR testing, data interpretation and reporting that have been drawn up and agreed by a consortium of 21 testing laboratories in the United Kingdom and Ireland in accordance with the procedures of the UK Clinical Molecular Genetics Society.

IntroductionChronic myeloid leukemia (CML) is a clonal disorder of pluripotent hematopoietic cells that is characterized by the presence of the Philadelphia chromosome (Ph ϩ ), the result of a reciprocal translocation between chromosomes 9 and 22. The translocation encodes a chimeric protein, BCR-ABL, which is a constitutively activated protein tyrosine kinase (PTK) 1 and which has an essential role in the molecular pathology of CML. CML is a progressive disease with an initial chronic phase in which there is a marked expansion in the late myeloid cell population (reviewed by Clarkson and Strife 2 ). CML progenitor cells possess only a subtle defect in maturation, while retaining their requirements for bone marrow stromal cells or cytokines to survive and proliferate. 3 This chronic phase, which is of variable duration, is usually followed by an accelerated phase leading to blast crisis. The blast crisis is the most severe manifestation of the disease in which differentiation is apparently blocked. Imatinib (Gleevec or STI571), an Abl tyrosine kinase inhibitor, is the first line and gold standard for treating CML. Nonetheless, there is clear evidence of resistance to this drug. The development of other approaches to treat the disease with smallmolecule inhibitors to new targets has been, and will be, a focus for future research into treatment of imatinib-resistant patients and those in accelerated phase or blast crisis. [4][5][6][7] Thus, understanding the process of leukemogenesis driven by this oncogene is still an important research objective.Most cell-line models expressing BCR-ABL PTK are already differentiation blocked, and assume a growth factor-independent phenotype. [8][9][10][11] In this respect they mirror the properties of cells from patients with CML in blast crisis. However, we have established a cell-line model for CML that has properties of chronic-phase progenitor cells that progressively change to those resembling accelerated phase by using an inducible temperaturesensitive BCR-ABL PTK (ts-BCR-ABL FDCP-Mix). 12-14 DNA microarray technology has been used to identify differential expression as a result of the initial activation of BCR-ABL. Activation of BCR-ABL in FDCP-Mix cells has identified transcriptional and secretory events regulated by BCR-ABL. These effects are observed to be due to BCR-ABL in primary CML cells. Materials and methods Cell linesFDCP-Mix cells transfected with the retroviral vector pM5-neo carrying a p210 ts-BCR-ABL cDNA were used as a model system for CML. 12 The L.M. carried out the majority of the practical work, data analysis, and interpretation, and contributed to preparation of the manuscript; S.P. played a major part in experimental design and execution; N.P. and B.P. provided essential biological material and made a major contribution to the interpretation of data; A.P. and A.D.W. provided essential biological reagents and contributed to experimental design and writing of the manuscript; A.E.I. was responsible for the overall conception and design of the project, in...