Targeting the PPM1D phenotype; 2,4-bisarylthiazoles cause highly selective apoptosis in PPM1D amplified cell-lines.

The metal-dependent phosphatase PPM1D (WIP1) is an important oncogene in cancer, with over-expression of the protein being associated with significantly worse clinical outcomes. In this communication we describe the discovery and optimization of novel 2,4-bisarylthiazoles that phenocopy the knockdown of PPM1D, without inhibiting its phosphatase activity. These compounds cause growth inhibition at nanomolar concentrations, induce apoptosis, activate p53 and display impressive cell-line selectivity. The results demonstrate the potential for targeting phenotypes in drug discovery when tackling challenging targets or unknown mechanisms.

A synthetic lethal siRNA screen identifying genes mediating sensitivity to a PARP inhibitor.

Inhibitors of poly (ADP-ribose)-polymerase-1 (PARP) are highly lethal to cells with deficiencies in BRCA1, BRCA2 or other components of the homologous recombination pathway. This has led to PARP inhibitors entering clinical trials as a potential therapy for cancer in carriers of BRCA1 and BRCA2 mutations. To discover new determinants of sensitivity to these drugs, we performed a PARP-inhibitor synthetic lethal short interfering RNA (siRNA) screen. We identified a number of kinases whose silencing strongly sensitised to PARP inhibitor, including cyclin-dependent kinase 5 (CDK5), MAPK12, PLK3, PNKP, STK22c and STK36. How CDK5 silencing mediates sensitivity was investigated. Previously, CDK5 has been suggested to be active only in a neuronal context, but here we show that CDK5 is required in non-neuronal cells for the DNA-damage response and, in particular, intra-S and G(2)/M cell-cycle checkpoints. These results highlight the potential of synthetic lethal siRNA screens with chemical inhibitors to define new determinants of sensitivity and potential therapeutic targets.

Tiling path genomic profiling of grade 3 invasive ductal breast cancers.

PURPOSE: To characterize the molecular genetic profiles of grade 3 invasive ductal carcinomas of no special type using high-resolution microarray-based comparative genomic hybridization (aCGH) and to identify recurrent amplicons harboring putative therapeutic targets associated with luminal, HER-2, and basal-like tumor phenotypes. EXPERIMENTAL DESIGN: Ninety-five grade 3 invasive ductal carcinomas of no special type were classified into luminal, HER-2, and basal-like subgroups using a previously validated immunohistochemical panel. Tumor samples were microdissected and subjected to aCGH using a tiling path 32K BAC array platform. Selected regions of recurrent amplification were validated by means of in situ hybridization. Expression of genes pertaining to selected amplicons was investigated using quantitative real-time PCR and gene silencing was done using previously validated short hairpin RNA constructs. RESULTS: We show that basal-like and HER-2 tumors are characterized by "sawtooth" and "firestorm" genetic patterns, respectively, whereas luminal cancers were more heterogeneous. Apart from confirming known amplifications associated with basal-like (1q21, 10p, and 12p), luminal (8p12, 11q13, and 11q14), and HER-2 (17q12) cancers, we identified previously unreported recurrent amplifications associated with each molecular subgroup: 19q12 in basal-like, 1q32.1 in luminal, and 14q12 in HER-2 cancers. PPM1D gene amplification (17q23.2) was found in 20% and 8% of HER-2 and luminal cancers, respectively. Silencing of PPM1D by short hairpin RNA resulted in selective loss of viability in tumor cell lines harboring the 17q23.2 amplification. CONCLUSIONS: Our results show the power of aCGH analysis in unraveling the genetic profiles of specific subgroups of cancer and for the identification of novel therapeutic targets.

PPM1D is a potential therapeutic target in ovarian clear cell carcinomas.

PURPOSE: To identify therapeutic targets in ovarian clear cell carcinomas, a chemoresistant and aggressive type of ovarian cancer. EXPERIMENTAL DESIGN: Twelve ovarian clear cell carcinoma cell lines were subjected to tiling path microarray comparative genomic hybridization and genome-wide expression profiling analysis. Regions of high-level amplification were defined and genes whose expression levels were determined by copy number and correlated with gene amplification were identified. The effects of inhibition of PPM1D were assessed using short hairpin RNA constructs and a small-molecule inhibitor (CCT007093). The prevalence of PPM1D amplification and mRNA expression was determined using chromogenic in situ hybridization and quantitative real-time reverse transcription-PCR in a cohort of pure ovarian clear cell carcinomas and on an independent series of unselected epithelial ovarian cancers. RESULTS: Array-based comparative genomic hybridization analysis revealed regions of high-level amplification on 1q32, 1q42, 2q11, 3q24-q26, 5p15, 7p21-p22, 11q13.2-q13.4, 11q22, 17q21-q22, 17q23.2, 19q12-q13, and 20q13.2. Thirty-four genes mapping to these regions displayed expression levels that correlated with copy number gains/amplification. PPM1D had significantly higher levels of mRNA expression in ovarian clear cell carcinoma cell lines harboring gains/amplifications of 17q23.2. PPM1D inhibition revealed that PPM1D expression and phosphatase activity are selectively required for the survival of ovarian clear cell carcinoma cell lines with 17q23.2 amplification. PPM1D amplification was significantly associated with ovarian clear cell carcinoma histology (P = 0.0003) and found in 10% of primary ovarian clear cell carcinomas. PPM1D expression levels were significantly correlated with PPM1D gene amplification in primary ovarian clear cell carcinomas. CONCLUSION: Our data provide strong circumstantial evidence that PPM1D is a potential therapeutic target for a subgroup of ovarian clear cell carcinomas.

LKB1 is crucial for TRAIL-mediated apoptosis induction in osteosarcoma.

BACKGROUND: Despite improvements in chemotherapy and surgery in the treatment of osteosarcoma, satisfactory results are still difficult to achieve. New therapeutic modalities need to be developed for the improvement of these treatments. TRAIL (TNF-related apoptosis inducing ligand) is known as a selective apoptosis inducer in most tumor cells, but not in normal cells. Therefore, TRAIL is a good candidate target for the treatment of tumors. However, sensitivity of osteosarcoma cells to TRAIL-induced apoptosis is lower than that of other types of tumor cells. Recently, DAP3 (death associated protein 3) was demonstrated to play a critical role in TRAIL-mediated apoptosis through activation of pro-caspase-8. Here, we found that LKB1, a serine/threonine kinase, expressed in bone and soft tissue sarcoma cells, associated with DAP3. We also demonstrated that expression of DAP3 induced apoptosis in osteosarcoma cells. Furthermore, expression of LKB1 induced apoptosis and co-expression of LKB1 with DAP3 strongly induced apoptosis in osteosarcoma cells. In addition, expression of LKB1 kinase dead mutant, LKB1 (K78M), inhibited DAP3-induced apoptosis in these cells. These results suggest that LKB1 is critical for TRAIL-induced apoptosis induction, cooperating with DAP3 in osteosarcoma cells. It is predicted that LKB1 and DAP3 could be critical target molecules for the treatment of osteosarcomas.

Regulation of the Wnt signalling component PAR1A by the Peutz-Jeghers syndrome kinase LKB1.

Loss-of-function mutations in the LKB1 (STK11) serine-threonine kinase gene cause Peutz-Jeghers syndrome, which is associated with inherited susceptibility to colorectal and other cancers. No downstream targets of LKB1 kinase activity have been identified. Here we show that LKB1 can direct the phosphorylation of the serine-threonine kinase PAR1A. The amino-acid residues phosphorylated as a result of LKB1 activity have been identified and phosphorylation at these residues is required for PAR1A kinase activity. PAR1A has previously been implicated as a positive regulator of the Wnt-betacatenin signalling pathway. We show here that LKB1 can modify transcription driven by the Wnt-regulated TCF response element, implicating LKB1 in a pathway known to play a key role in human colorectal tumorigenesis.