Biomedical subjects
Publications and source records attributed to Christoph Lengauer.
Thirty-five years after the 'war on cancer' was declared, the discovery of anticancer drugs remains a highly challenging endeavour. Here, we consider the factors responsible, such as tumour heterogeneity, and suggest strategies to improve the chances of short-term success in the development of novel anticancer drugs.
A cancer drug target is only truly validated by demonstrating that a given therapeutic agent is clinically effective and acts through the target against which it was designed. Nevertheless, it is desirable to declare an early-stage drug target as 'validated' before investing in a full-scale drug discovery programme dedicated to it. Although the outcome of validation studies can guide cancer research programmes, strictly defined universal validation criteria have not been established.
BACKGROUND & AIMS: How specifically to treat pancreatic and other cancers harboring Fanconi anemia gene mutations has raised great interest recently, yet preclinical studies have been hampered by the lack of well-controlled human cancer models. METHODS: We endogenously disrupted FANCC and FANCG in a human adenocarcinoma cell line and determined the impact of these genes on drug sensitivity, irradiation sensitivity, and genome maintenance. RESULTS: FANCC and FANCG disruption abrogated FANCD2 monoubiquitination, confirming an impaired Fanconi anemia pathway function. On treatment with DNA interstrand-cross-linking agents, FANCC and FANCG disruption caused increased clastogenic damage, G2/M arrest, and decreased proliferation. The extent of hypersensitivity varied among agents, with ratios of inhibitory concentration 50% ranging from 2-fold for oxaliplatin to 14-fold for melphalan, a drug infrequently used in solid tumors. No hypersensitivity was observed on gemcitabine, etoposide, 3-aminobenzamide, NU1025, or hydrogen peroxide. FANCC and FANCG disruption also resulted in increased clastogenic damage on irradiation, but only FANCG disruption caused a subsequent decrease in relative survival. Finally, FANCC and FANCG disruption increased spontaneous chromosomal breakage, supporting the role of these genes in genome maintenance and likely explaining why they are mutated in sporadic cancer. CONCLUSIONS: Our human cancer cell model provides optimal controls to elucidate fundamental biologic features of individual Fanconi anemia gene defects and facilitates preclinical studies of therapeutic options. The impact of Fanconi gene defects on drug and irradiation sensitivity renders these genes promising targets for a specific, genotype-based therapy for individual cancer patients, providing a strong rationale for clinical trials.
Protein kinases are enzymes that are important for controlling cellular growth and invasion, and their malfunction is implicated in the development of some tumours. We analysed human colorectal cancers for genetic mutations in 340 serine/threonine kinases and found mutations in eight genes, including in three members of the phosphatidylinositol-3-OH kinase (PI(3)K) pathway. The discovery of this mutational activation of a key cell-signalling pathway may provide new targets for therapeutic intervention.
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It has been shown that bone marrow-derived stem cells can form a major fraction of the tumor endothelium in mouse tumors. To determine the role of such cells in human tumor angiogenesis, we studied six individuals who developed cancers after bone marrow transplantation with donor cells derived from individuals of the opposite sex. By performing fluorescence in situ hybridization (FISH) with sex chromosome-specific probes in conjunction with fluorescent antibody staining, we found that such stem cells indeed contributed to tumor endothelium, but at low levels, averaging only 4.9% of the total. These results illustrate substantial differences between human tumors and many mouse models with respect to angiogenesis and have important implications for the translation of experimental antiangiogenic therapies to the clinic.
Through digital karyotyping of permanent medulloblastoma cell lines, we found that the homeobox gene OTX2 was amplified more than 10-fold in three cell lines. Gene expression analyses showed that OTX2 transcripts were present at high levels in 14 of 15 (93%) medulloblastomas with anaplastic histopathologic features. Knockdown of OTX2 expression by siRNAs inhibited medulloblastoma cell growth in vitro, whereas pharmacologic doses of all-trans retinoic acid repressed OTX2 expression and induced apoptosis only in medulloblastoma cell lines that expressed OTX2. These observations suggest that OTX2 is essential for the pathogenesis of anaplastic medulloblastomas and that these tumors may be amenable to therapy with all-trans-retinoic acid.
PIK3CA is mutated in diverse human cancers, but the functional effects of these mutations have not been defined. To evaluate the consequences of PIK3CA alterations, the two most common mutations were inactivated by gene targeting in colorectal cancer (CRC) cells. Biochemical analyses of these cells showed that mutant PIK3CA selectively regulated the phosphorylation of AKT and the forkhead transcription factors FKHR and FKHRL1. PIK3CA mutations had little effect on growth under standard conditions, but reduced cellular dependence on growth factors. PIK3CA mutations resulted in attenuation of apoptosis and facilitated tumor invasion. Treatment with the PI3K inhibitor LY294002 abrogated PIK3CA signaling and preferentially inhibited growth of PIK3CA mutant cells. These data have important implications for therapy of cancers harboring PIK3CA alterations.
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Cancers result from the accumulation of inherited and somatic mutations in oncogenes and tumor suppressor genes. These genes encode proteins that function in growth regulatory and differentiation pathways. Mutations in those genes increase the net reproductive rate of cells. Chromosomal instability (CIN) is a feature of most human cancers. Mutations in CIN genes increase the rate at which whole chromosomes or large parts of chromosomes are lost or gained during cell division. CIN causes an imbalance in chromosome number (aneuploidy) and an enhanced rate of loss of heterozygosity, which is an important mechanism of inactivating tumor suppressor genes. A crucial question of cancer biology is whether CIN is an early event and thus a driving force of tumorigenesis. Here we discuss mathematical models of situations where inactivation of one or two tumor suppressor genes is required for tumorigenesis. If two tumor suppressor genes have to be inactivated in rate-limiting steps, then CIN is likely to emerge before the inactivation of the first tumor suppressor gene.
Colorectal cancer results from an accumulation of mutations in tumor suppressor genes and oncogenes. An additional defining characteristic of colorectal cancer is its genetic instability. Two main types of genetic instability have been identified. Microsatellite instability leads to an increased point mutation rate, whereas chromosomal instability refers to an enhanced rate of accumulating gross chromosomal aberrations. All colon cancer cell lines are genetically unstable. An interesting question is whether genetic instability arises early in tumorigenesis. An early emergence of genetic instability could drive most of the somatic evolution of cancer. Here, we review mathematical models of colorectal tumorigenesis and discuss the role of genetic instability.
It has been two decades since cancer was first described as a genetic disease and researchers offered the promise of early diagnosis and targeted therapies. Today, most cancer patients still await life-saving treatments. Genomics and other '-omics' technologies have revealed a complexity among cancers that makes almost any tumour genetically unique; as a consequence, effective targeted therapies might be suitable only for small subgroups of patients. We suggest that by merging and organizing their core competencies, academia, biotechnology companies and the pharmaceutical industry can address existing bottlenecks in anticancer drug discovery and development.
The dietary carcinogen 2-amino-1-methyl-6-phenylimidazo(4,5-b)pyridine (PhIP) is a heterocyclic amine and is a common byproduct of cooked meat and fish. Although most cells undergo apoptosis when exposed to this mutagen, subsets develop resistance. Rather than die, these resistant cells persist and accumulate mutations, thereby driving tumorigenesis of exposed organs within the gastrointestinal tract. By applying a high-throughput cell-based screen of 32,000 small molecules, we have identified a family of compounds that specifically inhibit the growth of PhIP-resistant cancer cells. These compounds may prove useful for the treatment or prevention of gastrointestinal tumors arising after exposure to PhIP and related carcinogens.
The characterization of molecules recognized by patients with autoimmune diseases has provided significant insights into important biological pathways. In these studies, we define Ufd2 (a novel E4 polyubiquitylating enzyme) as a new autoantigen in scleroderma, and show that it regulates chromosome condensation and separation during mitosis in human cells. Ufd2 is regulated by phosphorylation in mitosis. Inhibition of Ufd2 expression results in mitotic arrest at the metaphase-anaphase transition, where cells manifest abnormal chromosome morphology, missegregated chromosomes, irregular spindles, and premature separation of sister chromatids. This is accompanied by premature separase activation, and accumulation of securin in a novel modified form. We further demonstrate that Ufd2 directly and efficiently ubiquitylates securin in vitro and is required for securin polyubiquitylation in vivo. This is the first description of a physiologic substrate for Ufd2, establishing this E4 enzyme as an important regulator of chromosome condensation and separation during mitosis in human cells. Its targeting in scleroderma, together with many other components of the mitotic machinery, reinforces the concept that mitotic cells may be an important focus of the autoimmune response in this disease.
Nonsteroidal antiinflammatory drugs (NSAIDs) form a paradigm for the chemoprevention of cancer, preventing colonic tumor progression in both experimental animals and humans. However, the mechanisms underlying the antineoplastic effects of NSAIDs are currently unclear. We found that the mitochondrial second mitochondrial-derived activator of caspase (SMAC)/direct inhibitor of apoptosis protein-binding protein with low pI (Diablo) protein translocates into the cytosol during NSAID-induced apoptosis in colon cancer cells. When SMAC/Diablo is disrupted by homologous recombination and RNA interference in these cells, the NSAID-induced apoptosis is abrogated. Biochemical markers of apoptosis, such as caspase activation, cytosolic release of cytochrome c and apoptosis-inducing factor, and mitochondrial membrane potential change, are accordingly decreased. These results establish that SMAC/Diablo is essential for the apoptosis induced by NSAIDs in colon cancer cells.
In contrast to normal cells, aneuploidy--alterations in the number of chromosomes--is consistently observed in virtually all cancers. A growing body of evidence suggests that aneuploidy is often caused by a particular type of genetic instability, called chromosomal instability, which may reflect defects in mitotic segregation in cancer cells. A better understanding of the molecular mechanisms leading to aneuploidy holds promise for the development of cancer drugs that target this process.
About twenty years ago, scientists began to discover that colorectal cancers are caused by the sequential acquisition of genetic alterations in specific genes. To this day, we are still dissecting the genome of colorectal cancers to identify specific "culprit" genes that play a role in tumorigenesis. At the same time, we have more recently begun to turn our attention to the features of cancer cells that distinguish them from normal cells and that may be targeted therapeutically. Aneuploidy is one such hallmark of cancers, but its role in tumorigenesis is heretofore undetermined. Our efforts have focused on elucidating the fundamental mechanisms underlying aneuploidy. The assertion that a genetic basis for aneuploidy would imply its importance in tumorigenesis, and consequently make it a potential therapeutic target, represents the rationale for our pursuit of this line of research. For the last few years, we have been trying to determine whether there is a genetic cause underlying this attribute of cancers. Our recently published work entitled, "Inactivation of hCDC4 can cause chromosomal instability," attempts to address this issue and raises more questions about the cause, mechanism, timing, and therapeutic potential of genetic instability.
Although most colorectal cancers are chromosomally unstable, the basis for this instability has not been defined. To determine whether genes shown to cause chromosomal instability in model systems were mutated in colorectal cancers, we identified their human homologues and determined their sequence in a panel of colorectal cancers. We found 19 somatic mutations in five genes representing three distinct instability pathways. Seven mutations were found in MRE11, whose product is involved in double-strand break repair. Four mutations were found among hZw10, hZwilch/FLJ10036, and hRod/KNTC, whose products bind to one another in a complex that localizes to kinetochores and controls chromosome segregation. Eight mutations were found in Ding, a previously uncharacterized gene with sequence similarity to the Saccharomyces cerevisiae Pds1, whose product is essential for proper chromosome disjunction. This analysis buttresses the evidence that chromosomal instability has a genetic basis and provides clues to the mechanistic basis of instability in cancers.