Molecular mechanisms of cisplatin resistance in lung cancer

Cisplatin is one of the most potent anticancer agents, displaying significant clinical activity against a variety of solid tumours. To date, cisplatin-based combination treatment remains the most effective systemic chemotherapy for non-small cell lung cancer (NSCLC) patients. Unfortunately, the outcome of cisplatin therapy in NSCLC has reached a plateau due to the development of both intrinsic and acquired resistance that have become a major obstacle in the use of cisplatin in the clinical setting. The molecular mechanisms that underlie chemoresistance are largely unknown. Mechanisms of acquired resistance to cisplatin include reduced intracellular accumulation of the drug, enhanced drug inactivation by metallothionine and glutathione, increased repair activity of DNA damage, and altered expression of oncogenes and regulatory proteins. Cisplatin-induced cytotoxicity is mediated through the induction of apoptosis and cell cycle arrest as a result of cisplatin-DNA adduct formation, which in turn, activates multiple signaling pathways and mediators. These include p53, Bcl-2 family, caspases, cyclins, CDKs, MAPK and PI3K/Akt. Increased expression of anti-apoptotic genes and mutations in the intrinsic apoptotic pathway may also contribute to the inability of cells to detect DNA damage or to induce apoptosis. This chapter will provide an insight into the mechanisms involved in cisplatin resistance and a better understanding of the molecular basis of the cellular response to cisplatin-based chemotherapy in lung cancer.

Targeting nuclear factor-kappa B to overcome resistance to chemotherapy

Intrinsic or acquired resistance to chemotherapeutic agents is a common phenomenon and a major challenge in the treatment of cancer patients. Chemoresistance is defined by a complex network of factors including multi-drug resistance proteins, reduced cellular uptake of the drug, enhanced DNA repair, intracellular drug inactivation, and evasion of apoptosis. Pre-clinical models have demonstrated that many chemotherapy drugs, such as platinum-based agents, antracyclines, and taxanes, promote the activation of the NF-κB pathway. NF-κB is a key transcription factor, playing a role in the development and progression of cancer and chemoresistance through the activation of a multitude of mediators including anti-apoptotic genes. Consequently, NF-κB has emerged as a promising anti-cancer target. Here, we describe the role of NF-κB in cancer and in the development of resistance, particularly cisplatin. Additionally, the potential benefits and disadvantages of targeting NF-κB signaling by pharmacological intervention will be addressed.

Integrin αvβ3 upregulates integrin-linked kinase expression in human ovarian cancer cells via enhancement of ILK gene transcription

We previously showed that integrin alphavbeta3 overexpression and engagement by its ligand vitronectin increased adhesion, motility, and proliferation of human ovarian cancer cells. In search of differentially regulated genes involved in these tumor biological events, we previously identified the integrin-linked kinase (ILK) to be under control of alphavbeta3. In the present investigation we demonstrated significantly upregulated ILK protein as a function of alphavbeta3 in two ovarian cancer cell lines, OV-MZ-6 and OVCAR-3, and proved co-localization at the surface of alphavbeta3-overexpressing cells adherent to vitronectin. Increase of ILK protein was reflected by enhanced ILK promoter activity, an effect, which we further characterized with regard to transcriptional response elements involved. Abrogation of NF-kappaB/c-rel or p53 binding augmented ILK promoter activity and preserved induction by alphavbeta3. The AP1-mutant exhibited decreased promoter activity but was also still inducible by alphavbeta3. Disruption of the two DNA consensus motifs for Ets proteins led to divergent observations: mutation of the Ets motif at promoter position -462 bp did not significantly alter promoter activity but still allowed response to alphavbeta3. In contrast, disruption of the second Ets motif at position -85 bp did not only lead to slightly diminished promoter activity but also, in that case, abrogated ILK promoter induction by alphavbeta3. Subsequent co-transfection studies with ets-1 in the presence of the second Ets motif led to additional induction of ILK promoter activity. Taken together, these data suggest that ets-1 binding to the second Ets DNA motif strongly contributes to alphavbeta3-mediated ILK upregulation. By increasing ILK as an important integrin-proximal kinase, alphavbeta3 may promote its intracellular signaling and tumor biological processes arising thereof in favor of ovarian cancer metastasis.

Normal human mammary epithelial cells spontaneously escape senescence and acquire genomic changes

Senescence and genomic integrity are thought to be important barriers in the development of malignant lesions. Human fibroblasts undergo a limited number of cell divisions before entering an irreversible arrest, called senescence. Here we show that human mammary epithelial cells (HMECs) do not conform to this paradigm of senescence. In contrast to fibroblasts, HMECs exhibit an initial growth phase that is followed by a transient growth plateau (termed selection or M0; refs 3-5), from which proliferative cells emerge to undergo further population doublings (approximately 20-70), before entering a second growth plateau (previously termed senescence or M1; refs 4-6). We find that the first growth plateau exhibits characteristics of senescence but is not an insurmountable barrier to further growth. HMECs emerge from senescence, exhibit eroding telomeric sequences and ultimately enter telomere-based crisis to generate the types of chromosomal abnormalities seen in the earliest lesions of breast cancer. Growth past senescent barriers may be a pivotal event in the earliest steps of carcinogenesis, providing many genetic changes that predicate oncogenic evolution. The differences between epithelial cells and fibroblasts provide new insights into the mechanistic basis of neoplastic transformation.

Integrin αvβ3 mediates upregulation of epidermal growth-factor receptor expression and activity in human ovarian cancer cells

Upon overexpression of integrin αvβ3 and its engagement by vitronectin, we previously showed enhanced adhesion, proliferation, and motility of human ovarian cancer cells. By studying differential expression of genes possibly related to these tumor biological events, we identified the epidermal growth-factor receptor (EGF-R) to be under control of αvβ3 expression levels. Thus in the present study we characterized αvβ3-dependent changes of EGF-R and found significant upregulation of its expression and activity which was reflected by prominent changes of EGF-R promoter activity. Upon disruption of DNA-binding motifs for the transcription factors p53, ETF, the repressor ETR, p50, and c-rel, respectively, we sought to identify DNA elements contributing to αvβ3-mediated EGF-R promoter induction. Both, the p53- and ETF-mutant, while exhibiting considerably lower EGF-R promoter activity than the wild type promoter, retained inducibility by αvβ3. Mutation of the repressor motif ETR, as expected, enhanced EGF-R promoter activity with a further moderate increase upon αvβ3 elevation. The p50-mutant displayed EGF-R promoter activity almost comparable to that of the wild type promoter with no impairment of induction by αvβ3. However, the activity of an EGF-R promoter mutant displaying a disrupted c-rel-binding motif did not only prominently decline, but, moreover, was not longer responsive to enhanced αvβ3, involving this DNA element in αvβ3-dependent EGF-R upregulation. Moreover, αvβ3 did not only increase the EGF-R but, moreover, also led to obvious co-clustering on the cancer cell surface. By studying αvβ3/EGF-R-effects on the focal adhesion kinase (FAK) and the mitogen activated protein kinases (MAPK) p44/42 (erk−1/erk−2), having important functions in synergistic crosstalk between integrins and growth-factor receptors, we found for both significant enhancement of expression and activity upon αvβ3/VN interaction and cell stimulation by EGF. Upregulation of the EGF-R by integrin αvβ3, both receptor molecules with a well-defined role as targets for cancer treatment, might represent an additional mechanism to adapt synergistic receptor signaling and crosstalk in response to an altered tumor cell microenvironment during ovarian cancer progression.

Signet-ring cell carcinoma of colorectum : current perspectives and molecular biology

PURPOSE Colorectal signet-ring cell carcinoma (SRCC) is rare, and very little detailed information on the molecular biology of the disease is available. METHODS The literature on the clinical, pathological and, in particular, the molecular biology of this rare entity was critically reviewed. The reviewed articles take into account a total of 1,817 cases of SRCC, but only 143 cases have molecular data available. The characteristics of two patients with colorectal SRCC were also discussed. RESULTS Colorectal SRCC mostly occurs in younger patients, is larger and has different site predilection compared with conventional colorectal adenocarcinoma. It can occur as one of the synchronous cancers in the colorectum. The cancer is usually diagnosed at advanced stages because of the late manifestation of symptoms, and aggressive treatment strategy is required. Limited reports in the literature have shown that the variant of colorectal cancer demonstrated a different pattern of genetic alterations of common growth kinase-related oncogenes (K-ras, BRAF), tumour suppressor genes (p53, p16), gene methylation and cell adhesion-related genes related to the Wingless signalling pathway (E-cadherin and beta-catenin) from conventional colorectal adenocarcinoma. Colorectal SRCC also showed high expression of mucin-related genes and genes related to the gastrointestinal system. There was also a higher prevalence of microsatellite instability-high tumours and low Cox-2 expression in colorectal SRCC as opposed to conventional adenocarcinoma. CONCLUSIONS Colorectal SRCC has unique molecular pathological features. The unique molecular profiles in SRCC may provide molecular-based improvements to patient management in colorectal SRCC.

Cytochrome p450 1b1, a new keystone in gene-environment interactions related to human head and neck cancer?

Alcohol consumption and tobacco smoking are major causes of head and neck cancers, and regional differences point to the importance of research into gene-environment interactions. Much interest has been focused on polymorphisms of CYP1A1 and of GSTM1 and GSTT1, but a number of studies have not demonstrated significant effects. This has mostly been ascribed to small sample sizes. In general, the impact of polymorphisms of metabolic enzymes appears inconsistent, with some reports of weak-to-moderate associations, and with others of no elevation of risks. The classical cytochrome P450 isoenzyme considered for metabolic activation of polycyclic aromatic hydrocarbons (PAH) is CYP1A1. A new member of the CYP1 family, CYP1B1, was cloned in 1994, currently representing the only member of the CYP1B subfamily. A number of single nucleotide polymorphisms of the CYP1B1 gene have been reported. The amino acid substitutions Val432Leu (CYP1B1*3) and Asn453Ser (CYP1B1*4), located in the heme binding domain of CYP1B1, appear as likely candidates to be linked with biological effects. CYP1B1 activates a wide range of PAH, aromatic and heterocyclic amines. Very recently, the CYP1B1 codon 432 polymorphism (CYP1B1*3) has been identified as a susceptibility factor in smoking-related head-and-neck squamous cell cancer. The impact of this polymorphic variant of CYP1B1 on cancer risk was also reflected by an association with the frequency of somatic mutations of the p53 gene. Combined genotype analysis of CYP1B1 and the glutathione transferases GSTM1 or GSTT1 has pointed to interactive effects. This provides new molecular evidence that tobacco smoke-specific compounds relevant to head and neck carcinogenesis are metabolically activated through CYP1B1 and is consistent with a major pathogenetic relevance of PAH as ingredients of tobacco smoke.