Although various mechanisms involved in anticancer multidrug resistance (MDR) can be identified, it remains a major problem in oncology. Beyond that, the introduction of new "targeted" drugs have not solved the problem. On the contrary, it has been demonstrated that the "classical" MDR-associated mechanisms are similar or identical to those causing resistance to these novel agents. These mechanisms include the enhanced activity of drug pumps, i.e. ABC or alternative transporters; modulation of cellular death pathways; alteration and repair of target molecules; and various less common mechanisms. Together they build a complex network of cellular pathways and molecular mechanisms mediating an individual MDR phenotype. Although the application of new high throughput "-omics" technologies have identified multiple new gene-/protein expression signatures or factors associated with drug resistance, so far none of these findings has been useful for creating improved diagnostic assays, for prediction of individual therapy response, or for development of updated chemosensitizers.

Overexpression of BCRP mRNA is frequently observed in multidrug-resistant cell lines selected with mitoxantrone, suggesting that BCRP is likely to be a major cellular defense mechanism elicited in response to exposure to this drug. It is likely that BCRP is the putative "mitoxantrone transporter" hypothesized to be present in these cell lines.

No abstract

For reversal of MDR1 gene-dependent multidrug resistance (MDR), two small interfering RNA (siRNA) constructs were designed to inhibit MDR1 expression by RNA interference. SiRNA duplexes were used to treat human pancreatic carcinoma (EPP85-181RDB) and gastric carcinoma (EPG85-257RDB) cells. In both cellular systems, siRNAs could speci¢-cally inhibit MDR1 expression up to 91% at the mRNA and protein levels. Resistance against daunorubicin was decreased to 89% (EPP85-181RDB) or 58% (EPG85-257RDB). The data indicate that this approach may be applicable to cancer patients as a speci¢c means to reverse tumors with a P-glycoproteindependent MDR phenotype back to a drug-sensitive one. ß

Cancer patients with tumors of similar grading, staging and histogenesis can have markedly different treatment responses to different chemotherapy agents. So far, individual markers have failed to correctly predict resistance against anticancer agents. We tested 30 cancer cell lines for sensitivity to 5-fluorouracil, cisplatin, cyclophosphamide, doxorubicin, etoposide, methotrexate, mitomycin C, mitoxantrone, paclitaxel, topotecan and vinblastine at drug concentrations that can be systemically achieved in patients. The resistance index was determined to designate the cell lines as sensitive or resistant, and then, the subset of resistant vs. sensitive cell lines for each drug was compared. Gene expression signatures for all cell lines were obtained by interrogating Affymetrix U133A arrays. Prediction Analysis of Microarrays was applied for feature selection. An individual prediction profile for the resistance against each chemotherapy agent was constructed, containing 42-297 genes. The overall accuracy of the predictions in a leave-oneout cross validation was 86%. A list of the top 67 multidrug resistance candidate genes that were associated with the resistance against at least 4 anticancer agents was identified. Moreover, the differential expressions of 46 selected genes were also measured by quantitative RT-PCR using a TaqMan micro fluidic card system. As a single gene can be correlated with resistance against several agents, associations with resistance were detected all together for 76 genes and resistance phenotypes, respectively. This study focuses on the resistance at the in vivo concentrations, making future clinical cancer response prediction feasible. The TaqManvalidated gene expression patterns provide new gene candidates for multidrug resistance. Supplementary material for this article can be found on the International Journal of Cancer website at

These findings are novel and support the clinical relevance of p21 in the suppression of both proliferation and apoptosis. Thus, the dynamic induction of p21WAF1/CIP1 was associated with a lower proliferative activity but an ultimately worse treatment outcome following neoadjuvant radiochemotherapy and tumor resection. Induction of p21, therefore, represents a novel resistance mechanism in rectal cancer undergoing preoperative radiochemotherapy.

Sagopilone (ZK-EPO) is the first fully synthetic epothilone undergoing clinical trials for the treatment of human tumors. Here, we investigate the cellular pathways by which sagopilone blocks tumor cell proliferation and compare the intracellular pharmacokinetics and the in vivo pharmacodynamics of sagopilone with other microtubule-stabilizing (or tubulinpolymerizing) agents. Cellular uptake and fractionation/ localization studies revealed that sagopilone enters cells more efficiently, associates more tightly with the cytoskeleton, and polymerizes tubulin more potently than paclitaxel. Moreover, in contrast to paclitaxel and other epothilones [such as the natural product epothilone B (patupilone) or its partially synthetic analogue ixabepilone], sagopilone is not a substrate of the P-glycoprotein efflux pumps. Microtubule stabilization by sagopilone caused mitotic arrest, followed by transient multinucleation and activation of the mitochondrial apoptotic pathway. Profiling of the proapoptotic signal transduction pathway induced by sagopilone with a panel of small interfering RNAs revealed that sagopilone acts similarly to paclitaxel. In HCT 116 colon carcinoma cells, sagopilone-induced apoptosis was partly antagonized by the knockdown of proapoptotic members of the Bcl-2 family, including Bax, Bak, and Puma, whereas knockdown of Bcl-2, Bcl-X L , or Chk1 sensitized cells to sagopilone-induced cell death. Related to its improved subcellular pharmacokinetics, however, sagopilone is more cytotoxic than other epothilones in a large panel of human cancer cell lines in vitro and in vivo. In particular, sagopilone is highly effective in reducing the growth of paclitaxel-resistant cancer cells. These results underline the processes behind the therapeutic efficacy of sagopilone, which is now evaluated in a broad phase II program. [Cancer Res 2008;68(13):5301-8]

The adenovirus early proteins E1A and E1B-55kDa are key regulators of viral DNA replication, and it was thought that targeting of p53 by E1B-55kDa is essential for this process. Here we have identified a previously unrecognized function of E1B for adenovirus replication. We found that E1B-55kDa is involved in targeting the transcription factor YB-1 to the nuclei of adenovirus type 5-infected cells where it is associated with viral inclusion bodies believed to be sites of viral transcription and replication. We show that YB-1 facilitates E2 gene expression through the E2 late promoter thus controlling E2 gene activity at later stages of infection. The role of YB-1 for adenovirus replication was demonstrated with an E1-minus adenovirus vector containing a YB-1 transgene. In infected cells, AdYB-1 efficiently replicated and produced infectious progeny particles. Thus, adenovirus E1B-55kDa protein and the host cell factor YB-1 act jointly to facilitate adenovirus replication in the late phase of infection.Adenoviruses have developed efficient strategies to force infected cells into the S phase of the cell cycle (1). This process involves the adenoviral E1A and E1B proteins, which are the first viral proteins to be expressed after infection, and both are essential for viral replication (2, 3). Replication of adenovirus DNA depends directly on interactions between the host cell replication factors NFI, NFII, and NFIII (4) and the three viral replication proteins encoded by the E2 region. The adenovirus E2 transcription unit consists of the E2A and E2B genes, which encode precursor terminal protein pTP, DNA polymerase, and DBP, a multifunctional DNA-binding protein (5). E2 gene expression is driven from two promoters. At early times of infection, E2 gene transcription is under control of the E2 early promoter. At intermediate stages of infection, E2 gene expression is controlled by the E2 late promoter (6). E2 early promoter activity is regulated by adenovirus E1A protein, which controls the activity of the E2F transcription factor by targeting the tumor suppressor protein pRB (7,8). In contrast, activity of the E2 late promoter is repressed by E1A (9). The E2 late promoter is characterized by the presence of a TATA box, two SP1 recognition sites, and three CCAAT boxes. Two of the inverted CCAAT boxes are located at positions Ϫ72 and Ϫ135 relative to the E2 late cap site in a 157-bp sequence of the of the E2 late promoter, which is sufficient for efficient E2 gene transcription (10, 11).Inverted CCAAT boxes have been identified as sites for Y box proteins, which are highly conserved through evolution from prokaryotes to eukaryotes, and they can function as transcriptional, translational, and developmental regulators (12)(13)(14). In eukaryotes, increased expression of Y box proteins in somatic cells is associated with drug resistance and a malignant phenotype (15), and it was discussed that Y box proteins are involved in activating certain genes that are expressed in the S phase of the cell cycle (16). Recently, it has...