Proteasomal Degradation of Topoisomerase I Is Preceded by c-Jun NH2-Terminal Kinase Activation, Fas Up-Regulation, and Poly(ADP-Ribose) Polymerase Cleavage in SN38-Mediated Cytotoxicity against Multiple Myeloma

The oncogenic receptor ErbB2 modulates gemcitabine and irinotecan/SN-38 chemoresistance of human pancreatic cancer cells via hCNT1 transporter and multidrug-resistance associated protein MRP-2

Pancreatic adenocarcinoma (PDAC) is one of the most deadly cancers because of a lack of early diagnotic markers and efficient therapeutics. The fluorinated analog of deoxycytidine, gemcitabine and emerging FOLFIRINOX protocol (5-fluorouracil (5-FU), irinotecan/SN-38, oxaliplatin and leucovorin) are the main chemotherapies to treat PDAC. The ErbB2/HER2 oncogenic receptor is commonly overexpressed in PDAC. In this context, we aimed to decipher the ErbB2-mediated mechanisms of chemoresistance to the two main chemotherapy protocols used to treat PDAC.

ErbB2 knocking down (KD) in CAPAN-1 and CAPAN-2 cells led to an increased sensitivity to gemcitabine and an increased resistance to irinotecan/SN-38 both in vitro and in vivo (subcuteanous xenografts) This was correlated to an increase of hCNT1 and hCNT3 transporters and ABCG2, MRP1 and MRP2 ATP-binding cassette transporters expression and resistance to cell death. We also show that MRP2 is repressed following activation of JNK, Erk1/2 and NF-κB pathways by ErbB2. Finally, in datasets of human PDAC samples, ErbB2 and MRP2 expression was conversely correlated. Altogether, we propose that ErbB2 mediates several intracellular mechanisms linked to PDAC cell chemoresistance that may represent potential targets in order to ameliorate chemotherapy response and allow stratification of patients eligible for either gemcitabine or FOLFIRINOX treatment.

In vitro and in vivo anti-tumor activity of miR-221/222 inhibitors in multiple myeloma

A rising body of evidence suggests that silencing microRNAs (miRNAs) with oncogenic potential may represent a successful therapeutic strategy for human cancer. We investigated the therapeutic activity of miR-221/222 inhibitors against human multiple myeloma (MM) cells. Enforced expression of miR-221/222 inhibitors triggered in vitro anti-proliferative effects and up-regulation of canonic miR-221/222 targets, including p27Kip1, PUMA, PTEN and p57Kip2, in MM cells highly expressing miR-221/222. Conversely, transfection of miR-221/222 mimics increased S-phase and down-regulated p27Kip1 protein expression in MM with low basal miR-221/222 levels. The effects of miR-221/222 inhibitors was also evaluated in MM xenografts in SCID/ NOD mice. Significant anti-tumor activity was achieved in xenografted mice by the treatment with miR-221/222 inhibitors, together with up-regulation of canonic protein targets in tumors retrieved from animals. These findings provide proof of principle that silencing the miR-221/222 cluster exerts significant therapeutic activity in MM cells with high miR-221/222 level of expression, which mostly occurs in TC2 and TC4 MM groups. These findings suggest that MM genotyping may predict the therapeutic response. All together our results support a framework for clinical development of miR-221/222 inhibitors-based therapeutic strategy in this still incurable disease.

Antimyeloma activity of NK012, a micelle-forming macromolecular prodrug of SN-38, in an orthotopic model

NK012 is a micelle-forming macromolecular prodrug of 7-ethyl-10-hydroxy camptothecin (SN-38), an active metabolite of irinotecan. It is accumulated and retained in tumor tissues and gradually releases SN-38 in an enzyme-independent manner. NK012 was previously demonstrated to have stronger antitumor activity than irinotecan in a broad range of human solid-tumor xenograft models. In our study, we used an orthotopic multiple myeloma (MM) model created by injecting CD138-positive U266B1, a myeloma cell line that produces human IgE lambda light chain (monoclonal protein, M protein), into immunodeficient NOD/Shi-scid, IL-2Rγc (null) mice. This model shows typical bone marrow infiltration by the human myeloma cells. We evaluated the antimyeloma activity of intravenously administered NK012 in this model and showed that it suppressed the M protein concentration in the plasma and proliferation of myeloma cells in the bone marrow in a dose-dependent manner. NK012 suppressed the progression of hind-leg paralysis and prolonged the survival time of the mice compared to the untreated control group. In combination with bortezomib (BTZ), NK012 increased the median survival time compared to that with BTZ alone. In conclusion, these results suggest that NK012 is a potential candidate for use-alone and in combination-in the treatment of MM in humans.

A review of lenalidomide in combination with dexamethasone for the treatment of multiple myeloma

Lenalidomide (also known as Revlimid^®, CC-5013) is an immunomodulatory derivative of thalidomide and has more potent anti-tumor and anti-inflammatory effects than thalidomide. The molecular mechanisms of anti-tumor activity of lenalidomide have been extensively studied in multiple myeloma (MM) both preclinical models and in clinical trials. Lenalidomide: directly triggers growth arrest and/or apoptosis of drug resistant MM cells; inhibits binding of MM cells to bone marrow (BM) extracellular matrix proteins and stromal cells; modulates cytokine secretion and inhibits angiogenesis in the BM milieu; and augments host anti-tumor immunity. Lenalidomide achieved responses in patients with relapsed refractory MM. Moreover, lenalidomide with dexamethasone (Dex) demonstrates more potent anti-MM activities than Dex both in vitro and in randomized phase III clinical trials. Specifically, the combination improved overall and extent of response, as well as prolonged time to progression and overall survival, resulting in FDA approval of lenalidomide with Dex for therapy MM relapsing after prior therapy.

Proteasome inhibitors in the treatment of multiple myeloma

Targeting intracellular protein turnover by inhibiting the ubiquitin-proteasome pathway as a strategy for cancer therapy is a new addition to our chemotherapeutic armamentarium, and has seen its greatest successes against multiple myeloma. The first-in-class proteasome inhibitor, bortezomib, was initially approved for treatment of patients in the relapsed/refractory setting as a single agent, and was recently shown to induce even greater benefits as part of rationally designed combinations that overcome chemoresistance. Modulation of proteasome function is also a rational approach to achieve chemosensitization to other antimyeloma agents, and bortezomib has now been incorporated into the front-line setting. Bortezomib-based induction regimens are able to achieve higher overall response rates and response qualities than was the case with prior standards of care, and unlike these older approaches, maintain efficacy in patients with clinically and molecularly defined high-risk disease. Second-generation proteasome inhibitors with novel properties, such as NPI-0052 and carfilzomib, are entering the clinical arena, and showing evidence of antimyeloma activity. In this spotlight review, we provide an overview of the current state of the art use of bortezomib and other proteasome inhibitors against multiple myeloma, and highlight areas for future study that will further optimize our ability to benefit patients with this disease.

Bcl-2 antagonists interact synergistically with bortezomib in DLBCL cells in association with JNK activation and induction of ER stress

Mechanisms underlying interactions between the proteasome inhibitor bortezomib and small molecule Bcl-2 antagonists were examined in GC- and ABC-type human DLBCL (diffuse lymphocytic B-cell lymphoma) cells. Concomitant or sequential exposure to non- or minimally toxic concentrations of bortezomib or other proteasome inhibitors and either HA14-1 or gossypol resulted in a striking increase in Bax/Bak conformational change/translocation, cytochrome c release, caspase activation and synergistic induction of apoptosis in both GC- and ABC-type cells. These events were associated with a sharp increase in activation of the stress kinase JNK and evidence of ER stress induction (e.g., eIF2alpha phosphorylation, activation of caspases-2 and -4, and Grp78 upregulation). Pharmacologic or genetic (e.g., shRNA knockdown) interruption of JNK signaling attenuated HA14-1/bortezomib lethality and ER stress induction. Genetic disruption of the ER stress pathway (e.g., in cells expressing caspase-4 shRNA or DN-eIF2alpha) significantly attenuated lethality. The toxicity of this regimen was independent of ROS generation. Finally, HA14-1 significantly increased bortezomib-mediated JNK activation, ER stress induction, and lethality in bortezomib-resistant cells. Collectively these findings indicate that small molecule Bcl-2 antagonists promote bortezomib-mediated mitochondrial injury and lethality in DLBCL cells in association with enhanced JNK activation and ER stress induction. They also raise the possibility that such a strategy may be effective in different DLBCL sub-types (e.g., GC- or ABC), and in bortezomib-resistant disease.

Targeting topoisomerase I: molecular mechanisms and cellular determinants of response to topoisomerase I inhibitors

BACKGROUND

Topoisomerase I is required for DNA relaxation during critical cellular functions. The identification of camptothecins as specific enzyme inhibitors and their clinical efficacy have stimulated extensive efforts to exploit topoisomerase I as a tumor target and explain the putative mechanisms of antitumor-specific action.

OBJECTIVE

This review provides an overview of the recent achievements in the development of topoisomerase I inhibitors and in the explanation of the biological pathways involved in tumor response.

RESULTS/CONCLUSION

In spite of the difficulty to identify novel topoisomerase I inhibitors with improved pharmacological properties, a growing body of evidence supports the possibility of optimizing the therapeutic profile of available agents. The explanation of defense mechanisms and the molecular determinants of tumor cell response is expected to provide a basis for the design of combination approaches for optimization of topoisomerase I inhibitors-based therapy.

Overexpression of carboxylesterase-2 results in enhanced efficacy of topoisomerase I inhibitor, irinotecan (CPT-11), for multiple myeloma

Multiple myeloma (MM) remains an incurable disease and further development of novel agents is needed. Because constitutive expression of topoisomerase I (TopoI) in MM cells and the efficacy of SN-38, an active metabolite of irinotecan (CPT-11), have been reported, we investigated the therapeutic potential of CPT-11. Of the eight MM cell lines analyzed, four showed 50% inhibitory concentration values of less than 2 microg/mL for CPT-11 and less than 2 ng/mL for SN-38. This efficacy was partly explained by the high expression level of human carboxylesterase-2 (hCE-2) in MM cells. Interestingly, high expression of hCE-2 represented the nature of normal plasma cells, suggesting that hCE-2 could efficiently generate SN-38 within the plasma cells. As expected, higher sensitivity to CPT-11 was observed in hCE-2-overexpressing U266 cells than mock U266 cells. On the other hand, the expression levels of hCE-1, TopoI, UGT1A and ABCG2 did not seem to be associated with the sensitivity of MM cells to CPT-11. In a murine xenograft model inoculated s.c. with RPMI8226 cells, administration of CPT-11 alone significantly reduced the tumor volume. When a combination of CPT-11 and bortezomib was administered, the subcutaneous tumors completely disappeared. Thus, clinical trials on CPT-11 in patients with relapsed or refractory MM are warranted.

In vitro pharmacogenomic database and chemosensitivity predictive genes in gastric cancer

Gastric cancer is one of the most common cancers worldwide, and there are clinical caveats in predicting tumor response to chemotherapy. This study describes the construction of an in vitro pharmacogenomic database, and the selection of genes associated with chemosensitivity in gastric cancer cell lines. Gene expression and chemosensitivity databases were integrated using the Pearson correlation coefficient to give the GC-matrix. The 85 genes were selected that were commonly associated with chemosensitivity of the major anticancer drugs. We then focused on the genes that were highly correlated with each specific drug. Classification of cell lines based on the set of genes associated with each drug was consistent with the division into resistant or sensitive groups according to the chemosensitivity results. The GC-matrix of the gastric cancer cell line database was used to identify different sets of chemosensitivity-related genes for specific drugs or multiple drugs.

Antiangiogenic and anticolorectal cancer effects of metronomic irinotecan chemotherapy alone and in combination with semaxinib

Metronomic chemotherapy refers to the administration of chemotherapy at low, nontoxic doses on a frequent schedule with no prolonged breaks. The aim of the study is to rationally develop a CPT-11 metronomic regimen in preclinical settings of colon cancer. In vitro cell proliferation, apoptosis and thrombospondin-1/vascular endothelial growth factor (TSP-1/VEGF) expression analyses were performed on endothelial (HUVEC, HMVEC-d) and colorectal cancer (HT-29, SW620) cells exposed for 144 h to metronomic concentrations of SN-38, the active metabolite of CPT-11. HT-29 human colorectal cancer xenograft model was used, and tumour growth, microvessel density and VEGF/TSP-1 quantification was performed in tumours. In vitro and in vivo combination studies with the tyrosine inhibitor semaxinib were also performed. SN-38 preferentially inhibited endothelial cell proliferation alone and interacted synergistically with semaxinib; it induced apoptosis and increased the expression and secretion of TSP-1. Metronomic CPT-11 alone and combined with semaxinib significantly inhibits tumour growth in the absence of toxicity, which was accompanied by decreases in microvessel density and increases in TSP-1 gene expression in tumour tissues. In vitro results show the antiangiogenic properties of low-concentration SN-38, suggesting a key role of TSP-1 in this effect. In vivo, the CPT-11 metronomic schedule is effective against tumour and microvessel growth without toxic effect on mice.

Role of the unfolded protein response in cell death

Unfolded protein response (UPR) is an important genomic response to endoplasmic reticulum (ER) stress. The ER chaperones, GRP78 and Gadd153, play critical roles in cell survival or cell death as part of the UPR, which is regulated by three signaling pathways: PERK/ATF4, IRE1/XBP1 and ATF6. During the UPR, accumulated unfolded protein is either correctly refolded, or unsuccessfully refolded and degraded by the ubiquitin-proteasome pathway. When the unfolded protein exceeds a threshold, damaged cells are committed to cell death, which is mediated by ATF4 and ATF6, as well as activation of the JNK/AP-1/Gadd153-signaling pathway. Gadd153 suppresses activation of Bcl-2 and NF-kappaB. UPR-mediated cell survival or cell death is regulated by the balance of GRP78 and Gadd153 expression, which is coregulated by NF-kappaB in accordance with the magnitude of ER stress. Less susceptibility to cell death upon activation of the UPR may contribute to tumor progression and drug resistance of solid tumors.

Targeted therapy of multiple myeloma based upon tumor-microenvironmental interactions

Multiple myeloma (MM) remains incurable, but recent advances in genomics and proteomics have allowed for advances in our understanding of disease pathogenesis, identified novel therapeutic targets, allowed for molecular classification, and provided the scientific rationale for combining targeted therapies to increase tumor cell cytotoxicity and abrogate drug resistance. Besides these advances, recognition of the role of the bone marrow (BM) milieu in conferring growth, survival, and drug resistance in MM cells, both in laboratory and animal models, has allowed for the establishment of a new treatment paradigm targeting the tumor cell and its microenvironment to overcome drug resistance and improve patient outcomes in MM. In particular, thalidomide, bortezomib, and lenalidamide all overcome conventional drug resistance, not only by directly inducing tumor cell cytotoxicity, but by inhibiting adhesion of MM cells to BM. This abrogates constitutive and MM-binding-induced transcription and secretion of cytokines, inhibits angiogenesis, and augments host anti-MM immunity. These three drugs have rapidly translated from bench to bedside and in treatment protocols of MM, first in patients with relapsed refractory disease, and then alone and in combination in newly diagnosed patients. Promising novel targeted agents include the novel proteasome inhibitor NPI-0052 and the heat shock protein inhibitor KOS-953. Importantly, gene-array, proteomic, and cell-signaling studies have not only helped to identify in vivo mechanisms of action and drug resistance to novel agents, but also aided in the design of promising combination-therapy protocols.

A Phase I study of bortezomib plus irinotecan in patients with advanced solid tumors

BACKGROUND

The authors conducted a Phase I dose-finding trial to study the use of combined bortezomib plus irinotecan in patients with advanced solid tumors.

METHODS

Patients who had received >/=1 prior chemotherapy regimen were eligible. Patients received bortezomib (1.0 mg/m(2), 1.3 mg/m(2), or 1.5 mg/m(2)) on Days 1, 4, 8, and 11 and received irinotecan (from 50 mg/m(2) to 125 mg/m(2)) on Days 1 and 8 of each 21-day cycle for a maximum of 8 cycles. Bortezomib followed irinotecan on coadministration days in Cycle 1 and Cycles 3 through 8 but preceded irinotecan in Cycle 2 to assess the effect of administration sequence on bortezomib pharmacodynamics.

RESULTS

Fifty-one enrolled patients with malignancies, including colorectal cancer (n = 23 patients), lung cancer (n = 6 patients), gastroesophageal cancer (n = 6 patients), and pancreatic cancer (n = 3 patients), received >/=1 dose of study drug. Nausea, vomiting, and diarrhea were the principal dose-limiting toxicities and led to the maximum tolerated doses of 1.3 mg/m(2) bortezomib and 125 mg/m(2) irinotecan. The most common grade >/=3 bortezomib-related nonhematologic adverse events were fatigue (n = 5 episodes), diarrhea (n = 4 episodes), and nausea (n = 4 episodes). grade >/=3 bortezomib-related hematologic adverse events included neutropenia (n = 6 episodes) and thrombocytopenia (n = 4 episodes) and rarely were dose limiting. Of 34 evaluable patients, no objective responses according to the Response Evaluation Criteria in Solid Tumors were seen; 10 patients achieved stable disease. The degree of proteasome inhibition in whole blood indicated that the biologic activity of bortezomib was unaffected by irinotecan coadministration.

CONCLUSIONS

The results of this Phase I study in patients with solid tumors indicated that bortezomib at a dose of 1.3 mg/m(2) on Days 1, 4, 8, and 11 plus irinotecan at a dose of 125 mg/m(2) on Days 1 and 8 every 21 days were the recommended Phase II doses.

Aggresome induction by proteasome inhibitor bortezomib and alpha-tubulin hyperacetylation by tubulin deacetylase (TDAC) inhibitor LBH589 are synergistic in myeloma cells

Histone deacetylase (HDAC) inhibitors have shown cytotoxicity as single agents in preclinical studies for multiple myeloma (MM) cells. LBH589 is a novel hydroxamic acid derivative that at low nanomolar concentrations induces apoptosis in MM cells resistant to conventional therapies via caspase activation and poly-(ADP-ribose) polymerase (PARP) cleavage. Significant synergistic cytotoxicity was observed with LBH589 in combination with bortezomib against MM cells that were sensitive and resistant to dexamethasone (Dex), as well as primary patient MM cells. LBH589 at low nanomolar concentrations also induced alpha-tubulin hyperacetylation. Aggresome formation was observed in the presence of bortezomib, and the combination of LBH589 plus bortezomib induced the formation of abnormal bundles of hyeracetylated alpha-tubulin but with diminished aggresome size and apoptotic nuclei. These data confirm the potential clinical benefit of combining HDAC inhibitors with proteasome inhibitors, and provide insight into the mechanisms of synergistic anti-MM activity of bortezomib in combination with LBH589.

Topoisomerase I inhibitors: camptothecins and beyond

Nuclear DNA topoisomerase I (TOP1) is an essential human enzyme. It is the only known target of the alkaloid camptothecin, from which the potent anticancer agents irinotecan and topotecan are derived. As camptothecins bind at the interface of the TOP1-DNA complex, they represent a paradigm for interfacial inhibitors that reversibly trap macromolecular complexes. Several camptothecin and non-camptothecin derivatives are being developed to further increase anti-tumour activity and reduce side effects. The mechanisms and molecular determinants of tumour response to TOP1 inhibitors are reviewed, and rational combinations of TOP1 inhibitors with other drugs are considered based on current knowledge of repair and checkpoint pathways that are associated with TOP1-mediated DNA damage.

Targeting signalling pathways for the treatment of multiple myeloma

Multiple myeloma (MM) is characterised by the expansion of monoclonal immunoglobulin-secreting plasma cells. Despite recent advances in systemic and supportive therapy, it remains incurable, with a median survival of about three years. Development of MM is a multistep process associated with an increasing frequency of chromosomal abnormalities and complex translocations, which induce mutations in several proto-oncogenes and tumour suppressor genes. Furthermore, differentiation, maintenance, expansion and drug resistance of MM cells are dependent on multiple growth factors, cytokines, and chemokines, secreted by tumour cells, bone marrow stromal cells, and non-haematopoietic organs; as well as on direct tumour cell-stromal cell contact. Therefore, signalling pathways initiated by both mutated genes in MM cells as well as signals originating in the bone marrow microenvironment represent potential targets for intervention. Close collaboration between basic researchers and clinicians will be required to further improve our knowledge of MM pathophysiologically in order to translate advances from the bench to the bedside and improve patient outcome.

1-Methoxy-Canthin-6-One Induces c-Jun NH2-Terminal Kinase–Dependent Apoptosis and Synergizes with Tumor Necrosis Factor–Related Apoptosis-Inducing Ligand Activity in Human Neoplastic Cells of Hematopoietic or Endodermal Origin

We investigated the effects of 1-methoxy-canthin-6-one, isolated from the medicinal plant Ailanthus altissima Swingle, on apoptosis in human leukemia (Jurkat), thyroid carcinoma (ARO and NPA), and hepatocellular carcinoma (HuH7) cell lines. Cultures incubated with the compound showed >50% of sub-G1 (hypodiploid) elements in flow cytometry analysis; the apoptosis-inducing activity was evident at <10 micromol/L and half-maximal at about 40 micromol/L 1-methoxy-canthin-6-one. The appearance of hypodiploid elements was preceded by mitochondrial membrane depolarization, mitochondrial release of cytochrome c, and Smac/DIABLO and procaspase-3 cleavage. We subsequently investigated the effect of 1-methoxy-canthin-6-one in combination with human recombinant tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in the four cell lines. Suboptimal concentrations (10 micromol/L 1-methoxy-canthin-6-one and 0.25 ng/mL TRAIL, respectively) of the two agents, unable to elicit apoptosis when used alone, induced mitochondrial depolarization, activation of caspase-3, and 45% to 85% of sub-G1 elements when added together to the cells. The synergism seemed to rely partly on the enhanced expression of TRAIL receptor 1 (TRAIL-R1; DR4), analyzed by immunofluorescence, by 1-methoxy-canthin-6-one. Cell incubation with 1-methoxy-canthin-6-one resulted in activating c-Jun NH2-terminal kinase (JNK), as revealed by Western blotting; induction of apoptosis and TRAIL-R1 up-regulation by 1-methoxy-canthin-6-one were >80% prevented by the addition of the JNK inhibitor (JNKI) SP600125JNKI, indicating that both effects were almost completely mediated by JNK activity. On the other hand, synergism with TRAIL was reduced by about 50%, suggesting that besides up-regulating TRAIL-R1, 1-methoxy-canthin-6-one could influence other factor(s) that participated in TRAIL-induced apoptosis. These findings indicate that 1-methoxy-canthin-6-one can represent a candidate for in vivo studies of monotherapies or combined antineoplastic therapies.

The tyrphostin adaphostin interacts synergistically with proteasome inhibitors to induce apoptosis in human leukemia cells through a reactive oxygen species (ROS)-dependent mechanism

Interactions between the tyrphostin adaphostin and proteasome inhibitors (eg, MG-132 and bortezomib) were examined in multiple human leukemia cell lines and primary acute myeloid leukemia (AML) specimens. Cotreatment of Jurkat cells with marginally toxic concentrations of adaphostin and proteasome inhibitors synergistically potentiated mitochondrial damage (eg, cytochrome c release), caspase activation, and apoptosis. Similar interactions occurred in other human leukemia cell types (eg, U937, HL-60, Raji). These interactions were associated with a marked increase in oxidative damage (eg, ROS generation), down-regulation of the Raf/MEK/ERK pathway, and JNK activation. Adaphostin/MG-132 lethality as well as mitochondrial damage, down-regulation of Raf/MEK/ERK, and activation of JNK were attenuated by the free-radical scavenger NAC, suggesting that oxidative damage plays a functional role in antileukemic effects. Ectopic expression of Raf-1 or constitutively active MEK/ERK or genetic interruption of the JNK pathway significantly diminished adaphostin/MG-132-mediated lethality. Interestingly, enforced Raf or MEK/ERK activation partially diminished adaphostin/MG-132-mediated ROS generation, suggesting the existence of an amplification loop. Finally, the adaphostin/MG-132 regimen displayed similar toxicity toward 5 primary AML samples but not normal hematopoietic progenitors (eg, bone marrow CD34+ cells). Collectively, these findings suggest that potentiating oxidative damage by combining adaphostin with proteasome inhibitors warrants attention as an antileukemic strategy.

Identification and Validation of Novel Therapeutic Targets for Multiple Myeloma

In vitro and in vivo models have been developed that have allowed for delineation of mechanisms of multiple myeloma (MM) cell homing to bone marrow (BM); tumor cell adhesion to extracellular matrix proteins and BM stromal cells; and cytokine-mediated growth, survival, drug resistance, and migration within the BM milieu. Delineation of the signaling cascades mediating these sequelae has identified multiple novel therapeutic targets in the tumor cell and its BM microenvironment. Importantly, novel therapies targeting the tumor cell and the BM, as well as those targeting the tumor cell or BM alone, can overcome the growth, survival, conventional drug resistance, and migration of MM cells bound to BM using both in vitro and in vivo severe combined immunodeficiency mouse models of human MM. These studies have translated rapidly from the bench to the bedside in derived clinical trials, and have already led to the United States Food and Drug Administration approval of the novel proteasome inhibitor bortezomib for treatment of relapsed/refractory MM. Novel agents will need to be combined to enhance cytotoxicity, avoid development of drug resistance, and allow for use of lower doses in combination therapies. Genomics, proteomics, and cell signaling studies have helped to identify in vivo mechanisms of sensitivity versus resistance to novel therapies, as well as aiding in the rational application of combination therapies. These studies have therefore provided the framework for a new treatment paradigm targeting the MM cell in its BM milieu to overcome drug resistance and improve patient outcome in MM.

Human DNA topoisomerase I: relaxation, roles, and damage control

Human DNA topoisomerase I is an essential enzyme involved in resolving the torsional stress associated with DNA replication, transcription, and chromatin condensation. The catalytic cycle of the enzyme consists of DNA cleavage to form a covalent enzyme-DNA intermediate, DNA relaxation, and finally, re-ligation of the phosphate backbone to restore the continuity of the DNA. Structure/function studies have elucidated a flexible enzyme that relaxes DNA through coordinated, controlled movements of distinct enzyme domains. The cellular roles of topoisomerase I are apparent throughout the nucleus, but the concentration of processes acting on ribosomal DNA results in topoisomerase I accumulation in the nucleolus. Although the activity of topoisomerase I is required in these processes, the enzyme can also have a deleterious effect on cells. In the event that the final re-ligation step of the reaction cycle is prevented, the covalent topoisomerase I-DNA intermediate becomes a toxic DNA lesion that must be repaired. The complexities of the relaxation reaction, the cellular roles, and the pathways that must exist to repair topoisomerase I-mediated DNA damage highlight the importance of continued study of this essential enzyme.

Pharmacogenomics in colorectal carcinomas: Future perspectives in personalized therapy

The recent introduction of new drugs such as capecitabine, irinotecan, and oxaliplatinum has greatly improved the clinical outcome of patients with advanced/metastatic colorectal cancer. Nevertheless, some patients may suffer from the adverse drug reactions which will probably be the main cause of chemotherapy failure. The goal of pharmacogenomics is to find correlations between therapeutic responses to drugs and the genetic profiles of patients; the different responses to a particular drug are due, in fact, not only to the specific clinico-pathological features of the patient or to environmental factors, but also to the ethnic origins and the particular individual's genetic profile. Genes which codify for the metabolism enzymes, receptor proteins, or protein targets of chemotherapy agents often present various genetic polymorphisms. The main aim of this review is to provide an overview of the known polymorphisms present in the genes which codify for factors (thymidylate synthase dihydropyrimidine dehydrogenase, uridine diphosphate (UDP)-glucuronosyl-transferase 1A1, enzymes implicated in DNA repair) involved in the action mechanisms of the drugs now utilized in chemotherapeutic treatment of colorectal carcinoma, such as fluoropyrimidines, irinotecan, and platinum agents.