Resistance of p53 knockout cells to doxorubicin is related to reduced formation of DNA strand breaks rather than impaired apoptotic signaling

The eEF2 kinase coordinates the DNA damage response to cisplatin by supporting p53 activation

Eukaryotic elongation factor 2 (eEF2) kinase (eEF2K) is a stress-responsive hub that inhibits the translation elongation factor eEF2, and consequently mRNA translation elongation, in response to hypoxia and nutrient deprivation. EEF2K is also involved in the response to DNA damage but its role in response to DNA crosslinks, as induced by cisplatin, is not known. Here we found that eEF2K is critical to mediate the cellular response to cisplatin. We uncovered that eEF2K deficient cells are more resistant to cisplatin treatment. Mechanistically, eEF2K deficiency blunts the activation of the DNA damage response associated ATM and ATR pathways, in turn preventing p53 activation and therefore compromising induction of cisplatin-induced apoptosis. We also report that loss of eEF2K delays the resolution of DNA damage triggered by cisplatin, suggesting that eEF2K contributes to DNA damage repair in response to cisplatin. In support of this, our data shows that eEF2K promotes the expression of the DNA repair protein ERCC1, critical for the repair of cisplatin-caused DNA damage. Finally, using Caenorhabditis elegans as an in vivo model, we find that deletion of efk-1, the worm eEF2K ortholog, mitigates the induction of germ cell death in response to cisplatin. Together, our data highlight that eEF2K represents an evolutionary conserved mediator of the DNA damage response to cisplatin which promotes p53 activation to induce cell death, or alternatively facilitates DNA repair, depending on the extent of DNA damage.

Chemosensitivity to doxorubicin in primary cells derived from tumor of FVB/N-Trp53tm1Hw1 with TALEN-mediated Trp53 mutant gene

BACKGROUND

To evaluate the chemosensitivity to doxorubicin (DOX) in two primary cells derived from a tumor of FVB/N-Trp53tm1Hw1 knockout (KO) mice with TALEN-mediated Trp53 mutant gene, we evaluated the cell survivability, cell cycle distribution, apoptotic cell numbers and apoptotic protein expression in solid tumor cells and ascetic tumor cells treated with DOX.

RESULTS

The primary tumor cells showed a significant (P < 0.05) defect for UV-induced upregulation of the Trp53 protein, and consisted of different ratios of leukocytes, fibroblasts, epithelial cells and mesenchymal cells. The IC50 level to DOX was lower in both primary cells (IC50 = 0.12 μM and 0.20 μM) as compared to the CT26 cells (IC50 = 0.32 μM), although the solid tumor was more sensitive. Also, the number of cells arrested at the G0/G1 stage was significantly decreased (24.7-23.1% in primary tumor cells treated with DOX, P < 0.05) while arrest at the G2 stage was enhanced to 296.8-254.3% in DOX-treated primary tumor cells compared with DOX-treated CT26 cells. Furthermore, apoptotic cells of early and late stage were greatly increased in the two primary cell-lines treated with DOX when compared to same conditions for CT26 cells. However, the Bax/Bcl-2 expression level was maintained constant in the primary tumor and CT26 cells.

CONCLUSIONS

To the best of our knowledge, these results are the first to successfully detect an alteration in chemosensitivity to DOX in solid tumor cells and ascetic tumor cells derived from tumor of FVB/N-Trp53tm1Hw1 mice TALEN-mediated Trp53 mutant gene.

TRP Channels: The Neglected Culprits in Breast Cancer Chemotherapy Resistance?

Breast cancer is a major health concern worldwide, and resistance to therapies remains a significant challenge in treating this disease. In breast cancer, Transient Receptor Potential (TRP) channels are well studied and constitute key players in nearly all carcinogenesis hallmarks. Recently, they have also emerged as important actors in resistance to therapy by modulating the response to various pharmaceutical agents. Targeting TRP channels may represent a promising approach to overcome resistance to therapies in breast cancer patients.

p53 Modulates Radiosensitivity in Head and Neck Cancers-From Classic to Future Horizons

p53, initially considered a tumor suppressor, has been the subject of research related to cancer treatment resistance in the last 30 years. The unfavorable response to multimodal therapy and the higher recurrence rate, despite an aggressive approach, make HNSCC a research topic of interest for improving therapeutic outcomes, even if it is only the sixth most common malignancy worldwide. New advances in molecular biology and genetics include the involvement of miRNA in the control of the p53 pathway, the understanding of mechanisms such as gain/loss of function, and the development of different methods to restore p53 function, especially for HPV-negative cases. The different ratio between mutant p53 status in the primary tumor and distant metastasis originating HNSCC may serve to select the best therapeutic target for activating an abscopal effect by radiotherapy as a "booster" of the immune system. P53 may also be a key player in choosing radiotherapy fractionation regimens. Targeting any pathway involving p53, including tumor metabolism, in particular the Warburg effect, could modulate the radiosensitivity and chemo-sensitivity of head and neck cancers.

Etoposide-induced DNA damage is increased in p53 mutants: identification of ATR and other genes that influence effects of p53 mutations on Top2-induced cytotoxicity

The functional status of the tumor suppressor p53 is a critical component in determining the sensitivity of cancer cells to many chemotherapeutic agents. DNA topoisomerase II (Top2) plays essential roles in DNA metabolism and is the target of FDA approved chemotherapeutic agents. Topoisomerase targeting drugs convert the enzyme into a DNA damaging agent and p53 influences cellular responses to these agents. We assessed the impact of the loss of p53 function on the formation of DNA damage induced by the Top2 poison etoposide. Using human HCT116 cells, we found resistance to etoposide in cell growth assays upon the functional loss of p53. Nonetheless, cells lacking fully functional p53 were etoposide hypersensitive in clonogenic survival assays. This complex role of p53 led us to directly examine the effects of p53 status on topoisomerase-induced DNA damage. A deficiency in functional p53 resulted in elevated levels of the Top2 covalent complexes (Top2cc) in multiple cell lines. Employing genome-wide siRNA screens, we identified a set of genes for which reduced expression resulted in enhanced synthetic lethality upon etoposide treatment of p53 defective cells. We focused on one hit from this screen, ATR, and showed that decreased expression sensitized the p53-defective cells to etoposide in all assays and generated elevated levels of Top2cc in both p53 proficient and deficient cells. Our findings suggest that a combination of etoposide treatment with functional inactivation of DNA repair in p53 defective cells could be used to enhance the therapeutic efficacy of Top2 targeting agents.

CIP2A silencing alleviates doxorubicin resistance in MCF7/ADR cells through activating PP2A and autophagy

Background

Cancerous inhibitor of protein phosphatase 2A (CIP2A) plays a critical role in the pathogenesis of various types of cancer. Here, we investigated whether manipulating CIP2A abundance could enhance the treatment effects of doxorubicin in MCF-7/ADR cells.

Methods

CIP2A silencing was achieved by specific siRNAs. Proliferation of breast cancer cell line MCF-7/ADR under effective doxorubicin concentrations after CIP2A silencing was examined by MTT assay. Wound healing assay was performed to quantify cell migration and caspase-3/-7 activities were measured for assessing the extent of apoptosis.

Results

First, our data confirmed that MCF-7/ADR cell proliferation was suppressed by doxorubicin in a dose-dependent manner. Additionally, knocking down of CIP2A could further decrease MCF-7 cell proliferation and migration, even in the presence of doxorubicin. Mechanistically, we have found that CIP2A silencing promoted cell apoptosis relative to doxorubicin alone or vehicle control groups. Lastly, phosphatase2A (PP2A) activity was potentiated and the autophagy markers, LC3B and Beclin1, were upregulated after knocking down CIP2A.

Conclusion

Our findings support the potential benefits of using CIP2A inhibitor as a therapeutic agent to treat doxorubicin-resistant breast cancer.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12094-021-02616-7.

The REGγ inhibitor NIP30 increases sensitivity to chemotherapy in p53-deficient tumor cells

A major challenge in chemotherapy is chemotherapy resistance in cells lacking p53. Here we demonstrate that NIP30, an inhibitor of the oncogenic REGγ-proteasome, attenuates cancer cell growth and sensitizes p53-compromised cells to chemotherapeutic agents. NIP30 acts by binding to REGγ via an evolutionarily-conserved serine-rich domain with 4-serine phosphorylation. We find the cyclin-dependent phosphatase CDC25A is a key regulator for NIP30 phosphorylation and modulation of REGγ activity during the cell cycle or after DNA damage. We validate CDC25A-NIP30-REGγ mediated regulation of the REGγ target protein p21 in vivo using p53-/- and p53/REGγ double-deficient mice. Moreover, Phosphor-NIP30 mimetics significantly increase the growth inhibitory effect of chemotherapeutic agents in vitro and in vivo. Given that NIP30 is frequently mutated in the TCGA cancer database, our results provide insight into the regulatory pathway controlling the REGγ-proteasome in carcinogenesis and offer a novel approach to drug-resistant cancer therapy.

Design and synthesis of anticancer 1-hydroxynaphthalene-2-carboxanilides with a p53 independent mechanism of action

A series of 116 small-molecule 1-hydroxynaphthalene-2-carboxanilides was designed based on the fragment-based approach and was synthesized according to the microwave-assisted protocol. The biological activity of all of the compounds was tested on human colon carcinoma cell lines including a deleted TP53 tumor suppressor gene. The mechanism of activity was studied according to the p53 status in the cell. Several compounds revealed a good to excellent activity that was similar to or better than the standard anticancer drugs. Some of these appeared to be more active against the p53 null cells than their wild-type counterparts. Intercalating the properties of these compounds could be responsible for their mechanism of action.

Anticancer activity of the thiosemicarbazones that are based on di-2-pyridine ketone and quinoline moiety

Thiosemicarbazones (TSC) are a subclass of iron-chelating agents that are believed to have an anticancer activity. The high potential for the application of this compound class can be illustrated by a fact that three TSC have entered clinical trials. The ability to chelate metal ions results in several biochemical changes in the cellular metabolism and growth. An important factor that determines the antitumor activity of TSC is a level of iron regulatory proteins and the antioxidant potential that is specific for each type of cancer cell. However, despite the increasing interest in TSC, their mechanism of anticancer activity is still unclear. For a more effective and rational design, it is crucial to determine and describe the abovementioned issues. In this report, we describe a series of new TSC that are designed on the four main structural scaffolds. The anticancer activity of these compounds was evaluated against a panel of cancer cell lines including colon and breast cancers and gliomas. Special attention was paid to the metal-dependent proteins. The impact of the tested TSC on the cell cycle and redox homeostasis was also determined. These results confirm a p53-independent mechanism of apoptosis.

p53-dependent autophagic degradation of TET2 modulates cancer therapeutic resistance

Tumor cells with p53 inactivation frequently exhibit chemotherapy resistance, which poses a long-standing challenge to cancer treatment. Here we unveiled a previously unrecognized role of TET2 in mediating p53-loss induced chemotherapy resistance in colon cancer. Deletion of TET2 in p53-null colon cancer cells enhanced DNA damage and restored chemotherapy sensitivity. By taking a two-pronged approach that combined pharmacological inhibition with genetic depletion, we discovered that p53 destabilized TET2 at the protein level by promoting its autophagic degradation. At the molecular level, we further revealed a physical association between TET2 and p53 that facilitated the nucleoplasmic shuttling of TET2, as well as its recruitment to the autophagosome for degradation. Our study has unveiled a functional interplay between TET2 and p53 during anti-cancer therapy. Our findings establish the rationale for targeting TET2 to overcome chemotherapy resistance associated with mutant p53 tumors.

VEGFR3 inhibition chemosensitizes lung adenocarcinoma A549 cells in the tumor-associated macrophage microenvironment through upregulation of p53 and PTEN

In lung adenocarcinoma, loss of p53 and PTEN in tumors are associated with decreased response to chemotherapy and decreased survival. A means to pharmacologically upregulate p53 and PTEN protein expression could improve the prognosis of patients with p53- and PTEN-deficient tumors. In the present study we revealed that vascular endothelial growth factor receptor 3 (VEGFR3) inhibition in lung adenocarcinoma cells was associated with improved expression levels of both p53 and PTEN in the tumor-associated macrophage (TAM) microenvironment. Inhibition of VEGFR3 in lung adenocarcinoma cells was associated with growth arrest and decreased migration and invasion. The upregulation of p53 and PTEN protein expression after VEGFR3 inhibition decreased chemotherapy resistance and improved chemosensitivity in co-cultured A549 cells in which p53 and PTEN expression were decreased. Finally, we demonstrated that TAMs promoted the expression of VEGF-C and its receptor VEGFR3. Western blot analysis revealed the co-cultured A549 cells with TAMs are a primary source of VEGF-C and VEGFR3 in the tumor microenvironment. Our studies revealed that VEGFR3 inhibition may be a pharmacological means to upregulate p53 and PTEN protein expression and improve the outcome of patients with p53- and PTEN-deficient tumors.

Metastatic triple-negative breast cancer patient with TP53 tumor mutation experienced 11 months progression-free survival on bortezomib monotherapy without adverse events after ending standard treatments with grade 3 adverse events

A triple-negative breast cancer patient had no hereditary BRCA1, BRCA2, or TP53 risk variants. After exhaustion of standard treatments, she underwent experimental treatments and whole-exome sequencing of tumor, blood, and a metastasis. Well-tolerated experimental bortezomib monotherapy was administered for a progression-free period of 11 mo. After progression, treatments were changed and the exome data were evaluated, expanded with RNA and exome sequencing of a late-stage metastasis. In the final stage, eribulin alone and in combination with anthracyclines were administered. While suffering from grade 3 adverse events, skin metastases progressed. She lived 51 mo after initial diagnosis.Toxicity from anthracyclines and cisplatin may have been due to associated germline variants CBR3 C4Y and V224M and GSTP1 I105V, respectively. Somatic mutations predicted or reported as pathogenic were detected in 38 genes in tumor tissues. All tumor samples harbored the heterozygous TP53 Y220C variant, known to destabilize p53 and down-regulate p53-mediated apoptosis. The success of bortezomib may be explained by the previously reported up-regulation of caspase-mediated apoptosis, which is p53-independent. Phylogenetic analysis of blood, primary tumor, and two metastases inferred an ancestral tumor cell with 12 expressed tumor mutations from which all three tumors may have evolved.Although our first urgent analysis could only include 40 genes, postmortem analysis uncovered the aggressiveness and suggested experimental therapies including 16 actionable targets, partly validated by immunohistochemistry. Exome and transcriptome analyses yielded comprehensive therapy-relevant information and should be considered for patients at first diagnosis.

P-Sulfocalix[6]arene as Nanocarrier for Controlled Delivery of Doxorubicin

Given the high toxicity of the anthracycline antibiotic doxorubicin (DOX), it is relevant to search for nanocarriers that decrease the side effects of the drug and are able to transport it towards a therapeutic target Here, the encapsulation of DOX by p-sulfocalix[6]arene (calix) has been studied. The interaction of DOX with the macrocycle, as well as with DNA, has been investigated and the equilibrium constant for each binding process estimated. The results showed that the binding constant of DOX to DNA, K_DNA , is three orders of magnitude higher than that to calix, K_calix . The ability of calixarenes to encapsulate DOX molecules, as well as the capability of the DOX molecules included into the inner cavity of the macrocycle to bind with DNA have been examined. Cytotoxicity measurements were done in different cancer and normal cell lines to probe the decrease in the toxicity of the encapsulated DOX. The low toxicity of calixarenes has also been demonstrated for different cell lines.

Marine-derived Fungi Extracts Enhance the Cytotoxic Activity of Doxorubicin in Nonsmall Cell Lung Cancer Cells A459

Background:

Drug resistance is a major concern in the current chemotherapeutic approaches and the combination with natural compounds may enhance the cytotoxic effects of the anticancer drugs. Therefore, this study evaluated the cytotoxicity of crude ethyl extracts of six marine-derived fungi – Neosartorya tsunodae KUFC 9213 (E1), Neosartorya laciniosa KUFC 7896 (E2), Neosartorya fischeri KUFC 6344 (E3), Aspergillus similanensis KUFA 0013 (E4), Neosartorya paulistensis KUFC 7894 (E5), and Talaromyces trachyspermum KUFC 0021 (E6) – when combined with doxorubicin (Dox), in seven human cancer cell lines.

Materials and Methods:

The antiproliferative activity was primarily assessed by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay.

Results:

Two extracts, E1 and E2, demonstrated a significant enhancement of Dox’s cytotoxicity in nonsmall cell lung cancer A549 cells. Accumulation of Dox in the nuclei increased when A549 cells were treated in combination with extracts E1 and E2, with induction of cell death observed by the nuclear condensation assay. The combination of E2 with Dox increased the DNA damage as detected by the comet assay. Ultrastructural observations by transmission electron microscopy suggest an autophagic cell death due to an increase of autophagic vesicles, namely with the combination of Dox with E1 and E2.

Conclusion:

These findings led to the conclusion that the fungal extracts E1 and E2 potentiate the anticancer action of Dox, through nuclear accumulation of Dox with induction of cell death mainly by cytotoxic autophagy.

SUMMARY

Fungal extracts increase the cytotoxic activity of doxorubicin (Dox) in lung cancer cells

Nuclear accumulation of Dox, DNA damage, and cell death as a mechanism of action

Fungal extracts may potentiate the anticancer activity of conventional drugs.

Abbreviations Used: A375: Human malignant melanoma cell line, A549: Human non small lung cancer cell line, DAPI: 4,6-Diamidino-2-phenylindole, DMEM: Dulbecco’s Modified Eagle Medium, DMSO: Dimethylsulfoxide, Dox: Doxorubicin, DSBs: DNA double-strand breaks, E1: Neosartorya tsunodae KUFC 9213, E2: Neosartorya laciniosa KUFC 7896, E3: Neosartorya fischeri KUFC 6344, E4: Aspergillus similanensis KUFA 0013, E5: Neosartorya paulistensis KUFC 7894, E6: Talaromyces trachyspermum KUFC 0021, FBS: Fetal bovine serum, HCT116: Human colorectal carcinoma cell line, HEPES: (N-[2-hydroxyethyl] piperazine-N’- [2-ethane-sulfonic acid]), HepG2: Human hepatocellular carcinoma cell line, HT29: Human Caucasian colon adenocarcinoma Grade II cell line, IC₅₀: Concentration of the extract or Dox that inhibits cell viability by 50%, LRP: Lung resistance-related protein, MCF7: Human breast adenocarcinoma cell line, MEM: Minimum Essential Medium Eagle, MRPs: Multidrug resistance-associated proteins, MTT: 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide, PBS: Phosphate-buffered saline, NSCLC: Nonsmall cell lung cancer, P-gp: P-glycoprotein, ROS: Reactive oxygen species, RPMI: Roswell Park Memorial Institute Medium, TEM: Transmission electron microscopy, U251: Human glioblastoma astrocytoma cell line.

Salt-induced stability and serum-resistance of polyglutamate polyelectrolyte brushes/nuclear factor-κB p65 siRNA Polyplex enhance the apoptosis and efficacy of doxorubicin

Short interfering RNAs (siRNAs) as chemotherapeutic RNAi agents hold great promise for a significant improvement in cancer therapy. Despite the promise, effective transport of siRNA with minimal side effects remains a challenge. The common problem associated with the low delivery efficiencies of current polycation-based gene delivery systems is their low stability in the presence of salt and serum. In the present study we developed the polyglutamate derivatives (PGS) polyelectrolyte brushes for NF-κB p65 siRNA delivery. The PGS polyelectrolyte brushes/siRNA polyplex was colloidally stable (150 nm diameter) in physiological saline (150 mM NaCl), likely due to the osmotic brushes of PGS. The size-controlled siRNA/PGS polyplex also showed the serum resistance resulting in their efficient cellular uptake was not negatively influenced by the presence of serum. The endothermic profile of ITC, their low values of Gibbs free energy and binding constants Kb under salt conditions provided the direct evidence that PGS polyelectrolyte brushes had a much lower binding affinity for serum proteins, compared with PEI 25KDa. PGS polyelectrolyte brushes delivering NF-κB p65 siRNA achieved efficient down-regulation of NF-κB p65 protein in HeLa cells. The NF-κB p65 down-regulation mediated by PGS polyelectrolyte brushes was more significant than PEI 25KDa and comparable to Lipofectamine 2000. Furthermore, the combination treatment with PGS polyelectrolyte brushes/NF-κB p65 siRNA polyplex and doxorubicin demonstrated synergistic apoptotic and cytotoxic effects on HeLa cancer cells. The high stability in physiological saline and salt-induced serum resistance of PGS polyelectrolyte brushes/siRNA polyplex has potential applications together with standard chemotherapies such as doxorubicin to be a viable method to improve the clinical outcomes in cancer therapies.

Inactivation and inducible oncogenic mutation of p53 in gene targeted pigs

Mutation of the tumor suppressor p53 plays a major role in human carcinogenesis. Here we describe gene-targeted porcine mesenchymal stem cells (MSCs) and live pigs carrying a latent TP53^R167H mutant allele, orthologous to oncogenic human mutant TP53^R175H and mouse Trp53^R172H, that can be activated by Cre recombination. MSCs carrying the latent TP53^R167H mutant allele were analyzed in vitro. Homozygous cells were p53 deficient, and on continued culture exhibited more rapid proliferation, anchorage independent growth, and resistance to the apoptosis-inducing chemotherapeutic drug doxorubicin, all characteristic of cellular transformation. Cre mediated recombination activated the latent TP53^R167H allele as predicted, and in homozygous cells expressed mutant p53-R167H protein at a level ten-fold greater than wild-type MSCs, consistent with the elevated levels found in human cancer cells. Gene targeted MSCs were used for nuclear transfer and fifteen viable piglets were produced carrying the latent TP53^R167H mutant allele in heterozygous form. These animals will allow study of p53 deficiency and expression of mutant p53-R167H to model human germline, or spontaneous somatic p53 mutation. This work represents the first inactivation and mutation of the gatekeeper tumor suppressor gene TP53 in a non-rodent mammal.

Doxorubicin induces cytotoxicity through upregulation of pERK-dependent ATF3

Although doxorubicin is commonly used in the treatment of many cancer types, its use in chemotherapy has been limited, largely because of its severe side effects, including cardiotoxicity and nephrotoxicity. In this study, we aimed to identify the mechanism of doxorubicin-induced cytotoxicity by using the human kidney proximal tubule cell line HK-2. Furthermore, we investigated the role of activating transcription factor 3 (ATF3) as a mediator of doxorubicin-induced cytotoxicity by using wild-type mouse embryonic fibroblasts (MEF) cells and ATF3 knockout (KO) cells. In HK-2 cells, doxorubicin decreased cell viability in a dose-dependent manner and induced an increase in cells in the sub G1 and G2/M phases at all doses. Doxorubicin treatment showed the following dose-dependent effects: increase in the secretion of tumor necrosis factor alpha; decrease in the expression of phosphorylated protein kinase A and Bcl-2; and increase in the expression of phosphorylated signal transducer and activator of transcription 3, phosphorylated extracellular signal-regulated kinase (ERK), and ATF3. Based on these results, we suggest that doxorubicin induces cytotoxicity through an ERK-dependent pathway, and ATF3 plays a pivotal role as a transcriptional regulator in this process.

Cardiomyocyte specific ablation of p53 is not sufficient to block doxorubicin induced cardiac fibrosis and associated cytoskeletal changes

Doxorubicin (Dox) is an anthracycline used to effectively treat several forms of cancer. Unfortunately, the use of Dox is limited due to its association with cardiovascular complications which are manifested as acute and chronic cardiotoxicity. The pathophysiological mechanism of Dox induced cardiotoxicity appears to involve increased expression of the tumor suppressor protein p53 in cardiomyocytes, followed by cellular apoptosis. It is not known whether downregulation of p53 expression in cardiomyocytes would result in decreased rates of myocardial fibrosis which occurs in response to cardiomyocyte loss. Further, it is not known whether Dox can induce perivascular necrosis and associated fibrosis in the heart. In this study we measured the effects of acute Dox treatment on myocardial and perivascular apoptosis and fibrosis in a conditional knockout (CKO) mouse model system which harbours inactive p53 alleles specifically in cardiomyocytes. CKO mice treated with a single dose of Dox (20 mg/kg), did not display lower levels of myocardial apoptosis or reactive oxygen and nitrogen species (ROS/RNS) compared to control mice with intact p53 alleles. Interestingly, CKO mice also displayed higher levels of interstitial and perivascular fibrosis compared to controls 3 or 7 days after Dox treatment. Additionally, the decrease in levels of the microtubule protein α-tubulin, which occurs in response to Dox treatment, was not prevented in CKO mice. Overall, these results indicate that selective loss of p53 in cardiomyocytes is not sufficient to prevent Dox induced myocardial ROS/RNS generation, apoptosis, interstitial fibrosis and perivascular fibrosis. Further, these results support a role for p53 independent apoptotic pathways leading to Dox induced myocardial damage and highlight the importance of vascular lesions in Dox induced cardiotoxicity.

Late activation of stress-activated protein kinases/c-Jun N-terminal kinases triggered by cisplatin-induced DNA damage in repair-defective cells

Although stress-activated protein kinases/c-Jun N-terminal kinases (SAPK/JNK) are rapidly activated by genotoxins, the role of DNA damage in this response is not well defined. Here we show that the SEK1/MKK4-mediated dual phosphorylation of SAPK/JNK (Thr-183/Tyr-185) correlates with the level of cisplatin-DNA adducts at late times (16-24 h) after drug treatment in both human and mouse cells. Transfection of platinated plasmid DNA also caused SAPK/JNK activation. A defect in transcription-coupled nucleotide excision repair resting on a mutation in Cockayne syndrome group B protein promoted the late SAPK/JNK activation following cisplatin exposure. Signaling to SAPK/JNK was accompanied by activation of Ataxia telangiectasia mutated- and Rad3-related kinase, replication protein A, and checkpoint kinases as well as by the formation of DNA double strand breaks (DSBs). Ionizing radiation-induced DSBs did not provoke SAPK/JNK activation, and inhibition of transcription also failed to provoke this response. Late activation of SAPK/JNK stimulated by cisplatin-induced DNA lesions was reduced in the absence of specific DNA repair proteins, such as xeroderma pigmentosum protein C, pointing to an essential function of individual repair factors in DNA damage signaling to SAPK/JNK. Collectively, the data indicate that late SAPK/JNK activation is triggered by non-repaired cisplatin adducts in transcribed genes and involves replication-associated events, DSBs, tyrosine kinases, Rho GTPases, and specific repair factors.

Increase in CIP2A expression is associated with doxorubicin resistance

The cancerous inhibitor of protein phosphatase 2A (CIP2A) increases the migration and metastasis of various cancer cells. Overexpression of CIP2A has been shown to increase the proliferation of MDA-MB-231 cells. We thus assessed whether CIP2A expression is associated with sensitivity to doxorubicin. MDA-MB-231 cells showed an increase in CIP2A expression after treatment with doxorubicin, while MCF-7 cells showed a decrease in CIP2A expression. The overexpression of CIP2A in MCF-7 cells overcame the inhibition of cell proliferation in response to doxorubicin treatment. CIP2A expression was not affected by wild-type or mutant p53. However, mutant p53 blocked doxorubicin-mediated CIP2A down-regulation in HCT116 cells. As a regulation mechanism of doxorubicin-mediated CIP2A expression, we showed that phosphorylated Akt was involved in the suppression of CIP2A expression.

Activation of CD44 facilitates DNA repair in T-cell lymphoma but has differential effects on apoptosis induced by chemotherapeutic agents and ionizing radiation

Expression of CD44s (standard form) in malignant lymphoma is a poor indicator of survival. To investigate whether activation of CD44s can protect from cell death, this study compared the extent of apoptosis induced by chemotherapeutic agents and ionizing radiation (IR) on T-lymphoma cell lines in the presence or absence of adherent hyaluronan and monoclonal antibodies (MoAbs). Growth in the presence of adherent ligands enhanced apoptosis induced by dexamethasone (Dex), but protected cells from epirubicin-induced apoptosis. In IR-induced apoptosis, mouse lymphoma cells had resistance against apoptosis when treated with hyaluronan (HA), although acute cell death reached the same plateau regardless of treatment with adherent MoAbs in human lymphoma cell line. However, the post-irradiated repopulation of lymphoma cells was strikingly accelerated in those treated with CD44 adherent ligands. This repopulation process correlated with the remarkable upregulation of proliferating cell nuclear antigen (PCNA), which is a protein involved in DNA repair. Unscheduled DNA synthesis (UDS), a measure of DNA repair, was consistently enhanced in CD44s-stimulated cells after exposure to radiation. The results suggest that the poor prognostic indication of CD44 expression is more a consequence of enhanced DNA repair following genotoxic damage than of direct resistance to apoptosis.

Comparative genome-wide screening identifies a conserved doxorubicin repair network that is diploid specific in Saccharomyces cerevisiae

The chemotherapeutic doxorubicin (DOX) induces DNA double-strand break (DSB) damage. In order to identify conserved genes that mediate DOX resistance, we screened the Saccharomyces cerevisiae diploid deletion collection and identified 376 deletion strains in which exposure to DOX was lethal or severely reduced growth fitness. This diploid screen identified 5-fold more DOX resistance genes than a comparable screen using the isogenic haploid derivative. Since DSB damage is repaired primarily by homologous recombination in yeast, and haploid cells lack an available DNA homolog in G1 and early S phase, this suggests that our diploid screen may have detected the loss of repair functions in G1 or early S phase prior to complete DNA replication. To test this, we compared the relative DOX sensitivity of 30 diploid deletion mutants identified under our screening conditions to their isogenic haploid counterpart, most of which (n = 26) were not detected in the haploid screen. For six mutants (bem1Delta, ctf4Delta, ctk1Delta, hfi1Delta,nup133Delta, tho2Delta) DOX-induced lethality was absent or greatly reduced in the haploid as compared to the isogenic diploid derivative. Moreover, unlike WT, all six diploid mutants displayed severe G1/S phase cell cycle progression defects when exposed to DOX and some were significantly enhanced (ctk1Delta and hfi1Delta) or deficient (tho2Delta) for recombination. Using these and other "THO2-like" hypo-recombinogenic, diploid-specific DOX sensitive mutants (mft1Delta, thp1Delta, thp2Delta) we utilized known genetic/proteomic interactions to construct an interactive functional genomic network which predicted additional DOX resistance genes not detected in the primary screen. Most (76%) of the DOX resistance genes detected in this diploid yeast screen are evolutionarily conserved suggesting the human orthologs are candidates for mediating DOX resistance by impacting on checkpoint and recombination functions in G1 and/or early S phases.

Interaction of Ganoderma triterpenes with doxorubicin and proteomic characterization of the possible molecular targets of Ganoderma triterpenes

Triterpenes are the main components with cytotoxicity in Ganoderma lucidum, which is used popularly as a complementary treatment for cancer therapy in traditional Chinese medicine. To investigate the possible interaction between chemotherapeutic agents and triterpenes extracted from G. lucidum, the cytotoxicity of doxorubicin (DOX) combined with Ganoderma triterpenes (GTS) or lucidenic acid N (LCN), a purified compound, was examined in HeLa cells. The combinations targeting DOX with GTS or LCN resulted in a synergistic interaction in HeLa cells. Moreover, to identify the molecular targets of GTS, two-dimensional gel electrophoresis-based comparative proteomics was carried out and proteins with altered expression levels after GTS treatment in HeLa cells were identified by matrix-assisted laser desorption/ionization time-of-flight tandem mass spectrometry. The results of our proteomic study indicated that the GTS treatment caused regulated expression of 14 proteins, which play important roles in cell proliferation, the cell cycle, apoptosis, and oxidative stress. Flow cytometric analysis confirmed that GTS could induce weak G(0)-G(1) phase arrest and combined use of GTS with DOX could induce apoptosis in cells. Furthermore, GTS enhanced the reactive oxygen species (ROS)-producing effect of DOX, and a ROS scavenger could affect the synergism between GTS and DOX. In cells with high Ku80 protein expression, the synergism between GTS and DOX was also partly affected. Importantly, in cells with high Ku80 expression that were treated with a ROS scavenger, the synergism between GTS and DOX totally disappeared. These results suggest that the synergism between GTS and DOX might be based on GTS-induced sensitization of cells to chemotherapeutics through enhanced oxidative stress, DNA damage, and apoptosis.

Cellular mechanisms of resistance to anthracyclines and taxanes in cancer: intrinsic and acquired

Taxanes and anthracyclines are two of the most potent and broadly effective classes of chemotherapeutic agents. However, resistance to these agents is common and significantly limits their potential. As such, there is a great need to understand the mechanisms underlying de novo and acquired resistance to these agents. Beyond the resistance barrier lies even greater potential to significantly alter the natural course of human cancer. This review discusses what we currently understand about the mechanisms of resistance to taxanes and anthracyclines. Preclinical models suggest a role for ATP-binding cassette transporters, tubulin isoforms, microtubule-associated proteins, tubulin gene mutations, and mitotic checkpoint signaling proteins in resistance to taxanes. Preclinical models also suggest that drug transport proteins, antioxidant defenses, apoptotic signaling, and topoisomerase modulation may mediate anthracycline resistance. Many of these hypotheses remain untested in appropriately designed clinical studies, but limited clinical evidence will be reviewed. Epothilones represent a novel class of non-taxane microtubule stabilizing agents with distinct drug-resistance profiles. Potential mechanisms behind these differences and their potential role in the treatment of both taxane- and anthracycline-refractory patients are discussed.

Evaluation of anticancer effects of newly synthesized dihydropyridine derivatives in comparison to verapamil and doxorubicin on T47D parental and resistant cell lines in vitro

Failure of current anticancer drugs mandates screening for new compounds of synthetic or biological origin to be used in cancer therapy. Multidrug resistance (MDR) is one of the main obstacles in the chemotherapy of cancer. Efflux of cytotoxic agents mediated by P-glycoprotein (P-gp or MDR1) is believed to be an important mechanism of multidrug resistance. Therefore, we decided to investigate the antiproliferative effects of seven newly synthesized 1,4-dihydropyridine (DHP) derivatives in comparison to verapamil (VP) and doxorubicin (DOX) on human breast cancer T47D cells and its MDR1 overexpressed and moderately resistant cells (RS cells) using MTT cytotoxicity assay. We also examined the effects of these compounds on cytotoxicity of DOX in these two cell types. The cytotoxicity assays using MTT showed that most of the tested new DHP derivatives and VP at 10 microM concentration had varying levels of toxicity on both T47D and RS cells. The toxicity was mostly in the range of 10-25%. However, the cytotoxicity of these DHP derivatives, similar to VP, was significantly less than DOX when comparing IC(50) values. Furthermore, these compounds in general had relatively more cytotoxicity on T47D vs RS cells at 10-microM concentration. Among new DHPs, compounds 7a (3,5-dibenzoyl-4-(2-methylthiazol-4-yl)-1,4-dihydro-2,6-dimethylpyridine) and 7d (3,5-diacetyl-4-[2-(2-chlorophenyl)thiazol-4-yl)]-1,4-dihydro-2,6-dimethylpyridine) showed noticeable potentiation of DOX cytotoxicity (reduction of DOX IC(50)) compared to DOX alone in both cells, particularly in RS cells. This effect was similar to that of VP, a known prototype of MDR1 reversal agent. In other words, compounds 7a and 7d resensitized RS cells to DOX or reversed their resistance. Results indicate that compound 7d exerts highest effect on RS cells. Therefore, these two newly synthesized DHP derivatives, compounds 7a and 7d, are promising as potential new MDR1 reversal agents and should be further studied on other highly resistant cells due to MDR1 overexpression and with further molecular investigation.

P-TEFb inhibitors interfere with activation of p53 by DNA-damaging agents

Tumor suppressor p53 is stabilized in response to gamma-irradiation or treatment with DNA-damaging agents, and as a result p53 transcriptionally activates its targets leading to cell-cycle arrest or apoptosis. P-TEFb (positive transcription elongation factor b) inhibitors such as flavopiridol or 4-amino-6-hydrazino-7-b-d-ribofuranosyl-7H-pyrrolo[2,3-d]-pyrimidine-5-carboxamide (ARC) upregulate p53 protein levels, but inhibit the expression of its targets p21 and hdm2. DNA-damaging agents, doxorubicin and cisplatin are being used in combination with P-TEFb inhibitor flavopiridol in clinical trials for the treatment of some cancer patients. In this study, we found that P-TEFb inhibitors block the phosphorylation of p53 induced by doxorubicin. Furthermore, treatment of cells with P-TEFb inhibitors together with doxorubicin inhibits doxorubicin-induced binding of p53 to DNA and p53 transcriptional activity. These data suggest that P-TEFb inhibitors may antagonize the activation of p53 by DNA-damaging agents in tumors with wild-type p53.

Lovastatin protects human endothelial cells from the genotoxic and cytotoxic effects of the anticancer drugs doxorubicin and etoposide

BACKGROUND AND PURPOSE

3-Hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase inhibitors (statins) are frequently used lipid-lowering drugs. Moreover, they exert pleiotropic effects on cellular stress responses and death. Here, we analysed whether lovastatin affects the sensitivity of primary human endothelial cells (HUVEC) to the anticancer drug doxorubicin.

EXPERIMENTAL APPROACH

We investigated whether pretreatment of HUVEC with low dose of lovastatin influences the cellular sensitivity to doxorubicin. To this end, cell viability, proliferation and apoptosis as well as DNA damage-triggered stress response were analysed.

KEY RESULTS

Lovastatin reduced the cytotoxic potency of doxorubicin in HUVEC. Lovastatin attenuated the doxorubicin-induced increase in p53 as well as activation of checkpoint kinase (Chk-1) and stress-activated protein kinase/c-Jun-N-terminal kinase (SAPK/JNK). Acquired doxorubicin resistance was independent of alterations in doxorubicin efflux and cell cycle progression. Also, doxorubicin-triggered production of reactive oxygen species (ROS) and formation of oxidative DNA lesions remained unaffected by lovastatin. However, lovastatin impaired DNA strand break formation induced by doxorubicin. Notably, lovastatin also conferred cross-resistance to the cytotoxic and genotoxic effects of etoposide, indicating that lovastatin shields topoisomerase II against poisons.

CONCLUSIONS AND IMPLICATIONS

Based on these data, we suggest that lovastatin-mediated resistance to topoisomerase II inhibitors is due to a reduction in DNA damage and, hence, it attenuates stress responses leading to cell death that are triggered by DNA damage. Therefore, lovastatin might be useful clinically for alleviating side-effects of anticancer therapies that include topoisomerase II inhibitors.

Design of β-carboline derivatives as DNA-targeting antitumor agents

This research studied the structure-activity relationship of beta-carboline derivatives as antitumor agents, in which 41 synthesized compounds and their cytotoxicity to tumor and normal cell lines were assayed. It was proved that substituent in position-9 of the beta-carboline ring could reinforce the DNA intercalating ability and consequently cytotoxicity to tumor cell lines, and the amidation of amino group at the end of the DNA targeting side chain in position-3 could cripple the DNA intercalating activity of these compounds, which resultingly initiated the cytotoxic selectivity to tumor cell lines rather than to normal ones. Furthermore, the S and G2-M arrest induced by these compounds confirmed that they could target DNA and lead to DNA destructions in Hela cells. In short, this study may provide a framework to design a novel antitumor drug that could surpass Adriamycin.

Topoisomerase II beta expression level correlates with doxorubicin-induced apoptosis in peripheral blood cells

Anthracyclines are widely used in oncology. Both the response and side-effects of anthracyclines are individually variable, but determinants or predictive markers of this variability are not available. We investigated the variability in the expression of the anthracycline targets topoisomerases II (topo II) alpha and beta and its significance for the apoptotic response following exposure to the anthracycline doxorubicin. Only topo II beta protein expression was detected in peripheral blood cells. Usually considered a constitutively expressed protein, topo II beta varied 3-, 18-, and 16-fold on the mRNA, protein and activity levels, respectively, among the volunteers tested. In addition, the expression of topo II beta was modified by several mitogens, suggesting a role in the regulation of cell cycle. Strikingly, topo II beta activity correlated statistically significantly with the apoptotic response in peripheral blood leukocytes exposed to 1 microM doxorubicin. A longitudinal study in a subset of study subjects demonstrated that 30% of the topo II expression variability may be inherited. However, resequencing of the TOP2B gene in 48 unrelated individuals revealed only 8 gene variants, none of them with obvious effects on the expression or protein sequence of topo II beta. Taken together, the apoptotic response to doxorubicin in peripheral blood cells may be mediated by topo II beta. The expression level of topo II beta is intra- and inter-individually variable, and may in part determine the apoptotic response to doxorubicin and other anthracyclines.

BM88 is a dual function molecule inducing cell cycle exit and neuronal differentiation of neuroblastoma cells via cyclin D1 down-regulation and retinoblastoma protein hypophosphorylation

Control of cell cycle progression/exit and differentiation of neuronal precursors is of paramount importance during brain development. BM88 is a neuronal protein associated with terminal neuron-generating divisions in vivo and is implicated in mechanisms underlying neuronal differentiation. Here we have used mouse neuroblastoma Neuro 2a cells as an in vitro model of neuronal differentiation to dissect the functional properties of BM88 by implementing gain- and loss-of-function approaches. We demonstrate that stably transfected cells overexpressing BM88 acquire a neuronal phenotype in the absence of external stimuli, as judged by enhanced expression of neuronal markers and neurite outgrowth-inducing signaling molecules. In addition, cell cycle measurements involving cell growth assays, BrdUrd incorporation, and fluorescence-activated cell sorting analysis revealed that the BM88-transfected cells have a prolonged G(1) phase, most probably corresponding to cell cycle exit at the G(0) restriction point, as compared with controls. BM88 overexpression also results in increased levels of the cell cycle regulatory protein p53, and accumulation of the hypophosphorylated form of the retinoblastoma protein leading to cell cycle arrest, with concomitant decreased levels and, in many cells, cytoplasmic localization of cyclin D1. Conversely, BM88 gene silencing using RNA interference experiments resulted in acceleration of cell proliferation accompanied by impairment of retinoic acid-induced neuronal differentiation of Neuro 2a cells. Taken together, our results suggest that BM88 plays an essential role in regulating cell cycle exit and differentiation of Neuro 2a cells toward a neuronal phenotype and further support its involvement in the proliferation/differentiation transition of neural stem/progenitor cells during embryonic development.

β-carboline derivatives: Novel photosensitizers that intercalate into DNA to cause direct DNA damage in photodynamic therapy

Novel 1,3,9-trisubstituted beta-carboline derivatives were found to exhibit DNA photocleavage properties under visible light irradiation in a cell-free system, which could be reduced by antioxidant vitamin E. Their photo-cytotoxicity to human tumor cell line HeLa was confirmed, in which apoptosis only contributed a small part to the cell death, and necrosis was the dominating outcome of HeLa cells in photodynamic therapy (PDT) using beta-carboline derivatives. Different from other clinical PDT drugs, beta-carboline derivatives were demonstrated to be able to distribute in the nucleus and intercalate into DNA, and consequently cause direct DNA damage by photochemical reaction products in PDT, which was proved by the distinct DNA tails in the comet assay and the considerable amount of DNA damaged cells quantified by flow cytometry. This mechanism could be the explanation for the delay of cell proliferation at DNA synthesis and mitosis.

MDM2 antagonists induce p53-dependent apoptosis in AML: implications for leukemia therapy

Although TP53 mutations are rare in acute myeloid leukemia (AML), inactivation of wild-type p53 protein frequently occurs through overexpression of its negative regulator MDM2 (murine double minute 2). Recently, small-molecule antagonists of MDM2, Nutlins, have been developed that inhibit the p53-MDM2 interaction and activate p53 signaling. Here, we study the effects of p53 activation by Nutlin-3 in AML cells. Treatment with MDM2 inhibitor triggered several molecular events consistent with induction of apoptosis: loss of mitochondrial membrane potential, caspase activation, phosphatidylserine externalization, and DNA fragmentation. There was a positive correlation in primary AML samples with wild-type p53 between baseline MDM2 protein levels and apoptosis induced by MDM2 inhibition. No induction of apoptosis was observed in AML samples harboring mutant p53. Colony formation of AML progenitors was inhibited in a dose-dependent fashion, whereas normal CD34+ progenitor cells were less affected. Mechanistic studies suggested that Nutlin-induced apoptosis was mediated by both transcriptional activation of proapoptotic Bcl-2 family proteins, and transcription-independent mitochondrial permeabilization resulting from mitochondrial p53 translocation. MDM2 inhibition synergistically enhanced cytotoxicity of cytosine arabinoside and doxorubicin in AML blasts but not in normal hematopoietic progenitor cells. p53 activation by targeting the p53-MDM2 interaction might offer a novel therapeutic strategy for AML that retain wild-type p53.

Major contribution of the multidrug transporter P-glycoprotein to reduced susceptibility of poly(ADP-ribose) polymerase-1 knock-out cells to doxorubicin action

Inactivation of poly(ADP-ribose) polymerase-1 (PARP-1) has been shown to potentiate the cytotoxicity of distinct DNA targeting agents including topoisomerase I inhibitors. On the other hand, the PARP-1 deficient cells exhibited resistance to conventional inhibitors of topoisomerase II such as etoposide or doxorubicin (DOX). Recently, we observed the extreme sensitivity of PARP-1 knock-out (KO) cells to C-1305, a new biologically active triazoloacridone compound. C-1305 permanently arrested the cells in G2-phase of the cell-cycle. These observations prompted us to investigate more thoroughly the susceptibility of PARP-1 KO cells to DOX and to examine the effect of DOX on the progression of cell-cycle. We determined the uptake of DOX and P-glycoprotein (P-gp) expression in mouse cells and compared it with that in human myeloma 8226/Dox40 cells overexpressing P-gp. Exposure of mouse cells to DOX revealed a reduced drug uptake in cells lacking PARP-1. However, combined treatment with verapamil, a potent MDR modulator increased the DOX accumulation. Detailed immunoblotting experiments revealed an approximately threefold higher P-gp level in PARP-1 KO cells as compared with normal counterparts. Interestingly, DOX induced in normal fibroblasts very rapidly G2 arrest whereas in PARP-1 KO cells it blocked primarily the transition between S and G2 resulting in the increase of cells remaining in S-phase. This coincided with the lack of the site-specific phosphorylation of CDK2. Simultaneous inhibition of P-gp in cells lacking PARP-1 resulted in an accumulation of cells in G2. Exposure of mouse cells to high DOX dose activated significantly caspase-3/7 in PARP-1 KO cells.

Molecular pathways involved in the anti-apoptotic effect of 1,25-dihydroxyvitamin D3 in primary human keratinocytes

We previously reported that 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] protects primary human keratinocytes against ultraviolet (UV)B-induced apoptosis. Here, we confirmed the anti-apoptotic effect of 1,25(OH)2D3 in keratinocytes, using cisplatin and doxorubicin as apoptotic triggers. We further showed that 1,25(OH)2D3 activates two survival pathways in keratinocytes: the MEK/extracellular signal regulated kinase (ERK) and the phosphatidylinositol 3-kinase (PI-3K)/Akt pathway. Activation of ERK and Akt by 1,25(OH)2D3 was transient, required a minimal dose of 10(-9) M and could be blocked by actinomycin D and cycloheximide. Moreover, inhibition of Akt or ERK activity with respectively a PI-3K inhibitor (LY294002) or MEK inhibitors (PD98059, UO126), partially or totally suppressed the anti-apoptotic capacity of 1,25(OH)2D3. Finally, 1,25(OH)2D3 changed the expression of different apoptosis regulators belonging to the Bcl-2 family. Indeed, 1,25(OH)2D3 treatment increased levels of the anti-apoptotic protein Bcl-2 and decreased levels of the pro-apoptotic proteins Bax and Bad in a time- and dose-dependent way. Induction of Bcl-2 by 1,25(OH)2D3 was further shown to be mediated by ERK and, to a lesser extent, by Akt. In conclusion, 1,25(OH)2D3 clearly protects keratinocytes against apoptosis (1) by activating the MEK/ERK and the PI-3K/Akt survival pathways and (2) by increasing the Bcl-2 to Bax and Bad ratio.

Induction of p53 Up-Regulated Modulator of Apoptosis Messenger RNA by Chemotherapeutic Treatment of Locally Advanced Breast Cancer

PURPOSE

In biopsies of patients with locally advanced breast cancer, we investigated the in vivo changes of the gene expression pattern induced by chemotherapy to find genes that are potentially responsible for the efficacy of the drug.

EXPERIMENTAL DESIGN

Early cellular responses to chemotherapy-induced damage, both in vivo and in vitro, were investigated by analyzing chemotherapy-induced changes in gene expression profiles. Core biopsies were taken from nine patients with locally advanced breast cancer, before and at 6 hours after initiation of doxorubicin-based chemotherapy. Both samples were cohybridized on the same microarray containing 18,000 cDNA spots.

RESULTS

The analysis revealed marked differences in gene expression profile between treated and untreated samples. The gene which was most frequently found to be differentially expressed was p53 up-regulated modulator of apoptosis (PUMA). This gene was up-regulated in eight of nine patients with an average factor of 1.80 (range, 1.36-2.73). In vitro MCF-7 breast cancer cells exposed to clinically achievable doxorubicin concentrations for 6 hours revealed marked induction of PUMA mRNA, as well.

CONCLUSIONS

This is the first report describing PUMA mRNA to be up-regulated as a response to chemotherapy in patients. Because PUMA is a known member of the family of BH3-only proapoptotic proteins, this finding suggests PUMA's potential importance for the response to anticancer drugs.

Retinoic acid increases the expression of p53 and proapoptotic caspases and sensitizes keratinocytes to apoptosis: a possible explanation for tumor preventive action of retinoids

Retinoids influence growth and differentiation of keratinocytes (KCs) and are widely used for the management of skin diseases and for prevention of nonmelanoma skin cancer (NMSC) in predisposed patients. Here we investigated the effect of all-trans-retinoic acid (ATRA) on KC apoptosis. When KCs were cultured in confluent monolayers for several days, they acquired resistance against UVB-induced apoptosis. In contrast, when the cells were treated with 1 micromol/L ATRA for 6 days and subsequently irradiated with different doses of UVB, they underwent massive apoptosis as assessed by morphology, expression of activated caspase-3, and DNA fragmentation. The same effect was observed when doxorubicin was used instead of UVB. Analysis by real-time PCR and Western blot revealed that ATRA treatment strongly increased the mRNA and protein expression of p53 and caspase-3, -6, -7, and -9, which are key regulators of apoptosis. UVB irradiation of ATRA-treated cells but not of control cells led to the accumulation of p53 protein and of its target gene Noxa. Inhibition of p53 and caspases with alpha-pifithrin and z-Val-Ala-Asp-fluoromethyl ketone, respectively, blocked UVB- and doxorubicin-induced apoptosis in ATRA-treated KCs. Analogous to the observed ATRA effects in monolayer cultures, in vitro-generated organotypic skin cultures reacted with up-regulation of p53 and proapoptotic caspases and displayed increased sensitivity to UVB-induced apoptosis. The ability of retinoic acid to regulate the expression of proapoptotic genes and to sensitize KCs to apoptosis may play a role in their prevention of NMSC in transplant patients and patients with DNA-repair deficiencies.

Anthracyclines: Molecular Advances and Pharmacologic Developments in Antitumor Activity and Cardiotoxicity

The clinical use of anthracyclines like doxorubicin and daunorubicin can be viewed as a sort of double-edged sword. On the one hand, anthracyclines play an undisputed key role in the treatment of many neoplastic diseases; on the other hand, chronic administration of anthracyclines induces cardiomyopathy and congestive heart failure usually refractory to common medications. Second-generation analogs like epirubicin or idarubicin exhibit improvements in their therapeutic index, but the risk of inducing cardiomyopathy is not abated. It is because of their janus behavior (activity in tumors vis-à-vis toxicity in cardiomyocytes) that anthracyclines continue to attract the interest of preclinical and clinical investigations despite their longer-than-40-year record of longevity. Here we review recent progresses that may serve as a framework for reappraising the activity and toxicity of anthracyclines on basic and clinical pharmacology grounds. We review 1) new aspects of anthracycline-induced DNA damage in cancer cells; 2) the role of iron and free radicals as causative factors of apoptosis or other forms of cardiac damage; 3) molecular mechanisms of cardiotoxic synergism between anthracyclines and other anticancer agents; 4) the pharmacologic rationale and clinical recommendations for using cardioprotectants while not interfering with tumor response; 5) the development of tumor-targeted anthracycline formulations; and 6) the designing of third-generation analogs and their assessment in preclinical or clinical settings. An overview of these issues confirms that anthracyclines remain "evergreen" drugs with broad clinical indications but have still an improvable therapeutic index.

Molecular and cytogenetic characterization of a novel translocation t(4;22) involving the breakpoint cluster region and platelet-derived growth factor receptor-alpha genes in a patient with atypical chronic myeloid leukemia

We report a case of BCR-ABL-negative atypical chronic myeloid leukemia (CML) with translocation t(4;22) (q12;q11.2) juxtaposing the breakpoint cluster region (BCR) and platelet-derived growth factor receptor-alpha (PDGFRA) genes. The patient was a 57-year-old man with a history of stage IV diffuse large B-cell lymphoma, status post-6 cycles of combination chemotherapy in 1999, who presented in August 2002 with enlarged lymph nodes, anemia, and marked leukocytosis (50 x 10(9) g/dL) consistent with a myeloproliferative disorder (MPD). A bone marrow biopsy showed granulocytic hyperplasia, neutrophilia, and mild eosinophilia. Initial cytogenetic evaluation by interphase FISH for BCR-ABL, to rule out a translocation 9;22, showed a variant signal pattern consistent with rearrangement of BCR at 22q11.2, but not ABL at 9q34. Analysis of the patient's cDNA by polymerase chain reaction (PCR) for BCR-ABL was negative. Cytogenetic analysis showed an abnormal karyotype with rearrangement of chromosomes 4 and 22. PCR amplification and subsequent sequence analysis demonstrated an in-frame 5'-BCR/3'-PDGFRA fusion in the patient's cDNA. PDGFRA encodes a receptor tyrosine kinase and shares structural and organizational homology with the KIT and CSf1R receptor genes. However, although the incidence of MPD involving translocations of PDGFRB has been well established, to our knowledge there are only two previous reports describing a BCR-PDGFRA fusion gene, in 3 patients diagnosed with atypical CML. Here, we report the molecular and cytogenetic characterization of a patient with BCR-PDGFRA-positive MPD who had a complete hematologic response after treatment with imatinib mesylate.

Gene silencing by lentivirus-mediated delivery of siRNA in human CD34+ cells

To derive an efficient system for gene silencing in human hematopoietic stem cells (HSCs) we modified a lentiviral vector for small interfering RNA (siRNA) delivery. For this purpose, an H1 promoter-driven siRNA expression cassette was introduced into a lentiviral vector, and the p53 mRNA was chosen as a target for siRNA-mediated gene silencing. Using the recombinant lentivirus we infected human cord blood-derived CD34+ cells and obtained a transfection efficiency of up to 50%, as determined by expression of enhanced green fluorescent protein (EGFP). In EGFP-positive long-term culture-initiating cell (LTC-IC)- and colony-forming unit cell (CFU-C)-derived cells, we observed a reduction of p53 mRNA of up to 95%. Importantly, this reduction remained stable during several weeks of cell culture. Furthermore, p53 gene silencing resulted in decreased p21 mRNA levels and reduced the sensitivity of CD34+ cells toward the cytotoxic drug etoposide. Thus, lentiviral delivery of siRNA can allow for efficient and stable gene silencing in human HSCs and will be very valuable for further gene function studies.

Multi-modality Imaging Identifies Key Times for Annexin V Imaging as an Early Predictor of Therapeutic Outcome

Radiolabeled annexin V may provide an early indication of the success or failure of anticancer therapy on a patient-by-patient basis as an in vivo marker of tumor cell killing. An important question that remains is when, after initiation of treatment, should annexin V imaging be performed. To address this issue, we obtained simultaneous in vivo measurements of tumor burden and uptake of radiolabeled annexin V in the syngeneic orthotopic murine BCL1 lymphoma model using in vivo bioluminescence imaging (BLI) and small animal single-photon emission computed tomography (SPECT). BCL1 cells labeled for fluorescence and bioluminescence assays (BCL1-gfp/luc) were injected into mice at a dose that leads to progressive disease within two to three weeks. Tumor response was followed by BLI and SPECT before and after treatment with a single dose of 10 mg/kg doxorubicin. Biodistribution analyses revealed a biphasic increase of annexin V uptake within the tumor-bearing tissues of mice. An early peak occurring before actual tumor cells loss was observed between 1 and 5 hr after treatment, and a second longer sustained rise from 9 to 24 hr after therapy, which heralds the onset of tumor cell loss as confirmed by BLI. Multimodality imaging revealed the temporal patterns of tumor cell loss and annexin V uptake revealing a better understanding of the timing of radiolabeled annexin V uptake for its development as a marker of therapeutic efficacy.

DNA damage-triggered apoptosis: critical role of DNA repair, double-strand breaks, cell proliferation and signaling

Genotoxic DNA damaging agents may activate both membrane death receptors and the endogenous mitochondrial damage pathway leading to cell death via apoptosis. Here, apoptotic responses in cells exhibiting a defect in various DNA repair pathways such as alkyltransferase, base excision repair, nucleotide excision repair and mismatch repair are reviewed. The HSVTk/ganciclovir and VZV/BVDU suicide system will also be discussed. Data are available to show that critical DNA damage triggers apoptosis in a DNA replication dependent way by activating the mitochondrial damage pathway in fibroblasts. It is proposed that DNA double-strand breaks (DSBs) are common ultimate apoptosis-triggering lesions arising from primary DNA lesions during DNA replication. Thus, DNA replication is a necessary component in DNA damage-triggered apoptosis, at least in fibroblasts treated with genotoxins not inducing DSBs themselves. For methylating agents inducing O(6)-methylguanine, an additional requirement is mismatch repair provoking DSB formation that triggers Bcl-2 decline and caspase-9/-3 activation. This occurs independent of p53 since most of the repair deficient cell lines under study were mutated for p53. Moreover, p53 knockout fibroblasts are more sensitive to methylating agents and UV light than p53 wt cells, suggesting p53 to play a protective rather than a pro-apoptotic role in this cell system, probably by its involvement in DNA repair. However, for lymphoblastoid cells p53 wt variants are more sensitive to DNA damage indicating that p53 participates in apoptotic signaling in a cell type-specific fashion. The role of topoisomerase II inhibitors and c-Fos/AP-1 in apoptosis will also be discussed.

Inhibition of p53, p21 and Bax by pifithrin-alpha does not affect UV induced apoptotic response in CS-B cells

Cockayne syndrome (CS) is a human autosomal recessive disorder characterized by many neurological and developmental abnormalities. CS cells are defective in transcription coupled repair (TCR) pathway that removes DNA damage from the transcribed strand of active genes. In spite of a TCR deficiency at the cellular level, CS patients do not develop cancer. The lack of cancer incidence in CS patients may be due to the selective elimination of cells by an apoptotic pathway. In order to verify the role of p53-associated pathway in ultraviolet (UV) induced apoptosis in human CS-B cells, the expression of p53 and p53 responsive genes was analysed in UV irradiated human cells after treatment with pifithrin-alpha (PFTalpha). PTFalpha effectively inhibited the induction of p53, p21 and Bax after UV treatment without affecting the apoptotic response in CS-B cells. Our results indicate that the p53-associated pathway involving p21 and Bax does not largely contribute to UV induced apoptosis in TCR defective human CS-B cells.