Adenovirus-mediated TA-p73β gene transfer increases chemosensitivity of human malignant melanomas

p53 Family in Resistance to Targeted Therapy of Melanoma

Metastatic melanoma is one of the most aggressive tumors, with frequent mutations affecting components of the MAPK pathway, mainly protein kinase BRAF. Despite promising initial response to BRAF inhibitors, melanoma progresses due to development of resistance. In addition to frequent reactivation of MAPK or activation of PI3K/AKT signaling pathways, recently, the p53 pathway has been shown to contribute to acquired resistance to targeted MAPK inhibitor therapy. Canonical tumor suppressor p53 is inactivated in melanoma by diverse mechanisms. The TP53 gene and two other family members, TP63 and TP73, encode numerous protein isoforms that exhibit diverse functions during tumorigenesis. The p53 family isoforms can be produced by usage of alternative promoters and/or splicing on the C- and N-terminus. Various p53 family isoforms are expressed in melanoma cell lines and tumor samples, and several of them have already shown to have specific functions in melanoma, affecting proliferation, survival, metastatic potential, invasion, migration, and response to therapy. Of special interest are p53 family isoforms with increased expression and direct involvement in acquired resistance to MAPK inhibitors in melanoma cells, implying that modulating their expression or targeting their functional pathways could be a potential therapeutic strategy to overcome resistance to MAPK inhibitors in melanoma.

Metformin pretreatment reduces effect to dacarbazine and suppresses melanoma cell resistance

Oxidative stress role on metformin process of dacarbazine (DTIC) inducing resistance of B16F10 melanoma murine cells are investigated. To induce resistance to DTIC, murine melanoma cells were exposed to increasing concentrations of dacarabazine (DTIC-res group). Metformin was administered before and during the induction of resistance to DTIC (MET-DTIC). The oxidative stress parameters of the DTIC-res group showed increased levels of malondialdehyde (MDA), thiol, and reduced nuclear p53, 8-hydroxy-2'-deoxyguanosine (8-OH-DG), nuclear factor kappa B (NF-ĸB), and Nrf2. In presence of metformin in the resistant induction process to DTIC, (MET-DTIC) cells had increased antioxidant thiols, MDA, nuclear p53, 8-OH-DG, Nrf2, and reducing NF-ĸB, weakening the DTIC-resistant phenotype. The exclusive administration of metformin (MET group) also induced the cellular resistance to DTIC. The MET group presented high levels of total thiols, MDA, and reduced percentage of nuclear p53. It also presented reduced nuclear 8-OH-DG, NF-ĸB, and Nrf2 when compared with the control. Oxidative stress and the studied biomarkers seem to be part of the alterations evidenced in DTIC-resistant B16F10 cells. In addition, metformin administration is able to play a dual role according to the experimental protocol, preventing or inducing a DTIC-resistant phenotype. These findings should help future research with the aim of investigating DTIC resistance in melanoma.

P53 in skin cancer: From a master player to a privileged target for prevention and therapy

The increasing incidence of skin cancer (SC) is a global health concern. The commonly reported side effects and resistance mechanisms have imposed the pursuit for new therapeutic alternatives. Moreover, additional preventive strategies should be adopted to strengthen prevention and reduce the rising number of newly SC cases. This review provides relevant insights on the role of p53 tumour suppressor protein in melanoma and non-melanoma skin carcinogenesis, also highlighting the therapeutic potential of p53-targeting drugs against SC. In fact, several evidences are provided demonstrating the encouraging outcomes achieved with p53-activating drugs, alone and in combination with currently available therapies in SC. Another pertinent perspective falls on targeting p53 mutations, as molecular signatures in premature phases of photocarcinogenesis, in future SC preventive approaches. Overall, this review affords a critical and timely discussion of relevant issues related to SC prevention and therapy. Importantly, it paves the way to future studies that may boost the clinical translation of p53-activating agents, making them new effective alternatives in precision medicine of SC therapy and prevention.

Melanoma cells resistant towards MAPK inhibitors exhibit reduced TAp73 expression mediating enhanced sensitivity to platinum-based drugs

The efficacy of targeted MAPK signalling pathway inhibitors (MAPKi) in metastatic melanoma therapy is limited by the development of resistance mechanisms that results in disease relapse. This situation still requires treatment alternatives for melanoma patients with acquired resistance to targeted therapy. We found that melanoma cells, which developed resistance towards MAPKi show an enhanced susceptibility to platinum-based drugs, such as cisplatin and carboplatin. We found that this enhanced susceptibility inversely correlates with the expression level of the p53 family member TAp73. We show that the lower expression of the TAp73 isoform in MAPKi-resistant melanoma cells enhances accumulation of DNA double-strand breaks upon cisplatin and carboplatin treatment by reducing the efficiency of nucleotide excision repair. These data suggest that a subgroup of melanoma patients with acquired resistance to MAPKi treatment and low TAp73 expression can benefit from chemotherapy with platinum-based drugs as a second-line therapy.

Synergistic antitumoral efficacy of a novel replicative adenovirus SG611-PDCD5 and daunorubicin in human leukemic cells

Background

Daunorubicin is a traditional chemotherapeutic agent that plays a pivotal role in leukemia therapy. However, the dose-related toxicity remains a considerable challenge. The apoptosis-regulating gene, PDCD5, is downregulated in various tumors, including leukemias, and may provide a potential target for the diagnosis and treatment of leukemia. The purpose of this study was to construct a triple-regulated oncolytic adenovirus carrying a PDCD5 gene expression cassette (SG611-PDCD5) and explore the combined antitumor efficacy of SG611-PDCD5 in combination with low dose daunorubicin on leukemic cells.

Materials and methods

A variety of leukemic cell lines, including K562, MEG-01, KG-1a, HL-60, SUP-B15, and BV-173, were cultured according to the providers’ instructions. The insertion and orientation of all recombined plasmids were confirmed by restriction enzyme digestion and PCR. The tumor-selective replication of the constructed conditionally replicating SG611-PDCD5 and its antitumor efficacy in combination with daunorubicin were characterized in leukemic cell lines in vitro and in a nude mouse xenograft model. Cell viability was detected using cell-counting kit-8. Apoptosis was detected in whole living cells using flow cytometry and in paraffin-embedded tumor tissues using a terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay.

Results

The triple-regulated CRAd carrying SG611-PDCD5 and nude mouse xenograft models of K562 cells were successfully constructed. In vitro treatment with SG611-PDCD5 in combination with low-dose daunorubicin elicited more potent anti-proliferative and proapoptotic effects in leukemic cells in a dose-dependent manner. The Chou-Talalay analysis revealed synergistic anti-proliferative effects in all of the above cell lines. In the nude mice xenograft model, the tumor size in the control, daunorubicin, SG611-PDCD5, and combined treatment groups on day 10 were 170.1±47.8, 111.9±81.1, 60.7±12.3, and 33.2±17.5 mm³, respectively (all P<0.05). The results of the TUNEL assay showed significantly more apoptotic cells in the SG611-PDCD5 plus daunorubicin group than in the SG611-PDCD5 or daunorubicin groups alone (25±0.82, 12.5±2.27, and 7.8±2.67 apoptotic cells/field, respectively) (P<0.05).

Conclusion

The findings suggest that combined treatment with SG611-PDCD5 and daunorubicin may be a promising strategy for enhancing chemosensitivity and thus lowering the dose-related toxicity of daunorubicin in leukemia therapy.

ΔNp73 overexpression promotes resistance to apoptosis but does not cooperate with PML/RARA in the induction of an APL-leukemic phenotype

Here, we evaluated whether the overexpression of transcriptionally inactive ΔNp73 cooperates with PML/RARA fusion protein in the induction of an APL-leukemic phenotype, as well as its role in vitro in proliferation, myeloid differentiation, and drug-induced apoptosis. Using lentiviral gene transfer, we showed in vitro that ΔNp73 overexpression resulted in increased proliferation in murine bone marrow (BM) cells from hCG-PML/RARA transgenic mice and their wild-type (WT) counterpart, with no accumulation of cells at G2/M or S phases; instead, ΔNp73-expressing cells had a lower rate of induced apoptosis. Next, we evaluated the effect of ΔNp73 on stem-cell self-renewal and myeloid differentiation. Primary BM cells lentivirally infected with human ΔNp73 were not immortalized in culture and did not present significant changes in the percentage of CD11b. Finally, we assessed the impact of ΔNp73 on leukemogenesis or its possible cooperation with PML/RARA fusion protein in the induction of an APL-leukemic phenotype. After 120 days of follow-up, all transplanted mice were clinically healthy and, no evidence of leukemia/myelodysplasia was apparent. Taken together, our data suggest that ΔNp73 had no leukemic transformation capacity by itself and apparently did not cooperate with the PML/RARA fusion protein to induce a leukemic phenotype in a murine BM transplantation model. In addition, the forced expression of ΔNp73 in murine BM progenitors did not alter the ATRA-induced differentiation rate in vitro or induce aberrant cell proliferation, but exerted an important role in cell survival, providing resistance to drug-induced apoptosis.

Combining Oncolytic Virotherapy with p53 Tumor Suppressor Gene Therapy

Oncolytic virus (OV) therapy utilizes replication-competent viruses to kill cancer cells, leaving non-malignant cells unharmed. With the first U.S. Food and Drug Administration-approved OV, dozens of clinical trials ongoing, and an abundance of translational research in the field, OV therapy is poised to be one of the leading treatments for cancer. A number of recombinant OVs expressing a transgene for p53 (TP53) or another p53 family member (TP63 or TP73) were engineered with the goal of generating more potent OVs that function synergistically with host immunity and/or other therapies to reduce or eliminate tumor burden. Such transgenes have proven effective at improving OV therapies, and basic research has shown mechanisms of p53-mediated enhancement of OV therapy, provided optimized p53 transgenes, explored drug-OV combinational treatments, and challenged canonical roles for p53 in virus-host interactions and tumor suppression. This review summarizes studies combining p53 gene therapy with replication-competent OV therapy, reviews preclinical and clinical studies with replication-deficient gene therapy vectors expressing p53 transgene, examines how wild-type p53 and p53 modifications affect OV replication and anti-tumor effects of OV therapy, and explores future directions for rational design of OV therapy combined with p53 gene therapy.

Eradication of metastatic melanoma through cooperative expression of RNA-based HDAC1 inhibitor and p73 by oncolytic adenovirus

Malignant melanoma is a highly aggressive cancer that retains functional p53 and p73, and drug unresponsiveness largely depends on defects in death pathways after epigenetic gene silencing in conjunction with an imbalanced p73/DNp73 ratio. We constructed oncolytic viruses armed with an inhibitor of deacetylation and/or p73 to specifically target metastatic cancer. Arming of the viruses is aimed at lifting epigenetic blockage and re-opening apoptotic programs in a staggered manner enabling both, efficient virus replication and balanced destruction of target cells through apoptosis. Our results showed that cooperative expression of shHDAC1 and p73 efficiently enhances apoptosis induction and autophagy of infected cells which reinforces progeny production. In vitro analyses revealed 100% cytotoxicity after infecting cells with OV.shHDAC1.p73 at a lower virus dose compared to control viruses. Intriguingly, OV.shHDAC1.p73 acts as a potent inhibitor of highly metastatic xenograft tumors in vivo. Tumor expansion was significantly reduced after intratumoral injection of 3 × 10⁸ PFU of either OV.shHDAC1 or OV.p73 and, most important, complete regression could be achieved in 100% of tumors treated with OV.shHDAC1.p73. Our results point out that the combination of high replication capacity and simultaneous restoration of cell death routes significantly enhance antitumor activity.

Functions, divergence and clinical value of TAp73 isoforms in cancer

The p73 gene encodes the tumour suppressive full-length TAp73 and N-terminal-truncated DNp73 isoforms that act as dominant negative inhibitors of TAp73. The overall effect of p73 in oncogenesis is thought to depend on the TAp73 to DNp73 isoforms' ratio. TAp73 isoforms include a number of C-terminal variants as a result of alternative splicing in 3'-end. TAp73 isoforms protect cells from oncogenic alterations in a multifaceted way since they are implicated in the suppression of all demonstrated hallmarks and enabling characteristics of cancer. Their best established role is in apoptosis, a process which seems to be differently affected by each TAp73 C-terminal variant. Based on previous findings and our thorough bioinformatics analysis, we highlight that TAp73 variants are functionally non-equivalent, since they present major differences in their transactivation efficiencies, protein interactions, response to DNA damage and apoptotic effects that are attributable to the primary structure of their C terminus. In this review, we summarise these differences and we unveil the link between crucial C-terminal motifs/residues and the oncosuppressive potential of TAp73 isoforms, emphasising on the importance of considering C terminus during the development of p73-based anticancer biologics.

p63 is an alternative p53 repressor in melanoma that confers chemoresistance and a poor prognosis

p63 is up-regulated in melanoma and prevents nuclear accumulation of p53.

The role of apoptosis in melanoma pathogenesis and chemoresistance is poorly characterized. Mutations in TP53 occur infrequently, yet the TP53 apoptotic pathway is often abrogated. This may result from alterations in TP53 family members, including the TP53 homologue TP63. Here we demonstrate that TP63 has an antiapoptotic role in melanoma and is responsible for mediating chemoresistance. Although p63 was not expressed in primary melanocytes, up-regulation of p63 mRNA and protein was observed in melanoma cell lines and clinical samples, providing the first evidence of significant p63 expression in this lineage. Upon genotoxic stress, endogenous p63 isoforms were stabilized in both nuclear and mitochondrial subcellular compartments. Our data provide evidence of a physiological interaction between p63 with p53 whereby translocation of p63 to the mitochondria occurred through a codependent process with p53, whereas accumulation of p53 in the nucleus was prevented by p63. Using RNA interference technology, both isoforms of p63 (TA and ΔNp63) were demonstrated to confer chemoresistance, revealing a novel oncogenic role for p63 in melanoma cells. Furthermore, expression of p63 in both primary and metastatic melanoma clinical samples significantly correlated with melanoma-specific deaths in these patients. Ultimately, these observations provide a possible explanation for abrogation of the p53-mediated apoptotic pathway in melanoma, implicating novel approaches aimed at sensitizing melanoma to therapeutic agents.

Tumour suppressor genes in chemotherapeutic drug response

Since cancer is one of the leading causes of death worldwide, there is an urgent need to find better treatments. Currently, the use of chemotherapeutics remains the predominant option for cancer therapy. However, one of the major obstacles for successful cancer therapy using these chemotherapeutics is that patients often do not respond or eventually develop resistance after initial treatment. Therefore identification of genes involved in chemotherapeutic response is critical for predicting tumour response and treating drug-resistant cancer patients. A group of genes commonly lost or inactivated are tumour suppressor genes, which can promote the initiation and progression of cancer through regulation of various biological processes such as cell proliferation, cell death and cell migration/invasion. Recently, mounting evidence suggests that these tumour suppressor genes also play a very important role in the response of cancers to a variety of chemotherapeutic drugs. In the present review, we will provide a comprehensive overview on how major tumour suppressor genes [Rb (retinoblastoma), p53 family, cyclin-dependent kinase inhibitors, BRCA1 (breast-cancer susceptibility gene 1), PTEN (phosphatase and tensin homologue deleted on chromosome 10), Hippo pathway, etc.] are involved in chemotherapeutic drug response and discuss their applications in predicting the clinical outcome of chemotherapy for cancer patients. We also propose that tumour suppressor genes are critical chemotherapeutic targets for the successful treatment of drug-resistant cancer patients in future applications.

The anti-tumor role and mechanism of integrated and truncated PDCD5 proteins in osteosarcoma cells

Osteosarcoma (OS) is a high-grade malignant bone tumor. In these studies, the cell apoptosis-related gene, programmed cell death 5 gene (PDCD5), and various fragments of it, were overexpressed in the OS cell line, MG-63. The effects of PDCD5 on MG-63 cells both in vivo and in vitro were then identified. Our results indicate that PDCD5 can induce apoptosis and G(2) phase arrest in MG-63 cells. Moreover, expression of PDCD5 in established xenografted tumors was associated with a decrease in tumor size and weight. Accordingly, the survival rate of these mice was significantly higher than that of mice bearing tumors that did not express PDCD5. To analyze the signaling pathway involved, western blotting was performed. In these assays, PDCD5 was found to inhibit the Ras/Raf/MEK/ERK signaling pathway, leading to inhibition of cyclin B and CDK1. In addition, down-regulation of ERK resulted in activation of caspase 3 and caspase 9. These results are consistent with the G(2) phase arrest observed with overexpression of PDCD5. However, a G(1) phase arrest was not observed. Therefore, proteins associated with the G(1) phase of the cell cycle were overexpressed in combination with PDCD5 overexpression. Overall, these studies demonstrate the anti-tumor activity of PDCD5 in the OS cell line, MG-63, and provide insight into relevant mechanisms that may lead to novel treatments for OS.

Tumor regression following intravenous administration of a tumor-targeted p73 gene delivery system

The potential of gene therapy to treat cancer is hampered by the lack of safe and efficacious gene delivery systems able to selectively deliver therapeutic genes to tumors by intravenous administration. With the long-term aim of developing an efficacious cancer-targeted gene medicine, we demonstrated that transferrin-bearing polypropylenimine dendrimer complexed to a plasmid DNA encoding p73 led to an enhanced anti-proliferative activity in vitro, by up to 120-fold in A431 compared to the unmodified dendriplex. In vivo, the intravenous administration of this p73-encoding dendriplex resulted in a rapid and sustained inhibition of tumor growth over one month, with complete tumor suppression for 10% of A431 and B16-F10 tumors and long-term survival of the animals. The treatment was well tolerated by the animals, with no apparent signs of toxicity. These results suggest that the p73-encoding tumor-targeted polypropylenimine dendrimer should be further explored as a therapeutic strategy for cancer therapy.

Terfenadine induces apoptosis and autophagy in melanoma cells through ROS-dependent and -independent mechanisms

Previously we found that terfenadine, an H1 histamine receptor antagonist, acts as a potent apoptosis inducer in melanoma cells through modulation of Ca²⁺ homeostasis. In this report, focusing our attention on the apoptotic mechanisms activated by terfenadine, we show that this drug can potentially activate distinct intrinsic signaling pathways depending on culture conditions. Serum-deprived conditions enhance the cytotoxic effect of terfenadine and caspase-4 and -2 are activated upstream of caspase-9. Moreover, although we found an increase in ROS levels, the apoptosis was ROS independent. Conversely, terfenadine treatment in complete medium induced ROS-dependent apoptosis. Caspase-4, -2, and -9 were simultaneously activated and p73 and Noxa induction were involved. ROS inhibition prevented p73 and Noxa expression but not p53 and p21 expression, suggesting a role for Noxa in p53-independent apoptosis in melanoma cells. Finally, we found that terfenadine induced autophagy, that can promote apoptosis. These findings demonstrate the great potential of terfenadine to kill melanoma cells through different cellular signaling pathways and could contribute to define new therapeutic strategies in melanoma.

Activation of the human immune system by chemotherapeutic or targeted agents combined with the oncolytic parvovirus H-1

Background

Parvovirus H-1 (H-1PV) infects and lyses human tumor cells including melanoma, hepatoma, gastric, colorectal, cervix and pancreatic cancers. We assessed whether the beneficial effects of chemotherapeutic agents or targeted agents could be combined with the oncolytic and immunostimmulatory properties of H-1PV.

Methods

Using human ex vivo models we evaluated the biological and immunological effects of H-1PV-induced tumor cell lysis alone or in combination with chemotherapeutic or targeted agents in human melanoma cells +/- characterized human cytotoxic T-cells (CTL) and HLA-A2-restricted dendritic cells (DC).

Results

H-1PV-infected MZ7-Mel cells showed a clear reduction in cell viability of >50%, which appeared to occur primarily through apoptosis. This correlated with viral NS1 expression levels and was enhanced by combination with chemotherapeutic agents or sunitinib. Tumor cell preparations were phagocytosed by DC whose maturation was measured according to the treatment administered. Immature DC incubated with H-1PV-induced MZ7-Mel lysates significantly increased DC maturation compared with non-infected or necrotic MZ7-Mel cells. Tumor necrosis factor-α and interleukin-6 release was clearly increased by DC incubated with H-1PV-induced SK29-Mel tumor cell lysates (TCL) and was also high with DC-CTL co-cultures incubated with H-1PV-induced TCL. Similarly, DC co-cultures with TCL incubated with H-1PV combined with cytotoxic agents or sunitinib enhanced DC maturation to a greater extent than cytotoxic agents or sunitinib alone. Again, these combinations increased pro-inflammatory responses in DC-CTL co-cultures compared with chemotherapy or sunitinib alone.

Conclusions

In our human models, chemotherapeutic or targeted agents did not only interfere with the pronounced immunomodulatory properties of H-1PV, but also reinforced drug-induced tumor cell killing. H-1PV combined with cisplatin, vincristine or sunitinib induced effective immunostimulation via a pronounced DC maturation, better cytokine release and cytotoxic T-cell activation compared with agents alone. Thus, the clinical assessment of H-1PV oncolytic tumor therapy not only alone but also in combination strategies is warranted.

A novel triple-regulated oncolytic adenovirus carrying PDCD5 gene exerts potent antitumor efficacy on common human leukemic cell lines

PDCD5 (programmed cell death 5) accelerates apoptosis of certain tumor cells and the replication-defective Ad-PDCD5 may be a promising agent for enhancing chemosensitivity. In this study, a triple-regulated conditionally replicating adenoviruses (CRAd) carrying PDCD5 gene expression cassette, SG611-PDCD5, was engineered. In SG611-PDCD5, the E1a gene with a deletion of 24 nucleotides within CR2 region is controlled under the human telomerase reverse transcriptase (hTERT) promoter, the E1b gene expression is directed by the hypoxia response element (HRE), whereas the PDCD5 gene is controlled by the cytomegalovirus promoter. The tumor-selective replication of this virus and its antitumor efficacy were characterized in several leukemic cell lines in vitro and in xenograft models of human leukemic cell line in nude mice. It was found by RQ-RT-PCR assay that SG611-PDCD5 expressed PDCD5 efficiently in leukemic cells. In K562 tumor xenograft models, SG611-PDCD5 displayed a tumor killing capacity. At a dose of 1 x 10(9) plaque-forming units, SG611-PDCD5 alone could completely inhibit the tumor growth and more effective than replication-defective Ad-PDCD5. Histopathologic examination revealed that SG611-PDCD5 administration resulted in leukemic cell apoptosis. We concluded that the triple-regulated SG611-PDCD5, as a more potent and safer antitumor therapeutic, could provide a new strategy for leukemia biotherapy.

Adenovirus-mediated PDCD5 gene transfer sensitizes K562 cells to apoptosis induced by idarubicin in vitro and in vivo

PDCD5 (programmed cell death 5) accelerates apoptosis of certain tumor cells and is expressed at low levels in marrow-nucleated cells of AML and CML patients. In the present study, we evaluated the effects of PDCD5 overexpression on drug sensitivity of leukemia cells. K562 cells were treated with idarubicin (IDR) alone or in combination with adenoviral vectors expressing PDCD5 (Ad-PDCD5). As shown by annexin-V-FITC/PI dual labeling, apoptosis rates were markedly increased after combined treatment with Ad-PDCD5 compared to IDR treatment alone. We observed that PDCD5 overexpression significantly improves the antitumor effects of low dose IDR treatment in vivo. Tumor sizes were significantly decreased in combined Ad-PDCD5 and low dose IDR treatment groups compared with single IDR treatment groups. Similar results were obtained with combined systemic treatment of Ad-PDCD5 and low dose IDR, and combined treatment with Ad-PDCD5 local injection and low dose IDR i.p. injection. These results indicate that Ad-PDCD5 may be a promising agent for enhancing chemosensitivity.

DNp73 a matter of cancer: mechanisms and clinical implications

The p53 family proteins carry on a wide spectrum of biological functions from differentiation, cell cycle arrest, apoptosis, and chemosensitivity of tumors. NH2-terminally truncated p73 (referred to as DNp73) acts as a potent inhibitor of all these tumor suppressor properties, implying that it has oncogenic functions in human tumorigenesis. This was favored by the observation that high DNp73 expression levels in a variety of cancers are associated with adverse clinico-pathological characteristics and the response failure to chemotherapy. The actual challenge is the deciphering of the molecular mechanisms by which DNp73 promotes malignancy and to unravel the regulatory pathways for controlling TP73 isoform expression. This review is focused on recent findings leaving no doubt that N-terminally truncated p73 proteins are operative during oncogenesis, thus underscoring its significance as a marker for disease severity in patients and as target for cancer therapy.

Overcoming apoptosis deficiency of melanoma-hope for new therapeutic approaches

The increased incidence of malignant melanoma in the last decades, its high mortality and pronounced therapy resistance pose an enormous challenge. Important therapeutic targets for melanoma are the induction of apoptosis and suppression of survival pathways. Preclinical studies have demonstrated the efficacy of pro-apoptotic Bcl-2 proteins and of death receptor ligands to trigger apoptosis in melanoma cells. In the clinical setting, BH3 domain mimics and death receptor agonists are therefore considered as promising, specific novel treatments to add to the conventional pro-apoptotic strategies such as chemo- or radiotherapy. However, constitutively activated survival pathways, in particular the mitogen-activated protein kinases, protein kinase B/Akt and nuclear factor (NF)-kappaB, all may work in concert to prevent effective therapy. Thus, selective biologicals developed with the aim to inhibit pro-survival signaling are currently tested in melanoma. For highly therapy-resistant tumors such as melanoma, development of novel drug combinations will be essential, and combinations of survival inhibitors and pro-apoptotic mediators appear most promising. The challenge of the near future will be to make a rational choice of the multiple possible combinations and protocols. This review gives a critical overview of proteins involved in melanoma chemoresistance, which are targets for current drug development leading to the best choice for future trials.

E2F1 death pathways as targets for cancer therapy

Defects in apoptotic programs contribute to a number of human diseases, ranging from neurodegenerative disorders to malignancy, and treatment failure. The genetic basis for apoptosis implies that cell death can be disrupted by mutations, raising the intriguing possibility that cell numbers can be regulated by factors that influence cell survival. It is well documented that the E2F1 transcription factor is a key regulator of apoptotic programs. E2F1-induced cell death occurs via multiple pathways, some of which involve the tumour suppressor p53, and autonomous of p53. This has led to the opinion that E2F1 functions as a tumour surveillance factor, detecting aberrant proliferation and engaging apoptotic pathways to protect the organism from developing tumours. Frequently, novel players are discovered that expand the interpretation of apoptosis control by E2F1. This information will help to produce new strategies to exploit E2F1-induced apoptosis for therapeutic benefit.

Cellular immune therapy for chronic lymphocytic leukemia

Although chemotherapy can induce complete responses in patients with chronic lymphocytic leukemia (CLL), it is not considered curative. Treated patients generally develop recurrent disease requiring additional therapy, which can cause worsening immune dysfunction, myelosuppression, and selection for chemotherapy-resistant leukemia-cell subclones. Cellular immune therapy promises to mitigate these complications and potentially provide for curative treatment. Most experience with this is in the use of allogeneic hematopoietic stem-cell transplantation (allo-HSCT), in which graft-versus-leukemia (GVL) effects can be observed and shown responsible for long-term disease-free survival. However, use of allo-HSCT for CLL is limited because of the lack of suitable donors and the treatment-related morbidity/mortality for elderly patients, who constitute the majority at risk for developing this disease. The GVL effect, however, suggests there are specific CLL-associated antigens that could be targeted in autologous cellular immune therapy. Effective strategies for this will have to overcome the disease-related acquired immune deficiency and the capacity of the leukemia-cell to induce T-cell tolerance, thereby compromising the activity of even conventional vaccines in patients with this disease. We will discuss the different strategies being developed to overcome these limitations that might provide for effective cellular immune therapy of CLL.

E2F1-induced apoptosis: turning killers into therapeutics

The cellular transcription factor E2F1 is part of an anti-tumor safeguard mechanism: it engages cell-death pathways either alone or in cooperation with p53 to protect organisms from the development of tumors. E2F1 activates downstream factors, which in turn produce secondary changes in gene expression that trigger apoptosis. Although the mechanisms are incompletely understood, several studies have demonstrated that E2F1 is involved in many different aspects of programmed cell death depending on the cellular background. Here, these findings are highlighted in the context of the most recent follow-up studies that have used apoptotic E2F1 genes as new therapeutics or drug targets, thereby providing insight into the basic mechanisms of E2F1-induced apoptosis and its possible clinical implications.