Targeting tumor cell resistance to apoptosis induction with antisense oligonucleotides: progress and therapeutic potential

A DNA/RNA heteroduplex oligonucleotide coupling asparagine depletion restricts FGFR2 fusion-driven intrahepatic cholangiocarcinoma

Pemigatinib, a pan-FGFR inhibitor, is approved to treat intrahepatic cholangiocarcinoma (ICC) harboring FGFR2 fusion mutations. Improving its targeting of FGFR2 fusions remains an unmet clinical need due to its pan selectivity and resistance. Here, we report a cholesterol-conjugated DNA/RNA heteroduplex oligonucleotide targeting the chimeric site in FGFR2-AHCYL1 (F-A Cho-HDO) that accumulates in ICC through endocytosis of low-density lipoprotein receptor (LDLR), which is highly expressed in both human and murine ICC. F-A Cho-HDO was determined to be a highly specific, sustainable, and well-tolerated agent for inhibiting ICC progression through posttranscriptional suppression of F-A in ICC patient-derived xenograft mouse models. Moreover, we identified an EGFR-orchestrated bypass signaling axis that partially offset the efficacy of F-A Cho-HDO. Mechanistically, EGFR-induced STAT1 upregulation promoted asparagine (Asn) synthesis through direct transcriptional upregulation of asparagine synthetase (ASNS) and dictated cell survival by preventing p53-dependent cell cycle arrest. Asn restriction with ASNase or ASNS inhibitors reduced the intracellular Asn, thereby reactivating p53 and sensitizing ICC to F-A Cho-HDO. Our findings highlight the application of genetic engineering therapies in ICC harboring FGFR2 fusions and reveal an axis of adaptation to FGFR2 inhibition that presents a rationale for the clinical evaluation of a strategy combining FGFR2 inhibitors with Asn depletion.

BCL-2 protein family: attractive targets for cancer therapy

Acquired resistance to cell death is a hallmark of cancer. The BCL-2 protein family members play important roles in controlling apoptotic cell death. Abnormal over-expression of pro-survival BCL-2 family members or abnormal reduction of pro-apoptotic BCL-2 family proteins, both resulting in the inhibition of apoptosis, are frequently detected in diverse malignancies. The critical role of the pro-survival and pro-apoptotic BCL-2 family proteins in the regulation of apoptosis makes them attractive targets for the development of agents for the treatment of cancer. This review describes the roles of the various pro-survival and pro-apoptotic members of the BCL-2 protein family in normal development and organismal function and how defects in the control of apoptosis promote the development and therapy resistance of cancer. Finally, we discuss the development of inhibitors of pro-survival BCL-2 proteins, termed BH3-mimetic drugs, as novel agents for cancer therapy.

Targeting Cell Survival Proteins for Cancer Cell Death

Escaping from cell death is one of the adaptations that enable cancer cells to stave off anticancer therapies. The key players in avoiding apoptosis are collectively known as survival proteins. Survival proteins comprise the Bcl-2, inhibitor of apoptosis (IAP), and heat shock protein (HSP) families. The aberrant expression of these proteins is associated with a range of biological activities that promote cancer cell survival, proliferation, and resistance to therapy. Several therapeutic strategies that target survival proteins are based on mimicking BH3 domains or the IAP-binding motif or competing with ATP for the Hsp90 ATP-binding pocket. Alternative strategies, including use of nutraceuticals, transcriptional repression, and antisense oligonucleotides, provide options to target survival proteins. This review focuses on the role of survival proteins in chemoresistance and current therapeutic strategies in preclinical or clinical trials that target survival protein signaling pathways. Recent approaches to target survival proteins-including nutraceuticals, small-molecule inhibitors, peptides, and Bcl-2-specific mimetic are explored. Therapeutic inventions targeting survival proteins are promising strategies to inhibit cancer cell survival and chemoresistance. However, complete eradication of resistance is a distant dream. For a successful clinical outcome, pretreatment with novel survival protein inhibitors alone or in combination with conventional therapies holds great promise.

Targeting Cell Survival Proteins for Cancer Cell Death

Escaping from cell death is one of the adaptations that enable cancer cells to stave off anticancer therapies. The key players in avoiding apoptosis are collectively known as survival proteins. Survival proteins comprise the Bcl-2, inhibitor of apoptosis (IAP), and heat shock protein (HSP) families. The aberrant expression of these proteins is associated with a range of biological activities that promote cancer cell survival, proliferation, and resistance to therapy. Several therapeutic strategies that target survival proteins are based on mimicking BH3 domains or the IAP-binding motif or competing with ATP for the Hsp90 ATP-binding pocket. Alternative strategies, including use of nutraceuticals, transcriptional repression, and antisense oligonucleotides, provide options to target survival proteins. This review focuses on the role of survival proteins in chemoresistance and current therapeutic strategies in preclinical or clinical trials that target survival protein signaling pathways. Recent approaches to target survival proteins-including nutraceuticals, small-molecule inhibitors, peptides, and Bcl-2-specific mimetic are explored. Therapeutic inventions targeting survival proteins are promising strategies to inhibit cancer cell survival and chemoresistance. However, complete eradication of resistance is a distant dream. For a successful clinical outcome, pretreatment with novel survival protein inhibitors alone or in combination with conventional therapies holds great promise.

Targeting the Bcl-2 family for cancer therapy

INTRODUCTION

Programmed cell death is well-orchestrated process regulated by multiple pro-apoptotic and anti-apoptotic genes, particularly those of the Bcl-2 gene family. These genes are well documented in cancer with aberrant expression being strongly associated with resistance to chemotherapy and radiation.

AREAS COVERED

This review focuses on the resistance induced by the Bcl-2 family of anti-apoptotic proteins and current therapeutic interventions currently in preclinical or clinical trials that target this pathway. Major resistance mechanisms that are regulated by Bcl-2 family proteins and potential strategies to circumvent resistance are also examined. Although antisense and gene therapy strategies are used to nullify Bcl-2 family proteins, recent approaches use small molecule inhibitors (SMIs) and peptides. Structural similarity of the Bcl-2 family of proteins greatly favors development of inhibitors that target the BH3 domain, called BH3 mimetics.

EXPERT OPINION

Strategies to specifically identify and inhibit critical determinants that promote therapy resistance and tumor progression represent viable approaches for developing effective cancer therapies. From a clinical perspective, pretreatment with novel, potent Bcl-2 inhibitors either alone or in combination with conventional therapies hold significant promise for providing beneficial clinical outcomes. Identifying SMIs with broader and higher affinities for inhibiting all of the Bcl-2 pro-survival proteins will facilitate development of superior cancer therapies.

Skeletal muscle phenotypically converts and selectively inhibits metastatic cells in mice

Skeletal muscle is rarely a site of malignant metastasis; the molecular and cellular basis for this rarity is not understood. We report that myogenic cells exert pronounced effects upon co-culture with metastatic melanoma (B16-F10) or carcinoma (LLC1) cells including conversion to the myogenic lineage in vitro and in vivo, as well as inhibition of melanin production in melanoma cells coupled with cytotoxic and cytostatic effects. No effect is seen with non-tumorigenic cells. Tumor suppression assays reveal that the muscle-mediated tumor suppressor effects do not generate resistant clones but function through the down-regulation of the transcription factor MiTF, a master regulator of melanocyte development and a melanoma oncogene. Our findings point to skeletal muscle as a source of therapeutic agents in the treatment of metastatic cancers.

Downregulation of miR-21 Enhances Chemotherapeutic Effect of Taxol in Breast Carcinoma Cells

The successful of anti-cancer treatment are often limited by the development of drug resistance. Recent work has highlighted the involvement of non-coding RNAs, microRNAs(miRNAs) in cancer development, and their possible involvement in the evolution of drug resistance has been proposed. In this study, we combine taxol chemotherapy and miR-21 inhibitor treatment via polyamidoamine (PAMAM) dendrimers vector to evaluate the effects of combination therapy on suppression of breast cancer cells. The 50% inhibitory concentration (IC50) values for taxol were significantly decreased to a greater extent in the cells transfected with miR-21 inhibitor compared with cells treated with taxol alone. Taxol treatment also increased the percentage of apoptotic breast cancer cells in miR-21 inhibitor transfected cells compared with control cells. Furthermore, treatment of the miR-21 inhibitor-transfected cells with the anti-cancer drugs taxol resulted in significantly reduced cell viability and invasiveness compared with control cells. These results indicated that the miR-21 plays an important role in the resistance of breast carcinoma cells to chemotherapeutic drugs. Therefore, miR-21 inhibitor gene therapy combined with taxol chemotherapy might represent a promising novel therapeutic approach for the treatment of breast malignancies.

Protein kinase CK2 in health and disease: CK2: a key player in cancer biology

Elevated levels of protein kinase CK2 (formerly casein kinase 2 or II) have long been associated with increased cell growth and proliferation both in normal and cancer cells. The ability of CK2 to also act as a potent suppressor of apoptosis offers an important link to its involvement in cancer since deregulation of both cell proliferation and apoptosis are among the key features of cancer cell biology. Dysregulated CK2 may impact both of these processes in cancer cells. All cancers that have been examined show increased CK2 expression, which may also relate to prognosis. The extensive involvement of CK2 in cancer derives from its impact on diverse molecular pathways controlling cell proliferation and cell death. Downregulation of CK2 by various approaches results in induction of apoptosis in cultured cell and xenograft cancer models suggesting its potential as a therapeutic target.

Mitochondrial electron-transport-chain inhibitors of complexes I and II induce autophagic cell death mediated by reactive oxygen species

Autophagy is a self-digestion process important for cell survival during starvation. It has also been described as a form of programmed cell death. Mitochondria are important regulators of autophagy-induced cell death and damaged mitochondria are often degraded by autophagosomes. Inhibition of the mitochondrial electron transport chain (mETC) induces cell death through generating reactive oxygen species (ROS). The role of mETC inhibitors in autophagy-induced cell death is unknown. Herein, we determined that inhibitors of complex I (rotenone) and complex II (TTFA) induce cell death and autophagy in the transformed cell line HEK 293, and in cancer cell lines U87 and HeLa. Blocking the expression of autophagic genes (beclin 1 and ATG5) by siRNAs or using the autophagy inhibitor 3-methyladenine (3-MA) decreased cell death that was induced by rotenone or TTFA. Rotenone and TTFA induce ROS production, and the ROS scavenger tiron decreased autophagy and cell death induced by rotenone and TTFA. Overexpression of manganese-superoxide dismutase (SOD2) in HeLa cells decreased autophagy and cell death induced by rotenone and TTFA. Furthermore, blocking SOD2 expression by siRNA in HeLa cells increased ROS generation, autophagy and cell death induced by rotenone and TTFA. Rotenone- and TTFA-induced ROS generation was not affected by 3-MA, or by beclin 1 and ATG5 siRNAs. By contrast, treatment of non-transformed primary mouse astrocytes with rotenone or TTFA failed to significantly increase levels of ROS or autophagy. These results indicate that targeting mETC complex I and II selectively induces autophagic cell death through a ROS-mediated mechanism.

Anticlusterin treatment of breast cancer cells increases the sensitivities of chemotherapy and tamoxifen and counteracts the inhibitory action of dexamethasone on chemotherapy-induced cytotoxicity

INTRODUCTION

Overexpression of the apoptosis-related protein clusterin is associated with breast cancer development and tumor progression. We describe the use of clusterin-specific antisense oligonucleotides and antibodies to sensitize breast carcinoma cells to anticancer drugs routinely used in breast cancer therapy.

METHODS

MCF-7 and MDA-MB-231 cells were treated with the oligonucleotide or antibody, chemotherapeutic agents (doxorubicin or paclitaxel), tamoxifen, or with combinations of these.

RESULTS

Treatments that include antisense clusterin oligonucleotide or antibody to clusterin have been shown to reduce the number of viable cells more effectively than treatment with the drugs alone. We also demonstrate that dexamethasone pretreatment of breast cancer cell lines inhibits chemotherapy-induced cytotoxicity and is associated with the transcriptional induction of clusterin. However, anticlusterin treatment increases chemotherapy-induced cytotoxicity, even in the presence of glucocorticoids, suggesting a possible role for these proteins in glucocorticoid-mediated survival.

CONCLUSION

These data suggest that combined treatment with antibodies to clusterin or antisense clusterin oligodeoxynucleotides and paclitaxel, doxorubicin, or tamoxifen could be a novel and attractive strategy to inhibit the progression of breast carcinoma by regulation of the clusterin function. Moreover, glucocorticoid activation in breast cancer cells regulates survival signaling by the direct transactivation of genes like clusterin which encode proteins that decrease susceptibility to apoptosis. Given the widespread clinical administration of dexamethasone before chemotherapy, understanding glucocorticoid-induced survival mechanisms is essential for achieving optimal therapeutic responses.

Apoptosis pathway-targeted drugs--from the bench to the clinic

It is an exciting time for cancer researchers in the field of apoptotic cell death. The avalanche of discoveries over the past decade or so regarding how apoptosis is regulated begins to be exploited for therapeutic benefit as the first apoptosis-targeted drugs enter early clinical trials. This chapter provides a selective review on the development of such drugs. We also outline issues regarding the regulation and design of early clinical trials of this type of molecularly targeted agent. Finally, we discuss the biomarkers and surrogate pharmacodynamic endpoint assays currently available to chart the efficacy of apoptosis-inducing anticancer therapy.

Induction of Apoptosis by Antisense CK2 in Human Prostate Cancer Xenograft Model

Protein serine/threonine kinase CK2 (formerly casein kinase 2) is a ubiquitous protein kinase that plays key roles in cell growth, proliferation, and survival. We have shown previously that its molecular down-regulation induces apoptosis in cancer cells in culture. Here, we have employed a xenograft model of prostate cancer to extend these studies to determine whether antisense CK2α evokes a similar response in vivo. A single dose of antisense CK2α oligodeoxynucleotide given directly into the PC3-LN4 xenograft tumor in nude mouse induced a dose- and time-dependent tumor cell death in vivo. The tumor was completely resolved at the higher tested dose of the antisense. Cell death was due to apoptosis and correlated with a potent down-regulation of the CK2α message and loss of CK2 from the nuclear matrix in the xenograft tissue as well as in cancer cells in culture. These observations accorded with several of the earlier studies indicating that loss of CK2 from the nuclear matrix is associated with induction of apoptosis. Comparison of the effects of antisense CK2α oligodeoxynucleotide on cancer versus normal or noncancer cells showed that the concentration of antisense CK2α that elicited extensive apoptosis in tumor cells in culture or xenograft tumors in vivo had a relatively small or minimal effect on noncancer cells in culture or on normal prostate gland subjected to orthotopic injection of antisense oligodeoxynucleotide in vivo. The basis for the difference in sensitivity of cancer versus noncancer cells to antisense CK2α is unknown at this time; however, this differential response under similar conditions of treatment may be significant in considering the potential feasibility of targeting the CK2 signal for induction of apoptosis in cancer cells in vivo. Although much further work will be needed to establish the feasibility of targeting CK2 for cancer therapy, to our knowledge, this is the first report to provide important new evidence as an initial “proof of principle” for the potential application of antisense CK2α in cancer therapy, paving the way for future detailed studies of approaches to targeting CK2 in vivo to induce cancer cell death.

Strategies for reversing drug resistance

Drug resistance, intrinsic or acquired, is a problem for all chemotherapeutic agents. In this review, we examine numerous strategies that have been tested or proposed to reverse drug resistance. Included among these strategies are approaches targeting the apoptosis pathway. Although the process of apoptosis is complex, it provides several potential sites for therapeutic intervention. A variety of targets and approaches are being pursued, including the suppression of proteins inhibiting apoptosis using antisense oligonucleotides (ASOs), and small molecules targeted at proteins that modulate apoptosis. An alternate strategy is based on numerous studies that have documented methylation of critical regions in the genome in human cancers. Consequently, efforts have been directed at re-expressing genes, including genes that affect drug sensitivity, using 5-azacytidine and 2'-deoxy-5-azacytidine (DAC, decitabine) as demethylating agents. While this strategy may be effective as a single modality, success will most likely be achieved if it is used to modulate gene expression in combination with other modalities such as chemotherapy. At a more basic level, attempts have been made to modulate glutathione (GSH) levels. Owing to its reactivity and high intracellular concentrations, GSH has been implicated in resistance to several chemotherapeutic agents. Several approaches designed to deplete intracellular GSH levels have been pursued including the use of buthionine-(S,R)-sulfoxime (BSO), a potent and specific inhibitor of gamma-glutamyl cysteine synthetase (gamma-GCS), the rate-limiting step in the synthesis of GSH, a hammerhead ribozyme against gamma-GCS mRNA to downregulate specifically its levels and targeting cJun expression to reduce GSH levels. Alternate strategies have targeted p53. The frequent occurrence of p53 mutations in human cancer has led to the development of numerous approaches to restore wild-type (wt) p53. The goals of these interventions are to either revert the malignant phenotype or enhance drug sensitivity. The approach most extensively investigated has utilized one of several viral vectors. An alternate approach, the use of small molecules to restore wt function to mutant p53, remains an option. Finally, the conceptually simplest mechanism of resistance is one that reduces intracellular drug accumulation. Such reduction can be effected by a variety of drug efflux pumps, of which the most widely studied is P-glycoprotein (Pgp). The first strategy utilized to inhibit Pgp function relied on the identification of non-chemotherapeutic agents as competitors. Other approaches have included the use of hammerhead ribozymes against the MDR-1 gene and MDR-1-targeted ASOs. Although modulation of drug resistance has not yet been proven to be an effective clinical tool, we have learned an enormous amount about drug resistance. Should we succeed, these pioneering basic and clinical studies will have paved the road for future developments.

Resistance to cytotoxic and anti-angiogenic anticancer agents: similarities and differences

Intrinsic resistance to anticancer drugs, or resistance developed during chemotherapy, remains a major obstacle to successful treatment. This is the case both for resistance to cytotoxic agents, directed at malignant cells, and for resistance to anti-angiogenic agents, directed at non-malignant endothelial cells. In this review, we will discuss mechanisms of resistance which have a bearing on both these conceptually different classes of drugs. The complexity of drug resistance, involving drug transporters, such as P-glycoprotein, as well as resistance related to the tissue structure of solid tumors and its consequences for drug delivery is discussed. Possible mechanisms of resistance to endothelial cell-targeted drugs, including inhibitors of the VEGF receptor and EGF receptor family, are reviewed. The resistance of cancer cells as well as endothelial cells related to anti-apoptotic signaling events initiated by cell integrin-matrix interactions is discussed. Current strategies to overcome resistance mechanisms are summarized; they include high-dose chemotherapy, tumor targeting of cytotoxics to improve tumor uptake, low-dose protracted (metronomic) chemotherapy and combinations of classical agents with anti-angiogenic agents. This review discusses primarily literature published in 2001 and 2002.

Molecular pathology of tumor metastasis III. Target array and combinatorial therapies

Therapy of tumor progression and the metastatic disease is the biggest challenge of clinical oncology. Discovery of the diverse molecular pathways behind this complex disease outlined an approach to better treatment strategies. The development of combined cytotoxic treatment protocols has produced promising results but no breakthrough in the clinical management of metastatic disease. The multiple - specific and non-specific pathways and cellular targets of tumor progression are outlined in this review. Such an approach, individually designed for various cancer types, may have a better chance to treat or even cure cancer patients with progressive disease.

Cellular response to an antisense-mediated shift of Bcl-x pre-mRNA splicing and antineoplastic agents

Overexpression of Bcl-xL, an anti-apoptotic member of the Bcl-2 family, negatively correlates with the sensitivity of various cancers to chemotherapeutic agents. We show here that high levels of expression of Bcl-xL promoted apoptosis of cells treated with an antisense oligonucleotide (5'Bcl-x AS) that shifts the splicing pattern of Bcl-x pre-mRNA from the anti-apoptotic variant, Bcl-xL, to the pro-apoptotic variant, Bcl-xS. This surprising finding illustrates the advantage of antisense-induced modulation of alternative splicing versus down-regulation of targeted genes. It also suggests a specificity of the oligonucleotide effects since non-cancerous cells with low levels of Bcl-xL should resist the treatment. 5'Bcl-x AS sensitized cells to several antineoplastic agents and radiation and was effective in promoting apoptosis of MCF-7/ADR cells, a breast cancer cell line resistant to doxorubicin via overexpression of the mdr1 gene. Efficacy of 5'Bcl-x AS combined with chemotherapeutic agents in the PC3 prostate cancer cell line may be translated to clinical prostate cancer since recurrent prostate cancer tissue samples expressed higher levels of Bcl-xL than benign prostate tissue. Treatment with 5'Bcl-x AS may enhance the efficacy of standard anti-cancer regimens and should be explored, especially in recurrent prostate cancer.

Bcl-2/bcl-xL bispecific antisense treatment sensitizes breast carcinoma cells to doxorubicin, paclitaxel and cyclophosphamide

Overexpression of the anti-apoptotic proteins bcl-2 and bcl-xL is implicated in breast cancer development, tumor progression and drug resistance. Here we describe the use of the bcl-2/bcl-xL bispecific antisense oligonucleotide 4625 to sensitize breast carcinoma cells to anti-cancer drugs routinely used in breast cancer therapy. MCF7 cells were treated with oligonucleotide 4625, doxorubicin, paclitaxel or cyclophosphamide alone, or with combinations of oligonucleotide and the anti-cancer drugs. As measured in cell viability assays, treatment with the various combinations reduced the number of viable MCF7 cells more effectively than treatment with the single drugs alone. Treatment with a sequence control oligonucleotide did not affect cell viability. All combination treatments induced apoptosis as demonstrated by the appearance of massive nuclear condensation in a high proportion of the cells. To further characterize the interaction between 4625 and doxorubicin, paclitaxel or cyclophosphamide, the median-effect method was used. In MCF7 cells all combinations resulted in potent synergistic effects over a broad range of toxicity with combination indices ranging from 0.8 to 0.1. Similarly, strong synergistic interactions between oligonucleotide 4625 and the anti-cancer drugs were also observed in cultures of the breast carcinoma cell line MDA-MB-231. Our data suggest the use of 4625 as a potent adjuvant in breast cancer chemotherapy.

Novel strategies for overcoming multidrug resistance in cancer

The problems of why metastatic cancers develop pleiotropic resistance to all available therapies, and how this might be countered, are the most pressing in cancer chemotherapy. It is likely that such resistance involves a combination of mechanisms including changes in drug transport/drug targets, reduction in the degree of drug-induced apoptosis/cell loss, and increased rate of tumour repopulation following therapy. Current research must consider not only which mechanisms contribute, eventually relating this to individual patients with cancer, but also what strategies might be utilised to counter each of the important resistance mechanisms. A considerable amount of work has been devoted to the development of inhibitors of membrane-associated transport proteins such as P-glycoprotein, which mediate drug efflux. This work is now being complemented by approaches that target cell death pathways such as those mediated by release of mitochondrial proteins and by activation of surface receptors such as Fas. Rapid progress has been made in developing small-molecular-weight drugs that influence the rate of apoptosis, for instance by binding to the bcl-2 family of proteins regulating mitochondrial permeability. Antisense approaches aimed at reducing bcl-2 expression, and thus increasing the rate of cell death, are also showing promise. Modification of repopulation kinetics provides a further approach but has not received as much attention as other aspects of tumour resistance. New therapeutic approaches will have to be complemented by improved diagnostic tests to evaluate the contributions of different resistance mechanisms in individual patients with cancer.

Analysis of ribosyl-modified, mixed backbone analogs of a bcl-2/bcl-xL antisense oligonucleotide

Progress in oligonucleotide chemistry has provided second-generation antisense oligonucleotides with increased efficacy and reduced non-antisense-related toxicity. The ability of the 2'-O-(2-methoxyethylribose) (2'-MOE)-modified phosphorothioate gapmer oligonucleotide 4625, which matches the bcl-2 mRNA and has three base-mismatches to bcl-xL, to inhibit bcl-2 and bcl-xL expression and induce tumor cell apoptosis has been described. Here we investigated the consequences of adding of 2'-MOE or 2'-Me modifications to ribonucleotides at either the two ends of the sequence, or the center region together with different combinations of phosphodiester/phosphorothioate backbones on the activity of oligonucleotide 4625. The ability of the various 4625 analogs, including the parental first-generation oligonucleotide 3005, to inhibit bcl-2 and bcl-xL expression, and diminish cell growth or induce tumor cell death was assessed in SW2 lung cancer cells using real-time PCR, Western blotting and cell viability assays. Only oligonucleotide 4625 exhibited a potent bispecific antisense activity against bcl-2 and bcl-xL, which effectively reduced tumor cell viability. The other antisense oligonucleotides were either uniquely active against bcl-2 or completely inactive. Our data suggest that the 2'-MOE modification in combination with the phophorothioate gapmer chemistry is the optimal format of the 4625 sequence in terms of antisense activity and biological efficacy.

Bcl-2 and bcl-xL antisense oligonucleotides induce apoptosis in melanoma cells of different clinical stages

Recent clinical studies have shown the promise of bcl-2 antisense therapy in patients with melanoma. To further demonstrate the importance of bcl-2 and validate the related antiapoptotic protein bcl-xL as targets for antisense therapy in melanoma, their implication as survival factors in melanoma cells of different clinical stages as well as in normal melanocytes was investigated. Primary cell cultures derived from 17 melanomas, the cell line A375, and normal melanocytes from healthy donors were treated with antisense oligonucleotides targeting either the bcl-xL mRNA or the bcl-2 and the bcl-xL mRNAs simultaneously. Bcl-2 and bcl-xL expression in cells was analyzed by real-time polymerase chain reaction and Western blotting. Cell viability was assessed in 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide and apoptosis assays. Bcl-2 expression was low in melanoma cells of stages I, II, and III, hardly detectable in A375 cells, but high in normal melanocytes. Bcl-xL expression was high in all cell types tested. As shown in A375 cells and the stage III melanoma cells 0513, both the bcl-xL monospecific oligonucleotide 4259 and the bcl-2/bcl-xL bispecific oligonucleotide 4625 effectively reduced tumor cell viability by induction of apoptosis with IC50 values ranging from 200 to 350 nM. Oligonucleotide 4625 proved to be superior to 4259, as it significantly reduced the viability of cells from all melanoma stages. Both oligonucleotides reduced also the viability of normal melanocytes. Our data suggest that bcl-2 and bcl-xL are promising targets for antisense therapy of melanoma, and that the simultaneous downregulation of their expression may provide additional clinical benefit.

Cancer research 2001: drug resistance, new targets and drug combinations

The development of new anticancer drugs and the identification of novel targets represent major focus areas for pharmaceutical and biotech companies, universities and research institutes worldwide. The 92nd Annual Meeting of the American Association for Cancer Research (AACR) provided a glimpse of the latest developments in the cancer field. We highlight here presentations on resistance mechanisms (efflux, target modulation), new targets and drugs in development (topoisomerase, angiogenesis, cell cycle inhibitors) and new molecular technologies. The emergence of technologies for concurrently screening for expression of thousands of genes, has provided a new approach for the identification of molecular targets and mechanisms of both action and resistance of new compounds. The importance of inhibiting multiple targets simultaneously was brought up in several presentations.