Therapeutic potential of antisense Bcl-2 as a chemosensitizer for cancer therapy

Bcl-2 protein plays a critical role in inhibiting anticancer drug-induced apoptosis, which is mediated by a mitochondria-dependent pathway that controls the release of cytochrome c from mitochondria through anion channels. Constitutive overexpression of Bcl-2 or unchanged expression after treatment with anticancer drugs confers drug resistance not only to hematologic malignancies but also to solid tumors. The down-regulation of Bcl-2 protein by the antisense (AS) Bcl-2 (oblimesen sodium) may be a useful method for targeting the antiapoptotic protein and thereby increasing the chemotherapeutic effect of anticancer drugs. Several randomized, controlled, Phase III trials have compared standard chemotherapy with a combination of AS Bcl-2 and standard chemotherapy for the treatment of patients with chronic lymphocytic leukemia, multiple myeloma, malignant melanoma, and nonsmall cell lung carcinoma. Nonrandomized clinical trials and preclinical evaluations of AS Bcl-2 also are underway for patients with other malignancies. Here, the authors review the current clinical and preclinical evaluations of AS Bcl-2 and discuss its potential to act as a chemosensitizer and to enhance the therapeutic effect of cancer chemotherapy.     

Antisense Bcl-2 and HER-2 oligonucleotide treatment of breast cancer cells enhances their sensitivity to anticancer drugs

Overexpression of the HER-2 correlates with drug-resistance and a poor prognosis in breast cancer, however the mechanism(s) of HER-2-mediated drug-resistance are unknown. We examined the effects of antisense Bcl-2 and HER-2 oligonucleotides (ODN) to assess the mechanism(s) through which down-regulation of Bcl-2 and HER-2 enhances drug-sensitivity. Using two human breast cancer cell lines, MDA-MB-231 and BT-474, the antitumor effects of a combination of antisense ODN and anticancer drugs, including mitomycin C (MMC), adriamycin (ADM), paclitaxel (TXL), and docetaxel (TXT) was evaluated. The expression of Bcl-2 protein was suppressed by treatment with antisense Bcl-2 ODN in a dose-dependent manner. An enhanced drug-sensitivity to MMC and TXL upon pretreatment with antisense Bcl-2 ODN was observed, with the IC50 values increasing 1.9- and 2.0-fold, respectively. Treatment of BT-474 cells with antisense HER-2 at 1.0 micro M suppressed HER-2 overexpression by 60.5%. Pretreatment with antisense HER-2 ODN increased the sensitivity of these cells to ADM and TXL 20.8- and 10.8-fold, respectively. In vivo experiments using a combination of antisense HER-2 and TXL showed the similar enhancement of antitumor effect of TXL as compared to that of antisense HER-2 or TXL alone (p=0.068). Enhancement of drug-sensitivity was associated with the induction of apoptosis. Of interest, treatment with antisense HER-2 ODN also suppressed the expression of Bcl-2 and pAkt. These results indicate that down-regulation of Bcl-2 and HER-2 increased drug-sensitivity by modulating drug-induced apoptotic pathways in breast cancer cells, and that antisense ODN therapy, targeting Bcl-2 and HER-2 may be a useful strategy to enhance drug-sensitivity.     

Antisense and nonantisense effects of antisense Bcl-2 on multiple roles of Bcl-2 as a chemosensitizer in cancer therapy

Bcl-2 is an oncoprotein that plays a critical role in inhibiting apoptotic cell death in the mitochondria-dependent pathway in cancer chemotherapy. As a strategy for blocking Bcl-2 for enhancement of the chemotherapeutic effect, antisense Bcl-2 (AS Bcl-2; G3139, oblimersen sodium, Genasense) has shown promise, and there are several ongoing clinical studies with hematological malignancies as well as solid tumors. Although several preclinical and clinical studies have shown the therapeutic efficacy of Bcl-2 in combination with an anticancer drug as a chemosensitizer, in clinical trials the downregulation of Bcl-2 has not been observed with a high frequency in tumor cells. Nevertheless, previous studies showed nonantisense effects such as production of reactive oxygen species and immunostimulatory action through cytosine-phosphate-guanosine-motif in the antisense oligodeoxynucleotides. Further, Bcl-2 is able to inhibit Beclin 1-dependent autophagic cell death, which is a nonapoptotic cell death. The current status and future directions of AS Bcl-2 and the potential mechanisms for multiple roles that Bcl-2 has in cancer therapy are reviewed.     

Antisense oligonucleotides targeting the epidermal growth factor receptor inhibit proliferation, induce apoptosis, and cooperate with cytotoxic drugs in human cancer cell lines.

We have constructed a series of 22 phosphorothioate 20-mer antisense oligonucleotides directed against different regions of the human (EGFR) mRNA. Treatment with EGFR antisense oligonucleotides showed a dose-dependent inhibition of human GEO colon cancer cell growth in soft agar. Western blot analysis demonstrated a significant reduction in EGFR expression after treatment with each EGFR antisense oligonucleotide. The ability to inhibit GEO anchorage-independent growth, however, varied among the EGFR antisense sequences with an IC(50) ranging between 0.5 and 3.5 microM. Two of these antisense oligonucleotides targeting the regions between 2457-2476 and 614-4633 bases of the human EGFR mRNA have been modified as hybrid DNA/RNA mixed backbone oligonucleotides (MBO) to examine their anticancer properties in vivo. The 2 EGFR antisense MBOs retained the same biological properties of the fully phosphorothioate EGFR antisense oligonucleotides targeting the same EGFR mRNA sequences, such as blocking EGFR synthesis, inhibiting cell growth and enhancing programmed cell death in human cancer cell lines that express functional EGFRs. Furthermore, a potentiation in the growth inhibitory effect on GEO cancer cells was observed after treatment with these EGFR antisense MBOs in combination with cytotoxic drugs, including cisplatin, doxorubicin, paclitaxel, or topotecan. These results show the antiproliferative activity of specific EGFR antisense oligonucleotides and allow to identify novel EGFR antisense MBOs that deserve further evaluation as potential selective anticancer agents alone or in combination with cytotoxic drugs in human carcinomas that express functional EGFRs.     

Oblimersen sodium (G3139 Bcl-2 antisense oligonucleotide) therapy in Waldenstrom's macroglobulinemia: a targeted approach to enhance apoptosis

The components of the apoptotic pathway are targets for anticancer therapy. Bcl-2 protein inhibits apoptosis and confers resistance to treatment with traditional cytotoxic chemotherapy, radiotherapy, and monoclonal antibodies. Oblimersen sodium (G3139, Genasense, Genta Inc, Berkeley Heights, NJ) is an antisense oligonucleotide compound designed to specifically bind to the first six codons of the human bcl-2 mRNA sequence, resulting in degradation of bcl-2 mRNA and subsequent decrease in Bcl-2 protein translation. Oblimersen is the first oligonucleotide to demonstrate proof of principle of an antisense effect in human tumors by the documented downregulation of the target Bcl-2 protein. A growing body of preclinical and clinical evidence suggests that oblimersen synergizes with many cytotoxic and biologic/immunotherapeutic agents against a variety of hematologic malignancies and solid tumors. Randomized clinical trials are currently underway to evaluate the efficacy and tolerability of oblimersen in combination with cytotoxic chemotherapy in chronic lymphocytic leukemia (CLL), multiple myeloma (MM), malignant melanoma, and non-small cell lung cancer. In addition, nonrandomized trials are underway to evaluate oblimersen in non-Hodgkin's lymphoma (NHL), acute myeloid leukemia (AML), and hormone-refractory prostate cancer. Preclinical data support the clinical evaluation of oblimersen in additional tumor types, including chronic myelogenous leukemia, and breast, small cell lung, gastric, colon, bladder (CML), and Merkel cell cancers. Enhancement of the efficacy of anticancer treatments with oblimersen Bcl-2 antisense therapy represents a promising new apoptosis-modulating strategy, and ongoing clinical trials will test this therapeutic approach.     

Rationale for sequential tamoxifen and anticancer drugs in adjuvant setting for patients with node- and receptor-positive breast cancer

Since the survival benefit of tamoxifen (TAM) combined with anticancer drugs in treating node- and receptor-positive breast cancer is small, appropriate treatment schedules and the rationale for the combination remains unclear. We examined the effect of estradiol (E2) on sensitivity to anticancer drugs to clarify the survival benefit of tamoxifen combined with anticancer drugs. We used the MTT assay to assess the effect of E2 on sensitivity to anticancer drugs in the E2 receptor-positive and -negative breast cancer cell lines, MCF-7 and MDA-MB-231, respectively. We assessed the expression of apoptosis-related proteins by Western blotting, and evaluated apoptosis using the TUNEL method. Serum levels of E2 were measured using an enzyme-labeled radioimmunoassay in patients with premenopausal breast cancer before and during treatment with tamoxifen. Estrogen administration decreased sensitivity in MCF-7 cells to the anticancer drugs, adriamycin (ADM), mitomycin C (MMC), and paclitaxel (TXL), evaluated as increases in the IC50 values for ADM (4.1-fold), MMC (1.9-fold) and TXL (13.0-fold), compared with those of each drug alone. Estradiol in MDA-MB-231 cells similarly increased the IC50 values for ADM (9.5-fold), MMC (15.6-fold), and TXL (2.4-fold). The decreased sensitivity to these anticancer drugs was associated with the attenuation of apoptosis. Estrogen dose-dependently increased the expression of Bcl-2 protein in MCF-7, but not in MDA-MB-231 cells, and suppressed the expression of Bax and cytochrome c induced by anticancer drugs in association with decreased apoptosis compared with the effect of each drug alone. Phosphorylation of the Bcl-2 protein induced by TXL was decreased in the presence of E2 in MCF-7 cells. Serum levels of E2 were increased in 5 patients without amenorrhea and in 1 patient with amenorrhea after treatment with TAM alone in adjuvant therapy, compared with levels before treatment. Estradiol decreased sensitivity to ADM, MMC, and TXL in MCF-7 and MDA-MB-231 breast cancer cells, and this was associated in part with an increase in the amount of Bcl-2 protein, and decreases in levels of Bax and cytochrome c leading to apoptosis. These results suggest that therapy with TAM and anticancer drugs should be sequentially scheduled with anticancer drugs followed by TAM in an adjuvant setting to treat patients with breast cancer for a potentially improved survival benefit.     

Antisense-mediated downregulation of anti-apoptotic proteins induces apoptosis and sensitizes head and neck squamous cell carcinoma cells to chemotherapy

We have earlier reported that the inhibition of apoptosis in head and neck squamous cell carcinomas (HNSCC) is because of upregulated expression of Bcl-2, Bcl-X(L) and Survivin. Hence, we addressed the question whether antisense approach towards these inhibitors of apoptosis could restore the apoptosis in HNSCC. Further, we wanted to see whether chemotherapeutic efficacy of Cisplatin and Etoposide could be enhanced by using these drugs in combination with antisense oligonucleotides in human laryngeal carcinoma HeP2 and tongue carcinoma Cal27 cells. The effect of these antisense oligonucleotides was examined on the mRNA expression by RT-PCR and on protein expression by Western blotting. Apoptosis was measured by flowcytometry, TUNEL assay and caspase-3 activity assay. Treatment of HeP2 and Cal27 cells with 400 nM antisense oligonucleotides against Bcl-2, Bcl-X(L) and Survivin for 48 hrs decreased their expression both at the mRNA as well as at the protein level, resulting in the induction of apoptosis. Treatment of HeP2 and Cal27 cells with these antisense oligonucleotides augmented Cisplatin and Etoposide induced apoptosis. Our findings emphasize the importance of Bcl-2, Bcl-X(L) and Survivin as survival factors in HNSCC cells. Antisense treatment against these survival factors in combination with lower doses of chemotherapy offers potential as a less toxic chemoadjuvant therapy.     

A pitfall in the survival benefit of adjuvant chemotherapy for node- and hormone receptor-positive patients with breast cancer: the paradoxical role of Bcl-2 oncoprotein (review)

The survival benefit of adjuvant chemotherapy in node-positive patients with breast cancer compared with surgery alone has been established. The survival benefit differs considerably between hormone receptor-positive and -negative patients, and it is believed that the effectiveness of adjuvant chemotherapy can be increased by hormonal therapy with tamoxifen. In the present review, we discuss the rationale behind the effectiveness of combination treatment with anticancer drugs and tamoxifen in terms of the paradoxical role of Bcl-2 in apoptosis in breast cancer. The survival benefit between receptor-positive and -negative patients was assessed using previous reports of randomized controlled studies for postoperative adjuvant chemotherapy in node-positive breast cancer. Tamoxifen induces the anti-apoptotic gene, Bcl-2, by its effect on estradiol (E2), via an E2-response element in the promotor region of Bcl-2. The efficicacy of chemoendocrine therapy was assessed in terms of the influence of tamoxifen on the effect of anticancer drugs. Adjuvant chemotherapy, including anthracycline and non-anthracycline based regimens, has an overall survival benefit in node-positive breast cancer, with a 23.5% reduction in the annual odds of recurrence and a 15% reduction in mortality (P<0.00001). A comparison of the reduction of the relative risk indicates that the survival benefit in receptor-negative patients is superior to that in receptor-positive patients by approximately 3-fold. Further, in contrast to receptor-negative patients, there is no additional benefit from paclitaxel over doxorubicin and cyclophosphamide (AC) in receptor-positive patients. The possible reasons that the chemotherapy benefit in receptor-positive patients is small and marginal are the following: i) concurrent treatment or pretreatment with tamoxifen can increase plasma E2 levels in premenopausal patients, thereby inducing Bcl-2 in residual cancer cells, which might decrease drug-sensitivity in combination with chemotherapy; ii) induction of Bcl-2 might be involved predominantly in the resistance to taxanes, the cytotoxic action of which targets Bcl-2. Co-treatment or pretreatment with tamoxifen for adjuvant therapy might decrease the efficacy of anticancer drugs, an effect that is mediated by induction of Bcl-2, especially in premenopausal patients with node-positive breast cancer. Treatment with anticancer drugs should be followed by treatment with tamoxifen to produce a survival benefit from combination therapy in receptor-positive patients.     

Current status of the molecular mechanisms of anticancer drug-induced apoptosis. The contribution of molecular-level analysis to cancer chemotherapy

Apoptosis is an important phenomenon in cytotoxicity induced by anticancer drugs. Here, we review the current status of the molecular mechanisms of anticancer drug-induced apoptosis in order to assess the contribution of molecular-level analysis to cancer chemotherapy. It is apparent that the molecular mechanisms by which anticancer drugs induce apoptosis are mediated by death receptor-dependent and -independent pathways, which are related to the release of cytochrome c through voltage-dependent anion channels in the mitochondrial inner membrane. The release of cytochrome c is the central gate in turning on/off apoptosis, and is regulated by the interaction of proapoptotic proteins, including Bid, Bax and Bak, and antiapoptotic proteins including Bcl-2 and Bcl-X(L), and a specific class of inhibitors of apoptosis proteins (IAPs) including Akt, survivin, and heat-shock proteins. The caspase cascade is activated by the release of cytochrome c, which is initiated by the formation of apoptosomes consisting of procaspase-9, Apaf-1 and cytochrome c in the presence of dATP, and results in the activation of caspase-9 and caspase-3, thereby leading to apoptosis. Drug sensitivity can be enhanced by the introduction of proapoptotic genes and the inhibition of antiapoptotic proteins. The latter process is mediated by antisense oligonucleotides and is associated with apoptosis. The signal transduction pathways that are triggered by the central gate in mitochondria play a critical role in anticancer drug-induced apoptosis. The modulation of signal transduction pathways targeting the proteins involved in these signal transduction pathways using antisense IAPs, and growth factor antibodies may be a good strategy for enhancing therapeutic efficacy of anticancer drugs in cancer chemotherapy.     

ERK inhibitor PD98059 enhances docetaxel-induced apoptosis of androgen-independent human prostate cancer cells

Anticancer drugs docetaxel and vinorelbine suppress cell growth by altering microtubule assembly and activating the proapoptotic signal pathway. Vinorelbine and docetaxel have been approved for treating several advanced cancers. However, their efficacy in the management of advanced hormone-refractory prostate cancer remains to be clarified. Microtubule damage by some anticancer drugs can activate the ERK survival pathway, which conversely compromises chemotherapeutic efficacy. We analyzed the effect of ERK inhibitors PD98059 and U0126 on vinorelbine- and docetaxel-induced cell growth suppression of androgen-independent prostate cancer cells. In androgen-independent C-81 LNCaP cells, inhibition of ERK by PD98059, but not U0126, plus docetaxel resulted in enhanced growth suppression by an additional 20% compared to the sum of each agent alone (p < 0.02). The combination treatment of docetaxel plus PD98059 also increased cellular apoptosis, which was in part due to the inactivation of Bcl-2 by increasing phosphorylated Bcl-2 by more than 6-fold and Bax expression by 3-fold over each agent alone. At these dosages, docetaxel alone caused only marginal phosphorylation of Bcl-2 (10%). Docetaxel plus U0126 had only 20% added effect on Bcl-2 phosphorylation compared to docetaxel alone. Nevertheless, both U0126 and PD98059 exhibited an enhanced effect on docetaxel-induced growth suppression in PC-3 cells. No enhanced effect was observed for vinorelbine plus PD98059 or U0126. Thus, the combination therapy of docetaxel plus PD98059 may represent a new anticancer strategy, requiring lower drug dosages compared to docetaxel monotherapy. This may lower the cytotoxicity and enhance tumor suppression in vivo. This finding of a combination effect could be of potential clinical importance in treating hormone-refractory prostate cancer.     

Development of a novel gene therapy using survivin antisense expressing adenoviral vectors

BACKGROUND: Survivin, a novel inhibitor of apoptosis, is undetectable in normal adult tissues but becomes notably expressed in the most common human cancers, and is recognized as a potential target in anticancer therapy. METHODS: In this study we evaluated a survivin antisense expressing replication-incompetent adenoviral vector under the control of the cytomegalovirus promoter (pAd.CMV-SAS) for cytoreductive effects in human HT-29 colon cancer cells in vitro and in vivo. RESULTS: Infection of tumor cells with pAd.CMV-SAS caused down-regulation of survivin expression and the potential for spontaneous apoptosis in tumor cells. In contrast, pAd.CMV-SAS did not affect cell viability of normal human cells including fibroblasts. In addition, infection of tumor cells with pAd.CMV-SAS resulted in an increase of the G0/G1 phase population in the cell cycle, and increased their sensitivity to chemotherapeutic drugs in vitro. The efficacies of pAd.CMV-SAS were inversely correlated with survivin expression level. In nude mice, pAd.CMV-SAS suppressed tumor formation, as well as decreased the tumor volumes to approximately 30% of the control tumors. Furthermore, it was confirmed that the anti-tumor efficacy of pAd.CMV-SAS was also enhanced in combination with chemotherapeutic drugs in vivo. CONCLUSIONS: These findings suggest that targeting of survivin using adenoviral antisense vectors may have a potential role in the selective therapy of colon cancer.     

Magnolol, a natural compound, induces apoptosis of SGC-7901 human gastric adenocarcinoma cells via the mitochondrial and PI3K/Akt signaling pathways

Gastric cancer is the fourth most commonly diagnosed cancer with the second highest mortality rate worldwide. Surgery, chemotherapy and radiation therapy are generally used for the treatment of stomach cancer but only limited clinical response is shown by these therapies and still no effectual therapy for advanced gastric adenocarcinoma patients is available. Therefore, there is a need to identify other therapeutic agents against this life-threatening disease. Plants are considered as one of the most important sources for the development of anticancer drugs. Magnolol, a natural compound possesses anticancer properties. However, effects of Magnolol on human gastric cancer remain unexplored. The effects of Magnolol on the viability of SGC-7901 cells were determined by the MTT assay. Apoptosis, mitochondrial membrane potential and cell cycle were evaluated by flow cytometry. Protein expression of Bcl-2, Bax, caspase-3 and PI3K/Akt was analysed by Western blotting. Magnolol induced morphological changes in SGC-7901 cells and its cytotoxic effects were linked with DNA damage, apoptosis and S-phase arrest in a dose-dependent manner. Magnolol triggered the mitochondrial-mediated apoptosis pathway as shown by an increased ratio of Bax/Bcl-2, dissipation of mitochondrial membrane potential (ΔΨm), and sequential activation of caspase-3 and inhibition of PI3K/Akt. Additionally, Magnolol induced autophagy in SGC-7901 cells at high concentration but was not involved in cell death. Magnolol-induced apoptosis of SGC-7901 cells involves mitochondria and PI3K/Akt-dependent pathways. These findings provide evidence that Magnolol is a promising natural compound for the treatment of gastric cancer and may represent a candidate for in vivo studies of monotherapies or combination antitumor therapies.     

Why anti-Bcl-2 clinical trials fail: a solution

The alteration in expression of B cell lymphoma-2 (Bcl-2) family of protein members in cancer is involved mainly in the regulation of apoptosis. Bcl-2 family proteins are currently used as major targets in the development of methods to improve treatment outcomes for cancer patients that underwent clinical trials. Although many agents have been developed for targeting Bcl-2 in the past decade, some previous attempts to target Bcl-2 have not resulted in beneficial clinical outcome for reasons unknown. Here, we propose that this was due in part for not considering the cellular level of a different antiapoptotic protein, i.e., galectin-3 (Gal-3). Gal-3 is a member of the β-galactoside binding protein family and a multifunctional oncogenic protein which regulates cell growth, cell adhesion, cell proliferation, angiogenesis, and apoptosis. Gal-3 is the sole protein that contains the NWGR anti-death motif of the Bcl-2 family and inhibits cell apoptosis induced by chemotherapeutic agents through phosphorylation, translocation and regulation of survival signaling pathways. It is now established that Gal-3 is a candidate target protein to suppress antiapoptotic activity and anticancer drug resistance. In this review, we describe the role and relevance of Gal-3 and Bcl-2 protein family in the regulation of apoptosis and propose a novel combination therapy modality. Combination therapy that targets Gal-3 could be essential for improvement of the efficacy of Bcl-2 targeting therapy in cancers and should be studied in future clinical trials. Otherwise, not considering Gal-3 cellular level could lead to trial failure.     

Downregulation of survivin expression by induction of the effector cell protease receptor-1 reduces tumor growth potential and results in an increased sensitivity to anticancer agents in human colon cancer

Survivin, a novel inhibitor of apoptosis, is expressed in cancer cells and not in normal adult tissues, and is recognised as a potential target in anticancer therapy. The induction of a natural antisense of survivin, effector cell protease receptor-1 (EPR-1), in a human colon cancer cell line resulted in a downregulation of survivin expression, with a similar decrease in cell proliferation, an increase in apoptosis and an increase in the sensitivity to anticancer agents. In addition, subcutaneous (s.c.) tumours from EPR-1 transfectants showed a significant reduction in size compared with parental cells, and this antitumour efficacy was further enhanced in combination with anticancer agents. These findings suggest that regulation of survivin by the induction of EPR-1 cDNA may have significant potential as a therapy for human colon cancer.     

Synergism of PI3K/Akt inhibition and Fas activation on colon cancer cell death

Fas and PI3K/Akt signaling pathways pivotally impact on cancer cell death and survival respectively and are considered as promising targets for innovative anticancer therapies. To better characterize the combination effect of PI3K/Akt inhibitors and Fas agonists and understand the profile of the interaction between PI3K/Akt and Fas signaling, we qualitatively and quantitatively evaluated the combination effect of PI3K/Akt inhibitors LY294002, Akt inhibitor VIII and FasL. At the concentration that can block cell cycle progression and DNA synthesis but not elicit apoptosis, these inhibitors potentiate FasL to induce apoptosis. At higher concentrations, when the PI3K/Akt inhibitors induce apoptosis, they synergize FasL to induce apoptosis. In addition, PI3K/Akt inhibition significantly facilitates the Fas-mediated apoptotic signaling. Understanding the combination effects between PI3K/Akt inhibition and Fas activation not only leads to rational design of effective combination therapy of PI3K/Akt inhibitors but also improve our knowledge about the impact of PI3K-Akt pathway on Fas signaling and the potential modulation of innate immune system by PI3K-Akt-targeting drugs in anticancer treatment.     

Tumor regression by combination antisense therapy against Plk1 and Bcl-2

Increased expression of the cell proliferation-associated polo-like kinase 1 (PLK1) and apoptosis-associated BCL-2 genes has been observed in different human malignancies. Inhibition of cell proliferation and reactivation of apoptosis are basic principles in anticancer therapy. The efficiency of this approach is often limited by insuf-ficient targeting and delivery of anticancer drugs into the tumors. Phosphorothioate antisense oligodeoxynucleotides (ODNs) directed against PLK1 and BCL-2 were administered systemically via the tail vein into nude mice bearing A549, MDA-MB-435, and Detroit562 xenografts. To enhance tumor-specific uptake and to reduce systemic toxicity of antisense ODNs membrane electroporation transfer was applied in vivo. Northern and Western blot analyses were used to assess PLK1 and BCL-2 expression. Tumor mass was assessed after resection of tumors. All three cell lines and corresponding xenografts expressed high levels of PLK1 and were sensitive towards antisense PLK1 treatment. Antisense BCL-2 therapy was effective in tumors expressing high levels of BCL-2, but not in A549 cells and corresponding xenografts, which express low levels of BCL-2. Administration of antisense ODNs in a dose of 5 mg/kg, twice weekly during four weeks supported by the membrane electroporation transfer, eradicated 60-100% of the xenografted tumors. Antitumor effect in BCL-2 overexpressing MDA-MB-435 cells was synergistic for BCL-2 and PLK1 combination therapy. This study provides evidence that combined systemic administration of antisense ODNs against proliferation and pro- survival associated targets and in vivo electroporation of tumors represents a promising antitumor therapeutic approach.     

Sensitization for anticancer drug-induced apoptosis by betulinic Acid

We previously described that betulinic acid (BetA), a naturally occurring pentacyclic triterpenoid, induces apoptosis in tumor cells through the mitochondrial pathway. Here, for the first time, we provide evidence that BetA cooperated with anticancer drugs to induce apoptosis and to inhibit clonogenic survival of tumor cells. Combined treatment with BetA and anticancer drugs acted in concert to induce loss of mitochondrial membrane potential and the release of cytochrome c and Smac from mitochondria, resulting in activation of caspases and apoptosis. Overexpression of Bcl-2, which blocked mitochondrial perturbations, also inhibited the cooperative effect of BetA and anticancer drugs, indicating that cooperative interaction involved the mitochondrial pathway. Notably, cooperation of BetA and anticancer drugs was found for various cytotoxic compounds with different modes of action (e.g., doxorubicin, cisplatin, Taxol, VP16, or actino-mycin D). Importantly, BetA and anticancer drugs cooperated to induce apoptosis in different tumor cell lines, including p53 mutant cells, and also in primary tumor cells, but not in human fibroblasts indicating some tumor specificity. These findings indicate that using BetA as sensitizer in chemotherapy-based combination regimens may be a novel strategy to enhance the efficacy of anticancer therapy, which warrants further investigation.     

Combination bcl-2 antisense and radiation therapy for nasopharyngeal cancer.

PURPOSE: A wide variety of tumors depend on the dysregulation of Bcl-2 family proteins for survival. The resulting apoptotic block can often provide a mechanism for resistance to anticancer treatments, such as chemotherapy and radiation. This current study evaluates the efficacy of combining systemically delivered Bcl-2 phosphorothioate antisense (Bcl-2 ASO) and radiation for nasopharyngeal cancer therapy. RESULTS: Antisense uptake was unaffected by 0, 3, or 6 Gy radiation. Radiation decreased the fraction of viable C666-1 cells to 60%, with a further decrease to 40% in combination with Bcl-2 ASO. Despite a modest in vitro effect, Bcl-2 ASO alone caused the regression of established xenograft tumors in mice, extending survival by 15 days in a C666-1 and by 6 days in a C15 model. The survival times for mice treated with both Bcl-2 ASO and radiation increased by 52 days in C666-1 and by 20 days in C15 tumors. This combination resulted in a more-than-additive effect in C666-1 tumors. Less impressive gains observed in C15 tumors might be attributable to higher expression of antiapoptotic Bcl-2 family proteins and limited drug distribution in the tumor. Retreatment of C666-1 tumors with the Bcl-2 ASO-radiation combination, however, was effective, resulting in mice surviving for >80 days relative to untreated controls. CONCLUSIONS: Our results show that the Bcl-2 ASO and radiation combination is a highly potent therapy for nasopharyngeal cancer. Further examination of combination therapy with radiation and other Bcl-2 family-targeted anticancer agents in both preclinical and clinical settings is definitely warranted.     

Antisense oligonucleotides for cancer therapy-an overview

Antisense technology has emerged as an exciting and promising strategy of cancer therapy. The principle of this technology is the sequence-specific binding of an antisense oligonucleotide to target mRNA, resulting in the prevention of gene translation. The specificity of hybridization by Watson-Crick base pairing make antisense oligonucleotides attractive as tools for targeted validation and functionalization, and as therapeutics to selectively modulate the expression of genes involved in the pathogenesis of malignancies and other genetic diseases. A variety of genes known to be key regulators of apoptosis, cell growth, metastasis, and angiogenesis which are associated with the malignant phenotype of cancer cells rather than with normal cell physiology, have been validated as molecular targets for antisense therapy. One antisense compound has been approved for local treatment of cytomegalovirus-induced retinitis, and several others are in clinical trials, including those targeting the mRNA of Bcl-2, protein kinase C-alpha (PKC-alpha), c-raf or Ha-ras. In this review, we focus on the mechanism of action of antisense oligonucleotides and new technical developments, look at new targets provided by coordinated functional genomics and proteomics initiatives and summarize the most promising clinical data.