Effects of Bcl-2 modulation with G3139 antisense oligonucleotide on human breast cancer cells are independent of inherent Bcl-2 protein expression

Growth inhibition and chemosensitization of human carcinoma cells by human serum albumin-coated liposomal antisense oligodeoxyribonucleotide against bcl-2

Previous study has shown human serum albumin (HSA) coated liposomes can deliver bcl-2 antisense oligodeoxyribonucleotide (ODN) into KB carcinoma cells, and decrease bcl-2 mRNA and protein expression level. In the current study, cell growth inhibition and chemosensitization of KB cells were evaluated. Liposomes composed of dimethyldioctadecyl ammonium bromide/egg phosphatidylcholine/α-tocopheryl polyethylene glycol 1000 succinate (58:40:2 molar ratio) complexed with bcl-2 antisense ODN and coated with HSA were examined for cell growth inhibition and sensitization to a commonly used chemotherapeutic drug, doxorubicin. HSA-coated liposome-ODN complexes effectively inhibited cell growth in the range of ODN concentration of 0.45-7.2 µM. Upon posttreatment with doxorubicin, the cytotoxicity was further significantly increased compared to the ODN complexes alone. The cytotoxicity was dependent on antisense ODN concentration, incubation time and doxorubicin concentration, and relatively independent on HSA concentration. This study suggests that HSA-coated liposomes are effective delivery vehicles for antisense ODN with potential therapeutic application and can be effectively combined with doxorubicin.

Steroid receptor coactivator 3 regulates autophagy in breast cancer cells through macrophage migration inhibitory factor

SRC-3/AIB1 (steroid receptor coactivator 3/amplified in breast cancer 1) is an authentic oncogene that contributes to the development of drug resistance and poor disease-free survival in cancer patients. Autophagy is also an important cell death mechanism that has tumor suppressor function. In this study, we identified macrophage migration inhibitory factor (MIF) as a novel target gene of SRC-3 and demonstrated its importance in cell survival. Specifically, we showed that MIF is a strong suppressor of autophagic cell death. We further showed that suppression of MIF, in turn, induced autophagic cell death, enhanced chemosensitivity and inhibited tumorigenesis in a xenograft mouse tumorigenesis model. Our study demonstrated that regulation of MIF expression and suppression of autophagic cell death is a potent mechanism by which SRC-3 contributes to increased chemoresistance and tumorigenicity.

Bcl-2: a prime regulator of mitochondrial redox metabolism in cancer cells

SIGNIFICANCE

Mitochondria play a critical role as death amplifiers during drug-induced apoptosis in cancer cells by providing pro-apoptotic factors that are released from the mitochondrial inter-membranous space upon the induction of mitochondrial outer membrane permeabilization. This intrinsic death signaling pathway is the preferred mechanism employed by most anticancer compounds, and as such, resistance to drug-induced apoptosis is invariably associated with inhibition of mitochondrial death signaling network. The latter is a function of a balance between the pro- and the anti-apoptotic members of the Bcl-2 family. Bcl-2 is the prototype anti-apoptotic protein that localizes to the mitochondria and blocks the recruitment and activation of pro-apoptotic proteins, such as Bax, to the mitochondria.

RECENT ADVANCES AND CRITICAL ISSUES

Recent evidence has highlighted a novel mechanism of anti-apoptotic activity of Bcl-2 in addition to its canonical activity in regulating mitochondrial outer membrane permeabilization. This novel activity is a function of cellular redox regulation, in particular, mitochondrial metabolism in cancer cells.

FUTURE DIRECTIONS

Here we review the current state of our understanding of the death inhibitory activity of Bcl-2 and provide insight into the novel functional biology of this remarkable protein, which could have implications for designing innovative strategies to overcome the problem of drug resistance in the clinical settings.

The role of stress proteins in prostate cancer

The development of therapeutic resistance, after hormone or chemotherapy for example, is the underlying basis for most cancer deaths. Exposure to anticancer therapies induces expression of many stress related proteins, including small heat shock proteins (HSPs). HSPs interact with various client proteins to assist in their folding and enhance the cellular recovery from stress, thus restoring protein homeostasis and promoting cell survival. The vents of cell stress and cell death are linked, as the induction of molecular chaperones appears to function at key regulatory points in the control of apoptosis. On the basis of these observations and on the role of molecular chaperones in the regulation of steroid receptors, kinases, caspases, and other protein remodelling events involved in chromosome replication and changes in cell structure, it is not surprising that molecular chaperones have been implicated in the control of cell growth and in resistance to various anticancer treatments that induce apoptosis. Recently, several molecular chaperones such as Clusterin and HSP27 have been reported to be involved in development and progression of hormone-refractory prostate cancer. In this review, we address some of the molecular and cellular events initiated by treatment induced stress, and discuss the potential role of chaperone proteins as targets for prostate cancer treatment.

Slow release and delivery of antisense oligonucleotide drug by self-assembled peptide amphiphile nanofibers

Antisense oligonucleotides provide a promising therapeutic approach for several disorders including cancer. Chemical stability, controlled release, and intracellular delivery are crucial factors determining their efficacy. Gels composed of nanofibrous peptide network have been previously suggested as carriers for controlled delivery of drugs to improve stability and to provide controlled release, but have not been used for oligonucleotide delivery. In this work, a self-assembled peptide nanofibrous system is formed by mixing a cationic peptide amphiphile (PA) with Bcl-2 antisense oligodeoxynucleotide (ODN), G3139, through electrostatic interactions. The self-assembly of PA-ODN gel was characterized by circular dichroism, rheology, atomic force microscopy (AFM) and scanning electron microscopy (SEM). AFM and SEM images revealed establishment of the nanofibrous PA-ODN network. Due to the electrostatic interactions between PA and ODN, ODN release can be controlled by changing PA and ODN concentrations in the PA-ODN gel. Cellular delivery of the ODN by PA-ODN nanofiber complex was observed by using fluorescently labeled ODN molecule. Cells incubated with PA-ODN complex had enhanced cellular uptake compared to cells incubated with naked ODN. Furthermore, Bcl-2 mRNA amounts were lower in MCF-7 human breast cancer cells in the presence of PA-ODN complex compared to naked ODN and mismatch ODN evidenced by quantitative RT-PCR studies. These results suggest that PA molecules can control ODN release, enhance cellular uptake and present a novel efficient approach for gene therapy studies and oligonucleotide based drug delivery.

Intrinsic Resistance to Chemotherapy in Breast Cancer

Systemic therapy improves disease-free survival in patients with breast cancer, but does not cure patients with advanced or metastatic disease, and fails to benefit the majority of patients with localized breast cancer. Intrinsic resistance to chemotherapy is emerging as a significant cause of treatment failure and evolving research has identified several potential causes of resistance, such as drug efflux pumps, disregulation of apoptosis and cancer stem cells. Building upon preclinical models, drugs designed to reverse resistance to therapy are currently under investigation in clinical trials for the treatment of breast cancer.

Overcoming drug resistance in patients with metastatic breast cancer

Metastatic breast cancer is generally considered to be incurable, with response rates and duration of response progressively declining with subsequent lines of treatment. Tumors are either intrinsically resistant to systemic therapy or acquire resistance at some point during multiple courses of therapy. Mechanisms of drug resistance are numerous and include accelerated drug efflux, drug activation and inactivation, alterations in drug target, processing of drug-induced damage, and evasion of apoptosis. Targeted anticancer agents for the treatment of breast cancer, such as hormonal agents or the more recently approved epidermal growth factor receptor inhibitors, are also associated with intrinsic and acquired resistance. A variety of strategies have been devised to prevent or overcome resistance to systemic anticancer therapy, including drug combinations and sequential regimens. However, it appears that resistance to established cytotoxic and targeted agents is inevitable. Novel agents with reduced susceptibility to resistance may prevent or delay the emergence of resistance and improve survival in patients with common solid tumors, including metastatic breast cancer. We are hopeful that further elucidation of the cellular and molecular processes that allow tumor cells to develop resistance and the use of new agents to combat these mechanisms will improve outcomes for patients with metastatic breast cancer.

Phase I/II study of G3139 (Bcl-2 antisense oligonucleotide) in combination with doxorubicin and docetaxel in breast cancer

PURPOSE

Preclinical data showed enhancement of breast cancer cell death when G3139 was combined with anthracyclines and taxanes. We evaluated the efficacy and safety of a Bcl-2 antisense oligonucleotide, G3139, in combination with doxorubicin (A) and docetaxel (T) in patients with locally advanced breast cancer (LABC).

EXPERIMENTAL DESIGN

Following a brief phase I to determine the phase II dose, patients with locally advanced breast cancer received G3139 administered by continuous i.v. infusion for 5 to 7 days with bolus A (50 mg/m2) and T (75 mg/m2) administered on either day 3 or 6 of therapy with G3139. Cycles were repeated every 21 days x 6 in the neoadjuvant setting. Serial plasma samples were obtained for pharmacokinetic analysis. Tissue samples were obtained before and after therapy for pharmacodynamic analysis of Bcl-2 expression.

RESULTS

Thirty patients (median age, 49 years; range, 24-71 years) received 160 cycles. During the phase I portion of the trial, the dose of G3139 was escalated from 3 to 7 mg/kg/d (i.v. for 5 days) in combination with AT. During the phase II portion of the trial, several doses and schedules of G3139 were evaluated. There were no pathologic complete responses. Pharmacodynamic studies showed limited Bcl-2 down-regulation in the primary tumors.

CONCLUSIONS

G3139 in combination with doxorubicin and docetaxel is well tolerated. No pathologic complete response was seen and pharmacodynamic studies showed very little down-regulation of Bcl-2 in primary tumors, perhaps related to issues with insufficient drug delivery to the intact tumor.

The effect of small interfering RNA (siRNA) against the Bcl-2 gene on apoptosis and chemosensitivity in a canine mammary gland tumor cell line

The aim of this study was to investigate whether downregulation of Bcl-2 expression by small interfering RNA (siRNA) against the canine Bcl-2 gene would enhance the apoptosis and sensitivity of a canine mammary gland tumor cell line (CF33) to doxorubicin. Transfections of CF33 with siRNA were performed using cationic liposomes. Sequence-specific downregulation of Bcl-2 expression was measured by semiquantitative RT-PCR and Western blot analysis. Total viable cells were determined by MTS assay and apoptotic cell rates were determined by the immunohistochemical analysis on ssDNA. Our data showed the siRNA downregulated Bcl-2 expression which increased apotosis and also increased the sensitivity of CF33 to doxorubicin. This study indicated that downregulation of Bcl-2 expression by siRNA would be useful as a new protocol to increase the effect of doxorubicin on treatment of canine mammary gland tumors, requiring a detailed evaluation of siRNA in vivo.

Prognostic value of the apoptosis related genes BCL2 and BCL2L12 in breast cancer

Many members of BCL2 (Bcl-2) apoptosis-related genes were found to be differentially expressed in various malignancies and were proposed as prognostic cancer biomarkers. Recently, a new member of the BCL2 gene family, BCL2L12, was cloned and was found to be expressed in mammary gland. In the present study, 55 specimens from patients with, histologically confirmed, epithelial breast carcinoma were analyzed for BCL2 and BCL2L12 gene expression by RT-PCR. Increased expression of BCL2 gene was found in patients belonging to the age groups <45 or >55 years, as well as in estrogen receptors (ER)-positive patients and in BCL2L12-positive tumors. In addition, BCL2 or BCL2L12-positive patients were found to be almost four times less likely to relapse or die in comparison to BCL2 or BCL2L12-negative patients, respectively. Multivariate analysis revealed that BCL2 and BCL2L12 might be used as independent prognostic biomarkers in breast cancer.

A label-free photonic crystal biosensor imaging method for detection of cancer cell cytotoxicity and proliferation

A label-free method for detecting the attachment of human cancer cells to a biosensor surface for rapid screening for biological activity is described, in which attachment of a cell results in highly localized increase of the resonant reflected wavelength of a photonic crystal narrowband reflectance filter incorporated into a standard 96-well microplate. An imaging detection instrument is used to determine the spatial distribution of attached cells by mapping the shift in reflected resonant wavelength as a function of position. The method enables monitoring of cancer cell attachment, cell proliferation, and cell detachment that is induced by exposure of the cells to drug compounds. We demonstrate the efficacy of this method as an early screening technique for the rapid quantification of the rate of cancer cell proliferation on the sensor surface, and subsequently as a means for quantifying cell detachment resulting from apoptosis that is induced by exposure of the cells to cytotoxic chemicals.

B cell translocation gene 1 contributes to antisense Bcl-2-mediated apoptosis in breast cancer cells

The antiapoptotic protein Bcl-2 is overexpressed in a majority of breast cancers, and is associated with a diminished apoptotic response and resistance to various antitumor agents. Bcl-2 inhibition is currently being explored as a possible strategy for sensitizing breast cancer cells to standard chemotherapeutic agents. Antisense Bcl-2 oligonucleotides represent one method for blocking the antiapoptotic effects of Bcl-2. In this study, we show that antisense Bcl-2 efficiently blocks Bcl-2 expression, resulting in the apoptosis of breast cancer cells. Antisense Bcl-2-mediated cytotoxicity was associated with the induction of the B cell translocation gene 1 (BTG1). Importantly, knockdown of BTG1 reduced antisense Bcl-2-mediated cytotoxicity in breast cancer cells. Furthermore, BTG1 expression seems to be negatively regulated by Bcl-2, and exogenous expression of BTG1 induced apoptosis. These results suggest that BTG1 is a Bcl-2-regulated mediator of apoptosis in breast cancer cells, and that its induction contributes to antisense Bcl-2-mediated cytotoxic effects.

Specific lipoplex-mediated antisense against Bcl-2 in breast cancer cells: a comparison between different formulations

G3139 is an antisense oligonucleotide (ODN) that can down-regulate bcl-2, thus potentially acting as a potent anticancer drug. However, effective therapy requires efficient ODN delivery, which may be achieved by employing G3139 lipoplexes. Yet, lipofection is a complex, multifactorial process that is still poorly understood. In order to shed more light on this issue, we prepared 18 different G3139 lipoplex formulations and compared them in terms of their capability to transfect MCF-7 breast cancer cells. Each formulation was composed of a cationic lipid and sometimes a helper lipid. The cationic lipid was either DOTAP (N-(1-(2,3-dioleoyloxy)propyl)-N,N,N-trimethylammonium chloride), DC-CHOL (3ss[N-(N',N'-dimethylaminoethane)carbamoyl]-cholesterol), or CCS (ceramide carbomoyl spermine). The helper lipid was either DOPC, DOPE, or cholesterol. Each lipid combination existed in two different structural forms--either large unilamellar vesicles (approximately 100 nm LUV) or unsized heterolamellar vesicles (UHV). Cell proliferation assays were used to evaluate the cytotoxicity of G3139 lipoplexes, control cationic lipid assemblies, and free G3139. Western blots were used to confirm the specific activity of G3139 as an anti-bcl-2 antisense agent. We determined that treatment of MCF-7 cells with G3139:CCS lipoplexes (UHV-derived) produced a maximal 50-fold improvement in antisense efficacy compared to treatment with free G3139. The other G3139 lipoplexes were not superior to free G3139. Thus, successful lipofection requires precise optimization of lipoplex lipid composition, structure, and concentration.

BCL2 family of apoptosis-related genes: functions and clinical implications in cancer

One of the most effective ways to combat different types of cancer is through early diagnosis and administration of effective treatment, followed by efficient monitoring that will allow physicians to detect relapsing disease and treat it at the earliest possible time. Apoptosis, a normal physiological form of cell death, is critically involved in the regulation of cellular homeostasis. Dysregulation of programmed cell death mechanisms plays an important role in the pathogenesis and progression of cancer as well as in the responses of tumours to therapeutic interventions. Many members of the BCL2 (B-cell CLL/lymphoma 2; Bcl-2) family of apoptosis-related genes have been found to be differentially expressed in various malignancies, and some are useful prognostic cancer biomarkers. We have recently cloned a new member of this family, BCL2L12, which was found to be differentially expressed in many tumours. Most of the BCL2 family genes have been found to play a central regulatory role in apoptosis induction. Results have made it clear that a number of coordinating alterations in the BCL2 family of genes must occur to inhibit apoptosis and provoke carcinogenesis in a wide variety of cancers. However, more research is required to increase our understanding of the extent to which and the mechanisms by which they are involved in cancer development, providing the basis for earlier and more accurate cancer diagnosis, prognosis and therapeutic intervention that targets the apoptosis pathways. In the present review, we describe current knowledge of the function and molecular characteristics of a series of classic but also newly discovered genes of the BCL2 family as well as their implications in cancer development, prognosis and treatment.

[Antisense therapy in oncology: present situation]

The purpose of antisense therapy is to control the regulation of genes contributing to cancer progression while sparing normal cell growth, which represents a novel alternative with fewer side effects when compared to conventional chemotherapy. Antisense oligonucleotides control cell proliferation by specifically blocking the expression of selected genes, and hence they are being developed as molecular drugs with potential activity for cancer treatment. Extensive clinical information and a number of clinical trials show encouraging results. This review discusses the most significant aspects of this new therapeutic alternative in oncology. Clinical trials performed thus far have demonstrated their short- to mid-term efficacy and safety; however, long-term studies are needed to definitely define their clinical effectiveness and true toxic profile.

G3139 and Other CpG-Containing Immunostimulatory Phosphorothioate Oligodeoxynucleotides Are Potent Suppressors of the Growth of Human Tumor Xenografts in Nude Mice

Several phosphorothioate antisense oligodeoxynucleotides (ODN) are developed to target factors potentially involved in tumor growth and apoptosis suppression. Among them, the 18-mer G3139 (Oblimersen), which targets Bcl-2, is currently being tested in phase II and phase III clinical trials for various tumors in combination with chemotherapy. On the other hand, ODNs containing CpG dinucleotides (CpG-ODN) within specific-sequence contexts (CpG motifs) have been shown to activate rodent or primate immune cells via toll-like receptor 9 (TLR9) and have demonstrated remarkable T cell-dependent antitumor efficacy in a series of murine tumor models. However, immune cell activation by CpG-ODN is largely diminished upon C-5 methylation at CpG cytosine. As G3139 contains CpG motifs, we questioned whether the antitumor effects seen in human tumor xenografts might be abrogated by cytosine C-5 methylation of G3139, which retained the ability of G3139 to suppress Bcl-2 expression in tissue culture, or by similar derivatization of other phosphorothioate ODNs developed for the immune activation of rodent or human cells. The in vivo antitumor efficacy of the immunostimulatory H1826 and H2006 ODNs was compared with that of G3139. Bcl-2 suppression achieved by G3139 purportedly sensitizes tumor cells toward cytotoxic agents, and some of the experiments employed combinations of ODN with such drugs as cisplatin or etoposide. H1826, H2006, and G3139 all produced similar, striking, growth inhibitory effects on either H69 SCLC, A2780 ovarian carcinoma, or A549 lung adenocarcinoma human tumor xenografts at doses of 0.3 mg/kg and 1 mg/kg (H1826, H2006) or 12 mg/kg (G3139) per day. In contrast, the H2006-mC (1 mg/kg) or G3139-mC (12 mg/kg) derivatives demonstrated no significant antitumor effects. The combination of G3139 (12 mg/kg) with cisplatin produced some additive antitumor efficacy, which was not seen in combinations of G3139-mC (12 mg/kg) or H1826 (1 mg/kg) with cisplatin. G3139, at a dose of 12 mg/kg, alone induced extensive enlargement of the spleen. Immunostimulation was evaluated in vitro by flow cytometric measurements of the CD80 and CD86 activation markers found on CD19+ murine splenocytes. The CpG-ODN producing strong antitumor effects in vivo also induced these activation markers in vitro, in contrast to the in vivo inactive G3139-mC. Our data indicate a significant contribution of the immunostimulatory properties of CpG-ODN (including G3139) to the antitumor effects observed in nude mouse xenograft models. This is in contrast to previous data presented by other authors indicating that the activity of G3139 in human tumor xenografts was Bcl-2 specific. Furthermore, as nude mice are devoid of T cells, a T cell-mediated immune response apparently is not required for the potent antitumor responses observed here; innate immune responses are sufficient.

Antisense Bcl-2 sensitizes prostate cancer cells to radiation

BACKGROUND

Bcl-2 is anti-apoptotic and overexpression is associated with prostate tumor aggressiveness. We hypothesized that Bcl-2 has a role in prostate cancer radiation (RT) response. The relationship of Bcl-2 expression in four prostate cancer cell lines, and the effect of modulating expression with a Bcl-2 antisense oligonucleotide (G3139, Genasense, oblimersen sodium, Genta Incorporated), to RT was examined.

METHODS

The four cell lines studied were LNCaP (wild type-p53), PC3 (p53 null), Bcl-2 stably transfected LNCaP (LNCaP-BST), and Bcl-2 stably transfected PC3 (PC3-BST) cells. Cells were treated with antisense (AS) Bcl-2 alone or with RT (2-6 Gy). Following RT, cells were processed at 3-6 hr for Western blots, 18 hr for Annexin V staining and flow cytometric analysis, 24 hr for caspases 3+7 quantification by fluorometric assay, and immediately for clonogenic survival.

RESULTS

AS caused a significant reduction in Bcl-2 expression in all cell lines. P53 expression was elevated following RT treatment in LNCaP and LNCaP-BST cells. P21 was increased by RT treatment in all cell lines. AS caused a significant increase in caspase 3+7 activity over the mismatch (MM) controls in all cell lines. When AS was combined with RT, caspase 3+7 activity was further increased significantly over all other groups in all cell lines. Moreover, AS+RT resulted in significantly reduced clonogenic survival over MM+RT, which was dampened in the Bcl-2 overexpressing lines.

CONCLUSIONS

To our knowledge, these data demonstrate for the first time that a Bcl-2 specific AS oligonucleotide sensitizes prostate cancer cells to RT. p53 is not required for this effect.

BCL-2 antisense and cisplatin combination treatment of MCF-7 breast cancer cells with or without functional p53

Chemotherapy has been used for treatment of breast cancer but with limited success. We characterized the effects of bcl-2 antisense and cisplatin combination therapy in two human isogenic breast carcinoma cells p53(+)MCF-7 and p53(-)MCF-7/E6. The transferrin-facilitated lipofection strategy we have developed yielded same transfection efficiency in both cells. Bcl-2 antisense delivered with this strategy significantly induced more cell death, apoptosis, and cytochrome c release in MCF-7/E6 than in MCF-7, but did not affect Fas level in both cells and activated caspase-8 equally. Cisplatin exerted same effects on cell viability and apoptosis in both cells, but released smaller amounts of cytochrome c while activated more caspase-8 in MCF-7/E6. The combination treatment yielded greater effects on cell viability, apoptosis, cytochrome c release, and caspase-8 activation than individual treatments in both cells although p53(-) cells were more sensitive. The potentiated activation of caspase-8 in the combination treatment suggested that caspase-8-mediated (but cytochrome c-independent) apoptotic pathway is the major contributor of the enhanced cell killing. Thus, bcl-2 antisense delivered with transferrin-facilitated lipofection can achieve the efficacy of killing breast cancer cells and sensitizing them to chemotherapy. Bcl-2 antisense and cisplatin combination treatment is a potentially useful therapeutic strategy for breast cancer irrespective of p53 status.

Relative Bcl-2 independence of drug-induced cytotoxicity and resistance in 518A2 melanoma cells

PURPOSE

Inhibition of the function of Bcl-2 protein has been postulated to sensitize cells to cytotoxic chemotherapy. G3139 (Genasense) is a phosphorothioate anti-Bcl-2 antisense oligonucleotide, but its mechanism of action is uncertain. The aim of the present work is to investigate inhibition of Bcl-2 expression in 518A2 melanoma cells, the cell line on which recent phase II and phase III clinical trials employing this agent were based.

EXPERIMENTAL DESIGN

We down-regulated the expression of Bcl-2 protein by two different strategies in these cells: one employing G3139 and controls, and the other using a small interfering RNA approach. Cell viability after treatment with oligonucleotides or small interfering RNA and cytotoxic agents including gemcitibine, DDP, docetaxel, and thapsigargin was measured by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. A 518A2 melanoma cell line stably overexpressing Bcl-2 protein was constructed and treated with either these cytotoxic agents or G3139.

RESULTS

The cytotoxic effects of either G3139 or small interfering RNA treatment of 518A2 melanoma cells are Bcl-2 independent. In addition, in the Bcl-2-overexpressing cells, only a modest increment in chemoresistance was observed, and treatment with G3139 not only did not down-regulate Bcl-2 expression but produced essentially identical toxicity as was observed in the wild-type or mock-transfected cells.

CONCLUSIONS

Our results suggest that the mechanism whereby G3139 produces drug-induced cytotoxicity in the 518A2 melanoma line is not dependent on levels of Bcl-2. These findings emphasize the nonsequence specific effects of this phosphorothioate oligonucleotide and call into question the validity of Bcl-2 as a target in this cell line.

Targeted therapy against Bcl-2-related proteins in breast cancer cells

Introduction

Bcl-2 and Bcl-xL confer resistance to apoptosis, thereby reducing the effectiveness of chemotherapy. We examined the relationship between the expression of Bcl-2 and Bcl-xL and chemosensitivity of breast cancer cells, with the aim of developing specific targeted therapy.

Methods

Four human breast cancer cell lines were examined, and the effects of antisense (AS) Bcl-2 and AS Bcl-xL phosphorothioate oligodeoxynucleotides (ODNs) on chemosensitivity were tested in vitro and in vivo. Chemosensitivity was evaluated by the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide) assay, and the antitumor effect was assessed in vivo by the success of xenograft transplantation into athymic mice.

Results

Treatment with AS Bcl-2 and Bcl-xL ODNs resulted in a sequence-specific decrease in protein expression, compared with controls. Treatment of BT-474, ZR-75-1, and MDA-MB-231 cells with AS Bcl-2 increased chemosensitivity to doxorubicin (DOX), mitomycin C (MMC), paclitaxel (TXL), and docetaxel (TXT). Transfection of the Bcl-2 gene into MDA-MB-453 cells decreased sensitivity to DOX and MMC. Treatment of MDA-MB-231, BT-474, and ZR-75-1 cells with AS Bcl-xL increased chemosensitivity to DOX, MMC and taxanes to a smaller extent than AS Bcl-2. This occurred in the setting of increased Bax and cleaved poly(ADP-ribose) polymerase, as well as decreased Bcl-2 and pAkt. AS Bcl-2 ODNs induced splenomegaly in association with increased serum IL-12, which was attenuated by methylation of the CpG motifs of AS Bcl-2; however, methylated CpG failed to negate the increased antitumor effect of AS Bcl-2. Bcl-2 and Bcl-xL, to a smaller extent, are major determinants of chemosensitivity in breast cancer cells.

Conclusion

Targeted therapy against Bcl-2 protein with the use of AS ODNs might enhance the effects of chemotherapy in patients with breast cancer.

Antitumor efficacy of bcl-2 and c-myc antisense oligonucleotides in combination with cisplatin in human melanoma xenografts: relevance of the administration sequence

PURPOSE

bcl-2 and c-myc oncogenes are frequently overexpressed in different human tumors, including melanoma. Here, we evaluate the combined efficacy of two antisense oligonucleotides targeting bcl-2 mRNA (ODN bcl-2) and c-myc mRNA (ODN c-myc) in combination with cis-diammine dichloroplatinum (cisplatin, DDP) on three human melanoma lines (LM, NG, and M20).

EXPERIMENTAL DESIGN

Two different sequences were designed to treat tumor-bearing mice: in the first one, ODN bcl-2 at a dose of 0.2 mg/day x4, followed by DDP given i.p. at a dose of 3.3 mg/kg/day x3 and ODN c-myc i.v. at 0.5 mg/day x7, whereas the other sequence consisted of ODN c-myc given as first agent followed by DDP and ODN bcl-2 at the same doses. Mice received three complete cycles of treatment in 1-week intervals.

RESULTS

The treatment sequence with ODN bcl-2/DDP/ODN c-myc combination completely inhibited growth in NG tumor and induced a 35-day delay in LM tumor growth. In contrast, the M20 tumor growth was unaffected by the combination. A discrete amount of c-Myc and bcl-2 protein expression in both LM and NG tumors was detected, whereas no detectable levels of the two proteins were observed in M20 tumors. Compared with the other combination, the sequence (ODN bcl-2/DDP/ODN c-myc) produced the most effective results, producing a significant decrease in bcl-2 and c-Myc protein expression, which in turn significantly increased the survival of NG- and LM-bearing mice, with 4 mice out of 11 and 1 out of 7 mice being cured, respectively. Finally, this combination increased the apoptotic rate and produced an antiangiogenetic effect.

CONCLUSIONS

These results show that an antisense approach to the treatment of melanoma xenografts overexpressing either bcl-2 or c-myc oncogenes represents a successful strategy to improve the response to chemotherapy in melanoma, with particular attention to the treatment sequence.

Antitumor efficacy of oblimersen Bcl-2 antisense oligonucleotide alone and in combination with vinorelbine in xenograft models of human non-small cell lung cancer

Overexpression of Bcl-2 protein in cancer cells can inhibit programmed cell death and engender chemoresistance. Reducing Bcl-2 protein levels by using antisense oligonucleotides targeting the gene message can increase the sensitivity of cancer cells to cytotoxic agents. The objective of this work was to investigate the antitumor efficacy of the Bcl-2 antisense oligonucleotide oblimersen (Genasense; G3139), alone and in combination with vinorelbine (VNB), in an ectopic and orthotopic xenograft model of NCI-H460 human non-small-cell lung cancer. In addition to assessing therapeutic effect, Bcl-2 protein expression in tumor tissue isolated from lung and heart was measured. In the ectopic xenograft model, oblimersen at 5 and 10 mg/kg significantly inhibited tumor growth compared with saline-treated control groups, and furthermore, the antitumor effect of oblimersen was associated with down-regulation of Bcl-2 protein in isolated tumor tissue. Moreover, the combination of oblimersen with VNB was more active in inhibiting tumor growth than either drug used alone. In the orthotopic model, oblimersen treatment (5 mg/kg) increased the median survival time of mice to 33 days in comparison with a median survival time of 21 days in the control animals. With this model, the anticancer effect was demonstrated by assessing tumor growth in lung and heart tissues by hematoxylin and eosin staining and Bcl-2 expression by immunohistochemistry. When VNB at 5 mg/kg was combined with oblimersen administered at 5 mg/kg, 33% of mice survived more than 90 days. These data suggest that the combination of oblimersen and VNB may provide enhanced antitumor activities against non-small-cell lung cancer.

Trastuzumab down-regulates Bcl-2 expression and potentiates apoptosis induction by Bcl-2/Bcl-XL bispecific antisense oligonucleotides in HER-2 gene--amplified breast cancer cells

PURPOSE

To investigate the possible existence of an antiapoptotic cross-talk between HER-2 and antiapoptotic Bcl-2 family members.

EXPERIMENTAL DESIGN

Bcl-2 and Bcl-XL expression and apoptosis induction were analyzed in HER-2 gene-amplified (BT474) and nonamplified (ZR 75-1) breast cancer cell lines exposed to trastuzumab, alone or in combination with either Bcl-2/Bcl-XL bispecific antisense oligonucleotides (AS-4625) or the small-molecule Bcl-2 antagonist HA14-1.

RESULTS

In addition to HER-2 and epidermal growth factor receptor, trastuzumab down-regulated Bcl-2, but not Bcl-XL, protein, and mRNA expression in BT474 cells. Interestingly, trastuzumab-induced down-regulation of HER-2 and Bcl-2 was also observed in three of five and two of three breast cancer patients undergoing trastuzumab treatment, respectively. Despite Bcl-2 down-regulation, however, trastuzumab only marginally increased the rate of apoptosis (7.3 +/- 3.5%). We therefore investigated whether a combination of AS-4625 and trastuzumab might increase proapoptotic efficiency. AS-4625 treatment of BT474 cells decreased both Bcl-2 and Bcl-XL expression, resulting in a 21 +/- 7% net apoptosis induction; the combination of AS-4625 followed by trastuzumab resulted in a significantly stronger induction of apoptosis (37 +/- 6%, P <0.01) that was not observed with the reverse treatment sequence (trastuzumab followed by AS-4625). Similar results were obtained with the Bcl-2 antagonist HA14-1; indeed, exposure of BT474 cells to HA14-1 followed by trastuzumab resulted in a striking proapoptotic synergism (combination index=0.58 +/- 0.18), as assessed by isobologram analysis.

CONCLUSIONS

Altogether our findings suggest that combined targeting of HER-2 and Bcl-2 may represent a novel, rational approach to more effective breast cancer therapy.

An antisense oligodeoxynucleotide-doxorubicin conjugate: preparation and its reversal multidrug resistance of human carcinoma cell line in vitro

An antisense oligodeoxynucleotide-doxorubicin conjugate was synthesized by an aminocaproic acid linker. The synthetic conjugate was identified by HPLC analysis and UV-vis spectra. Properties of the conjugate in vitro conditions were investigated. The results demonstrated that the conjugate was remarkably stabilized by doxorubicin. When incubated in Dulbecco Phosphate-Buflered Saline (pH 7.4) at 37 degrees C, the conjugate was more stable than doxorubicin or the mixture of doxorubicin and antisense oligodeoxynucleotide. When incubated in 10% fetal serum at 37 degrees C, the conjugate showed a remarkable stabilization as compared to the unmodified oligodeoxynucleotide. Melting experiments demonstrated that the covalent attachment of doxorubicin strongly stabilized the binding of the oligodeoxynucleotide to its complementary sequence. In addition, in vitro reversion of multidrug resistance by the conjugate was assayed in a human carcinoma cell line (KB-A-1) resisting to doxorubicin. The result showed that the conjugate displayed very high reversal multdrug resistance activity in KB-A-1 cells in vitro. The conjugate lowered the IC50 value from 21.5 microM to 2.2 microM with a fold-reversal factor of 10. In contrast, a slight decrease of the IC50 value was observed when they combined with the "free" antisense oligodeoxynucleotide: the IC50 value was down from 21.5 microM to 16.8 microM. This study suggested that antisense oligodeoxynucleotide-doxorubicin conjugate might be helpful in multidrug resistance reversal.

Bcl-2 inhibitors potentiate the cytotoxic effects of radiation in Bcl-2 overexpressing radioresistant tumor cells

PURPOSE

Bcl-2, an inhibitor of apoptosis frequently shows elevated expression in human tumors, thus resulting in resistance to radiation therapy. Therefore, inhibiting Bcl-2 function may enhance the radiosensitivity of tumor cells. Tetrocarcin A (TC-A) and bcl-2 antisense oligonucleotides exhibit antitumor activity by inhibiting Bcl-2 function and transcription, respectively. We investigated whether these antitumor agents would enhance the cytotoxic effects of radiation in tumor cells overexpressing Bcl-2.

METHODS AND MATERIALS

We used HeLa/bcl-2 cells, a stable Bcl-2-expressing cell line derived from wild-type HeLa (HeLa/wt) cells. Cells were incubated with TC-A and bcl-2 antisense oligonucleotides for 24 h after irradiation, and cell viability was then determined. Apoptotic cells were quantified by flow cytometric assay.

RESULTS

The HeLa/bcl-2 cells were more resistant to radiation than HeLa/wt cells. At concentrations that are not inherently cytotoxic, both TC-A and bcl-2 antisense oligonucleotides increased the cytotoxic effects of radiation in HeLa/bcl-2 cells, but not in HeLa/wt cells. However, in HeLa/bcl-2 cells, additional treatment with TC-A in combination with radiation did not significantly increase apoptosis.

CONCLUSIONS

The present results suggest that TC-A and bcl-2 antisense oligonucleotides reduce radioresistance of tumor cells overexpressing Bcl-2. Therefore, a combination of radiotherapy and Bcl-2 inhibitors may prove to be a useful therapeutic approach for treating tumors that overexpress Bcl-2.

Targeting Bcl-2 with oblimersen for patients with hormone refractory prostate cancer

Patients with metastatic hormone refractory prostate cancer (HRPC) have limited treatment options and new therapies are needed. Advances in the understanding of the molecular mechanisms implicated in prostate cancer progression have identified many potential therapeutic gene targets including Bcl-2, an important pro-survival regulator of apoptotic cell death. Bcl-2 is overexpressed in a variety of human malignancies including prostate cancer where it has also been associated with androgen independent progression and treatment resistance. Oblimersen is a phosphorothioate antisense oligonucleotide complimentary to the Bcl-2 mRNA and a potent inhibitor of Bcl-2 expression which in pre-clinical testing can significantly enhance the therapeutic effect of chemotherapy, hormone and radiation therapy. Clinical trials evaluating oblimersen in combination with chemotherapy in a variety of cancers have shown good tolerability and promising response rates. Randomized trials are required to determine if oblimersen can enhance the effectiveness of docetaxel in patients with HRPC.

Phosphorothioate oligodeoxynucleotides and G3139 induce apoptosis in 518A2 melanoma cells

In a previous study, we showed that G3139, an antisense phosphorothioate oligonucleotide that down-regulates the expression of Bcl-2 protein, did not cause chemosensitization of 518A2 melanoma cells. In this work, we show that G3139, and the 2-base mismatch, G4126, can initiate apoptosis in this and other melanoma cell lines as shown by increased cell surface Annexin V expression, typical nuclear phenotypic changes as assessed by 4′,6-diamidino-2-phenylindole staining, activation of caspase-3 (but not caspase-8) and Bid, appearance of DEVDase (but not IETDase) activity, and cleavage of poly(ADP-ribose)-polymerase 1. Depolarization of the mitochondrial membrane occurs as a relatively late event. All of these processes seem to be substantially, but perhaps not totally, Bcl-2 independent as shown by experiments employing an anti-Bcl-2 small interfering RNA, which as shown previously down-regulated Bcl-2 protein expression but did not produce apoptosis or chemosensitization in melanoma cells. In fact, these G3139-induced molecular events were not dramatically altered in cells that forcibly overexpressed high levels of Bcl-2 protein. Addition of irreversible caspase inhibitors (e.g., the pan-caspase inhibitor zVAD-fmk) to G3139-treated cells almost completely blocked cytotoxicity. Examination of the time course of the appearance of caspase-3 and cleaved poly(ADP-ribose)-polymerase 1 showed that this could be correlated with the release of cytochrome c from the mitochondria, an event that begins only ∼4 hours after the end of the oligonucleotide/LipofectAMINE 2000 5-hour transfection period. Thus, both G3139 and cytotoxic chemotherapy activate the intrinsic pathway of apoptosis in these cells, although Bcl-2 expression does not seem to contribute strongly to chemoresistance. These findings suggest that the attainment of G3139-induced chemosensitization in these cells will be difficult.

Apoptotic Pathways and Therapy Resistance in Human Malignancies

Apoptosis and necrosis are two morphologically distinct forms of cell death that are important for maintaining of cellular homeostasis. Almost all agents can provoke either response when applied to cells; however, the duration of treatment and the dose of the used agents determine which type of death (apoptosis or necrosis) is initiated. The response of tumors to chemo-, radio-, and hormone therapy or to treatment with biologically active agents may depend at least in part on the propensity of these tumors to undergo cell death. Some tumors, e.g., leukemias, small cell lung cancer, and seminomas, respond quickly to first-line therapy; this fast response is thought to result from induction of apoptosis. Solid tumors, on the other hand, usually respond slowly and less effectively, with cell death characterized not only by apoptosis but also by necrosis, or mitotic catastrophe. It is likely that resistance of tumors to treatment might be associated with defects in, or dysregulation of, different steps of the apoptotic pathways. Several attempts were undertaken to use the knowledge of these defects to design new drugs, which might either activate or re-activate the apoptotic machinery of tumor cells. Here we discuss the apoptotic pathways and their role in therapy resistance of human malignancies. Although such studies are still in progress, they offer great promise for future cancer therapy. We hope that some of these agents will turn out to be valuable additions to the future therapeutic arsenal, which will most probably include a combination of conventional cytotoxic drugs and molecular target-based pro-apoptotic drugs.

Changes in gene expression induced by phosphorothioate oligodeoxynucleotides (including G3139) in PC3 prostate carcinoma cells are recapitulated at least in part by treatment with interferon-beta and -gamma

PURPOSE

G3139 is an antisense bcl-2 phosphorothioate oligodeoxyribonucleotide that is currently being evaluated in Phase III clinical trials in several human cancers. The aim of the present work was to further identify the apparent non-bcl-2-dependent mechanism of this action of this compound in PC3 prostate cancer cells.

EXPERIMENTAL DESIGN

We performed Affymetrix U95A oligonucleotide microarray studies on mRNA isolated from cells treated with G3139 and related oligonucleotides.

RESULTS

Hierarchical clustering revealed the presence of a set of genes of which the expression was elevated on both 1 and 3 days after oligonucleotide treatment. Significantly, the persistence of expression of the up-regulation of these genes, many of which are members of the IFN cascade, was greater for G3139 than for any other oligomer evaluated. Furthermore, many of the genes with the greatest up-regulation of expression are also those of which the expression is up-regulated after treatment of cells with IFNs. Treatment of PC3 cells with either IFN-beta or -gamma recapitulated some of the aspects of the molecular and phenotypic changes observed after treatment with a G3139/Lipofectin complex. These include down-regulation of bcl-2 protein expression itself, down-regulation of protein kinase C alpha protein expression (but not that of other protein kinase C isoforms), alteration in p21/Waf1/Cip1 protein expression, up-regulation of MHC-I cell surface expression, and profound suppression of cell growth in the absence of a notable increase in cellular apoptosis. However, G3139 (when complexed with Lipofectin) did not induce the up-regulation of expression of either type I or type II IFNs, nor could IFNs be found in conditioned media from treated cells.

CONCLUSIONS

Oligonucleotide microarray experiments demonstrated that G3139 could induce elements of the IFN cascade in PC3 cells in vitro. In addition, the cellular phenotype obtained after treatment with exogenous IFN could, at least in part, recapitulate that obtained after G3139 treatment. Nevertheless, the oligonucleotide microarray experiments we performed also demonstrated that there are extremely large qualitative and quantitative differences between the two treatments.

Chemosensitization of breast carcinoma cells with the use of bcl-2 antisense oligodeoxynucleotide

This study was designed to observe whether the rates of apoptosis induced in the breast cancer cell line MCF-7 by 5-fluorouracil (5-FU) could be enhanced by transfecting bcl-2 antisense oligonucleotide (ASODN). In our experiment, bcl-2 ASODNs and control ODNs including untreated control, sense ODN and scrambled ODN, were transfected into MCF-7 cells. Changes in expression of the bcl-2 gene were examined by Western blot; cell growths were detected by MTT assay, and apoptosis rates were detected by flow cytometry (FCM). Expression of bcl-2 protein after transfection of bcl-2 ASODN was significantly lower than control ODNs. Moreover, incubation of MCF-7 with bcl-2 ASODN prior to 5-FU treatment caused remarkable loss of viable cells compared with all other control ODNs (P < 0.01). FCM showed the apoptosis rates for ASODN, untreated control, sense ODN and scrambled ODN (29.8 +/- 7.4)%, (8.0 +/- 2.3)%, (15.0 +/- 5.1)% and (16.5 +/- 7.1)%, respectively. Compared with control ODNs, ASODN achieved the strongest effect in terms of enhancing apoptosis (P < 0.01). These results suggest that combining bcl-2 ASODN with 5-FU led to synergistic cytotoxicity.

The role of Bcl-2 family members in tumorigenesis

The Bcl-2 family consists of about 20 homologues of important pro- and anti-apoptotic regulators of programmed cell death. The established mode of function of the individual members is to either preserve or disturb mitochondrial integrity, thereby inducing or preventing release of apoptogenic factors like Cytochrome c (Cyt c) from mitochondria. Recent findings also indicate further Bcl-2-controlled mitochondria-independent apoptosis pathways. Bcl-2 represents the founding member of the new and growing class of cell death inhibiting oncoproteins. In this review, we try to briefly summarize current models of Bcl-2 family function and to outline the work demonstrating the influence of deregulated Bcl-2 family member expression on tumorigenesis and cancer therapy. Since several Bcl-2 homologues, in addition to influencing apoptotic behaviour, also impinge on cell cycle progression, we discuss possible implications of this additional role for the expression of Bcl-2 family members in tumor cells.

The future of antisense therapy: combination with anticancer treatments

The current direction in cancer research is rational drug design, which is based on the evidence that transformed cells are characterized by alterations of genes devoted to the regulation of both cell proliferation and apoptosis. A variety of approaches have been carried out to develop new agents selective for cancer cells. Among these, antisense oligonucleotides (ASOs) are one of such class of new agents able to inhibit specifically the synthesis of a particular cancer-associated protein by binding to protein-encoding RNA, thereby preventing RNA function. In the past decade, several ASOs have been developed and tested in preclinical and clinical studies. Many have shown convincing in vitro reduction in target gene expression and promising activity against a wide variety of tumors. However, because of the multigenic alterations of tumors, the use of ASOs as single agents does not seem to be effective in the treatment of malignancies. Antisense therapy that interferes with signaling pathways involved in cell proliferation and apoptosis are particularly promising in combination with conventional anticancer treatment. An overview of the progress of ASOs used in combination therapy is provided.

Bcl-2 down-regulation is a novel mechanism of paclitaxel resistance

Taxanes act by inhibiting microtubule dynamics; in this study, we have investigated mitochondria as an additional target of taxanes. We incubated isolated mitochondria in the presence of taxanes with or without stimulation of the mitochondrial respiratory state. Results showed that they rapidly induced the loss of deltapsim after stimulation of the respiratory state. To evaluate the binding of [14C]paclitaxel to isolated mitochondria, mitochondrial proteins were precipitated yielding 18.6 +/- 2.1 cpm/microg of protein. After stimulation of the respiratory state, binding of [14C]paclitaxel increased up to 163.2 +/- 46.7 cpm/microg of protein. CPM values after Bcl-2 immunoprecipitation was 62.8-fold higher than those of the control antibody, thereby indicating the involvement of Bcl-2 in paclitaxel binding. Then, we established a panel of A2780 cell lines resistant to increasing doses of paclitaxel alone or to high doses of paclitaxel/cyclosporin A (A2780 TC cells). In both cases, Bcl-2 expression was consistently down-regulated, whereas levels of other members of the Bcl-2 family, such as Bax and Bcl-x, did not change in paclitaxel-resistant cell lines. When A2780TC cells were stably transfected with a Bcl-2 construct, paclitaxel sensitivity was partially restored, thereby supporting a direct role of Bcl-2 down-regulation in the maintenance of drug-resistance. Finally, we examined Bcl-2 by immunohistochemistry in a small subset of ovarian cancer paclitaxel-resistant patients and we noticed that the protein is down-regulated in this clinical setting with respect to the expression levels found in drug-sensitive tumors. These findings demonstrate that Bcl-2 is an additional intracellular target of taxanes and that its down-regulation is involved in taxane resistance.

Novel pharmacological approaches in the treatment of breast cancer

Breast cancer is the most common malignancy among women. Novel pharmacological agents, including hormonal, cytotoxic and biological therapies, are currently being developed and tested in clinical trials and may offer patients more treatment options and an improved chance of long-term survival. Signal transduction inhibitors that block endocrine or growth factor pathways have demonstrated exciting antitumour effects in clinical trials. In addition to new chemotherapeutic drugs, numerous biological agents including growth factor receptor-directed monoclonal antibodies and tyrosine kinase inhibitors that target specific molecular lesions are being examined as potential breast cancer treatments.

Human growth hormone-regulated HOXA1 is a human mammary epithelial oncogene

Increased mammary epithelial expression of the human growth hormone (hGH) gene is associated with the acquisition of pathological proliferation. We report here that autocrine hGH production by human mammary carcinoma cells increased the expression and transcriptional activity of the homeobox domain containing protein HOXA1. Forced expression of HOXA1 in human mammary carcinoma cells resulted in increased total cell number primarily by the promotion of cell survival mediated by the transcriptional up-regulation of Bcl-2. HOXA1 also abrogated the apoptotic response of mammary carcinoma cells to doxorubicin. Forced expression of HOXA1 in mammary carcinoma cells, in a Bcl-2-dependent manner, resulted in dramatic enhancement of anchorage-independent proliferation and colony formation in soft agar. Finally, forced expression of HOXA1 was sufficient to result in the oncogenic transformation of immortalized human mammary epithelial cells with aggressive in vivo tumor formation. Herein, we have therefore provided a molecular mechanism by which autocrine hGH stimulation of human mammary epithelial cells may result in oncogenic transformation.

Plasma protein binding, lipoprotein distribution and uptake of free and lipid-associated BCL-2 antisense oligodeoxynucleotides (G3139) in human melanoma cells

The objectives of this study were to determine the protein binding and lipoprotein distribution of G3139 and G3139 lipoplexes following incubation in human plasma, assess complement activation of, and the effect of pre-incubation of G3139 and G3139 lipoplexes in human plasma on in vitro cellular uptake of G3139. Effect of concentration and time on incorporation of free and lipid associated (lipoplexes) [3H]Bcl-2 AO (25-600 ng/ml) into normolipidemic human plasma lipoproteins was determined by density gradient ultracentrifugation after incubation at 37 degrees C for 5, 30, 60 and 120 min. Protein binding in the lipoprotein deficient fractions (LPDP) was determined by equilibrium dialysis. Complement interaction was determined by ELISA after exposure of human plasma to AO+/- liposomes prepared in serial dilution. In vitro uptake of G3139 and G3139 lipoplexes into human melanoma cells was assessed qualitatively by fluorescence microscopy after 4-h exposure to G3139 (free or as lipoplexes) with or without pre-incubation of G3139 in normal human plasma. Analysis of Bcl-2 AO-lipoprotein interaction over time and concentration indicated no significant movement of the compound within the different lipoprotein and LPDP fractions. Majority of drug was recovered within LPDP fraction, and more than 85% of drug recovered within LPDP fraction was protein bound. No significant activation of complement was noted for either free AO or lipoplexes. Pre-incubation of free AO or AO-lipoplexes in human plasma resulted in a greater cellular uptake of AO-lipoplexes compared with plasma free controls. These findings suggest that the majority of [3H]Bcl-2 AO is plasma protein bound with little lipoprotein association and no significant movement between different lipoprotein and LPDP fractions. Plasma protein binding other than lipoprotein binding may be responsible for the difference in cellular uptake of free AO vs. cationic lipoplexes.

Oblimersen Bcl-2 antisense: facilitating apoptosis in anticancer treatment

The components of the apoptotic program are targets for anticancer therapy. Bcl-2 protein inhibits apoptosis and confers resistance to treatment with traditional cytotoxic chemotherapy, radiotherapy, and monoclonal antibodies (mAb). Oblimersen sodium (G3139, Genasense, Genta Inc., Berkeley Heights, NJ) is an antisense oligonucleotide (AS-ON) compound designed to specifically bind to the first 6 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, multiple myeloma, malignant melanoma, and non-small cell lung cancer. In addition, nonrandomized trials are under way to evaluate oblimersen in non-Hodgkin's lymphoma, acute myeloid leukemia, and hormone-refractory prostate cancer. Preclinical data also support the clinical evaluation of oblimersen in additional tumor types, including chronic myelogenous leukemia and breast, small cell lung, gastric, colon, bladder, 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.

10th International Conference on gene therapy of cancer: 13 - 15 December 2001, San Diego, CA, USA

This annual meeting was organised by R Sobol and A Deisseroth (Sidney Kimmel Cancer Center, San Diego, CA, USA) and K Scanlon (Keck Graduate Institute, Claremont, CA, USA). The meeting covered a wide range of topics in cancer gene therapy and included five sessions. The topics were: (1) Tumour suppressors/apoptosis/antisense-ribozymes/angiogenesis; (2) Vector systems; (3) Therapy sensitisation/'suicide' gene therapy; (4) Haematopoietic gene transfer; and (5) Poster/discussion sessions. The following meeting highlights have focused mainly on the recent progress in antisense/ribozyme-based approaches useful for cancer gene target validation and drug development.

Oligonucleotide lipoplexes: the influence of oligonucleotide composition on complexation

Despite extensive investigations into oligonucleotide lipoplexes, virtually no work has addressed whether the physicochemical properties of these assemblies vary as a function of the constituent oligonucleotide (ODN) sequence and/or composition. The present study was aimed at answering this question. To this end, we complexed N-(1-(2,3-dioleoyloxy)propyl)-N,N,N-trimethylammonium chloride (DOTAP) liposomes, in dispersion, with either 18-mer phosphorothiote homo-oligonucleotides composed of either adenine, thymidine or cytosine; or one of three structurally related 18-mer phosphorothioate oligonucleotides (S-ODNs) (G3139, its reverse sequence and its two-base mismatch). After ODN addition to vesicles at different mole ratios, changes in pH and electrical surface potential at the lipid-water interface were analyzed by using the fluorophore heptadecyl-7-hydroxycoumarin while particle size distributions were analyzed by static-light scattering. The results indicate that each homo-oligonucleotide does indeed exhibit different complexation behavior. In particular, the maximal level of DOTAP neutralization by the polyadenine S-ODN is much lower than that for the two other homo-oligonucleotides and hence its lipoplex is much more positively charged. Much smaller electrostatic differences are also apparent between lipoplexes formed from each of the G3139-related ODNs. This paper identifies nucleotide base selection and sequence as a variable that can affect the physicochemical properties of oligonucleotide lipoplexes and hence probably their transfection competency.

Inhibition of potentially anti-apoptotic proteins by antisense protein kinase C-alpha (Isis 3521) and antisense bcl-2 (G3139) phosphorothioate oligodeoxynucleotides: relationship to the decreased viability of T24 bladder and PC3 prostate cancer cells

Isis 3521 and G3139 are 20- and 18-mer phosphorothioate oligonucleotides, respectively, targeted to the protein kinase C (PKC)-alpha and bcl-2 mRNAs. Treatment of T24 bladder and PC3 prostate carcinoma cells with full-length and 3'-truncation mutants of Isis 3521 causes down-regulation of PKC-alpha protein and mRNA. However, at the level of a 15-mer and shorter, down-regulation of mRNA expression is no longer observed. Further, no diminution in cellular viability, as measured by 3-(4,5-dimethylthiazol-2-yl)2,5-diphenyl tetrazolium bromide assay, in response to increasing concentrations of paclitaxel, can be observed for these shorter oligomers. These observations not only indicate that PKC-alpha protein expression can be down-regulated by both RNase H-dependent and -independent mechanisms but also that down-regulation of PKC-alpha is insufficient by itself to "chemosensitize" cells. G3139, which down-regulates bcl-2 protein and mRNA expression, also down-regulates PKC-alpha protein and mRNA expression but not that of PKC-betaI, -epsilon, or -zeta. However, the down-regulation of PKC-alpha and bcl-2 are not linked. When the carrier Eufectin 5 is employed, only bcl-2 is down-regulated in both T24 and PC3 cells at 50 nM oligonucleotide concentration. At 100 nM, both bcl-2 and PKC-alpha expression are down-regulated, and only at this concentration can "chemosensitization" to paclitaxel and carboplatin be observed. In contrast, the down-regulation of bcl-2 seems to be linked with that of RelA (p65). However, this too is also not sufficient for chemosensitization, even though it leads to the loss of expression of genes under the putative control of nuclear factor-kappaB and to detachment of the cells from plastic surfaces. These results underscore the complexity of the intracellular requirements for the initiation of chemosensitization to anti-neoplastic agents.