oblimersen and Prostatic-Neoplasms

Review the recent advances in the treatment of androgen independent prostate cancer (AIPC).. Review recent abstracts and literature utilizing Medline/PubMed using key words: androgen independent/hormone refractory prostate cancer, novel treatment options, Phase II, III trials and meeting abstracts/presentations.. Two pivotal trials SWOG (Southwest Oncology Group) study 9916 and Taxotere 327 have shown that survival can be improved in this population by administration of chemotherapy with docetaxel every three weeks intravenously. An overall survival of 19 months could be achieved with docetaxel/prednisone compared to 16 months with mitoxantrone/prednisone. Despite this, there is a need to improve on this survival benefit because the relapse free survival among responders is often short (6 months) and patients often would have progression of their cancer leading to death. Satraplatin, a novel platinum analogue had been found to provide an additional 1.5 week progression free survival benefit in this population in the second line setting. There is however, a need to develop less toxic drugs that would improve survival significantly.

Topics: Adenocarcinoma; Animals; Antibodies, Monoclonal; Antibodies, Monoclonal, Humanized; Antineoplastic Agents, Phytogenic; Antineoplastic Combined Chemotherapy Protocols; Atrasentan; Benzamides; Benzenesulfonates; Bevacizumab; Calcitriol; Cancer Vaccines; Docetaxel; Drug Screening Assays, Antitumor; Epothilones; Forecasting; Humans; Imatinib Mesylate; Male; Niacinamide; Phenylurea Compounds; Piperazines; Prostatic Neoplasms; Pyridines; Pyrimidines; Pyrrolidines; Randomized Controlled Trials as Topic; Salvage Therapy; Sorafenib; Taxoids; Thionucleotides

The identification of activated oncogenes, such as the bcl-2, in several types of cancer has made it possible to consider such genes as targets for antitumor therapy. Bcl-2 is an anti-apoptotic protein, whose overexpression is associated with chemotherapy resistant cancer, aggressive clinical course and poor survival. The development of novel targeted gene-silencing strategies, such as those based on the use of antisense oligonucleotides, represents a renewed hope in the treatment of cancer. Within this scope, this review covers the main pre-clinical aspects and the most recent clinical data obtained with Oblimersen sodium (Genta Inc.). Oblimersen is a 18-mer phosphorothioate antisense oligonucleotide designed to bind to the first six codons of the human bcl-2 mRNA. Phase I/II trials indicate that infusion of Oblimersen provides biologically relevant plasma levels that lead to downregulation of target Bcl-2 protein. Moreover, the use of Oblimersen in combination with chemotherapy in a variety of cancers has shown promising response rates with good tolerability. Randomized phase III trials are currently underway to evaluate whether the combined use of Oblimersen with standard treatment is superior to standard treatment alone in chronic lymphocytic leukaemia, malignant melanoma and multiple myeloma. Overall, the enhanced efficacy of anticancer treatments of this bcl-2-targeted antisense therapy represents a promising new apoptosis-modulating strategy.

Topics: Breast Neoplasms; Carcinoma, Small Cell; Clinical Trials as Topic; Colorectal Neoplasms; Down-Regulation; Drug Therapy, Combination; Female; Humans; Leukemia, Lymphocytic, Chronic, B-Cell; Leukemia, Myeloid, Acute; Lymphoma, Non-Hodgkin; Male; Melanoma; Oligonucleotides, Antisense; Prostatic Neoplasms; Proto-Oncogene Proteins c-bcl-2; Thionucleotides

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.

Topics: Apoptosis; Gene Targeting; Genes, bcl-2; Humans; Male; Prostatic Neoplasms; Thionucleotides

Topics: Animals; Antineoplastic Agents; Humans; Lymphoma, Non-Hodgkin; Male; Melanoma; Neoplasms; Oligonucleotides, Antisense; Prostatic Neoplasms; Thionucleotides

This randomized, phase II study assessed the activity of oblimersen sodium, a Bcl-2 antisense oligonucleotide, administered before docetaxel (Taxotere) to patients with castration-resistant prostate cancer.. Chemotherapy-naive patients with prostate-specific antigen (PSA) progression and testosterone < or = 0.5 ng/ml received docetaxel 75 mg/m2 on day 1 or oblimersen 7 mg/kg/day continuous i.v. infusion on days 1-7 with docetaxel 75 mg/m2 on day 5 every 3 weeks for < or = 12 cycles. Primary end points were confirmed PSA response (Bubley criteria) and major toxic events.. Confirmed PSA response was observed in 46% and 37% of 57 and 54 patients treated with docetaxel and docetaxel-oblimersen, respectively. Partial response (RECIST) was achieved in 18% and 24%, respectively. Oblimersen added to docetaxel was associated with an increase in the incidence of grade > or = 3 fatigue, mucositis, and thrombocytopenia. Major toxic events were reported in 22.8% and 40.7% of patients with docetaxel and docetaxel-oblimersen, respectively.. The primary end points of the study were not met: a rate of confirmed PSA response >30% and a major toxic event rate <45% were not observed with docetaxel-oblimersen.

Topics: Aged; Aged, 80 and over; Antineoplastic Combined Chemotherapy Protocols; Castration; Docetaxel; Dose-Response Relationship, Drug; Drug Administration Schedule; Humans; Infusions, Intravenous; Male; Middle Aged; Prostate-Specific Antigen; Prostatic Neoplasms; Taxoids; Thionucleotides; Treatment Outcome

To determine the antitumor activity and safety of oblimersen sodium, a phosphorothioate antisense oligonucleotide directed to the bcl-2 mRNA, with docetaxel in patients with hormone-refractory prostate cancer (HRPC) and to determine if relevant pharmacokinetic and pharmacodynamic variables of oblimersen or docetaxel influence response to this therapy.. Patients with HRPC were treated with oblimersen sodium by continuous i.v. infusion on days 1 to 8 with docetaxel given i.v. over 1 hour on day 6 every 3 weeks. Plasma samples were analyzed to characterize the pharmacokinetic variables of both oblimersen and docetaxel, and paired collections of peripheral blood mononuclear cells were collected to determine Bcl-2 protein expression pretreatment and post-treatment.. Twenty-eight patients received 173 courses of oblimersen (7 mg/kg/d continuous i.v. infusion on days 1-8) and docetaxel (75 mg/m(2) i.v. on day 6). Prostate-specific antigen responses were observed in 14 of 27 (52%) patients, whereas 4 of 12 (33%) patients with bidimensionally measurable disease had objective responses. The mean oblimersen steady-state concentration (C(ss)) was a significant determinant of antitumor activity; mean C(ss) values were higher in responders compared with nonresponders (6.24 +/- 1.68 versus 4.27 +/- 1.22; P = 0.008). The median survival of all patients was 19.8 months. Bcl-2 protein expression decreased a median of 49.9% in peripheral blood mononuclear cells post-treatment, but the individual incremental change did not correlate with either oblimersen C(ss) or response.. Oblimersen combined with docetaxel is an active combination in HRPC patients demonstrating both an encouraging response rate and an overall median survival. The absence of severe toxicities at this recommended dose, evidence of Bcl-2 protein inhibition, and encouraging antitumor activity in HPRC patients warrant further clinical evaluation of this combination, including studies to optimize oblimersen C(ss).

Topics: Adult; Aged; Aged, 80 and over; Antineoplastic Agents, Hormonal; Antineoplastic Combined Chemotherapy Protocols; Docetaxel; Drug Resistance, Neoplasm; Humans; Male; Middle Aged; Oligonucleotides, Antisense; Prostatic Neoplasms; Proto-Oncogene Proteins c-bcl-2; Survival Analysis; Taxoids; Thionucleotides; Treatment Outcome

To assess the feasibility of administering oblimersen sodium, a phosphorothioate antisense oligonucleotide directed to the Bcl-2 mRNA, with docetaxel to patients with hormone-refractory prostate cancer; to characterize the pertinent pharmacokinetic parameters, Bcl-2 protein inhibition in peripheral blood mononuclear cell(s) (PBMC) and tumor; and to seek preliminary evidence of antitumor activity.. Patients were treated with increasing doses of oblimersen sodium administered by continuous i.v. infusion on days 1 to 6 and docetaxel administered i.v. over 1 h on day 6 every 3 weeks. Plasma was sampled to characterize the pharmacokinetic parameters of both oblimersen and docetaxel, and Bcl-2 protein expression was measured from paired collections of PBMCs pretreatment and post-treatment.. Twenty patients received 124 courses of the oblimersen and docetaxel combination at doses ranging from 5 to 7 mg/kg/day oblimersen and 60 to 100 mg/m(2) docetaxel. The rate of severe fatigue accompanied by severe neutropenia was unacceptably high at doses exceeding 7 mg/kg/day oblimersen and 75 mg/m(2) docetaxel. Nausea, vomiting, and fever were common, but rarely severe. Oblimersen mean steady-state concentrations were 3.44 +/- 1.31 and 5.32 +/- 2.34 at the 5- and 7-mg/kg dose levels, respectively. Prostate-specific antigen responses were observed in 7 of 12 taxane-naïve patients, but in taxane-refractory patients no responses were observed. Preliminary evaluation of Bcl-2 expression in diagnostic tumor specimens was not predictive of response to this therapy.. The recommended Phase II doses for oblimersen and docetaxel on this schedule are 7 mg/kg/day continuous i.v. infusion days 1 to 6, and 75 mg/m(2) i.v. day 6, respectively, once every 3 weeks. The absence of severe toxicities at this recommended dose, evidence of Bcl-2 protein inhibition in PBMC and tumor tissue, and encouraging antitumor activity in HPRC patients warrant further clinical evaluation of this combination.

Topics: Aged; Antineoplastic Agents; Area Under Curve; Biopsy; Docetaxel; Dose-Response Relationship, Drug; Drug Resistance, Neoplasm; Humans; Immunohistochemistry; Infusions, Intravenous; Leukocytes, Mononuclear; Male; Middle Aged; Oligonucleotides, Antisense; Phosphorylation; Prostate-Specific Antigen; Prostatic Neoplasms; Proto-Oncogene Proteins c-bcl-2; RNA, Messenger; Taxoids; Thionucleotides; Time Factors

The transition from androgen-dependent to androgen-independent prostate cancer is accompanied by a number of molecular genetic changes, including overexpression of the bcl-2 gene. Overexpression of Bcl-2 protein decreases the pro-apoptotic response to such cellular insults as irradiation, chemotherapy, and androgen withdrawal. Reduction of Bcl-2 expression in hormone-refractory prostate cancer (HRPC) preclinical models markedly increases the antitumor efficacy of docetaxel both in vitro and in vivo. Thus, a phase I/II pharmacokinetic and biologic correlative study has been initiated in patients with HRPC to examine whether docetaxel therapy can be enhanced with a therapeutic antisense oligodeoxynucleotide (G3139) directed at bcl-2 gene expression. Semin Oncol 28 (suppl 15):67-70.

Topics: Aged; Antineoplastic Agents; Docetaxel; Genes, bcl-2; Humans; Male; Middle Aged; Oligonucleotides, Antisense; Paclitaxel; Prostatic Neoplasms; Taxoids; Thionucleotides

Bcl-2 is a negative prognostic indicator in prostate cancer, implicated in the development of androgen independence and treatment resistance, and is overexpressed in hormone-refractory prostate cancer (HRPC). Genasense is a phosphorothioate antisense oligonucleotide complementary to the bcl-2 mRNA open reading frame that in preclinical studies has shown significant activity in inhibiting expression of Bcl-2, delaying androgen independence, and improving chemosensitivity in prostate and other cancer models. In this dose escalation study, we evaluated the combination of Genasense and mitoxantrone, a standard chemotherapy for patients with HRPC.. Twenty-six patients with HRPC were treated at seven dose levels receiving Genasense at a dose ranging from 0.6 to 5.0 mg/kg/day and mitoxantrone from 4 mg/m(2) to 12 mg/m(2). Genasense was administered as a 14-day i.v. continuous infusion every 28 days with mitoxantrone given as an i.v. bolus on day 8.. No dose-limiting toxicities were observed. Hematological toxicities were transient and included neutropenia, thrombocytopenia, and lymphopenia. Nonhematological toxicities included fatigue, fever, nausea, arthralgias, myalgias, and transient elevations in serum creatinine, none of which were severe. Two patients had >50% reductions in prostate-specific antigen. One patient, who received six cycles of Genasense at 1.2 mg/kg/day and a low dose (4 mg/m(2)) of mitoxantrone, also had symptomatic improvement in bone pain. Peripheral blood lymphocyte Bcl-2 protein expression decreased in five of five patients given Genasense at 5mg/kg/day (mean change from baseline, -12.8%; SD, 16.4%) as assessed by flow cytometry. Serum concentrations of Genasense given at doses of 3 mg/kg/day and greater, exceeded 1 microg/ml.. Genasense and mitoxantrone are well tolerated in combination, and mitoxantrone can be delivered at a standard dose with biologically active doses of Genasense without significant additional toxicity. This observation allays concerns about trials that combine Genasense with full doses of other cytotoxic agents seeking greater evidence of activity.

Topics: Aged; Antineoplastic Agents; Antineoplastic Combined Chemotherapy Protocols; Disease Progression; Dose-Response Relationship, Drug; Humans; Male; Middle Aged; Mitoxantrone; Neoplasm Metastasis; Patient Selection; Prostatic Neoplasms; Proto-Oncogene Proteins c-bcl-2; Thionucleotides

Prostate cancer is the most frequent malignancy of the male population. Every year in Germany approximately 12,000 patients die of their hormone-refractory prostate cancer even though early detection is able to find more curable prostate cancers. In a hormone-refractory stage we only have limited options for treatment. Although docetaxel is currently the standard of care in most hormone-refractory prostate cancers, it is not the magic therapy that will dramatically change the patient's poor survival. This drug provides an overall survival advantage of 2 months. During recent years, significant progress has been made in the field of molecular therapy in urologic oncology. Targeted therapy leads to an inhibition of angiogenesis and proliferation in malignant tumors. Even if there is a great theoretical potential, mono- and combination therapies with target substances are not relevant in the clinical routine.

Topics: Angiogenesis Inhibitors; Antineoplastic Agents; Atrasentan; Calcitriol; Drug Delivery Systems; Humans; Male; Neoplasm Staging; Prostatic Neoplasms; Protein-Tyrosine Kinases; Pyrrolidines; Sirolimus; Survival Rate; Thionucleotides

Topics: Antineoplastic Agents; Docetaxel; Humans; Male; Mitoxantrone; Organoplatinum Compounds; Prostatic Neoplasms; Randomized Controlled Trials as Topic; Taxoids; Thionucleotides; Tissue Extracts

To investigate whether irradiation before antisense Bcl-2 oligodeoxynucleotide (ODN) administration enhances tissue uptake, and whether periodic dosing enhances cellular uptake of fluorescently labeled ODN relative to constant dosing.. PC-3-Bcl-2 cells (prostate cancer cell line engineered to overexpress Bcl-2) were subjected to increasing doses of irradiation (0-10 Gy) with or without increasing concentrations of fluorescently labeled antisense Bcl-2 ODN (G4243). The fluorescent signal intensity was quantified as the total grain area with commercial software. In addition, PC-3-Bcl-2 subcutaneous xenograft tumors were treated with or without irradiation in combination with various dosing schemas of G4243. The uptake of fluorescent G4243 in tumors was quantitated.. The uptake of G4243 was increased in prostate cancer cells exposed to low doses of irradiation both in vitro and in vivo. Irradiation before G4243 treatment resulted in increased fluorescent signal intensity in xenograft tumors compared with those irradiated after G4243 treatment. A single weekly dose of G4243 produced higher G4243 uptake in xenograft tumors than daily dosing, even when the total dose administered per week was held constant.. These findings suggest that ionizing radiation increases the uptake of therapeutic ODN in target tissues and, thus, has potential to increase the efficacy of ODN in clinical applications.

Topics: Animals; Cell Line, Tumor; Combined Modality Therapy; Fluorescence; Male; Mice; Mice, Inbred BALB C; Mice, Nude; Oligonucleotides, Antisense; Prostatic Neoplasms; Radiation Dosage; Thionucleotides; Transplantation, Heterologous

The response of hormone-refractory prostate cancer (HRPC) to chemotherapy remains modest, necessitating the search for new forms of treatment to improve the prognosis. Since an increased expression of oncogenes, including c-myc and bcl-2, accompanies the transition to HRPC, we evaluated whether the concomitant downregulation of these oncogenes by antisense strategy sensitized HRPC to chemotherapy.. PC-3 prostate cancer cells were exposed in vitro to c-myc (INX-6295) and bcl-2 (G3139) antisense oligodeoxynucleotides (ODNs) and docetaxel given alone or in combination. Therapeutic efficacy of the different treatments was also evaluated in xenografts.. We show that the triple combination of drugs given in the sequence G3139/docetaxel/INX-6295 was the most active in reducing the survival of PC-3. Likewise, the combination triggered apoptosis in more than 80% of cells. A marked tumor weight inhibition was observed in PC-3 xenografts after G3139/docetaxel/INX-6295 treatment, with a complete tumor regression being noted in half the mice. A 111% overall increase in life survival and a complete cure in two out of eight mice was also reported. This treatment remained effective even when started at a very late stage of tumor growth producing about 80% tumor weight inhibition (TWI), with tumor regression being maintained for 1 month. Finally, the antitumor effect resulted in a significant increase (70%) in mice survival.. These data indicate that the combined targeting of genes involved in uncontrolled proliferation and evasion of apoptosis renders HRPC responsive to chemotherapy making this treatment a promising antineoplastic strategy.

Topics: Animals; Antineoplastic Combined Chemotherapy Protocols; Apoptosis; Blotting, Western; Cell Line, Tumor; Cell Proliferation; Docetaxel; Humans; In Situ Nick-End Labeling; Kaplan-Meier Estimate; Male; Mice; Mice, Nude; Oligodeoxyribonucleotides; Oligonucleotides, Antisense; Prostatic Neoplasms; Proto-Oncogene Proteins c-bcl-2; Proto-Oncogene Proteins c-myc; Taxoids; Thionucleotides

G3139 is a phosphorothioate oligodeoxyribonucleotide that is targeted to the initiation codon region of the Bcl-2 mRNA, which downregulates Bcl-2 protein and mRNA expression via an antisense mechanism. In previous work, we have demonstrated that the phenotype observed in several prostate and melanoma cell lines after treatment with G3139 appears to be Bcl-2 independent. In contrast, downregulation of Bcl-2 expression by a small interfering RNA (siRNA) produced little or no phenotype change. In the present work, we performed an Agilent oligonucleotide microarray assay on mRNA isolated from PC3 prostate cancer cells that were treated with two different oligonucleotide gene-silencing reagents. G3139 and a Bcl-2-targeting siRNA both downregulate Bcl-2 expression, but via different mechanisms. A side-by-side comparative analysis showed that the expression profile generated by these molecules differs substantially. The study revealed upregulation of the expression of stress-inducible genes in PC3 cells at 1 and 3 days after a 5-h transfection with G3139 complexed with Lipofectamine 2000. In contrast, only a very diminished stress response was seen 1 and 3 days after a 24-h transfection of siRNA/Lipofectamine 2000 complexes. These results highlight the profound differences in off-target effects in cells treated with the phosphorothioate oligonucleotide G3139 and with an siRNA targeted to the same gene, and provide further evidence that the mechanism of action of G3139 is not related to Bcl-2 silencing.

Topics: Cell Line, Tumor; Cell Proliferation; Gene Expression Profiling; Gene Expression Regulation, Neoplastic; Gene Silencing; Humans; Male; Oligonucleotide Array Sequence Analysis; Prostatic Neoplasms; Proto-Oncogene Proteins c-bcl-2; RNA Interference; RNA, Small Interfering; Thionucleotides; Time Factors; Transfection

Inhibition of the function of the bcl-2 protein has been postulated to sensitize cells to cytotoxic chemotherapy, and thus provides an attractive target for investigative therapies. G3139, a phosphorothioate antisense oligonucleotide targeted to the initiation codon region of the bcl-2 mRNA, is currently being evaluated in several Phase II and Phase III clinical trials. However, the mechanism of action of this molecule appears to depend on a combination of antisense plus nonantisense events. Indeed, the very idea that bcl-2 is a critical target is, at least in part, an extrapolation from experiments in which intracellular bcl-2 protein concentrations have been dramatically increased, yielding chemoresistant cells.. In this work, we down-regulated the expression of bcl-2 protein by 80-90% by two different antisense RNA strategies (antisense RNA and small interfering RNA) in DU145 prostate cancer cells.. Even after down-regulation of bcl-2 protein expression by either one of these strategies, the cellular phenotype induced by subsequent G3139 treatment (inhibition of cellular growth and the generation of reactive oxygen species) was essentially identical to that induced in mock-infected or wild-type DU145 cells in which bcl-2 protein expression had not been down-regulated previously.. These results strongly suggest that bcl-2 expression in DU145 cells is not strongly associated with the prolife phenotype and that the mechanism by which G3139 produces its cytostatic effects in this cell line is bcl-2 independent.

Topics: Apoptosis; Catalase; Cell Cycle; Cell Division; Cell Line, Tumor; Down-Regulation; Flow Cytometry; Humans; Inhibitor of Apoptosis Proteins; Male; Oligonucleotides; Prostatic Neoplasms; Protein Kinase C; Protein Kinase C-alpha; Proteins; Proto-Oncogene Proteins c-bcl-2; Reactive Oxygen Species; RNA, Antisense; RNA, Messenger; RNA, Small Interfering; Thionucleotides; Time Factors

G3139 is an 18-mer phosphorothioate oligodeoxyribonucleotide, which is targeted to the initiation codon region of the bcl-2mRNA. Although treatment of PC3 prostate cancer cells with G3139, which contains two CpG motifs, causes a dramatic decrease in bcl-2 protein expression after 3 days, it did not result in significant cellular apoptosis, as it does in many other cell lines. The absence of apoptosis was demonstrated by the absence of pro-caspase 3 cleavage products and of Annexin V cell surface expression. In addition, ATP production and the mitochondrial membrane potential DeltaPsim were preserved. Despite this, G3139 significantly inhibited the rate of cellular proliferation in complete media and blocked cloning in soft agar. G4232, a variant of G3139 that down-regulates bcl-2 expression to the same extent but has both CpG cytidines C5 methylated, was only minimally antiproliferative. A series of mismatched G3139-related oligomers were synthesized that could also substantially down-regulate bcl-2 protein expression, but only if the CpG motifs were preserved, demonstrating the presence of additional non-antisense mechanisms. G3139 caused production of reactive oxygen species in growth-arrested cells and oxidation of nuclear guanosine to 8-hydroxy-2'-deoxyguanosine, as determined by 1F7 monoclonal antibody staining. Bromodeoxyuridine incorporation studies demonstrated that G3139 induced a G1-S entry block and an intra-S-phase block in PC3 cells that persisted as long as 3 days. This finding coincides with the observation that expression of several proteins encoded by S-phase genes, including c-myb and poly(ADP-ribose) polymerase, were significantly reduced. These results illustrate the complexity of the mechanism of action of G3139 in PC3 cells.

Topics: Agar; Amino Acid Motifs; Annexin A5; Blotting, Northern; Blotting, Western; Bromodeoxyuridine; Cell Cycle; Cell Division; Cell Line, Tumor; Cell Membrane; Coloring Agents; CpG Islands; DNA; DNA Methylation; Down-Regulation; Enzyme Inhibitors; Flow Cytometry; G1 Phase; Guanosine; Humans; Male; Membrane Potentials; Mitochondria; Mutation; Oligonucleotides; Oligonucleotides, Antisense; Poly(ADP-ribose) Polymerases; Prostatic Neoplasms; Reactive Oxygen Species; S Phase; Thionucleotides; Time Factors; Transfection

Topics: Antineoplastic Agents, Phytogenic; Clinical Trials as Topic; Humans; Male; Portugal; Prostate-Specific Antigen; Prostatic Neoplasms; Thionucleotides; Vinblastine; Vinorelbine

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.

Topics: Antineoplastic Agents, Phytogenic; Apoptosis; Cell Survival; Down-Regulation; Gene Deletion; Humans; Isoenzymes; Male; NF-kappa B; Oligodeoxyribonucleotides, Antisense; Paclitaxel; Prostatic Neoplasms; Protein Kinase C; Protein Kinase C-alpha; Proto-Oncogene Proteins c-bcl-2; Ribonuclease H; RNA, Messenger; Thionucleotides; Transcription Factor RelA; Tumor Cells, Cultured; Urinary Bladder Neoplasms