Inhibitory effects of the nucleoside analogue gemcitabine on prostatic carcinoma cells

The CHK1 inhibitor MU380 significantly increases the sensitivity of human docetaxel-resistant prostate cancer cells to gemcitabine through the induction of mitotic catastrophe

As treatment options for patients with incurable metastatic castration-resistant prostate cancer (mCRPC) are considerably limited, novel effective therapeutic options are needed. Checkpoint kinase 1 (CHK1) is a highly conserved protein kinase implicated in the DNA damage response (DDR) pathway that prevents the accumulation of DNA damage and controls regular genome duplication. CHK1 has been associated with prostate cancer (PCa) induction, progression, and lethality; hence, CHK1 inhibitors SCH900776 (also known as MK-8776) and the more effective SCH900776 analog MU380 may have clinical applications in the therapy of PCa. Synergistic induction of DNA damage with CHK1 inhibition represents a promising therapeutic approach that has been tested in many types of malignancies, but not in chemoresistant mCRPC. Here, we report that such therapeutic approach may be exploited using the synergistic action of the antimetabolite gemcitabine (GEM) and CHK1 inhibitors SCH900776 and MU380 in docetaxel-resistant (DR) mCRPC. Given the results, both CHK1 inhibitors significantly potentiated the sensitivity to GEM in a panel of chemo-naïve and matched DR PCa cell lines under 2D conditions. MU380 exhibited a stronger synergistic effect with GEM than clinical candidate SCH900776. MU380 alone or in combination with GEM significantly reduced spheroid size and increased apoptosis in all patient-derived xenograft 3D cultures, with a higher impact in DR models. Combined treatment induced premature mitosis from G1 phase resulting in the mitotic catastrophe as a prestage of apoptosis. Finally, treatment by MU380 alone, or in combination with GEM, significantly inhibited tumor growth of both PC339-DOC and PC346C-DOC xenograft models in mice. Taken together, our data suggest that metabolically robust and selective CHK1 inhibitor MU380 can bypass docetaxel resistance and improve the effectiveness of GEM in DR mCRPC models. This approach might allow for dose reduction of GEM and thereby minimize undesired toxicity and may represent a therapeutic option for patients with incurable DR mCRPC.

Development of potent CPP6-gemcitabine conjugates against human prostate cancer cell line (PC-3)

Gemcitabine (dFdC) is a nucleoside analogue used in the treatment of various cancers, being a standard treatment for advanced pancreatic cancer. The effect of gemcitabine is severely compromised due to its rapid plasma degradation, systemic toxicity and drug resistance, which restricts its therapeutic efficacy. Our main goal was to develop new active conjugates of dFdC with novel cell-penetrating hexapeptides (CPP6) to facilitate intracellular delivery of this drug. All new peptides were prepared by solid phase peptide synthesis (SPPS), purified and characterized by HPLC and LC-MS. Cell-penetrating peptides (CPP) contain a considerably high ratio of positively charged amino acids, imparting them with cationic character. Tumor cells are characterized by an increased anionic nature of their membrane surface, a property that could be used by CPP to target these cells. The BxPC-3, MCF-7 and PC-3 cancer cell lines were used to evaluate the in vitro cytotoxicity of conjugates and the results showed that conjugating dFdC with CPP6 significantly enhanced cell growth inhibitory activity on PC-3 cells, with IC₅₀ between 14 and 15 nM. These new conjugates have potential to become new therapeutic tools for cancer therapy.

Expression of oncogenic HMGN5 increases the sensitivity of prostate cancer cells to gemcitabine

Prostate cancer is a leading cause of cancer-related death among men. Early diagnosis and treatment are successful against prostate cancer, yet the clinical treatment of advanced prostate cancer remains a challenge. Gemcitabine is used to treat a broad spectrum of solid tumors; however, the clinical response of prostate cancer patients to gemcitabine is limited. In the present study, we showed that HMGN5, a nucleosome binding protein that can unfold chromatin by binding to histone (H1), is overexpressed in prostate cancer cells and plays an oncogenic role in prostate cancer tumorigenesis and development by activating the MAPK signaling pathway. We also found that sensitivity of prostate cancer cells to gemcitabine was positively correlated with HMGN5 expression. Knockdown of HMGN5 expression reduced the sensitivity of PC-3 cells to gemcitabine, and ectopic HMGN5 expression in DU145 cells enhanced the sensitivity to gemcitabine. Gemcitabine decreased HMGN5 expression, consequently leading to inactivation of the MAPK signaling pathway and cleavage of the PARP protein. Finally, we showed that PC-3 cells acquire gemcitabine resistance by gradual loss of HMGN5 expression. The present study suggests that HMGN5 is a potential biomarker for treating prostate cancer, and patients with a high level HMGN5 will benefit from gemcitabine treatment.

Gemcitabine-oxaliplatin plus prednisolone is active in patients with castration-resistant prostate cancer for whom docetaxel-based chemotherapy failed

Background:

There has been no previous study on the activity of gemcitabine in combination with oxaliplatin (GemOx) for castration-resistant prostate cancer (CRPC).

Methods:

The GemOx was preclinically tested for cytotoxic activity in human prostate cancer cell lines. Clinically, patients with CRPC who failed prior docetaxel were treated with gemcitabine 1000 mg m⁻² and oxaliplatin 100 mg m⁻² intravenously every 2 weeks and prednisolone 5 mg orally twice daily. The primary end point was the prostate-specific antigen (PSA) response rate.

Results:

The GemOx displayed synergistic effects based on Chou and Talalay analysis. In the phase II study, 33 patients were accrued. The median dose of docetaxel exposure was 518 mg m⁻². A total of 270 cycles were administered with a median of eight cycles per patient. A PSA response rate was 55% (95% CI, 38–72) and radiologic response rate was 82% (9 out of 11). With a median follow-up duration of 20.5 months, the median time to PSA progression was 5.8 months (95% CI, 4.4–7.2) and the median overall survival was 17.6 months (95% CI, 12.6–22.6). The most frequently observed grade 3 or 4 toxicities were neutropenia (13%) and thrombocytopenia (13%).

Conclusions:

The GemOx is active and tolerable in patients with metastatic CRPC after docetaxel failure (NCT 01487720).

Anti-metastatic effects of liposomal gemcitabine in a human orthotopic LNCaP prostate cancer xenograft model

Fatal outcomes of prostate carcinoma (PCa) mostly result from metastatic spread rather than from primary tumor burden. Here, we monitored growth and metastatic spread of an orthotopic luciferase/GFP-expressing LNCaP PCa xenograft model in SCID mice by in vivo imaging and in vitro luciferase assay of tissues homogenates. Although the metastatic spread generally shows a significant correlation to primary tumor volumes, the susceptibility of various tissues to metastatic invasion was different in the number of affected animals as well as in absolute metastatic burden in the individual tissues. Using this xenograft model we showed that treatment with liposomal gemcitabine (GemLip) inhibited growth of the primary tumors (83.9 +/- 6.4%; P = 0.009) as well as metastatic burden in lymph nodes (95.6 +/- 24.0%; P = 0.047), lung (86.5 +/- 10.5%; P = 0.015), kidney (88.4 +/- 9.2%; P = 0.045) and stomach (79.5 +/- 6.6%; P = 0.036) already at very low efficient concentrations (8 mg/kg) as compared to conventional gemcitabine (360 mg/kg). Our data show that this orthotopic LNCaP xenograft PCa model seems to reflect the clinical situation characterized by the fact that at time of diagnosis, prostate neoplasms are biologically heterogeneous and thus, it is a useful model to investigate new anti-metastatic therapies.

Liposomal gemcitabine (GemLip)-efficient drug against hormone-refractory Du145 and PC-3 prostate cancer xenografts

BACKGROUND

Gemcitabine (Gemc) is an efficient chemotherapeutic drug in various cancer types (e.g., pancreas) but has only limited effects on hormone-refractory prostate cancer (HRPCa). Since HRPCa cells are highly sensitive to even low doses of Gemc in vitro, the lack of clinical effects might be due to rapid degradation of Gemc by deaminases combined with impaired accumulation in tumor tissue and PCa cells. Liposomal formulation (GemLip) is expected to protect the entrapped cytotoxic substance from enzymatic degradation and furthermore augment its accumulation within tumor tissues due to an enhanced permeability of the tumor vessels.

METHODS

Anti-tumoral and anti-metastatic activity of GemLip and Gemc were investigated in two luciferase-expressing, human hormone-refractory PC-3 and Du145 HRPCa xenograft models in immunodeficient mice. Tumor growth was monitored by in vivo luminescence imaging (orthotopic) or callipering (subcutaneous). Anti-metastatic effects of treatment were determined by in vitro luciferase assay of the tissues.

RESULTS

Tumor growth of subcutaneous Du145 xenografts was significantly inhibited only by GemLip (8 mg/kg: P = 0.014 and 6 mg/kg: P = 0.011) but not by conventional Gemc (360 mg/kg). In contrast, growth of orthotopic PC-3 xenografts was significantly inhibited by both, GemLip (P = 0.041) and Gemc (P = 0.002). The drugs furthermore strongly reduced spleen and liver metastases in this model.

CONCLUSIONS

As shown by the very low efficient concentration of GemLip, liposomal entrapment of Gemc greatly enhances its activity. GemLip has, even at very low doses, a significant anti-tumoral and anti-metastatic therapeutic effect in HRPCa xenografts in vivo and was beneficial even when the conventional Gemc failed.

Anticancer and antimalarial efficacy and safety of artemisinin-derived trioxane dimers in rodents

In only four chemical steps from naturally occurring artemisinin (1), trioxane dimers 6 and 7 were prepared on a multigram scale in overall 32-44% yields. In mice, both isonicotinate N-oxide dimer 6 and isobutyric acid dimer 7 were considerably more antimalarially efficacious than clinically used sodium artesunate (2) via both oral and intravenous administration. In the transgenic adenocarcinoma of mouse prostate model, some of the trioxane dimers had potent anticancer activity.

Radiation enhancement by gemcitabine-mediated cell cycle modulations

The purpose of this study was to investigate the exact dose dependency and time dependency of the radiation-enhancing effect of gemcitabine (2',2'difluoro desoxycytidine [dFdC]) in in vitro experiments (HeLa cells: cancer of the uterine cervix, #4197 cells: oropharyngeal squamous cell carcinoma), and to correlate this effect with the underlying changes in cell cycle distribution. Cell viability was determined fluorometrically after exposure to dFdC (0-20.0 micro mol/l), irradiation (0-37.5 Gy), and both modalities. Combining both therapies, cells were exposed to dFdC (0-10.0 micro mol/l) for 24 hours before further treatment and irradiated (0-30 Gy) immediately afterwards with or without removal of dFdC. For cell cycle analysis by flow cytometry, cells were irradiated (0-40 Gy) or treated with dFdC (0.012-1.0 micro mol/l, 24-48 hours). Additionally, cells were exposed to dFdC (2.0 micro mol/l, 0-4 hours). Cell cycle kinetics were evaluated using bromodeoxyuridine (BrdU) (10 micro mol/l) S-phase labeling, given either 30 minutes before or in the last hour of dFdC treatment (2.0 micro mol/l, 0-6 hours). The fluorometric assay revealed that dFdC enhances radiation-induced cytotoxicity at marginally toxic or nontoxic concentrations (<37 nmol/l). Radiation resulted in the anticipated G2/M arrest already at 2 Gy. DFdC induced concentration and exposure time-dependent cell cycle changes that were better resolved using BrdU, demonstrating a pronounced S-phase arrest already at 12 nmol/l. BrdU-pulse labeling revealed that the cell cycle block occurred at the G1/S boundary. Our data reconfirm the already known radiation enhancement, the S-phase specific activities of dFdC, and the relevance of the synchronized progression of cells through the S-phase with regard to the radiosensitizing properties of low-dose dFdC. However, we could demonstrate that before progressing in the S-phase, cells were blocked and partially synchronized at the more radiosensitive G1/S boundary. Furthermore, cells progressing past the block might accumulate proapoptotic signals caused by both radiation and dFdC, which will also results in cell death.

Future directions for gemcitabine in the treatment of genitourinary cancer

Because of an annual morbidity of 225,000 patients and mortality of over 56,000 patients per year in the United States from metastatic genitourinary malignancies, there is a great need for new systemic agents. With its activity and low toxicity, gemcitabine has begun to play a growing role in genitourinary cancer treatment and clinical trials. Substantial activity has been reported for gemcitabine combinations in the treatment of bladder cancer (median survival in one study of nearly 20 months) and for gemcitabine alone or in combinations in testicular cancer patients. Lower (but real) levels of activity have also been observed for gemcitabine combinations in renal carcinoma (17% response rate) and for monotherapy in hormone-refractory prostate cancer (7%). These data suggest the need for further trials of gemcitabine alone or in combinations in genitourinary cancer patients.

Differential expression of matrix metalloproteinases and their tissue inhibitors in human primary cultured prostatic cells and malignant prostate cell lines

BACKGROUND

The aim was to investigate the expression of matrix metalloproteinases (MMPs), membrane type MMPs (MT-MMPs), and their inhibitors (TIMPs) in human primary cultured prostatic cells and malignant prostate cell lines.

METHODS

Reverse transcription-polymerase chain reaction-based measurements of the mRNA levels of MMP-2, MMP-7, MT1-MMP, MT3-MMP, TIMP-1, and TIMP-2 in relation to the house-keeping gene glyceraldehyde phosphate dehydrogenase were performed in cancerous and non-cancerous prostatic tissue samples, in primary cell cultures of epithelial cells, in both fibroblasts, and smooth-muscle cells as stromal cells, and in the human malignant prostatic cell lines DU-145, LNCaP, and PC-3.

RESULTS

MMP-2 was mainly expressed in the stromal cells and MMP-7 showed their highest values in the epithelial cells. MT1-MMP, MT3-MMP, TIMP-1, and TIMP-2 were found both in the stromal and in the epithelial cells, but there were some differences between the expressions in fibroblasts and smooth-muscle cells. Different expressions were also observed between the cells deriving from the primary cell cultures, the benign cell line BPH-1, and the malignant cell lines LNCaP, D-145, and PC-3.

CONCLUSIONS

These exemplary results concerning different expressions of MMPs and TIMPs in cells from prostatic tissue suggest that a better insight into changes observed in prostatic tissue needs studies on cells cultured from the tissue.

Induction of cell cycle-dependent cytotoxicity and apoptosis by new heterodinucleoside phosphate dimers of 5-fluorodeoxyuridine in PC-3 human prostate cancer cells

Fluorodeoxyuridine (5-FdUrd) is an antineoplastic agent with clinical activity against different types of solid tumours. To enhance the effectiveness of this drug, we have synthesised new heterodinucleoside phosphate dimers of 5-FdUrd. These dimers were compared to 5-FdUrd for their cytotoxic effect and the cell cycle dependence of cytotoxicity, as well as for their capacity to induce apoptosis and inhibit thymidylate synthetase (TS) in androgen-independent human PC-3 prostate tumour cells. Incubation of the cells with the dimers N(4)-palmitoyl-2'-deoxycytidylyl-(3'-->5')-5-fluoro-2'-deoxyuri din e (dCpam-5-FdUrd) and 2'-deoxy-5-flourouridylyl-(3'-->5')-2'-deoxy-5-fluoro-N(4)-octa decylc ytidine (5-FdUrd-5-FdC18) resulted in a marked cytotoxicity with IC(50) values of 4 microM, similar to 5-FdUrd. In contrast to 5-FdUrd, 100% toxicity was achieved with concentrations of 100-200 microM 5-FdUrd-5-FdC18. Flow cytometric analysis revealed an increase in the cell population in S-phase after treatment with 5-FdUrd, 5-FdUrd-5-FdC18, and dCpam-5-FdUrd from 36 to 63%, 50%, and 77%, respectively. dCpam-5-FdUrd was more potent than 5-FdUrd in arresting the cell cycle. Significant S-phase arrest was indicated by a decreased proportion of cells in G1- and G2/M-phases. Cell cycle arrest and inhibition of cell proliferation were followed by apoptosis, as shown by a 6- to 8-fold increased binding of Apo2.7 antibody, a 9- to 11-fold increase in caspase-3 activity, DNA fragmentation, and by cell morphology showing the appearance of apoptotic bodies. Importantly, 5-FdUrd-5-FdC18 increased the number of apoptotic cells to 160% compared to 5-FdUrd under the same conditions. As with 5-FdUrd, the two dimers also inhibited TS in a time- and concentration-dependent manner, although requiring 100-fold higher concentrations. In conclusion, dCpam-5-FdUrd and 5-FdUrd-5-FdC18 exert stronger cytotoxicity and induce more S-phase arrest and apoptosis than does 5-FdUrd in PC-3 cells, suggesting their potential role in the treatment of human prostate cancer.

Basis for effective combination cancer chemotherapy with antimetabolites

Most current chemotherapy regimens for cancer consist of empirically designed combinations, based on efficacy and lack of overlapping toxicity. In the development of combinations, several aspects are often overlooked: (1) possible metabolic and biological interactions between drugs, (2) scheduling, and (3) different pharmacokinetic profiles. Antimetabolites are used widely in chemotherapy combinations for treatment of various leukemias and solid tumors. Ideally, the combination of two or more agents should be more effective than each agent separately (synergism), although additive and even antagonistic combinations may result in a higher therapeutic efficacy in the clinic. The median-drug effect analysis method is one of the most widely used methods for in vitro evaluation of combinations. Several examples of classical effective antimetabolite-(anti)metabolite combinations are discussed, such as that of methotrexate with 6-mercaptopurine or leucovorin in (childhood) leukemia and 5-fluorouracil (5FU) with leucovorin in colon cancer. More recent combinations include treatment of acute-myeloid leukemia with fludarabine and arabinosylcytosine. Other combinations, currently frequently used in the treatment of solid malignancies, include an antimetabolite with a DNA-damaging agent, such as gemcitabine with cisplatin and 5FU with the cisplatin analog oxaliplatin. The combination of 5FU and the topoisomerase inhibitor irinotecan is based on decreased repair of irinotecan-induced DNA damage. These combinations may increase induction of apoptosis. The latter combinations have dramatically changed the treatment of incurable cancers, such as lung and colon cancer, and have demonstrated that rationally designed drug combinations offer new possibilities to treat solid malignancies.

Response and palliation in a phase II trial of gemcitabine in hormone-refractory metastatic prostatic carcinoma. Swiss Group for Clinical Cancer Research (SAKK)

BACKGROUND

In a phase II trial, 43 patients with hormone-refractory prostate cancer were treated with gemcitabine at a dose of 1,200 mg/m2 over 2 hours (later decreased to 1,000 mg/m2 due to hematological toxicity) on days 1, 8 and 15 of a 28 day cycle.

PATIENTS AND METHODS

Inclusion criteria were proven tumor progression after hormonal treatment and increased PSA levels, a WHO PS < or = 2, adequate bone marrow reserve, liver and renal function and age < or =, 80 years. Response criteria were based on PSA levels (CR: normalization of PSA, PR: > 50% decrease). Quality of life (QL) was assessed with the EORTC QLQ-C30 on day 1 of each treatment cycle and on day 8 of the first cycle (range of scales 0-100). Physician-rated pain intensity and use of pain medication were assessed at the same timepoints.

RESULTS

Hematological toxicity of gemcitabine led to a dose-reduction in 48% of all cycles. Three of forty-three patients (RR = 7%) showed a PSA response: one CR and three PR with time to treatment failure of 8.7, 6.6 and > or = 9.3 months. Seven patients (16%) had stable disease (NC) for a median duration of 7.1 months (range 6.1-11.7 months). There was one case with objective regression of lymph node metastases. Patients reported a considerably impaired health status/QL (n = 41, median = 50) and severe fatigue (n = 41, median = 55.6) at baseline, with no change under treatment. Pain (QLQ-C30) was also severe at baseline (N=41, median=50) but was improved at the end of cycles 1 (n = 33, median change = -16.7, P = 0.0002), 2 (n = 19, median change = -33.3, P = 0.0006), 3 (n = 14, median change = -16.7, P = 0.06) and 4 (n = 9, median change = -33.3, P = 0.04). Patient-rated pain and use of analgesics as combined endpoint yielded palliation for at least 8 weeks in 14 patients (32%). Nine of these patients showed at least stable disease (CR/PR or NC by PSA level), five indicated a benefit in spite of progressive disease.

CONCLUSIONS

Gemcitabine in the dose and schedule indicated above has a significant beneficial impact on pain in patients with hormone-refractory prostatic carcinoma despite its limited activity in terms of PSA response and considerable, especially hematological, toxicity.

Switch from antagonist to agonist of the androgen receptor bicalutamide is associated with prostate tumour progression in a new model system

Advanced prostate cancer is treated by androgen ablation and/or androgen receptor (AR) antagonists. In order to investigate the mechanisms relevant to the development of therapy-resistant tumours, we established a new tumour model which closely resembles the situation in patients who receive androgen ablation therapy. Androgen-sensitive LNCaP cells were kept in androgen-depleted medium for 87 passages. The new LNCaP cell subline established in this manner, LNCaP-abl, displayed a hypersensitive biphasic proliferative response to androgen until passage 75. Maximal proliferation of LNCaP-abl cells was achieved at 0.001 nM of the synthetic androgen methyltrienolone (R1881), whereas 0.01 nM of this compound induced the same effect in parental cells. At later passages (> 75), androgen exerted an inhibitory effect on growth of LNCaP-abl cells. The non-steroidal anti-androgen bicalutamide stimulated proliferation of LNCaP-abl cells. AR protein expression in LNCaP-abl cells increased approximately fourfold. The basal AR transcriptional activity was 30-fold higher in LNCaP-abl than in LNCaP cells. R1881 stimulated reporter gene activity in LNCaP-abl cells even at 0.01 nM, whereas 0.1 nM of R1881 was needed for induction of the same level of reporter gene activity in LNCaP cells. Bicalutamide that acts as a pure antagonist in parental LNCaP cells showed agonistic effects on AR transactivation activity in LNCaP-abl cells and was not able to block the effects of androgen in these cells. The non-steroidal AR blocker hydroxyflutamide exerted stimulatory effects on AR activity in both LNCaP and LNCaP-abl cells; however, the induction of reporter gene activity by hydroxyflutamide was 2.4- to 4-fold higher in the LNCaP-abl subline. The changes in AR activity were associated neither with a new alteration in AR cDNA sequence nor with amplification of the AR gene. Growth of LNCaP-abl xenografts in nude mice was stimulated by bicalutamide and repressed by testosterone. In conclusion, our results show for the first time that the nonsteroidal anti-androgen bicalutamide acquires agonistic properties during long-term androgen ablation. These findings may have repercussions on the natural course of prostate cancer with androgen deprivation and on strategies of therapeutic intervention.

Gemcitabine cytotoxicity of human malignant glioma cells: modulation by antioxidants, BCL-2 and dexamethasone

Gemcitabine is a novel antimetabolite drug that acts by multiple mechanisms, including inhibition of ribonucleoside diphosphate reductase, of dCMP deaminase and of dCTP incorporation into DNA and RNA. Here, we report that gemcitabine induces cytotoxic and clonogenic death of 12 human malignant glioma cell lines at clinically relevant concentrations around 1 microM. Gemcitabine is thus approximately 100-fold more active than the congener drug, cytarabine. Gemcitabine cytotoxicity of glioma cells does not require wild-type p53 activity: (i) there was no difference in the susceptibility to gemcitabine between cell lines with wild-type p53 and cell lines with mutant or deleted p53; (ii) ectopic expression of a temperature-sensitive p53 protein either at wild-type (32.5 degrees C) or at mutant (38.5 degrees C) conformation had no significant influence on gemcitabine-induced cell death. Gemcitabine cytotoxicity was unaffected by the antioxidants, N-acetylcysteine and phenyl-N-tert-butyl-alpha-phenylnitrone. There was no correlation between the susceptibility to gemcitabine and the endogenous expression of the B cell lymphoma-2 (BCL-2)-family proteins BCL-2, BCL-XL, myeloid cell leukemia-1 (MCL-1), BCL-2-associated X protein (BAX), BCL-2 homologous antagonist/killer (BAK) and BCL-XS. Ectopic expression of BCL-2 moderately attenuated gemcitabine-induced cell death. Similarly, preexposure to the synthetic steroid, dexamethasone, which is commonly used to control cerebral edema in brain tumor patients, reduced gemcitabine cytotoxicity. We conclude that the clinical evaluation of gemcitabine for the adjuvant chemotherapy of malignant glioma is warranted.

Nucleoside transporters of mammalian cells

In this review, we have summarized recent advances in our understanding of the biology of nucleoside transport arising from new insights provided by the isolation and functional expression of cDNAs encoding the major nucleoside transporters of mammalian cells. Nucleoside transporters are required for permeation of nucleosides across biological membranes and are present in the plasma membranes of most cell types. There is growing evidence that functional nucleoside transporters are required for translocation of nucleosides between intracellular compartments and thus are also present in organellar membranes. Functional studies during the 1980s established that nucleoside transport in mammalian cells occurs by two mechanistically distinct processes, facilitated diffusion and Na(+)-nucleoside cotransport. The determination of the primary amino acid sequences of the equilibrative and concentrative transporters of human and rat cells has provided a structural basis for the functional differences among the different transporter subtypes. Although nucleoside transporter proteins were first purified from human erythrocytes a decade ago, the low abundance of nucleoside transporter proteins in membranes of mammalian cells has hindered analysis of relationships between transporter structure and function. The molecular cloning of cDNAs encoding nucleoside transporters and the development of heterologous expression systems for production of recombinant nucleoside transporters, when combined with recombinant DNA technologies, provide powerful tools for characterization of functional domains within transporter proteins that are involved in nucleoside recognition and translocation. As relationships between molecular structure and function are determined, it should be possible to develop new approaches for optimizing the transportability of nucleoside drugs into diseased tissues, for development of new transport inhibitors, including reagents that are targeted to the concentrative transporters, and, eventually, for manipulation of transporter function through an understanding of the regulation of transport activity.

Cathepsins B, H, L and cysteine protease inhibitors in malignant prostate cell lines, primary cultured prostatic cells and prostatic tissue

Elevated activities of cysteine proteinases, the cathepsins B, H, L (CB, CH, CL) and diminished cysteine protease inhibitors (CPI) have been demonstrated in a variety of tumours and have been suggested to contribute to invasion and metastasis. The situation for prostate cancer is still unknown. In this study, using fluorimetric assays, the catalytic activities of CB, CH, CL were measured in prostatic tissue samples after radical prostatectomy, adenomectomy, transurethral resection of the prostate, in cell cultures grown from cancerous and non-cancerous parts of human prostate after prostatectomy and in the cell lines LNCaP, DU 145 and PC 3. CPIs were determined using heat activation before testing their inhibitory activity against purified CB. Comparing matched pairs of normal and cancerous tissue samples from the prostate, significantly decreased levels of CB, CL in malignant parts of the prostate were found. In contrast, primary cell cultures from cancerous samples showed elevated levels of CB, CH, CL and increased ratios of cathepsins to CPI compared with cell cultures from normal prostate. Established cell lines showed a similar distribution pattern of each cathepsin, DU 145 containing the highest levels, followed by LNCaP and PC 3. Our results suggest that elevated cathepsin levels and consequently increased ratios of cathepsins to CPI in primary cell cultures from cancerous versus non-cancerous parts of the prostate may be indicative of a cellular proteolytic imbalance in prostatic cancer cells. In this respect, primary cell culture experiments should be preferred to determinations in tissue samples.

Interleukin 1beta mediates the modulatory effects of monocytes on LNCaP human prostate cancer cells

Proliferative and secretory responses in androgen-sensitive prostate cancer LNCaP cells are regulated by steroid and peptide hormones and by differentiation-promoting substances. In the present study, we evaluated whether peripheral blood monocytes that exhibit anti-tumour activity in haematopoietic and solid tumours influence growth and secretion in the LNCaP cell line. For this purpose, LNCaP cells were incubated with monocyte-conditioned medium (MCM), and proliferation as well as expression of androgen receptor (AR) and secretion of prostate-specific antigen (PSA) were assessed. Conditioned medium from monocytes reduced proliferation in a dose-dependent manner. Incubation with 40% MCM caused a 50% reduction in cell proliferation. AR protein decreased by 70% and PSA levels in supernatants from LNCaP cells were reduced by approximately 80% following treatment with MCM. We focused on the contribution of two major products of activated monocytes, prostaglandin E2 and interleukin 1beta (IL-1beta), to the MCM modulatory action. LNCaP cells treated with prostaglandin E2 showed neither a reduction in proliferation nor a down-regulation of AR and PSA levels. The effects of MCM on cellular proliferation, AR protein and PSA secretion were abolished by pretreatment of MCM with a neutralizing anti-IL-1beta antibody. In addition, recombinant IL-1beta was able to replace MCM for the inhibition of proliferation and down-regulation of AR and PSA proteins. LNCaP cells were shown to express the IL-1beta receptor type 1, which transduces IL-1beta signal. Our findings reveal that monocyte-derived IL-1beta inhibits the proliferation of androgen-responsive prostate tumour cells and reduces AR and PSA levels.

Antitumor effect of the nucleoside analogs 2-chlorodeoxyadenosine and 2',2'-difluorodeoxycytidine on human hepatoma HepG2 cells

BACKGROUND/AIMS

Hepatocellular carcinoma is one of the most malignant tumors in the world. Although a wide range of therapeutic options is available, the efficacy of these methods and the prognosis of hepatocellular carcinoma are still very poor. The nucleoside analogs 2-chlorodeoxyadenosine (Cladribine, 2-CdA) and 2',2'-difluorodeoxycytidine (Gemcitabine, dFdC) have shown potent cytotoxic effects on various human tumor cell lines in vitro and marked therapeutic efficacy in the treatment of lymphoproliferative disorders and several solid tumors in vivo. In the present study we evaluated the antitumor effect of 2-CdA and dFdC on human hepatoma HepG2 cells.

METHODS

HepG2 cells were grown in the absence and presence of increasing concentrations of 2-CdA and dFdC. Antitumor activity was assessed by inhibition of cell growth, evaluated by counting cell numbers in a hemocytometer and by 3H-thymidine uptake, and by reduction of cell viability as determined by exclusion of 0.1% trypan blue. For rescue experiments, the natural pyrimidine deoxycytidine (dCyd) was added simultaneously or delayed.

RESULTS

A strong antitumor activity was observed for both compounds. dFdC showed a more pronounced effect with an inhibition constant (IC50) of 3.98+/-0.03 nM in comparison to 2-CdA with an IC50 of 16.66+/-0.40 nM. Both drugs achieved their half-maximal antitumor activity after 31 h. With respect to dFdC, fractionated daily administrations showed a distinctly greater antitumor activity than a single transient administration. The cytotoxic effects of 2-CdA and dFdC were completely reversed by simultaneous addition of dCyd.

CONCLUSION

In this paper we show strong antitumor effects of the nucleoside analogs 2-CdA and dFdC on the human hepatoma cell line HepG2. These findings suggest that both compounds, but in particular dFdC, are promising substances for further evaluations in the treatment of hepatocellular carcinoma.

Gemcitabine. A review of its pharmacology and clinical potential in non-small cell lung cancer and pancreatic cancer

Gemcitabine [2'-deoxy-2',2'-difluorocytidine monohydrochloride (beta isomer); dFdC] is a novel deoxycytidine analogue which was originally investigated for its antiviral effects but has since been developed as an anticancer therapy. Gemcitabine monotherapy produced an objective tumour response in 18 to 26% of patients with advanced non-small cell lung cancer (NSCLC) and appears to have similar efficacy to cisplatin plus etoposide. Objective response rates ranging from 26 to 54% were recorded when gemcitabine was combined with cisplatin, and 1-year survival duration after such treatment ranged from 35 to 61%. Improvements in a range of NSCLC disease symptoms and/or in general performance status occurred in many patients who received gemcitabine, with or without cisplatin, in 3 clinical trials. Gemcitabine appears to be cost effective compared with best supportive care for NSCLC. In addition, direct costs associated with administration of gemcitabine monotherapy may be lower than those for some other NSCLC chemotherapy options, according to retrospective cost-minimisation analyses. The combination of gemcitabine plus cisplatin was associated with a lower cost per tumour response than cisplatin plus etoposide or cisplatin plus vinorelbine, according to a retrospective cost-effectiveness analysis. In a single comparative study in patients with advanced pancreatic cancer, gemcitabine was more effective than fluorouracil with respect to survival duration and general clinical status. It also showed modest antitumour and palliative efficacy in patients refractory to fluorouracil. Gemcitabine appears to be well tolerated, although further comparisons with other chemotherapy regimens are required. The available data indicate that gemcitabine monotherapy is better tolerated than cisplatin plus etoposide in patients with NSCLC. Data from noncomparative studies suggest that the combination of gemcitabine and cisplatin has an acceptable tolerabilty profile. In a single trial in patients with pancreatic cancer, fluorouracil was better tolerated than gemcitabine; however, gemcitabine was generally well tolerated overall in this study. Thus, gemcitabine (with or without cisplatin) may prove attractive to patients with advanced NSCLC, given their limited life expectancy and the toxicity associated with many other chemotherapy regimens. More detailed characterisation of its risk-benefit profile compared with those of current and developing regimens for NSCLC should be possible once results from several ongoing studies are available. Gemcitabine is a valuable new chemotherapy option for patients with advanced pancreatic cancer, a disease considered incurable at present. Its apparent survival and palliative benefits over fluorouracil require confirmation, but are encouraging, as the need to improve both the duration and quality of survival in these patients is well recognised.

Synergistic activation of androgen receptor by androgen and luteinizing hormone-releasing hormone in prostatic carcinoma cells

BACKGROUND

We investigated modulation of androgen receptor (AR) activity in prostatic tumor cells by luteinizing hormone-releasing hormone (LHRH)-induced increase of the intracellular cyclic adenosine monophosphate (cAMP) level.

METHODS

AR transactivation activity was assessed in transiently transfected DU-145 and in LNCaP cells.

RESULTS

LHRH and cAMP derivative, respectively, induced reporter gene activity to about 15% of the maximal level in DU-145 cells transfected with an AR expression vector and an androgen-inducible reporter gene. LHRH or the cAMP analogue acted synergistically in combination with low concentrations of androgen thus lowering the androgen concentration required for maximal AR activation by a factor of 100. A similar activation of the AR by cAMP analogue was observed in LNCaP cells when enhancement of androgen-induced secretion of prostate-specific antigen was determined. The two nonsteroidal antiandrogens hydroxyflutamide and Casodex(R) inhibited reporter gene activity.

CONCLUSIONS

The AR is synergistically activated by low doses of androgen and LHRH or the second messenger cAMP. This may have implications for the treatment of advanced prostate cancer.

Antioxidant enzymes in malignant prostate cell lines and in primary cultured prostatic cells

The antioxidant enzymes catalase, glutathione reductase (GR), glutathione S-transferase (GST), glutathione peroxidase (GPx), and superoxide dismutase (SOD) were determined in the androgen-response LNCaP and androgen-nonresponsive PC-3 and DU 145 cells as well as in prostatic epithelial cell cultures of benign and malignant human prostatic tissue. There were no differences between the enzyme activities of the human primary cell cultures from cancerous tissue and their normal counterparts. The enzyme activities of the three permanent cell lines were either higher (SOD, catalase, GR) or lower (GST, GPx) than in the primary cell cultures. In LNCaP cells catalase and GR were significantly higher, GST, in contrast, was significantly lower than in PC-3 and DU 145 cells. GST in PC-3 and DU 145 cells, and SOD in all the three cell lines showed no significant differences. Catalase, GPx and GR values were significantly different in the three permanent cell lines. The different enzymatic equipment of the prostate cancer cell lines provides the basis for experimental testing of new concepts of cancer treatment with the help of systematic modulations of the antioxidant defence systems in prostate cancer.