Docetaxel Pretreatment Research Articles

Prostate-specific antigen response after Abiraterone treatment in mCRPC: PSA as a predictor of overall survival

Abiraterone Acetate (AA) is an important agent in the treatment of advanced prostate cancer. It was primarily approved for the treatment of metastatic castration-resistant prostate cancer (mCRPC) after failure of androgen deprivation therapy. There is still no available strong data regarding the impact of early decline of prostate-specific antigen (PSA) in the overall survival. The aim of this study was to evaluate the clinical efficacy of an early prostate-specific antigen response as a predictor of overall survival (OS) in metastatic castration-resistant prostate cancer when treated with Abiraterone Acetate. A dual center, retrospective, cohort study on patients diagnosed with mCRPC treated with abiraterone between 2013 and 2020 was performed. Primary end-point was to demonstrate the efficacy of AA, with the analysis of PSA decline, and the correlation with overall survival. The cohort analysis consisted of 84 patients with a median age of 71 ± 9 years. A PSA response of > 30% and > 50% at 60 and 90 days was associated with improved OS. Multivariate analysis revealed that a 60 day PSA decline of > 30% was predictive of overall survival. Median OS of diag-nosed mCRPC patients was 28 months. Docetaxel pre-treatment was not associated with longer OS. The median duration of drug exposure for patients submitted to AA was found to be 14 months. Early PSA response rate can offer clinically meaningful information and can be considered a surrogate of longer OS. A > 30% or > 50% prostate-specific antigen decline at 60 and 90 days provided an important low-cost clinical tool to predict subsequent events in mCRPC patients treated with abiraterone.

TITAN-Studie – Evaluation von Apalutamid bei Patienten mit metastasiertem hormonsensitivem Prostatakarzinom

The TITAN study, which compares apalutamide plus ADT with placebo plus ADT in an all-comers population of patients with metastatic hormone-sensitive prostate cancer (mHSPC), reached both primary endpoints, rPFS and OS, at the first planned interim analysis 1. After a median follow-up of 22.7 months, the risk of radiographic progression was reduced by 52 % (p < 0.001) 1. The rPFS benefit was observed in all subgroups and independently of tumour burden or docetaxel pre-treatment 1. The OS interim analysis showed a mortality risk reduced by 33 % in favour of apalutamide plus ADT (p = 0.0053) 1. The secondary endpoint of time to cytotoxic chemotherapy as well as the exploratory endpoints of time to PSA progression and second progression-free survival (PFS2), defined as time between randomisation and second disease progression or death under the first subsequent therapy, were also significantly improved 1 2. Overall, apalutamide showed good tolerability, with a higher rate of apalutamide-typical rash and hypothyroidism but no relevant increase in fatigue, falls or fractures compared with placebo, and with quality of life being maintained 1. Apalutamide plus ADT can thus be an effective and well-tolerated new treatment option in many patients with mHSPC.

Early prostate-specific antigen response post-abiraterone as predictor of overall survival in metastatic castrate-resistant prostate cancer

BackgroundAbiraterone is an important agent in the treatment of advanced prostate cancer. Early changes in prostate-specific antigen while on abiraterone in patients with metastatic castrate-resistant prostate cancer potentially have financial and health implications for patients. Limited data is available on early prostate-specific antigen change and subsequent survival given phase III trials did not measure prostate-specific antigen changes before 12 weeks.MethodsA single-center retrospective study was performed. Metastatic castrate-resistant prostate cancer patients treated with abiraterone (without prior enzalutamide) at Tulane Cancer Center were reviewed with a focus on early prostate-specific antigen decline and relationship to overall survival.ResultsA total of 110 patients were analyzed for prostate-specific antigen response of ≥ 30 and > 50% at 4, 8, and 12 weeks. A prostate-specific antigen response of either > 30% or > 50% at 4, 8, or 12 weeks was associated with improved overall survival at all time points except > 50% decline at 8 weeks. Multivariate analysis indicated, for all time points, that early prostate-specific antigen declines were predictive of overall survival. The neutrophil to lymphocyte ratio and docetaxel pretreatment also were predictive in many, but not all, of the multivariate analyses.ConclusionsA > 30% or > 50% prostate-specific antigen decline at 4, 8, or 12 weeks provides important information regarding subsequent overall survival for patients with metastatic castrate-resistant prostate cancer. While these data require validation with a large, multi-institutional trial, they can provide physicians with information regarding prognosis and the timing of expected outcomes. These data affirms the notion that prostate-specific antigen responses as early as 4 weeks after abiraterone initiation can be used to inform both patients and physicians about metastatic castrate-resistant prostate cancer outcomes after initiating treatment with this important but costly therapeutic choice.

Sequential Treatment of Cell Cycle Regulator and Nanoradiosensitizer Achieves Enhanced Radiotherapeutic Outcome.

Nanoradiosensitizers are promising agents for enhancing cancer radiotherapeutic efficiency. Although many attempts have been adopted to improve their radiation enhancement effect through regulation of their size, shape, and/or surface chemistry, few methods have achieved satisfactory radiotherapeutic outcomes. Herein, we propose a sequential drug treatment strategy through cell cycle regulation for achieving improved radiotherapeutic performance of the nanoradiosensitizers. Docetaxel (DTX), a clinically approved first-line drug in breast cancer treatment, is first used to affect the cell cycle distribution and arrest cells in the G2/M phase, which has been proven to be the most effective phase for endocytosis and the most radiosensitive phase for radiotherapy. The cells are then exposed to a commonly used nanoradiosensitizer, gold nanoparticles (GNPs), followed by X-ray irradiation. It is found that by arresting the cancer cells in G2/M phase via the DTX pretreatment, the cellular internalization of GNPs is significantly promoted, therefore enhancing the radiosensitivity of cancer cells. The sensitization enhancement ratioof this sequential DTX/GNP treatment reaches 1.91, which is significantly higher than that (1.29) of GNP treatment. Considering its low cost, simple design, and high feasibility, this sequential drug delivery strategy may hold great potential in radiotherapy.

Does Gleason pattern 5 influence the efficacy of enzalutamide against castration-resistant prostate cancer?

e598 Background: In this study, we evaluated our cohort treated with enzalutamide retrospectively. We focused on Gleason pattern 5 prostate cancer which was very aggressive cancer and we investigated the difference in efficacy of enzalutamide between the groups including Gleason pattern 5 or not, to understand if initial aggressiveness of prostate cancer influence the enzalutamide responses. Methods: A total of 190 CRPC cases treated with enzalutamide between June 2014 and July 2016 at our university and affiliated institutions were included in this study. We evaluated clinical and pathological factors, Prostate specific antigen(PSA) responses, and overall survival, retrospectively. Results: Of these, 80 cases did not have Gleason pattern 5 and 110 cases had Gleason pattern 5 (Gleason Score 4+5, 5+4 or 5+5). Initial PSA level was higher and metastasis was more frequent in Gleason pattern 5 group (p = 0.0328, and 0.0171, respectively). Docetaxel pretreatment, abiraterone pretreatment, PSA and other serological data at starting enzalutamide were not different between the groups other than steroidal use (p = 0.0441). Overall survival rate at 1 year and 2 years were 84.3% and 77.2% in Gleason pattern 5 negative cohort, and 81.2% and 63.5% in Gleason pattern 5 cohort (p = 0.2459). There were no differences in terms of PSA responses between these groups. Mean PSA decline rate (pattern 5 negative vs. positive) were 57.1% vs. 54.6% (p = 0.6555). ≥ 50% PSA decline rate were 62.5% vs. 60.9% (p = 0.8329), ≥ 90% decline rate were 28.75% vs. 28.2% (p = 0.9317). Conclusions: In this study, we concluded that aggressiveness of initial status did not influence the efficacy of enzalutamide treatment. And disease status might be almost same when introducing enzalutamide. Of course, we need to recognize that initial androgen deprivation therapy (ADT) could be more efficient for lower Gleeson pattern than higher Gleeson pattern. However there is possibility that aggressiveness of prostate cancer cell would change through ADT and/or chemotherapy. We should investigate how prostate cancer is changing and should evaluate the prostate cancer cell status before starting treatment to predict the efficacy and to decide the treatment agents.

Microtubule stabilisers docetaxel and paclitaxel reduce spindle damage and maintain the developmental competence of in vitro-mature bovine oocytes during vitrification.

This study compared the efficacy of docetaxel (DT) and paclitaxel (PT) in reducing spindle damage during vitrification and maintaining the developmental competence of in vitro-matured (IVM) bovine oocytes after vitrification and warming. Pretreatment of IVM oocytes with 0.05µM DT for 30min before vitrification resulted in significantly higher (P<0.05) rates of oocyte survival and cleavage after IVF, as well as subsequent blastocyst rates on Days 7-9 and hatching on Days 8-9, compared with oocytes pretreated with 1.0µM PT before vitrification or those vitrified without pretreatment. When nuclear status and spindle morphology of vitrified oocytes were assess after warming by immunostaining, DT pretreatment before vitrification resulted in a significantly higher (P<0.05) percentage of oocytes at the MII stage with a normal, intact spindle compared with PT pretreatment or no pretreatment, but the percentage of MII oocytes was still significantly lower (P<0.05) than in the control group. Pretreatment of IVM bovine oocytes with 0.05µM DT or 1.0µM PT for 30min before vitrification reduces spindle damage to the same extent, without side effects on fertilisation and development. Pretreatment with 0.05µM DT improved the developmental competence of vitrified-warmed oocytes to a greater degree than 1.0µM PT pretreatment.

A biodistribution study of solid lipid-polyethyleneimine hybrid nanocarrier for cancer RNAi therapy

Solid lipid-polymer hybrid nanocarrier (LPN) was previously reported to achieve high siRNA transfection efficiency and induce sustained RNAi-based chemosensitizing effect at cellular level. In this study, our objectives were to evaluate the in vivo biodistribution of LPNs in a prostate cancer model and determine the factors that potentially affect tumor penetration by LPNs. The LPN formulation with the highest transfection efficiency (64%) and stability was selected for the study. Mice bearing tumors of PC-3Mcells were treated with LPNs labeled with IR780 or AF647-siRNA. Near infrared imaging showed that LPNs achieved favorable in vivo biodistribution with high tumor/low organ ratios. LPN accumulation was also observed in liver metastatic tissue. Result of extravasation study confirmed that encapsulated siRNA molecules were able to escape into the tumor tissue at the extravascular area. When LPN levels in large (volume>750mm3) and small (<500mm3) tumors were compared, no significant difference was observed. However, both docetaxel pretreatment (72hbefore LPN) and concurrent docetaxel treatment significantly enhanced the tumor LPN levels by 3.9- and 3.1-fold, respectively (both p<0.01). In conclusion, LPN is a promising carrier system to deliver RNAi therapy to solid malignancies that also receive chemotherapy.

Docetaxel induced-JNK2/PHD1 signaling pathway increases degradation of HIF-1α and causes cancer cell death under hypoxia.

HIF-1 (hypoxia-inducible factor-1) regulates the expression of more than 70 genes involved in angiogenesis, tumor growth, metastasis, chemoresistance, and radioresistance. Thus, there is growing interest in using HIF-1 inhibitors as anticancer drugs. Docetaxel, a Food and Drug Administration-approved anticancer drug, is reported to enhance HIF-1α degradation. Here, we investigated the molecular mechanism underlying docetaxel-induced HIF-1α degradation and cancer cell death under hypoxic conditions. Docetaxel pretreatment enhanced the polyubiquitination and proteasome-mediated degradation of HIF-1α, and increased cancer cell death under hypoxic conditions. Docetaxel also activated the prolyl hydroxylase, PHD1, in hypoxia, and pharmacological inhibition or siRNA-mediated knockdown of PHD1 prevented docetaxel-induced HIF-1α degradation and cancer cell death. Additionally, siRNA-mediated JNK2 knockdown blocked docetaxel-induced HIF-1α degradation and cancer cell death by inhibiting PHD1 activation. A luciferase reporter assay revealed that inhibition of the JNK2/PHD1 signaling pathway significantly increased the transcriptional activity of HIF-1 in docetaxel-treated cancer cells under hypoxia. Consistent with these results, docetaxel-treated JNK2-knockdown tumors grew much faster than control tumors through inhibition of docetaxel-induced PHD1 activation and degradation of HIF-1α. Our results collectively show that, under hypoxic conditions, docetaxel induces apoptotic cell death through JNK2/PHD1 signaling-mediated HIF-1α degradation.

Efficacy and Safety Assessment of Paclitaxel in Patients with Docetaxel-Resistant Esophageal Squamous Cell Carcinoma

Background: Incomplete cross-resistances between paclitaxel (PTX) and docetaxel (DTX) has been demonstrated in several types of cancer. The objective of the present study was to assess the existence of cross-resistance between PTX and DTX in esophageal squamous cell carcinoma. Methods: Patients in the PTX group received PTX without DTX pretreatment, patients in the prior DTX (Pr-DTX) group received PTX after the development of resistance to DTX, and patients in the DTX group received DTX without subsequent PTX treatment. Results: A total of 73 patients were enrolled. The response rates to PTX in the PTX and Pr-DTX groups were 22.7 and 20.0%, respectively. The median progression-free survival times from the first day of PTX treatment in the PTX and Pr-DTX groups were 113 (95% CI 56-154) and 97 days (95% CI 36-189), respectively. The median overall survival times from the first day of DTX treatment in the Pr-DTX and DTX groups were 315 (95% CI 124-453) and 148 days (95% CI 139-177), respectively. Conclusions: There is no or incomplete clinical cross-resistance between PTX and DTX in esophageal squamous cell carcinoma. Replacement of DTX with PTX is a suitable treatment option for patients with DTX-resistant esophageal squamous cell carcinoma.

Abstract 1395: Docetaxel pretreatment is associated with increased incidence of CNS-metastases in a murine model of HER2-positive breast cancer

Abstract Breast cancer is the most frequent neoplasm in females as it affects 1:10 women. In populations of early breast cancer subsequent brain metastases develop in 5%, while in metastatic breast cancer (mBC), the incidence of CNS-metastases reaches 10-16% [Ann Oncol 2006; 17:935]. The incidence is particularly high (30%-50%) in patients (pts) with HER2-positive mBC [Ann Oncol 2008; 19:1837]. Similarly, the incidence of CNS-metastases is high in pts treated with taxanes for mBC [Ann Oncol 2001; 12:353]. Therefore, we aimed to investigate the role of taxanes on CNS metastases in a murine breast cancer model using the MDA-MB-231BR cell line which has a tropism to metastasize into the CNS upon intracardiac injection [J Natl Ca Inst 2008;100:1092]. Groups of Balb/c nude mice were injected intravenously with docetaxel at a dose of 10mg/kg every 2 weeks for 5 injections (long tax, N=17) or with only 2 similar injections (short tax, N=16) or no injection (control, N=14). Two weeks later MDA-MB-231 BR tumor cells (500′000 cells in 0.1mL PBS) were injected into the left ventricle. Four weeks after that, animals were sacrificed for collection of organs and analysis by histology. The main finding was that metastatic foci were significantly increased in long-tax mice (median number of foci 52, range 0-76) compared to control mice (median number of foci 20, range 0-52; p=0.015). In short-tax animals an intermediate incidence of foci was found (median 30, range 0-79), with a trend, but not a significant difference compared to untreated animals (p=0.7) Histologically we observed a mainly perivascular intraparenchymal infiltration pattern while superficial metastases or a spread to the cerebrospinal fluid was only rarely seen. We therefore assessed changes of the blood-brain barrier (BBB) by ultrastructural approaches. However, we have not found obvious differences in the BBB configuration after taxane treatment. In summary, our results provide evidence that taxane treatment might facilitate spread of breast cancer cells into the CNS, however underlying mechanisms remain to be determined. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 1395. doi:1538-7445.AM2012-1395

Mechanism of the Cardioprotective Effects of Docetaxel Pre-administration Against Adriamycin-Induced Cardiotoxicity

We revealed that pre-treatment with docetaxel (DOC) 12 h before adriamycin (ADR) administration significantly reduced ADR-induced toxic death compared with the simultaneous dosing schedule that was commonly used in previous studies. We considered that pre-treatment with DOC relieves ADR-induced cardiotoxicity. In this study, we investigated the influence of DOC on the pharmacokinetics and pharmacodynamics of ADR in order to clarify the mechanism by which DOC pre-treatment relieves ADR-induced cardiotoxicity. When ADR and/or DOC was intravenously administered, the DOC pre-treatment (DOC-ADR) group showed significantly less toxic death than the ADR-alone group. We examined hepatopathy, nephropathy, leukopenia, and cardiotoxicity, all of which can cause toxic death. Of these toxicities, ADR-induced cardiotoxicity was significantly relieved in the DOC-ADR group. To elucidate the mechanism by which DOC pre-treatment relieved ADR-induced cardiotoxicity, lipid peroxidation as a proxy for the free radical level and the pharmacokinetics of ADR were measured. There was no difference in the pharmacokinetics of ADR between the ADR and DOC-ADR groups. On the other hand, the DOC-ADR group showed significantly inhibited lipid peroxidation in the heart compared with the ADR group. It was considered that DOC pre-administration inhibited ADR-induced free radicals and decreased cardiotoxicity.

Pre-radiation enhances the cytotoxicity of docetaxel in head and neck squamous cell carcinoma cells

This study was designed to determine the effect of the treatment schedule on the interaction between docetaxel and irradiation. Human head and neck squamous cell carcinoma (HNSCC) cells with different p53 status, and HSC4 (p53 wild-type) and CAL27 (p53 mutant type) cells were treated with docetaxel and irradiation using three schedules: i) concurrent treatment, ii) docetaxel pretreatment and iii) pre-radiation. Docetaxel and radiation inhibited the proliferation of HSC4 and CAL27 cells in a dose-dependent manner. However, irradiation pretreatment was more effective than the other treatment regimens in all cells. Our data suggest that pre-radiation in HNSCC cells significantly enhances docetaxel cytotoxity by arresting S-phase, and this provides the most effective treatment sequence of docetaxel and radiation combination therapy. Therefore, radiation followed by docetaxel may be the most effective sequence for head and neck cancer therapy.

Fas-mediated killing of primary prostate cancer cells is increased by mitoxantrone and docetaxel

Therapies for prostate cancer based on Fas (CD95) modulation have been under active development at the preclinical stage using immortalized cell lines. To address clinical applicability, the potential of 11 cultures of primary prostate cancer cells to be killed by Fas-mediated apoptosis was investigated. In addition, the effect of the chemotherapeutic agents mitoxantrone and docetaxel on this killing was determined. Apoptosis was induced in patient-derived, primary prostate cancer cells using effector cells engineered by recombinant lentivirus infection to express Fas ligand (FasL) and measured by 51Cr release assays. All cultured prostate cells were found to undergo Fas-mediated killing; cytotoxicity ranged from 12% to 87% after 6 h. These cells were significantly more sensitive to FasL-mediated killing than PC-3 cells. The basal expression of Fas or the expression of five inhibitors of apoptosis (c-FLIP, survivin, cellular inhibitors of apoptosis protein 1 and 2, and bcl-2) was not found to correlate with susceptibility to Fas-mediated killing. Both mitoxantrone and docetaxel were able to induce Fas receptor expression on primary prostate cancer cells, which translated into a 1.5- to 3-fold enhancement of apoptosis mediated by FasL. Whereas mitoxantrone increased the Fas-induced apoptotic response of all cultured prostate cells tested, docetaxel pretreatment was found to preferentially enhance the killing of bcl-2-expressing cells. These findings show that cultured primary prostate cancer cells are sensitive to Fas-mediated apoptosis. Furthermore, the incidence of apoptosis was found to be improved by combining Fas-mediated therapy with standard chemotherapeutic agents. These findings may have significant implications for prostate cancer therapy.

Schedule Dependent Efficacy of Gefitinib and Docetaxel for Bladder Cancer

We determined the sequence specific efficacy of gefitinib and docetaxel treatment for bladder cancer. This combination was selected because it is currently under study in a phase II clinical trial. In vitro antiproliferative effects of gefitinib, docetaxel and a combination were determined in the 4 bladder cancer cell lines 253J B-V, UM-UC-3, KU-7 and UM-UC-13 by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay. Cell cycle analysis was analyzed using flow cytometry and propidium iodide labeling. Epidermal growth factor receptor downstream signaling was assessed by Western blot analysis. In vivo nude mice were injected subcutaneously with 253J B-V cells and treated with placebo, gefitinib, docetaxel, docetaxel followed by gefitinib or gefitinib followed by docetaxel. Tumor kinetics were established. Gefitinib demonstrated antiproliferative effect against 253J B-V cells (50% inhibitory concentration less than 0.5 muM) but no apoptotic effect in vitro, whereas docetaxel demonstrated antiproliferative and apoptotic effects. When gefitinib and docetaxel were combined, gefitinib enhanced the apoptotic and antiproliferative effects of docetaxel only when gefitinib was administered following docetaxel pretreatment. Apoptosis increased from 45% to 66%. In vivo there were significant differences in tumor weight in mice treated with combination therapy vs gefitinib or docetaxel alone. Importantly improved efficacy was observed when docetaxel was followed by gefitinib administration compared with gefitinib followed by docetaxel (mean tumor weight 42 vs 93 mg, p = 0.022). Sequence specific efficacy was not observed in UM-UC-3, UM-UC-13 and KU-7 cells, which are resistant to gefitinib. Docetaxel followed by gefitinib demonstrated sequence specific efficacy against gefitinib sensitive bladder cancer compared with gefitinib followed by docetaxel or either drug alone. Accordingly gefitinib administration concurrently or after chemotherapy might be the sequence of choice and it should be considered for future clinical trials.

Docetaxel and capecitabine in metastatic androgen independent prostate cancer (AIPC): Phase II trial to detect clinical efficacy of a synergistic combination

4703 Background: Docetaxel plus prednisone is the current therapeutic choice in the management of metastatic AIPC. Capecitabine is an oral prodrug of 5-fluorouracil which is selectively converted intratumorally to 5-flourouracil by thymidine phosphorylase (TP). Differential overexpression of TP is noted in tumors as compared to normal tissue. Docetaxel pretreatment when followed by capecitabine therapy has demonstrated synergy in preclinical studies with xenograft models. The purpose of this phase II trial was to evaluate the efficacy and safety of this combination in metastatic AIPC. Methods: Eligible patients had metastatic AIPC with no prior chemotherapy for metastatic disease. Other requirements included castrate levels of testosterone adequate renal, liver and marrow function and evidence of disease progression either by PSA, new metastatic sites, or progression of measurable disease sites. Docetaxel was administered intravenously on days 1, 8 and 15 of a 28 day cycle at a dose of 36 mg/m2. Capecitabine was administered at a dose of 1250 mg/m2/day in two divided doses orally from days 5 to 18 of each cycle. Results: 11 of 15 patients planned in the first stage have been enrolled to date. Baseline characteristics were, median age 73 years (range 38–78 years).;baseline PSA 131ng/ml (Range 8.9–3716ng/ml); three patients had progressive measurable disease, 5 patients had progression of bony metastases and 3 patients had PSA progression alone. 7 of the 8 evaluable patients demonstrated >50% decline in PSA and both of the measurable disease patients evaluated had a partial remission. 41 cycles of therapy (median 5 cycles) have been administered. Three patients required dose reduction. No grade 4/5 toxicities were noted. Only 1 patient had grade 3 neutropenia. No therapy related hospitalizations or deaths were observed. Conclusions: Preliminary data suggest that the combination of capecitabine and docetaxel is well tolerated and demonstrates promising activity in metastatic AIPC. Author Disclosure Employment or Leadership Consultant or Advisory Role Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Aventis, Roche Aventis

Docetaxel enhances the cytotoxicity of cisplatin to gastric cancer cells by modification of intracellular platinum metabolism.

We have examined the combined anticancer effects of docetaxel (DOC) and cisplatin (CDDP) in vitro using the gastric cancer cell lines MKN-45, MKN-74, and TMK-1. Treatment of the cell lines with 30 microg/ml of DOC for 24 h followed by incubation with 3 or 10 microg/ml of CDDP for 24 h showed a clear synergistic effect. Sequence dependency of the agents was observed in these cell lines: DOC followed by CDDP (DC) showed a stronger antitumor effect than CDDP followed by DOC (CD) in all cell lines. To clarify the mechanism of action of the DC combination, total intracellular platinum (Pt) levels were evaluated after treatment with CDDP alone or combined with DC. For the MKN-45 and -74 cell lines, cells treated with DOC (10 microg/ml for 12 h) and then CDDP showed significantly increased intracellular Pt accumulation compared to cells treated with CDDP alone. We also investigated alterations in intracellular glutathione (GSH) concentration in response to DOC and CDDP. MKN-45 and -74 cells pretreated with DOC (10 microg/ml for 12 h) showed significantly increased intracellular GSH levels compared to cells administered CDDP only. To explain these findings, messenger RNA (mRNA) levels for multidrug resistance-associated protein-1 (MRP-1), the ATP-dependent pump for Pt-GSH complexes, were quantified in CDDP-treated MKN-45 cells with and without DOC pretreatment. While CDDP administration increased MRP-1 mRNA expression in MKN-45 cells, MRP-1 was not up-regulated after CDDP administration in DOC pretreated MKN-45 cells. Our results suggested that the enhanced CDDP toxicity due to DOC pretreatment may be related to the accumulation of intracellular Pt-GSH complexes, because DOC appears to suppress the MRP-1 up-regulation induced by CDDP exposure in gastric cancer cells.

Docetaxel enhances the cytotoxicity of anthracyclines by increasing intracellular drug accumulation

We assessed the combined antitumor activity of docetaxel and doxorubicin (DXR) and tetrahydropyranyl-adriamycin (THP) using the human breast carcinoma cell lines R-27 and MDA-MB-231. Synergistic antitumor activity was observed for both combined docetaxel and DXR, and docetaxel and THP against R-27 cells when contacted simultaneously. However, only additive effects were observed against MDA-MB-231 cells. Intracellular concentrations of DXR and THP in R-27 cells were significantly increased by docetaxel pretreatment, however, this increase was not observed in MDA-MB-231 cells, which exhibited only additive sensitivity to the treatment. Thus, docetaxel increased the antitumor activity of anthracyclines by increasing their intracellular concentrations.