Efficacy and Safety of Sitafloxacin in Treating Low-risk Febrile Neutropenia in Patients with Lung Cancer.

Introduction: Febrile episodes in patients with cancer and chemotherapy-induced neutropenia can be life-threatening and generally require prompt administration of broad-spectrum antimicrobials. However, little evidence exists for treating patients with solid tumors and febrile neutropenia (FN) with oral antimicrobials. Methods: In this prospective study, we aimed to determine the efficacy and safety of sitafloxacin (STFX) for treating FN in lung cancer patients. In this prospective study, low-risk FN patients with lung cancer received STFX. The primary endpoint was response rate, defined as 5 sequential days of absence of fever without adverse events. The study was registered as UMIN000010911. Results: As a result, STFX was administered to 26 patients, all of whom survived during its administration. Of the 26, 14 completed primary endpoint (53.85%). The low response rate was attributed to occurrence of fevers of unknown cause rather than failure of FN treatment. Only two patients received antibacterial agents other than STFX. If response rate omitted absence of fever and been defined only as recovery from FN without changing microbial agents or serious complications, the response rate would have been 91.67%. Adverse events occurred in eight patients, none of which were serious. Conclusions: In conclusion, STFX might be used to treat low-risk FN in patients with lung cancer; however, a more detailed study will be required in future.

Gefitinib ("Iressa", ZD1839), an epidermal growth factor receptor tyrosine kinase inhibitor, reverses breast cancer resistance protein/ABCG2-mediated drug resistance.

Gefitinib ("Iressa", ZD1839) is an orally active, selective epidermal growth factor receptor tyrosine kinase inhibitor, and the single agent is clinically effective in non-small cell lung cancer. Although gefitinib combined with various cytotoxic agents has been reported to enhance cytotoxicity in vitro and in mouse models, the mechanism remains undetermined. Here, to explore the mechanism with topoisomerase I inhibitors, we focused on the efflux pump of the breast cancer resistance protein (BCRP/ABCG2), and then examined whether gefitinib restored drug sensitivity in multidrug-resistant cancer cells overexpressing BCRP. We used PC-6 human small cell lung cancer cells and multidrug-resistant PC-6/SN2-5H cells selected with SN-38 of the active metabolite of irinotecan, and BCRP-overexpressing MCF-7/MX cells selected with mitoxantrone and BCRP cDNA transfectant MCF-7/clone 8 cells. Drug sensitivity against anticancer drugs was determined by tetrazolium dye assay, and intracellular topotecan accumulation by FACScan. The topotecan transport study was done using the plasma membrane vesicles of PC-6/SN2-5H cells. The resistant PC-6/SN2-5H cells overexpressed BCRP but not epidermal growth factor receptor mRNA. Ten micromoles of gefitinib reversed topotecan, SN-38, and mitoxantrone resistance, and increased the intracellular topotecan accumulation in the resistant cells but not in the parental cells. Furthermore, gefitinib inhibited the topotecan transport into the vesicles, and the K(i) value was 1.01 +/- 0.09 micromol/L in the Dixon plot analysis, indicating direct inhibition of BCRP by gefitinib. However, gefitinib was not transported into the vesicles with the high-performance liquid chromatography method. These results indicate that gefitinib reverses BCRP-mediated drug resistance by direct inhibition other than competitive inhibition as a BCRP substrate. Combination of gefitinib and topoisomerase I inhibitors could be clinically effective in cancers expressing BCRP.

[Nontuberculous mycobacterial infections involving solitary pulmonary nodules].

Over the course of 11 years (1993-2003) we encountered 5 cases of pulmonary nontuberculous mycobacterium (NTM) involving a solitary pulmonary nodule. In this report we analyze the chest computed tomography (CT) of these patients, the utility of bronchoscope and transthoracic fine-needle aspiration techniques, the mycobacterium species involved, and treatment results. Four of the 5 NTM cases were due to infection with M. avium and one was due to infection with M. intracellulare. The characteristic findings of the chest CTs were as follows: A solitary nodule was present just under the pleura. No definite distribution pattern was evident. Some cases had agglutinated nodules or fine calcifications. Although fiberoptic bronchoscopy was not used as a diagnostic tool in all 5 NTM cases and histological samples did not contain granulomas, we determined the presence of NTM and we also verified that no cancer cells were present in any of the 5 NTM patients, using transthoracic fine-needle aspiration. Four out of the 5 NTM patients were treated only with drug therapy and they displayed clinical improvement. We resected a solitary nodule in one of the 5 NTM patients because of slow response to drug therapy. We conclude that the solitary pulmonary nodule of NTM is often due to M. avium and that transthoracic fine-needle aspiration is an easy and effective method of detecting NTM.

A case of Mycobacterium nonchromogenicum pulmonary infection showing multiple nodular shadows in an immunocompetent patient.

Mycobacterium nonchromogenicum is generally considered nonpathogenic. However, M. nonchromogenicum rarely causes human disease; particularly, pulmonary disease is extremely rare. The common finding of M. nonchromogenicum pulmonary infection on chest X-ray is a solitary cavity. The present report describes an unusual case of M. nonchromogenicum primary pulmonary infection showing multiple nodular shadows.

A phase I trial of carboplatin and etoposide for elderly (>or=75 year-old) patients with small-cell lung cancer.

PURPOSE: The combination of carboplatin and etoposide is currently considered the most appropriate regimen for treating elderly patients with small-cell lung cancer (SCLC). Previous reports on elderly patients, 70 years or older, found that the recommended dose was close to that of younger patients. Then, we conducted a phase I study of carboplatin and etoposide in elderly patients, 75 years or older, with SCLC. This study aimed to determine the maximum tolerated dose (MTD) and dose-limiting toxicity (DLT). METHODS: Twenty-six patients fulfilling the eligibility criteria, chemotherapy-naive, performance status (PS) of 0-2, age>or=75, and adequate organ functions were enrolled. Patients' characteristics were: male/female=21/5; PS 0/1/2=9/11/6; median age (range)=78 (75-82); and limited/extensive stage=16/10. The patients intravenously received carboplatin with a target AUC of 4 or 5 mg min/ml (Chatelut formula) on day 1 and etoposide at 80-120 mg/m2 on days 1, 2 and 3. Therapy was repeated four times in every 4 weeks. RESULTS: The MTD of carboplatin/etoposide was AUC=5/80, 4/110, and 4/120. The DLTs were thrombocytopenia, neutropenia, leukopenia, and febrile neutropenia. Overall, grade 4 thrombocytopenia, neutropenia (>or=4 days), leukopenia (>or=4 days), and febrile neutropenia occurred in 27, 20, 7, and 13% of cases at MTD levels, respectively, and 0% at other levels. Twenty of 26 patients showed objective responses (2CR, 18PR; RR=77%). CONCLUSION: A dose of carboplatin of AUC=4 and etoposide of 100 mg/m2 was recommended in this regimen.

Tubular adenocarcinoma of the thymus: case report and review of the literature.

Primary carcinomas of the thymus are rare. A variety of histologic patterns have been reported, and the most common are squamous cell carcinoma, lymphoepithelioma like carcinoma, and basaloid carcinoma. Adenocarcinomas of the thymus are extremely rare. As determined from a literature search, a pure tubular adenocarcinoma has never been previously described, and thus, this is first case report of tubular adenocarcinoma of the thymus. A combined resection of the superior vena cava and pericardium was performed. Immunohistochemically, the tumor cells were positive for CD5.

[A case of systemic sarcoidosis diagnosed initially by tonsillar biopsy, with discontinuous nodules in a straight line in the subcutaneous tissue of the upper arm].

A 31-year-old woman was admitted due to swollen cervical lymph nodes and swollen tonsils. These did not respond to treatment by antibiotics, and histological findings of epithelioid cell granulomas were obtained by tonsillar biopsy. After corticosteroid therapy in the subcutaneous tissue of the upper arm 5 nodules were found discontinuously in a straight line. A biopsy of one of these nodules revealed non-caseous epithelioid cell granuloma with Langhans giant cells in the superficial lymph nodes. Her older brother was strongly suspected to have neurogenic sarcoidosis. Familial sarcoidosis was considered related to this case.

An Autopsy Case of Lepidic Pulmonary Metastasis from Cholangiocarcinoma.

We herein report the first case of pulmonary metastasis with lepidic growth that originated from cholangiocarcinoma. A 77-year-old man was admitted to our hospital due to exertional dyspnea and liver dysfunction. Computed tomography showed widespread infiltration and a ground-glass opacity in the lung and dilation of the intrahepatic bile duct. The pulmonary lesion progressed rapidly, and the patient died of respiratory failure. Cholangiocarcinoma and lepidic pulmonary metastasis were pathologically diagnosed by an autopsy. Lepidic pulmonary growth is an atypical pattern of metastasis, and immunopathological staining is useful to distinguish pulmonary metastasis from extrapulmonary cancer and primary pulmonary adenocarcinoma.

Gefitinib inhibits MUC5AC synthesis in mucin-secreting non-small cell lung cancer cells.

Gefitinib, an epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor, is an active agent in non-small cell lung cancer, and rapidly relieves bronchorrhea in patients with bronchioloalveolar carcinoma before the improvement of radiological findings. In addition, epidermal growth factor regulates mucin secretion in normal airway goblet cells. The present study was designed to clarify whether gefitinib modifies mucin production in lung cancer cell lines apart from its anti-proliferative effects, using A549 adenocarcinoma and NCI-H292 mucoepidermoid carcinoma cells expressing EGFR and MUC5AC mRNA. Mucin synthesis was measured by RT-PCR and ELISA, and MAPK and Akt, the downstream targets of EGFR, were examined by Western blotting assay. The clinically-achievable concentration of 1muM gefitinib inhibited the growth of both cells by only 10%, but gefitinib suppressed MUC5AC mRNA levels subsequent to a decrease in intracellular and secreted MUC5AC protein. Gefitinib also inhibited the phosphorylation of MAPK and Akt, and the selective inhibitors PD98059 and LY294002 also suppressed MUC5AC protein synthesis. These findings suggest that gefitinib may inhibits MUC5AC synthesis, at least in part, through MAPK and Akt signaling pathways. Thus, gefitinib inhibits mucin production, which is encouraging for trials involving its use against bronchorrhea in patients with lung cancer.

Gefitinib, an EGFR tyrosine kinase inhibitor, directly inhibits the function of P-glycoprotein in multidrug resistant cancer cells.

Gefitinib (Iressa) is a selective epidermal growth factor receptor tyrosine kinase inhibitor and is used for the treatment of lung cancer. Recently, we discovered that it inhibits the breast cancer resistance protein, which is an ATP-binding cassette transporter. P-glycoprotein (Pgp) also pumps multiple types of drugs out of the cell using energy generated from ATP, and confers multidrug resistance on cancer cells. This study was designed to examine whether gefitinib inhibits the function of Pgp. We used multidrug resistant PC-6/PTX lung cancer and MCF-7/Adr breast cancer cells which overexpress Pgp and measured their drug sensitivity and drug-efflux function by tetrazolium assay and flowcytometry, respectively. In addition, the drug-stimulated ATPase activity of Pgp was measured using insect membranes that express human Pgp. Epidermal growth factor receptor was expressed in MCF-7/Adr, but not in PC-6/PTX cells, and the overexpression of Pgp did not confer resistance to gefitinib to both cell types. However, clinically achievable levels of gefitinib moderately reversed the Pgp-mediated resistance to paclitaxel and docetaxel in Pgp overexpressing cells. In addition, gefitinib increased the intracellular accumulation of the Pgp substrate rhodamine-123 in resistant cells, and activated ATPase in a preparation of pure Pgp-expressing membrane. These findings suggest that gefitinib directly interacts with Pgp and inhibits its function. Gefitinib may clinically inhibit the excretion of Pgp substrate drugs including anticancer agents, and its drug-interaction should therefore be considered.

Expression and functional analyses of breast cancer resistance protein in lung cancer.

PURPOSE: Breast cancer resistance protein (BCRP/ABCG2), an ATP binding cassette half-transporter, confers resistance to mitoxantrone, doxorubicin, and topoisomerase I inhibitors of irinotecan and topotecan. Recently, we reported that BCRP efficiently transported SN-38 (the active metabolite of irinotecan) with a high affinity in lung cancer cells in vitro (K. Nakatomi et al., Biochem. Biophys. Res. Commun., 288: 827-832, 2001). The aim of this study is to explore the role of BCRP in the drug resistance of lung cancer. EXPERIMENTAL DESIGN: The BCRP mRNA expression in lung cancer cells and 23 untreated non-small cell lung cancer (NSCLC) tissues was quantitated by real-time reverse transcription-PCR. To evaluate the drug-efflux function of BCRP, the intracellular topotecan accumulation and drug sensitivity were measured in lung cancer cells with various levels of the BCRP mRNA expression by flow cytometric and tetrazolium dye assay, respectively. RESULTS: The levels of BCRP mRNA expression in the cell lines were significantly correlated with the BCRP function and the sensitivity to SN-38 and topotecan. In NSCLC tissues, the BCRP mRNA expression levels were widely dispersed. Five (22%) of 23 tissues expressed higher levels of the BCRP mRNA than that in NCI-H441 cells with active BCRP function conferring high resistance to topotecan in vitro. CONCLUSIONS: Some NSCLC tissues expressed sufficient levels of the BCRP mRNA to confer drug resistance in vitro.

The histone deacetylase inhibitor FR901228 induces caspase-dependent apoptosis via the mitochondrial pathway in small cell lung cancer cells.

Histone deacetylase inhibitors modulate the transcription of target genes and represent a new class of anticancer agents. The histone deacetylase inhibitor FR901228 has been reported to show antiproliferative and apoptotic effects in various malignancies including small cell lung cancer (SCLC) in vitro; however, the underlying mechanism is not fully understood. BCL-2 and BCL-XL are antiapoptotic proteins, of which overexpression has been reported to confer resistance to anticancer agents. High levels of BCL-2 and BCL-XL are frequently expressed in SCLC tumors. The present study was designed to clarify the apoptotic pathway of FR901228 in SCLC cells in vitro. FR901228 induced apoptosis in three SCLC cell lines after 24 hours of treatment. FR901228 activated caspase-9 and caspase-3 but not caspase-8, and the caspase-3 inhibitor Z-DEVD-fmk blocked the cytotoxicity of FR901228. FR901228 down-regulated the expression of bcl-2 and bcl-xL mRNA through de novo protein synthesis and suppressed the expression of BCL-2 and BCL-XL proteins. In addition, the combination of bcl-2 antisense oligonucleotides with FR901228 enhanced FR901228-induced caspase-3 activity and cytotoxicity. These findings suggest that FR901228 induces caspase-dependent apoptosis via the mitochondrial pathway rather than the death receptor pathway. Considering the possible contributions of BCL-2 and BCL-XL to multidrug resistance, FR901228 is a promising agent in the treatment of refractory as well as primary SCLC tumors.

Analysis of intratumor heterogeneity of EGFR mutations in mixed type lung adenocarcinoma.

BACKGROUND: Epidermal growth factor receptor mutations are predictive of the success of EGFR tyrosine kinase inhibitor treatment in patients with advanced non--small-cell lung cancer. As with other solid tumors, lung cancer is thought to be the result of an accumulation of genetic alterations after exposure to carcinogens. The aim of the present study was to clarify the relationship between multistep carcinogenesis and the accumulation of EGFR mutations. PATIENTS AND METHODS: The intratumor heterogeneity of EGFR mutations was analyzed in 38 patients with resected mixed-type lung adenocarcinoma according to histological patterns, and the clinical features of the patients harboring intratumor heterogeneity of EGFR mutations were evaluated. RESULTS: Intratumor heterogeneity of EGFR mutations was detected in 9 of 38 tumors. EGFR mutations were more common in the bronchioloalveolar (lepidic) carcinoma pattern than in the papillary and acinar patterns, although this difference was not significant. However, there was a significant correlation between intratumor heterogeneity of EGFR mutations and smoking history (P < .043). CONCLUSION: Intratumor heterogeneity of EGFR mutations correlates with the distribution of histological subtype in mixed type adenocarcinoma and is associated with smoking history.

Direct comparison of 3 PCR methods in detecting EGFR mutations in patients with advanced non-small-cell lung cancer.

BACKGROUND: Epidermal growth factor receptor (EGFR) mutations are predictive of response to EGFR tyrosine kinase inhibitors (TKIs) in NSCLC. Several methods have been used to detect EGFR mutations; however, it is not clear which is the most suitable for use in the clinic. In this study, we directly compare the clinical sensitivity and specificity of 3 PCR methods. PATIENTS AND METHODS: We compared the 3 PCR methods (mutant-enriched PCR, PNA-LNA PCR, and PCR clamp) in patients with advanced NSCLC. A patient who showed sensitive mutations by at least 1 PCR method was treated with gefitinib. A patient who showed no sensitive mutations was treated with chemotherapy with cytotoxic agents. RESULTS: Fifty patients with advanced NSCLC previously untreated with EGFR-TKIs were enrolled in this trial. Seventeen patients were harboring EGFR mutations, 5 of whom showed discrepancies between the results of different PCR methods. All 5 patients responded to gefitinib. All patients harboring EGFR mutations received gefitinib treatment and 21 of 33 EGFR-mutation-negative patients received chemotherapy with cytotoxic agents. Median progression-free survival of the gefitinib group and the chemotherapy group were 8.2 and 5.9 months, respectively. CONCLUSION: We considered that all the discrepancies might be false negatives because the patients responded to gefitinib. To clarify the reason for the false negatives of each PCR method, and establish the clinical sensitivity and specificity of each PCR method, a large prospective clinical trial is warranted.

Serum levels of surfactant protein D predict the anti-tumor activity of gefitinib in patients with advanced non-small cell lung cancer.

PURPOSE: Gefitinib is an epidermal growth factor receptor tyrosine kinase inhibitor (EGFR-TKI) that has dramatic effects in selective patients with non-small cell lung cancer (NSCLC). A simple non-invasive method for predicting the efficacy of gefitinib is preferable in clinical settings. In this study, we evaluated prospectively whether surfactant protein-A (SP-A) and -D (SP-D) may be new conventional predictors of the efficacy of gefitinib treatment. METHODS: We measured serum SP-A and SP-D levels on days 0 and 29 in 40 patients with advanced NSCLC treated with 250 mg gefitinib daily. Eligibility criteria included performance status ≤3, age ≤80 years, and stage IIIB-IV disease. In addition, EGFR mutations were analyzed in 24 patients. RESULTS: Multivariate analysis showed that favorable progression-free survival (PFS) after gefitinib treatment was associated with adenocarcinoma and high serum SP-D levels before treatment. EGFR mutation analysis of 24 patients showed that 16 patients had exon 19 deletion and/or exon 21 point mutations. EGFR mutations were significantly correlated with response to gefitinib and serum SP-D levels before treatment was significantly high in patients with the EGFR mutations. Serum SP-A levels were not associated with PFS. CONCLUSIONS: The present study showed that measurement of serum SP-D levels before treatment in patients with NSCLC may be a new surrogate marker for predicting the response to gefitinib.

A case of intravascular large B-cell lymphoma (IVLBCL) with no abnormal findings on chest computed tomography diagnosed by random transbronchial lung biopsy.

A 58-year-old woman was admitted with refractory fever despite receiving broad-spectrum antibiotics. She had hypoxemia, severe anemia, elevated levels of serum lactic dehydrogenase and soluble interleukin-2 receptor, and a positive direct Coombs test, which suggested an underlying autoimmune hemolytic anemia (AIHA). Chest computed tomography (CT) showed no abnormal findings, but she had hypoxia, and her alveolar-arterial oxygen difference (A-aDO2) was increased. A random transbronchial lung biopsy (TBLB) was performed, and pathological analysis showed massive proliferation of tumor cells in the lumina of the small vessels. Intravascular large B-cell lymphoma (IVLBCL) was diagnosed, and her general status improved after chemotherapy.

A phase I study of amrubicin and carboplatin for previously untreated patients with extensive-disease small cell lung cancer.

BACKGROUND: Amrubicin and cisplatin are active in the treatment of small cell lung cancer (SCLC), and carboplatin is an analogue of cisplatin with less nonhematological toxicity. The appropriate dose of amrubicin and carboplatin combination chemotherapy for previously untreated patients with extensive-disease (ED) SCLC has not been established. PURPOSE: To determine the maximum-tolerated dose and dose-limiting toxicity (DLT) of amrubicin and carboplatin in ED-SCLC. PATIENTS AND METHODS: Eligibility criteria were chemotherapy-naive ED-SCLC patients, performance status 0-1, age < or =75, and adequate hematological, hepatic, and renal function. Patients received escalating amrubicin doses under a fixed target area under the curve (AUC) 5 of carboplatin (Chatelut formula). Amrubicin and carboplatin were administered by intravenous (IV) infusion on days 1, 2, and 3, and day 1, respectively. The initial dose of amrubicin was 30 mg/m(2), and the dose was escalated to 35 and 40 mg/m(2). RESULTS: Sixteen patients were enrolled and 15 eligible patients were evaluated. One of six patients in level 1, one of six in level 2, and three of three in level 3 experienced DLTs. The presentation of DLTs included neutropenia, leukopenia, thrombocytopenia, febrile neutropenia, and liver dysfunction. Evaluation of responses were two complete response, nine partial response, three stable disease, and one progressive disease (response rate 73%), and the median survival time was 13.6 months. The maximum-tolerated doses of amrubicin and carboplatin were determined as 40 mg/m(2) and AUC 5. A dose of 35 mg/m(2) amrubicin and carboplatin AUC 5 was recommended in this regimen. CONCLUSIONS: This regimen is associated with an acceptable tolerability profile, and warrants evaluation in the phase II setting.

Antiproliferative effects of the histone deacetylase inhibitor FR901228 on small-cell lung cancer lines and drug-resistant sublines.

FR901228 is a novel histone deacetylase (HDAC) inhibitor, and its antiproliferative effects on non-small cell lung cancer cells have been shown in vitro. However, there have been no reports concerning the effects on small-cell lung cancer (SCLC). We have recently demonstrated that the HDAC inhibitors trichostatin A and sodium butyrate inhibit expression of the catalytic subunit of telomerase (hTERT) mRNA and telomerase activity in prostate cancer cells. The present study was designed to evaluate the effects of FR901228 on proliferation and telomerase activity in SCLC cells in vitro. FR901228 at 5 to 10 nM increased the fraction of cells in the G(2)/M and sub-G(1) phases of the cell-cycle, and inhibited the growth of H69, H526 and H82 cell lines. The expression of hTERT mRNA was inhibited 6 hr after treatment, prior to obvious inhibition of cell growth or cell-cycle distribution shifts. The inhibition of hTERT mRNA expression and telomerase activity was not a consequence of cell-growth arrest or apoptosis. Cycloheximide blocked the suppression of hTERT mRNA induced by FR901228, and the inhibition of hTERT mRNA by FR901228 required newly synthesized proteins. FR901228 also effectively inhibited growth of etoposide-resistant UMCC-1/VP-16, irinotecan-resistant PC-6/SN2-5H and cisplatin-resistant H526/CDDP cells having decreased expression of hTERT mRNA and telomerase activity, as well as their parental cells. This implies that SCLC resistant to these key drugs are not cross-resistant to FR901228. The present study suggests that FR901228 may be a promising drug for chemotherapy of cancers including SCLC, even for refractory or relapsing tumors after conventional chemotherapy.

Reversal of breast cancer resistance protein (BCRP/ABCG2)-mediated drug resistance by novobiocin, a coumermycin antibiotic.

Breast cancer resistance protein (BCRP/ABCG2) of an ATP-binding cassette half-transporter confers resistance against mitoxantrone and camptothecin derivatives of topotecan and irinotecan. Novobiocin, a coumermycin antibiotic, is known to enhance anticancer drug sensitivity of cancer cells in vitro and in vivo, the mechanism of which remains undetermined. Here we focused on drug efflux pump and examined whether novobiocin reversed drug resistance in multidrug-resistant cells highly expressing BCRP. To explore the reversal mechanisms, intracellular drug accumulation was measured by flow cytometry, and a topotecan transport study using plasma membrane vesicles was performed. We used PC-6/SN2-5H2 small cell lung cancer and MCF-7/MX breast cancer cells selected with SN-38 of the active irinotecan metabolite and mitoxantrone, respectively, and the BCRP cDNA transfectant MCF-7/clone 8 cells. These cells expressed high levels of BCRP mRNA but not other known transporters. Compared to the parental PC-6 cells, PC-6/SN2-5H2 cells were 141-, 173- and 57.2-fold resistant to topotecan, SN-38 and mitoxantrone, respectively. Novobiocin at 60 microM decreased the degree of the above resistance by approximately 26-fold in PC-6/SN2-5H2 cells, and similarly reversed resistance in MCF-7/MX, MCF-7/clone 8 and un-selected NCI-H460 cells highly expressing BCRP. Furthermore, novobiocin increased the intracellular topotecan accumulation in these cells and inhibited the topotecan transport into the membrane vesicles of PC-6/SN2-5H2 cells. No effects of novobiocin in these assay were observed in the parental PC-6 and MCF-7 cells. The kinetic parameters in the transport study indicated that novobiocin was a inhibitor for BCRP, resulting in competitive inhibition of BCRP-mediated topotecan transport. These findings suggest that novobiocin effectively overcomes BCRP-mediated drug resistance at acceptable concentrations.