Godefridus J. Peters

Comparison of the sulforhodamine B protein and tetrazolium (MTT) assays for in vitro chemosensitivity testing

The sulforhodamine B (SRB) protein stain assay was compared with the tetrazolium (MTT) colorimetric assay for in vitro chemosensitivity testing of various human tumour cell lines. The SRB assay provided a better linearity with cell number and a higher sensitivity, and its staining was not cell-line dependent. In contrast to the MTT assay, the SRB assay stained recently lysed cells. Cell debris, however, was not stained by SRB and therefore the drug sensitivity data were not affected.

MicroRNA-21 in Pancreatic Cancer: Correlation with Clinical Outcome and Pharmacologic Aspects Underlying Its Role in the Modulation of Gemcitabine Activity

MicroRNA-21 (miR-21) was reported to be overexpressed and contributes to invasion and gemcitabine resistance in pancreatic ductal adenocarcinoma (PDAC). The aim of this study was to evaluate whether miR-21 expression was associated with the overall survival (OS) of PDAC patients treated with gemcitabine and to provide mechanistic insights for new therapeutic targets. miR-21 expression was evaluated in cells (including 7 PDAC cell lines, 7 primary cultures, fibroblasts, and a normal pancreatic ductal cell line) and tissues (neoplastic specimens from 81 PDAC patients and normal ductal samples) isolated by laser microdissection. The role of miR-21 on the pharmacologic effects of gemcitabine was studied with a specific miR-21 precursor (pre-miR-21). Patients with high miR-21 expression had a significantly shorter OS both in the metastatic and in the adjuvant setting. Multivariate analysis confirmed the prognostic significance of miR-21. miR-21 expression in primary cultures correlated with expression in their respective tissues and with gemcitabine resistance. Pre-miR-21 transfection significantly decreased antiproliferative effects and apoptosis induction by gemcitabine, whereas matrix metalloproteinase (MMP)-2/MMP-9 and vascular endothelial growth factor expression were upregulated. Addition of inhibitors of phosphoinositide 3-kinase and mammalian target of rapamycin resulted in decrease of phospho-Akt and prevented pre-miR-21-induced resistance to the proapoptotic effects of gemcitabine. miR-21 expression correlated with outcome in PDAC patients treated with gemcitabine. Modulation of apoptosis, Akt phosphorylation, and expression of genes involved in invasive behavior may contribute to the role of miR-21 in gemcitabine chemoresistance and to the rational development of new targeted combinations.

Patient preference and pharmacokinetics of oral modulated UFT versus intravenous fluorouracil and leucovorin: a randomised crossover trial in advanced colorectal cancer.

The aim of this study was to determine the patients preference for oral UFT/leucovorin (LV) or intravenous (i.v.) 5-fluorouracil (5-FU)/LV chemotherapy in metastatic colorectal cancer and to compare 5-FU exposure with these two treatment options. A total of 37 previously untreated patients with advanced colorectal cancer were randomised to start treatment with either oral UFT 300 mg/m2/day plus oral LV 90 mg/day for 28 days every 5 weeks or i.v. 5-FU 425 mg/m2/day plus LV 20 mg/m2/day for 5 days every 4 weeks. For the second treatment cycle, patients were crossed-over to the alternative treatment regimen. Prior to the first and after the second therapy cycle, patients were required to complete a therapy preference questionnaire (TPQ). The pharmacokinetics of 5-FU were determined by taking blood samples on days 8, 15 or 22 and 28 for UFT and on days 1 and 5 for i.v. 5-FU. 36 patients were eligible. 84% of the patients preferred oral UFT over i.v. 5-FU. After having experienced both treatment modalities, patients indicated taking the medication at home, less stomatitis and diarrhoea, and pill over injection as the most important reasons for their preference. The area under the plasma concentration curve (AUC) for 5-FU after UFT administration was 113 microM x min on day 8, 114 on day 15 and 98 on day 28; the peak levels (Cmax) were 1.2, 1.3 and 1.0 microM, respectively. The AUC for the 5-FU/LV courses was 3083 microM x min for day 1 and 3809 for day 5 (P=0.002). The Cmax was 170.1 and 196.2 microM (P=0.06) and the clearance 2.6 and 1.9 l/min, respectively (P=0.002). Patients with metastatic colorectal cancer clearly preferred oral over i.v. chemotherapy treatment. This choice was most importantly influenced by convenience and toxicity considerations. Although i.v. bolus 5-FU leads to higher peak 5-FU concentrations and AUC values compared with oral UFT, this pharmacokinetic advantage of i.v. 5-FU seems to translate mainly into higher toxicity as seen in large randomised studies comparing oral UFT/LV with i.v. 5-FU/LV. Oral UFT/LV compares favourably with i.v. 5-FU/LV in terms of toxicity and patients preference and leads to prolonged 5-FU exposure, which is comparable to continuous i.v. 5-FU treatment.

Molecular basis of bortezomib resistance: proteasome subunit β5 (PSMB5) gene mutation and overexpression of PSMB5 protein

The proteasome inhibitor bortezomib is a novel anticancer drug that has shown promise in the treatment of refractory multiple myeloma. However, its clinical efficacy has been hampered by the emergence of drug-resistance phenomena, the molecular basis of which remains elusive. Toward this end, we here developed high levels (45- to 129-fold) of acquired resistance to bortezomib in human myelomonocytic THP1 cells by exposure to stepwise increasing (2.5-200 nM) concentrations of bortezomib. Study of the molecular mechanism of bortezomib resistance in these cells revealed (1) an Ala49Thr mutation residing in a highly conserved bortezomib-binding pocket in the proteasome beta5-subunit (PSMB5) protein, (2) a dramatic overexpression (up to 60-fold) of PSMB5 protein but not of other proteasome subunits including PSMB6, PSMB7, and PSMA7, (3) high levels of cross-resistance to beta5 subunit-targeted cytotoxic peptides 4A6, MG132, MG262, and ALLN, but not to a broad spectrum of chemotherapeutic drugs, (4) no marked changes in chymotrypsin-like proteasome activity, and (5) restoration of bortezomib sensitivity in bortezomib-resistant cells by siRNA-mediated silencing of PSMB5 gene expression. Collectively, these findings establish a novel mechanism of bortezomib resistance associated with the selective overexpression of a mutant PSMB5 protein.

Dose-Finding and Pharmacokinetic Study of Cisplatin, Gemcitabine, and SU5416 in Patients With Solid Tumors

PURPOSE To investigate the feasibility and pharmacokinetics of the combination cisplatin, gemcitabine, and SU5416. PATIENTS AND METHODS Patients received cisplatin 80 mg/m(2) on day 1, gemcitabine 1,250 mg/m(2) on days 1 and 8, repeated every 3 weeks, and SU5416 (85 and 145 mg/m(2)) intravenously twice weekly. Pharmacokinetics of all three agents, side effects, and antitumor response were investigated in patients with solid tumors amenable to therapy with cisplatin/gemcitabine. RESULTS In the first cohort of three patients entered at the 85 mg/m(2) dose, no dose-limiting toxicities were observed. In the next cohort (145 mg/m(2)), three patients developed a thromboembolic event. After entry was restricted to patients with low thromboembolic risk, three additional patients enrolled at 145 mg/m(2) developed a thromboembolic event. The dose was then reduced to 85 mg/m(2) in all patients still on the study, and three additional patients were entered on this dose level. In 19 treated patients, eight patients developed nine thromboembolic events (three transient ischemic attacks, two cerebrovascular accidents, and four deep venous thromboses). The most common toxicities observed were those previously reported for SU5416 alone (headache and phlebitis) and for this chemotherapy regimen (nausea, thrombocytopenia, and leucopenia). No significant pharmacologic interaction among the three drugs was observed. Response rates were similar to those expected in the patient population selected for this study. Analysis of variables of the coagulation cascade and of vessel wall activation was performed in three patients and showed significant increases in thrombin generation and endothelial cell perturbation in a treatment cycle-dependent manner. CONCLUSION The incidence of thromboembolic events, possibly related to the particular regimen tested in this study, discourages further investigation of this regimen.

Identification of MicroRNA-21 as a Biomarker for Chemoresistance and Clinical Outcome Following Adjuvant Therapy in Resectable Pancreatic Cancer

Background Pancreatic ductal adenocarcinoma (PDAC) has a dismal prognosis. The high risk of recurrence following surgical resection provides the rationale for adjuvant therapy. However, only a subset of patients benefit from adjuvant therapy. Identification of molecular markers to predict treatment outcome is therefore warranted. The aim of the present study was to evaluate whether expression of novel candidate biomarkers, including microRNAs, can predict clinical outcome in PDAC patients treated with adjuvant therapy. Methodology/Principal Findings Formalin-fixed paraffin embedded specimens from a cohort of 82 resected Korean PDAC cases were analyzed for protein expression by immunohistochemistry and for microRNA expression using quantitative Real-Time PCR. Cox proportional hazards model analysis in the subgroup of patients treated with adjuvant therapy (N = 52) showed that lower than median miR-21 expression was associated with a significantly lower hazard ratio (HR) for death (HR = 0.316; 95%CI = 0.166–0.600; P = 0.0004) and recurrence (HR = 0.521; 95%CI = 0.280–0.967; P = 0.04). MiR-21 expression status emerged as the single most predictive biomarker for treatment outcome among all 27 biological and 9 clinicopathological factors evaluated. No significant association was detected in patients not treated with adjuvant therapy. In an independent validation cohort of 45 frozen PDAC tissues from Italian cases, all treated with adjuvant therapy, lower than median miR-21 expression was confirmed to be correlated with longer overall as well as disease-free survival. Furthermore, transfection with anti-miR-21 enhanced the chemosensitivity of PDAC cells. Conclusions Significance Low miR-21 expression was associated with benefit from adjuvant treatment in two independent cohorts of PDAC cases, and anti-miR-21 increased anticancer drug activity in vitro. These data provide evidence that miR-21 may allow stratification for adjuvant therapy, and represents a new potential target for therapy in PDAC.

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.

2',2'-Difluoro-deoxycytidine (gemcitabine) incorporation into RNA and DNA of tumour cell lines

Gemcitabine (dFdC) is a new cytidine analogue which is active mainly by the incorporation of its triphosphate (dFdCTP) into DNA, leading to cell death. We determined incorporation of dFdC into nucleic acids of two solid tumour cell lines: the murine colon carcinoma cell line Colon 26-10, the human ovarian carcinoma cell line A2780, and the human leukemic cell line CCRF-CEM. dFdC was not only incorporated into DNA, but also into RNA. The extent of incorporation into DNA was highest in A2780 cells and lowest in CCRF-CEM cells (2-4-fold difference). The same pattern was observed for incorporation into RNA, but with a 10-20-fold difference. In A2780, incorporation into DNA was about twice that of the incorporation into RNA, in CEM cells 10-20-fold that of RNA. Incorporation into RNA was verified using two methods for separation of RNA and DNA, acid precipitation and CsCl-gradient centrifugation. Incorporation into DNA was time and concentration dependent, but incorporation into RNA seemed to be only concentration dependent. We also determined the effect of dFdC on DNA and RNA synthesis by measurement of thymidine and uridine incorporation, respectively, using similar conditions as for the incorporation studies. In all three cell lines DNA synthesis was inhibited almost completely, even at 0.1 microM dFdC and at 4-hr exposure. RNA synthesis inhibition did not exceed 50% in both solid tumour cell lines, even at 1 microM dFdC exposure for 24 hr. A clear concentration effect was only observed in the CCRF-CEM cell line and only after 24 hr exposure. At a 1 microM dFdC exposure for 24 hr, RNA synthesis was completely inhibited in these cells. Incorporation of dFdC into RNA and inhibition of RNA synthesis represent an unrecognized but possibly important mechanism of action of this drug.

Correlation of CDA, ERCC1, and XPD polymorphisms with response and survival in gemcitabine/cisplatin-treated advanced non-small cell lung cancer patients.

Purpose: Selecting patients according to key genetic characteristics may help to tailor chemotherapy and optimize the treatment in non–small cell lung cancer (NSCLC). Polymorphisms at the xeroderma pigmentosum group D (XPD), excision repair cross-complementing 1 (ERCC1), and cytidine deaminase (CDA) genes have been associated with alterations in enzymatic activity and may change sensitivity to the widely used cisplatin-gemcitabine regimen. Experimental Design: Analyses of CDA, XPD, and ERCC1 polymorphisms were done on blood samples of 65 chemotherapy-naïve, advanced NSCLC patients treated with cisplatin-gemcitabine. Furthermore, CDA enzymatic activity was evaluated by high-performance liquid chromatography analysis. Association between XPD Asp312Asn and Lys751Gln, ERCC1 C118T, and CDA Lys27Gln polymorphisms and response, clinical benefit, toxicity, time to progression (TTP), and overall survival (OS) was estimated using Pearsons χ2 tests, the Kaplan-Meier method, the log-rank test, and the Cox proportional hazards model. Results: The CDA Lys27Lys polymorphism significantly correlated with better clinical benefit (P = 0.04) and grade ≥3 neutropenia and thrombocytopenia, as well as with longer TTP and OS (P = 0.006 and P = 0.002, respectively), whereas no significant associations were found among ERCC1 and XPD polymorphisms and both response and clinical outcome. Finally, the enzymatic activity assay showed a significant lower mean in subjects harboring the CDA Lys27Lys polymorphism. Conclusions: Our data suggested the role of CDA Lys27Lys polymorphism as a possible predictive marker of activity, toxicity, TTP, and OS in advanced NSCLC patients treated with cisplatin and gemcitabine. These results may be explained by the lower enzymatic activity associated with the Lys27Lys CDA and offer a potential new tool for treatment optimization.

Mechanisms of synergism between cisplatin and gemcitabine in ovarian and non-small-cell lung cancer cell lines

Summary2′,2′-Difluorodeoxycytidine (gemcitabine, dFdC) and cis-diammine-dichloroplatinum (cisplatin, CDDP) are active agents against ovarian cancer and non-small-cell lung cancer (NSCLC). CDDP acts by formation of platinum (Pt)–DNA adducts; dFdC by dFdCTP incorporation into DNA, subsequently leading to inhibition of exonuclease and DNA repair. Previously, synergism between both compounds was found in several human and murine cancer cell lines when cells were treated with these drugs in a constant ratio. In the present study we used different combinations of both drugs (one drug at its IC25 and the other in a concentration range) in the human ovarian cancer cell line A2780, its CDDP-resistant variant ADDP, its dFdC-resistant variant AG6000 and two NSCLC cell lines, H322 (human) and Lewis lung (LL) (murine). Cells were exposed for 4, 24 and 72 h with a total culture time of 96 h, and possible synergism was evaluated by median drug effect analysis by calculating a combination index (CI; CI < 1 indicates synergism). With CDDP at its IC25, the average CIs calculated at the IC50, IC75 IC90 and IC95 after 4, 24 and 72 h of exposure were < 1 for all cell lines, indicating synergism, except for the CI after 4 h exposure in the LL cell line which showed an additive effect. With dFdC at its IC25, the CIs for the combination with CDDP after 24 h were < 1 in all cell lines, except for the Cls after 4 h exposure in the LL and H322 cell lines which showed an additive effect. At 72 h exposure all Cls were < 1. CDDP did not significantly affect dFdCTP accumulation in all cell lines. CDDP increased dFdC incorporation into both DNA and RNA of the A2780 cell lines 33- and 79-fold (P < 0.01) respectively, and tended to increase the dFdC incorporation into RNA in all cell lines. In the AG6000 and LL cell lines, CDDP and dFdC induced > 25% more DNA strand breaks (DSB) than each drug alone; however, in the other cell lines no effect, or even a decrease in DSB, was observed. dFdC increased the cellular Pt accumulation after 24 h incubation only in the ADDP cell line. However, dFdC did enhance the Pt–DNA adduct formation in the A2780, AG6000, ADDP and LL cell lines (1.6-, 1.4-, 2.9- and 1.6-fold respectively). This increase in Pt–DNA adduct formation seems to be related to the incorporation of dFdC into DNA (r = 0.91). No increase in DNA platination was found in the H322 cell line. dFdC only increased Pt–DNA adduct retention in the A2780 and LL cell lines, but decreased the Pt–DNA adduct retention in the AG6000 cell line. In conclusion, the synergism between dFdC and CDDP appears to be mainly due to an increase in Pt–DNA adduct formation possibly related to changes in DNA due to dFdC incorporation into DNA.