Tumor Drug Concentration and Phosphoproteomic Profiles After Two Weeks of Treatment With Sunitinib in Patients with Newly Diagnosed Glioblastoma

PURPOSE

Tyrosine kinase inhibitors (TKI) have poor efficacy in patients with glioblastoma (GBM). Here, we studied whether this is predominantly due to restricted blood-brain barrier penetration or more to biological characteristics of GBM.

PATIENTS AND METHODS

Tumor drug concentrations of the TKI sunitinib after 2 weeks of preoperative treatment was determined in 5 patients with GBM and compared with its in vitro inhibitory concentration (IC50) in GBM cell lines. In addition, phosphotyrosine (pTyr)-directed mass spectrometry (MS)-based proteomics was performed to evaluate sunitinib-treated versus control GBM tumors.

RESULTS

The median tumor sunitinib concentration of 1.9 μmol/L (range 1.0-3.4) was 10-fold higher than in concurrent plasma, but three times lower than sunitinib IC50s in GBM cell lines (median 5.4 μmol/L, 3.0-8.5; P = 0.01). pTyr-phosphoproteomic profiles of tumor samples from 4 sunitinib-treated versus 7 control patients revealed 108 significantly up- and 23 downregulated (P < 0.05) phosphopeptides for sunitinib treatment, resulting in an EGFR-centered signaling network. Outlier analysis of kinase activities as a potential strategy to identify drug targets in individual tumors identified nine kinases, including MAPK10 and INSR/IGF1R.

CONCLUSIONS

Achieved tumor sunitinib concentrations in patients with GBM are higher than in plasma, but lower than reported for other tumor types and insufficient to significantly inhibit tumor cell growth in vitro. Therefore, alternative TKI dosing to increase intratumoral sunitinib concentrations might improve clinical benefit for patients with GBM. In parallel, a complex profile of kinase activity in GBM was found, supporting the potential of (phospho)proteomic analysis for the identification of targets for (combination) treatment.

Carboplatin Dosing in Children Using Estimated Glomerular Filtration Rate: Equation Matters

Renal function-based carboplatin dosing using measured glomerular filtration rate (GFR) results in more consistent drug exposure than anthropometric dosing. We aimed to validate the Newell dosing equation using estimated GFR (eGFR) and study which equation most accurately predicts carboplatin clearance in children with retinoblastoma. In 13 children with retinoblastoma 38 carboplatin clearance values were obtained from individual fits using MWPharm++. Carboplatin exposure (AUC) was calculated from administered dose and observed carboplatin clearance and compared to predicted AUC calculated with a carboplatin dosing equation (Newell) using different GFR estimates. Different dosing regimens were compared in terms of accuracy, bias and precision. All patients had normal eGFR. Carboplatin exposure using cystatin C-based eGFR equations tended to be more accurate compared to creatinine-based eGFR (30% accuracy 76.3-89.5% versus 76.3-78.9%, respectively), which led to significant overexposure, especially in younger (aged ≤ 2 years) children. Of all equations, the Schwartz cystatin C-based equation had the highest accuracy and lowest bias. Although anthropometric dosing performed comparably to many of the eGFR equations overall, we observed a weight-dependent change in bias leading to underdosing in the smallest patients. Using cystatin C-based eGFR equations for carboplatin dosing in children leads to more accurate carboplatin-exposure in patients with normal renal function compared to anthropometric dosing. In children with impaired kidney function, this trend might be more pronounced. Anthropometric dosing is hampered by a weight-dependent bias.

11C-Sorafenib and 15O-H2O PET for Early Evaluation of Sorafenib Therapy

Sorafenib leads to clinical benefit in a subgroup of patients, whereas all are exposed to potential toxicity. Currently, no predictive biomarkers are available. The purpose of this study was to evaluate whether ¹¹C-sorafenib and ¹⁵O-H₂O PET have potential to predict treatment efficacy. Methods: In this prospective exploratory study, 8 patients with advanced solid malignancies and an indication for sorafenib treatment were included. Microdose ¹¹C-sorafenib and perfusion ¹⁵O-H₂O dynamic PET scans were performed before and after 2 wk of sorafenib therapy. The main objective was to assess whether tumor ¹¹C-sorafenib uptake predicts sorafenib concentrations during therapy in corresponding tumor biopsy samples measured with liquid chromatography tandem mass spectrometry. Secondary objectives included determining the association of ¹¹C-sorafenib PET findings, perfusion ¹⁵O-H₂O PET findings, and sorafenib concentrations after therapeutic dosing with response. Results: ¹¹C-sorafenib PET findings did not predict sorafenib concentrations in tumor biopsy samples during therapy. In addition, sorafenib plasma and tumor concentrations were not associated with clinical outcome in this exploratory study. Higher ¹¹C-sorafenib accumulation in tumors at baseline and day 14 of treatment showed an association with poorer prognosis and correlated with tumor perfusion (Spearman correlation coefficient = 0.671, P = 0.020). Interestingly, a decrease in tumor perfusion measured with ¹⁵O-H₂O PET after only 14 d of therapy showed an association with response, with a decrease in tumor perfusion of 56% ± 23% (mean ± SD) versus 18% ± 32% in patients with stable and progressive disease, respectively. Conclusion: Microdose ¹¹C-sorafenib PET did not predict intratumoral sorafenib concentrations after therapeutic dosing, but the association between a decrease in tumor perfusion and clinical benefit warrants further investigation.

The prognostic impact of circulating miRNAs in patients with advanced esophagogastric cancer during palliative chemotherapy

The prognosis of patients with advanced oesophageal cancer (EC) and gastric cancer (GC) is poor. Circulating microRNAs (ci-miRNAs) may have prognostic and predictive value to improve patient selection for palliative treatment. The purpose of this study is to assess the prognostic and predictive value of specific ci-miRNAs in plasma of patients with EC and GC treated with first-line palliative gemcitabine and cisplatin. Droplet digital PCR (ddPCR) was used to quantify miR-200c-3p, miR-375, miR-21-5p, miR-148a-3p, miR-146a-5p, miR-141-3p and miR-218-5p in plasma from 68 patients. ci-miRNA expression was analyzed in relation to overall survival (OS), progression-free survival (PFS), and response to chemotherapy. ci-miRNA levels were detectable in 36 baseline (71%) samples and in 14 (47%) follow-up samples. Increased circulating miR-200c-3p in GC showed a trend (p = 0.06) towards a shorter OS. High circulating miR-375 was associated with a longer OS (p = 0.02) in patients with esophageal adenocarcinoma (EAC). No significant difference was observed in ci-miRNA expression between paired pre- and on-treatment samples. ci-miRNA expression was not associated with response to chemotherapy. ci-miRNAs can be measured in plasma samples of patients treated with first-line palliative chemotherapy using ddPCR despite prolonged storage in heparin. Elevated circulating miR-375 might be a prognostic marker for patients with EAC.

Epithelial Transfer of the Tyrosine Kinase Inhibitors Erlotinib, Gefitinib, Afatinib, Crizotinib, Sorafenib, Sunitinib, and Dasatinib: Implications for Clinical Resistance

Simple Summary

Tyrosine kinase inhibitors (TKIs) specifically inhibit phosphorylation of signaling pathways of cancer cells, thereby inhibiting their growth. They are characterized by a poor solubility and high protein binding, leading to a large variability in gut uptake after oral administration and variation in the clinical efficacy. We used the CaCo2 gut epithelial model to characterize the gut absorption of 7 TKIs and observed a large variation in apical/basolateral (mimicking gut/blood) transfer, with 4 TKIs showing a negative and 3 a neutral transfer. A highly negative transfer may lead to pharmacokinetic resistance. Intracellular uptake of TKIs was high for sunitinib and crizotinib, intermediate for gefitinib, dasatinib and sorafenib, low for afatinib and not detectable for erlotinib. These properties may explain a high red blood cell to plasma ratio for most TKIs investigated. Although TKIs are poorly absorbed the latter property may compensate for this.

Abstract

Background: tyrosine kinase inhibitors (TKIs) inhibit phosphorylation of signaling proteins. TKIs often show large variations in the clinic due to poor pharmacology, possibly leading to resistance. We compared gut absorption of inhibitors of epidermal growth factor receptor (erlotinib, gefitinib, and afatinib), ALK-cMET (crizotinib), PDGFR/BCR-Abl (dasatinib), and multikinase inhibitors (sunitinib and sorafenib). In clinical samples, we measured the disposition of each compound within various blood compartments. Methods: we used an optimized CaCo2 gut epithelial model to characterize 20 µM TKI absorption. The apical/basolateral transfer is considered to represent the gut/blood transfer. Drugs were measured using LC-MS/MS. Results: sorafenib and sunitinib showed the highest apical/basolateral transfer (Papp 14.1 and 7.7 × 10⁻⁶ cm/s, respectively), followed by dasatinib (3.4), afatinib (1.5), gefitinib (0.38), erlotinib (0.13), and crizotinib (n.d.). However, the net absorptions for dasatinib, afatinib, crizotinib, and erlotinib were highly negative (efflux ratios >5) or neutral/negative, sorafenib (0.86), gefitinib (1.0), and sunitinib (1.6). A high negative absorption may result in resistance because of a poor exposure of tissues to the drug. Accumulation of the TKIs at the end of the transfer period (A->B) was not detectable for erlotinib, very low for afatinib 0.45 pmol/μg protein), followed by gefitinib (0.79), dasatinib (1.1), sorafenib (1.65), and crizotinib (2.11), being highest for sunitinib (11.9). A similar pattern was found for accumulation of these drugs in other colon cell lines, WiDr and HT29. In clinical samples, drugs accumulated consistently in red blood cells; blood to plasma ratios were all >3 (sorafenib) or over 30 for erlotinib. Conclusions: TKIs are consistently poorly absorbed, but accumulation in red blood cells seems to compensate for this.

RX-3117 (Fluorocyclopentenyl-Cytosine)-Mediated Down-Regulation of DNA Methyltransferase 1 Leads to Protein Expression of Tumor-Suppressor Genes and Increased Functionality of the Proton-Coupled Folate Carrier

(1) Background: RX-3117 (fluorocyclopentenyl-cytosine) is a cytidine analog that inhibits DNA methyltransferase 1 (DNMT1). We investigated the mechanism and potential of RX-3117 as a demethylating agent in several in vitro models. (2) Methods: we used western blotting to measure expression of several proteins known to be down-regulated by DNA methylation: O⁶-methylguanine-DNA methyltransferase (MGMT) and the tumor-suppressor genes, p16 and E-cadherin. Transport of methotrexate (MTX) mediated by the proton-coupled folate transporter (PCFT) was used as a functional assay. (3) Results: RX-3117 treatment decreased total DNA-cytosine-methylation in A549 non-small cell lung cancer (NSCLC) cells, and induced protein expression of MGMT, p16 and E-cadherin in A549 and SW1573 NSCLC cells. Leukemic CCRF-CEM cells and the MTX-resistant variant (CEM/MTX, with a deficient reduced folate carrier) have a very low expression of PCFT due to promoter hypermethylation. In CEM/MTX cells, pre-treatment with RX-3117 increased PCFT-mediated MTX uptake 8-fold, and in CEM cells 4-fold. With the reference hypomethylating agent 5-aza-2′-deoxycytidine similar values were obtained. RX-3117 also increased PCFT gene expression and PCFT protein. (4) Conclusion: RX-3117 down-regulates DNMT1, leading to hypomethylation of DNA. From the increased protein expression of tumor-suppressor genes and functional activation of PCFT, we concluded that RX-3117 might have induced hypomethylation of the promotor.

Kinase Inhibitor Treatment of Patients with Advanced Cancer Results in High Tumor Drug Concentrations and in Specific Alterations of the Tumor Phosphoproteome

Identification of predictive biomarkers for targeted therapies requires information on drug exposure at the target site as well as its effect on the signaling context of a tumor. To obtain more insight in the clinical mechanism of action of protein kinase inhibitors (PKIs), we studied tumor drug concentrations of protein kinase inhibitors (PKIs) and their effect on the tyrosine-(pTyr)-phosphoproteome in patients with advanced cancer. Tumor biopsies were obtained from 31 patients with advanced cancer before and after 2 weeks of treatment with sorafenib (SOR), erlotinib (ERL), dasatinib (DAS), vemurafenib (VEM), sunitinib (SUN) or everolimus (EVE). Tumor concentrations were determined by LC-MS/MS. pTyr-phosphoproteomics was performed by pTyr-immunoprecipitation followed by LC-MS/MS. Median tumor concentrations were 2–10 µM for SOR, ERL, DAS, SUN, EVE and >1 mM for VEM. These were 2–178 × higher than median plasma concentrations. Unsupervised hierarchical clustering of pTyr-phosphopeptide intensities revealed patient-specific clustering of pre- and on-treatment profiles. Drug-specific alterations of peptide phosphorylation was demonstrated by marginal overlap of robustly up- and downregulated phosphopeptides. These findings demonstrate that tumor drug concentrations are higher than anticipated and result in drug specific alterations of the phosphoproteome. Further development of phosphoproteomics-based personalized medicine is warranted.

Crizotinib sensitizes the erlotinib resistant HCC827GR5 cell line by influencing lysosomal function

In non-small cell lung cancer, sensitizing mutations in epidermal growth factor receptor (EGFR) or cMET amplification serve as good biomarkers for targeted therapies against EGFR or cMET, respectively. Here we aimed to determine how this different genetic background would affect the interaction between the EGFR-inhibitor erlotinib and the cMET-inhibitor crizotinib. To unravel the mechanism of synergy we investigated the effect of the drugs on various parameters, including cell cycle arrest, migration, protein phosphorylation, kinase activity, the expression of drug efflux pumps, intracellular drug concentrations, and live-cell microscopy. We observed additive effects in EBC-1, H1975, and HCC827, and a strong synergism in the HCC827GR5 cell line. This cell line is a clone of the HCC827 cells that harbor an EGFR exon 19 deletion and has been made resistant to the EGFR-inhibitor gefitinib, resulting in cMET amplification. Remarkably, the intracellular concentration of crizotinib was significantly higher in HCC827GR5 compared to the parental HCC827 cell line. Furthermore, live-cell microscopy with a pH-sensitive probe showed a differential reaction of the pH in the cytoplasm and the lysosomes after drug treatment in the HCC827GR5 in comparison with the HCC827 cells. This change in pH could influence the process of lysosomal sequestration of drugs. These results led us to the conclusion that lysosomal sequestration is involved in the strong synergistic reaction of the HCC827GR5 cell line to crizotinib-erlotinib combination. This finding warrants future clinical studies to evaluate whether genetic background and lysosomal sequestration could guide tailored therapeutic interventions.

Coexisting Molecular Determinants of Acquired Oxaliplatin Resistance in Human Colorectal and Ovarian Cancer Cell Lines

Oxaliplatin (OHP) treatment of colorectal cancer (CRC) frequently leads to resistance. OHP resistance was induced in CRC cell lines LoVo-92 and LoVo-Li and a platinum-sensitive ovarian cancer cell line, A2780, and related to cellular platinum accumulation, platinum-DNA adducts, transporter expression, DNA repair genes, gene expression arrays, and array-CGH profiling. Pulse (4 h, 4OHP) and continuous exposure (72 h, cOHP) resulted in 4.0 to 7.9-fold and 5.0 to 11.8-fold drug resistance, respectively. Cellular oxaliplatin accumulation and DNA-adduct formation were decreased and related to OCT1-3 and ATP7A expression. Gene expression profiling and pathway analysis showed significantly altered p53 signaling, xenobiotic metabolism, role of BRCA1 in DNA damage response, and aryl hydrocarbon receptor signaling pathways, were related to decreased ALDH1L2, Bax, and BBC3 (PUMA) and increased aldo-keto reductases C1 and C3. The array-CGH profiles showed focal aberrations. In conclusion, OHP resistance was correlated with total platinum accumulation and OCT1-3 expression, decreased proapoptotic, and increased anti-apoptosis and homologous repair genes.

RX-3117 (fluorocyclopentenyl cytosine): a novel specific antimetabolite for selective cancer treatment

INTRODUCTION

RX-3117 is an oral, small molecule cytidine analog anticancer agent with an improved pharmacological profile relative to gemcitabine and other nucleoside analogs. The agent has excellent activity against various cancer cell lines and xenografts including gemcitabine-resistant variants and it has excellent oral bioavailability; it is not a substrate for the degradation enzyme cytidine deaminase. RX-3117 is being evaluated at a daily oral schedule of 700 mg (5 days/week for 3 weeks) which results in plasma levels in the micromolar range that have been shown to be cytotoxic to cancer cells. It has shown clinical activity in refractory bladder cancer and pancreatic cancer. Areas covered: The review provides an overview of the relevant market and describes the mechanism of action, main pharmacokinetic/pharmacodynamic features and clinical development of this investigational small molecule. Expert opinion: RX-3117 is selectively activated by uridine-cytidine kinase 2 (UCK2), which is expressed only in tumors and has a dual mechanism of action: DNA damage and inhibition of DNA methyltransferase 1 (DNMT1). Because of its tumor selective activation, novel mechanism of action, excellent oral bioavailability and candidate biomarkers for patient selection, RX-3117 has the potential to replace gemcitabine in the treatment of a spectrum of cancer types.

DNA methyltransferases expression in normal tissues and various human cancer cell lines, xenografts and tumors

DNA methylation plays an important role in carcinogenesis and aberrant methylation patterns have been found in many tumors. Methylation is regulated by DNA methyltransferases (DNMT), catalyzing DNA methylation. Therefore inhibition of DNMT is an interesting target for anticancer treatment. RX-3117 (fluorocyclopentenylcytosine) is a novel demethylating antimetabolite that is currently being studied in clinical trials in metastatic bladder and pancreatic cancers. The active nucleotide of RX-3117 is incorporated into DNA leading to downregulation of DNMT1, the maintenance DNA methylation enzyme. Since DNMT1 is a major target for the activity of RX-3117, DNMT1 may be a potential predictive biomarker. Therefore, DNMT1 protein and mRNA expression was investigated in 19 cancer cell lines, 26 human xenografts (hematological, lung, pancreatic, colon, bladder cancer) and 10 colorectal cancer patients. The DNMT1 mRNA expression showed large variation between cell lines (100-fold) and the 26 xenografts (1100-fold) investigated. The DNMT1 protein was overexpressed in colon tumours from patients compared to non-malignant mucosa from the same patients (P = 0.02). The DNA methylation in these patients was significantly higher in tumour tissues compared to normal mucosa (P = 0.001). DNMT1 expression in normal white blood cells also showed a large variation. In conclusion, the large variation in DNMT1 expression may serve as a potential biomarker for demethylating therapy such as with RX-3117.

Phase I Dose-Escalation Study of Once Weekly or Once Every Two Weeks Administration of High-Dose Sunitinib in Patients With Refractory Solid Tumors

PURPOSE

Dose and schedule optimization of treatment with tyrosine kinase inhibitors is of utmost importance. On the basis of preclinical data, a phase I clinical trial of once weekly or once every 2 weeks administration of high-dose sunitinib in patients with refractory solid malignancies was conducted.

PATIENTS AND METHODS

Patients with advanced cancer refractory to standard treatment were eligible. With use of a standard 3 + 3 phase I design, patients received escalating doses of sunitinib, in 100 mg increments, starting at 200 mg once weekly. In both the once weekly and once every 2 weeks cohorts, 10 more patients were included at the maximum tolerated dose level. Primary end points were safety and tolerability.

RESULTS

Sixty-nine patients with advanced cancer, predominantly colorectal cancer (42%), were treated with this alternative dosing regimen. Maximum tolerated dose was established at 300 mg once weekly and 700 mg once every 2 weeks, resulting in nine- and 18-fold higher maximum plasma concentrations compared with standard dose, respectively. Treatment was well tolerated, with fatigue (81%), nausea (48%), and anorexia (33%) being the most frequent adverse events. The only grade 3 or 4 treatment-related adverse event in 5% or more of patients was fatigue (6%). Sixty-three percent of patients had significant clinical benefit, with a 30% progression-free survival of 5 months or more.

CONCLUSION

Sunitinib administered once weekly at 300 mg or once every 2 weeks at 700 mg is feasible, with comparable tolerability as daily administration. Administration of 700 mg once every 2 weeks can be considered as the most optimal schedule because of the highest maximum plasma concentration being reached. The promising preliminary antitumor activity of this alternative schedule in heavily pretreated patients warrants further clinical evaluation and might ultimately indicate a class characteristic of tyrosine kinase inhibitors.

Randomized phase 2 study of gemcitabine and cisplatin with or without vitamin supplementation in patients with advanced esophagogastric cancer

Purpose

Preclinical research and prior clinical observations demonstrated reduced toxicity and suggested enhanced efficacy of cisplatin due to folic acid and vitamin B12 suppletion. In this randomized phase 2 trial, we evaluated the addition of folic acid and vitamin B12 to first-line palliative cisplatin and gemcitabine in patients with advanced esophagogastric cancer (AEGC).

Methods

Patients with AEGC were randomized to gemcitabine 1250 mg/m² (i.v. days 1, 8) and cisplatin 80 mg/m² (i.v. day 1) q 3 weeks with or without folic acid (450 µg/day p.o.) and vitamin B12 (1000 µg i.m. q 9 weeks). The primary endpoint was response rate (RR). Secondary endpoints included overall survival (OS), time to progression (TTP), toxicity, and exploratory biomarker analyses. Cisplatin sensitivity and intracellular platinum levels were determined in adenocarcinoma cell lines cultured under high and low folate conditions in vitro.

Results

Adenocarcinoma cells cultured in medium with high folate levels were more sensitive to cisplatin and this was associated with increased intracellular platinum levels. In the randomized phase 2 clinical trial, which ran from October 2004 to September 2013, treatment was initiated in 78 of 82 randomized pts, 39 in each study arm. The RR was similar; 42.1% for supplemented patients vs. 32.4% for unsupplemented patients; p = 0.4. Median OS and TTP were 10.0 and 5.9 months for supplemented vs. 7.7 and 5.4 months for unsupplemented patients (OS, p = 0.9; TTP, p = 0.9). Plasma homocysteine was lower in the supplemented group [n = 20, 6.9 ± 1.6 (mean ± standard error of mean, SEM) µM; vs. 12.5 ± 4.0 µM; p < 0.001]. There was no significant difference in the C_max of gemcitabine and cisplatin in the two treatment groups.

Conclusion

Folic acid and vitamin B12 supplementation do not improve the RR, PFS, or OS of cisplatin and gemcitabine in patients with AEGC.

Sensitive liquid chromatography mass spectrometry (LC-MS) assay reveals novel insights on DNA methylation and incorporation of gemcitabine, its metabolite difluorodeoxyuridine, deoxyuridine, and RX-3117 into DNA

Antimetabolites are incorporated into DNA and RNA, affecting their function. Liquid-chromatography-mass-spectrometry (LC-MS-MS) permits the sensitive, selective analysis of normal nucleosides. The method was adapted to measure the incorporation of deoxyuridine, gemcitabine (difluorodeoxycytidine), its metabolite difluorodeoxyuridine (dFdU), and the novel compound fluorocyclopentenylcytosine (RX3117). DNA was degraded to its deoxynucleotides for quantification by LC-MS-MS, gradient chromatography on a Phenomenex prodigy-3-ODS with positive ionization. The range of deoxyuridine DNA-mis-incorporation varied nine-fold in 27 cell lines (leukemia, colon, ovarian, lung cancer). At low-folate conditions a 2.1-fold increase in deoxyuridine was observed. Global methylation (given as % 5-methyl-deoxycytidine) was comparable between the cell lines (4.6-6.5%). Exposure of A2780 cells to 1 μM gemcitabine (4 hours) resulted in 3.6 pmol gemcitabine/μg DNA, but in AG6000 cells (deoxycytidine-kinase-deficient) no incorporation was found. However, when A2780, AG6000, or CCRF-CEM cells were exposed to 100 μM dFdU we found it as gemcitabine, 20.5, 19.6, and 0.51 pmol gemcitabine/μg DNA, respectively. Preincubation of CCRF-CEM cells with cyclopentenyl-cytosine (a CTP-synthetase inhibitor) increased dFdU incorporation four-fold. Apparently dFdU is activated independently of deoxycytidine-kinase and possibly converted in-situ to dFdCMP. RX3117 was incorporated into both DNA and RNA (0.0037 and 0.00515 pmol/μg, respectively). In summary, a sensitive method to quantify the incorporation of gemcitabine, deoxyuridine, and RX-3117 was developed, which revealed that dFdU was incorporated into DNA as the parent compound gemcitabine.

Tissue distribution of crizotinib and gemcitabine combination in a patient-derived orthotopic mouse model of pancreatic cancer

<p class="ADMETabstracttext">Pharmacokinetics focuses on the question whether a drug actually reaches its target in therapeutic concentrations or accumulates elsewhere, potentially causing toxicological or unpredictable side effects. We determined tissue distribution of gemcitabine, an antimetabolite, and crizotinib, a tyrosine-kinase inhibitor targeted against the anaplastic lymphoma kinase (ALK) and mesenchymal-epithelial transition factor (c-Met) receptors, in a validated orthotopic mouse model for pancreatic cancer. Mice with pancreatic cancer were treated with either oral crizotinib at 25 mg/kg, gemcitabine at 100 mg/kg or with their combination. Two hours after the last gemcitabine dose mice were sacrificed and all available blood/organs/tissues were sampled. Tissue was subsequently analyzed for drug concentrations using a validated liquid chromatography-mass spectrometry (LC-MS/MS) technique. In whole blood gemcitabine was about 1.0 µM and crizotinib 2.4 µM in the single treatment, whereas in the combination crizotinib increased the levels of gemcitabine. Crizotinib was found in all major tissues, being highest in the intestine. Comparison of crizotinib alone to the gemcitabine-crizotinib combination showed that crizotinib tissue concentrations were 3-6 fold lower in liver, lung, kidney and spleen, 30-fold lower in the skin, heart and pancreas and 200-fold lower in the brain. Tissue gemcitabine was highest in spleen and skin, being about 5-10 fold higher than in the other tissues, including brain, which still had a relatively high accumulation.<strong> </strong>In conclusion, both gemcitabine and crizotinib accumulate at clinically active but variable levels in tissues, possibly relating to the effects exerted by these drugs.</p>

Adherence and Patients' Experiences with the Use of Capecitabine in Daily Practice

Introduction: Capecitabine is a widely prescribed oral anticancer agent. We studied medication adherence and explored its use in daily practice from a patients' perspective.

Patients and Methods: Patients (n = 92) starting capecitabine were followed up to five 3-week cycles. Adherence was assessed using a pill count, pharmacy data and dosing information from the patients' medical file. Self-reported adherence was measured using the Medication Adherence Report Scale (MARS). At baseline and during week 2 of cycles 1, 3, and 5, patients filled out questionnaires about quality of life, symptoms, attitude toward medicines and disease and use in daily practice. Simultaneously, blood samples were taken to determine the area under the curve (AUC) of 5′-deoxy-5-fluorouridine (5′-DFUR), 5-fluorouracil (5-FU), and α-fluoro-β-alanine (FBAL) by a population pharmacokinetic model. Associations between AUCs and patient-reported symptoms were tested for cycles 3 and 5.

Results: Most patients (84/92; 91%) had an adherence rate of ≥95 and ≤ 105%. The percentage of patients reporting any non-adherence behavior measured with MARS increased from 16% at cycle 1 to 29% at cycle 5. Symptoms were reported frequently and the dosing regimen was adjusted by the physician at least once in 62% of patients. In multivariate analysis the probability of an adjustment increased with the number of co-medication (OR 1.19, 95% CI: 1.03–1.39) and a stronger emotional response to the disease (OR 1.32, 95% CI: 1.10–1.59). The AUC of 5′-DFUR was associated with weight loss (OR 1.10, 95% CI: 1.01–1.19), AUC of FBAL with hand-foot syndrome (OR 0.90, 95% CI: 0.83–0.99), rhinorrhea (OR 1.21, 95% CI: 1.03–1.42 weight loss (OR 1.09, 95% CI: 1.00–1.20) and depression (OR 0.90, 95% CI: 0.82–0.99). Side effects were reported by one third of patients as the reason to discontinue treatment.

Conclusion: Adherence to capecitabine was generally high. Nevertheless, adherence measured with MARS decreased over time Adherence management to support implementation of correct capecitabine use is specifically relevant in longer term treatment. In addition, it appears that adverse event management is important to support persistence. With the extending armamentarium of oral targeted anticancer agents and prolonged treatment duration, we expect the issue of medication adherence of increasing importance in oncology.

Alternative scheduling of pulsatile, high dose sunitinib efficiently suppresses tumor growth

Background

Increased exposure to multitargeted kinase inhibitor sunitinib is associated with improved outcome, emphasizing the importance of maintaining adequate dosing and drug levels. The currently approved schedule (50 mg daily, four weeks on, two weeks off) precludes further dose-intensification. Recent data suggest that sunitinib, although initially developed as an antiangiogenic agent, has direct antitumor activity.

Methods

In this study, we tested whether a chemotherapy-like schedule of pulsatile high dose sunitinib would result in improved antitumor activity.

Results

In vitro, a single exposure to 20 μM sunitinib for 6-9 h resulted in complete inhibition of tumor cell growth and cell death conveyed through activation of caspases and autophagy upregulation. Notably, repeated exposure of tumor cells to pulses of high concentrations of sunitinib did not induce resistance. In vivo, once-weekly treatment with high dose sunitinib of tumors growing on the chorioallantoic membrane (CAM) of the chicken embryo significantly impaired tumor growth by 57 % compared to vehicle, outperforming the daily, standard scheduling.

Conclusions

These results prompted the initiation of a phase I clinical trial, where intermittent, high dose sunitinib is being investigated in patients with advanced solid tumors (registration number and date: NCT02058901, 30 September 2013, respectively). The trial is actively recruiting patients and promising preliminary indications of antitumor activity have been observed.

Transport of six tyrosine kinase inhibitors: active or passive?

<p class="ADMETabstracttext">Transport of erlotinib, gefitinib, sorafenib, sunitinib, dasatinib and crizotinib can be active or passive, which was studied by measuring uptake  at low (4 °C; passive) and normal temperature (37 °C; active and passive) and by the use of specific organic cation transporter (OCT) inhibitors. Intracellular accumulation was determined using Caco-2 as monolayers, while for gut permeation we used differentiated Caco-2 as model for intestinal epithelium in the Transwell system. Sorafenib and crizotinib uptake are likely to be dependent on passive transport. Gefitinib, dasatinib and sunitinib uptake seem to be active. Erlotinib’s transport also seems to be active. This study suggests that hOCTs might be involved in the apical to basolateral transport of gefitinib and crizotinib. Overall it can be concluded that the accumulation and transport of these six TKIs are very different, despite the fact that they are all tyrosine kinase inhibitors.</p>

Overcoming crizotinib resistance in ALK-rearranged NSCLC with the second-generation ALK-inhibitor ceritinib

In up to 5% of non-small cell lung cancer (NSCLC) patients, the EML4-ALK translocation drives tumor progression. Treatment with the ALK inhibitor crizotinib is more effective than standard chemotherapy. However, resistance to crizotinib occurs after approximately 8 months. Ceritinib is the first second-generation ALK inhibitor approved for treatment of crizotinib-resistant NSCLC. Ceritinib inhibits two of the most common ALK-mutants that confer resistance to crizotinib: L1196 M and G1269A. Cells with ALK expression are more sensitive to ceritinib than crizotinib (IC50 25 nM vs. 150 nM, respectively). Alternative second-generation ALK inhibitors such as Alectinib, Brigatinib and PF-06463922 are currently in development, each affecting different crizotinib-resistant ALK target mutations. Genetic identification of crizotinib-resistant mutants is essential for selecting the optimal treatment strategy in NSCLC patients to overcome resistance and to increase progression-free survival.

Selection of the best blood compartment to measure cytidine deaminase activity to stratify for optimal gemcitabine or cytarabine treatment

Cytidine deaminase (CDA) plays a crucial role in the degradation of cytidine analogs, such as gemcitabine and cytarabine. Several studies showed that a low CDA activity is associated with more toxicity but a higher efficacy, while a high activity will lead to a lower efficacy but less toxicity. A stratified dosing strategy based on the relative CDA activity would increase efficiency. In order to predict these events, a reliable measurement of CDA with a validated method is crucial. We aimed to determine which phenotype assay would be most suitable; a spectrophotometric assay using cytidine as a substrate, or an HPLC assay using gemcitabine as a substrate. In serum and whole blood of 26 volunteers, both assays showed an excellent correlation (R>0.999), but not in plasma nor in red blood cells. Moreover, there was no difference between males and females. In conclusion, the spectrophotometric assay seems the most simple and cost-effective test. It should be performed in serum, while it should be normalized on protein content as measured by the Bicinchoninic Acid.

Physicochemical properties of novel protein kinase inhibitors in relation to their substrate specificity for drug transporters

INTRODUCTION

Small molecule tyrosine and serine-threonine kinase inhibitors (TKIs and STKIs) are emerging drugs that interfere with downstream signaling pathways involved in cancer proliferation, invasion, metastasis and angiogenesis. The understanding of their pharmacokinetics, the identification of their transporters and the modulating activity exerted on transporters is pivotal to predict therapy efficacy and to avoid unwarranted drug treatment combinations.

AREAS COVERED

Experimental or in silico data were collected and summarized on TKIs and STKIs physico-chemical properties, which influence their transport, metabolism and efficacy, and TKIs and STKIs as influx transporter substrates and inhibitors. In addition, the uptake by tumor cell influx transporters and some factors in the tumor microenvironment affecting the uptake of TKIs and STKIs by cancer cells are briefly covered.

EXPERT OPINION

Membrane transporters play an important role in the pharmacokinetics and hence the efficacy of anticancer drugs, including TKIs and STKIs. These drugs are substrates and inhibitors of various transporters. Drug resistance may be bypassed not only by identifying the proper transporter but also by selective combinations, which may either downregulate or increase transporter activity. However, care has to be taken because this profile might be disease, drug and patient specific.

Acquired tumor cell resistance to sunitinib causes resistance in a HT-29 human colon cancer xenograft mouse model without affecting sunitinib biodistribution or the tumor microvasculature

Acquired resistance to anti-angiogenic tyrosine kinase inhibitors is an important clinical problem in treating various cancers. To what extent acquired resistance is determined by microenvironmental host-factors or by tumor cells directly is unknown. We previously found that tumor cells can become resistant to sunitinib in vitro. Here, we studied to what extent in vitro induced resistance of tumor cells determines in vivo resistance to sunitinib. In severe combined immunodeficient mice, tumors were established from HT-29 parental colon cancer cells (HT-29PAR) or the in vitro induced sunitinib resistant HT-29 cells (HT-29SUN). Treatment with sunitinib (40mg/kg/day) inhibited tumor growth of HT-29PAR tumors by 71±5%, while no inhibition of HT-29SUN tumor growth was observed. Intratumoral sunitinib concentrations and reduced MVD were similar in both groups. Ki67 staining revealed that tumor cell proliferation was significantly reduced with 30% in HT-29PAR tumors, but unaffected in HT-29SUN tumors upon sunitinib treatment. The lysosomal capacity reflected by LAMP-1 and -2 expression was higher in HT-29SUN compared to HT-29PAR tumors indicating an increased sequestration of sunitinib in lysosomes of resistant tumors. In conclusion, we demonstrate that tumor cells rather than host-factors may play a crucial role in acquired resistance to sunitinib in vivo.

Overexpression of MRP4 (ABCC4) and MRP5 (ABCC5) confer resistance to the nucleoside analogs cytarabine and troxacitabine, but not gemcitabine

We aimed to determine whether the multidrug-resistance-proteins MRP4 (ABCC4) and MRP5 (ABCC5) confer resistance to the antimetabolites cytarabine (Ara-C), gemcitabine (GEM), and the L-nucleoside analog troxacitabine. For this purpose we used HEK293 and the transfected HEK/MRP4 (59-fold increased MRP4) or HEK/MRP5i (991-fold increased MRP5) as model systems and tested the cells for drug sensitivity using a proliferation test. Drug accumulation was performed by using radioactive Ara-C, and for GEM and troxacitabine with HPLC with tandem-MS or UV detection. At 4-hr exposure HEK/MRP4 cells were 2-4-fold resistant to troxacitabine, ara-C and 9-(2-phosphonylmethoxyethyl)adenine (PMEA), and HEK/MRP5i to ara-C and PMEA, but none to GEM. The inhibitors probenecid and indomethacin reversed resistance. After 4-hr exposure ara-C-nucleotides were 2-3-fold lower in MRP4/5 cells, in which they decreased more rapidly after washing with drug-free medium (DFM). Trocacitabine accumulation was similar in the 3 cell lines, but after the DFM period troxacitabine decreased 2-4-fold faster in MRP4/5 cells. Troxacitabine-nucleotides were about 25% lower in MRP4/5 cells and decreased rapidly in MRP4, but not in MRP5 cells. Accumulation of GEM-nucleotides was higher in the MRP4/5 cells. In conclusion: MRP4 and MRP5 overexpression confer resistance to troxacitabine and ara-C, but not to GEM, which was associated with a rapid decline of the ara-C and troxacitabine-nucleotides in HEK/MRP4-5 cells.

Abstract 2989: High-dose, intermittent sunitinib as an alternative treatment strategy

Background: Increased exposure to sunitinib treatment is associated with improved outcome indicative of the importance of dose intensity in the efficacy/toxicity balance. The currently approved schedule (50 mg daily, 4 weeks on, 2 weeks off) precludes further dose intensification. We hypothesized that high doses of sunitinib would improve tumor response with limited toxicity, when applied intermittently.

Methods: In vitro proliferation was studied with MTT assays, one week after 3-9 hrs exposure of a panel of cancer cell lines (786-0, HT29, MDA-MB231, HCC827, A431) to high (5 and 20uM) concentrations of tyrosine kinase inhibitors (TKIs), namely sunitinib, sorafenib, erlotinib, pazopanib and axitinib. Apo-ONETM Homogenous Caspase 3/7 Assay (Promega) was applied to detect activation of apoptosis. The chick embryo chorioallantoic membrane (CAM) in vivo model was employed to further test the efficacy of the new scheduling, where sunitinib was topically administered on HT29 tumors growing on the CAM either daily at the commonly used dose of 40 mg/kg or once weekly at 200 mg/kg. Microvessel density (MVD) was determined by CD31 immunohistochemical staining. Plasma sunitinib concentrations were determined by LC-MS-MS from refractory patients with solid tumors participating in a phase I clinical trial (classical 3+3 design, EudraCT No: 2012-005756-41) in which high-dose, intermittent sunitinib treatment is being studied.

Results: Sunitinib was identified as one of the most potent inhibitors of cell growth from the panel of TKIs; 6 hrs exposure to 20 uM of sunitinib resulted in tumor cell death. This effect was tumor cell line-independent and mediated via activation of caspase 3/7 pathway. High dose treatment of CAM tumors resulted in significant decrease in tumor growth compared to the control (mean 0.17 mg vs. 0.23 mg respectively, p=0.04), irrespective of angiogenesis inhibition as denoted by lack of inhibitory effect on MVD. It also led to higher intratumoral sunitinib concentrations compared to the daily schedule (14.3 vs. 8 ng/mg tissue, respectively), while blood concentrations were identical between the two schedules, averaging at 170 ng/ml. Patients enrolled in the first cohort of the clinical trial received 200 mg sunitinib orally weekly. This schedule was well tolerated and no dose limiting toxicities occurred. Overall, sunitinib exhibited moderate interpatient variability. Maximum plasma concentrations on Day 1 averaged on 161 ng/ml (range 118-239.5 ng/ml) and were reached approximately 6 hours after administration. Plasma drug concentrations decreased to undetectable from one cycle to the other. We have proceeded to escalate the dose for the next cohort of patients.

Conclusion: Optimization of therapy with targeted agents remains an unmet challenge. Thus far, high-dose, intermittent sunitinib is well tolerated. These findings open new avenues that might contribute to improved treatment with sunitinib.

Citation Format: Maria Rovithi, Richard R. de Haas, Richard J. Honeywell, Johannes Voortman, Arjan W. Griffioen, Mariette Labots, Anne Marije Luik, Godefridus J. Peters, Henk J. Broxterman, Henk M.w. Verheul. High-dose, intermittent sunitinib as an alternative treatment strategy. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2989. doi:10.1158/1538-7445.AM2014-2989

Abstract C82: Role of influx and efflux transporters on gut absorption of selected tyrosine kinase inhibitors in a polarized gut epithelium model system

Tyrosine kinase inhibitors (TKI) are a family of small molecules which inhibit the ATP driven phosphorylation of signaling proteins that normally activate transduction cascades. Aberrations in signal cascades have been linked to the development of tumors and their survival pathways. TKIs tend to be alkali in nature with a correspondingly high pKa (5-8) while absorption properties have been linked to both ABC and Organic Cation Transporters (OCT). Because of their poor solubility, TKI are administered orally but available pharmacokinetic data indicate that in most cases bioavailability is relatively low (∼60% or lower). Despite a molecular weight in a similar range, doses vary significantly: Sunitinib (Sun) - 50 mg/d, Dasatinib (Das) - 150 mg/d, Erlotinib (Erl) - 150 mg/d, Gefitinib (Gef) - 250 mg/d, Crizotinib (Cri) - 250 mg BID and Sorafenib (Sor) - 400 mg BID. Steady state plasma levels vary from 0.13 (Sun), 0.21 (Das), 0.29 (Gef), 0.7 (Cri), 2.54 (Erl) to 12.1 µM (Sor). Variations in intestinal absorption may seriously affect plasma concentrations, tumour exposure and antitumor effect. To investigate the mechanisms behind these differences a well-established model for intestinal transport was used: the human colon cell line, CaCo2, when grown in special coated transwell plates forms a confluent differentiated polarised monolayer resembling gut epithelium. This model was used to determine the permeability of Gef, Erl, Sun, Cri, Sor, and Das, using LC-MS-MS to determine drug concentrations. Absorption from the gut given as the transfer rates from Apical to Basolateral (A/B) sides using 20 µM TKI at the apical side was determined over a 3 hour period. Transfer was linear in this period. Transfer rates varied from about 30 for Cri, 43 for Sun, 209 for Das, 180 for Gef, 223 for Sor, to 479 pmol/hr for Erl. In order to determine the role of ABC pumps, we depleted ATP with azide, which partially reduced transfer of Gef, Sun and Sor, but did not affect Erl. Ko143, a specific ABCG2 inhibitor decreased transfer of Gef and Sor but unexpectedly increased Sun. Remarkably, permeability transfer rates from the basolateral (blood) side to gut (B/A) were much higher (252 for Gef, 621 for Sor, 685 for Sun, 1623 for Erl and 4630 pmol/hr for Das) than A/B transfer. Verapamil, an inhibitor of P-glycoprotein and to some extend OCT1 increased A/B transfer of Sor and Das, but did not affect the transfer of the other compounds. Desipramine, a general OCT inhibitor, did not affect transfer of Erl, increased that of Gef and Cri about 2-fold and that of Sun 1.5-fold, but hardly affected that of Sor and Das. In conclusion, absorption of TKI from the apical side (gut epithelium) is relatively poor, while there was a relatively high negative flow (B/A); this is in line with the low bioavailability of most TKI. Some ABC transporters and OCTs play a role in the absorption, in line with their substrate specificity.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):C82.

Citation Format: Richard J. Honeywell, Christien Fatmawati, Marita Boeddha, Sarina Hitzerd, Ietje Kathmann, Elisa Giovannetti, Godefridus J. Peters. Role of influx and efflux transporters on gut absorption of selected tyrosine kinase inhibitors in a polarized gut epithelium model system. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr C82.

Crizotinib inhibits metabolic inactivation of gemcitabine in c-Met-driven pancreatic carcinoma

Pancreatic ductal adenocarcinoma (PDAC) remains a major unsolved health problem. Most drugs that pass preclinical tests fail in these patients, emphasizing the need of improved preclinical models to test novel anticancer strategies. Here, we developed four orthotopic mouse models using primary human PDAC cells genetically engineered to express firefly- and Gaussia luciferase, simplifying the ability to monitor tumor growth and metastasis longitudinally in individual animals with MRI and high-frequency ultrasound. In these models, we conducted detailed histopathologic and immunohistochemical analyses on paraffin-embedded pancreatic tissues and metastatic lesions in liver, lungs, and lymph nodes. Genetic characteristics were compared with the originator tumor and primary tumor cells using array-based comparative genomic hybridization, using frozen specimens obtained by laser microdissection. Notably, the orthotopic human xenografts in these models recapitulated the phenotype of human PDACs, including hypovascular and hypoxic areas. Pursuing genomic and immunohistochemical evidence revealed an increased copy number and overexpression of c-Met in one of the models; we examined the preclinical efficacy of c-Met inhibitors in vitro and in vivo. In particular, we found that crizotinib decreased tumor dimension, prolonged survival, and increased blood and tissue concentrations of gemcitabine, synergizing with a cytidine deaminase-mediated mechanism of action. Together, these more readily imaged orthotopic PDAC models displayed genetic, histopathologic, and metastatic features similar to their human tumors of origin. Moreover, their use pointed to c-Met as a candidate therapeutic target in PDAC and highlighted crizotinib and gemcitabine as a synergistic combination of drugs warranting clinical evaluation for PDAC treatment.

DNA-bound platinum is the major determinant of cisplatin sensitivity in head and neck squamous carcinoma cells

PURPOSE

The combination of systemic cisplatin with local and regional radiotherapy as primary treatment of head and neck squamous cell carcinoma (HNSCC) leads to cure in approximately half of the patients. The addition of cisplatin has significant effects on outcome, but despite extensive research the mechanism underlying cisplatin response is still not well understood.

METHODS

We examined 19 HNSCC cell lines with variable cisplatin sensitivity. We determined the TP53 mutational status of each cell line and investigated the expression levels of 11 potentially relevant genes by quantitative real-time PCR. In addition, we measured cisplatin accumulation and retention, as well as the level of platinum-DNA adducts.

RESULTS

We found that the IC50 value was significantly correlated with the platinum-DNA adduct levels that accumulated during four hours of cisplatin incubation (p = 0.002). We could not find a significant correlation between cisplatin sensitivity and any of the other parameters tested, including the expression levels of established cisplatin influx and efflux transporters. Furthermore, adduct accumulation did not correlate with mRNA expression of the investigated influx pumps (CTR1 and OCT3) nor with that of the examined DNA repair genes (ATR, ATM, BRCA1, BRCA2 and ERCC1).

CONCLUSION

Our findings suggest that the cisplatin-DNA adduct level is the most important determinant of cisplatin sensitivity in HNSCC cells. Imaging with radio-labeled cisplatin might have major associations with outcome.

Abstract 1613: In vitro acquired tumor cell resistance to sunitinib contributes to an in vivo resistant phenotype

Background: Resistance to sunitinib and other TKIs is a major clinical problem. Previously we have shown that tumor cells acquire transient resistance in vitro by continuous incubation with sunitinib and found that in resistant tumor cells sunitinib is sequestered in intracellular lysosomes as the potential underlying mechanism of resistance. In vivo resistance to sunitinib may be related to its anti-angiogenic action and/or direct tumor cell-directed action. Here we studied the mechanism of resistance to sunitinib in vivo by comparing in vitro established sunitinib resistant HT-29 tumor cells (HT-29 SUN) with their parental cells (HT-29 PAR).

Methods: From HT-29 SUN and HT-29 PAR cell lines, tumors were established in severe combined immunodeficient (SCID) mice by subcutaneous injection or by tumor transplantation from sacrificed mice into a new cohort of mice with n=6 and n=8 mice per treatment group respectively. Mice were treated with sunitinib malate, provided by Pfizer Inc., at a dose of 40 mg/kg/d or vehicle. Tumor growth was monitored in time and tumor weights were measured after sacrificing the mice. Sunitinib concentrations were measured by LC-MS/MS. In addition, microvessel density (MVD) and proliferation rate of tumor cells were determined by immunohistochemical staining of CD31 and ki67.

Results: Tumor growth inhibition by sunitinib of HT-29 SUN and HT-29 PAR tumor bearing mice revealed comparable resistance of HT-29 SUN in vivo (23-38% growth inhibition; p=ns) to in vitro, while sunitinib significantly inhibited growth of HT-29 PAR (74-79%; p&lt;0.01) in two independent experiments. The intratumoral concentration of sunitinib in HT-29 SUN and HT-29 PAR treated tumors was comparable (8.5 ± 2.8 vs 9.2 ± 1.9 μM (mean ± SD; n=8; p=ns). MVD was significantly reduced in both HT-29 SUN and HT-29 PAR sunitinib treated tumors compared to control (HT-29 SUN: 3.8 ± 2.6 vs 9.3 ± 4.8 vessels for sunitinib vs vehicle treatment (p&lt;0.05), HT-29 PAR: 4.7 ± 1.7 vs 10.9 ± 4.5 vessels per field, respectively (p&lt;0.01)). In contrast, ki67 staining revealed no inhibition of tumor cell proliferation in HT-29 SUN treated tumors (57 ± 17 vs 61 ± 14 % for sunitinib vs vehicle treatment (p=ns)), while in HT-29 PAR tumors proliferation was significantly reduced upon sunitinib treatment (52 ± 8 vs 88 ± 5 %, respectively (p&lt;0.001)).

Conclusions: Our findings suggest that sunitinib resistance in this model is tumor cell- rather than host-mediated and is independent of intratumoral drug delivery. Further analyses of potential lysosomal involvement in this in vivo resistance mechanism are ongoing.

Citation Format: Kristy J. Gotink, Roberto Pili, Richard J. Honeywell, Arjan W. Griffioen, Godefridus J. Peters, Henk J. Broxterman, Henk MW Verheul. In vitro acquired tumor cell resistance to sunitinib contributes to an in vivo resistant phenotype. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1613. doi:10.1158/1538-7445.AM2013-1613

Abstract 2719: Development of bioluminescence orthotopic pancreatic-ductal-adenocarcinoma (PDAC) mouse models from primary PDAC cells as a new tool for therapeutic discovery

Pancreatic-ductal-adenocarcinoma (PDAC) remains a major unsolved health problem, and most drugs that successfully pass preclinical tests fail in the patients. The aim of this study was to establish orthotopic PDAC mice models from primary pancreatic tumor cells engineered for bioluminescent imaging as appropriate platform for development/screening of effective anticancer-drugs.

Early passages of four primary PDAC-cultures (PDAC-1, PDAC-2, PDAC-3 and PDAC-8) were successfully transduced with lentiviral vectors containing mCherry/Firefly-luciferase (Fluc), and CFP/Gaussia-luciferase (Gluc), as detected by fluorescence microscope and FACS analysis, and then injected orthotopically into the pancreas of at least 3 immunosuppressed athymic mice. The intensities of bioluminescence-signals (BLI), Fluc or Gluc, were monitored for 60 days by CCD camera and in blood samples, using Xenogen IVIS Lumina system and an illuminometer, respectively. In particular, BLI intensities of Fluc signals were increased within the range of 105-109 p/s/cm2/sr in PDAC-8 and 107-1011 p/s/cm2/sr in PDAC-2. Similarly, the Gluc signal in blood samples was increased overtime in all the developed PDAC-mouse-models. Additional imaging analyses to define tumor spatial characteristics were performed by magnetic resonance imaging (MRI) and Echo-Doppler.

Histopathological and immunohistochemical analyses were performed on paraffin-embedded slices of pancreas, as well as on metastatic lesions in liver, lungs and lymph nodes, while genetic characteristics of the xenografts were compared to the originator tumor and primary tumor cells using array-based comparative-genomic-hybridization (Agilent Human CGH Microarray 4x180K platform), in frozen specimens after laser-microdissection with the Leica LMD6000 instrument. These models presented extremely similar histopathological and genetics profile compared to their originator human tumors. The immunohistological analyses showed the overexpression of c-Met and phospho-c-Met in one tumor model (PDAC-3). Therefore, we tested the activity of the c-Met inhibitor crizotinib, alone or in combination with gemcitabine. Crizotinib significantly reduced tumor growth compared to untreated mice, while increasing gemcitabine concentrations, as monitored in blood and tissues samples with a LC-MS/MS validated method.

In conclusion, we developed orthotopic PDAC mice models enabled for bioluminescent imaging, showing similar genetic and histopathological features compared to their originator primary pancreatic tumors. Moreover, we demonstrated that these models provide a platform to monitor the effectiveness of targeted innovative anticancer drugs, representing a step toward personalized treatment in PDAC.

Citation Format: Amir Avan, Viola Caretti, Niccola Funel, Elena Galvani, Tonny Lagerweij, Richard J. Honeywell, Ugo Boggi, Gerrit Jan Schuurhuis, Godefridus J. Peters, Thomas Würdinger, Elisa Giovannetti. Development of bioluminescence orthotopic pancreatic-ductal-adenocarcinoma (PDAC) mouse models from primary PDAC cells as a new tool for therapeutic discovery. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 2719. doi:10.1158/1538-7445.AM2013-2719

Abstract 4425: Characterisation of cellular transport and accumulation of six clinically approved tyrosine kinase inhibitors (TKIs) in colon cancer cells

TKIs are a loosely characterised family of small molecules which inhibit the ATP driven phosphorylation of signalling proteins that normally activate transduction cascades. Aberrations in signal cascades have been linked to the development of tumours and their survival pathways; TKIs are targeted at these pathways. However, promising preclinical studies on structurally different TKIs often did not translate into clinical success due to cellular resistance, cascade mutations and poor bioavailability. TKIs tend to be alkali in nature with a correspondingly high pKa (5-8) while absorption properties have been linked to both ABC and Organic Cation Transporters (OCT). Previously we demonstrated in a gut epithelium model that absorption of TKIs is relatively poor, while a correspondingly high negative flow was observed. In this study we aimed to characterize tumour cell uptake and accumulation of TKIs using specific transporter inhibitors. We used a sensitive and specific LC-MS-MS method to characterize the role of the transport inhibitors Ko143 (BCRP inhibitor), amantadine (Am;hOCT1&2), cimetidine (Ci;hOCT1&2&3), desipramine (Ds;hOCT1&2&3), β-estradiol (Be; hOCT1&3) and verapamil (Ve; hOCT1&P-gp).

Uptake of TKIs at 4°C and 37°C in CaCo2 and WiDr colon cancer cells showed large differences; uptake of Gefitinib (G - 10μM), Erlotinib (E - 10 μM) & Dasatinib (D - 1μM) was partially active since after 2hr uptake at 4°C was lower compared to 37°C. Uptake of Sunitinib (Su - 10μM), Sorafenib (So - 10 μM) and Crizotinib (Cr - 10 μM) was predominantly passive since values were comparable at 4°C and 37°C. Absolute accumulation over 24hr (37°C) was very different with E and D reaching 20-150 ng/mg protein, while G was 20 fold higher. Su, So and Cr accumulation were even higher reaching 2 to 12 μg/mg protein. This pattern matched accumulation of some TKIs observed in the clinical setting. Accumulation for Su and Cr showed a similar pattern suggesting that Cr accumulated in lysosomes similar to Su. Bafilomycin, a lysosomal inhibitor, decreased total accumulation of Su 14.1-fold, and that of Cr 2.4-fold indicating lysosomal accumulation. The hOCT inhibitor Ds consistently (25-55%) decreased accumulation of G, So Su and Cr; Ci, Be and Am had little effect on cellular accumulation for all TKIs tested. Ve, De and Ci increased accumulation of E, and Ve that of D, suggesting inhibition of efflux via P-gp, MRP or BCRP. Ko143 increased accumulation for G, E, So and Su in WiDr but only for Su in CaCo2 cells indicating a differential role for BCRP depending on TKI and tumour type. In conclusion, several transporters appear to be involved to differing degrees for each molecule, indicating TKIs pharmacokinetics should be investigated on an individual basis.

Citation Format: Richard J. Honeywell, Sarina Hitzerd, Ietje Kathmann, Elisa Giovannetti, Henk Verheul, Frits Peters. Characterisation of cellular transport and accumulation of six clinically approved tyrosine kinase inhibitors (TKIs) in colon cancer cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4425. doi:10.1158/1538-7445.AM2013-4425

Molecular mechanisms involved in the synergistic interaction of the EZH2 inhibitor 3-deazaneplanocin A with gemcitabine in pancreatic cancer cells

Pancreatic ductal adenocarcinoma (PDAC) is characterized by overexpression of enhancer of Zeste homolog-2 (EZH2), which plays a pivotal role in cancer stem cell (CSC) self-renewal through methylation of histone H3 lysine-27 (H3K27me3). Against this background, EZH2 was identified as an attractive target, and we investigated the interaction of the EZH2 inhibitor DZNeP with gemcitabine. EZH2 expression was detected by quantitative PCR in 15 PDAC cells, including seven primary cell cultures, showing that expression values correlated with their originator tumors (Spearman R(2) = 0.89, P = 0.01). EZH2 expression in cancer cells was significantly higher than in normal ductal pancreatic cells and fibroblasts. The 3-deazaneplanocin A (DZNeP; 5 μmol/L, 72-hour exposure) modulated EZH2 and H3K27me3 protein expression and synergistically enhanced the antiproliferative activity of gemcitabine, with combination index values of 0.2 (PANC-1), 0.3 (MIA-PaCa-2), and 0.7 (LPC006). The drug combination reduced the percentages of cells in G(2)-M phase (e.g., from 27% to 19% in PANC-1, P < 0.05) and significantly increased apoptosis compared with gemcitabine alone. Moreover, DZNeP enhanced the mRNA and protein expression of the nucleoside transporters hENT1/hCNT1, possibly because of the significant reduction of deoxynucleotide content (e.g., 25% reduction of deoxycytidine nucleotides in PANC-1), as detected by liquid chromatography/tandem mass spectrometry. DZNeP decreased cell migration, which was additionally reduced by DZNeP/gemcitabine combination (-20% in LPC006, after 8-hour exposure, P < 0.05) and associated with increased E-cadherin mRNA and protein expression. Furthermore, DZNeP and DZNeP/gemcitabine combination significantly reduced the volume of PDAC spheroids growing in CSC-selective medium and decreased the proportion of CD133+ cells. All these molecular mechanisms underlying the synergism of DZNeP/gemcitabine combination support further studies on this novel therapeutic approach for treatment of PDACs.

Abstract 3785: Human pharmacokinetics (PK) of selected tyrosine kinase inhibitors (TKI) in relation to transport characteristics in a polarized gut epithelium model system

TKI represent the largest group of novel anticancer drugs. Loosely based on a core pyrimidine structure TKI selectively target the ATP activity of a TK. Their poor solubility represents a challenge in administration. TKI are administered orally but available PK indicates that in most cases bioavailability is relatively low (∼60% or lower). Despite a molecular weight in a similar range, doses vary significantly: Sunitinib (Sun) - 50 mg/d, Dasatinib (Das) - 150 mg/d, Erlotinib (Erl) - 150 mg/d, Gefitinib (Gef) - 250 mg/d and Sorafenib (Sor) - 400 mg BID. Steady state plasma levels vary from 0.13 (Sun), 0.21 (Das), 0.29 (Gef), 2.54 (Erl) to 12.1 µM (Sor). In combination Erl increased systemic plasma levels of Sor. Variations in intestinal absorption may seriously affect plasma concentrations, tumour exposure and anti tumour effect. To investigate the mechanisms behind these differences a well established model for intestinal transport was used: the human colon cell line, CaCo2, when grown in special coated Transwell plates forms a confluent differentiated polarised monolayer resembling gut epithelium. This model was used to determine the permeability of Gef, Erl, Sun, Sor, Das and combined Erl/Sor. Absorption from the gut given as the transfer rates from Apical to Basolateral (A/B) sides using 20 µM TKI at the apical side was determined over a 3 hour period. Transfer was linear in this period. Transfer rates varied from 43 for Sun, 209 for Das, 180 for Gef, 223 for Sor, to 479 pmol/hr for Erl. At 10 µM Erl increased transfer rate of Sor from 145 to 185.7 pmol/hr in line with observed plasma levels. In order to determine the role of ABC pumps, we depleted ATP with azide, which partially reduced transfer of Gef, Sun and Sor, but did not affect Erl. Ko143, a specific ABCG2 inhibitor decreased transfer of Gef and Sor but unexpectedly increased Sun. Remarkably, permeability transfer rates from the basolateral (blood) side to gut (B/A) were much higher (252 for Gef, 621 for Sor, 685 for Sun, 1623 for Erl and 4630 pmol/hr for Das) than A/B transfer. In order to explain this difference we determined cellular accumulation in the monolayer cells at the end of the experiments. For the A/B experiments this was undetectable for Erl, 0.79 for Gef, 1.65 for Sor, 11.9 for Sun and 1.1 for Das (pmol/µg protein). For the B/A experiments a proportional decrease in accumulation relative to the observed increased transfer rate was seen with Gef as the exception, with values from undetectable for Erl, 2.1 for Gef, 0.15 for Sor, 4.72 for Sun and 0.26 pmol/µg protein for Das. In conclusion, absorption of TKI from the apical side (gut epithelium) is relatively poor, while there was a relatively high negative flow (B/A); this is in line with the low bioavailability of most TKI. Some ABC transporters play a role in the absorption, in line with their substrate specificity. This may also affect retention of TKI in tumour cells

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 3785. doi:1538-7445.AM2012-3785

Determination of the phosphorylated metabolites of gemcitabine and of difluorodeoxyuridine by LCMSMS

Gemcitabine is an established chemotherapy agent in several solid tumors. Its mechanism of action has been theoretically established and this is supported with strong experimental evidence. However, certain aspects of the resistance mechanism for this agent remain elusive. We present a method of analysis using tandem liquid chromatography and mass spectrometry that provides a broader, yet more focused view of the action of gemcitabine and its primary metabolite, difluorodeoxyuridine in relation to the (deoxy) nucleoside and (deoxy) nucleotide pools in tumor cell lines. Alcoholic cytosole extracts were incubated with alkaline phosphatase reducing the nucleotide pools to their respective nucleosides. Determination of the nucleoside content by a sensitive LCMSMS method before and after incubation enables the calculation of the total amount of phosphorylation of each (deoxy) nucleoside in the cell. Incubation with clinically relevant levels of gemcitabine (dFdC) or difluorodeoxyuridine (dFdU) for 24 hours enabled the determination of the changes in the (deoxy) nucleotide pools in relation to chemotherapeutic and toxicological effects. Confirmation of the presence of dFdC phosphorylation is presented as well as direct evidence of dFdU phosphorylation after both dFdC and dFdU treatment. Differences in the nucleotide pools are presented after dFdC and dFdU incubation, indicating that dFdU might have more chemotherapeutic properties than previously believed.

Metabolism and accumulation of the lipophilic deoxynucleoside analogs elacytarabine and CP-4126

Cytarabine (ara-C) and gemcitabine (dFdC) are commonly used anticancer drugs, which depend on the equilibrative (ENT) and concentrative-nucleoside-transporters to enter the cell. To bypass transport-related drug resistance, lipophilic derivatives elacytarabine (CP-4055), ara-C-5′elaidic-acid-ester, and CP-4126, (CO 1.01) gemcitabine-5′elaidic-acid-ester, were investigated for the entry into the cell, distribution, metabolism and retention. The leukemic CEM-cell-line and its deoxycytidine-kinase deficient variant (CEM/dCK-) were exposed for 30 and 60 min to the radiolabeled drugs; followed by culture in drug-free medium in order to determine drug retention in the cell. The cellular fractions were analyzed with thin-layer-chromatography and HPLC. Elacytarabine and CP-4126 were converted to the parent compounds both inside and outside the cell (35–45%). The ENT-inhibitor dipyridamole did not affect their uptake or retention. Inside the cell Elacytarabine and CP-4126 predominantly localized in the membrane and cytosolic fraction, leading to a long retention after removal of the medium. In contrast, in cells exposed to the parent drugs ara-C and dFdC, intracellular drug concentration increased during exposure but decreased to undetectable levels after drug removal. In the dCK- cell line, no metabolism was observed. The concentrations of ara-CTP and dFdCTP reached a peak at the end of the incubation with the drugs, and decreased after drug removal; peak levels of dFdCTP were 35 times higher than ara-CTP and was retained better. In contrast, after exposure to elacytarabine or CP-4126, ara-CTP and dFdCTP levels continued to increase not only during exposure but also during 120 min after removal of the elacytarabine and CP-4126. Levels of ara-CTP and dFdCTP were higher than after exposure to the parent drugs. In conclusion, the lipophilic derivatives elacytarabine and CP-4126 showed a nucleoside-transporter independent uptake, with long retention of the active nucleotides. These lipophilic nucleoside analogues are new chemical entities suitable for novel clinical applications.

Lysosomal sequestration of sunitinib: a novel mechanism of drug resistance

PURPOSE

Resistance to antiangiogenic tyrosine kinase inhibitors such as sunitinib is an important clinical problem, but its underlying mechanisms are largely unknown. We analyzed tumor sunitinib levels in mice and patients and studied sensitivity and resistance mechanisms to sunitinib.

EXPERIMENTAL DESIGN

Intratumoral and plasma sunitinib concentrations in mice and patients were determined. Sunitinib exposure on tumor cell proliferation was examined. Resistant tumor cells were derived by continuous exposure and studied for alterations in intracellular sunitinib accumulation and activity.

RESULTS

Intratumoral concentrations of sunitinib in mice and patients were 10.9 ± 0.5 and 9.5 ± 2.4 μmol/L, respectively, whereas plasma concentrations were 10-fold lower, 1.0 ± 0.1 and 0.3 ± 0.1 μmol/L, respectively. Sunitinib inhibited tumor cell growth at clinically relevant concentrations in vitro, with IC(50) values of 1.4 to 2.3 μmol/L. Continuous exposure to sunitinib resulted in resistance of 786-O renal and HT-29 colon cancer cells. Fluorescent microscopy revealed intracellular sunitinib distribution to acidic lysosomes, which were significantly higher expressed in resistant cells. A 1.7- to 2.5-fold higher sunitinib concentration in resistant cells was measured because of increased lysosomal sequestration. Despite the higher intracellular sunitinib accumulation, levels of the key signaling p-Akt and p-ERK 1/2 were unaffected and comparable with untreated parental cells, indicating reduced effectiveness of sunitinib.

CONCLUSION

We report that sunitinib inhibits tumor cell proliferation at clinically relevant concentrations and found lysosomal sequestration to be a novel mechanism of sunitinib resistance. This finding warrants clinical evaluation whether targeting lysosomal function will overcome sunitinib resistance.

Abstract 2852: Lysosomal sequestration of sunitinib may play a role in its resistance

Resistance to tyrosine kinase inhibitors (TKIs) is a major clinical problem. Mechanisms that mediate drug resistance include gene mutations, multidrug efflux and activation of alternative growth factor pathways. Sunitinib, a multi-targeted antiangiogenic TKI, has demonstrated clinical efficacy in advanced renal cell cancer (RCC) and gastrointestinal stromal tumors, but is hampered by resistance. In this study we aimed to unravel mechanisms of sunitinib resistance.

Based on its large volume of distribution, we hypothesized that sunitinib concentrations intratumoral would be higher compared to plasma. Indeed we found that in patients harboring different tumors, intratumoral sunitinib concentrations were &gt;30-fold higher than parallel plasma concentrations: 9.5±2.4 µM versus 0.28±0.06 µM (n=3, mean±SEM), respectively, as measured by LC-MS/MS.

Subsequently, we studied the in vitro sensitivity to sunitinib (provided by Pfizer Inc.) of 1 RCC and 8 colorectal cancer cell lines and found clinically relevant inhibitory concentrations (IC) on proliferation of IC50 = 1.3±0.1 µM and IC90 = 4.6±0.6 µM sunitinib.

In parallel experiments, we induced resistance in vitro in 786-O and HT-29 cells by continuous exposure to increasing concentrations of sunitinib for &gt; 1 year. These resistant tumor cells continued to stably grow on exposures to clinically achieved intratumoral concentrations of 6 µM (786-O) and 12 µM (HT-29) sunitinib, whereas their parental cells died at these concentrations.

Microscopy of sensitive and resistant tumor cells revealed sequestration of sunitinib in specific subcellular compartments. Because sunitinib is a hydrophobic (logP=5.2) weak base (pKa = 8.95), we reasoned that it might preferentially accumulate in acidic lysosomes. Indeed, staining with a lysosome-specific fluorescent dye revealed predominant co-localization of sunitinib in lysosomes. In addition, compared to sensitive cells, lysosomal accumulation capacity was increased in resistant cells, which was confirmed by flow cytometry and Western blot analysis (LAMP-1 and LAMP-2 expression). Intracellular concentrations were increased in the resistant tumor cells compared to their parental cells, 4.6±1.1 mM and 2.3±0.4 mM, respectively, and were up to 1000-fold higher than the micromolar concentrations used for in vitro exposure. Growth of resistant cells in drug-free medium resulted in restoration of drug sensitivity and normalization of lysosomal drug accumulation capacity within 12 weeks.

In conclusion, our data show that: 1) sunitinib inhibits proliferation of tumor cells in vitro at clinically relevant intratumoral concentrations, 2) tumor cells acquire a transient drug-resistant phenotype under continuous exposure to sunitinib, 3) sunitinib is sequestered in acidic lysosomes and 4) increased lysosomal sequestration may contribute to sunitinib resistance.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2852. doi:10.1158/1538-7445.AM2011-2852

A multicenter phase II study of erlotinib and sorafenib in chemotherapy-naive patients with advanced non-small cell lung cancer

PURPOSE

This multicenter, phase II study evaluates the efficacy and safety of erlotinib, an epidermal growth factor receptor (EGFR) inhibitor, plus sorafenib, a multityrosine kinase inhibitor against vascular endothelial growth factor receptors, in patients with previously untreated advanced non-small cell lung cancer (NSCLC).

EXPERIMENTAL DESIGN

Chemotherapy-naïve patients with stage IIIB/IV NSCLC received erlotinib (150 mg once a day) and sorafenib (400 mg twice a day) until disease progression or unacceptable toxicity. The primary end point was the rate of nonprogression at 6 weeks. Secondary end points included objective response rate (ORR), time to progression, overall survival, and adverse events. Exploratory end points included pretreatment EGFR and KRAS mutation status, pharmacokinetics, and cytochrome P450 polymorphisms.

RESULTS

Fifty patients initiated therapy. The nonprogression rate at 6 weeks was 74%: 12 (24%) partial response and 25 (50%) stable disease. Ultimately, the ORR was 28%. Median time to progression was 5.0 months [95% confidence interval (95% CI), 3.2-6.8 months]. Median overall survival was 10.9 months (95% CI, 3.8-18.1 months). Grade 3/4 adverse events included fatigue (16%), hand-foot skin reaction (16%), rash (16%), diarrhea (14%), and hypophosphatemia (42%). There was one treatment-related fatal pulmonary hemorrhage. Patients with wild-type EGFR had a higher ORR (19%) than previously reported for single-agent erlotinib/sorafenib. Erlotinib levels were lowered. This was associated with CYP3A4 polymorphism and was possibly due to sorafenib.

CONCLUSION

Despite a possible drug interaction, sorafenib plus erlotinib has promising clinical activity in patients with stage IIIB/IV NSCLC and has an acceptable safety profile. Further evaluation of this combination as potential salvage therapy in EGFR mutation-negative patients and the possible drug interaction is warranted.

Trifluorothymidine resistance is associated with decreased thymidine kinase and equilibrative nucleoside transporter expression or increased secretory phospholipase A2

Trifluorothymidine (TFT) is part of the novel oral formulation TAS-102, which is currently evaluated in phase II studies. Drug resistance is an important limitation of cancer therapy. The aim of the present study was to induce resistance to TFT in H630 colon cancer cells using two different schedules and to analyze the resistance mechanism. Cells were exposed either continuously or intermittently to TFT, resulting in H630-cTFT and H630-4TFT, respectively. Cells were analyzed for cross-resistance, cell cycle, protein expression, and activity of thymidine phosphorylase (TP), thymidine kinase (TK), thymidylate synthase (TS), equilibrative nucleoside transporter (hENT), gene expression (microarray), and genomic alterations. Both cell lines were cross-resistant to 2'-deoxy-5-fluorouridine (>170-fold). Exposure to IC(75)-TFT increased the S/G(2)-M phase of H630 cells, whereas in the resistant variants, no change was observed. The two main target enzymes TS and TP remained unchanged in both TFT-resistant variants. In H630-4TFT cells, TK protein expression and activity were decreased, resulting in less activated TFT and was most likely the mechanism of TFT resistance. In H630-cTFT cells, hENT mRNA expression was decreased 2- to 3-fold, resulting in a 5- to 10-fold decreased TFT-nucleotide accumulation. Surprisingly, microarray-mRNA analysis revealed a strong increase of secretory phospholipase-A2 (sPLA2; 47-fold), which was also found by reverse transcription-PCR (RT-PCR; 211-fold). sPLA2 inhibition reversed TFT resistance partially. H630-cTFT had many chromosomal aberrations, but the exact role of sPLA2 in TFT resistance remains unclear. Altogether, resistance induction to TFT can lead to different mechanisms of resistance, including decreased TK protein expression and enzyme activity, decreased hENT expression, as well as (phospho)lipid metabolism. Mol Cancer Ther; 9(4); 1047-57. (c)2010 AACR.

Abstract B65: Overexpression of MRP4 or MRP5 confers resistance to the nucleoside analogs cytarabine and troxacitabine, but not gemcitabine

Multidrug resistance proteins (MRP) confer resistance to drugs from different classes. MRP4 and MRP5 are related MRP proteins and can transport organic anions. Hence their overexpression has been associated with resistance to several purine analogs, such as 6-mercaptopurine and adefovir (PMEA; 9′-(2′-phosphonylmethoxyethyl)adenine)), and antifolates, such as methotrexate (MTX). 6MP itself is not a substrate for MRP4 and 5, but its monophosphate is, in contrast to the di- (DP) and triphosphates (TP). Similarly MTX (a monoglutamate) is a substrate for various MRPs but the higher glutamates are usually not. Resistance to MTX was not observed at a long exposure because of accumulation of polyglutamates, but a 4-hr exposure to MTX conferred resistance. The aim of this study was to investigate whether MRP4 and 5 overexpression would confer resistance to the widely used nucleoside analogs cytarabine (ara-C) and gemcitabine (GEM), and the novel L-nucleoside analog Troxacitabine (TROX). As model systems we used HEK293 cells transfected with either MRP4 (HEK/MRP4; 59-fold increased MRP4 level) or MRP5 (HEK/MRP5i; 991-fold increased MRP5 level) and determined sensitivity after an exposure for 4 hr (followed by 68 hr drug-free medium) and 72 hr. Uptake and accumulation of GEM and TROX were measured with HPLC coupled to either UV or MS-MS, that of ara-C with the radioactive drug. HEK293 cells were moderately sensitive to ara-C (IC50 1.8 µM) and TROX (2.1 µM) and more sensitive to GEM (46 nM) at 72 hr exposure. At 4 hr exposure, the IC50s increased 5-, 5- and 10-fold, respectively. At 4 and 72 hr exposure a 2-3-fold resistance to TROX and ara-C was found in HEK/MRP4 cells, and a 2.5-fold resistance to ara-C in HEK/MRP5 cells. No resistance to GEM was found. PMEA showed a 3-fold resistance in both cell lines. Resistance in the MRP4/5 cells could be reversed by the specific inhibitors probenecid and indomethacine. In order to explain this resistance, accumulation and retention of the active nucleotides were evaluated. GEM-TP even tended to be higher in the MRP4/5 cells. However, accumulation of ara-C nucleotides after 4 hr was 3- and 2-fold lower in MRP4 and MRP5 cells, respectively. After washing with drug-free medium (DFM), the concentration of ara-CTP declined more rapidly in MRP4 compared to the wild-type. Although TROX accumulation was similar in the 3 cell lines, in MRP4 and MRP5 cells it decreased 4- and 2-fold faster, respectively, after the DFM period. TROX-phosphates were about 25% lower in MRP4/5 cells and decreased rapidly in MRP4, but not in MRP5 cells. In conclusion, MRP4 and MRP5 overexpression confer resistance to TROX and ara-C, but not to GEM, which was associated with a rapid decline of the ara-C and TROX-nucleotides in HEK/MRP4-5 cells.

Citation Information: Mol Cancer Ther 2009;8(12 Suppl):B65.

Cellular pharmacology of multi- and duplex drugs consisting of ethynylcytidine and 5-fluoro-2'-deoxyuridine

Prodrugs can have the advantage over parent drugs in increased activation and cellular uptake. The multidrug ETC-L-FdUrd and the duplex drug ETC-FdUrd are composed of two different monophosphate-nucleosides, 5-fluoro-2′deoxyuridine (FdUrd) and ethynylcytidine (ETC), coupled via a glycerolipid or phosphodiester, respectively. The aim of the study was to determine cytotoxicity levels and mode of drug cleavage. Moreover, we determined whether a liposomal formulation of ETC-L-FdUrd would improve cytotoxic activity and/or cleavage. Drug effects/cleavage were studied with standard radioactivity assays, HPLC and LC-MS/MS in FM3A/0 mammary cancer cells and their FdUrd resistant variants FM3A/TK⁻. ETC-FdUrd was active (IC₅₀ of 2.2 and 79 nM) in FM3A/0 and TK⁻ cells, respectively. ETC-L-FdUrd was less active (IC₅₀: 7 nM in FM3A/0 vs 4500 nM in FM3A/TK⁻). Although the liposomal formulation was less active than ETC-L-FdUrd in FM3A/0 cells (IC₅₀:19.3 nM), resistance due to thymidine kinase (TK) deficiency was greatly reduced. The prodrugs inhibited thymidylate synthase (TS) in FM3A/0 cells (80–90%), but to a lower extent in FM3A/TK⁻ (10–50%). FdUMP was hardly detected in FM3A/TK⁻ cells. Inhibition of the transporters and nucleotidases/phosphatases resulted in a reduction of cytotoxicity of ETC-FdUrd, indicating that this drug was cleaved outside the cells to the monophosphates, which was verified by the presence of FdUrd and ETC in the medium. ETC-L-FdUrd and the liposomal formulation were neither affected by transporter nor nucleotidase/phosphatase inhibition, indicating circumvention of active transporters. In vivo, ETC-FdUrd and ETC-L-FdURd were orally active. ETC nucleotides accumulated in both tumor and liver tissues. These formulations seem to be effective when a lipophilic linker is used combined with a liposomal formulation.

Cell cycle effects and increased adduct formation by temozolomide enhance the effect of cytotoxic and targeted agents in lung cancer cell lines

Temozolomide (TMZ) exerts its cytotoxic effects by methylating guanine in DNA, resulting in a mismatch with thymine. We studied possible enhancement of the cytotoxic activity of several other targeted drugs in four lung cancer cell lines by TMZ. the data are in relation to O(6)-alkylguanine-DNA-alkyltransferase (AGT) expression, gene methylation, cell cycle distribution and adduct formation. Synergism/additivity was found with O(6)-BG), gemcitabine, lonafarnib and paclitaxel, but not with platinum analogs and topoisomerase-inhibitors. O(6)-BG enhanced TMZ-induced accumulation in the G2/m-phase by increasing formation and retention of the O(6)-methyldeoxyguanosine adducts. TMZ combinations with drugs showing a different individual effect on the cell cycle (e.g. gemcitabine-induced S-phase) were most effective. The results show that O(6)-BG enhanced the TMZ effect in all cell lines. TMZ enhanced the cytotoxicity of gemcitabine, paclitaxel and lonafarnib in most cell lines, possibly by affecting the cell cycle, supporting possible application of TMZ in the treatment of lung cancer.

Gemcitabine uptake in glioblastoma multiforme: potential as a radiosensitizer

Glioblastoma multiforme (GBM), the most frequent malignant brain tumor, has a poor prognosis, but is relatively sensitive to radiation. Both gemcitabine and its metabolite difluorodeoxyuridine (dFdU) are potent radiosensitizers. The aim of this phase 0 study was to investigate whether gemcitabine passes the blood-tumor barrier, and is phosphorylated in the tumor by deoxycytidine kinase (dCK) to gemcitabine nucleotides in order to enable radiosensitization, and whether it is deaminated by deoxycytidine deaminase (dCDA) to dFdU. Gemcitabine was administered at 500 or 1000 mg/m(2) just before surgery to 10 GBM patients, who were biopsied after 1-4 h. Plasma gemcitabine and dFdU levels varied between 0.9 and 9.2 microM and 24.9 and 72.6 microM, respectively. Tumor gemcitabine and dFdU levels varied from 60 to 3580 pmol/g tissue and from 29 to 72 nmol/g tissue, respectively. The gene expression of dCK (beta-actin ratio) varied between 0.44 and 2.56. The dCK and dCDA activities varied from 1.06 to 2.32 nmol/h/mg protein and from 1.51 to 5.50 nmol/h/mg protein, respectively. These enzyme levels were sufficient to enable gemcitabine phosphorylation, leading to 130-3083 pmol gemcitabine nucleotides/g tissue. These data demonstrate for the first time that gemcitabine passes the blood-tumor barrier in GBM patients. In tumor samples, both gemcitabine and dFdU concentrations are high enough to enable radiosensitization, which warrants clinical studies using gemcitabine in combination with radiation.