Chemical biology fluorescent tools for in vitro investigation of the multidrug resistant P-glycoprotein (P-gp) expression in tumor cells.

Selective P-glycoprotein (P-gp)-targeted fluorescent conjugates are desirable tools to investigate the role of P-gp, a protein strongly implicated in mediating multidrug resistance and a major cause of chemotherapy failure. Herein, we report the development of 25 novel fluorescent small-molecule conjugates with varying physicochemical and optical properties, and their biological evaluation in a cell model as P-gp targeted constructs. This investigation revealed relationships between molecular structure and cell behavior and uncovered the capacity of conjugates with varying fluorophores to selectively target P-gp. Sulfocyanine 3 labeled conjugates (5, 10, 24, 29, 34) showed a particular intracellular staining pattern. Other conjugates bearing a boron dipyrromethene (BODIPY) core (3, 8, 13, 22, 27 (BODIPY FL), 12 (BODIPY 564/570) and 4, 9 (BODIPY 650/665)) or a 7-nitrobenz-2-oxa-1,3-diazole (NBD) core (11, 30) showed potential for global P-gp direct detection and quantification. These fluorescent conjugates holds key advantages over existing methods for drug resistance evaluation with regards to P-gp expression and could be used as innovative tools in preclinical assays and clinical diagnosis.

LightSpot®-FL-1 Fluorescent Probe: An Innovative Tool for Cancer Drug Resistance Analysis by Direct Detection and Quantification of the P-glycoprotein (P-gp) on Monolayer Culture and Spheroid Triple Negative Breast Cancer Models.

P-gp is the most widely studied MDR protein conferring cellular resistance to many standard or targeted therapeutic agents. For this reason, P-gp chemoresistance evaluation, established before or during chemotherapy, can be very relevant in order to optimize the efficacy of treatments, particularly for aggressive tumoral subtypes such as triple-negative breast cancer (TNBC). In this context, our team developed an innovative cell-permeant fluorescent probe called the LightSpot®-FL-1, which is able to specifically localize and quantify the P-gp in cells or cell masses, as evidenced on different TNBC cell models. First, flow cytometry analysis showed LightSpot®-FL-1 cell penetration and persistence in time, in TNBC cells. Then, LightSpot®-FL-1 staining was compared to anti-P-gp immunostaining by fluorescence microscopy on five TNBC cell lines. Results showed a clear similarity of P-gp localization and expression level, confirmed by Pearson's and Mander's colocalization coefficients with 92.1% and 100.0%, and a strong correlation coefficient of R2 = 0.99. In addition, the LightSpot®-FL-1 staining allowed the quantification of a P-gp induction (33% expression increase) following a 6-hour spheroid model exposure to the anti-PARP Olaparib. Thus, the new LightSpot®-FL-1 cell-permeant probe, targeting P-gp, appears to be an effective tool for drug resistance evaluation in preclinical models and shows promising possibilities for future use in clinical diagnosis.

The New Serum-Free OptiPASS® Medium in Cold and Oxygen-Free Conditions: An Innovative Conservation Method for the Preservation of MDA-MB-231 Triple Negative Breast Cancer Spheroids.

Cancer spheroids are very effective preclinical models to improve anticancer drug screening. In order to optimize and extend the use of spheroid models, these works were focused on the development of a new storage concept to maintain these models in the longer term using the Triple-Negative Breast Cancer MDA-MB-231 spheroid models. The results highlight that the combination of a temperature of 4 °C and oxygen-free conditions allowed the spheroid characteristics of OptiPASS® serum-free culture medium to preserve the spheroid characteristics during 3-, 5- or 7-day-long storage. Indeed, after storage they were returned to normal culture conditions, with recovered spheroids presenting similar growth rates (recovery = 96.2%), viability (Live/Dead® profiles) and metabolic activities (recovery = 90.4%) compared to nonstored control spheroids. Likewise, both recovered spheroids (after storage) and nonstored controls presented the same response profiles as two conventional drugs, i.e., epirubicin and cisplatin, and two anti-PARP1 targeted drugs-i.e., olaparib and veliparib. This new original storage concept seems to induce a temporary stop in spheroid growth while maintaining their principal characteristics for further use. In this way, this innovative and simple storage concept may instigate future biological sample preservation strategies.

The New Synthetic Serum-Free Medium OptiPASS Promotes High Proliferation and Drug Efficacy Prediction on Spheroids from MDA-MB-231 and SUM1315 Triple-Negative Breast Cancer Cell Lines.

Triple-negative breast cancers are particularly aggressive. In vitro cultures are one of the major pathways for developing anticancer strategies. The effectiveness and reproducibility of the drug screenings depend largely on the homogeneity of culture media. In order to optimize the predictive responses of triple-negative breast cancer 3D cell culture models, these works were focused on the development of SUM1315 and MDA-MB-231 cell lines in OptiPASS medium, a new serum-free formulation (BIOPASS). In monolayer cell culture, OptiPASS medium was more suitable for MDA-MB-231 than SUM1315 cell line but maintained cell phenotype and allowed sufficient proliferation. For spheroids produced in OptiPASS, the size monitoring showed a 1.3 and 1.5-fold increase for MDA-MB-231 and SUM1315 cell lines, respectively and viability/mortality profiles were maintained. Spheroids drug sensitivity thresholds were also improved allowing quicker high throughput drug screenings. These results showed the suitability of OptiPASS for 2D and 3D cell cultures of these two triple-negative breast cancer cell lines, with reproducibility of spheroid formation superior to 98%. This opens the way to the common use of this synthetic medium in future preclinical breast cancer research studies.

Low-Dose and Long-Term Olaparib Treatment Sensitizes MDA-MB-231 and SUM1315 Triple-Negative Breast Cancers Spheroids to Fractioned Radiotherapy.

The Triple-Negative Breast Cancer subtype (TNBC) is particularly aggressive and heterogeneous. Thus, Poly-ADP-Ribose Polymerase inhibitors were developed to improve the prognosis of patients and treatment protocols are still being evaluated. In this context, we modelized the efficacy of Olaparib (i.e., 5 and 50 µM), combined with fractioned irradiation (i.e., 5 × 2 Gy) on two aggressive TNBC cell lines MDA-MB-231 (BRCAness) and SUM1315 (BRCA1-mutated). In 2D cell culture and for both models, the clonogenicity drop was 95-fold higher after 5 µM Olaparib and 10 Gy irradiation than Olaparib treatment alone and was only 2-fold higher after 50 µM and 10 Gy. Similar responses were obtained on TNBC tumor-like spheroid models after 10 days of co-treatment. Indeed, the ratio of metabolic activity decrease was of 1.2 for SUM1315 and 3.3 for MDA-MB-231 after 5 µM and 10 Gy and of only 0.9 (both models) after 50 µM and 10 Gy. MDA-MB-231, exhibiting a strong proliferation profile and an overexpression of AURKA, was more sensitive to the co-treatment than SUM1315 cell line, with a stem-cell like phenotype. These results suggest that, with the studied models, the potentiation of Olaparib treatment could be reached with low-dose and long-term exposure combined with fractioned irradiation.

Development and validation of a high-performance liquid chromatography method for the quantitation of intracellular PARP inhibitor Olaparib in cancer cells.

Olaparib is a potent PARP inhibitor in clinical use for cancer therapy. A bioanalytical assay was developed and validated for quantitation of intracellular level of olaparib in cells exposed to the drug. The assay involves an optimized and straightforward sample pretreatment with acetonitrile for olaparib solubilization, cell lysis and protein precipitation, and a high performance liquid chromatography (HPLC) method with ultraviolet detection. Several parameters in both the sample preparation and the detection steps were investigated. Optimal chromatographic conditions were achieved with a 5 µL injection on a Nova-Pak® C18 column (150 × 3.9 mm, 4 µm) using a mobile phase consisting of acetonitrile and ultra-pure water in gradient mode, at a constant 1.2 mL/min flow rate, at 35 °C. Detection was carried out at 254 nm and a diode array detector was used to insure purity of the olaparib peak. The method was validated according to Food and Drug Administration guidelines. Linearity, accuracy and precisions were satisfactory over the concentration range of 200-2000 ng/mL. Limits of detection and quantification for olaparib were 50 ng/mL and 200 ng/mL, respectively. Good stability was showed in three relevant analytical conditions. Finally, the validated analytical method was successfully used to estimate the intracellular level of olaparib in SUM1315 breast cancer cells. A significant difference was observed in intracellular drug level after 1 and 3 h incubations. This method permitting measurement of drug level in tumor cells would allow dosage optimization and improvement of treatment response predictions.

Development and cytotoxic response of two proliferative MDA-MB-231 and non-proliferative SUM1315 three-dimensional cell culture models of triple-negative basal-like breast cancer cell lines.

Triple-Negative Basal-Like tumors, representing 15 to 20% of breast cancers, are very aggressive and with poor prognosis. Targeted therapies have been developed extensively in preclinical and clinical studies to open the way for new treatment strategies. The present study has focused on developing 3D cell cultures from SUM1315 and MDA-MB-231, two triple-negative basal-like (TNBL) breast cancer cell lines, using the liquid overlay technique. Extracellular matrix concentration, cell density, proliferation, cell viability, topology and ultrastructure parameters were determined. The results showed that for both cell lines, the best conditioning regimen for compact and homogeneous spheroid formation was to use 1000 cells per well and 2% Geltrex®. This conditioning regimen highlighted two 3D cell models: non-proliferative SUM1315 spheroids and proliferative MDA-MB-231 spheroids. In both cell lines, the comparison of 2D vs 3D cell culture viability in the presence of increasing concentrations of chemotherapeutic agents i.e. cisplatin, docetaxel and epirubicin, showed that spheroids were clearly less sensitive than monolayer cell cultures. Moreover, a proliferative or non-proliferative 3D cell line property would enable determination of cytotoxic and/or cytostatic drug activity. 3D cell culture could be an excellent tool in addition to the arsenal of techniques currently used in preclinical studies.

BCRP and P-gp relay overexpression in triple negative basal-like breast cancer cell line: a prospective role in resistance to Olaparib.

The triple negative basal-like (TNBL) breast carcinoma is an aggressive and unfavorable prognosis disease. Inhibitors of poly(ADP-ribose) polymerase such as Olaparib could represent a promising targeted therapy but their sensitivity against Multidrug Resistance proteins (MDR), which causes resistance, is not well defined. Thus, our work focused on the analysis of P-gp and BCRP coexpression in the SUM1315 TNBL human cell line, in correlation with Olaparib intracellular concentration. Western blot analyses showed a clear coexpression of P-gp and BCRP in SUM1315 cells. A low cytotoxic Olaparib treatment clearly led to an increased expression of both BCRP and P-gp in these cells. Indeed, after 1.5 h of treatment, BCRP expression was increased with a 1.8 fold increase rate. Then, P-gp took over from 3 h to 15 h with an average increase rate of 1.8 fold, and finally returned to control value at 24 h. HPLC-UV analyses showed that, in the same treatment conditions, the intracellular Olaparib concentration increased from 1 h to 3 h and remained relatively stable until 24 h. Results suggest that the resistance mechanism induced by Olaparib in TNBL SUM1315 cell line may be overpassed if a cytotoxic and stable intracellular level of the drug can be maintained.

Synthesis and evaluation of (18)F-labeled ATP competitive inhibitors of topoisomerase II as probes for imaging topoisomerase II expression.

Type II topoisomerase (Topo-II) is an ATP-dependent enzyme that is essential in the transcription, replication, and chromosome segregation processes and, as such, represents an attractive target for cancer therapy. Numerous studies indicate that the response to treatment with Topo-II inhibitors is highly dependent on both the levels and the activity of the enzyme. Consequently, a non-invasive assay to measure tumoral Topo-II levels has the potential to differentiate responders from non-responders. With the ultimate goal of developing a radiofluorinated tracer for positron emission tomography (PET) imaging, we have designed, synthesized, and evaluated a set of fluorinated compounds based on the structure of the ATP-competitive Topo-II inhibitor QAP1. Compounds 18 and 19b showed inhibition of Topo-II in in vitro assays and exhibited moderate, Topo-II level dependent cytotoxicity in SK-BR-3 and MCF-7 cell lines. Based on these results, (18)F-labeled analogs of these two compounds were synthesized and evaluated as PET probes for imaging Topo-II overexpression in mice bearing SK-BR-3 xenografts. [(18)F]-18 and [(18)F]-19b were synthesized from their corresponding protected tosylated derivatives by fluorination and subsequent deprotection. Small animal PET imaging studies indicated that both compounds do not accumulate in tumors and exhibit poor pharmacokinetics, clearing from the blood pool very rapidly and getting metabolized over. The insights gained from the current study will surely aid in the design and construction of future generations of PET agents for the non-invasive delineation of Topo-II expression.

Efficient (18)F-labeling of large 37-amino-acid pHLIP peptide analogues and their biological evaluation.

Solid tumors often develop an acidic microenvironment, which plays a critical role in tumor progression and is associated with increased level of invasion and metastasis. The 37-residue pH (low) insertion peptide (pHLIP) is under study as an imaging platform because of its unique ability to insert into cell membranes at a low extracellular pH (pH(e) < 7). Labeling of peptides with [(18)F]-fluorine is usually performed via prosthetic groups using chemoselective coupling reactions. One of the most successful procedures involves the alkyne-azide copper(I) catalyzed cycloaddition (CuAAC). However, none of the known "click" methods have been applied to peptides as large as pHLIP. We designed a novel prosthetic group and extended the use of the CuAAC "click chemistry" for the simple and efficient (18)F-labeling of large peptides. For the evaluation of this labeling approach, a D-amino acid analogue of WT-pHLIP and an L-amino acid control peptide K-pHLIP, both functionalized at the N-terminus with 6-azidohexanoic acid, were used. The novel 6-[(18)F]fluoro-2-ethynylpyridine prosthetic group, was obtained via nucleophilic substitution on the corresponding bromo-precursor after 10 min at 130 °C with a radiochemical yield of 27.5 ± 6.6% (decay corrected) with high radiochemical purity ≥98%. The subsequent Cu(I)-catalyzed "click" reaction with the azido functionalized pHLIP peptides was quantitative within 5 min at 70 °C in a mixture of water and ethanol using Cu-acetate and sodium L-ascorbate. [(18)F]-D-WT-pHLIP and [(18)F]-L-K-pHLIP were obtained with total radiochemical yields of 5-20% after HPLC purification. The total reaction time was 85 min including formulation. In vitro stability tests revealed high stability of the [(18)F]-D-WT-pHLIP in human and mouse plasma after 120 min, with the parent tracer remaining intact at 65% and 85%, respectively. PET imaging and biodistribution studies in LNCaP and PC-3 xenografted mice with the [(18)F]-D-WT-pHLIP and the negative control [(18)F]-L-K-pHLIP revealed pH-dependent tumor retention. This reliable and efficient protocol promises to be useful for the (18)F-labeling of large peptides such as pHLIP and will accelerate the evaluation of numerous [(18)F]-pHLIP analogues as potential PET tracers.

The next generation of positron emission tomography radiopharmaceuticals in oncology.

Although (18)F-fluorodeoxyglucose ((18)F-FDG) is still the most widely used positron emission tomography (PET) radiotracer, there are a few well-known limitations to its use. The last decade has seen the development of new PET probes for in vivo visualization of specific molecular targets, along with important technical advances in the production of positron-emitting radionuclides and their related labeling methods. As such, a broad range of new PET tracers are in preclinical development or have recently entered clinical trials. The topics covered in this review include labeling methods, biological targets, and the most recent preclinical or clinical data of some of the next generation of PET radiopharmaceuticals. This review, which is by no means exhaustive, has been separated into sections related to the PET radionuclide used for radiolabeling: fluorine-18, for the labeling of agents such as FACBC, FDHT, choline, and Galacto-RGD; carbon-11, for the labeling of choline; gallium-68, for the labeling of peptides such as DOTATOC and bombesin analogs; and the long-lived radionuclides iodine-124 and zirconium-89 for the labeling of monoclonal antibodies cG250, and J591 and trastuzumab, respectively.

Design, synthesis and in vitro drug release investigation of new potential 5-FU prodrugs.

In order to identify new efficient prodrugs of 5-fluorouracil (5-FU) and to develop an original targeting approach using 2-fluoro-2-deoxyglucose (FDG) as a potential drug carrier, eight original 5-FU derivatives were synthesized: 5-FU was attached by the N1 position of the pyrimidinic ring to the C1 position of the FDG structure either by direct coupling (2a) or via various spacers (3, 6a-c, 10b and 19). A new sensitive high-performance liquid chromatography method was developed to simultaneously quantify 5-FU and its derivatives in human plasma and other relevant media at physiological temperatures. Half-lives were determined from the degradation profiles of these conjugates. Slow degradation of compounds 2a, 3, 10b and 19 was observed in vitro at 37 °C, but no 5-FU release was noticed. By contrast, the in vitro drug release profiles of compounds 6a-c followed pseudo-first-order kinetics, and 5-FU was found in all the media. The antiproliferative activity of the eight compounds was assessed in vitro by a fluorometric assay against two human solid cancer cell lines and one healthy cell line. A correlation was found between the activities of the compounds and their ability to release 5-FU efficiently.