In Vitro and in Vivo Reversal of Resistance to 5-Fluorouracil in Colorectal Cancer Cells with a Novel Stealth Double-Liposomal Formulation

British Journal of Cancer (2007) 97, 919 – 926 & 2007 Cancer Research UK All rights reserved 0007 – 0920/07 $30.00 www.bjcancer.com In vitro and in vivo reversal of resistance to 5-fluorouracil in colorectal cancer cells with a novel stealth double-liposomal formulation 1 1 1 1 2 3 *,1 R Fanciullino , S Giacometti , C Mercier , C Aubert , C Blanquicett , P Piccerelle and J Ciccolini 1 2 EA3286-Laboratoire de Pharmacocine´tique, Universite´ de la Me´diterrane´e, Marseille, France; Department of Medicine, School of Medicine, Emory 3 University, Atlanta, GA, USA; Laboratoire de Pharmacie Gale´nique, Faculte´ de Pharmacie, 27 Bd Jean Moulin, Marseille 05 13385, France Drug resistance is a major cause of treatment failure in cancer chemotherapy, including that with the extensively prescribed antimetabolite, 5-fluorouracil (5-FU). In this study, we tried to reverse 5-FU resistance by using a double-punch strategy: combining 5-FU with a biochemical modulator to improve its tumoural activation and encapsulating both these agents in one same stealth liposome. Experiments carried out in the highly resistant, canonical SW620 human colorectal model showed a up to 80% sensitisation to 5-FU when these cells were treated with our liposomal formulation. Results with this formulation demonstrated 30% higher tumoural drug uptake, better activation with increased active metabolites including critical-5-fluoro-2-deoxyuridine-5-monophosphate, superior inhibition (98%) of tumour thymidylate synthase, and subsequently, higher induction of both early and late apoptosis. Drug monitoring showed that higher and sustained exposure was achieved in rats treated with liposomal formulation. When examined in a xenograft animal model, our dual-agent liposomal formulation caused a 74% reduction in tumour size with a mean doubling in survival time, whereas standard 5-FU failed to exhibit significant antiproliferative activity as well as to increase the lifespan of tumour-bearing mice. Taken collectively, our data suggest that resistance to 5-FU can be overcome through a better control of its intratumoural activation and the use of an encapsulated formulation. British Journal of Cancer (2007) 97, 919–926. doi:10.1038/sj.bjc.6603970 www.bjcancer.com Translational Therapeutics Published online 11 September 2007 & 2007 Cancer Research UK Keywords: stealth liposome; 5-FU; modulation; resistance; xenografts Despite the fact that 5-fluorouracil (5-FU) has been in use for half apoptosis induction (Pinedo and Peters, 1988; Diasio and Harris, a century, it remains the gold standard for chemotherapy of 1989; Langley et al, 2003). Overexpression of TS has been colorectal cancer, the third cause of death due to cancer demonstrated to be associated with 5-FU resistance in patients worldwide. With a mere 20% response rate when used as with colorectal cancer (Johnston et al, 1995; Peters et al, 2002). In monotherapy, numerous attempts have been made to improve this respect, controlling the pattern of 5-FU activation, preferen- its therapeutic index, both at the bench and at the bedside. 5- tially towards inhibiting TS FdUMP synthesis, is a major goal for Fluorouracil was rationally designed to target thymidylate synthase optimising its anticancer efficacy. (TS), an enzyme that is essential for DNA synthesis and cell The key enzyme in the process of yielding intratumoural proliferation; however, the biochemical mechanisms responsible FdUMP is thymidine phosphorylase (TP), the rate-limiting enzyme for its antitumour properties are complex and actually require in the activation of 5-FU via the DNA pathway (Ciccolini et al, anabolism of this prodrug into specific 5-FU nucleotides within 2001; De Bruin et al, 2004). Several attempts to boost tumoural TP cancer cells. Several enzymes involved in its metabolic activation levels have been published in an effort to improve cell sensitivity to eventually lead to the formation of active cytotoxic nucleotides 5-FU or oral 5-FU (capecitabine), by using either ‘Suicide Gene’ or deoxynucleotides (Boyer et al, 2004). However, the major strategies (Schwartz et al, 1995a, b; Evrard et al, 1999; Ciccolini mechanism for 5-FU cytotoxicity is the formation of competitive 5- et al, 2001), co-treating tumour cells with modulators such as IFN, fluoro-2-deoxyuridine-5-monophosphate (FdUMP), thereby inhi- taxoı¨d drugs, mitomycine C, or with radiotherapy (Ciccolini et al, biting TS activity with subsequent depletion of intracellular 2004; Blanquicett et al, 2005). Among the numerous compounds thymidine, suppression of DNA synthesis, and ultimately, tested as putative modulators, 20-deoxyinosine (d-Ino) is a non- toxic precursor of the TP cofactor, deoxyribose 1-phosphate, that has been shown to enhance 5-FU’s antiproliferative activity in *Correspondence: Dr J Ciccolini, EA3286, Laboratoire de Pharmaco- several in vitro and in vivo models, when either used alone or cine´tique, Faculte´ de Pharmacie, 27 Bd Jean Moulin 13385, Marseille 05, combined with gene therapy strategies targeting TP (Ciccolini France; E-mail: [email protected] et al, 2000a, b; Fanciullino et al, 2006). So far, extensive Revised 18 July 2007; accepted 10 August 2007; published online 11 erythrocytic metabolism and a failure to improve its pharmaco- September 2007 kinetic profile have prevented d-Ino from being considered In vitro and in vivo reversal of resistance to 5-fluorouracil R Fanciullino et al 920 clinically, as a possible modulator of 5-FU. To achieve this goal, Encapsulation rate and releasing study our group previously developed the first encapsulated formulation of d-Ino alone (d-InoL), which was designed to spare it from Encapsulation rates of both 5-FU and d-Ino were performed by erythrocytic clearance. This d-InoL proved to increase 5-FU HPLC, using a previously published method (Fanciullino et al, efficacy in vitro and in mice xenografts, at doses much lower than 2005). Liposomal release of 5-FU and d-Ino was monitored by the ones used thus far (Fanciullino et al, 2005). The purpose of the dialysis as described elsewhere (Fanciullino et al, 2005). Sampling present study was to develop a novel, stealth double-liposomal was performed every 30 min, up to 4 h. The total amount of 5-FU formulation encapsulating both 5-FU and its modulator, d-Ino, to and d-Ino released was determined by UV spectrophotometry at enhance further the therapeutic index of 5-FU through a two- 248 nm (Beckman, Villepinte, France). pronged strategy: modulation þ controlled release. Antiproliferative assays MATERIALS AND METHODS Cells were seeded at a density of 8 Â 104 cells per well in 96-well plates. After overnight attachment, exponentially growing cells Cell lines were exposed to increasing concentrations of 5-FU alone, 5-FU combined with free d-Ino, or the liposomal formulation [5-FU þ d- All experiments were carried out in the 5-FU-resistant, human Ino]-L, with gentle shaking for 24 h. Next, drug was removed and colon carcinoma cell line SW620 (also known as CCL227), which the cells were allowed to grow in fresh medium for an additional overexpresses TS. Cells were maintained in RPMI supplemented 48 h. After 72 h of discontinuous exposure, cell viability was with 10% fetal calf serum, 5% glutamine, 10% penicillin, 10% evaluated using the classic colorimetric MTT assay (Alley et al, Translational Therapeutics streptomycin and 1% kanamycin in a humidified CO incubator at 2 1988). The IC was defined as the 5-FU concentration inhibiting 371C. All experiments were performed in exponentially growing 50 50% of cell growth. cells. Drugs and chemicals 5-Fluorouracil tumoural metabolism study Egg yolk phosphatidylcholine (PC), phosphatidylglycerol (PG), Exponentially growing cells were exposed to 1 mM of tritiated 5-FU cholesterol (C), polyethylene glycol (PEG) covalently binded to alone, combined with free d-Ino or as a liposomal preparation phosphatidylethanolamine, 20-deoxyinosine (d-Ino), 5-FU and [5-FU þ d-Ino]-L. After 3, 4 and 6 h exposure, cells were harvested, 50-dFUR were all purchased from Sigma (St Quentin, France). lysed into 70% methanol and cytosols were isolated by centrifuga- tion (15 000 r.p.m., 30 min) and stored at –801C until analysis. Di-kalium hydrogenous phosphate (K2HPO4) buffer, tetrabutyl ammonium nitrate, acetonitrile, ether and methanol were bought Separation of 5-FU and its main metabolites was achieved using a from CarboErba (Milan, Italy). Dimethyl sulphoxide, the apoptosis HP1090 HPLC system (Agilent, Massy, France) coupled to a Flo- kit and culture media were purchased from Euromedex (Souffel- One radioactive detector (Packard, Les Ulis, France) and equipped weyersheim, France). Tritiated 5-FU (12Ci mmolÀ1) was obtained with an RP18 column (Agilent, France), followed by elution with from Moraveck Biochemical (Brea, CA, USA). All reagents were of aK2HPO4-TBAN/methanol gradient as described previously analytical grade. (Ciccolini et al, 2000b). Liposome preparation Thymidylate synthase inhibition Liposomes ((5-FU þ d-Ino)-L) were prepared by the classic thin Thymidylate synthase activity was assessed as described previously film method (Olson et al, 1979). In brief, a lipid mixture composed (Chazal et al, 1997). Briefly, exponentially growing cells were of egg PC/PG/CHOL/PEG (molar ratios of 7.3 : 0.73 : 1.43 : 0.47) in exposed to various combinations of 100 mM of 5-FU alone, 5-FU methanol was evaporated under nitrogen in a round-bottom flask combined with 250 mM d-Ino, or the liposomal formulation [5- to form a dried thin film. This film was then hydrated with an FU þ d-Ino]-L for 12 h. Inhibition of TS activity was evaluated at 8, isotonic carbonate solution (pH 4.2–7.4). The ratio – neutral 24, 48 and 72 h. Cells were then harvested and the pellet was stored phospholipid/cholesterol was 30% and when present, the nega- at À801C until further analysis. Thymidylate synthase activity was assayed following the standard Roberts’ method based on tritiated tively charged lipid was 10% of the neutral lipid.

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