Possible antitumor activity of 1-(3-C-ethynyl-beta-D-ribo-pentofuranosyl)cytosine (ECyd, TAS-106) against an established gemcitabine (dFdCyd)-resistant human pancreatic cancer cell line

Overcoming tumor cell chemoresistance using nanoparticles: lysosomes are beneficial for (stearoyl) gemcitabine-incorporated solid lipid nanoparticles

Despite recent advances in targeted therapies and immunotherapies, chemotherapy using cytotoxic agents remains an indispensable modality in cancer treatment. Recently, there has been a growing emphasis in using nanomedicine in cancer chemotherapy, and several nanomedicines have already been used clinically to treat cancers. There is evidence that formulating small molecular cancer chemotherapeutic agents into nanomedicines significantly modifies their pharmacokinetics and often improves their efficacy. Importantly, cancer cells often develop resistance to chemotherapy, and formulating anticancer drugs into nanomedicines also helps overcome chemoresistance. In this review, we briefly describe the different classes of cancer chemotherapeutic agents, their mechanisms of action and resistance, and evidence of overcoming the resistance using nanomedicines. We then emphasize on gemcitabine and our experience in discovering the unique (stearoyl) gemcitabine solid lipid nanoparticles that are effective against tumor cells resistant to gemcitabine and elucidate the underlying mechanisms. It seems that lysosomes, which are an obstacle in the delivery of many drugs, are actually beneficial for our (stearoyl) gemcitabine solid lipid nanoparticles to overcome tumor cell resistance to gemcitabine.

Gemcitabine resistance in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDA) ranks fourth among cancer related deaths. The disappointing 5-year survival rate of below 5% stems from drug resistance to all known therapies, as well as from disease presentation at a late stage when PDA is already metastatic. Gemcitabine has been the cornerstone of PDA treatment in all stages of the disease for the last two decades, but gemcitabine resistance develops within weeks of chemotherapy initiation. From a mechanistic perspective, gemcitabine resistance may result from alterations in drug metabolism until the point that the cytidine analog is incorporated into the DNA, or from mitigation of gemcitabine-induced apoptosis. Both of these drug resistance modalities can be either intrinsic to the cancer cell, or influenced by the cancer microenvironment. Mechanisms of intrinsic gemcitabine resistance are difficult to tackle, as many of the genes that drive the carcinogenic process itself also interfere with gemcitabine-induced apoptosis. In this regard, recent understanding of the involvement of microRNAs in gemcitabine resistance may offer new opportunities to overcome intrinsic gemcitabine resistance. The characteristically fibrotic and immune infiltrated stroma of PDA that accompanies tumor inception and expansion is a lush ground for treatments aimed at targeting tumor microenvironment-mediated drug resistance. In the last couple of years, drugs interfering with tumor microenvironment have matured to clinical trials. Although drugs inducing 'stromal depletion' have yet failed to improve survival, they have greatly increased our understanding of tumor microenvironment-mediated drug resistance. In this review we summarize the current knowledge on intrinsic and environment-mediated gemcitabine resistance, and discuss the impact of these pathways on patient screening, and on future treatments aimed to potentiate gemcitabine activity.

Establishment of human pancreatic cancer gemcitabine‑resistant cell line with ribonucleotide reductase overexpression

A gemcitabine (GEM)-resistant human pancreatic cancer cell line (PANC-1RG7) was established in vitro by gradually increasing GEM concentrations and cloning cell cultures to develop a cellular model of acquired drug resistance studies. We found that PANC-1RG7 cells exhibited significantly different morphological characteristics from parental cells. PANC-1RG7 cells grew slowly (p<0.05), yet the cell cycle remained unchanged (p>0.05). PANC-1RG7, with a resistance index to GEM of 39.9, showed cross-resistance characteristics to methotrexate, gefitinib, cisplatin and 5-fluorouracil. The proliferation inhibition of GEM was significantly reduced in vivo (p<0.05). The known resistance-associated genes and proteins we detected remained unchanged, with the exception of cytidine deaminase, multidrug resistance-related protein and breast cancer resistance protein genes, which decreased; by contrast, 5'-nucleotidase, ribonucleotide reductase (RRM) 1 and RRM2 proteins increased (p<0.05). Therefore, a cell line with acquired GEM resistance was established successfully. Resistance was acquired by overexpressing RRM1 and RRM2 proteins.

Attenuation of phosphorylation by deoxycytidine kinase is key to acquired gemcitabine resistance in a pancreatic cancer cell line: targeted proteomic and metabolomic analyses in PK9 cells

PURPOSE

Multiple proteins are involved in activation and inactivation of 2',2'-difluorodeoxycytidine (gemcitabine, dFdC). We aimed to clarify the mechanism of dFdC resistance in a pancreatic cancer cell line by applying a combination of targeted proteomic and metabolomic analyses.

METHODS

Twenty-five enzyme and transporter proteins and 6 metabolites were quantified in sensitive and resistant pancreatic cancer cell lines, PK9 and RPK9, respectively.

RESULTS

The protein concentration of deoxycytidine kinase (dCK) in RPK9 cells was less than 0.02-fold (2 %) compared with that in PK9 cells, whereas the differences (fold) were within a factor of 3 for other proteins. Targeted metabolomic analysis revealed that phosphorylated forms of dFdC were reduced to less than 0.2 % in RPK9 cells. The extracellular concentration of 2',2'-difluorodeoxyuridine (dFdU), an inactive metabolite of dFdC, reached the same level as the initial dFdC concentration in RPK9 cells. However, tetrahydrouridine treatment did not increase phosphorylated forms of dFdC and did not reverse dFdC resistance in RPK9 cells, though this treatment inhibits production of dFdU.

CONCLUSIONS

Combining targeted proteomics and metabolomics suggests that acquisition of resistance in RPK9 cells is due to attenuation of dFdC phosphorylation via suppression of dCK.

Disrupted plasma membrane localization of equilibrative nucleoside transporter 2 in the chemoresistance of human pancreatic cells to gemcitabine (dFdCyd)

Although the nucleoside pyrimidine analogue gemcitabine is the most effective single agent in the palliation of advanced pancreatic cancer, cellular resistance to gemcitabine treatment is a major problem in the clinical scene. To clarify the molecular mechanisms responsible for chemoresistance to gemcitabine, mRNA expression of the key enzymes including cytidine deaminase (CDA), deoxycytidine kinase (dCK), 5'-nucleotidase (NT5), equilibrative nucleoside transporter 1 and 2 (ENT1 and ENT2), dCMP deaminase (dCMPK), ribonucleotide reductase M1 and M2 (RRM1 and RRM2), thymidylate synthase (TS) and CTP synthase (CTPS) was examined. The interacellular uptake of gemcitabine was greatly impaired in the chemoresistant cell lines due to dysfunction of ENT1 and ENT2. Protein expression of ENT1 and ENT2 and their protein coding sequences were not altered. Immunohistochemical and western blot analyses revealed that localization of ENT2 on the plasma membrane was disrupted. These data suggest that the disrupted localization of ENT2 is one of causes of the impaired uptake of gemcitabine, resulting in a gain of chemoresistance to gemcitabine.

The ribonucleotide reductase large subunit (RRM1) as a predictive factor in patients with cancer

The large subunit of human ribonucleotide reductase, RRM1, is involved in the regulation of cell proliferation, cell migration, tumour and metastasis development, and the synthesis of deoxyribonucleotides for DNA synthesis. It is also a cellular target for the chemotherapeutic agent, gemcitabine. RRM1 has been studied in a large number of patients with different types of cancer, such as non-small-cell lung cancer, pancreatic cancer, breast cancer, and biliary tract cancer, to establish its prognostic or predictive value when patients were treated with gemcitabine, and mRNA expression and genetic variants as determined by genotyping have in some cases been associated with clinical outcome of patients with cancer. Here, we review preclinical and clinical studies of RRM1 assessment and discuss the further steps in the development of this clinically pertinent biomarker.

Identifying molecular markers for chemosensitivity to gemcitabine in pancreatic cancer: increased expression of interferon-stimulated gene 15 kd is associated with intrinsic chemoresistance

OBJECTIVES

Gemcitabine is the standard chemotherapeutic agent for pancreatic cancer. Nevertheless, the prognosis of pancreatic cancer patients is still poor. Evaluating the mechanisms of chemoresistance to gemcitabine will be helpful for the improvement of the therapeutic outcome.

METHODS

Using 11 pancreatic cancer cell lines and global gene expression profiling, molecular markers were detected for acquired and intrinsic gemcitabine sensitivity. Acquired gemcitabine resistance in vitro was obtained by continual exposure to gradually increased concentrations of gemcitabine; however, intrinsic sensitivity is originally provided and differs between cell lines.

RESULTS

Microarray analysis of intrinsic sensitivity showed no correlation to that of acquired resistance. Fifteen overexpressed and 49 downexpressed genes in accordance with intrinsic gemcitabine resistance were identified, and we selected those highly expressed in resected pancreatic cancer tissue. Interferon-stimulated gene 15 (ISG15), which plays a role in cellular defense from infection and carcinogenesis, was identified as the gene related to gemcitabine chemosensitivity. By inhibition of ISG15 in gemcitabine-resistant cell lines using siRNA, gemcitabine resistance was reversed.

CONCLUSIONS

It was demonstrated that ISG15 is one of the genes associated with intrinsic gemcitabine sensitivity, having a possibility to be a candidate of molecular targeting for the improvement of chemotherapy against pancreatic cancer.

Combination of human tumor necrosis factor-alpha (hTNF-alpha) gene delivery with gemcitabine is effective in models of pancreatic cancer

Pancreatic adenocarcinoma is an aggressive and highly lethal malignancy. Currently, gemcitabine is commonly used in patients with pancreatic cancer. However, the life expectancy of pancreatic cancer patients remains poor. We explored the possibility of increased anti-tumor activity by combining human tumor necrosis factor-alpha (hTNF-alpha) with current front-line therapy. Human TNF-alpha displays potent anti-tumor activity, but its use is limited by the toxicity of systemic administration. We developed a gene delivery approach using intratumoral injections of an adenoviral vector expressing hTNF-alpha, AdEgr.TNF.11D (TNFerade), to increase local concentrations of hTNF-alpha within the tumor, thereby maximizing local anti-tumor activity and yet minimizing the systemic toxicities. An ongoing phase III clinical trial is testing the efficacy of AdEgr.TNF.11D-injected intratumorally and combining with chemotherapy in locally advanced pancreatic cancer. In this study, we show that treatment with AdEgr.TNF.11D and gemcitabine results in a high level of hTNF-alpha expression in human pancreatic cancer cell lines. The combined treatment was well tolerated, highly active and produced marked delays in the growth of human pancreatic xenograft tumors relative to either agent alone. Our results strongly suggest that combination of AdEgr.TNF.11D and gemcitabine may be a potentially useful therapeutic approach for the improved treatment of pancreatic cancer.

Recent advances in the treatment of peritoneal dissemination of gastrointestinal cancers by nucleoside antimetabolites

Peritoneal dissemination is the most common cause of metastasis from malignancies in the abdominal cavity. There are no standard treatments for peritoneal dissemination and the results are poor. The reasons for this are as follows: (1) no effective chemotherapeutic agents have been identified or developed; (2) surgical cytoreduction has little effect on survival improvement; and (3) the molecular mechanisms of peritoneal dissemination have not been clarified and no therapy against the target molecules has been developed. However, studies on the molecular mechanisms of peritoneal dissemination have elucidated some of the target molecules and the development of new multimodal therapies has also improved survival. Early postoperative intraperitoneal chemotherapy, hyperthermic intraperitoneal perfusion chemotherapy and neoadjuvant intraperitoneal-systemic chemotherapy have been newly developed, and a novel surgical therapy named peritonectomy has been proposed to perform complete cytoreduction of peritoneal dissemination. At present, these approaches appear to be effective therapeutic modalities for peritoneal dissemination. However, TS-1 and capecitabine have shown worthwhile results in recent clinical trials for patients with advanced gastric cancer. We recently found that newly developed antitumor cytosine nucleoside analogs show a survival advantage in peritoneal dissemination models using human cancer cells. These non-fluoropyrimidine nucleosides may potentially help to improve the poor prognosis observed in patients with advanced cancers involving peritoneal dissemination.

Synthesis of 3′-β-carbamoylmethylcytidine (CAMC) and its derivatives as potential antitumor agents

3'-beta-Carbamoylmethylcytidine (CAMC) and its derivatives were synthesized using an intramolecular Reformatsky-type reaction promoted by SmI2 as the key step. In vitro tumor cell growth inhibitory activity was evaluated and CAMC was found to exhibit potent cytotoxicity against various human tumor cell lines. From a structure-activity relationship study it was postulated that the cytotoxic mechanism of action of CAMC did not require phosphorylation at the 5'-hydroxyl group. This study provides a novel strategy for the development of a new type of antitumor nucleoside.