Antiproliferative activity, mechanism of action and oral antitumor activity of CP-4126, a fatty acid derivative of gemcitabine, in in vitro and in vivo tumor models

Nucleo(s)tide metabolism as basis for drug development; the Anne Simmonds award lecture

Aberrant metabolism of purines and pyrimidines led to development of drugs for treatment of various diseases, such as inflammatory, neurological, cardiovascular, viral infections and cancer. Purine and Pyrimidine Symposia are characterized by close interactions, leading to extensive cross-fertilization on methodology and translating not only from bench-to-bedside, but also between various disciplines such as medicinal chemistry, pharmacology, oncology, virology, rheumatology, biochemistry, pediatrics, cardiology, surgery and immunology. This background was fundamental in our studies on how to optimize application of existing drugs (5-fluorouracil [5FU], thiopurines, antifolates such as methotrexate) but also to support development of novel drugs such as gemcitabine, novel antifolates, S-1, TAS-102 and fluorocyclopentenylcytosine. Knowledge of their metabolism helped to design rational combinations such as of gemcitabine with cisplatin, one of the most widely used drug combinations for various cancers. The combination of 5FU with uridine, led to the development of triacetyluridine registered for emergency treatment of patients with lethal 5FU toxicity. Mechanisms of action were studied by careful analysis of their metabolism, using classical enzyme assays with radioactive precursors and HPLC analysis. Drug metabolism moved from manually operated HPLC systems with UV-detection for peak identification and paper rolls for quantification, to computer-operated HPLC with automatic multi-wavelength and fluorometric peak detection and more recently to ultrasensitive, highly specific mass-spectrometry-based systems. Some aspects, however, never changed; careful analysis of the results and being prepared for the unexpected. The latter actually led to the most interesting results. Investigation of (nucleoside/nucleotide) metabolism remains an exciting field of research.

Effects of nucleoside analogues, lipophilic prodrugs and elaidic acids on core signaling pathways in cancer cells

OBJECTIVES

Nucleoside analogs such as gemcitabine (GEM; dFdC) and cytarabine (Ara-C) require nucleoside transporters to enter cells, and deficiency in equilibrative nucleoside transporter 1 (ENT1) can lead to resistance to these drugs. To facilitate transport-independent uptake, prodrugs with a fatty acid chain attached to the 5'-position of the ribose group of gemcitabine or cytarabine were developed (CP-4126 and CP-4055, respectively). As antimetabolites can activate cellular survival pathways, we investigated whether the prodrugs or their side-chains had similar or decreased effects.

METHODS

Two cell lines A549 (non-small cell lung cancer) and WiDr (colon cancer cells) were exposed for 2-24hr to IC50 concentrations of GEM, Ara-C, CP-4126, CP4055 and elaidic acid (EA) concentrations corresponding to the CP-4126 and CP-4055 IC50. Cells were harvested and analyzed for proteins in cell survival pathways (p-AKT/AKT, p-ERK/ERK, p-P38/P38, GSK-3β/pGSK-3β) by using Western Blotting.

RESULTS

All drugs and their derivatives showed time- and cell-line-dependent effects. In A549 cells, GEM, CP-4126 and EA-4126 decreased the p-AKT/AKT ratio at 2 and 24 hr. For the p-ERK/ERK ratio, GEM, EA-4126, Ara-C, CP-4045 and EA-4055 exposure led to an increase after 6 hr in A549 cells. Interestingly, Ara-C, CP-4055 and EA-4055 decreased p-ERK/ERK ratio in WiDr cells after 4 hr. In A549 cells, the p-GSK-3β/GSK-3β ratio decreased after exposure to Ara-C and CP-4055 but in WiDr cells increased after 24 hr. In A549 cells treatment with Ara-C, CP-4055 and EA-4126 decreased the p-P38/P38 after 6 hr.

CONCLUSIONS

The findings suggest that both parent drugs, prodrugs, and the EA chain influence cell survival and signaling pathways.

Gemcitabine elaidate and ONC201 combination therapy for inhibiting pancreatic cancer in a KRAS mutated syngeneic mouse model

Approximately 90% of pancreatic cancer (PC) contain KRAS mutations. Mutated KRAS activates the downstream oncogenic PI3K/AKT and MEK signaling pathways and induces drug resistance. However, targeting both pathways with different drugs can also lead to excessive toxicity. ONC201 is a dual PI3K/AKT and MEK pathway inhibitor with an excellent safety profile that targets death receptor 5 (DR5) to induce apoptosis. Gemcitabine (GEM) is a first-line chemotherapy in PC, but it is metabolically unstable and can be stabilized by a prodrug approach. In this study, phospho-Akt, phospho-mTOR, and phospho-ERK protein expressions were evaluated in patient PDAC-tissues (n = 10). We used lipid-gemcitabine (L_GEM) conjugate, which is more stable and enters the cells by passive diffusion. Further, we evaluated the efficacy of L_GEM and ONC201 in PC cells and "KrasLSL-G12D; p53LoxP; Pdx1-CreER (KPC) triple mutant xenograft tumor-bearing mice. PDAC patient tissues showed significantly higher levels of p-AKT (Ser473), p-ERK (T202/T204), and p-mTOR compared to surrounding non-cancerous tissues. ONC201 in combination with L_GEM, showed a superior inhibitory effect on the growth of MIA PaCa-2 cells. In our in-vivo study, we found that ONC201 and L_GEM combination prevented neoplastic proliferation via AKT/ERK blockade to overcome chemoresistance and increased T-cell tumor surveillance. Simultaneous inhibition of the PI3K/AKT and MEK pathways with ONC201 is an attractive approach to potentiate the effect of GEM. Our findings provide insight into rational-directed precision chemo and immunotherapy therapy in PDAC.

Exploring the Inclusion Complex of an Anticancer Drug with β-Cyclodextrin for Reducing Cytotoxicity Toward the Normal Human Cell Line by an Experimental and Computational Approach

The toxicity of any drug against normal cells is a health hazard for all humans. At present, health and disease researchers from all over the world are trying to synthesize designer drugs with diminished toxicity and side effects. The purpose of the present study is to enhance the bioavailability and biocompatibility of gemcitabine (GEM) by decreasing its toxicity and reducing deamination during drug delivery by incorporating it inside the hydrophobic cavity of β-cyclodextrin (β-CD) without affecting the drug ability of the parent compound (GEM). The newly synthesized inclusion complex (IC) was characterized by different physical and spectroscopic techniques, thereby confirming the successful incorporation of the GEM molecule into the nanocage of β-CD. The molecular docking study revealed the orientation of the GEM molecule into the β-CD cavity (-5.40 kcal/mol) to be stably posed for ligand binding. Photostability studies confirmed that the inclusion of GEM using β-CD could lead to better stabilization of GEM (≥96%) for further optical and clinical applications. IC (GEM-β-CD) and GEM exhibited effective antibacterial and antiproliferative activities without being metabolized in a dose-dependent manner. The CT-DNA analysis showed sufficiently strong IC (GEM-β-CD) binding (Ka = 8.1575 × 1010), and this interaction suggests that IC (GEM-β-CD) may possibly exert its biological effects by targeting nucleic acids in the host cell. The newly synthesized biologically active IC (GEM-β-CD), a derivative of GEM, has pharmaceutical development potentiality.

Gemcitabine elaidate and ONC201 combination therapy inhibits pancreatic cancer in a KRAS mutated syngeneic mouse model

Approximately 90% of pancreatic cancer (PC) contain KRAS mutations. Mutated KRAS activates the downstream oncogenic PI3K/AKT and MEK signaling pathways and induces drug resistance. However, targeting both pathways with different drugs can also lead to access of toxicity. ONC201 targets DR5 to induce apoptosis in several types of cancers and has an excellent safety profile. ONC201 is also a dual PI3K/AKT and MEK pathways inhibitor. Gemcitabine (GEM) is a first-line chemotherapy in PC, but it is metabolically unstable, which can be stabilized by prodrug approach. Here, we used lipid-gemcitabine (L_GEM) conjugate, which is more stable and enters the cells by passive diffusion. We evaluated the efficacy of L_GEM and ONC201 in PanCan cells, and "KrasLSL-G12D; p53LoxP; Pdx1-CreER (KPC) triple mutant xenograft tumor-bearing mice. ONC201, in combination with L_GEM, showed a superior inhibitory effect on the growth of MIA PaCa-2 cells. ONC201 and L_GEM combination prevented neoplastic proliferation via AKT/ERK blockade, to overcome chemoresistance, and increased T-cell tumor surveillance. Simultaneous inhibition of the PI3K/AKT and MEK pathways with ONC201 is an attractive approach to potentiate GEM. Our findings provide insight into rational-directed precision chemo and immunotherapy therapy in PDAC.

Tumor microenvironment stimuli-responsive lipid-drug conjugates for cancer treatment

Lipid drug conjugates (LDCs) have attracted considerable attention in the fields of drug delivery and pharmacology due to their ability to target specific cells, increase drug solubility, reduce toxicity, and improve therapeutic efficacy. These unique features make LDCs promising candidates for the treatment cancer, inflammation, and infectious diseases. In fact, by choosing specific linkers between the lipid and drug molecules, stimuli-responsive LDCs can be designed to target cancer cells based on the unique properties of the tumor microenvironment. Despite the fact that many reviews have described LDCs, few articles have focused on tumor microenvironmental stimuli-responsive LDCs for cancer treatment. Therefore, the key elements of these types of LDCs in cancer treatment will be outlined and discussed in this paper. Our paper goes into detail on the concepts and benefits of LDCs, the various types of tumor microenvironment stimuli-responsive LDCs (such as pH, redox, enzyme, or reactive oxygen species-responsive LDCs), and the current status of LDCs in clinical trials.

Incorporating a Lipophilic Disulfide-Bridged Linoleic Prodrug into a Self-Microemulsifying Drug Delivery System to Facilitate Oral Absorption of Paclitaxel

The oral absorption of paclitaxel (PTX) is restricted by poor solubility in the gastrointestinal tract (GIT), low permeability, and high first-pass metabolism. Lipid carriers, such as a self-microemulsifying drug delivery system (SMEDDS), have been deemed as promising vehicles for promoting oral delivery of PTX. Herein, a lipophilic disulfide-bridged linoleic prodrug (PTX-S-S-LA) was synthesized and efficiently incorporated into SMEDDS to facilitate the oral absorption of PTX. This study mainly aims to evaluate the usefulness of the disulfide-bridged linoleic prodrug incorporated with SMEDDS and provides a new strategy for efficient oral delivery of PTX. The prodrug SMEDDS showed a markedly higher drug loading efficiency (3-fold) compared to that of parent PTX. PTX-S-S-LA SMEDDS significantly increased the drug partition (about 1.9-fold) in the intestinal micellar aqueous phase compared to PTX in the in vitro lipolysis study. Additionally, the gastrointestinal (GI) biodistribution study demonstrated that SMEDDS could enhance the GI biological adhesion and go through the lymphatic system to transport. Moreover, it was found that the reduction-sensitive prodrug (PTX-S-S-LA) has good stability in the GIT, leading to an improved antitumor efficiency without significant GI toxicity. Overall, the PTX-linoleic prodrug (PTX-S-S-LA) in combination with SMEDDS provides a promising way to enable effective oral delivery of PTX.

Advanced prodrug strategies in nucleoside analogues targeting the treatment of gastrointestinal malignancies

Gastrointestinal malignancies are common digestive system tumor worldwide. Nucleoside analogues have been widely used as anticancer drugs for the treatment of a variety of conditions, including gastrointestinal malignancies. However, low permeability, enzymatic deamination, inefficiently phosphorylation, the emergence of chemoresistance and some other issues have limited its efficacy. The prodrug strategies have been widely applied in drug design to improve pharmacokinetic properties and address safety and drug-resistance issues. This review will provide an overview of the recent developments of prodrug strategies in nucleoside analogues for the treatment of gastrointestinal malignancies.

Palmitoyl Carnitine-Anchored Nanoliposomes for Neovasculature-Specific Delivery of Gemcitabine Elaidate to Treat Pancreatic Cancer

Being the fourth most fatal malignancy worldwide, pancreatic cancer is on track to become the second leading cause of cancer-related deaths in the United States by 2030. Gemcitabine is a first-line chemotherapeutic agent for pancreatic ductal adenocarcinoma (PDAC). Gemcitabine Elaidate (Gem Elaidate) is a lipophilic derivative which allows hENT1-independent intracellular delivery of gemcitabine and better pharmacokinetics and entrapment in a nanocarrier. Cancer cells and neovasculature are negatively charged compared to healthy cells. Palmitoyl-DL-carnitine chloride (PC) is a Protein kinase C (PKC) inhibitor which also provides a cationic surface charge to nanoliposomes for targeting tumor neovasculature and augmented anticancer potency. The objectives of our study are: (a) to develop and characterize a PKC inhibitor-anchored Gem Elaidate-loaded PEGylated nanoliposome (PGPLs) and (b) to investigate the anticancer activity of Gem Elaidate and PGPLs in 2D and 3D models of pancreatic cancer. The optimized PGPLs resulted in a particle size of 80 ± 2.31 nm, a polydispersity index of 0.15 ± 0.05 and a ζ-potential of +31.6 ± 3.54 mV, with a 93.25% encapsulation efficiency of Gem Elaidate in PGPLs. Our results demonstrate higher cellular uptake, inhibition in migration, as well as angiogenesis potential and significant apoptosis induced by PGPLs in 3D multicellular tumor spheroids of pancreatic cancer cells. Hence, PGPLs could be an effective and novel nanoformulation for the neovasculature-specific delivery of Gemcitabine Elaidate to treat PDAC.

Antiproliferative and apoptotic activity of gemcitabine-lauric acid conjugate on human bladder cancer cells

Objectives

Gemcitabine is a first-line drug for the treatment of bladder cancer. One of the most important mechanisms of gemcitabine resistance is the low expression of cellular membrane transporter hENT1. Various derivatives containing fatty acid side chains have been developed in order to facilitate gemcitabine uptake and prolong its retention in cells, such as CP-4126. In this study, the anti-tumor effect and mechanism of a new derivative of gemcitabine named SZY-200 on bladder cancer cells were investigated. SZY-200 was assembled from the gemcitabine-lauric acid conjugate.

Materials and Methods

Antiproliferative activities of SZY-200 and lauric acid were evaluated using CCK-8 assay and clonogenic survival assay. The hENT1 inhibitor NBMPR was employed to determine the role of hENT1 in the apoptotic activity of GEM, CP-4126, and SZY-200. RT-qPCR, flow cytometry, fluorescence microscope, western blotting, and wound healing assay were used to study the mechanisms of SZY-200. The target genes were predicted using the BATMAN-TCM database.

Results

Our data showed that SZY-200 could inhibit the proliferation of bladder cancer cells by inducing cell cycle arrest and apoptosis. The inhibitory effects were comparable to gemcitabine and CP-4126. SZY-200 does not rely on hENT1 to help it enter bladder cancer cells. Also, we found that lauric acid could inhibit the proliferation of bladder cancer cells. SZY-200 could down-regulate the expressions of PPARG and PTGS2 which were related to the occurrence and development of bladder cancer.

Conclusion

SZY-200 has the same or more advantages as CP-4126 and could be an ideal candidate drug for further in vivo investigation.

Gemcitabine Lipid Prodrugs: The Key Role of the Lipid Moiety on the Self-Assembly into Nanoparticles

A small library of amphiphilic prodrugs has been synthesized by conjugation of gemcitabine (Gem) (a hydrophilic nucleoside analogue) to a series of lipid moieties and investigated for their capacity to spontaneously self-assemble into nanosized objects by simple nanoprecipitation. Four of these conjugates formed stable nanoparticles (NPs), while with the others, immediate aggregation occurred, whatever the tested experimental conditions. Whether such capacity could have been predicted based on the prodrug physicochemical features was a matter of question. Among various parameters, the hydrophilic-lipophilic balance (HLB) value seemed to hold a predictive character. Indeed, we identified a threshold value which well correlated with the tendency (or not) of the synthesized prodrugs to form stable nanoparticles. Such a hypothesis was further confirmed by broadening the analysis to Gem and other nucleoside prodrugs already described in the literature. We also observed that, in the case of Gem prodrugs, the lipid moiety affected not only the colloidal properties but also the in vitro anticancer efficacy of the resulting nanoparticles. Overall, this study provides a useful demonstration of the predictive potential of the HLB value for lipid prodrug NP formulation and highlights the need of their opportune in vitro screening, as optimal drug loading does not always translate in an efficient biological activity.

"Open Sesame?": Biomarker Status of the Human Equilibrative Nucleoside Transporter-1 and Molecular Mechanisms Influencing its Expression and Activity in the Uptake and Cytotoxicity of Gemcitabine in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is an extremely aggressive tumor characterized by early invasiveness, rapid progression and resistance to treatment. For more than twenty years, gemcitabine has been the main therapy for PDAC both in the palliative and adjuvant setting. After the introduction of FOLFIRINOX as an upfront treatment for metastatic disease, gemcitabine is still commonly used in combination with nab-paclitaxel as an alternative first-line regimen, as well as a monotherapy in elderly patients unfit for combination chemotherapy. As a hydrophilic nucleoside analogue, gemcitabine requires nucleoside transporters to permeate the plasma membrane, and a major role in the uptake of this drug is played by human equilibrative nucleoside transporter 1 (hENT-1). Several studies have proposed hENT-1 as a biomarker for gemcitabine efficacy in PDAC. A recent comprehensive multimodal analysis of hENT-1 status evaluated its predictive role by both immunohistochemistry (with five different antibodies), and quantitative-PCR, supporting the use of the 10D7G2 antibody. High hENT-1 levels observed with this antibody were associated with prolonged disease-free status and overall-survival in patients receiving gemcitabine adjuvant chemotherapy. This commentary aims to critically discuss this analysis and lists molecular factors influencing hENT-1 expression. Improved knowledge on these factors should help the identification of subgroups of patients who may benefit from specific therapies and overcome the limitations of traditional biomarker studies.

Emerging insights on drug delivery by fatty acid mediated synthesis of lipophilic prodrugs as novel nanomedicines

Many drug molecules that are currently in the market suffer from short half-life, poor absorption, low specificity, rapid degradation, and resistance development. The design and development of lipophilic prodrugs can provide numerous benefits to overcome these challenges. Fatty acids (FAs), which are lipophilic biomolecules constituted of essential components of the living cells, carry out many necessary functions required for the development of efficient prodrugs. Chemical conjugation of FAs to drug molecules may change their pharmacodynamics/pharmacokinetics in vivo and even their toxicity profile. Well-designed FA-based prodrugs can also present other benefits, such as improved oral bioavailability, promoted tumor targeting efficiency, controlled drug release, and enhanced cellular penetration, leading to improved therapeutic efficacy. In this review, we discuss diverse drug molecules conjugated to various unsaturated FAs. Furthermore, various drug-FA conjugates loaded into various nanostructure delivery systems, including liposomes, solid lipid nanoparticles, emulsions, nano-assemblies, micelles, and polymeric nanoparticles, are reviewed. The present review aims to inspire readers to explore new avenues in prodrug design based on the various FAs with or without nanostructured delivery systems.

Patient-Derived Xenograft Models of Pancreatic Cancer: Overview and Comparison with Other Types of Models

Pancreatic cancer (PC) is anticipated to be second only to lung cancer as the leading cause of cancer-related deaths in the United States by 2030. Surgery remains the only potentially curative treatment for patients with pancreatic ductal adenocarcinoma (PDAC), the most common form of PC. Multiple recent preclinical studies focus on identifying effective treatments for PDAC, but the models available for these studies often fail to reproduce the heterogeneity of this tumor type. Data generated with such models are of unknown clinical relevance. Patient-derived xenograft (PDX) models offer several advantages over human cell line-based in vitro and in vivo models and models of non-human origin. PDX models retain genetic characteristics of the human tumor specimens from which they were derived, have intact stromal components, and are more predictive of patient response than traditional models. This review briefly describes the advantages and disadvantages of 2D cultures, organoids and genetically engineered mouse (GEM) models of PDAC, and focuses on the applications, characteristics, advantages, limitations, and the future potential of PDX models for improving the management of PDAC.

Evaluation of NUC-1031: a first-in-class ProTide in biliary tract cancer

PURPOSE

NUC1031 is a first-in-class ProTide, that is a gemcitabine pro-drug designed to overcome putative mechanisms of resistance, including decreased expression of hENT/hCNT transporters, absence of activating enzymes such as deoxycytidine kinase (dCK) and presence of degrading enzymes such as cytidine deaminase (CDA). We undertook comprehensive pre-clinical evaluation of NUC1031 in biliary tract cancer (BTC) models, given that gemcitabine/cisplatin is a standard first-line therapy in advanced BTC.

METHODS

Here, we compared the in vitro activity of NUC1031 in comparison to gemcitabine, validate putative mechanism(s) of action, assessed potential biomarkers of sensitivity or resistance, and performed combination studies with cisplatin. We also evaluated the in vivo efficacy of NUC1031 and gemcitabine using a CDA-high cholangiocarcinoma patient-derived xenograft (PDX) model.

RESULTS

In a panel of BTC cell lines (N = 10), NUC1031 had less potency than gemcitabine in multiple cellular assays. NUC1031 did not demonstrate evidence of greater synergy over gemcitabine in combination with cisplatin. Surprisingly, efficacy of both gemcitabine and NUC1031 was not found to be correlated with hENT/hCTN, dCK or CDA transcript levels. Gemcitabine and NUC1031 showed equivalent efficacy in a CDA-high PDX model in vivo contradicting the primary rationale of NUC1031 design.

CONCLUSION

NUC1031 did not exhibit evidence of superior activity over gemcitabine, as a single-agent, or in combination with cisplatin, in either our in vivo or in vitro BTC models. Given that the largest Phase 3 study (ClinicalTrials.gov: NCT0314666) to date in BTC is underway (N = 828) comparing NUC1031/cisplatin to gemcitabine/cisplatin, our results suggest that a more conservative clinical evaluation path would be more appropriate.

Expression of the nucleoside transporters hENT1 (SLC29) and hCNT1 (SLC28) in pediatric acute myeloid leukemia

Cellular uptake of clinically important deoxynucleoside analogs is mediated by nucleoside transporters including the human equilibrative nucleoside transporter 1 (hENT1) and the concentrative nucleoside transporter-1 (hCNT1). These transporters are responsible for influx of cytarabine and reduced hENT1 expression is a major resistance mechanism in acute myeloid leukemia. We determined hENT1 and hCNT1 protein expression by immunocytochemistry in 50 diagnostic pediatric acute myeloid leukemia patient samples. All samples expressed hENT1 [9/43 (21%) low; 26/43 (60%) medium and 8/43 (19%) high] and hCNT1 [2/42 (5%) low; 35/42 (83%) medium and 5/42 (12%) high] at the cell membrane and cytoplasm. Statistical analysis showed a non-significant relationship between survival and transporter expression and in vitro drug sensitivity. In conclusion, the nucleoside transporters hENT1 and hCNT1 are broadly expressed in pediatric acute myeloid leukemia at diagnosis.

Intestinal OCTN2- and MCT1-targeted drug delivery to improve oral bioavailability

Various drug transporters are widely expressed throughout the intestine and play important roles in absorbing nutrients and drugs, thus providing high quality targets for the design of prodrugs or nanoparticles to facilitate oral drug delivery. In particular, intestinal carnitine/organic cation transporter 2 (OCTN2) and mono-carboxylate transporter protein 1 (MCT1) possess high transport capacities and complementary distributions. Therefore, we outline recent developments in transporter-targeted oral drug delivery with regard to the OCTN2 and MCT1 proteins in this review. First, basic information of the two transporters is reviewed, including their topological structures, characteristics and functions, expression and key features of their substrates. Furthermore, progress in transporter-targeting prodrugs and nanoparticles to increase oral drug delivery is discussed, including improvements in the oral absorption of anti-inflammatory drugs, antiepileptic drugs and anticancer drugs. Finally, the potential of a dual transporter-targeting strategy is discussed.

Metabolism of bioconjugate therapeutics: why, when, and how?

Bioconjugation of therapeutic agents has been used as a selective drug delivery platform for many therapeutic areas. Bioconjugates are prepared by the covalent linkage of active compounds (small or large molecule) to a carrier molecule (lipids, proteins, peptides, carbohydrates, and polymers) through a chemical linker. The linkage of the active component to a carrier molecule enhances the therapeutic window through a targeted delivery and by reducing toxicity. Bioconjugates also possess improved pharmacokinetic properties such as a long half-life, increased stability, and cleavage by intracellular enzymes/environment. However, premature cleavage of the bioconjugates and the resulting metabolites/catabolites may produce undesirable toxic effects and, hence, it is critical to understand cleavage mechanisms, metabolism of bioconjugates, and translatability to human in the discovery stages. This article provides a comprehensive overview of linker cleavage pathways and catabolism/metabolism of antibody-drug conjugates, glycoconjugates, polymer-drug conjugates, lipid-drug conjugates, folate-targeted small molecule-drug conjugates, and drug-drug conjugates.

Anticancer activities of fatty acids and their heterocyclic derivatives

Traditional chemotherapy relies on the premise that rapidly proliferating cancer cells are more likely to be killed by a cytotoxic agent, but in reality, the long-standing problem of chemotherapy is the lack of tumor-specific treatments. Apart from the impact on tumor cells, the drugs' major limitation is their severe adverse side effects on normal cells and tissues. Nutritional and epidemiological studies have indicated that cancer progression is correlated with the consumption of fatty acids, but the exact mechanisms still remain unknown. In the first part of our review, we discussed the beneficial effects of free fatty acids (saturated and unsaturated) on the progress of carcinogenesis in different tumor cell lines. We presented various mechanisms proposed in the literature, which explain the possible impact on the cells metabolism. The second part describes modifications of different fatty acids with existing anticancer drugs and heterocyclic moieties by condensation reactions. Such conjugations increased the tissue selectivity and made chemotherapy potentially more effective and less toxic in in vivo and in vitro studies. This fatty acid modifications, which change the activity of compounds, their uptake selectivity and alter drug delivery methods, may be the key to unlocking true medical potential of fatty acids.

Overcoming the delivery barrier of oligonucleotide drugs and enhancing nucleoside drug efficiency: The use of nucleolipids

With the rapid development of synthetic technology and biological technology, many nucleic acid-based drugs have entered the clinical trials. However, their inherent disabilities in actively and efficiently penetrating cell membranes still severely restrict their further application. The main drawback of cationic lipids, which have been widely used as nonviral vectors of nucleic acids, is their high cytotoxicity. A series of nucleoside-based or nucleotide-based nucleolipids have been reported in recent years, due to their oligonucleotide delivery capacity and low toxicity in comparison with cationic lipids. Lipophilic prodrugs of nucleoside analogs have extremely similar structures with nucleolipid vectors and are thus helpful for improving the transmembrane ability. This review introduces the progress of nucleolipids and provides new strategies for improving the delivery efficiency of nucleic acid-based drugs, as well as lipophilic prodrugs of nucleosides or nucleotides for antiviral or anticancer therapies.

Chemoresistance in Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC), generally known as pancreatic cancer (PC), ranks the fourth leading cause of cancer-related deaths in the western world. While the incidence of pancreatic cancer is displaying a rising tendency every year, the mortality rate has not decreased significantly because of late diagnosis, early metastasis, and limited reaction to chemotherapy or radiotherapy. Adjuvant chemotherapy after surgical resection is typically the preferred option to treat early pancreatic cancer. Although 5-fluorouracil/leucovorin with irinotecan and oxaliplatin (FOLFIRINOX) and gemcitabine/nab-paclitaxel can profoundly improve the prognosis of advanced pancreatic cancer, the development of chemoresistance still leads to poor clinical outcomes. Chemoresistance is multifactorial as a result of the interaction among pancreatic cancer cells, cancer stem cells, and the tumor microenvironment. Nevertheless, more pancreatic cancer patients will benefit from precision treatment and targeted drugs. Therefore, we outline new perspectives for enhancing the efficacy of gemcitabine after reviewing the related factors of gemcitabine metabolism, mechanism of action, and chemoresistance.

Di-O-lauroyl-decitabine-lipid nanocapsules: toward extending decitabine activity

Background

Acute myeloid leukemia mainly affects adult patients. Complete remission for patients younger than 60 years, who are candidates for standard induction therapy, is achieved in 60%–80% of cases. However, the prognosis is still poor for older patients, who are unfit for intensive chemotherapy, and only a few therapies are available. Hypomethylating agents, such as decitabine, are approved for such patients. The current dosing regimen consists of one administration per day, for 5 days, each 4 weeks.

Methods

Here, we present the synthesis of a decitabine prodrug, combined with its encapsulation into a lipid-based nanocapsule formulation. Decitabine (C12)₂ was synthetized, then loaded into nanocapsules. Its stability in phosphate buffer ans human plasma was checked. Its activity was evaluated by Cell proliferation assays and cell-cycle analysis on human erythroleukemia cells. Then its pharmacokinetics was determined on a rat model.

Results

Decitabine (C12)₂ was obtained with a yield of 50%. Drug loading into nanocarriers of 27.45±0.05 nm was 5.8±0.5 mg/mL. The stability of decitabine was improved and its activity on leukemia cells was not altered. Finally, pharmacokinetics studies showed a prolonged mean residence time of the drug.

Conclusion

Decitabine (C12)₂ as a prodrug showed high encapsulation efficiency, a good stability in plasma with no impact on its activity on leukemia cells and improved pharmacokinetics.

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.

4-N-Alkanoyl and 4-N-alkyl gemcitabine analogues with NOTA chelators for 68-gallium labelling

The conjugation of 4-N-(3-aminopropanyl)-2'-deoxy-2',2'-difluorocytidine with 2-(p-isothiocyanatobenzyl)-1,4,7-triazacyclononane-1,4,7-triacetic acid (SCN-Bn-NOTA) ligand in 0.1 M Na₂CO₃ buffer (pH 11) at ambient temperature provided 4-N-alkylgemcitabine-NOTA chelator. Incubation of latter with excess of gallium(III) chloride (GaCl₃) (0.6 N AcONa/H₂O, pH = 9.3) over 15 min gave gallium 4-N-alkylgemcitabine-NOTA complex which was characterized by HRMS. Analogous [⁶⁸Ga]-complexation of 4-N-alkylgemcitabine-NOTA conjugate proceeded with high labeling efficiency (94%-96%) with the radioligand almost exclusively found in the aqueous layer (∼95%). The high polarity of the gallium 4-N-alkylgemctiabine-NOTA complex resulted in rapid renal clearance of the ⁶⁸Ga-labelled radioligand in BALB/c mice.

The evolution of nucleoside analogue antivirals: A review for chemists and non-chemists. Part 1: Early structural modifications to the nucleoside scaffold

This is the first of two invited articles reviewing the development of nucleoside-analogue antiviral drugs, written for a target audience of virologists and other non-chemists, as well as chemists who may not be familiar with the field. Rather than providing a simple chronological account, we have examined and attempted to explain the thought processes, advances in synthetic chemistry and lessons learned from antiviral testing that led to a few molecules being moved forward to eventual approval for human therapies, while others were discarded. The present paper focuses on early, relatively simplistic changes made to the nucleoside scaffold, beginning with modifications of the nucleoside sugars of Ara-C and other arabinose-derived nucleoside analogues in the 1960's. A future paper will review more recent developments, focusing especially on more complex modifications, particularly those involving multiple changes to the nucleoside scaffold. We hope that these articles will help virologists and others outside the field of medicinal chemistry to understand why certain drugs were successfully developed, while the majority of candidate compounds encountered barriers due to low-yielding synthetic routes, toxicity or other problems that led to their abandonment.

Gemcitabine analogues with 4-N-alkyl chain modified with fluoromethyl ketone group

Gemcitabine analogues with a lipophilic 4-N-alkyl chain bearing a terminal β-keto sulfonate moiety suitable for fluorination compatible with ¹⁸F-radiolabeling have been explored. Displacement of p-toluenesulfonylamino in protected 4-N-tosylgemcitabine with 1-amino-10-undecene gave 4-N-(10-undecenyl)-3',5'-di-O-benzoyl-2'-deoxy-2',2'-difluorocytidine. Oxidation of the terminal double bond in the latter with OsO₄/NMO afforded 4-N-(10,11-dihydroxyundecanyl) derivative. Regioselective sulfonation of primary hydroxyl followed by oxidation of secondary hydroxyl with Collin's reagent yielded desired β-keto sulfonate analogues 8 or 9. Subsequent displacement of the mesylate or tosylate group with KF in the presence of Kryptofix 2.2.2. or 18-crown-6 ether followed by deprotection with NH₃/MeOH gave 4-N-(11-fluoro-10-oxoundecanyl)-2'-deoxy-2',2'-difluorocytidine 11.

The 4-N-acyl and 4-N-alkyl gemcitabine analogues with silicon-fluoride-acceptor: Application to 18F-Radiolabeling

The coupling of gemcitabine with functionalized carboxylic acids using peptide coupling conditions afforded 4-N-alkanoyl analogues with a terminal alkyne or azido moiety. Reaction of 4-N-tosylgemcitabine with azidoalkyl amine provided 4-N-alkyl gemcitabine with a terminal azido group. Click reaction with silane building blocks afforded 4-N-alkanoyl or 4-N-alkyl gemcitabine analogues suitable for fluorination. RP-HPLC analysis indicated better chemical stability of 4-N-alkyl gemcitabine analogues versus 4-N-alkanoyl analogues in acidic aqueous conditions. The 4-N-alkanoyl gemcitabine analogues showed potent cytostatic activity against L1210 cell line, but cytotoxicity of the 4-N-alkylgemcitabine analogues was low. However, 4-N-alkanoyl and 4-N-alkyl analogues had comparable antiproliferative activities in the HEK293 cells. The 4-N-alkyl analogue with a terminal azide group was shown to be localized inside HEK293 cells by fluorescence microscopy after labelling with Fluor 488-alkyne. The [18F]4-N-alkyl or alkanoyl silane gemcitabine analogues were successfully synthesized using microscale and conventional silane-labeling radiochemical protocols. Preliminary positron-emission tomography (PET) imaging in mice showed the biodistribution of [18F]4-N-alkyl to have initial concentration in the liver, kidneys and GI tract followed by increasing signal in the bone.

Vitamin E Phosphate Nucleoside Prodrugs: A Platform for Intracellular Delivery of Monophosphorylated Nucleosides

Vitamin E phosphate (VEP) nucleoside prodrugs are designed to bypass two mechanisms of tumor resistance to therapeutic nucleosides: nucleoside transport and kinase downregulation. Certain isoforms of vitamin E (VE) have shown activity against solid and hematologic tumors and result in chemosensitization. Because gemcitabine is one of the most common chemotherapeutics for the treatment of cancer, it was used to demonstrate the constructs utility. Four different VE isoforms were conjugated with gemcitabine at the 5′ position. Two of these were δ-tocopherol-monophosphate (MP) gemcitabine (NUC050) and δ-tocotrienol-MP gemcitabine (NUC052). NUC050 was shown to be able to deliver gemcitabine-MP intracellularly by a nucleoside transport independent mechanism. Its half-life administered IV in mice was 3.9 h. In a mouse xenograft model of non-small cell lung cancer (NSCLC) NCI-H460, NUC050 at a dose of 40 mg/kg IV qwk × 4 resulted in significant inhibition to tumor growth on days 11–31 (p < 0.05) compared to saline control (SC). Median survival was 33 days (NUC050) vs. 25.5 days (SC) ((hazard ratio) HR = 0.24, p = 0.017). Further, NUC050 significantly inhibited tumor growth compared to historic data with gemcitabine at 135 mg/kg IV q5d × 3 on days 14–41 (p < 0.05). NUC052 was administered at a dose of 40 mg/kg IV qwk × 2 followed by 50 mg/kg qwk × 2. NUC052 resulted in inhibition to tumor growth on days 14–27 (p < 0.05) and median survival was 34 days (HR = 0.27, p = 0.033). NUC050 and NUC052 have been shown to be safe and effective in a mouse xenograft of NSCLC.

Pancreatic Cancer Chemoresistance to Gemcitabine

Pancreatic ductal adenocarcinoma (PDAC), commonly referred to as pancreatic cancer, ranks among the leading causes of cancer-related deaths in the Western world due to disease presentation at an advanced stage, early metastasis and generally a very limited response to chemotherapy or radiotherapy. Gemcitabine remains a cornerstone of PDAC treatment in all stages of the disease despite suboptimal clinical effects primarily caused by molecular mechanisms limiting its cellular uptake and activation and overall efficacy, as well as the development of chemoresistance within weeks of treatment initiation. To circumvent gemcitabine resistance in PDAC, several novel therapeutic approaches, including chemical modifications of the gemcitabine molecule generating numerous new prodrugs, as well as new entrapment designs of gemcitabine in colloidal systems such as nanoparticles and liposomes, are currently being investigated. Many of these approaches are reported to be more efficient than the parent gemcitabine molecule when tested in cellular systems and in vivo in murine tumor model systems; however, although promising, their translation to clinical use is still in a very early phase. This review discusses gemcitabine metabolism, activation and chemoresistance entities in the gemcitabine cytotoxicity pathway and provides an overview of approaches to override chemoresistance in pancreatic cancer.

Oral 4-(N)-stearoyl gemcitabine nanoparticles inhibit tumor growth in mouse models

In spite of recent advances in targeted tumor therapy, systemic chemotherapy with cytotoxic agents remains a vital cancer treatment modality. Gemcitabine is a nucleoside analog commonly used in the treatment of various solid tumors, but an oral gemcitabine dosage form remain unavailable. Previously, we developed the 4-(N)-stearoyl gemcitabine solid lipid nanoparticles (GemC18-SLNs) by incorporating 4-(N)-stearoyl gemcitabine (GemC18), an amide prodrug of gemcitabine, into solid lipid nanoparticles. GemC18-SLNs, when administered intravenously, showed strong antitumor activity against various human and mouse tumors in mouse models. In the present study, we defined the plasma pharmacokinetics of gemcitabine when GemC18-SLNs were given orally to healthy mice and evaluated the antitumor activity of GemC18-SLNs when given orally in mouse models of lung cancer. In mice orally gavaged with GemC18-SLNs, plasma gemcitabine concentration followed an absorption phase and then clearance phase, with a Tmax of ~2 h. The absolute oral bioavailability of gemcitabine in the GemC18-SLNs was ~70% (based on AUC0-24 h values). In mice with pre-established tumors (i.e. mouse TC-1 or LLC lung cancer cells), oral GemC18-SLNs significantly inhibited the tumor growth and increased mouse survival time, as compared to the molar equivalent dose of gemcitabine hydrochloride or GemC18 in vegetable oil or in Tween 20. Immunohistostaining revealed that oral GemC18-SLNs also have significant antiproliferative, antiangiogenic, and proapoptotic activity in LLC tumors. Formulating a lipophilic amide prodrug of gemcitabine into solid lipid nanoparticles may represent a viable approach toward developing a safe and efficacious gemcitabine oral dosage form.

Fluorinated nucleosides as an important class of anticancer and antiviral agents

Fluorine-containing nucleoside analogs (NAs) represent a significant class of the US FDA-approved chemotherapeutics widely used in the clinic. The incorporation of fluorine into drug-like agents modulates lipophilic, electronic and steric parameters, thus influencing pharmacodynamic and pharmacokinetic properties of drugs. Fluorine can block oxidative metabolism of drugs and the formation of undesired metabolites by changing H-bonding interactions. In this review, we focus our attention on chemical fluorination reagents and methods used in the NAs field, including positron emission tomography radiochemistry. We briefly discuss both the cellular biology and clinical properties of FDA-approved and fluorine-containing nucleoside/nucleotide analogs in development as well as common resistance mechanisms associated with their use. Finally, we emphasize pronucleotide strategies used to improve therapeutic outcome of NAs in the clinic.

Pharmacological factors affecting accumulation of gemcitabine's active metabolite, gemcitabine triphosphate

Gemcitabine is an anticancer agent acting against several solid tumors. It requires nucleoside transporters for cellular uptake and deoxycytidine kinase for activation into active gemcitabine-triphosphate, which is incorporated into the DNA and RNA. However, it can also be deaminated in the plasma. The intracellular level of gemcitabine-triphosphate is affected by scheduling or by combination with other chemotherapeutic regimens. Moreover, higher concentrations of gemcitabine-triphosphate may affect the toxicity, and possibly the clinical efficacy. As a consequence, different nucleoside analogs have been synthetized with the aim to increase the concentration of gemcitabine-triphosphate into cells. In this review, we summarize currently published evidence on pharmacological factors affecting the intracellular level of gemcitabine-triphosphate to guide future trials on the use of new nucleoside analogs.

Gemcitabine anti-proliferative activity significantly enhanced upon conjugation with cell-penetrating peptides

Gemcitabine proven efficiency against a wide range of solid tumors and undergoes deamination to its inactive uridine metabolite, which underlies its low bioavailability, and tumour resistance was also associated with nucleoside transporter alterations. Hence, we have conjugated gemcitabine to cell-penetrating peptides (CPP), in an effort to both mask its aniline moiety and facilitate its delivery into cancer cells. Two CPP-drug conjugates have been synthesized and studied regarding both the time-dependent kinetics of gemcitabine release and their anti-proliferative activity on three different human cancer cell lines. Results obtained reveal a dramatic increase in the anti-proliferative activity of gemcitabine in vitro, upon conjugation with the CPPs. As such, CPP-gemcitabine conjugates emerge as promising leads for cancer therapy.

Metabolism, Biochemical Actions, and Chemical Synthesis of Anticancer Nucleosides, Nucleotides, and Base Analogs

Nucleoside, nucleotide, and base analogs have been in the clinic for decades to treat both viral pathogens and neoplasms. More than 20% of patients on anticancer chemotherapy have been treated with one or more of these analogs. This review focuses on the chemical synthesis and biology of anticancer nucleoside, nucleotide, and base analogs that are FDA-approved and in clinical development since 2000. We highlight the cellular biology and clinical biology of analogs, drug resistance mechanisms, and compound specificity towards different cancer types. Furthermore, we explore analog syntheses as well as improved and scale-up syntheses. We conclude with a discussion on what might lie ahead for medicinal chemists, biologists, and physicians as they try to improve analog efficacy through prodrug strategies and drug combinations.

Development and characterization of a long-acting nanoformulated abacavir prodrug

AIM

A myristoylated abacavir (ABC) prodrug was synthesized to extend drug half-life and bioavailability.

METHODS

Myristoylated ABC (MABC) was made by esterifying myristic acid to the drug's 5-hydroxy-cyclopentene group. Chemical composition, antiretroviral activity, cell uptake and retention and cellular trafficking of free MABC and poloxamer nanoformulations of MABC were assessed by proton nuclear magnetic resonance and tested in human monocyte-derived macrophages. Pharmacokinetics of ABC and nanoformulated MABC were evaluated after intramuscular injection into mice.

RESULTS

MABC antiretroviral activity in monocyte-derived macrophages was comparable to native drug. Encasement of MABC into poloxamer nanoparticles extended drug bioavailability for 2 weeks.

CONCLUSION

MABC synthesis and encasement in polymeric nanoformulations improved intracellular drug accumulation and demonstrate translational potential as part of a long-acting antiretroviral regimen.

Improving nucleoside analogs via lipid conjugation: Is fatter any better?

In the past few decades, nucleoside analog drugs have been used to treat a large variety of cancers. These anti-metabolite drugs mimic nucleosides and interfere with chain lengthening upon incorporation into the DNA or RNA of actively replicating cells. However, efficient delivery of these drugs is limited due to their pharmacokinetic properties, and tumors often develop drug resistance. In addition, nucleoside analogs are generally hydrophilic, resulting in poor bioavailability and impaired blood-brain barrier penetration. Conjugating these drugs to lipids modifies their pharmacokinetic properties and may improve in vivo efficacy. This review will cover recent advances in the field of conjugation of phospholipids to nucleoside analogs. This includes conjugation of myristic acid, 12-thioethyldodecanoic acid, 5-elaidic acid esters, phosphoramidate, and self-emulsifying formulations. Relevant in vitro and in vivo data will be discussed for each drug, as well as any available data from clinical trials.

A first-in-human phase I and pharmacokinetic study of CP-4126 (CO-101), a nucleoside analogue, in patients with advanced solid tumours

BACKGROUND

CP-4126 (gemcitabine elaidate, previously CO-101) is a lipid-drug conjugate of gemcitabine designed to circumvent human equilibrative nucleoside transporter1-related resistance to gemcitabine. The purpose of this study was to determine the maximum tolerated dose (MTD) and the recommended phase II dose (RP2D) of CP-4126, and to describe its pharmacokinetic profile.

METHODS

Eligible patients with advanced refractory solid tumours, and adequate performance status, haematological, renal and hepatic function, were treated with one of escalating doses of CP-4126 administered by a 30-min intravenous infusion on days 1, 8 and 15 of a 28-day cycle. Blood and urine samples were collected to determine the pharmacokinetics (PKs) of CP-4126.

RESULTS

Forty-three patients, median age 59 years (range 18-76; male = 27, female = 16), received one of ten dose levels (30-1600 mg/m(2)). Dose-limiting toxicities included grade 3 anaemia, grade 3 fatigue and grade 3 elevation of transaminases. The MTD and RP2D were 1250 mg/m(2) on basis of the toxicity and PK data. CP-4126 followed dose-dependent kinetics and maximum plasma concentrations occurred at the end of CP-4126 infusion. Seven patients achieved stable disease sustained for ≥3 months, including two patients with pancreatic cancer who had progressed on or after gemcitabine exposure.

CONCLUSIONS

CP-4126 was well tolerated with comparable toxicity profile to gemcitabine. Future studies are required to determine its anti-tumour efficacy, either alone or in combination with other cytotoxic chemotherapy regimens.

Novel developments in the use of antimetabolites

Antimetabolites are the most widely used and most efficacious group of anticancer drugs. Antimetabolites are also the oldest rationally designed anticancer drugs, targeted against RNA and DNA, and can, therefore, be considered as the first generation of targeted drugs. Unfortunately, resistance often develops, leading to the design of new antimetabolites, which either have a novel mechanism of action, bypass resistance or in combination enhance the effect of other drugs, such as another antimetabolite, other DNA, or protein kinase targeted anticancer drugs. Several novel antimetabolites are in clinical development. The cytidine-analog fluorocyclopentenylcytosine (RX-3117) is active in gemcitabine-resistant tumors and is activated by uridine-cytidine-kinase, can be incorporated into RNA and DNA and can downregulate DNA-methyltransferase-1. TAS-114 is a new generation dUTPase inhibitor. dUTPase normally prevents incorporation of dUTP and of the 5FU-nucleotide FdUTP into DNA. However, inhibition of dUTPase will enhance their incorporation, thereby increasing thymine-less cell-death. The formulation TAS-102 (trifluorothymidine and thymidine-phosphorylase-inhibitor) acts by incorporation into DNA and has shown efficacy in tumors progressing on 5FU therapy. Gemcitabine and cytarabine prodrugs were tested in model systems and have entered clinical evaluation. The elaidic-acid prodrugs of gemcitabine (CP-4126, CO101) and cytarabine (elacytarabine) failed in randomized Phase III studies. Two other gemcitabine prodrugs LY2334737 (gemcitabine with a valproic acid at the 5'-position) and NUC1031 (a 5'-arylphosphoamidate prodrug, with a side-chain at the 5'-phosphate) are in early clinical development. In summary, several novel antimetabolites show promise in clinical development, either because of a novel mechanism of action, or clever combination or by innovative prodrug design.

Application of ProTide technology to gemcitabine: a successful approach to overcome the key cancer resistance mechanisms leads to a new agent (NUC-1031) in clinical development

Gemcitabine is a nucleoside analogue commonly used in cancer therapy but with limited efficacy due to a high susceptibility to cancer cell resistance. The addition of a phosphoramidate motif to the gemcitabine can protect it against many of the key cancer resistance mechanisms. We have synthesized a series of gemcitabine phosphoramidate prodrugs and screened for cytostatic activity in a range of different tumor cell lines. Among the synthesized compounds, one in particular (NUC-1031, 6f) was shown to be potent in vitro. Importantly, compared with gemcitabine, 6f activation was significantly less dependent on deoxycytidine kinase and on nucleoside transporters, and it was resistant to cytidine deaminase-mediated degradation. Moreover, 6f showed a significant reduction in tumor volumes in vivo in pancreatic cancer xenografts. The ProTide 6f is now in clinical development with encouraging efficacy signals in a Phase I/II study, which strongly supports the ProTide approach to generate promising new anticancer agents.

Oral anticancer drugs: mechanisms of low bioavailability and strategies for improvement

The use of oral anticancer drugs has increased during the last decade, because of patient preference, lower costs, proven efficacy, lack of infusion-related inconveniences, and the opportunity to develop chronic treatment regimens. Oral administration of anticancer drugs is, however, often hampered by limited bioavailability of the drug, which is associated with a wide variability. Since most anticancer drugs have a narrow therapeutic window and are dosed at or close to the maximum tolerated dose, a wide variability in the bioavailability can have a negative impact on treatment outcome. This review discusses mechanisms of low bioavailability of oral anticancer drugs and strategies for improvement. The extent of oral bioavailability depends on many factors, including release of the drug from the pharmaceutical dosage form, a drug's stability in the gastrointestinal tract, factors affecting dissolution, the rate of passage through the gut wall, and the pre-systemic metabolism in the gut wall and liver. These factors are divided into pharmaceutical limitations, physiological endogenous limitations, and patient-specific limitations. There are several strategies to reduce or overcome these limitations. First, pharmaceutical adjustment of the formulation or the physicochemical characteristics of the drug can improve the dissolution rate and absorption. Second, pharmacological interventions by combining the drug with inhibitors of transporter proteins and/or pre-systemic metabolizing enzymes can overcome the physiological endogenous limitations. Third, chemical modification of a drug by synthesis of a derivative, salt form, or prodrug could enhance the bioavailability by improving the absorption and bypassing physiological endogenous limitations. Although the bioavailability can be enhanced by various strategies, the development of novel oral products with low solubility or cell membrane permeability remains cumbersome and is often unsuccessful. The main reasons are unacceptable variation in the bioavailability and high investment costs. Furthermore, novel oral anticancer drugs are frequently associated with toxic effects including unacceptable gastrointestinal adverse effects. Therefore, compliance is often suboptimal, which may negatively influence treatment outcome.

Synthesis and cytostatic evaluation of 4-N-alkanoyl and 4-N-alkyl gemcitabine analogues

The coupling of gemcitabine with functionalized carboxylic acids (C9-C13) or reactions of 4-N-tosylgemcitabine with the corresponding alkyl amines afforded 4-N-alkanoyl and 4-N-alkyl gemcitabine derivatives. The analogues with a terminal hydroxyl group on the alkyl chain were efficiently fluorinated under conditions that are compatible with protocols for (18)F labeling. The 4-N-alkanoylgemcitabines showed potent cytostatic activities in the low nanomolar range against a panel of tumor cell lines, whereas cytotoxicity of the 4-N-alkylgemcitabines were in the low micromolar range. The cytotoxicity for the 4-N-alkanoylgemcitabine analogues was reduced approximately by 2 orders of magnitude in the 2'-deoxycytidine kinase (dCK)-deficient CEM/dCK(-) cell line, whereas cytotoxicity of the 4-N-alkylgemcitabines was only 2-5 times lower. None of the compounds acted as efficient substrates for cytosolic dCK; therefore, the 4-N-alkanoyl analogues need to be converted first to gemcitabine to display a significant cytostatic potential, whereas 4-N-alkyl derivatives attain modest activity without measurable conversion to gemcitabine.

Randomized, Multicenter, Phase II Study of CO-101 Versus Gemcitabine in Patients With Metastatic Pancreatic Ductal Adenocarcinoma: Including a Prospective Evaluation of the Role of hENT1 in Gemcitabine or CO-101 Sensitivity

Purpose

Gemcitabine requires transporter proteins to cross cell membranes. Low expression of human equilibrative nucleoside transporter-1 (hENT1) may result in gemcitabine resistance in pancreatic ductal adenocarcinoma (PDAC). CO-101, a lipid-drug conjugate of gemcitabine, was rationally designed to enter cells independently of hENT1. We conducted a randomized controlled trial to determine whether CO-101 improved survival versus gemcitabine in patients with metastatic PDAC (mPDAC) with low hENT1. The study also tested the hypothesis that gemcitabine is more active in patients with mPDAC tumors with high versus low hENT1 expression.

Patients and Methods

Patients were randomly assigned to CO-101 or gemcitabine, after providing a metastasis sample for blinded hENT1 assessment. An immunohistochemistry test measuring tumor hENT1 was developed. To dichotomize the population, an hENT1 cutoff value was defined using primary PDAC samples from an adjuvant trial, and a high/low cutoff was applied. The primary end point was overall survival (OS) in the low hENT1 subgroup.

Results

Of 367 patients enrolled, hENT1 status was measured in 358 patients (97.5%). Two hundred thirty-two (64.8%) of 358 patients were hENT1 low. There was no difference in OS between treatments in the low hENT1 subgroup or overall, with hazard ratios (HRs) of 0.994 (95% CI, 0.746 to 1.326) and 1.072 (95% CI, 0.856 to 1.344), respectively. The toxicity profiles in both arms were similar. Within the gemcitabine arm, there was no difference in survival between the high and low hENT1 subgroups (HR, 1.147; 95% CI, 0.809 to 1.626).

Conclusion

CO-101 is not superior to gemcitabine in patients with mPDAC and low tumor hENT1. Metastasis hENT1 expression did not predict gemcitabine outcome.

Folate-chitosan-gemcitabine core-shell nanoparticles targeted to pancreatic cancer

OBJECTIVE

Human pancreatic cancer is one of the most common clinical malignancies. The effect of comprehensive treatment based on surgery is general. The effects of chemotherapy were not obvious mainly because of lack of targeting and chemoresistance in pancreatic cancer. This study aimed to investigate the effects of folate receptor (FR)-mediated gemcitabine FA-Chi-Gem nanoparticles with a core-shell structure by electrostatic spray on pancreatic cancer.

METHODS

In this study, the levels of expression of FR in six human pancreatic cancer cell lines were studied by immunohistochemical analysis. The uptake rate of isothiocyanate-labeled FA-Chi nanoparticles in FR high expression cell line COLO357 was assessed by fluorescence microscope and the inhibition rate of FA-Chi-Gem nanoparticles on COLO357 cells was evaluated by MTT assay. Moreover, the biodistribution of PEG-FA-ICGDER02-Chi in the orthotopic pancreatic tumor model was observed using near-infrared imaging and the human pancreatic cancer orthotopic xenografts were treated with different nanoparticles and normal saline control.

RESULTS

The expression of FR in COLO357 was the highest among the six pancreatic cancer cell lines. The FR mainly distributed on cell membrane and fewer in the cytoplasm in pancreatic cancer. Moreover, the absorption rate of the FA-Chi-Gem nanoparticles was more than the Chi nanoparticles without FA modified. The proliferation of COLO357 was significantly inhibited by FA-Chi-Gem nanoparticles. The PEG-FA-ICGDER02-Chi nanoparticles were enriched in tumor tissue in human pancreatic cancer xenografts, while non-targeted nanoparticles were mainly in normal liver tissue. PEG-FA-Gem-Chi significantly inhibited the growth of human pancreatic cancer xenografts (PEG-FA-Gem-Chi vs. Gem, t=22.950, P=0.000).

CONCLUSIONS

PEG-FA-FITC-Chi nanoparticles might be an effective targeted drug for treating human FR-positive pancreatic cancer.