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.

A preclinical evaluation of cytarabine prodrug nanofibers assembled from cytarabine-lauric acid conjugate toward solid tumors

Cytarabine (Ara-C) has become cornerstones for the treatment of hatmatological malignancies for several decades; however, it still faces serious challenges in clinical applications due to its side effects such as hand foot syndrome (HFS) and stomatitis. Therefore, considerable researchers have devoted to looking for the new derivative with desirable activity and low toxicity. A new prodrug based on the conjugation of cytarabine with lauric acid (LA-Ara) was synthesized in our group, and it could self-assemble into nanofibers (NFs) in aqueous solution with high drug loading (57 wt%). The lauric acid moiety protects NH₂ group of from the enzymatic attachment and simultaneously raises the lipophilicity of Ara-C, thus obviously prolongs its plasma half-life. The oil/water partition coefficient (lg P) and the permeability of cell membrane of LA-Ara were obviously increased compared with Ara-C. Furthermore, the in vitro gastrointestinal stability results indicated the prodrug was suitable to be administrated orally. In the current study, the in vitro cytotoxicity and in vivo anti breast cancer experimental results indicate LA-Ara markedly improved antitumor activity compared with free Ara-C. The favorable safety evaluations elucidated its potentiality for oral alternative treatment to Ara-C. Importantly, LA-Ara can effectively decrease the incidence of toxic effects (HFS and stomatitis) of Ara-C, thereby exhibiting favorable skin safety profile. Overall, these results indicated the LA-Ara would be an excellent candidate for further clinical investigation and simultaneously highlight the prospects of Ara-C prodrug strategies in solid tumors therapy.

Nanomedicines for the treatment of hematological malignancies

Hematological malignancies (HM) are a collection of malignant transformations originating from cells in the primary or secondary lymphoid organs. Leukemia, lymphoma, and multiple myeloma comprise the three major types of HM. Current treatment consists of bone marrow transplantation, radiotherapy, immunotherapy and chemotherapy. Although, many chemotherapeutic drugs are clinically available for the treatment of HM, the use of these agents is limited due to dose-related toxicity and lack of specificity to tumor tissue. Moreover, the poor pharmacokinetic profile of most of the chemotherapeutics requires high dosage and frequent administration to maintain therapeutic levels at the target site, both increasing adverse effects. This underlines an urgent need for a suitable drug delivery system to improve efficacy, safety, and pharmacokinetic properties of conventional therapeutics. Nanomedicines have proven to enhance these properties for anticancer therapeutics. The most extensively studied nanomedicine systems are lipid-based nanoparticles and polymeric nanoparticles. Typically, nanomedicines are small sub-micron sized particles in the size range of 20-200 nm. The biocompatible and biodegradable nature of nanomedicines makes them attractive vehicles to improve drug delivery. Their small size allows them to extravasate and accumulate at malignant sites passively by means of the enhanced permeability and retention (EPR) effect, resulting from rapid angiogenesis and inflammation. Moreover, the specificity to the target tissue can be further enhanced by surface modification of nanoparticles. This review describes currently available therapies as well as limitations and potential advantages of nanomedicine formulations for treatment of various types of HM. Additionally, recent investigational and approved nanomedicine formulations and their limited applications in HM are discussed.

Rational design of a new cytarabine-based prodrug for highly efficient oral delivery of cytarabine

Because of the drawbacks of cytarabine (Ara-C) such as poor lipid solubility, deamination inactivation and low oral bioavailability limiting its application by oral administration, herein we propose a novel amphiphilic low molecular weight cytarabine prodrug (PA-Ara) by conjugating palmitic acid (PA) to Ara-C, making it possible to avoid the deamination inactivation by protecting the active 4-amino, as well as improving lipid solubility. Thanks to the rational design, the oil/water partition coefficient (P) of PA-Ara was improved tremendously compared with Ara-C, and the PA-Ara conjugation was stable enough in artificial digestive juice, ensuring that most molecules could be absorbed in the form of the prodrug. Results from an MTT assay conducted to measure the cytotoxicity of Ara-C and PA-Ara to HL60 (acute myeloblastic leukemia cell line) and K562 cells (chronic granulocytic leukemia cell line) showed that PA-Ara had significantly stronger antiproliferation activities than Ara-C. Significantly, we firstly compared the bioavailability of the oral fatty acid chain modified cytarabine prodrug preparation with injection and the relative bioavailability was up to 61.77% for our PA-Ara, which was much superior to that of oral Ara-C solution (3.23%). Overall, these findings make it clear that the PA-Ara suspension has the potential to be a promising new cytarabine oral preparation for leukemia therapy.

To overcome the drawbacks of cytarabine such as bad liposolubility and low bioavailability, we rationally designed a new cytarabine-based prodrug for oral cytarabine delivery, realizing significantly enhanced bioavailability 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.

Clinical potential of elacytarabine in patients with acute myeloid leukemia

Acute myeloid leukemia (AML) has been treated for over four decades with standard induction chemotherapy including seven days of cytosine arabinoside (cytarabine, ara-C) infusion. Cytarabine, while effective in killing leukemic cells, is subject to development of several resistance mechanisms rendering the drug ineffective in many patients. Elacytarabine, a lipophilic 5'-elaidic acid ester or nucleoside analogue of cytosine arabinoside, was created with the intent of overcoming resistance mechanisms including reduced expression of the human equilibrative nucleoside transporter 1 (hENT1) required for cytarabine entry into cells, as well as increased activity of cytidine deaminase (CDA) which breaks down the active metabolite of cytarabine, ara-CTP. Elacytarabine enters cells independently of transporters, has a longer half life compared with cytarabine and is not subject to deactivation by CDA. Preclinical data were encouraging although subsequent clinical studies have failed to show superiority of elacytarabine compared with standard of care as monotherapy in patients with AML. Clinical trials utilizing elacytarabine in combination with anthracyclines are ongoing. Use of hENT1 expression as a predictive marker for cytarabine or elacytarabine response has been studied with no conclusive validation to date. Despite promising early results, the jury is still out in regards to this novel agent as an effective alternative to standard cytarabine therapy in acute leukemias, especially in combination with additional agents such as anthracyclines.

Nanomedicine strategies for hematological malignancies: what is next?

The major obstacle in treating cancer depends on the low therapeutic index of most anticancer drugs. The lack of specificity, coupled with the large volumes of distribution, translates into a nonpreferential distribution of anticancer drugs to the tumor. Accordingly, the dose of the anticancer drug that is achievable within tumor is limited, resulting in suboptimal treatment and unwanted toxicity. Nanoparticles applied as drug-delivery systems are submicron-sized (3–200 nm) particles, that can enhance the selectivity of the active drug to cancer cells through a change of its pharmacokinetic profile, while avoiding toxicity in normal cells. This review will discuss the current uses of nanodrugs in hematology, with a focus on the most promising nanoparticles in development for the treatment of hematologic tumors.

Biomimetic nanoparticles for siRNA delivery in the treatment of leukaemia

Leukaemia is a bone marrow cancer occurring in acute and chronic subtypes. Acute leukaemia is a rapidly fatal cancer potentially causing death within a few weeks, if untreated. Leukaemia arises as a result of disruption to haematopoietic precursors, caused either by acquired gene fusions, gene mutations or inappropriate expression of the relevant oncogenes. Current treatment options have made significant progress, but the 5 year survival for acute leukaemia remains under 10% in elderly patients, and less than 50% for some types of acute leukaemia in younger adults. For chronic leukaemias longer survival is generally expected and for chronic myeloid leukaemia patients on tyrosine kinase inhibitors the median survival is not yet reached and is expected to exceed 10 years. Chemotherapy and haematopoietic stem cell transplantation (HSCT) for acute leukaemia provide the mainstay of therapy for patients under 65 and both carry significant morbidity and mortality. Alternative and superior therapeutic strategies for acute leukaemias are urgently required. Recent molecular-based knowledge of recurring chromosome rearrangements, in particular translocations and inversions, has resulted in significant advances in understanding the molecular pathogenesis of leukaemia. Identification of a number of unique fusion genes has facilitated the development of highly specific small interfering RNAs (siRNA). Although delivery of siRNA using multifunctional nanoparticles has been investigated to treat solid cancers, the application of this approach to blood cancers is at an early stage. This review describes current treatments for leukaemia and highlights the potential of leukaemic fusion genes as therapeutic targets for RNA interference (RNAi). In addition, the design of biomimetic nanoparticles which are capable of responding to the physiological environment of leukaemia and their potential to advance RNAi therapeutics to the clinic will be critically evaluated.

F14512, a polyamine-vectorized anti-cancer drug, currently in clinical trials exhibits a marked preclinical anti-leukemic activity

Chemotherapy remains mainly used for the treatment of acute myeloid leukemia (AML). However, in the past 3 decades limited progress has been achieved in improving the long-term disease-free survival. Therefore the development of more effective drugs for AML represents a high level of priority. F14512 combines an epipodophyllotoxin core targeting topoisomerase II with a spermine moiety introduced as a cell delivery vector. The polyamine moiety facilitates F14512 selective uptake by tumour cells via the polyamine transport system, a machinery overactivated in cancer cells. F14512 has been characterized as a potent drug candidate and is currently in Phase I clinical trials. Here, we demonstrated marked survival benefit and therapeutic efficacy of F14512 treatments in a series of human AML models, established either from AML cell lines or from patient AML samples. Furthermore, we reported in vitro synergistic anti-leukemic effects of F14512 in combination with cytosine arabinoside (Ara-C), doxorubicin, gemcitabine, bortezomib or SAHA. In vivo combination of suboptimal doses of F14512 with Ara-C also resulted in enhanced anti-leukemic activity. We further showed that F14512 triggered both senescence and apoptosis in vivo in primary AML models, but not autophagy. Overall, these results support the clinical development in onco-hematology of this novel promising drug candidate.