pH-Triggered Transformable Peptide Nanocarriers Extend Drug Retention for Breast Cancer Combination Therapy.

Increasing the penetration and accumulation of antitumor drugs at the tumor site are crucial in chemotherapy. Smaller drug-loaded nanoparticles (NPs) typically exhibit increased tumor penetration and more effective permeation through the nuclear membrane, whereas larger drug-loaded NPs show extended retention at the tumor site. In addition, cancer stem cells (CSCs) have unlimited proliferative potential and are crucial for the onset, progression, and metastasis of cancer. Therefore, a drug-loaded amphiphilic peptide, DDP- and ATRA-loaded Pep1 (DA/Pep1), is designed that self-assembles into spherical NPs upon the encapsulation of cis-diamminedichloroplatinum (DDP) and all-trans retinoic acid (ATRA). In an acidic environment, DA/Pep1 transforms into aggregates containing sheet-like structures, which significantly increases drug accumulation at the tumor site, thereby increasing antitumor effects and inhibiting metastasis. Moreover, although DDP treatment can increase the number of CSCs present, ATRA can induce the differentiation of CSCs in breast cancer to increase the therapeutic effect of DDP. In conclusion, this peptide nanodelivery system that transforms in response to the acidic tumor microenvironment is an extremely promising nanoplatform that suggests a new idea for the combined treatment of tumors.

All-Trans Retinoic Acid and Doxorubicin Delivery by Folic Acid Modified Polymeric Micelles for the Modulation of Pin1-Mediated DOX-Induced Breast Cancer Stemness and Metastasis.

Stemness and metastasis are the two main challenges in cancer therapy and are related to disease relapse post-treatment. They both have a strong correlation with chemoresistance and poor prognosis, ultimately leading to treatment failure. It has been reported that chemotherapy can induce stemness and metastasis in many cancer types, especially treatment with the chemotherapeutic agent doxorubicin (DOX) in breast cancer. A combination treatment is an efficient and elegant approach in cancer therapy through simultaneous delivery of two or more drugs with a delivery system for its synergistic effect, which is not an additive of two individual drugs. Herein, we report a combinatorial system with DOX and all-trans retinoic acid (ATRA) to address both of the above issues. As a common critical regulatory factor for oncogenic signal transduction pathways, Pin1 is a specific isomerase highly expressed within various tumor cells. ATRA, a newly identified Pin1 inhibitor, can abolish several oncogenic pathways by effectively inhibiting and degrading overexpressed Pin1. We successfully developed a folic acid (FA)-modified chitosan (CSO)-derived polymer (FA-CSOSA) and obtained FA-CSOSA/DOX and FA-CSOSA/ATRA drug-loaded micelles. FA modification can improve the uptake of the nanoparticles in tumor cells and tumor sites via folate receptor-mediated cell internalization. Compared to treatment with DOX alone, the combined treatment induced 4T1 cell apoptosis in a synergistic manner. Reduced stemness-related protein expression and inhibited metastasis were observed during treatment with FA-CSOSA/DOX and FA-CSOSA/ATRA and were found to be associated with Pin1. Further in vivo experiments showed that treatment with FA-CSOSA/DOX and FA-CSOSA/ATRA resulted in 85.5% tumor inhibition, which was 2.5-fold greater than that of cells treated with DOX·HCl alone. This work presents a new paradigm for addressing chemotherapy-induced side effects via degradation of Pin1 induced by tumor-targeted delivery of DOX and ATRA.

Polyplexes of retinoic acid: an in vitro study of complex nanostructures against colorectal cancer cell line (HCT-15).

Despite recent advances in the treatment of human colon cancer, the chemotherapeutic efficacy against colon cancer is still unsatisfactory. The complexity in colorectal cancer treatment leads to new research in combination therapy to overcome multidrug resistance in cancer and increase apoptosis. The objective of the present research work was to develop polyplexes for co-delivery of plasmid DNA with retinoic acid against colorectal cancer cell line (HCT-15). Plain polyplexes were prepared using chitosan and hyaluronic acid solution (0.1% w/v), whereas retinoic acid polyplexes were prepared using ethanol: water (1:9 v/v) system. The particle size was observed in the order of chitosan solution > blank polyplex > retinoic acid-loaded polyplex. Encapsulation efficiency of retinoic acid was found to be 81.51 ± 4.33% for retinoic acid-loaded polyplex formulation. The drug release was observed to be in a controlled pattern with 72.23 ± 1.32% release of retenoic acid from polyplex formulation. Cell line studies of the formulation displayed better cell inhibition and low cytotoxicity for the retinoic acid-loaded polyplexes in comparison to pure retinoic acid, thus demonstrating better potential action against colorectal cancer cell line HCT-15. Retinoic acid-loaded polyplexes indicated higher potential for the delivery of the active whereas the cell line studies displayed the efficacy of the formulation against colorectal cancer cell line HCT-15.

Superparamagnetic iron oxide-gold nanoparticles conjugated with porous coordination cages: Towards controlled drug release for non-invasive neuroregeneration.

This paper reports a smart intracellular nanocarrier for sustainable and controlled drug release in non-invasive neuroregeneration. The nanocarrier is composed by superparamagnetic iron oxide-gold (SPIO-Au) core-shell nanoparticles (NPs) conjugated with porous coordination cages (PCCs) through the thiol-containing molecules as bridges. The negatively charged PCC-2 and positively charged PCC-3 are compared for intracellular targeting. Both types result in intracellular targeting via direct penetration across cellular membranes. However, the pyrene (Py)-PEG-SH bridge enabled functionalization of SPIO-Au NPs with PCC-3 exhibits higher interaction with PC-12 neuron-like cells, compared with the rhodamine B (RhB)-PEG-SH bridge enabled case and the stand-alone SPIO-Au NPs. With neglectable toxicities to PC-12 cells, the proposed SPIO-Au-RhB(Py)-PCC-2(3) nanocarriers exhibit effective drug loading capacity of retinoic acid (RA) at 13.505 µg/mg of RA/NPs within 24 h. A controlled release of RA is achieved by using a low-intensity 525 nm LED light (100% compared to 40% for control group within 96 h).

A nanotherapeutic strategy to overcome chemotherapeutic resistance of cancer stem-like cells.

Tumour heterogeneity remains a major challenge in cancer therapy owing to the different susceptibility of cells to chemotherapy within a solid tumour. Cancer stem-like cells (CSCs), which reside in hypoxic tumour regions, are characterized by high tumourigenicity and chemoresistance and are often responsible for tumour progression and recurrence. Here we report a nanotherapeutic strategy to kill CSCs in tumours using nanoparticles that are co-loaded with the differentiation-inducing agent, all-trans retinoic acid, and the chemotherapeutic drug, camptothecin. All-trans retinoic acid is released under hypoxic conditions, leading to CSC differentiation in the hypoxic niche. In differentiating CSC, the reactive oxygen species levels increase, which then causes the release of camptothecin and subsequent cell death. This dual strategy enables controlled drug release in CSCs and reduces stemness-related drug resistance, enhancing the chemotherapeutic response. In breast tumour mouse models, treatment with the nanoparticles suppresses tumour growth and prevents post-surgical tumour relapse and metastasis.

Enhanced Oral Absorption of All-trans Retinoic Acid upon Encapsulation in Solid Lipid Nanoparticles.

BACKGROUND: All-trans retinoic acid (ATRA) is widely employed in the treatment of various proliferative and inflammatory diseases. However, its therapeutic efficacy is imperiled due to its poor solubility and stability. Latter was surmounted by its incorporation into a solid matrix of lipidic nanoparticles (SLNs). METHODS: ATRA loaded SLNs (ATRA-SLNs) were prepared using a novel microemulsification technique (USPTO 9907758) and an optimal composition and were characterized in terms of morphology, differential scanning calorimetry (DSC), and powder X-ray diffraction studies (PXRD). In vitro release, oral plasma pharmacokinetics (in rats) and stability studies were also done. RESULTS: Rod-shaped ATRA-SLNs could successfully incorporate 3.7 mg/mL of ATRA, increasing its solubility (from 4.7 µg/mL) by 787 times, having an average particle size of 131.30 ± 5.0 nm and polydispersibility of 0.283. PXRD, DSC, and FTIR studies confirmed the formation of SLNs. Assay/total drug content and entrapment efficiency of ATRA-SLNs was 92.50 ± 2.10% and 84.60 ± 3.20% (n=6), respectively, which was maintained even on storage for one year under refrigerated conditions as an aqueous dispersion. In vitro release in 0.01 M phosphate buffer (pH 7.4) with 3% tween 80 was extended 12 times from 2h for free ATRA to 24 h for ATRA-SLNs depicting Korsmeyer Peppas release. Oral administration in rats showed 35.03 times enhanced bioavailability for ATRA-SLNs. CONCLUSION: Present work reports preparation and evaluation of bioenhanced ATRA-SLNs containing a high concentration of ATRA (>15 times than that reported by others). Latter is attributed to the novel preparation process and intelligent selection of components. Lay Summary: All-trans retinoic acid (ATRA) shows an array of pharmacological activities but its efficacy is limited due to poor solubility, stability and side effects. In present study its solubility and efficacy is improved by 787 and 35.5 times, respectively upon incorporation into solid lipid nanoparticles (ATRA-SLNs). Latter extended its release by 12 times and provided stability for at least a year under refrigeration. A controlled and sustained release will reduce dose related side effects. ATRA-SLNs reported presently can thus be used in treatment /prophylaxis of disorders like cancers, tuberculosis, age related macular degeneration and acne and as an immune-booster.

Phase I clinical trial repurposing all-trans retinoic acid as a stromal targeting agent for pancreatic cancer.

Pre-clinical models have shown that targeting pancreatic stellate cells with all-trans-retinoic-acid (ATRA) reprograms pancreatic stroma to suppress pancreatic ductal adenocarcinoma (PDAC) growth. Here, in a phase Ib, dose escalation and expansion, trial for patients with advanced, unresectable PDAC (n = 27), ATRA is re-purposed as a stromal-targeting agent in combination with gemcitabine-nab-paclitaxel chemotherapy using a two-step adaptive continual re-assessment method trial design. The maximum tolerated dose (MTD) and recommended phase 2 dose (RP2D, primary outcome) is the FDA/EMEA approved dose of gemcitabine-nab-paclitaxel along-with ATRA (45 mg/m2 orally, days 1-15/cycle). Dose limiting toxicity (DLT) is grade 4 thrombocytopenia (n = 2). Secondary outcomes show no detriment to ATRA pharmacokinetics.. Median overall survival for RP2D treated evaluable population, is 11.7 months (95%CI 8.6-15.7 m, n = 15, locally advanced (2) and metastatic (13)). Exploratory pharmacodynamics studies including changes in diffusion-weighted (DW)-MRI measured apparent diffusion coefficient after one cycle, and, modulation of cycle-specific serum pentraxin 3 levels over various cycles indicate stromal modulation. Baseline stromal-specific retinoid transport protein (FABP5, CRABP2) expression may be predicitve of response. Re-purposing ATRA as a stromal-targeting agent with gemcitabine-nab-paclitaxel is safe and tolerable. This combination will be evaluated in a phase II randomized controlled trial for locally advanced PDAC. Clinical trial numbers: EudraCT: 2015-002662-23; NCT03307148. Trial acronym: STARPAC.

CRABP2 and FABP5 expression levels in diseased and normal pancreas.

Recently, stromal targeting, by agents such as All trans retinoic acid (ATRA), has been regarded as a promising avenue for the treatment of pancreatic ductal adenocarcinoma (PDAC). The intra-cellular transportation of ATRA to the nuclear receptors is performed by either: fatty acid binding protein 5 (FABP5) or cellular retinoic acid binding protein 2 (CRABP2), dictating the transcription of downstream genes and, thus, eventual cell phenotype. Here, we explored the levels of each protein, in pancreatic tissues of patients presenting with a range of pancreatic diseases (pancreatic ductal adenocarcinoma (PDAC), chronic pancreatitis (CP), cholangiocarcinoma (CC)). We demonstrate that there is a significantly lower CRABP2 and FABP5 expression in activated fibroblasts or pancreatic stellate cells (PSC) in PDAC, as well as other diseased pancreas as in CC and CP, versus quiescent fibroblasts. The quiescent fibroblasts consistently show a pattern of high FABP5:CRABP2 ratio, whereas PSC in all non-PDAC tissues showed a low FABP5:CRABP2 ratio. PSC in PDAC patients had a range of FABP5:CRABP2 ratios (high, even and low). There was a lower CRABP2 expression in cancerous epithelial cells (PDAC) versus normal epithelial cells. This is also present in other disease states (CP, CC). Contrasting to the patterns seen for fibroblasts, the FABP5 expression in PDAC epithelial cells matched that of the normal epithelial cells. However, the normal epithelial cells had a high FABP5:CRABP2 ratio, compared to the PDAC epithelial cells. These ratios may have correlation with tumor progression, and overall survival. These findings could be confirmed in in vitro cell lysates. CRABP2 and FABP5 levels and ratios could serve as valuable biomarkers.

Multicompartmental lipid-protein nanohybrids for combined tretinoin/herbal lung cancer therapy.

Aim: Multicompartmental lipid-protein nanohybrids (MLPNs) were developed for combined delivery of the anticancer drugs tretinoin (TRE) and genistein (GEN) as synergistic therapy of lung cancer. Materials & methods: The GEN-loaded lipid core was first prepared and then coated with TRE-loaded zein shell via nanoprecipitation. Results: TRE/GEN-MLPNs demonstrated a size of 154.5 nm. In situ ion pair formation between anionic TRE and the cationic stearyl amine improved the drug encapsulation with enhanced stability of MLPNs. TRE/GEN-coloaded MLPNs were more cytotoxic against A549 cancer cells compared with combined free GEN/TRE. In vivo, lung cancer bearing mice treated with TRE/GEN-MLPNs displayed higher apoptotic caspase activation compared with mice-treated free combined GEN/TRE. Conclusion: TRE/GEN-MLPNs might serve as a promising parenteral nanovehicles for lung cancer therapy.

Analysis of the role of thrombomodulin in all-trans retinoic acid treatment of coagulation disorders in cancer patients.

BACKGROUND: Clinical studies have shown that all-trans retinoic acid (RA), which is often used in treatment of cancer patients, improves hemostatic parameters and bleeding complications such as disseminated intravascular coagulation (DIC). However, the mechanisms underlying this improvement have yet to be elucidated. In vitro studies have reported that RA upregulates thrombomodulin (TM) expression on the endothelial cell surface. The objective of this study was to investigate how and to what extent the TM concentration changes after RA treatment in cancer patients, and how this variation influences the blood coagulation cascade. RESULTS: In this study, we introduced an ordinary differential equation (ODE) model of gene expression for the RA-induced upregulation of TM concentration. Coupling the gene expression model with a two-compartment pharmacokinetic model of RA, we obtained the time-dependent changes in TM and thrombomodulin-mRNA (TMR) concentrations following oral administration of RA. Our results indicated that the TM concentration reached its peak level almost 14 h after taking a single oral dose (110 [Formula: see text]) of RA. Continuous treatment with RA resulted in oscillatory expression of TM on the endothelial cell surface. We then coupled the gene expression model with a mechanistic model of the coagulation cascade, and showed that the elevated levels of TM over the course of RA therapy with a single daily oral dose (110 [Formula: see text]) of RA, reduced the peak thrombin levels and endogenous thrombin potential (ETP) up to 50 and 49%, respectively. We showed that progressive reductions in plasma levels of RA, observed in continuous RA therapy with a once-daily oral dose (110 [Formula: see text]) of RA, did not affect TM-mediated reduction of thrombin generation significantly. This finding prompts the hypothesis that continuous RA treatment has more consistent therapeutic effects on coagulation disorders than on cancer. CONCLUSIONS: Our results indicate that the oscillatory upregulation of TM expression on the endothelial cells over the course of RA therapy could potentially contribute to the treatment of coagulation abnormalities in cancer patients. Further studies on the impacts of RA therapy on the procoagulant activity of cancer cells are needed to better elucidate the mechanisms by which RA therapy improves hemostatic abnormalities in cancer.

Reversal of pancreatic desmoplasia by re-educating stellate cells with a tumour microenvironment-activated nanosystem.

Pancreatic ductal adenocarcinoma is characterised by a dense desmoplastic stroma composed of stromal cells and extracellular matrix (ECM). This barrier severely impairs drug delivery and penetration. Activated pancreatic stellate cells (PSCs) play a key role in establishing this unique pathological obstacle, but also offer a potential target for anti-tumour therapy. Here, we construct a tumour microenvironment-responsive nanosystem, based on PEGylated polyethylenimine-coated gold nanoparticles, and utilise it to co-deliver all-trans retinoic acid (ATRA, an inducer of PSC quiescence) and siRNA targeting heat shock protein 47 (HSP47, a collagen-specific molecular chaperone) to re-educate PSCs. The nanosystem simultaneously induces PSC quiescence and inhibits ECM hyperplasia, thereby promoting drug delivery to pancreatic tumours and significantly enhancing the anti-tumour efficacy of chemotherapeutics. Our combination strategy to restore homoeostatic stromal function by targeting activated PSCs represents a promising approach to improving the efficacy of chemotherapy and other therapeutic modalities in a wide range of stroma-rich tumours.

Lipophilic activated ester prodrug approach for drug delivery to the intestinal lymphatic system.

The intestinal lymphatic system plays an important role in the pathophysiology of multiple diseases including lymphomas, cancer metastasis, autoimmune diseases, and human immunodeficiency virus (HIV) infection. It is thus an important compartment for delivery of drugs in order to treat diseases associated with the lymphatic system. Lipophilic prodrug approaches have been used in the past to take advantage of the intestinal lymphatic transport processes to deliver drugs to the intestinal lymphatics. Most of the approaches previously adopted were based on very bulky prodrug moieties such as those mimicking triglycerides (TG). We now report a study in which a lipophilic prodrug approach was used to efficiently deliver bexarotene (BEX) and retinoic acid (RA) to the intestinal lymphatic system using activated ester prodrugs. A range of carboxylic ester prodrugs of BEX were designed and synthesised and all of the esters showed improved association with chylomicrons, which indicated an improved potential for delivery to the intestinal lymphatic system. The conversion rate of the prodrugs to BEX was the main determinant in delivery of BEX to the intestinal lymphatics, and activated ester prodrugs were prepared to enhance the conversion rate. As a result, an 4-(hydroxymethyl)-1,3-dioxol-2-one ester prodrug of BEX was able to increase the exposure of the mesenteric lymph nodes (MLNs) to BEX 17-fold compared to when BEX itself was administered. The activated ester prodrug approach was also applied to another drug, RA, where the exposure of the MLNs was increased 2.4-fold through the application of a similar cyclic activated prodrug. Synergism between BEX and RA was also demonstrated in vitro by cell growth inhibition assays using lymphoma cell lines. In conclusion, the activated ester prodrug approach results in efficient delivery of drugs to the intestinal lymphatic system, which could benefit patients affected by a large number of pathological conditions.

A phase-1 study of dasatinib plus all-trans retinoic acid in acute myeloid leukemia.

Src family kinases (SFKs) are hyperactivated in acute myeloid leukemia (AML). SFKs impede the retinoic acid receptor, and SFK inhibitors enhance all-trans retinoic acid (ATRA)-mediated cellular differentiation in AML cell lines and primary blasts. To translate these findings into the clinic, we undertook a phase-I dose-escalation study of the combination of the SFK inhibitor dasatinib and ATRA in patients with high-risk myeloid neoplasms. Nine subjects were enrolled: six received 70 mg dasatinib plus 45 mg/m2 ATRA daily, and three received 100 mg dasatinib plus 45 mg/m2 ATRA daily for 28 days. Headache and QTc prolongations were the only two grade 3 adverse events observed. No significant clinical responses were observed. We conclude that the combination of 70 mg dasatinib and 45 mg/m2 ATRA daily is safe with acceptable toxicity. Our results provide the safety profile for further investigations into the clinical efficacy of this combination therapy in myeloid malignancies.

A novel controlled release formulation of the Pin1 inhibitor ATRA to improve liver cancer therapy by simultaneously blocking multiple cancer pathways.

Hepatocellular carcinoma (HCC) is the second leading cause of cancer deaths worldwide largely due to lack of effective targeted drugs to simultaneously block multiple cancer-driving pathways. The identification of all-trans retinoic acid (ATRA) as a potent Pin1 inhibitor provides a promising candidate for HCC targeted therapy because Pin1 is overexpressed in most HCC and activates numerous cancer-driving pathways. However, the efficacy of ATRA against solid tumors is limited due to its short half-life of 45min in humans. A slow-releasing ATRA formulation inhibits solid tumors such as HCC, but can be used only in animals. Here, we developed a one-step, cost-effective route to produce a novel biocompatible, biodegradable, and non-toxic controlled release formulation of ATRA for effective HCC therapy. We used supercritical carbon dioxide process to encapsulate ATRA in largely uniform poly L-lactic acid (PLLA) microparticles, with the efficiency of 91.4% and yield of 68.3%, and ~4-fold higher Cmax and AUC over the slow-releasing ATRA formulation. ATRA-PLLA microparticles had good biocompatibility, and significantly enhanced the inhibitory potency of ATRA on HCC cell growth, improving IC50 by over 3-fold. ATRA-PLLA microparticles exerted its efficacy likely through degrading Pin1 and inhibiting multiple Pin1-regulated cancer pathways and cell cycle progression. Indeed, Pin1 knock-down abolished ATRA inhibitory effects on HCC cells and ATRA-PLLA did not inhibit normal liver cells, as expected because ATRA selectively inhibits active Pin1 in cancer cells. Moreover ATRA-PLLA microparticles significantly enhanced the efficacy of ATRA against HCC tumor growth in mice through reducing Pin1, with a better potency than the slow-releasing ATRA formulation, consistent with its improved pharmacokinetic profiles. This study illustrates an effective platform to produce controlled release formulation of anti-cancer drugs, and ATRA-PLLA microparticles might be a promising targeted drug for HCC therapy as PLLA is biocompatible, biodegradable and nontoxic to humans.

Liposomes assembled from dimeric retinoic acid phospholipid with improved pharmacokinetic properties.

All-trans-retinoic acid (ATRA) exhibits potent cytotoxicities against different cancer cells by binding to retinoic acid receptors (RARs), which is regarded as the first example of targeted therapy in acute promyelocytic leukemia (APL). However, its extensive clinical applications have been limited because of poor aqueous solubility, short half-life time and side effects. In this report, dimeric ATRA phosphorylcholine prodrug (Di-ATRA-PC) was designed and assembled into nanoliposomes to improve its pharmacokinetic properties. Di-ATRA-PC prodrug was synthesized by a facile esterification and characterized by mass spectrometry (MS) and nuclear magnetic resonance spectroscopy (NMR). The Di-ATRA-PC assembled liposomes were prepared by thin film hydration method with ATRA loading efficiency up to 73wt%. The liposomes have a uniform particle size (73.1±3.6nm) with negatively charged surface (-20.5±2.5mV) and typical lipid bilayer structure as measured by dynamic light scattering (DLS), transmission electron microscope (TEM) and cryogenic transmission electron microscope (cryo-TEM). In vitro drug release study confirmed that Di-ATRA-PC liposomes could sustainedly release free ATRA in a weakly acidic condition. Furthermore, cellular uptake, MTT and cell apoptosis analysis demonstrated that the liposomes could be successfully internalized into tumor cells to induce apoptosis of MCF-7 and HL-60 cells. More importantly, in vivo pharmacokinetic assay indicated that Di-ATRA-PC liposomes had much longer retention time in comparison with ATRA. In conclusion, Di-ATRA-PC liposomal formulation could be a potential drug delivery system of ATRA with enhanced pharmacokinetic properties.

Cellular retinoic acid bioavailability in various pathologies and its therapeutic implication.

Retinoic acid (RA), an active metabolite of vitamin A, is a critical signaling molecule in various cell types. We found that RA depletion caused by expression of the RA-metabolizing enzyme CYP26A1 promotes carcinogenesis, implicating CYP26A1 as a candidate oncogene. Several studies of CYP26s have suggested that the biological effect of RA on target cells is primarily determined by "cellular RA bioavailability", which is defined as the RA level in an individual cell, rather than by the serum concentration of RA. Consistently, stellate cells store approximately 80% of vitamin A in the body, and the state of cellular RA bioavailability regulates their function. Based on the similarities between stellate cells and astrocytes, we demonstrated that retinal astrocytes regulate tight junction-based endothelial integrity in a paracrine manner. Since diabetic retinopathy is characterized by increased vascular permeability in its early pathogenesis, RA normalized retinal astrocytes that are compromised in diabetes, resulting in suppression of vascular leakiness. RA also attenuated the loss of the epithelial barrier in murine experimental colitis. The concept of "cellular RA bioavailability" in various diseases will be directed at understanding various pathologies caused by RA insufficiency, implying the potential feasibility of a therapeutic strategy targeting the stellate cell system.

Physiologically Based Pharmacokinetic Model of All-trans-Retinoic Acid with Application to Cancer Populations and Drug Interactions.

All-trans retinoic acid (atRA) is a front-line treatment of acute promyelocytic leukemia (APL). Due to its activity in regulating the cell cycle, it has also been evaluated for the treatment of other cancers. However, the efficacy of atRA has been limited by atRA inducing its own metabolism during therapy, resulting in a decrease of atRA exposure during continuous dosing. Frequent relapse occurs in patients receiving atRA monotherapy. In an attempt to combat therapy resistance, inhibitors of atRA metabolism have been developed. Of these, ketoconazole and liarozole have shown some benefits, but their usage is limited by side effects and low potency toward the cytochrome P450 26A1 isoform (CYP26A1), the main atRA hydroxylase. We determined the pharmacokinetic basis of therapy resistance to atRA and tested whether the complex disposition kinetics of atRA could be predicted in healthy subjects and in cancer patients in the presence and absence of inhibitors of atRA metabolism using physiologically based pharmacokinetic (PBPK) modeling. A PBPK model of atRA disposition was developed and verified in healthy individuals and in cancer patients. The population-based PBPK model of atRA disposition incorporated saturable metabolic clearance of atRA, induction of CYP26A1 by atRA, and the absorption and distribution kinetics of atRA. It accurately predicted the changes in atRA exposure after continuous dosing and when coadministered with ketoconazole and liarozole. The developed model will be useful in interpretation of atRA disposition and efficacy, design of novel dosing strategies, and development of next-generation atRA metabolism inhibitors.

HPMA copolymer-based polymer conjugates for the delivery and controlled release of retinoids.

In this paper, we describe the synthesis, physicochemical characterization, drug release kinetics and preliminary biological evaluation of several N-(2-hydroxypropyl)methacrylamide (HPMA)-based polymer-retinoid conjugates designed for solid tumor immunotherapy. The conjugates are supposed to inhibit the immunosuppressive activity of myeloid-derived suppressor cells (MDSC) accumulated in the solid tumor microenvironment. All-trans retinoic acid (ATRA) was derivatized to hydrazide (AtrHy) and then attached to the polymer backbone via a spacer that is stable at the normal pH of blood (7.4) and hydrolytically degradable in mildly acidic environments (e.g. in endosomes or lysosomes, pH~5.0-6.5). Polymer-AtrHy conjugates were designed to achieve prolonged blood circulation and release of the immunomodulator intracellularly or extracellularly in solid tumor tissue. Three types of polymer precursors, differing in the structure of the keto acid-containing side chains, were synthesized. A linkage susceptible to hydrolytic cleavage was formed by the conjugation reaction of the carbonyl group-terminated side chains of the polymer precursors with the hydrazide group of a drug derivative. In vitro incubation of the conjugates in buffers resulted in much faster release of the drugs or their derivatives from the polymer at pH 5.0 than at pH 7.4, with the rate depending on the detailed structure of the spacer. Both the AtrHy derivative and its polymer conjugates showed the ability to induce the differentiation of retinoid-responsive HL-60 cells, thus demonstrating the required biological activity.

Improved In Vitro Antileukemic Activity of All-Trans Retinoic Acid Loaded in Cholesteryl Butyrate Solid Lipid Nanoparticles.

All-trans retinoic acid, a hydrophobic drug, has become one of the most successful examples of differentiation agents used for treatment of acute promyelocytic leukemia. On the other hand, histone deacetylase inhibitors, such as cholesteryl butyrate, present differentiating activity and.can potentiate action of drugs such as all-trans retinoic acid. Solid lipid nanoparticles represent a promising alternative for administration of hydrophobic drugs such as ATRA. This study aimed to develop, characterize, and evaluate the cytotoxicity of all-trans retinoic acid-loaded solid lipid nanoparticles for leukemia treatment. The influence of in situ formation of an ion pairing between all-trans retinoic acid and lipophilic amines on the characteristics of the particles (size, zeta potential, encapsulation efficiency) was evaluated. Cholesteryl butyrate, a butyric acid donor, was used as a component of the lipid matrix. In vitro activity on cell viability and distribution of cell cycle phases were evaluated for HL-60, Jurkat, and THP-1 cell lines. The encapsulation efficiency of all-trans retinoic acid in cholesteryl butyrate-solid lipid nanoparticles was significantly increased by the presence of the amine. Inhibition of cell viability by all-trans retinoic acid-loaded solid lipid nanoparticles was more pronounced than the free drug. Analysis of the distribution of cell cycle phases also showed increased activity for all-trans retinoic acid-loaded cholesteryl butyrate-solid lipid nanoparticles, with a clear increase in subdiploid DNA content. The ion pair formation in SLN containing cholesteryl butyrate can be explored as a simple and inexpensive strategy to improve the efficacy and bioavail-ability of ATRA in the treatment of the cancer and metabolic diseases in which this retinoid plays an important role.