Pharmacokinetics and Antitumor Efficacy of XMT-1001, a Novel, Polymeric Topoisomerase I Inhibitor, in Mice Bearing HT-29 Human Colon Carcinoma Xenografts

PEGylated liposomes enhance the effect of cytotoxic drug: A review

Cancer is a second leading disease-causing death worldwide that will continuously grow as much as 70% in the next 20 years. Chemotherapy is still becoming a choice for cancer treatment despite its severity of side effects and low success rate due to ineffective delivery of the chemodrugs. Since it was introduced in 1960, significant progress has been achieved in the use of liposomes in drug delivery. The study aims to review relevant literatures on role of PEGylated liposome in enhancing cytotoxic activity of several agents. A systematic literature on the use of PEGylated liposomes in anticancer research via Scopus, Google scholar and PubMed databases was conducted for studies published from 2000 to 2022. A total of 15 articles were selected and reviewed from 312 articles identified covering a variety of anticancer treatments by using PEGylated liposomes. PEGylated liposome which is purposed to achieve steric equilibrium is one of enhanced strategies to deliver anticancer drugs. It has been shown that some improvement of delivery and protection form a harsh gastric environment of several anticancer drugs when they are formulated in a PEGylated liposome. One of the successful drugs that has been clinically used is Doxil®, followed by some other drugs in the pipeline Various drugs (compounds) had been used to enhance the efficacy of PEGylated liposomes for targeted cancer cells in vitro and in vivo. In conclusion, PEGylated liposomes enhance drug activities and have great potential to become efficient anticancer delivery to follow Doxil® in the clinical setting.

Minibeam radiation therapy enhanced tumor delivery of PEGylated liposomal doxorubicin in a triple-negative breast cancer mouse model

BACKGROUND

Minibeam radiation therapy is an experimental radiation therapy utilizing an array of parallel submillimeter planar X-ray beams. In preclinical studies, minibeam radiation therapy has been shown to eradicate tumors and cause significantly less damage to normal tissue compared to equivalent radiation doses delivered by conventional broadbeam radiation therapy, where radiation dose is uniformly distributed.

METHODS

Expanding on prior studies that suggested minibeam radiation therapy increased perfusion in tumors, we compared a single fraction of minibeam radiation therapy (peak dose:valley dose of 28 Gy:2.1 Gy and 100 Gy:7.5 Gy) and broadbeam radiation therapy (7 Gy) in their ability to enhance tumor delivery of PEGylated liposomal doxorubicin and alter the tumor microenvironment in a murine tumor model. Plasma and tumor pharmacokinetic studies of PEGylated liposomal doxorubicin and tumor microenvironment profiling were performed in a genetically engineered mouse model of claudin-low triple-negative breast cancer (T11).

RESULTS

Minibeam radiation therapy (28 Gy) and broadbeam radiation therapy (7 Gy) increased PEGylated liposomal doxorubicin tumor delivery by 7.1-fold and 2.7-fold, respectively, compared to PEGylated liposomal doxorubicin alone, without altering the plasma disposition. The enhanced tumor delivery of PEGylated liposomal doxorubicin by minibeam radiation therapy is consistent after repeated dosing, is associated with changes in tumor macrophages but not collagen or angiogenesis, and nontoxic to local tissues. Our study indicated that the minibeam radiation therapy's ability to enhance the drug delivery decreases from 28 to 100 Gy peak dose.

DISCUSSION

Our studies suggest that low-dose minibeam radiation therapy is a safe and effective method to significantly enhance the tumor delivery of nanoparticle agents.

Oligosaccharide-camptothecin conjugates as potential antineoplastic drugs: Design, synthesis and biological evaluation

Thirty novel 20 (S)-O-linked camptothecin (CPT) glycoconjugates were synthesized. They showed more potent in vitro cytotoxicities over irinotecan, but very weak direct topoisomerase I (Topo I) inhibition was observed at 100.0 μM. Oligosaccharide types, length of a PEG linker and acetyl groups exerted obvious effects on cytotoxicity, selectivity, water solubility and stability of the newly synthesized CPT glycoconjugates. Construct 40, with a bleomycin (BLM) disaccharide linked to diethylene glycol in the introduced ester moiety, demonstrated a superior antitumor activity and a distinct selectivity compared to CPT. No toxicity was detectable in animal acute toxicity intravenously (160 mg/kg). Collectively, attachment of oligosaccharides with tumor targeting to 20 (S)-OH of CPT could offer a solution to the daunting problems posed by current Topo I poisons.

Oleic acid-conjugated silver nanoparticles as efficient antiamoebic agent against Acanthamoeba castellanii

Acanthamoeba castellanii belonging to the T4 genotype is an opportunistic pathogen which is associated with blinding eye keratitis and rare but fatal central nervous system infection. A. castellanii pose serious challenges in antimicrobial chemotherapy due to its ability to convert into resistant, hardy shell-protected cyst form that leads to infection recurrence. The fatty acid composition of A. castellanii trophozoites is known to be most abundant in oleic acid which chemically is an unsaturated cis-9-Octadecanoic acid and naturally found in animal and vegetable fats and oils. This study was designed to evaluate antiacanthamoebic effects of oleic acid against trophozoites, cysts as well as parasite-mediated host cell cytotoxicity. Moreover, oleic acid-conjugated silver nanoparticles (AgNPs) were also synthesized and tested against A. castellanii. Oleic acid-AgNPs were synthesized by chemical reduction method and characterized by ultraviolet-visible spectrophotometry, atomic force microscopy, dynamic light scattering analysis, and Fourier transform infrared spectroscopy. Viability, growth inhibition, encystation, and excystation assays were performed with 10 and 5 μM concentration of oleic acid alone and oleic acid-conjugated AgNPs. Bioassays revealed that oleic acid alone and oleic acid-conjugated AgNPs exhibited significant antiamoebic properties, whereas nanoparticle conjugation further enhanced the efficacy of oleic acid. Phenotype differentiation assays also showed significant inhibition of encystation and excystation at 5 μM. Furthermore, oleic acid and oleic acid-conjugated AgNPs also inhibited amoebae-mediated host cell cytotoxicity as determined by lactate dehydrogenase release. These findings for the first time suggest that oleic acid-conjugated AgNPs exhibit antiacanthamoebic activity that hold potential for therapeutic applications against A. castellanii.

Supramolecular chemotherapy based on host-guest molecular recognition: a novel strategy in the battle against cancer with a bright future

Chemotherapy is currently one of the most effective ways to treat cancer. However, traditional chemotherapy faces several obstacles to clinical trials, such as poor solubility/stability, non-targeting capability and uncontrollable release of the drugs, greatly limiting their anticancer efficacy and causing severe side effects towards normal tissues. Supramolecular chemotherapy integrating non-covalent interactions and traditional chemotherapy is a highly promising candidate in this regard and can be appropriately used for targeted drug delivery. By taking advantage of supramolecular chemistry, some limitations impeding traditional chemotherapy for clinical applications can be solved effectively. Therefore, we present here a review summarizing the progress of supramolecular chemotherapy in cancer treatment based on host-guest recognition and provide guidance on the design of new targeting supramolecular chemotherapy combining diagnostic and therapeutic functions. Based on a large number of state-of-the-art studies, our review will advance supramolecular chemotherapy on the basis of host-guest recognition and promote translational clinical applications.

Methods and Study Designs for Characterizing the Pharmacokinetics and Pharmacodynamics of Carrier-Mediated Agents

Major advances in carrier-mediated agents (CMAs), which include nanoparticles, nanosomes, and conjugates, have revolutionized drug delivery capabilities over the past decade. While providing numerous advantages, such as greater solubility, duration of exposure, and delivery to the site of action over their small molecule counterparts, there is substantial variability in systemic clearance and distribution, tumor delivery, and pharmacologic effects (efficacy and toxicity) of these agents. In this chapter, we focus on the analytical and phenotypic methods required to design a study that characterizes the pharmacokinetics (PK) and pharmacodynamics (PD) of all forms of these nanoparticle-based drug agents. These methods include separation of encapsulated and released drugs, ultrafiltration for measurement of non-protein bound active drug, microdialysis to measure intra-tumor drug concentrations, immunomagnetic separation and flow cytometry for sorting cell types, and evaluation of spatial distribution of drug forms relative to tissue architecture by mass spectrometry imaging and immunohistochemistry.

Silver nanoparticle conjugation affects antiacanthamoebic activities of amphotericin B, nystatin, and fluconazole

Infectious diseases are the leading cause of morbidity and mortality, killing more than 15 million people worldwide. This is despite our advances in antimicrobial chemotherapy and supportive care. Nanoparticles offer a promising technology to enhance drug efficacy and formation of effective vehicles for drug delivery. Here, we conjugated amphotericin B, nystatin (macrocyclic polyenes), and fluconazole (azole) with silver nanoparticles. Silver-conjugated drugs were synthesized successfully and characterized by ultraviolet-visible spectrophotometry, Fourier transform infrared spectroscopy, and atomic force microscopy. Conjugated and unconjugated drugs were tested against Acanthamoeba castellanii belonging to the T4 genotype using amoebicidal assay and host cell cytotoxicity assay. Viability assays revealed that silver nanoparticles conjugated with amphotericin B (Amp-AgNPs) and nystatin (Nys-AgNPs) exhibited significant antiamoebic properties compared with drugs alone or AgNPs alone (P < 0.05) as determined by Trypan blue exclusion assay. In contrast, conjugation of fluconazole with AgNPs had limited effect on its antiamoebic properties. Notably, AgNP-coated drugs inhibited amoebae-mediated host cell cytotoxicity as determined by measuring lactate dehydrogenase release. Overall, here we present the development of a new formulation of more effective antiamoebic agents based on AgNPs coated with drugs that hold promise for future applications.

Complex effects of tumor microenvironment on the tumor disposition of carrier-mediated agents

Major advances in carrier-mediated agents, including nanoparticle, conjugates and antibody-drug conjugates, have created revolutionary drug delivery systems in cancer over the past two decades. While these agents provide several advantages, such as greater duration of exposure and solubility, compared with their small-molecule counterparts, there is substantial variability in delivery of these agents to tissues and especially tumors. This review provides an overview of tumor microenvironment factors that affect the pharmacokinetics and pharmacodynamics of carrier-mediated agents observed in preclinical models and patients.

Implementation of Nanoparticles in Cancer Therapy

Cancer is a wide group of diseases and generally characterized by uncontrolled proliferation of cells whose metabolic activities are disrupted. Conventionally, chemotherapy, radiotherapy, and surgery are used in the treatment of cancer. However, in theory, even a single cancer cell may trigger recurrence. Therefore, these treatments cannot provide high survival rate for deadly types. Identification of alternative methods in treatment of cancers is inevitable because of adverse effects of conventional methods. In the last few decades, nanotechnology developed by scientists working in different disciplines—physics, chemistry, and biology—offers great opportunities. It is providing elimination of both circulating tumor cells and solid cancer cells by targeting cancer cells. In this chapter, inadequate parts of conventional treatment methods, nanoparticle types used in new treatment methods of cancer, and targeting methods of nanoparticles are summarized; furthermore, recommendations of future are provided.

Safe approaches for camptothecin delivery: Structural analogues and nanomedicines

Twenty-(S)-camptothecin is a strongly cytotoxic molecule with excellent antitumor activity over a wide spectrum of human cancers. However, the direct formulation is limited by its poor water solubility, low plasmatic stability and severe toxicity, which currently limits its clinical use. As a consequence, two strategies have been developed in order to achieve safe and efficient delivery of camptothecin to target cells: structural analogues and nanomedicines. In this review, we summarize recent advances in the design, synthesis and development of camptothecin molecular derivatives and supramolecular vehicles, following a systematic classification according to structure-activity relationships (structural analogues) or chemical nature (nanomedicines). A series of organic, inorganic and hybrid materials are presented as nanoplatforms to overcome camptothecin restrictions in administration, biodistribution, pharmacokinetics and toxicity. Nanocarriers which respond to a variety of stimuli endogenously (e.g., pH, redox potential, enzyme activity) or exogenously (e.g., magnetic field, light, temperature, ultrasound) seem the best positioned therapeutic materials for optimal spatial and temporal control over drug release. The main goal of this review is to be used as a source of relevant literature for others interested in the field of camptothecin-based therapeutics. To this end, final remarks on the most important formulations currently under clinical trial are provided.

Efficacy and pharmacokinetics of a modified acid-labile docetaxel-PRINT(®) nanoparticle formulation against non-small-cell lung cancer brain metastases

AIM

Particle Replication in Nonwetting Templates (PRINT(®)) PLGA nanoparticles of docetaxel and acid-labile C2-dimethyl-Si-Docetaxel were evaluated with small molecule docetaxel as treatments for non-small-cell lung cancer brain metastases.

MATERIALS & METHODS

Pharmacokinetics, survival, tumor growth and mice weight change were efficacy measures against intracranial A549 tumors in nude mice. Treatments were administered by intravenous injection.

RESULTS

Intracranial tumor concentrations of PRINT-docetaxel and PRINT-C2-docetaxel were 13- and sevenfold greater, respectively, than SM-docetaxel. C2-docetaxel conversion to docetaxel was threefold higher in intracranial tumor as compared with nontumor tissues. PRINT-C2-docetaxel increased median survival by 35% with less toxicity as compared with other treatments.

CONCLUSION

The decreased toxicity of the PRINT-C2-docetaxel improved treatment efficacy against non-small-cell lung cancer brain metastasis.

Clinical advances of nanocarrier-based cancer therapy and diagnostics

INTRODUCTION

Cancer is a leading cause of death worldwide and efficient new strategies are urgently needed to combat its high mortality and morbidity statistics. Fortunately, over the years, nanotechnology has evolved as a frontrunner in the areas of imaging, diagnostics and therapy, giving the possibility of monitoring, evaluating and individualizing cancer treatments in real-time. Areas covered: Polymer-based nanocarriers have been extensively studied to maximize cancer treatment efficacy and minimize the adverse effects of standard therapeutics. Regarding diagnosis, nanomaterials like quantum dots, iron oxide nanoparticles or gold nanoparticles have been developed to provide rapid, sensitive detection of cancer and, therefore, facilitate early treatment and monitoring of the disease. Therefore, multifunctional nanosystems with both imaging and therapy functionalities bring us a step closer to delivering precision/personalized medicine in the cancer setting. Expert opinion: There are multiple barriers for these new nanosystems to enter the clinic, but it is expected that in the near future, nanocarriers, together with new 'targeted drugs', could replace our current treatments and cancer could become a nonfatal disease with good recovery rates. Joint efforts between scientists, clinicians, the pharmaceutical industry and legislative bodies are needed to bring to fruition the application of nanosystems in the clinical management of cancer.

Natural Products as a Vital Source for the Discovery of Cancer Chemotherapeutic and Chemopreventive Agents

Throughout history, natural products have played a dominant role in the treatment of human ailments. For example, the legendary discovery of penicillin transformed global existence. Presently, natural products comprise a large portion of current-day pharmaceutical agents, most notably in the area of cancer therapy. Examples include Taxol, vinblastine, and camptothecin. These structurally unique agents function by novel mechanisms of action; isolation from natural sources is the only plausible method that could have led to their discovery. In addition to terrestrial plants as sources for starting materials, the marine environment (e.g., ecteinascidin 743, halichondrin B, and dolastatins), microbes (e.g., bleomycin, doxorubicin, and staurosporin), and slime molds (e.g., epothilone B) have yielded remarkable cancer chemotherapeutic agents. Irrespective of these advances, cancer remains a leading cause of death worldwide. Undoubtedly, the prevention of human cancer is highly preferable to treatment. Cancer chemoprevention, the use of vaccines or pharmaceutical agents to inhibit, retard, or reverse the process of carcinogenesis, is another important approach for easing this formidable public health burden. Similar to cancer chemotherapeutic agents, natural products play an important role in this field. There are many examples, including dietary phytochemicals such as sulforaphane and phenethyl isothiocyanate (cruciferous vegetables) and resveratrol (grapes and grape products). Overall, natural product research is a powerful approach for discovering biologically active compounds with unique structures and mechanisms of action. Given the unfathomable diversity of nature, it is reasonable to suggest that chemical leads can be generated that are capable of interacting with most or possibly all therapeutic targets.

Pharmacokinetics and antitumor efficacy of micelles assembled from multiarmed amphiphilic copolymers with drug conjugates in comparison with drug-encapsulated micelles

The premature drug release and structural dissociation before reaching pathological sites have posed major challenges for self-assembled micelles. To address these challenges, star-shaped amphiphilic copolymers derived from 4-armed poly(ethylene glycol) (PEG) were proposed for chemical conjugation of chemotherapeutic drugs and assembly into drug-conjugated micelles (DCM) with reductive sensitivity. The current study aimed to elucidate the in vitro and in vivo performance of DCM and a comparison with conventional drug-encapsulated micelles (DEM) was initially launched. DEM carriers were constructed with a similar structure to DCM from 4-armed PEG, and disulfide linkages were located between the hydrophilic and hydrophobic segments. Both DCM and DEM had an average size of around 130 nm, camptothecin (CPT) loadings of around 7.7% and critical micelle concentrations of around 0.95 μg/ml. Compared with DEM, DCM showed a lower initial drug release, a lower sensitivity of drug release to glutathione, and a higher structural stability after incubation with human serum albumin (HSA). The CPT derivatives (CPT-SH) released from DCM indicated cytotoxicities similar to CPT and remained a higher lactone stability than CPT in the presence of HSA. DCM showed slightly higher cytotoxicities to 4T1 cells and significantly lower cytotoxicities to normal cells than DEM. Pharmacokinetic analyses after intravenous administration of DCM indicated around 2.65 folds higher AUC0-∞, 2.66 folds lower clearance, and 1.87 folds higher tumor accumulation than those of DEM. In addition to a less disturbance to hematological and biochemical parameters and a lower acute toxicity to small intestines, DCM showed more significant tumor suppression efficacy and less tumor metastasis to lungs than DEM. It is suggested that DCM could overcome the limitation of conventional micelles by alleviating the premature drug release during blood circulation, relieving the systemic toxicity and promoting the therapeutic efficacy.

Cancer nanotherapeutics in clinical trials

To be legally sold in the United States, all drugs must go through the FDA approval process. This chapter introduces the FDA approval process and describes the clinical trials required for a drug to gain approval. We then look at the different cancer nanotherapeutics and in vivo diagnostics that are currently in clinical trials or have already received approval. These nanotechnologies are catagorized and described based on the delivery vehicle: liposomes, polymer micelles, albumin-bound chemotherapeutics, polymer-bound chemotherapeutics, and inorganic particles.

Evaluation of the efficiency of tumor and tissue delivery of carrier-mediated agents (CMA) and small molecule (SM) agents in mice using a novel pharmacokinetic (PK) metric: relative distribution index over time (RDI-OT)

The pharmacokinetics (PK) of carrier-mediated agents (CMA) is dependent upon the carrier system. As a result, CMA PK differs greatly from the PK of small molecule (SM) drugs. Advantages of CMAs over SMs include prolonged circulation time in plasma, increased delivery to tumors, increased antitumor response, and decreased toxicity. In theory, CMAs provide greater tumor drug delivery than SMs due to their prolonged plasma circulation time. We sought to create a novel PK metric to evaluate the efficiency of tumor and tissue delivery of CMAs and SMs. We conducted a study evaluating the plasma, tumor, liver, and spleen PK of CMAs and SMs in mice bearing subcutaneous flank tumors using standard PK parameters and a novel PK metric entitled relative distribution over time (RDI-OT), which measures efficiency of delivery. RDI-OT is defined as the ratio of tissue drug concentration to plasma drug concentration at each time point. The standard concentration versus time area under the curve values (AUC) of CMAs were higher in all tissues and plasma compared with SMs. However, 8 of 17 SMs had greater tumor RDI-OT AUC_0-last values than their CMA comparators and all SMs had greater tumor RDI-OT AUC_{0-6 h} values than their CMA comparators. Our results indicate that in mice bearing flank tumor xenografts, SMs distribute into tumor more efficiently than CMAs. Further research in additional tumor models that may more closely resemble tumors seen in patients is needed to determine if our results are consistent in different model systems.

Phase 1 evaluation of EZN-2208, a polyethylene glycol conjugate of SN38, in children adolescents and young adults with relapsed or refractory solid tumors

BACKGROUND

EZN-2208 is a water-soluble PEGylated conjugate of the topoisomerase inhibitor SN38, the active metabolite of irinotecan. Compared to irinotecan, EZN-2208 has a prolonged half-life permitting extended exposure to SN38. EZN-2208 has demonstrated clinical tolerability and antitumor activity in adults with advanced solid tumors. This Phase 1 study evaluated the safety, pharmacokinetics, and preliminary antitumor activity of EZN-2208 in children with relapsed or refractory solid tumors.

PROCEDURE

EZN-2208 was administered as a 1-hour intravenous infusion once every 21 days at five dose levels (12-30 mg/m(2) ). Filgrastim or pegfilgrastim was administered 24-48 hours after treatment with EZN-2208. The rolling-six design was used for dose determination.

RESULTS

Thirty eligible patients (15 females; median [range] age 11.5 years [2-21 years]) were treated with EZN-2208. Dose-limiting diarrhea occurred in one patient receiving 16 mg/m(2) and dose-limiting dehydration was seen in one patient receiving 24 mg/m(2) . At dose levels above 16 mg/m(2) , Grade ≥3 myelosuppression was demonstrated in the majority of patients. Additional adverse events included nausea, vomiting, and fatigue. The maximum tolerated dose was identified as 24 mg/m(2) due to dose-limiting thrombocytopenia in two patients receiving 30 mg/m(2) . Two of nine patients with neuroblastoma who were evaluable for response had partial responses. Five patients (four with neuroblastoma) remained on study for ≥8 cycles.

CONCLUSIONS

EZN-2208 was generally well-tolerated and was associated with clinical benefit in patients with neuroblastoma.

Synergistic anti-tumor effects of combined gemcitabine and cisplatin nanoparticles in a stroma-rich bladder carcinoma model

Tumors grown in a stroma-rich mouse model resembling clinically advanced bladder carcinoma with UMUC3 and NIH 3T3 cells have high levels of fibroblasts and an accelerated tumor growth rate. We used this model to investigate the synergistic effect of combined gemcitabine monophosphate (GMP) nanoparticles and Cisplatin nanoparticles (Combo NP) on tumor-associated fibroblasts (TAFs). A single injection of Combo NP had synergistic anti-tumor effects while the same molar ratio of combined GMP and Cisplatin delivered as free drug (Combo Free) fell outside of the synergistic range. Combo NP nearly halted tumor growth with little evidence of general toxicity while Combo Free had only a modest inhibitory effect at 16mg/kg GMP and 1.6mg/kg Cisplatin. Combo NP increased levels of apoptosis within the tumor by approximately 1.3 folds (TUNEL analysis) and decreased α-SMA-positive fibroblast recruitment by more than 87% (immunofluorescence) after multiple injections compared with Combo Free, GMP NP or Cisplatin NP alone. The TAF-targeting capability of Combo NP was evaluated by double staining for TUNEL and α-SMA at various time points after a single injection. On day one after injection, 57% of the TUNEL-positive cells were identified as α-SMA-positive fibroblasts. By day four, tumor stroma was 85% depleted and 87% of the remaining TAFs were TUNEL-positive. Combo NP-treated tumors became 2.75 folds more permeable than those treated with Combo Free as measured by Evans Blue. We conclude that the antineoplastic effect of Combo NP works by first targeting TAFs and is more effective as an anti-tumor therapy than Combo Free, GMP NP or Cisplatin NP alone.

Nanoparticle drug loading as a design parameter to improve docetaxel pharmacokinetics and efficacy

Nanoparticle (NP) drug loading is one of the key defining characteristics of an NP formulation. However, the effect of NP drug loading on therapeutic efficacy and pharmacokinetics has not been thoroughly evaluated. Herein, we characterized the efficacy, toxicity and pharmacokinetic properties of NP docetaxel formulations that have differential drug loading but are otherwise identical. Particle Replication in Non-wetting Templates (PRINT(®)), a soft-lithography fabrication technique, was used to formulate NPs with identical size, shape and surface chemistry, but with variable docetaxel loading. The lower weight loading (9%-NP) of docetaxel was found to have a superior pharmacokinetic profile and enhanced efficacy in a murine cancer model when compared to that of a higher docetaxel loading (20%-NP). The 9%-NP docetaxel increased plasma and tumor docetaxel exposure and reduced liver, spleen and lung exposure when compared to that of 20%-NP docetaxel.

Pharmacokinetics and efficacy of PEGylated liposomal doxorubicin in an intracranial model of breast cancer

Introduction

Breast cancer brain metastases (BCBM) are a challenging consequence of advanced BC. Nanoparticle agents, including liposomes, have shown enhanced delivery to solid tumors and brain. We compared pharmacokinetics (PK) and efficacy of PEGylated liposomal doxorubicin (PLD) with non-liposomal doxorubicin (NonL-doxo) in an intracranial model of BC.

Methods

Athymic mice were inoculated intracerebrally with MDA-MB-231-BR-luciferase-expressing cells. Tumor-bearing mice were administered PLD or NonL-doxo at 6mg/kg IV×1 and were euthanized prior to and 0.083, 1, 3, 6, 24, 72 and 96 h post-treatment. Samples were processed to measure sum total doxorubicin via HPLC. PLD and NonL-doxo were administered IV weekly as single agents (6 mg/kg) or in combination (4.5 mg/kg) with the PARP inhibitor, ABT-888, PO 25 mg/kg/day. Efficacy was assessed by survival and bioluminescence.

Results

Treatment with PLD resulted in approximately 1,500-fold higher plasma and 20-fold higher intracranial tumor sum total doxorubicin AUC compared with NonL-doxo. PLD was detected at 96 h; NonL-doxo was undetectable after 24 h in plasma and tumor. Median survival of PLD-treated animals was 32 days (d, [CI] 31–38), which was significantly longer than controls (26d [CI 25–28]; p = 0.0012) or NonL-doxo treatment (23.5d [CI 18–28], p = 0.0002). Combination treatment with PLD/ABT-888 yielded improved survival compared to NonL-doxo/ABT-888 (35d [CI 31–38] versus 29.5d [CI 25–34]; p = 0.006).

Conclusions

PLD provides both PK and efficacy advantage over NonL-doxo in the treatment of an in vivo model of BCBM. The results provide preclinical rationale to translate findings into early phase trials of PLD, with or without ABT-888, for patients with BCBM.

Challenges and opportunities in the advancement of nanomedicines

Nanomedicine-based approaches to cancer treatment face several challenges that differ from those encountered by conventional medicines during clinical development. A systematic exploration of these issues has led us to identify the following needs and opportunities for further development: (1) robust and general methods for the accurate characterization of nanoparticle size, shape, and composition; (2) scalable approaches for producing nanomedicines with optimized bioavailability and excretion profiles; (3) particle engineering for maintaining low levels of nonspecific cytotoxicity and sufficient stability during storage; (4) optimization of surface chemistries for maximum targeted delivery and minimum nonspecific adsorption; (5) practical methods for quantifying ligand density and distributions on multivalent nanocarriers; and (6) the design of multifunctional nanomedicines for novel combination therapies with supportable levels of bioaccumulation.

Predictable and tunable half-life extension of therapeutic agents by controlled chemical release from macromolecular conjugates

Conjugation to macromolecular carriers is a proven strategy for improving the pharmacokinetics of drugs, with many stable polyethylene glycol conjugates having reached the market. Stable conjugates suffer several limitations: loss of drug potency due to conjugation, confining the drug to the extracellular space, and the requirement for a circulating conjugate. Current research is directed toward overcoming such limitations through releasable conjugates in which the drug is covalently linked to the carrier through a cleavable linker. Satisfactory linkers that provide predictable cleavage rates tunable over a wide time range that are useful for both circulating and noncirculating conjugates are not yet available. We describe such conjugation linkers on the basis of a nonenzymatic β-elimination reaction with preprogrammed, highly tunable cleavage rates. A set of modular linkers is described that bears a succinimidyl carbonate group for attachment to an amine-containing drug or prodrug, an azido group for conjugation to the carrier, and a tunable modulator that controls the rate of β-eliminative cleavage. The linkers provide predictable, tunable release rates of ligands from macromolecular conjugates both in vitro and in vivo, with half-lives spanning from a range of hours to >1 y at physiological pH. A circulating PEG conjugate achieved a 56-fold half-life extension of the 39-aa peptide exenatide in rats, and a noncirculating s.c. hydrogel conjugate achieved a 150-fold extension. Using slow-cleaving linkers, the latter may provide a generic format for once-a-month dosage forms of potent drugs. The releasable linkers provide additional benefits that include lowering C(max) and pharmacokinetic coordination of drug combinations.