The TLR2/TLR6 ligand FSL-1 mitigates radiation-induced hematopoietic injury in mice and nonhuman primates.

Thrombocytopenia, hemorrhage, anemia, and infection are life-threatening issues following accidental or intentional radiation exposure. Since few therapeutics are available, safe and efficacious small molecules to mitigate radiation-induced injury need to be developed. Our previous study showed the synthetic TLR2/TLR6 ligand fibroblast stimulating lipopeptide (FSL-1) prolonged survival and provided MyD88-dependent mitigation of hematopoietic acute radiation syndrome (H-ARS) in mice. Although mice and humans differ in TLR number, expression, and function, nonhuman primate (NHP) TLRs are like those of humans; therefore, studying both animal models is critical for drug development. The objectives of this study were to determine the efficacy of FSL-1 on hematopoietic recovery in small and large animal models subjected to sublethal total body irradiation and investigate its mechanism of action. In mice, we demonstrate a lack of adverse effects, an easy route of delivery (subcutaneous) and efficacy in promoting hematopoietic progenitor cell proliferation by FSL-1. NHP given radiation, followed a day later with a single subcutaneous administration of FSL-1, displayed no adversity but showed elevated hematopoietic cells. Our analyses revealed that FSL-1 promoted red blood cell development and induced soluble effectors following radiation exposure. Cytologic analysis of bone marrow aspirates revealed a striking enhancement of mononuclear progenitor cells in FSL-1-treated NHP. Combining the efficacy of FSL-1 in promoting hematopoietic cell recovery with the lack of adverse effects induced by a single administration supports the application of FSL-1 as a viable countermeasure against H-ARS.

Effect of Obesity on the Pharmacokinetics and Pharmacodynamics of Anticancer Agents.

An objective of the Precision Medicine Initiative, launched in 2015 by the US Food and Drug Administration and National Institutes of Health, is to optimize and individualize dosing of drugs, especially anticancer agents, with high pharmacokinetic and pharmacodynamic variability. The American Society of Clinical Oncology recently reported that 40% of obese patients receive insufficient chemotherapy doses and exposures, which may lead to reduced efficacy, and recommended pharmacokinetic studies to guide appropriate dosing in these patients. These issues will only increase in importance as the incidence of obesity in the population increases. This publication reviews the effects of obesity on (1) tumor biology, development of cancer, and antitumor response; (2) pharmacokinetics and pharmacodynamics of small-molecule anticancer drugs; and (3) pharmacokinetics and pharmacodynamics of complex anticancer drugs, such as carrier-mediated agents and biologics. These topics are not only important from a scientific research perspective but also from a drug development and regulator perspective. Thus, it is important to evaluate the effects of obesity on the pharmacokinetics and pharmacodynamics of anticancer agents in all categories of body habitus and especially in patients who are obese and morbidly obese. As the effects of obesity on the pharmacokinetics and pharmacodynamics of anticancer agents may be highly variable across drug types, the optimal dosing metric and algorithm for difference classes of drugs may be widely different. Thus, studies are needed to evaluate current and novel metrics and methods for measuring body habitus as related to optimizing the dose and reducing pharmacokinetic and pharmacodynamic variability of anticancer agents in patients who are obese and morbidly obese.

COVID-19 Vaccines and the Virus: Impact on Drug Metabolism and Pharmacokinetics.

This article reports on an American Society of Pharmacology and Therapeutics, Division of Drug Metabolism and Disposition symposium held at Experimental Biology on April 2, 2022, in Philadelphia. As of July 2022, over 500 million people have been infected with SARS-CoV-2 (the virus causing COVID-19) and over 12 billion vaccine doses have been administered. Clinically significant interactions between viral infections and hepatic drug metabolism were first recognized over 40 years ago during a cluster of pediatric theophylline toxicity cases attributed to reduced hepatic drug metabolism amid an influenza B outbreak. Today, a substantive body of research supports that the activated innate immune response generally decreases hepatic cytochrome P450 activity. The interactions extend to drug transporters and other organs and have the potential to impact drug absorption, distribution, metabolism, and excretion (ADME). Based on this knowledge, altered ADME is predicted with SARS-CoV-2 infection or vaccination. The report begins with a clinical case exploring the possibility of SARS-CoV-2 vaccination increasing clozapine levels. This is followed by discussions of how SARS-CoV-2 infection or vaccines alter the metabolism and disposition of complex drugs, such as nanoparticles and biologics and small molecule therapies. The review concludes with a discussion of the effects of viral infections on placental amino acid transport and their potential to impact fetal development. The session improved our understanding of the impact of emerging viral infections and vaccine technologies on drug metabolism and disposition, which will help mitigate drug toxicity and improve drug and vaccine safety and effectiveness. SIGNIFICANCE STATEMENT: Altered pharmacokinetics of small molecule and complex molecule drugs and fetal brain distribution of amino acids following SARS-CoV-2 infection or immunization are possible. The proposed mechanisms involve decreased liver cytochrome P450 metabolism of small molecules, enhanced innate immune system metabolism of complex molecules, and altered placental and fetal blood-brain barrier amino acid transport, respectively. Future research is needed to understand the effects of these interactions on adverse drug responses, drug and vaccine safety, and effectiveness and fetal neurodevelopment.

Investigation of the pharmacokinetic properties of synthetic heparan sulfate oligosaccharides.

Heparan sulfate (HS) is a sulfated polysaccharide with a wide range of biological activities. There is an increasing interest in the development of structurally homogeneous HS oligosaccharides as therapeutics. However, the factors influencing the pharmacokinetic properties of HS-based therapeutics remain unknown. Here, we report the pharmacokinetic properties of a panel of dodecasaccharides (12-mers) with varying sulfation patterns in healthy mice and uncover the pharmacokinetic properties of an octadecasaccharide (18-mer) in acutely injured mice. In the 12-mer panel, 1 12-mer, known as dekaparin, is anticoagulant, and 3 12-mers are nonanticoagulant. The concentrations of 12-mers in plasma and urine were determined by the disaccharide analysis using liquid chromatography coupled with tandem mass spectrometry. We observed a striking difference between anticoagulant and nonanticoagulant oligosaccharides in the 12-mer panel, showing that anticoagulant dekaparin had a 4.6-fold to 8.6-fold slower clearance and 4.4-fold to 8-fold higher plasma exposure compared to nonanticoagulant 12-mers. We also observed that the clearance of HS oligosaccharides is impacted by disease. Using an antiinflammatory 18-mer, we discovered that the clearance of 18-mer is reduced 2.8-fold in a liver failure mouse model compared to healthy mice. Our results suggest that oligosaccharides are rapidly cleared renally if they have low interaction with circulating proteins. We observed that the clearance rate of oligosaccharides is inversely associated with the degree of binding to target proteins, which can vary in response to pathophysiological conditions. Our findings uncover a contributing factor for the plasma and renal clearance of oligosaccharides which will aid the development of HS-based therapeutics.

A mucoadhesive biodissolvable thin film for localized and rapid delivery of lidocaine for the treatment of vestibulodynia.

Vestibulodynia (VBD), an idiopathic pain disorder characterized by erythema and pain of the vulvar vestibule (the inner aspect of the labia minora and vaginal opening), is the most common cause of sexual pain for women of reproductive age. Women also feel discomfort with contact with clothing and tampon use. As most women with this disorder only have pain with provocation of the tissue, topical anesthetics applied to the vestibule are the current first line treatment for temporary pain relief. Treatment options are limited due to anatomical constraints of the vestibular region, poor drug retention time, imprecise dosing, leakage, and overall product messiness. In this study we report a novel approach to treatment of VBD using thin film designed to fit the vulvar vestibule and deliver lidocaine locally. Two use cases for VBD treatment were identified 1) rapid drug release (<5 min), for use prior to intercourse and 2) long-acting release (≥120 min) for prolonged use and relief throughout the day. Cellulose-based mucoadhesive thin films were fabricated using a solvent casting method. Three polymers including hydroxyethylcellulose (HEC), hydroxypropylcellulose (HPC), and hydroxypropylmethycellulose (HMPC), were selected owing to their biocompatibility and ideal properties for film casting. Films casted with HEC, HPC, and HPMC exhibited mucoadhesive properties relative to a control, with the highest mucoadhesive force recorded for films casted with HPC. Effect of media volume, pH, presence of mucin and presence of drug on film dissolution rates were investigated. Dissolution rates were independent of media volume, media pH or drug presence, whereas faster dissolution rates were obtained for all films in presence of mucin. In vitro lidocaine release kinetics were influenced by polymer type, percent drug loading and film casting thickness. Lidocaine release was based on a diffusion mechanism rather than through film dissolution and faster release (∼5 min) was observed for HEC films compared HPC films (∼120 min). Higher drug loading and film thickness resulted in slower and more prolonged release kinetics of lidocaine. All films were biocompatible and exhibited good mechanical properties. Two film formulations (9% w/w HPC with 12% w/w LHC, 5% w/w HEC with 6% w/w LHC) were optimized to meet the two use case scenarios for VBD treatment and moved into in vivo testing. In vivo testing demonstrated the safety of the films in BALB/c mice, and the pharmacokinetic analysis demonstrated the delivery of lidocaine primarily to the vaginal tissue. We demonstrate the ability to develop a mucoadhesive, biodissolvable thin film and fine-tune drug release kinetics to optimize local delivery of lidocaine to the vulva.

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.

Imaging methods to evaluate tumor microenvironment factors affecting nanoparticle drug delivery and antitumor response.

Standard small molecule and nanoparticulate chemotherapies are used for cancer treatment; however, their effectiveness remains highly variable. One reason for this variable response is hypothesized to be due to nonspecific drug distribution and heterogeneity of the tumor microenvironment, which affect tumor delivery of the agents. Nanoparticle drugs have many theoretical advantages, but due to variability in tumor microenvironment (TME) factors, the overall drug delivery to tumors and associated antitumor response are low. The nanotechnology field would greatly benefit from a thorough analysis of the TME factors that create these physiological barriers to tumor delivery and treatment in preclinical models and in patients. Thus, there is a need to develop methods that can be used to reveal the content of the TME, determine how these TME factors affect drug delivery, and modulate TME factors to increase the tumor delivery and efficacy of nanoparticles. In this review, we will discuss TME factors involved in drug delivery, and how biomedical imaging tools can be used to evaluate tumor barriers and predict drug delivery to tumors and antitumor response.

Importance and Considerations of Antibody Engineering in Antibody-Drug Conjugates Development from a Clinical Pharmacologist's Perspective.

Antibody-drug conjugates (ADCs) appear to be in a developmental boom, with five FDA approvals in the last two years and a projected market value of over $4 billion by 2024. Major advancements in the engineering of these novel cytotoxic drug carriers have provided a few early success stories. Although the use of these immunoconjugate agents are still in their infancy, valuable lessons in the engineering of these agents have been learned from both preclinical and clinical failures. It is essential to appreciate how the various mechanisms used to engineer changes in ADCs can alter the complex pharmacology of these agents and allow the ADCs to navigate the modern-day therapeutic challenges within oncology. This review provides a global overview of ADC characteristics which can be engineered to alter the interaction with the immune system, pharmacokinetic and pharmacodynamic profiles, and therapeutic index of ADCs. In addition, this review will highlight some of the engineering approaches being explored in the creation of the next generation of ADCs.

Steroid Eluting Esophageal-Targeted Drug Delivery Devices for Treatment of Eosinophilic Esophagitis.

Eosinophilic esophagitis (EoE) is a chronic atopic disease that has become increasingly prevalent over the past 20 years. A first-line pharmacologic option is topical/swallowed corticosteroids, but these are adapted from asthma preparations such as fluticasone from an inhaler and yield suboptimal response rates. There are no FDA-approved medications for the treatment of EoE, and esophageal-specific drug formulations are lacking. We report the development of two novel esophageal-specific drug delivery platforms. The first is a fluticasone-eluting string that could be swallowed similar to the string test "entero-test" and used for overnight treatment, allowing for a rapid release along the entire length of esophagus. In vitro drug release studies showed a target release of 1 mg/day of fluticasone. In vivo pharmacokinetic studies were carried out after deploying the string in a porcine model, and our results showed a high local level of fluticasone in esophageal tissue persisting over 1 and 3 days, and a minimal systemic absorption in plasma. The second device is a fluticasone-eluting 3D printed ring for local and sustained release of fluticasone in the esophagus. We designed and fabricated biocompatible fluticasone-loaded rings using a top-down, Digital Light Processing (DLP) Gizmo 3D printer. We explored various strategies of drug loading into 3D printed rings, involving incorporation of drug during the print process (pre-loading) or after printing (post-loading). In vitro drug release studies of fluticasone-loaded rings (pre and post-loaded) showed that fluticasone elutes at a constant rate over a period of one month. Ex vivo pharmacokinetic studies in the porcine model also showed high tissue levels of fluticasone and both rings and strings were successfully deployed into the porcine esophagus in vivo. Given these preliminary proof-of-concept data, these devices now merit study in animal models of disease and ultimately subsequent translation to testing in humans.

First-in-human, phase I/IIa study of CRLX301, a nanoparticle drug conjugate containing docetaxel, in patients with advanced or metastatic solid malignancies.

Background This was a phase I/IIa study to investigate the tolerability, efficacy and pharmacokinetics (PK)/ pharmacodynamics (PD) of CRLX301, CDP-based nanoparticle formulation of docetaxel. Methods The study was conducted in two parts. In part 1, dose-escalation using a standard 3 + 3 design was performed in two dosing schedules (every week (QW) and every 3 weeks (Q3W)). Part 2 was comprised of a dose expansion at 75 mg/m2 Q3W. PK studies were performed on both dosing schedules. Results Forty-two patients were recruited onto the study with a median age of 64(range 38-76); median number of prior systemic therapies was 5(range 0-10). Grade 3/4 treatment-related toxicities included: neutropenia (21.4 %), infusion related reaction (11.9 %), anemia (7.1 %), fatigue (4.8 %), diarrhea (4.8 %), and peripheral neuropathy (4.8 %). The maximum tolerated dose was 75 mg/m2 given on the Q3W schedule and was not determined on the QW schedule. In this heavily pre-treated population, four patients (12.9 %) achieved stable disease (SD) ≥ 4 months and 2 patients (6.5 %) achieved partial response (PR) for a clinical benefit rate (CBR) of 19.4 % (6/31 patients). The PRs were seen in prostate and breast adenocarcinoma (one each). CRLX301 exhibited some PK advantages over docetaxel including higher retention of drug in plasma, slower clearance and controlled slow release of docetaxel from the carrier. Conclusions In this heavily pretreated patient population, the safety profile was acceptable for CRLX301 therapy. There was some evidence of preliminary tumor efficacy, but further work is necessary to find the optimal dose and schedule of this formulation.Clinicaltrials.gov trial registration number: NCT02380677 (Date of registration: March 2, 2015).

Complex Factors and Challenges that Affect the Pharmacology, Safety and Efficacy of Nanocarrier Drug Delivery Systems.

Major developments in nanomedicines, such as nanoparticles (NPs), nanosomes, and conjugates, have revolutionized drug delivery capabilities over the past four decades. Although nanocarrier agents provide numerous advantages (e.g., greater solubility and duration of systemic exposure) compared to their small-molecule counterparts, there is considerable inter-patient variability seen in the systemic disposition, tumor delivery and overall pharmacological effects (i.e., anti-tumor efficacy and unwanted toxicity) of NP agents. This review aims to provide a summary of fundamental factors that affect the disposition of NPs in the treatment of cancer and why they should be evaluated during preclinical and clinical development. Furthermore, this chapter will highlight some of the translational challenges associated with elements of NPs and how these issues can only be addressed by detailed and novel pharmacology studies.

Poly(2-oxazoline) nanoparticle delivery enhances the therapeutic potential of vismodegib for medulloblastoma by improving CNS pharmacokinetics and reducing systemic toxicity.

We report a nanoparticle formulation of the SHH-pathway inhibitor vismodegib that improves efficacy for medulloblastoma, while reducing toxicity. Limited blood-brain barrier (BBB) penetration and dose-limiting extitle/citraneural toxicities complicate systemic therapies for brain tumors. Vismodegib is FDA-approved for SHH-driven basal cell carcinoma, but implementation for medulloblastoma has been limited by inadequate efficacy and excessive bone toxicity. To address these issues through optimized drug delivery, we formulated vismodegib in polyoxazoline block copolymer micelles (POx-vismo). We then evaluated POx-vismo in transgenic mice that develop SHH-driven medulloblastomas with native vasculature and tumor microenvironment. POx-vismo improved CNS pharmacokinetics and reduced bone toxicity. Mechanistically, the nanoparticle carrier did not enter the CNS, and acted within the vascular compartment to improve drug delivery. Unlike conventional vismodegib, POx-vismo extended survival in medulloblastoma-bearing mice. Our results show the broad potential for non-targeted nanoparticle formulation to improve systemic brain tumor therapy, and specifically to improve vismodegib therapy for SHH-driven cancers.

Pharmacokinetic and pharmacodynamic analyses of cocaine and its metabolites in behaviorally divergent inbred mouse strains.

Cocaine (COC) is a psychostimulant with a high potential for abuse and addiction. Risk for COC use disorder is driven, in part, by genetic factors. Animal models of addiction-relevant behaviors have proven useful for studying both genetic and nongenetic contributions to drug response. In a previous study, we examined initial locomotor sensitivity to COC in genetically diverse inbred mouse strains. That work highlighted the relevance of pharmacokinetics (PK) in initial locomotor response to COC but was limited by a single dose and two sampling points. The objective of the present study was to characterize the PK and pharmacodynamics of COC and its metabolites (norcocaine and benzoylecgonine) in six inbred mouse strains (I/LnJ, C57BL/6J, FVB/NJ, BTBR T+ tf/J, LG/J and LP/J) that exhibit extreme locomotor responses to cocaine. Mice were administered COC at one of four doses and concentrations of cocaine, norcocaine and benzoylecgonine were analyzed in both plasma and brain tissue at 5 different time points. Initial locomotor sensitivity to COC was used as a pharmacodynamic endpoint. We developed an empirical population PK model that simultaneously characterizes cocaine, norcocaine and benzoylecgonine in plasma and brain tissues. We observed interstrain variability occurring in the brain compartment that may contribute to pharmacodynamic differences among select strains. Our current work paves the way for future studies to explore strain-specific pharmacokinetic differences and identify factors other than PK that are responsible for the diverse behavioral response to COC across these inbred mouse strains.

A reanalysis of nanoparticle tumor delivery using classical pharmacokinetic metrics.

Nanoparticle (NP) delivery to solid tumors has recently been questioned. To better understand the magnitude of NP tumor delivery, we reanalyzed published murine NP tumor pharmacokinetic (PK) data used in the Wilhelm et al. study. Studies included in their analysis reporting matched tumor and blood concentration versus time data were evaluated using classical PK endpoints and compared to the unestablished percent injected dose (%ID) in tumor metric from the Wilhelm et al. study. The %ID in tumor was poorly correlated with standard PK metrics that describe NP tumor delivery (AUCtumor/AUCblood ratio) and only moderately associated with maximal tumor concentration. The relative tumor delivery of NPs was ~100-fold greater as assessed by the standard AUCtumor/AUCblood ratio than by %ID in tumor. These results strongly suggest that PK metrics and calculations can influence the interpretation of NP tumor delivery and stress the need to properly validate novel PK metrics against traditional approaches.

MerTK inhibition decreases immune suppressive glioblastoma-associated macrophages and neoangiogenesis in glioblastoma microenvironment.

BACKGROUND: Glioblastoma-associated macrophages and microglia (GAMs) are the predominant immune cells in the tumor microenvironment. Activation of MerTK, a receptor tyrosine kinase, polarizes GAMs to an immunosuppressive phenotype, promoting tumor growth. Here, the role of MerTK inhibition in the glioblastoma microenvironment is investigated in vitro and in vivo. METHODS: Effects of MRX-2843 in glioblastoma microenvironment regulation were determined in vitro by cell viability, cytokine array, in vitro tube formation, Western blotting, and wound healing assays. A syngeneic GL261 orthotopic glioblastoma mouse model was used to evaluate the survival benefit of MRX-2843 treatment. Multiplex fluorescent immunohistochemistry was used to evaluate the expression of CD206, an anti-inflammatory marker on GAMs, and angiogenesis in murine brain tumor tissues. RESULTS: MRX-2843 inhibited cell growth and induced apoptosis in human glioblastoma cells and decreased protein expression of phosphorylated MerTK, AKT, and ERK, which are essential for cell survival signaling. Interleukin-8 and C-C motif chemokine ligand 2, the pro-glioma and pro-angiogenic cytokines, were decreased by MRX-2843. Decreased vascular formation and numbers of immunosuppressive (CD206+) GAMs were observed following MRX-2843 treatment in vivo, suggesting that in addition to alleviating immunosuppression, MRX-2843 also inhibits neoangiogenesis in the glioma microenvironment. These results were supported by a prolonged survival in the syngeneic mouse orthotopic GL261 glioblastoma model following MRX-2843 treatment. CONCLUSION: Our findings suggest that MRX-2843 has a therapeutic benefit via promoting GAM polarization away from immunosuppressive condition, inhibiting neoangiogenesis in the glioblastoma microenvironment and inducing tumor cell death.

Tumor Responsive and Tunable Polymeric Platform for Optimized Delivery of Paclitaxel to Treat Glioblastoma.

Current interstitial therapies for glioblastoma can overcome the blood-brain barrier but fail to optimally release therapy at a rate that stalls cancer reoccurrence. To address this lapse, acetalated dextran (Ace-DEX) nanofibrous scaffolds were used for their unique degradation rates that translate to a broad range of drug release kinetics. A distinctive range of drug release rates was illustrated via electrospun Ace-DEX or poly(lactic acid) (PLA) scaffolds. Scaffolds composed of fast, medium, and slow degrading Ace-DEX resulted in 14.1%, 2.9%, and 1.3% paclitaxel released per day. To better understand the impact of paclitaxel release rate on interstitial therapy, two clinically relevant orthotopic glioblastoma mouse models were explored: (1) a surgical model of resection and recurrence (resection model) and (2) a distant metastasis model. The effect of unique drug release was illustrated in the resection model when a 78% long-term survival was observed with combined fast and slow release scaffolds, in comparison to a survival of 20% when the same dose is delivered at a medium release rate. In contrast, only the fast release rate scaffold displayed treatment efficacy in the distant metastasis model. Additionally, the acid-sensitive Ace-DEX scaffolds were shown to respond to the lower pH conditions associated with GBM tumors, releasing more paclitaxel in vivo when a tumor was present in contrast to nonacid sensitive PLA scaffolds. The unique range of tunable degradation and stimuli-responsive nature makes Ace-DEX a promising drug delivery platform to improve interstitial therapy for glioblastoma.

Pharmacologic Considerations in the Disposition of Antibodies and Antibody-Drug Conjugates in Preclinical Models and in Patients.

The rapid advancement in the development of therapeutic proteins, including monoclonal antibodies (mAbs) and antibody-drug conjugates (ADCs), has created a novel mechanism to selectively deliver highly potent cytotoxic agents in the treatment of cancer. These agents provide numerous benefits compared to traditional small molecule drugs, though their clinical use still requires optimization. The pharmacology of mAbs/ADCs is complex and because ADCs are comprised of multiple components, individual agent characteristics and patient variables can affect their disposition. To further improve the clinical use and rational development of these agents, it is imperative to comprehend the complex mechanisms employed by antibody-based agents in traversing numerous biological barriers and how agent/patient factors affect tumor delivery, toxicities, efficacy, and ultimately, biodistribution. This review provides an updated summary of factors known to affect the disposition of mAbs/ADCs in development and in clinical use, as well as how these factors should be considered in the selection and design of preclinical studies of ADC agents in development.

Overcoming anti-PEG antibody mediated accelerated blood clearance of PEGylated liposomes by pre-infusion with high molecular weight free PEG.

Antibodies that specifically bind polyethylene glycol (PEG), i.e. anti-PEG antibodies (APA), are associated with reduced efficacy and increased risk of serious adverse events for several PEGylated therapeutics. Here, we explored the concept of using free PEG molecules to saturate circulating APA. Surprisingly, we found that 40 kDa free PEG effectively restored the prolonged circulation of PEGylated liposomes in the presence of high titers of pre-existing APA for at least 48 h in mice. In contrast, lower molecular weight free PEG (≤10 kDa) failed to restore circulation beyond a few hours. These in vivo results were consistent with estimates from a minimal physiologically based pharmacokinetic model. Importantly, the infusion of free PEG appeared to be safe in mice previously sensitized by injection of PEGylated liposomes, and free PEG did not elicit excess APA production even in mice with pre-existing adaptive immunity against PEG. Our results support further investigation of high molecular weight free PEG as a potential method to control and overcome high titers of APA, restoring the prolonged circulation of PEGylated liposomes and possibly other PEGylated therapeutics.

Pretargeted delivery of PEG-coated drug carriers to breast tumors using multivalent, bispecific antibody against polyethylene glycol and HER2.

Pretargeting is an increasingly explored strategy to improve nanoparticle targeting, in which pretargeting molecules that bind both selected epitopes on target cells and nanocarriers are first administered, followed by the drug-loaded nanocarriers. Bispecific antibodies (bsAb) represent a promising class of pretargeting molecules, but how different bsAb formats may impact the efficiency of pretargeting remains poorly understood, in particular Fab valency and Fc receptor (FcR)-binding of bsAb. We found the tetravalent bsAb markedly enhanced PEGylated nanoparticle binding to target HER2+ cells relative to the bivalent bsAb in vitro. Pretargeting with tetravalent bsAb with abrogated FcR binding increased tumor accumulation of PEGylated liposomal doxorubicin (PLD) 3-fold compared to passively targeted PLD alone, and 5-fold vs pretargeting with tetravalent bsAb with normal FcR binding in vivo. Our work demonstrates that multivalency and elimination of FcRn recycling are both important features of pretargeting molecules, and further supports pretargeting as a promising nanoparticle delivery strategy.