Hetero-modification of TRAIL trimer for improved drug delivery and in vivo antitumor activities

Significance of TRAIL/Apo-2 ligand and its death receptors in apoptosis and necroptosis signalling: Implications for cancer-targeted therapeutics

The human immune defensesystem routinely expresses the tumour necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), which is the most prevalent element for antitumor immunity. TRAIL associates with its death receptors (DRs), DR4 (TRAIL-R1), and DR5 (TRAIL-R2), in cancer cells to initiate the intracellular apoptosis cascade. Accordingly, numerous academic institutions and pharmaceutical companies havetried to exploreTRAIL's capacity to kill tumourcells by producing recombinant versions of it (rhTRAIL) or TRAIL receptor agonists (TRAs) [monoclonal antibody (mAb), synthetic and natural compounds, etc.] and molecules that sensitize TRAIL signalling pathway for therapeutic applications. Recently, several microRNAs (miRs) have been found to activate or inhibit death receptor signalling. Therefore, pharmacological regulation of these miRs may activate or resensitize the TRAIL DRs signal, and this is a novel approach for developing anticancer therapeutics. In this article, we will discuss TRAIL and its receptors and molecular pathways by which it induces various cell death events. We will unravel potential innovative applications of TRAIL-based therapeutics, and other investigated therapeutics targeting TRAIL-DRs and summarize the current preclinical pharmacological studies and clinical trials. Moreover, we will also emphasizea few situations where future efforts may be addressed to modulate the TRAIL signalling pathway.

The TRAIL in the Treatment of Human Cancer: An Update on Clinical Trials

TRAIL (tumor-necrosis factor related apoptosis-inducing ligand, CD253) and its death receptors TRAIL-R1 and TRAIL-R2 selectively trigger the apoptotic cell death in tumor cells. For that reason, TRAIL has been extensively studied as a target of cancer therapy. In spite of the promising preclinical observations, the TRAIL–based therapies in humans have certain limitations. The two main therapeutic approaches are based on either an administration of TRAIL-receptor (TRAIL-R) agonists or a recombinant TRAIL. These approaches, however, seem to elicit a limited therapeutic efficacy, and only a few drugs have entered the phase II clinical trials. To deliver TRAIL-based therapies with higher anti-tumor potential several novel TRAIL-derivates and modifications have been designed. These novel drugs are, however, mostly preclinical, and many problems continue to be unraveled. We have reviewed the current status of all TRAIL-based monotherapies and combination therapies that have reached phase II and phase III clinical trials in humans. We have also aimed to introduce all novel approaches of TRAIL utilization in cancer treatment and discussed the most promising drugs which are likely to enter clinical trials in humans. To date, different strategies were introduced in order to activate anti-tumor immune responses with the aim of achieving the highest efficacy and minimal toxicity.In this review, we discuss the most promising TRAIL-based clinical trials and their therapeutic strategies.

TRAIL stabilization and cancer cell sensitization to its pro-apoptotic activity achieved through genetic fusion with arginine deiminase

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) binds to death receptors and induces apoptosis in various cancer cell lines while sparing normal cells. Recombinant TRAIL has shown good safety and efficacy profiles in preclinical cancer models. However, clinical success has been limited due to poor PK and development of resistance to death receptor-induced apoptosis. We have addressed these issues by creating a fusion protein of TRAIL and arginine deiminase (ADI). The fusion protein benefits from structural and functional synergies between its two components and has an extended half-life in vivo. ADI downregulates survivin, upregulates DR5 receptor and sensitizes cancer cells to TRAIL induced apoptosis. ADI-TRAIL fusion protein was efficacious in a number of cell lines and synergized with some standard of care drugs. In an HCT116 xenograft model ADI-TRAIL localized to the tumor and induced dose-dependent tumor regression, the fusion protein was superior to rhTRAIL administered at the same molar amounts.

Nanoparticles for Immune Cytokine TRAIL-Based Cancer Therapy

The immune cytokine tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has received significant attention as a cancer therapeutic due to its ability to selectively trigger cancer cell apoptosis without causing toxicity in vivo. While TRAIL has demonstrated significant promise in preclinical studies in mice as a cancer therapeutic, challenges including poor circulation half-life, inefficient delivery to target sites, and TRAIL resistance have hindered clinical translation. Recent advances in drug delivery, materials science, and nanotechnology are now being exploited to develop next-generation nanoparticle platforms to overcome barriers to TRAIL therapeutic delivery. Here, we review the design and implementation of nanoparticles to enhance TRAIL-based cancer therapy. The platforms we discuss are diverse in their approaches to the delivery problem and provide valuable insight into guiding the design of future nanoparticle-based TRAIL cancer therapeutics to potentially enable future translation into the clinic.

Antibodies and Derivatives Targeting DR4 and DR5 for Cancer Therapy

Developing therapeutics that induce apoptosis in cancer cells has become an increasingly attractive approach for the past 30 years. The discovery of tumor necrosis factor (TNF) superfamily members and more specifically TNF-related apoptosis-inducing ligand (TRAIL), the only cytokine of the family capable of eradicating selectively cancer cells, led to the development of numerous TRAIL derivatives targeting death receptor 4 (DR4) and death receptor 5 (DR5) for cancer therapy. With a few exceptions, preliminary attempts to use recombinant TRAIL, agonistic antibodies, or derivatives to target TRAIL agonist receptors in the clinic have been fairly disappointing. Nonetheless, a tremendous effort, worldwide, is being put into the development of novel strategic options to target TRAIL receptors. Antibodies and derivatives allow for the design of novel and efficient agonists. We summarize and discuss here the advantages and drawbacks of the soar of TRAIL therapeutics, from the first developments to the next generation of agonistic products, with a particular insight on new concepts.

Optimizing Multistep Delivery of PEGylated Tumor-Necrosis-Factor-Related Apoptosis-Inducing Ligand-Toxin Conjugates for Improved Antitumor Activities

Although TRAIL (tumor-necrosis-factor (TNF)-related apoptosis-inducing ligand) has been considered a promising broad-spectrum antitumor agent, its further application was limited by poor drug delivery and TRAIL-resistant tumors. A three-step drug delivery strategy was applied to TRAIL for solving these two obstacles in the form of PEG-TRAIL-MMAE (Monomethyl Auristatin E). PEGylation of TRAIL in the first step was carried out to improve its in vivo pharmacokinetics, while the interaction between TRAIL conjugates with death receptors in the second step was designed to activate the TRAIL extrinsic apoptosis pathway, and the further release of MMAE from the lysosome was the third step for introducing another apoptosis pathway to overcome TRAIL resistance in some tumors. Herein, in order to reach a balance among the three steps, the PEG/MMAE ratio was optimized for PEG-TRAIL-MMAE conjugates. PEG-TRAIL-MMAE conjugates with various PEG/MMAE ratios were prepared and compared with each other regarding their pharmacokinetics (PK) and pharmacodynamics (PD). As a result, PEG-TRAIL-MMAE conjugates with a PEG/MMAE ratio of 1:2 showed prolonged half-life in rats (6.8 h), and the best antitumor activity in vitro (IC₅₀ 0.31 nM) and in vivo while no sign of toxicity in xenograft models, suggesting it as a promising multistep drug delivery and antitumor strategy after optimization.

Polymeric mechanical amplifiers of immune cytokine-mediated apoptosis

Physical forces affect tumour growth, progression and metastasis. Here, we develop polymeric mechanical amplifiers that exploit in vitro and in vivo physical forces to increase immune cytokine-mediated tumour cell apoptosis. Mechanical amplifiers, consisting of biodegradable polymeric particles tethered to the tumour cell surface via polyethylene glycol linkers, increase the apoptotic effect of an immune cytokine on tumour cells under fluid shear exposure by as much as 50% compared with treatment under static conditions. We show that targeted polymeric particles delivered to tumour cells in vivo amplify the apoptotic effect of a subsequent treatment of immune cytokine, reduce circulating tumour cells in blood and overall tumour cell burden by over 90% and reduce solid tumour growth in combination with the antioxidant resveratrol. The work introduces a potentially new application for a broad range of micro- and nanoparticles to maximize receptor-mediated signalling and function in the presence of physical forces.

Fluid shear stress plays a critical role in receptor-mediated signalling and has been shown to sensitize cancer cells to apoptosis. Here, Mitchell et al. introduce polymer micro- and nanoparticles tethered to tumour cells to amplify fluid shear stress effects, and find that they can enhance immune cytokine-mediated apoptosis of tumour cells in vitro and in vivo.