Evaluation of the antitumor mechanism of antibody-drug conjugates against tissue factor in stroma-rich allograft models

Selective Intracellular Delivery of Antibodies in Cancer Cells with Nanocarriers Sensing Endo/Lysosomal Enzymatic Activity

The differential enzymatic activity in the endo/lysosomes of particular cells could trigger targeted endosomal escape functions, enabling selective intracellular protein delivery. However, this strategy may be jeopardized due to protein degradation during endosomal trafficking. Herein, using custom made fluorescent probes to assess the endosomal activity of cathepsin B (CTSB) and protein degradation, we found that certain cancer cells with hyperacidified endosomes grant a spatiotemporal window where CTSB activity surpass protein digestion. This inspired the engineering of antibody-loaded polymeric nanocarriers having CTSB-activatable endosomal escape ability. The nanocarriers selectively escaped from the endo/lysosomes in the cells with high endosomal CTSB activity and delivered active antibodies to intracellular targets. This study provides a viable strategy for cell-specific protein delivery using stimuli-responsive nanocarriers with controlled endosomal escape.

Antibody drug conjugates: hitting the mark in pancreatic cancer?

Pancreatic cancer is one of the most common causes of cancer-related death, and the 5-year survival rate has only improved marginally over the last decade. Late detection of the disease means that in most cases the disease has advanced locally and/or metastasized, and curative surgery is not possible. Chemotherapy is still the first-line treatment however, this has only had a modest impact in improving survival, with associated toxicities. Therefore, there is an urgent need for targeted approaches to better treat pancreatic cancer, while minimizing treatment-induced side-effects. Antibody drug conjugates (ADCs) are one treatment option that could fill this gap. Here, a monoclonal antibody is used to deliver extremely potent drugs directly to the tumor site to improve on-target killing while reducing off-target toxicity. In this paper, we review the current literature for ADC targets that have been examined in vivo for treating pancreatic cancer, summarize current and on-going clinical trials using ADCs to treat pancreatic cancer and discuss potential strategies to improve their therapeutic window.

Enhanced Permeability and Retention Effect as a Ubiquitous and Epoch-Making Phenomenon for the Selective Drug Targeting of Solid Tumors

In 1979, development of the first polymer drug SMANCS [styrene-co-maleic acid (SMA) copolymer conjugated to neocarzinostatin (NCS)] by Maeda and colleagues was a breakthrough in the cancer field. When SMANCS was administered to mice, drug accumulation in tumors was markedly increased compared with accumulation of the parental drug NCS. This momentous result led to discovery of the enhanced permeability and retention effect (EPR effect) in 1986. Later, the EPR effect became known worldwide, especially in nanomedicine, and is still believed to be a universal mechanism for tumor-selective accumulation of nanomedicines. Some research groups recently characterized the EPR effect as a controversial concept and stated that it has not been fully demonstrated in clinical settings, but this erroneous belief is due to non-standard drug design and use of inappropriate tumor models in investigations. Many research groups recently provided solid evidence of the EPR effect in human cancers (e.g., renal and breast), with significant diversity and heterogeneity in various patients. In this review, we focus on the dynamics of the EPR effect and restoring tumor blood flow by using EPR effect enhancers. We also discuss new applications of EPR-based nanomedicine in boron neutron capture therapy and photodynamic therapy for solid tumors.

Antibody-drug conjugates: beyond current approvals and potential future strategies

The recent approvals for antibody-drug conjugates (ADCs) in multiple malignancies in recent years have fuelled the ongoing development of this class of drugs. These novel agents combine the benefits of high specific targeting of oncogenic cell surface antigens with the additional cell kill from high potency cytotoxic payloads, thus achieving wider therapeutic windows. This review will summarise the clinical activity of ADCs in tumour types not covered elsewhere in this issue, such as gastrointestinal (GI) and genitourinary (GU) cancers and glioblastoma (GBM). In addition to the ongoing clinical testing of existing ADCs, there is substantial preclinical and early phase testing of newer ADCs or ADC incorporating strategies. This review will provide selected insights into such future development, focusing on the development of novel ADCs against new antigen targets in the tumour microenvironment (TME) and combination of ADCs with immuno-oncology (IO) agents.

Platelet-Vesicles-Encapsulated RSL-3 Enable Anti-Angiogenesis and Induce Ferroptosis to Inhibit Pancreatic Cancer Progress

Pancreatic ductal adenocarcinoma (PDAC) is one of the most malignant cancers. It is characterized by stromal richness, lack of blood supply and special metabolic reprogramming in the tumor microenvironment, which is difficult to treat and easy to metastase. Great efforts have been made to develop new drugs which can pass through the stroma and are more effective than traditional chemotherapeutics, such as ferroptosis inducers-Erastin and RSL-3. As current anti-angiogenic therapy drugs alone are suboptimal for PDAC, novel vascular disruption agents in combination with ferroptosis inducers might provide a possible solution. Here, we designed human platelet vesicles (PVs) to camouflage RSL-3 to enhance drug uptake rate by tumor cells and circulation time in vivo, deteriorating the tumor vessels and resulting in tumor embolism to cut the nutrient supply as well as causing cell death due to excessive lipid peroxidation. The RSL-3@PVs can also cause the classic ferroptosis-related change of mitochondrial morphology, with changes in cellular redox levels. Besides that, RSL-3@PVs has been proved to have great biological safety profile in vitro and in vivo. This study demonstrates the promising potential of integrating PVs and RSL-3 as a combination therapy for improving the outcome of PDAC.

CC-223, NSC781406, and BGT226 Exerts a Cytotoxic Effect Against Pancreatic Cancer Cells via mTOR Signaling

The mTOR signaling pathway is abnormally activated in pancreatic cancer and is related to tumor glucose metabolism. However, its specific regulation mechanism is still unclear. Therefore, this study aims to investigate whether Sestrin2 affects the glucose metabolism of pancreatic cancer by modulating mTOR signal and then affects its biological behavior. We have observed that l-leucine can promote the proliferation of pancreatic cancer cells and increase the expression of Sestrin2 and p-mTOR proteins. In order to further study the role of Sestrin2 and mTOR signaling in pancreatic cancer, we conducted Sestrin2 overexpression and mTOR pharmacological inhibition experiments. We found that Sestrin2 overexpression can increase glycolysis of pancreatic cancer cells and promote their proliferation. This effect can be eliminated by mTOR inhibitors. Finally, we found that Sestrin2 knockdown could inhibit the growth of pancreatic cancer in vivo. In conclusion, these findings suggest that Sestrin2 may promote the occurrence and development of pancreatic cancer through mTOR signaling.

Exploiting the dynamics of the EPR effect and strategies to improve the therapeutic effects of nanomedicines by using EPR effect enhancers

The enhanced permeability and retention (EPR) effect is a unique phenomenon of solid tumors that is related to their particular anatomical and pathophysiological characteristics, e.g. defective vascular architecture; large gaps between endothelial cells in blood vessels; abundant vascular mediators such as bradykinin, nitric oxide, carbon monoxide, and vascular endothelial growth factor; and impaired lymphatic recovery. These features lead to tumor tissues showing considerable extravasation of plasma components and nanomedicines. These data comprise the basic theory underlying the development of macromolecular agents or nanomedicines. The EPR effect is not necessarily valid for all solid tumors, because tumor blood flow and vascular permeability vary greatly. Tumor blood flow is frequently obstructed as tumor size increases, as often seen clinically; early stage, small tumors show a more uniform EPR effect, whereas advanced large tumor show heterogeneity in EPR effect. Accordingly, it would be very important to apply enhancers of EPR effect in clinical setting to make EPR effect more uniform. In this review, we discuss the EPR effect: its history, factors involved, and dynamics and heterogeneity. Strategies to overcome the EPR effect's heterogeneity may guarantee better therapeutic outcomes of drug delivery to advanced cancers.

Evaluation of the antitumor mechanism of antibody-drug conjugates against tissue factor in stroma-rich allograft models

Tissue factor (TF) is known to be overexpressed in various cancers including pancreatic cancer. The upregulation of TF expression has been observed not only in tumor cells, but also in tumor stromal cells. Because of the potential of TF as a delivery target, several studies investigated the effectiveness of Ab-drug conjugates (ADCs) against TF for cancer therapy. However, it is still unclear whether anti-TF ADC can exert toxicity against both tumor cells and tumor stromal cells. Here, we prepared ADC using a rat anti-mouse TF mAb (clone.1157) and 2 types of in vivo murine pancreatic cancer models, one s.c. and other orthotopic with an abundant tumor stroma. We also compared the feasibility of bis-alkylating conjugation (bisAlk) with that of conventional maleimide-based conjugation (MC). In the s.c. models, anti-TF ADC showed greater antitumor effects than control ADC. The results also indicated that the bisAlk linker might be more suitable than the MC linker for cancer treatments. In the orthotopic model, anti-TF ADC showed greater in vivo efficacy and more extended survival time control ADC. Treatment with anti-TF ADC (20 mg/kg, three times a week) did not affect mouse body weight changes in any in vivo experiment. Furthermore, immunofluorescence staining indicated that anti-TF ADC delivered agents not only to TF-positive tumor cells, but also to TF-positive tumor vascular endothelial cells and other tumor stromal cells. We conclude that anti-TF ADC should be a selective and potent drug for pancreatic cancer therapy.