An optimized integrin α6-targeted peptide for positron emission tomography/magnetic resonance imaging of pancreatic cancer and its precancerous lesion

An optimized integrin α6-targeted peptide capable of delivering toxins for melanoma treatment

BACKGROUND

Peptide-based therapeutics for melanoma have received increasing attention in medical research. However, the local delivery of such therapeutics poses unique challenges. Cell-penetrating peptides (CPPs) with the ability to selectively enter cancer cells, with sufficient stability and increased endosomal escape mechanisms, can provide a new and improved delivery strategy for therapeutic agents for treating cancer.

METHODS

We developed a new combination strategy for the synthesis of penetrating peptides functionalized with targeting of integrin α6. The linear peptide S5 was multimerized with 4 copies in linear sequential order spaced by GSG between each copy to yield the 4S5 peptide. The multimerized 4S5 peptide coupled with an intracellular delivery peptide (N) and endosomal escape peptide (G) was separated by a GGS spacer. This optimized peptide was called 4S5NG. The 4S5NG, EGFP or PE24 peptide-protein conjugates were purified via a C-terminal His-tag. The uptake efficacy, intracellular distribution and integrin α6-targeting ability of these 4S5NG peptides were systematically characterized via IncuCyte, flow cytometry and in vivo imaging using 4S5NG-Cy5 or 4S5NG-EGFP. Moreover, 4S5NG-incorporated Pseudomonas aeruginosa (PE24) exotoxin A generated therapeutic peptides. The antitumor efficacy and underlying mechanism were studied in cell lines and a mouse model. In addition, the effect of 4S5NG-PE24 on antitumor immunity of a healthy immune system was investigated via a mouse model.

RESULTS

Images of living cells and mice indicated that 4S5NG accumulated at tumor sites in vitro and in vivo and was much more effective than the S5 and 4S5 peptides. 4S5NG-PE24 induced cell pyroptosis in integrin α6-expressing melanoma through the caspase 3/gasdermin E (GSDME) signaling pathway in the absence of histological alterations in other organs. 4S5NG-PE24 also promoted the response rate of programmed cell death protein-1 (PD-1) checkpoint blockade to increase antitumor efficacy.

CONCLUSIONS

Collectively, these results highlight the potential use of 4S5NG to deliver the toxin PE24 to selectively eliminate integrin α6+ cells in melanoma, which may represent a novel treatment approach for melanoma patients.

Integrin α6 Targeted Near Infrared Fluorescent Imaging and Photoacoustic Imaging of Hepatocellular Carcinoma in Mice

BACKGROUND AND AIMS

Hepatocellular carcinoma (HCC) is the fourth most common cause of cancer-related death and ranks sixth in terms of incident cases worldwide. The purpose of this study was to develop an effective and sensitive method to distinguish liver cancer tissues from normal tissues in HCC patients. Integrin α6 is a promising cell surface target for molecular imaging of HCC, where it is overexpressed and is a prognostic biomarker. We previously identified an integrin α6-targeted peptide CRWYDENAC (RWY) that has been used for positron emission tomography (PET) imaging of HCC in mouse models.

METHODS

We labeled the integrin α6-targeted RWY peptide with cyanine 7 (Cy7) to form an optical probe (Cy7-RWY) for near infrared fluorescent (NIRF) and photoacoustic (PA) imaging in HCC. Mice transplanted with subcutaneous HCC-LM3 or orthotopic HCC-H22 cells that overexpressed integrin α6 were intravenously injected with Cy7-RWY and its corresponding Cy7-control. NIRF and PA images of mice were collected from 0 to 48 h after injection.

RESULTS

Both NIRF and PA signals started to accumulate in the tumor 2 h after injection of Cy7-RWY and peaked at 24 h.

CONCLUSIONS

Cy7-RWY is a promising optical probe for NIRF and PA imaging of HCC in mice, and has potential clinical application for HCC detection.

Integrin α6-Targeted Molecular Imaging of Central Nervous System Leukemia in Mice

Central nervous system leukemia (CNS-L) is caused by leukemic cells infiltrating into the meninges or brain parenchyma and remains the main reason for disease relapse. Currently, it is hard to detect CNS-L accurately by clinically available imaging models due to the relatively low amount of tumor cells, confined blood supply, and the inferior glucose metabolism intensity. Recently, integrin α6-laminin interactions have been identified to mediate CNS-L, which suggests that integrin α6 may be a promising molecular imaging target for the detection of CNS-L. The acute lymphoblastic leukemia (ALL) cell line NALM6 stabled and transfected with luciferase was used to establish the CNS-L mouse model. CNS-L-bearing mice were monitored and confirmed by bioluminescence imaging. Three of our previously developed integrin α6-targeted peptide-based molecular imaging agents, Cy5-S5 for near-infrared fluorescence (NIRF), Gd-S5 for magnetic resonance (MR), and ¹⁸F-S5 for positron emission tomography (PET) imaging, were employed for the molecular imaging of these CNS-L-bearing mice. Bioluminescence imaging showed a local intensive signal in the heads among CNS-L-bearing mice; meanwhile, Cy5-S5/NIRF imaging produced intensive fluorescence intensity in the same head regions. Moreover, Gd-S5/MR imaging generated superior MR signal enhancement at the site of meninges, which were located between the skull bone and brain parenchyma. Comparatively, MR imaging with the clinically available MR enhancer Gd-DTPA did not produce the distinguishable MR signal in the same head regions. Additionally, ¹⁸F-S5/PET imaging also generated focal radio-concentration at the same head regions, which generated nearly 5-times tumor-to-background ratio compared to the clinically available PET radiotracer ¹⁸F-FDG. Finally, pathological examination identified layer-displayed leukemic cells in the superficial part of the brain parenchyma tissue, and immunohistochemical staining confirmed the overexpression of the integrin α6 within the lesion. These findings suggest the potential application of these integrin α6-targeted molecular imaging agents for the accurate detection of CNS-L.

Photodynamic Therapy for Pancreatic Ductal Adenocarcinoma

Simple Summary

Pancreatic ductal adenocarcinoma (PDAC) is among the most lethal of human cancers. Numerous clinical trials evaluating various combinations of chemotherapy and targeted agents and radiotherapy have failed to provide meaningful improvements in survival. A growing number of studies however have indicated that photodynamic therapy (PDT) may be a viable approach for treatment of some pancreatic tumors. PDT, which uses light to activate a photosensitizing agent in target tissue, has seen widespread adoption primarily for dermatological and other applications where superficial light delivery is relatively straightforward. Advances in fiber optic light delivery and dosimetry however have been leveraged to enable PDT even for challenging internal sites, including the pancreas. The aim of this article is to help inform future directions by reviewing relevant literature on the basic science, current clinical status, and potential challenges in the development of PDT as a treatment for PDAC.

Abstract

Pancreatic ductal adenocarcinoma (PDAC) is among the most lethal of human cancers. Clinical trials of various chemotherapy, radiotherapy, targeted agents and combination strategies have generally failed to provide meaningful improvement in survival for patients with unresectable disease. Photodynamic therapy (PDT) is a photochemistry-based approach that enables selective cell killing using tumor-localizing agents activated by visible or near-infrared light. In recent years, clinical studies have demonstrated the technical feasibility of PDT for patients with locally advanced PDAC while a growing body of preclinical literature has shown that PDT can overcome drug resistance and target problematic and aggressive disease. Emerging evidence also suggests the ability of PDT to target PDAC stroma, which is known to act as both a barrier to drug delivery and a tumor-promoting signaling partner. Here, we review the literature which indicates an emergent role of PDT in clinical management of PDAC, including the potential for combination with other targeted agents and RNA medicine.

An Optimized Integrin α6-Targeted Magnetic Resonance Probe for Molecular Imaging of Hepatocellular Carcinoma in Mice

Introduction

Integrin α6 is an attractive diagnostic biomarker for molecular imaging of hepatocellular carcinoma (HCC) as it has an extremely high positive rate (approximately 94%) in clinical early-stage HCC. In this study, based on our previously identified integrin α6-targeted peptide, we developed an optimized integrin α6-targeted magnetic resonance (MR) probe dubbed DOTA(Gd)-ANADYWR for MR imaging of HCC in mice.

Materials and Methods

The longitudinal (R₁) relaxivity of DOTA(Gd)-ANADYWR was measured on a 3.0 T MR system . The specific tumor enhancement of the agent was investigated in four distinct mouse models, including subcutaneous, orthotopic, genetically engineered and chemically induced HCC mice.

Results

The R₁ relaxivity value of DOTA(Gd)-ANADYWR is 5.11 mM⁻¹s⁻¹ at 3.0 T, which is similar to that of the nonspecific clinical agent Gadoteridol. DOTA(Gd)-ANADYWR generated superior enhanced MR signal in HCC lesions and provided complementary enhancement MR signals to the clinically available hepatobiliary MR contrast agent gadoxetate disodium (Gd-EOB-DTPA). Importantly, DOTA(Gd)-ANADYWR could efficiently visualize small HCC lesion (approximately 1 mm) which was hardly detected by the clinical Gd-EOB-DTPA.

Conclusion

These findings suggest the potential application of this integrin α6-targeted MR probe for the detection of HCC, particularly for small HCC.