Platelet-delivered therapeutics

Targeting cargo to an unconventional secretory system within megakaryocytes allows the release of transgenic proteins from platelets

BACKGROUND

Platelets are essential for hemostasis and thrombosis and play vital roles during metastatic cancer progression and infection. Hallmarks of platelet function are activation, cytoskeletal rearrangements, and the degranulation of their cellular contents upon stimulation. While α-granules and dense granules are the most studied platelet secretory granules, the dense tubular system (DTS) also functions as a secretory system for vascular thiol isomerases. However, how DTS cargo is packaged and transported from megakaryocytes (MKs) to platelets is poorly understood.

OBJECTIVES

To underpin the mechanisms responsible for DTS cargo transport and leverage those for therapeutic protein packaging into platelets.

METHODS

A retroviral expression system combined with immunofluorescence confocal microscopy was employed to track protein DTS cargo protein disulfide isomerase fused to enhanced green fluorescent protein (eGFP-PDI) during platelet production. Murine bone marrow transplantation models were used to determine the release of therapeutic proteins from platelets.

RESULTS

We demonstrated that the endoplasmic reticulum retrieval motif Lys-Asp-Glu-Leu (KDEL) located at the C-terminus of protein disulfide isomerase was essential for the regular transport of eGFP-PDI-containing granules. eGFP-PDIΔKDEL, in which the retrieval signal was deleted, was aberrantly packaged, and its expression was upregulated within clathrin-coated endosomes. Finally, we found that ectopic transgenic proteins, such as tissue factor pathway inhibitor and interleukin 2, can be packaged into MKs and proplatelets by adding a KDEL retrieval sequence.

CONCLUSION

Our data corroborate the DTS as a noncanonical secretory system in platelets and demonstrate that in vitro-generated MKs and platelets may be used as a delivery system for transgenic proteins during cellular therapy.

Platelet-targeted gene therapy induces immune tolerance in hemophilia and beyond

Blood platelets have unique storage and delivery capabilities. Platelets play fundamental roles in hemostasis, inflammatory reactions, and immune responses. Beyond their functions, platelets have been used as a target for gene therapy. Platelet-targeted gene therapy aims to deliver a sustained expression of neo-protein in vivo by genetically modifying the target cells, resulting in a cure for the disease. Even though there has been substantial progress in the field of gene therapy, the potential development of immune responses to transgene products or vectors remains a significant concern. Of note, multiple preclinical studies using platelet-specific lentiviral gene delivery to hematopoietic stem cells in hemophilia have demonstrated promising results with therapeutic levels of neo-protein that rescue the hemorrhagic bleeding phenotype and induce antigen-specific immune tolerance. Further studies using ovalbumin as a surrogate protein for platelet gene therapy have shown robust antigen-specific immune tolerance induced via peripheral clonal deletions of antigen-specific CD4- and CD8-T effector cells and induction of antigen-specific regulatory T (Treg) cells. This review discusses platelet-targeted gene therapy, focusing on immune tolerance induction.

Targeting transgenic proteins to alpha granules for platelet-directed gene therapy

Platelets are anucleate blood cells that are shed from megakaryocytes (MKs) into the bloodstream to maintain hemostasis and promote wound healing after vascular injury. To carry out their functions, platelets become activated and release bioactive substances from their secretory granules. As alpha granules (αGs) in resting platelets store proteins and release them only after activation, the packaging of proteins into αGs is an attractive strategy to deliver therapeutic proteins. Here, we propose an adjustable model for targeting transgenic proteins to platelet αGs using third-generation self-inactivating lentiviral vectors. The vectors express from the murine platelet factor 4 promoter (mPf4P), restricting transgene expression to the MK lineage. For the delivery and retention of expressed proteins in αGs, proteins are fused to short peptide sorting signals derived from the human cytokine RANTES or from the transmembrane protein P-selectin. We demonstrate effective targeting of GFP to αGs of murine and human in vitro-differentiated MKs and murine platelets in vivo. Furthermore, interferon-α (IFNα), as a potentially therapeutic cytokine, was successfully delivered to and stored in murine platelets in vivo, was released after activation, and inhibited virus replication in vitro. Our vectors create possibilities for numerous applications in cell therapy utilizing platelets as carriers of therapeutic proteins.

Pancreatic Cancer and Platelets Crosstalk: A Potential Biomarker and Target

Platelets have been recognized as key players in hemostasis, thrombosis, and cancer. Preclinical and clinical researches evidenced that tumorigenesis and metastasis can be promoted by platelets through a wide variety of crosstalk between cancer cells and platelets. Pancreatic cancer is a devastating disease with high morbidity and mortality worldwide. Although the relationship between pancreatic cancer and platelets in clinical diagnosis is described, the interplay between pancreatic cancer and platelets, the underlying pathological mechanism and pathways remain a matter of intensive study. This review summaries recent researches in connections between platelets and pancreatic cancer. The existing data showed different underlying mechanisms were involved in their complex crosstalk. Typically, pancreatic tumor accelerates platelet aggregation which forms thrombosis. Furthermore, extracellular vesicles released by platelets promote communication in a neoplastic microenvironment and illustrate how these interactions drive disease progression. We also discuss the advantages of novel model organoids in pancreatic cancer research. A more in-depth understanding of tumor and platelets crosstalk which is based on organoids and translational therapies may provide potential diagnostic and therapeutic strategies for pancreatic cancer progression.

Multifaceted Functions of Platelets in Cancer: From Tumorigenesis to Liquid Biopsy Tool and Drug Delivery System

Platelets contribute to several types of cancer through plenty of mechanisms. Upon activation, platelets release many molecules, including growth and angiogenic factors, lipids, and extracellular vesicles, and activate numerous cell types, including vascular and immune cells, fibroblasts, and cancer cells. Hence, platelets are a crucial component of cell-cell communication. In particular, their interaction with cancer cells can enhance their malignancy and facilitate the invasion and colonization of distant organs. These findings suggest the use of antiplatelet agents to restrain cancer development and progression. Another peculiarity of platelets is their capability to uptake proteins and transcripts from the circulation. Thus, cancer-patient platelets show specific proteomic and transcriptomic expression patterns, a phenomenon called tumor-educated platelets (TEP). The transcriptomic/proteomic profile of platelets can provide information for the early detection of cancer and disease monitoring. Platelet ability to interact with tumor cells and transfer their molecular cargo has been exploited to design platelet-mediated drug delivery systems to enhance the efficacy and reduce toxicity often associated with traditional chemotherapy. Platelets are extraordinary cells with many functions whose exploitation will improve cancer diagnosis and treatment.

Enhancing therapeutic efficacy of in vivo platelet-targeted gene therapy in hemophilia A mice

Our previous studies demonstrated that intraosseous (IO) infusion of lentiviral vectors (LVs) carrying a modified B domain-deleted factor VIII (FVIII) transgene driven by a megakaryocyte-specific promoter (GP1Bα promoter; G-F8/N6-LV) successfully transduced hematopoietic stem cells (HSCs) to produce FVIII stored in the platelet α-granules. Platelet FVIII corrected the bleeding phenotype with limited efficacy in hemophilia A (HemA) mice with and without preexisting anti-FVIII inhibitors. The present study sought to further enhance the therapeutic efficacy of this treatment protocol by increasing both the efficiency of LV transduction and the functional activity of platelet FVIII. A combined drug regimen of dexamethasone and anti-CD8α monoclonal antibody enhanced the percentage of transduced bone marrow and HSCs over time. In G-F8/N6-LV-treated HemA mice, significant improvement in phenotypic correction was observed on day 84. To improve platelet FVIII functionality, genes encoding FVIII variant F8X10K12 with increased expression or F8N6K12RH with increased functional activity compared with F8/N6 were incorporated into LVs. Treatment with G-F8X10K12-LV in HemA mice produced a higher level of platelet FVIII but induced anti-FVIII inhibitors. After treatment with combined drugs and IO infusion of G-F8/N6K12RH-LV, HemA mice showed significant phenotypic correction without anti-FVIII inhibitor formation. These results indicate that new human FVIII variant F8/N6K12RH combined with immune suppression could significantly enhance the therapeutic efficacy of in vivo platelet-targeted gene therapy for murine HemA via IO delivery. This protocol provides a safe and effective treatment for hemophilia that may be translatable to and particularly beneficial for patients with preexisting inhibitory antibodies to FVIII.

Platelet for drug delivery

Platelets play a vital physiological role in hemostasis, inflammation and tissue regeneration, which are associated with wound healing as well as cancer development and metastasis. These years, a variety of platelet-mediated drug delivery approaches have been developed due to their unique properties, such as quick replenishment and site-specific activation/adhesion. In this Current Opinion, focuses are put on strategies leveraging the physiological functions of platelets for the design of drug delivery systems, including platelet engineering, platelet hitchhiking, membrane coating, synthetic platelet fabrication and platelet-triggered drug release for different applications.

Randomized Phase III Trial of Standard Therapy Plus Low Molecular Weight Heparin in Patients With Lung Cancer: FRAGMATIC Trial

PURPOSE

Venous thromboembolism (VTE) is common in cancer patients. Evidence has suggested that low molecular weight heparin (LMWH) might improve survival in patients with cancer by preventing both VTE and the progression of metastases. No trial in a single cancer type has been powered to demonstrate a clinically significant survival difference. The aim of this trial was to investigate this question in patients with lung cancer.

PATIENTS AND METHODS

We conducted a multicenter, open-label, randomized trial to evaluate the addition of a primary prophylactic dose of LMWH for 24 weeks to standard treatment in patients with newly diagnosed lung cancer of any stage and histology. The primary outcome was 1-year survival. Secondary outcomes included metastasis-free survival, VTE-free survival, toxicity, and quality of life.

RESULTS

For this trial, 2,202 patients were randomly assigned to the two treatment arms over 4 years. The trial did not reach its intended number of events for the primary analysis (2,047 deaths), and data were analyzed after 2,013 deaths after discussion with the independent data monitoring committee. There was no evidence of a difference in overall or metastasis-free survival between the two arms (hazard ratio [HR], 1.01; 95% CI, 0.93 to 1.10; P = .814; and HR, 0.99; 95% CI, 0.91 to 1.08; P = .864, respectively). There was a reduction in the risk of VTE from 9.7% to 5.5% (HR, 0.57; 95% CI, 0.42 to 0.79; P = .001) in the LMWH arm and no difference in major bleeding events but evidence of an increase in the composite of major and clinically relevant nonmajor bleeding in the LMWH arm.

CONCLUSION

LMWH did not improve overall survival in the patients with lung cancer in this trial. A significant reduction in VTE is associated with an increase in clinically relevant nonmajor bleeding. Strategies to target those at greatest risk of VTE are warranted.