Modification of the cell-penetrating peptide PepFect14 for targeted tumor gene delivery and reduced toxicity

Abstract

Viimastel aastakümnetel on geeniteraapia alal toimunud olulised edasiminekud, mis on teinud võimalikuks haiguste ravimise geenitasandil vigast geeni asendades või selle ekspressiooni maha surudes. Terapeutilistel eesmärkidel kasutatavad nukleiinhappe molekulid nagu DNA ja RNA peavad efekti saavutamiseks rakkude sisse pääsema, kuid ei suuda seda iseseisvalt oma suurte mõõtmete ja kõrge negatiivse laengu tõttu teha. Seetõttu on nukleiinhapete rakku transportimiseks vaja kasutada transportvektoreid. Üheks transportvektorite tüübiks on rakku sisenevad peptiidid (RSP), mis seonduvad nukleiinhapetega ning suudavad need läbi rakumembraani toimetada. Samas on RSPd sageli mittespetsiifilised ning võivad omada toksilisi efekte. Just neid probleeme on antud doktoritöös käsitletud. Esiteks modifitseeriti RSPe, et suurendada nende kasvajaspetsiifilisust ning vähendada mittespetsiifilist kogunemist kudedesse nagu kops ja maks. Selle saavutamiseks kinnitati RSP külge polüetüleenglükooli (PEG) molekul, mis vähendab mittespetsiifilisi interaktsioone RSP/nukleiinhappe osakeste ja rakkude vahel. PEG molekul lisati RSPle kasvajatundliku vahelüli kaudu, mis tähendab, et PEG eemaldatakse RSP küljest alles kasvaja ümbruses, mille toimel RSP aktiveerub ning toimetab endaga seotud nukleiinhappe ümbritsevatesse kasvajarakkudesse. Seda kasvajaspetsiifilist RSP rakendati ka terapeutilise nukleiinhappe transpordiks hiire kasvajamudelis, et hinnata, kas loodud RSP/nukleiinhappe süsteem suudab kasvaja kasvukiirust vähendada. Teiseks uuriti RSP/nukleiinhappe osakeste valmistamise strateegia ning laengutiheduse ja hüdrofoobsuse modifitseerimise mõju RSP toksilisusele. Kokkuvõtteks tehti selle doktoritöö käigus RSPdele spetsiiflisi modifikatsioone, millega on võimalik suurendada nende kasvajaspetsiifilisust ja vähendada toksilisust. Neid disainipõhimõtteid on võimalik edaspidi rakendada ka uute ja turvalisemate RSPde disainil.

The advancement of gene technology has made it possible to connect malfunctioning genes with certain illnesses. This has led to the realization, that if we could “fix” these genes, we could also cure the disease at its root. This treatment strategy is called gene therapy, and it uses nucleic acids like DNA and RNA, as therapeutic agents. Those nucleic acid molecules have to get inside cells to be effective, but can’t cross the cell membranes by themselves because of their large size and high negative charge. For this reason, gene delivery vectors are needed to transport nucleic acids into cells. One type of gene delivery vectors are called cell penetrating peptides (CPPs). These are short peptides that bind to nucleic acids and are capable of delivering them across the cell membrane. However, many cell penetrating peptides tend to be non-specific, and exhibit acute toxic effects. These problems are addressed in the work presented in this dissertation, where the focus was on exploring different strategies to improve the safety and tissue specificity of cell penetrating peptides. First, the CPPs were modified to increase tumor specificity and reduce accumulation in non-targeted tissues like the liver and lung. This was done by introducing the hydrophilic polymer polyethylene glycol (PEG) to the CPPs which decreases non-specific interactions of the particles with cells. The PEG chain was introduced to the CPP in a tumor sensitive manner, meaning that the PEG is removed specifically in the tumor tissue, leading to CPP activation and delivery of the nucleic acid cargo into surrounding tumor cells. This tumor specific CPP was also used to deliver therapeutic nucleic acids to tumor bearing mice to confirm they are capable of reducing tumor growth. Secondly, the strategies of forming CPP/nucleic acid particles, changing cationic charge density and hydrophilicity were investigated in the context of decreasing acute toxicity of the peptide. To conclude, we saw that specific modifications can be introduced to CPPs to increase their tumor specificity and reduce acute toxicity, and these principles can be applied for the design of new safer and more efficient CPPs.