ANTI-CANCER ENZYME PRODRUG THERAPY: using biocatalytic implants and long-acting prodrugs for local intervention

Research output: Book/anthology/dissertation/reportPh.D. thesisResearch

8.8 million individuals died from cancer worldwide in 2015 and the global cancer burden has been estimated to reach 20 million new incidences by 2025. Current treatments include systemic and local intervention using chemotherapies and drug eluting implants, which in many cases triggers severe side-effects due to systemic rather than local activity. Benefits of pill- and injection-based therapies include the opportunity to change drug type, drug dose or terminate treatment on-demand, whilst drug eluting implants offers local delivery. A combination of the two is not currently available for clinical use, yet is provided via enzyme prodrug therapy (EPT). EPT utilize enzymes at the target site for local activation of externally administered benign prodrugs. The enzymes can be both endogenous and overexpressed at pathological conditions, such as tumors, or introduced from external sources, e.g. via implants (also known as substrate mediated EPT or SMEPT). Employing EPT for anticancer intervention may offer local delivery as known from drug eluting implants and external control as known from pill- and injection-based approaches, thus provide a more flexible, potent and safer alternative to current treatments. This work presents the preclinical evaluation of biocatalytic electrospun fibers prepared from poly(vinyl alcohol) (PVA) and liposomal β-glucuronidase (β-Glu), calcium (Ca)-alginate beads armed for bi-enzymatic embolization cancer therapy and long-acting glucuronide anticancer prodrugs.
Liposomal encapsulation of β-Glu was shown to minimize enzymatic inactivation when exposed to cell culture media for at least 48 h. Approximately 61% proliferation inhibition of cervical cancer cells was achieved from biocatalytic fibers upon 48 h exposure with the glucuronide prodrug of SN-38 (anticancer), which matched that of pristine SN-38.
With high reproducibility, homogeneously shaped Ca-alginate beads were manufactured in sizes ranging from ~300 μm to ~ 2 mm. The beads were successfully employed for immobilization of β-Glu and β-galactosidase (β-Gal) for envisioned SMEPT-based multidrug emobolization therapy. Via this implantable SMEPT platform, it was possible to fine-tune the elution of drug type and dose, combine elution of multiple drugs in binary dose combinations and initiate or terminate treatment on-demand via externally administered prodrugs. Furthermore, anti-proliferative effects on human cervical cancer and hepatocellular carcinoma cells were achieved in a concentration- dependent manner via administration of SN-38 glucuronide prodrug (SN-38 Glu) that was converted to SN-38 (anticancer). With high relevance for intravascular implantation, biocatalytic beads were capable of inducing vasodilation of rat mesenteric arteries upon incubation with a nitric oxide (NO) donor, β-Gal NONOate.
Albumin is the most abundant plasma protein and has a half-life of 19-26 days in humans, where it serves as an endogenous transporter of fatty acids and other compounds. For these reasons albumin has been extensively studied as a drug delivery vehicle via covalent or non-covalent attachment approaches. Conjugation to poly(ethylene glycol) (PEG) is an alternative approach to obtain improved pharmacokinetics. For circulatory half-life extension of glucuronide prodrugs, which are normally rapidly excreted, the albumin ligand 1,2-distearoyl-sn-glycero-3- phosphoethanolamine (DSPE) or PEG was conjugated to the glucuronide prodrug of highly potent anticancer drug monomethyl auristatin E (MMAE) (DSPE-MMAE-Glu and PEG-MMAE-Glu). Evaluation of DSPE-MMAE-Glu in vitro demonstrated a dose- and time-dependent potency in the nanomolar range once combined with β-Glu, whilst it was 30- to 77-fold less toxic in the absence of enzyme. Preclinical assessment of DSPE- MMAE-Glu and PEG-MMAE-Glu was conducted in human breast cancer xenograft mice. PEG-MMAE-Glu demonstrated excellent inhibition of tumor growth after once weekly administrations as the only tested MMAE glucuronide. Glucuronide prodrugs of MMAE, however, were generally well tolerated, whilst administration of pristine MMAE were lethal in the therapeutically relevant doses.
In conclusion it is believed that adoption of EPT-based strategies in anticancer intervention may provide the sought-after therapeutic flexibility for envisioned implementation in for example SMEPT-based intravascular anticancer therapies or EPT- based intervention using endogenous enzymes for treating metastases.
Original languageEnglish
Number of pages141
Publication statusPublished - 2018

Note re. dissertation

Time: Monday, 22 October 2018 at 13.15<br/><br/>Place: Building 1532, room 116, Lecture Theatre G1, Department of Mathematics, Ny Munkegade 118, Aarhus University, 8000 Aarhus C.<br/><br/>Title of PhD thesis: Anti-cancer enzyme prodrug therapy using biocatalytic implants and long-acting prodrugs for local intervention<br/>

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