Tracey Bradshaw - Investigating in vivo efficacy of apoferritin-encapsulated antitumour benzothiazole 5F203 against human-derived breast cancer xenografts 2020 Pilot Grant
Lay summary
Background: Experimental prodrug 5F203 stops the growth of human breast cancers in the flask and in mice. It acts by a unique mechanism utilizing the tumours own ability to convert the compound to a potent agent that kills cancer cells selectively. However, it is not soluble and formulation for clinical use is a challenge. We have proposed that the protein capsule apoferritin would be an ideal drug delivery vehicle. Apoferritin is ferritin without its iron cargo. Ferritin carries iron around our bodies to cells in need of iron. Cancer cells need iron and increase the number of receptors recognizing ferritin. We are able (instead of iron) to load 5F203 into apoferritin and have shown that cancer cells, including different types of breast cancer cells are more sensitive to apoferritin-loaded 5F203 than prodrug alone. Apoferritin itself is harmless.
Aims: In this proposal, we aim to test whether apoferritin-loaded 5F203 kills human breast cancers when they are grown in mice.
Techniques and Methodology: Human breast tumours will be transplanted into mice. Mice will be treated with apoferritin alone, 5F203 alone and apoferritin-loaded 5F203. Cancer growth will be monitored throughout the experiment as will the wellbeing of the mice. Blood samples will also be taken. At the end of the experiment we will examine the tumours and vital organs to test whether the compound is cancer-selective and working in the way we propose.
Impact on breast cancer research: Experiments, if successful, will give us confidence that development of a new, cancer-selective breast cancer therapy is possible, that will have relevance in treatment of hormone/growth factor receptor-positive and -negative disease.
Scientific Summary
Background: 5F203 (Figure 1), a potent, selective experimental anticancer agent with a unique mechanism of action inhibits growth of certain breast cancer models in vitro (nanomolar potency) and in vivo. A high-affinity arylhydrocarbon receptor ligand, 5F203 induces its own CYP1A1-biotransformation to cytotoxic species. However, poor aqueous solubility and bioavailability present pharmaceutical challenges.Apoferritin represents a biocompatible drug delivery vehicle that is recognized by transferrin receptor-1 and favourably internalized by cancer cells. We have encapsulated ~ 70 molecules of 5F203/AFt cage demonstrating potent growth inhibition in 5F203-sensitive breast cancer cells lines.
Aims: We aim to test the hypothesis that AFt-5F203 inhibits the growth of breast cancer xenografts in vivo. We aim to establish whether AFt represents a viable drug delivery system that may potentiate 5F203 efficacy and minimize systemic drug exposure.
Techniques and Methodology: We have optimized AFt-5F203 encapsulation, and demonstrated in vitro activity.Herein we will prepare AFt-5F203 and confirm its activity by MTT and clonogenic assays, before breast cancer xenografts (e.g. MCF-7, MDA-MB-468) are established in immunodeficient mice. Mice will be treated (i.v.) with AFt-5F203 at efficacious 5F203 doses and tolerability determined before efficacy studies are undertaken. Mice behaviour and weight as well as tumour growth will be monitored. At termination, tumours, lungs and livers will be snap frozen for pharmacodynamic biomarker analyses (CYP1A1; H2AX expression)
Impact on breast cancer research: Two areas of novelty are represented in this research: an experimental antitumour compound with distinct molecular targets and mechanism of action, delivered to tumours in a bioacompatible formulation – potentially amenable for AFt-delivery of other (therapeutic, imaging, diagnostic) agents. Proof of concept of in vivo 5F203 delivery would pave the way for AFt-encapsulation and delivery of multiple agents, aswell as development of targeted AFt- formulations to treat mammary carcinomas.
Research Update - 10th February 2025
What specific achievements were made possible through your pilot grant award?The proposal sought to encapsulate 5F 203 (Figure 1A) within Apoferritin (AFt) nano-sized protein cages. This was achieved. Table 1 and Figure 2 summarise AFt-5F 203 encapsulation and characterisation. In vivo, the tolerability and biocompatibility of this drug delivery vehicle was confirmed. The protein cage alone had no effect on animal weight or behaviour. It also did not impact tumour growth. The proposal sought to grow human-derived breast tumour xenografts in mice. Oestrogen receptor positive (ER+) MCF-7 human-derived tumours were grown subcutaneously (s.c.) and orthotopically – within the mammary fat pads (MFP) of R2G2 mice (Figure 3A). We sought to determine whether AFt-5F 203 is safe to administer and tolerated by the mice. No changes in animal behaviour were reported; weight loss was not significant following treatment of mice with AFt-5F 203. We sought also to examine in vivo tumour growth inhibitory potential of AFt-5F 203. Thus, the efficacy of 5F 203 prodrug Phortress (Figure 1B) was compared with the efficacy of AFt-encapsulated 5F 203. Phortress underwent phase 1 clinical evaluation under the auspices of CRUK. Despite no breast cancer patients being recruited to the trial, stable disease was achieved in ~30% patients – including those patients with renal, lung and colorectal carcinomas. Both Phortress and AFt-5F 203 can be administered i.v. Modest antitumour efficacy (MFP tumour growth inhibition) equivalent to Phortress was achieved with AFt-5F 203 (Figure 3B). Therefore, we conclude that AFt-5F 203 is safe, tolerated and modestly inhibits MFP MCF-7 tumour growth. Further preclinical evaluation is warranted to optimise treatment schedules, examine activity in other breast cancer models and phenotypes and investigate antitumour pharmacology.
How has NBCRC membership benefitted your research and career?Collaboration between colleagues at The University of Nottingham has been facilitated, as well as knowledge-sharing through NBCRC seminars.
Could you provide a brief update on your current research progress?Current research focusses on development of safe, cancer-selective theranostic agents for breast (and other e.g. brain) cancers. We have significant in vitro evidence of cancer-selectivity – a consequence of AFt-recognition by transferrin receptors, highly expressed (and upregulated) on the membranes of cancer cells leading to endocytosis of AFt-encapsulated cargo. Further preclinical research is required to corroborate translation of this effect in vivo. Current research corroborates the cancer-selectivity, biocompatibility, tolerability of the AFt nanodelivery system, and also demonstrates the ability of AFt delivery to overcome certain mechanisms of inherent or acquired drug resistance. We have recently received a UKRI Engineering Biology award (PI Prof. Neil Thomas; Co-Is DR Tracey Bradshaw, Dr Lyuda Turyanska) to develop, evaluate and optimise engineered AFt protein cages for targeted delivery and intracellular cargo release. AFt cages with HER2 or EGFR1 affibodies conjugated to heavy or light chains are being developed to target (e.g.) HER2+ breast or EGFR+ glioma cancers respectively. Encapsulated within the protein cages will be clinical or experimental anticancer therapeutic agents as well as lead sulfide quantum dots to image and diagnose malignant tissue. Thus, our current research focusses on development of theranostic and therapeutic cancer-targeting AFt delivery systems for breast and brain cancers.