Conference Abstracts | aptamer-theranostics

Selected Conference Abstracts

12th International NanoMedicine Conference 2022

Developing a platform technology to cross the blood brain barrier and deliver drugs to specific populations

Bakhtiar Bukar1, 2, Breanna Giles1, 2,Joanna Macdonald1,2, Delphine Denoyer3,4, Ingrid Burvenich4,5, Normand Pouliot3,4,6, and Sarah Shigdar*1,2

1 School of Medicine Deakin University, Geelong, Victoria, 3216, Australia

2 Centre for Molecular and Medical Research, Deakin University, Geelong, Victoria, 3216, Australia

3 Matrix Microenvironment & Metastasis Laboratory, Olivia Newton John Cancer Centre Research Institute, Heidelberg, Melbourne, Victoria, 3084, Australia

4 School of Cancer Medicine, La Trobe University, Bundoora, Victoria, 3086 Australia

5 Tumour Targeting Laboratory, Olivia Newton-John Cancer Research Institute, Heidelberg, Melbourne, Victoria, 3084, Australia

6 Department of Pathology, The University of Melbourne, Parkville, Victoria, 3010, Australia

Prognosis for cancers of the brain, whether primary or metastasis, remains poor, even with advances in treatment for other cancers. This is due to the limited number of drugs that can cross the blood brain barrier (BBB). While methods of overcoming this barrier have been developed and employed with current treatment options, the majority are highly invasive and non-specific treatments, leading to severe neurotoxic side effects. A novel approach to address these issues is the development of therapeutics targeting receptor mediated transport mechanisms on the BBB endothelial cell membranes. We have developed aptamers as targeted delivery agents that can also cross the blood brain barrier. Aptamers are smaller than antibodies, and thus can more effectively deliver drugs into the tumour. Numerous studies have demonstrated that, despite theoretical implications of rapid renal clearance, nuclease degradation, and electrostatic repulsion, aptamers are effective agents for the delivery of cytotoxic agents. These agents can either be used as singular agents, or given their different mechanism of action and suggested lack of drug-drug interaction, alongside antibodies to have a greater efficacy against solid tumours. We have combined two aptamers for the targeted delivery of chemotherapeutics to brain metastases which can cross the blood brain barrier and also specifically target cancer cells. Using this approach, we intercalated doxorubicin into this bifunctional aptamer targeting the transferrin receptor on the blood brain barrier and epithelial cell adhesion molecule on the metastatic cells. The ability of the doxorubicin loaded aptamer to transcytose the blood brain barrier and selectively deliver the drug to epithelial cell adhesion molecule-positive tumours was evaluated in an in vitro model and confirmed for the first time in vivo. We show that co-localised aptamer and doxorubicin fluorescent signals are clearly detectable within the brain lesions 75 minutes post administration. Following a short treatment schedule, brain metastases were shown to decrease following bifunctional-aptamer-doxorubicin treatment, as compared to control or free drug. As well, metastases decreased in bone and ovaries following treatment. Collectively, the results from this study demonstrate that through intercalation of a cytotoxic drug into the bifunctional aptamer, a therapeutic delivery vehicle can be developed for the specific targeting of epithelial cell adhesion molecule-positive brain and systemic metastases. We are now investigating this technology against primary brain cancers with different aptamers targeting other cell surface receptors.

Joanna Macdonald, Delphine Denoyer, Justin Henri, Adelaide Jamieson, Ingrid J.G. Burvenich, Normand Pouliot, and Sarah Shigdar. Nucleic Acid Therapeutics.2020.117-128.

Lorne Cancer Conference 2020

Bifunctional aptamer-doxorubicin conjugate crosses blood brain barrier and selectively delivers payload to Epithelial Cell Adhesion Molecule positive tumour cells

Joanna Macdonald 1 2 , Justin Henri 1 , Adelaide Jamieson 1 , Delphine Denoyer 3 4 , Ingrid Burvenich 4 5 , Normand Pouliot 3 4 6 , Sarah Shigdar 1 2

1.School of Medicine, Deakin University, Geelong, VIC, Australia

2.Centre for Molecular and Medical Research, Deakin University, Geelong, VIC, Australia

3.Matrix Microenvironment and Metastasis Laboratory, Olivia Newton-John Cancer Research Institute, Melbourne, Vic, Australia

4.School of Cancer Medicine, La Trobe University, Melbourne, Vic, Australia

5.Tumour Targeting Laboratory, Olivia Newton John Cancer Research Institute, Melbourne, Vic, Australia

6.Department of Pathology and University of Melbourne, Melbourne, Vic, Australia

10th International NanoMedicine Conference 2019

Targeted drug delivery reduces systemic and brain metastases.

Joanna Macdonald1,2, Delphine Denoyer3,4, Ingrid Burvenich4,5, Normand Pouliot3,4,6, and Sarah Shigdar*1,2

1 School of Medicine Deakin University, Geelong, Victoria, 3216, Australia

2 Centre for Molecular and Medical Research, Deakin University, Geelong, Victoria, 3216, Australia

3 Matrix Microenvironment & Metastasis Laboratory, Olivia Newton John Cancer Centre Research Institute, Heidelberg, Melbourne, Victoria, 3084, Australia

4 School of Cancer Medicine, La Trobe University, Bundoora, Victoria, 3086 Australia

5 Tumour Targeting Laboratory, Olivia Newton-John Cancer Research Institute, Heidelberg, Melbourne, Victoria, 3084, Australia

6 Department of Pathology, The University of Melbourne, Parkville, Victoria, 3010, Australia

Prognosis for breast cancer patients diagnosed with brain metastases is poor, with survival time measured merely in months. This can largely be attributed to the limited treatment options capable of reaching the tumour as a result of the highly restrictive blood-brain barrier. While methods of overcoming this barrier have been developed and employed with current treatment options, the majority are highly invasive and non-specific treatments, leading to severe neurotoxic side effects. A novel approach to address these issues is the development of therapeutics targeting receptor mediated transport mechanisms on the BBB endothelial cell membranes. We have developed aptamers as targeted delivery agents that can also cross the blood brain barrier. Aptamers are smaller than antibodies, and thus can more effectively deliver drugs into the tumour. Numerous studies have demonstrated that, despite theoretical implications of rapid renal clearance, nuclease degradation, and electrostatic repulsion, aptamers are effective agents for the delivery of cytotoxic agents. These agents can either be used as singular agents, or given their different mechanism of action and suggested lack of drug-drug interaction, alongside antibodies to have a greater efficacy against solid tumours. We have combined two aptamers for the targeted delivery of chemotherapeutics to brain metastases which can cross the blood brain barrier and also specifically target cancer cells. Using this approach, we intercalated doxorubicin into this bifunctional aptamer targeting the transferrin receptor on the blood brain barrier and epithelial cell adhesion molecule on the metastatic cells. The ability of the doxorubicin loaded aptamer to transcytose the blood brain barrier and selectively deliver the drug to epithelial cell adhesion molecule-positive tumours was evaluated in an in vitro model and confirmed for the first time in vivo. We show that co-localised aptamer and doxorubicin fluorescent signals are clearly detectable within the brain lesions 75 minutes post administration. Following a short treatment schedule, brain metastases were shown to decrease following bifunctional-aptamer-doxorubicin treatment, as compared to control or free drug. As well, metastases decreased in bone and ovaries following treatment. Collectively, the results from this study demonstrate that through intercalation of a cytotoxic drug into the bifunctional aptamer, a therapeutic delivery vehicle can be developed for the specific targeting of epithelial cell adhesion molecule-positive brain and systemic metastases.

Functional Nucleic Acids 2018

Aptamer drug delivery to breast cancer brain metastases

Joanna Macdonald1, Justin Henri1, Michelle Bauer1, Emma Hays1, Rakesh Naduvile Veedu2,3, Normand Pouliot4,5,6, Sarah Shigdar1,7

1School of Medicine, Deakin University, Geelong, VIC 3128, Australia

2Centre for Comparative Genomics, Murdoch University, Perth, WA 6150, Australia

3Perron Institute for Neurological and Translational Science, Perth, WA 6009, Australia

4Department of Pathology and University of Melbourne, Melbourne, VIC 3010, Australia

5Sir Peter MacCallum Department of Oncology, University of Melbourne, Melbourne, VIC 3000, Australia

6Matrix Microenvironment and Metastasis Laboratory, Olivia Newton-John Cancer Research Institute, School of Cancer Medicine, La Trobe University, Heidelberg, VIC 3084, Australia

7Centre for Molecular and Medical Research, Deakin University, Geelong, VIC 3128, Australia

The epithelial cell adhesion molecule (EpCAM), or CD326, was one of the first cancer associated biomarkers to be discovered. In the last forty years, this biomarker has been investigated for use in personalized cancer therapy, with the first monoclonal antibody, edrecolomab, being trialled in humans more than thirty years ago. Since then, several other monoclonal antibodies have been raised to EpCAM and tested in clinical trials. However, while monoclonal antibody therapy has been investigated against EpCAM for almost 40 years as primary or adjuvant therapy, it has not shown as much promise as initially heralded. Aptamers are smaller than antibodies, and thus can more effectively deliver drugs into the tumour. Numerous studies have demonstrated that, despite theoretical implications of rapid renal clearance, nuclease degradation, and electrostatic repulsion, aptamers are effective agents for the delivery of cytotoxic agents. These agents can either be used as singular agents, or given their different mechanism of action and suggested lack of drug-drug interaction, alongside antibodies to have a greater efficacy against solid tumours. We have investigated both DNA and RNA aptamers for the targeting of EpCAM for specific delivery of chemotherapeutics to tumour cells both in vitro and in vivo. We have also combined two aptamers for the targeted delivery of chemotherapeutics to brain metastases and demonstrated their potential for future development as novel therapeutics. Using an animal model of breast cancer brain metastases, we have demonstrated drug uptake only in tumour cells in the brain, sparing healthy brain tissue. Work is ongoing to demonstrate efficacy in a small treatment trial.

Aptamers 2017

Treating brain metastases with a bifunctional aptamer

Joanna Macdonald, Justin Henri, Wei Duan, Sarah Shigdar

School of Medicine, Deakin University, Waurn Ponds, Australia, 3216

A quarter of all cancer patients will be diagnosed with metastatic brain cancer following primary malignancy treatment, and the prognosis for these patients is very poor. The treatment of these metastatic tumours is greatly hindered by the presence of the blood brain barrier which restricts the overwhelming majority of small molecules from entering the brain. A novel approach to overcome this barrier is to target receptor mediated transport mechanisms present on the endothelial cell membranes, in particular the transferrin receptor. Given their specificity, safety profile and stability, nucleic acid based therapeutics are ideal for this purpose. Therefore, in this study an aptamer targeting the transferrin receptor was fused with an aptamer that binds to epithelial cell adhesion molecule-expressing cancer cells. The initial fusion of the two sequences enhanced the binding affinity of both aptamers while maintaining specificity, which was confirmed through flow cytometry and confocal microscopy. Using an in vitro blood brain barrier model, the aptamers ability to transcytose the barrier and target a specific population of cells was confirmed through the implementation of a co-culture of EpCAM positive and negative cells. Additionally, we confirmed the aptamers ability to transcytose the blood brain barrier in a healthy mouse model as well as a xenograft model of triple negative breast cancer (MDA-MB-231-BR) following a single i.v. injection (40 nmol/kg). These promising results demonstrate that through the fusion of two aptamer sequences, a bi-functional aptamer can be generated which has the potential to be developed for the specific treatment of EpCAM positive brain metastases.

COGNO 2017

Targeting brain cancer metastases – a double targeted strategy for effective drug delivery

Joanna Macdonald, Justin Henri, Sarah Shigdar*

School of Medicine

Deakin University

Geelong, Victoria, Australia

Aims: Brain metastases occur in up to a quarter of all cancer patients following primary malignancy treatment, and the prognosis for these patients is very poor. The treatment of these metastatic tumours is greatly hindered by the presence of the blood brain barrier (BBB) which restricts the overwhelming majority of small molecules from entering the brain. A novel approach to overcome this is to target receptor mediated transport mechanisms present on the endothelial cell membranes, in particular the transferrin receptor. Given their specificity, safety profile and stability, nucleic acid based therapeutics are ideal for this purpose.

Methods: An aptamer targeting the transferrin receptor was fused with an aptamer that binds to a cell surface marker on breast cancer cells, the epithelial cell adhesion molecule (EpCAM), enhancing binding affinity of both aptamers while maintaining specificity, and confirmed through flow cytometry and confocal microscopy.

Results: Using an in vitro BBB model, the aptamer transcytosed the barrier and targeted only EpCAM positive cells in a co-culture of EpCAM positive and negative cell. This aptamer also specifically delivered doxorubicin across the in vitro BBB in a timely manner. In vivo, we confirmed the aptamer’s ability to transcytose the BBB in a healthy mouse model following a single i.v. injection (40 nmol/kg)1, and in an animal model of breast cancer brain metastases.

Conclusions: These promising results demonstrate that through the fusion of two aptamer sequences, a bi-functional aptamer can be generated which has the potential to be developed for the specific treatment of EpCAM positive brain metastases.

1st Functional Nucleic Acid Conference 2015

Targeted aptamer therapeutics for the treatment of brain metastases

Joanna Macdonald, Wei Duan & Sarah Shigdar

School of Medicine, Deakin University, Waurn Ponds, Geelong, Victoria, Australia

Survival rates for patients with brain cancer or brain metastases have shown only a slight increase over the last twenty years, due in part to the effectiveness of the blood brain barrier (BBB) at keeping toxic substances out of the brain. Novel approaches to breach this barrier include actively targeting a transporter, such as the transferrin receptor, on the BBB. However, once drugs enter the brain, a second active targeting mechanism is required to ensure the drugs reach their target cells – the tumour cells – and thus minimise cytotoxicity in healthy brain cells. Aptamers are easy to combine, due to their nucleic acid nature and thus, we have generated a bi-functional aptamer that binds two different targets, the transferrin receptor on the BBB and EpCAM, a marker of metastatic cancer cells. We confirmed the specificity and sensitivity of this aptamer using flow cytometry with a number of cell lines positive for either transferrin receptor or EpCAM. Additionally, we assessed the ability of this aptamer to transcytose into the brain using an in vitro model of the BBB. Successful transcytosis was confirmed via endocytosis into EpCAM positive cancer cells in the base of a transwell. The ability of the aptamer to transcytose in a living system was confirmed by tail vein injection of 2 nmoles of bifunctional aptamer. The results of this study confirm initial proof of concept that aptamers targeting the transferrin receptor can breech the BBB and be used as effective agents to deliver therapeutics into the brain.

1st Australian Neurodegeneration and Dementia Conference 2015

Crossing the blood brain barrier: a novel strategy targeting neurodegenerative disorders

J Macdonald, P Houghton, W Duan & S Shigdar

School of Medicine, Deakin University, Waurn Ponds, Geelong, Victoria, Australia

Neurodegenerative disorders such as Alzheimer’s and Parkinson’s disease are incurable and debilitating conditions. Affecting millions of people of worldwide, these conditions are becoming more prevalent due to increases in life expectancy. While symptoms can be lessened through pharmacological intervention, there remains no treatment available capable of slowing down or stopping the degeneration and death of neurons in the brain. Limited treatment options can largely be attributed to the restrictive nature of the blood brain barrier (BBB), which through its highly selective nature limits drug bioavailability. An emerging strategy to overcome this barrier is to target active transport mechanisms present on the BBB. Given its high expression levels, the transferrin receptor has been studied extensively for this purpose. While promising results have been produced using monoclonal antibodies, nucleic acid based aptamers have emerged as a superior alternative due to their increased stability, safety profile and minimal batch-to-batch variation. From this, we have engineered DNA aptamers specific for the transferrin receptor which can act as a transport system for the delivery of therapeutics across the BBB. Aptamer specificity and sensitivity against both transferrin positive and negative cells has been confirmed via flow cytometry. The ability of the aptamers to be efficiently internalised was established via confocal microscopy. Transcytosis across the BBB was initially confirmed in an in vitro model subsequent to testing in an in vivo model which confirmed specific internalization within 10 minutes of injection. The results from the study highlight the great potential these aptamers have to be developed for the delivery of therapeutic agents across the BBB for the treatment of neurodegenerative disorders.

The 2015 Alzheimer's Disease Congress

Novel therapeutic strategies to target Alzheimer’s disease

J Macdonald, P Houghton, W Duan & S Shigdar

School of Medicine, Deakin University, Waurn Ponds, Geelong, Victoria, Australia

Neurodegenerative disorders such as Alzheimer’s disease are becoming more prevalent due to longer life expectancies. While pharmacological treatments can temporarily improve symptoms, there are no treatments available that can slow or stop the malfunction and death of neurons in the brain. One of the major problems associated with the treatment of neurodegenerative disorders is bioavailability as the blood brain barrier (BBB) is exceptional at preventing drugs from crossing into the brain. Several strategies have been proposed, such as disrupting the integrity, or inhibiting the drug efflux pumps on the BBB. However, these techniques will also allow other toxic substances access to the brain leading to potentially devastating side effects. A novel strategy is to use active transport mechanisms present on the BBB to transcytose, or slingshot, drugs into the brain. The transferrin receptor has been studied extensively for its potential to serve as a high affinity target for the delivery of a variety of drug vehicles. Aptamers have emerged as an alternative to conventional antibodies due to their safety profile, increased stability and minimal batch-to-batch variation. Here we describe the generation of nucleic acid aptamers to the transferrin receptor suitable for in vivo delivery of therapeutics across the BBB. The transferrin receptor aptamers were truncated and their specificity and sensitivity was confirmed against both transferrin receptor positive and negative cell lines. Their ability to be internalised was confirmed using confocal microscopy and colocalisation studies confirmed a similar uptake to the transferrin antibody. Transcytosis across the BBB was tested in vitro, prior to in vivo testing in a mouse model. The results from this study confirm the potential for these aptamers to be utilised for therapeutic delivery of drugs across the BBB for the treatment of neurodegenerative disorders.

Aptamers 2015

Getting the brain to take its medicine

Joanna Macdonald, Wei Duan & Sarah Shigdar

School of Medicine, Deakin University, Waurn Ponds, Geelong, Victoria, Australia

Presenter(s): Dr Sarah Shigdar

Email: Sarah.Shigdar@deakin.edu.au

Survival rates for patients with brain cancer or brain metastases have increased only slightly in the last twenty years. This is partly due to the effectiveness of the blood brain barrier at keeping toxic substances out of the brain. Novel approaches to breach this barrier are now being investigated, including the use of actively targeting a transporter on the blood brain barrier. Transferrin is one such receptor that can be used to effectively ‘slingshot’ a cargo into the brain. However, once drugs enter the brain, in order to minimise cytotoxicity to the healthy brain cells, a second active targeting mechanism is required to ensure the drugs reach their target cells – the tumour cells. Aptamers are easy to combine, due to their nucleic acid nature and thus, we have generated a bi-functional aptamer that binds to two different targets, the transferrin receptor on the blood brain barrier and EpCAM, a marker of metastatic cancer cells. We confirmed the specificity and sensitivity of this aptamer using flow cytometry with a number of cell lines positive for either transferrin receptor or EpCAM. Additionally, we assessed the ability of this aptamer to transcytose into the brain using an in vitro model of the blood brain barrier. Successful transcytosis was confirmed via endocytosis into EpCAM positive cancer cells in the base of a transwell. The ability of the aptamer to transcytose in a living system was confirmed by tail vein injection of 2 nmoles of bifunctional aptamer. The results of this study confirm initial proof of concept that aptamers targeting the transferrin receptor can breech the blood brain barrier and be used as effective agents to deliver therapeutics into the brain.

Lorne Cancer Conference 2015

Targeting Triple Negative Breast Cancer Brain Metastases

Joanna Macdonald, Wei Duan, Sarah Shigdar

Schoool of Medicine, Deakin University, Waurn Ponds, Australia, 3216

Triple negative breast cancer (TNBC) relapses more frequently then hormone receptor-positive subtypes and is often associated with poor outcomes. This is due to the fact that TNBC is more likely to spread to the brain, where current management strategies do not drastically alter outcomes. Indeed the overall survival for patients with a diagnosis of brain metastases is 4.3 months. Therefore, there is an urgent requirement for better therapeutic strategies. Having generated chemical antibodies against the cell surface marker, EpCAM, we sought to functionalise this aptamer to target brain metastases. A recent development has shown that targeting the transferrin receptor on the blood brain barrier can transport molecules into the brain via receptor-mediated transcytosis. We have generated a chemical antibody to the transferrin receptor and demonstrated that it can indeed enter the brain in an in vivo mouse model. Indeed, this aptamer specifically entered the brain within 10 minutes of tail vein injection. We have attached a second chemical antibody, targeting EpCAM, to this transcytosing aptamer and confirmed its specificity and sensitivity using flow cytometry against transferrin receptor positive or negative cell lines, as well as EpCAM positive or negative cells lines. Furthermore, we have shown that it is specifically internalized via receptor-mediated endocytosis into MDA-MB-231 cells. As well, we have attached the common chemotherapeutic, doxorubicin, to this bi-functional aptamer, and demonstrated that it is specifically internalized within the targeted cells. These results demonstrate that this bi-functional aptamer-doxorubicin conjugate has potential for the specific targeting and treatment of brain metastases in TNBC patients. Moreover, by specifically targeting the cancer cells in the brain, this novel modality is likely to mitigate the neurotoxic effects of chemotherapeutic agents on the healthy brain tissue.

IABCR 2014

Robust detection of cell surface markers in paraffin embedded tissue: Use of chemical antibodies in the diagnosis of breast cancer

Sarah Shigdar & Wei Duan

Antibodies have proven to be effective in immunohistochemistry for the diagnosis of tumours and for the detection of cell surface markers prior to commencement of immunotherapy. However, batch-to-batch variation and cross-reactivity can limit their effectiveness. Chemical antibodies, also known as aptamers, are small pieces of DNA or RNA that are generated in a similar manner to antibodies – incubation with the target protein – and bind in exactly the same manner as antibodies via the ‘lock and key’ mechanism. Aptamers show very high specificity to their target and, as they are chemically synthesised, they can be easily derivatised with detection moieties at one or many pre-specified locations along their sequence, depending on the application. Having generated an aptamer targeting EpCAM, we tested its sensitivity in number of invasive ductal carcinoma cases using a chromogenic staining system, and showed that aptamers directed against EpCAM demonstrated superior sensitivity in paraffin embedded tissues. In a number of cases, conventional monoclonal antibodies failed to detect low levels of EpCAM in the breast tumour or the lymph node. This aptamer showed no non-specific staining or cross-reactivity and displayed a much more robust detection of EpCAM. Notably, sensitive staining was achieved in less than 15 minutes. From a clinic-pathological point of view, this has both prognostic and therapeutic significance, the latter due to the potential for immunotherapy trials. Results from EpCAM immunotherapy trials has been mixed, as there is currently no EpCAM antibody that is robust enough to be able to detect EpCAM expression in all pathological tissues. Therefore, the results from this study have important clinical significance for breast cancer diagnosis and suggest that aptamers have a promising future in the diagnostic laboratory.

Aptamers 2014

Aptamers as effective cancer stem cell targeting modalities

Sarah Shigdar, Dongxi Xiang, Wei Duan

Schoool of Medicine, Deakin University, Waurn Ponds, Australia, 3216

Aptamers are becoming known for their ability to replace other agents, such as antibodies, in diagnostic and therapeutic applications. Within cancer research, aptamers can be very versatile molecules, capable of being used for in vitro diagnostic applications, therapeutics and in vivo molecular imaging. Having generated an aptamer against the cancer cell marker, EpCAM, we sought to develop this aptamer into a smart drug delivery vehicle. Using a common chemotherapeutic, doxorubicin, we intercalated this drug into the stem of the aptamer and tested its effectiveness to prevent the formation of tumour spheres, an indication of metastatic ability. The number of spheres formed was much reduced and the spheres were significantly smaller. When cancer cells were treated ex vivo and then injected subcutaneously into mice, no mouse formed tumours, in contrast to those treated with free drug. Using an in vivo model of colon cancer, we have shown a significant reduction in tumour size following a 3 day treatment schedule. When the cells from these tumours were serially transplanted in additional mice, 80% of mice failed to form a tumour even when 1,000,000 cells were transplanted, proving that we have ‘knocked out’ the self-renewal and proliferative ability of these tumour cells. These results show the potential of our aptamer-doxorubicin conjugate to potentially eradicate all of the cells within a tumourous mass and prevent remission. Importantly, the results in this study were achieved using a 4-fold lower concentration of doxorubicin to that used in the clinical setting, suggesting that this targeted delivery system can reduce the detrimental side effects experienced by cancer patients. The combination of aptamers with conventional drugs will likely represent the next step in the arsenal against cancer.

Lorne Cancer Conference 2014

The new kid on the block – are aptamers more effective targeted therapeutics?

Sarah Shigdar, Dongxi Xiang, Tao Wang, Hadi Al Shamaileh, Wei Duan

Schoool of Medicine, Deakin University, Waurn Ponds, Australia, 3216

Aptamers are short single-stranded DNA or RNA sequences that fold into complex three-dimensional structures capable of binding to specific targets in the same manner as antibodies. Due to their small size, aptamers can penetrate tumourous masses at a much more effective rate than therapeutic antibodies. Having generated aptamers against two well recognised cancer cell surface markers, EpCAM and CD133, and shown that these aptamers are efficiently internalised via receptor-mediated endocytosis, we sought to functionalise these aptamers into targeted therapeutic agents. We intercalated a common chemotherapeutic, doxorubicin, into the stem of the aptamer and tested its effectiveness to prevent the formation of colorectal tumour spheres, an indication of metastatic ability. Both the sphere size and number were significantly smaller/reduced following treatment with our novel therapeutic. When HT29 colorectal cancer cells were treated ex vivo and injected subcutaneously into mice, no mouse formed tumours, in contrast to those treated with free drug. Additionally, following an in vivo three-day treatment schedule of HT29 xenograft tumour, we showed a significant reduction in tumour size. When the cells from these tumours were serially transplanted into additional mice, 80% of mice failed to form a tumour, even when 1,000,000 cells were transplanted, indicating that we have ‘knocked out’ the tumourigenic potential of these cancer cells. These results show the potential of our aptamer-doxorubicin conjugate to potentially eradicate the tumourgenic/cancer initiating cells within a tumourous mass, and prevent relapse. Importantly, the results in this study were achieved using a 4-fold lower concentration of doxorubicin to that used in the clinical setting, suggesting that this targeted delivery system could improve the therapeutic index of doxorubicin, and reduce the detrimental side effects experienced by cancer patients. Therefore, the combination of aptamers with conventional drugs will likely represent one of the new arsenals against cancer.