Katherine Vallis, Professor of Experimental Radiotherapeutics at the University of Oxford’s Department of Oncology, has been awarded new funding from the MRC for her project concerning the use of cell-permeant antibodies for the treatment of acute leukaemia.
The MRC Developmental Pathway Gap Fund aims to support projects that will fill in critical evidence gaps to inform the development of novel therapeutics, devices, or diagnostic tools. The funding will allow Prof. Vallis and her team to generate in vivo data on the use of cell-penetrating peptides (CPPs) for cancer applications, a crucial step towards clinical translation.
The challenge of ‘undruggable’ proteins
It has been estimated that 85% of human proteins are ‘undruggable’ due to their location, structure, or mechanism of action. While great strides have been made in the development of novel small molecules and immunotherapeutic agents for cancer treatment, many putative targets remain unexploited. Intracellular proteins that lack binding pockets or have large protein-protein interaction interfaces are often considered undruggable, as small molecules can’t bind to them. Targeting these proteins is a key challenge in cancer research that requires the development of innovative technologies.
Antibodies are well suited to meet this need, as they are highly specific and don’t require a binding pocket to attach to their target. However, their large size prevents them from entering cells. Designing methods for the intracellular delivery of antibodies is of great interest to researchers in cancer medicine, but lack of efficacy and toxicity concerns associated with existing delivery vehicles has hindered progress.
The promise of cell-penetrating peptides
Prof. Vallis and her team previously reported the development of highly efficient CPPs that successfully transported functional antibodies into live cancer cells.
Antibody internalisation using a trimeric cell-penetrating peptide. The CPP facilitates cellular uptake and endosomal escape, enabling targeting of cytoplasmic and nuclear proteins.
The innovative trimeric structure set these CPPs apart from previously developed monomers. The team observed that CPPs naturally cluster together to cross the cell membrane more efficiently, inspiring them to design CPP trimers on a novel chemical scaffold. This enhanced delivery efficiency rendered the CPPs functional at concentrations low enough (<1μM) to be achievable in vivo.
Once across the membrane, intracellular antibodies face another major obstacle: entrapment in the endosome. Endosomal entrapment has long been a key challenge in intracellular targeting. However, the CPP trimers developed by the team showed promising endosomal release properties.
"CPP trimer/antibody combinations could increase the treatment options of patients whose cancers are not treatable with standard drugs and could reduce damage to healthy cells, delivering ‘kinder’ treatments with fewer unwanted side effects" - Katherine Vallis
Next steps: in vivo testing
Katherine Vallis - Professor of Experimental RadiotherapeuticsGenerating in vivo data is an important next step in the development of these CPPs towards clinical use. In collaboration with Terence Rabbitts, Professor of Molecular Immunology at the Institute of Cancer Research, London, Prof. Vallis and her team will test the CPPs in mouse models of T-cell acute lymphoblastic leukaemia (T-ALL), a rare and aggressive blood cancer most commonly affecting young children. They will assess the ability of the CPPs to internalise single-chain variable fragments targeting LMO2, an oncogenic protein that is almost always expressed in T-ALL.
“We will assess antibody internalisation, the efficiency of LMO2 targeting and the ability of the treatment to eradicate T-ALL tumour cells” - Katherine Vallis
This is an exciting technology with a wide range of potential applications. The ability to internalise antibodies would have significant implications for the future of cancer immunotherapy, unlocking the possibility of therapeutically targeting numerous pathways previously deemed undruggable. Other avenues of investigation include the addition of a biodegrader moiety to the CPP/antibody construct to promote targeted protein degradation, or addition of a radionuclide to act as a cytotoxic payload.
The MRC-funded project led by Prof. Vallis will provide crucial data to guide the ongoing development of these novel trimeric CPPs. If shown to be safe and effective in mouse models, they can be advanced to clinical testing. Additional funding from the University’s Medical and Life Sciences Translational Fund (MLSTF) will support the study of the same technology in breast cancer models.
For additional information:
Reeman J, et al. Strength in numbers: cell penetrating peptide clusters to build next-generation therapeutics. Trends in Chemistry. Nov 2024; 6(11):669-683. doi: 10.1016/j.trechm.2024.09.003.
Tietz O, et al. Tricyclic cell-penetrating peptides for efficient delivery of functional antibodies into cancer cells. Nat. Chem. Feb 2022; 14(3): 284–293. doi: 10.1038/s41557-021-00866-0