Low-dose cytokine immunotherapy of solid cancers enabled by phagocytic-competent protein co-crystals

Protein therapeutics are often compromised by sub-optimal biodistribution contributing to poor efficacy and adverse events. Drug delivery mechanisms better able to target protein drugs to the disease site and provide localized, sustained release have the potential to transform therapeutic standards. PODS crystals (PODS) are natural-mimetic, micron-scale protein co-crystals engineered to incorporate a protein cargo that can be sustainably released under the action of resident proteases. PODS are efficiently taken up by phagocytic cells with the cargo protein subsequently released in a bioactive form. Since blood-circulating phagocytic cells, including monocytes, are actively recruited into diseased and inflamed tissue, such as the tumour microenvironment, we postulated that monocyte/macrophage-mediated PODS delivery could be used as a molecular 'Trojan horse' to efficiently deliver therapeutic proteins to target cells. This could improve the pharmacodynamics and pharmacokinetics of protein drug delivery to treat systemic and disseminated diseases. Interleukin-2 (IL-2) is notoriously toxic at the high doses required for therapeutic efficacy. Here, we demonstrate the therapeutic efficacy and tolerability of low doses of PODS containing IL-2 cargo (PODS-IL-2) administered intravenously in a mouse model of melanoma. We further demonstrate the therapeutic benefit of PODS delivering IL-2, interleukin-15 (IL-15) and interferon gamma (IFN-gamma) in a mouse model of renal cell carcinoma at two doses. Efficacy was seen in both doses with the higher dose generating rapid and complete rejection of the tumour in some of the mice treated with each cytokine. This study provides proof-of-concept for the utility of intravenously administered PODS to provide a generalised and widely applicable mechanism to effectively deliver protein drugs for the therapy of cancer and potentially other diseases. ### Competing Interest Statement Michael Jones, Robert Smith, Simon Rudge and Jonathan Best are employees of Cell Guidance Systems which owns patents related to the use of PODs technology to treat cancer.