Biosorption-based 64Cu-labeling of bacteria for pharmacokinetic positron-emission tomography

Tumor-stromal opening via S. typhimurium VNP20009 administration for complete inhibition of refractory tumor growth with liposomal anticancer drugs

Many clinical tumors exhibit a vascular endothelium covered by mural cells and stroma with abundant collagen fibers, which greatly inhibit the penetration of nanoparticle drug delivery systems (DDS) formulations deep into the tumors. We previously found that Salmonella typhimurium VNP20009 attracting attention as live bacterial therapeutics, which is a novel pharmaceutical modality for cancer treatment, can grow within deep tumors with abundant stroma and tight vasculature. Because this finding interestingly indicates that VNP20009 administration disrupts vascular and stromal structures even in refractory tumors, we investigated the possibility that VNP20009 administration improves DDS formulations migrations into tumors in this study. VNP20009 co-administration drastically improved the translocation and diffusion of liposomes deep into the tumors, particularly in stroma-rich xenografted tumors, indicating its tumor stromal opening ability. Furthermore, this approach can completely inhibit tumors in various refractory tumor models, including pancreatic cancers, using liposomal doxorubicin (Doxil®) and liposomal irinotecan (Onivyde®). Notably, this remarkable anticancer effect is not simply attributed to the therapeutic effects of liposomal anticancer drugs and VNP20009, but it involves an additional effect, improving the intratumor pharmacokinetics of liposomal anticancer drugs following VNP20009 co-administration. The unique tumor stromal opening ability of VNP20009 demonstrated in this study is a promising strategy for resolving the major challenges faced by tumor DDS.

Assessing microbiota in vivo: debugging with medical imaging

The microbiota is integral to human health and has been mostly characterized through various ex vivo 'omic'-based approaches. To better understand the real-time function and impact of the microbiota, in vivo molecular imaging is required. With technologies such as positron emission tomography (PET), magnetic resonance imaging (MRI), and computed tomography (CT), insight into microbiological processes may be coupled to in vivo information. Noninvasive imaging enables longitudinal tracking of microbes and their components in real time; mapping of microbiota biodistribution, persistence and migration; and simultaneous monitoring of host physiological responses. The development of molecular imaging for clinical translation is an interdisciplinary science, with broad implications for deeper understanding of host-microbe interactions and the role(s) of the microbiome in health and disease.

Impact of tumoral structure and bacterial species on growth and biodistribution of live bacterial therapeutics in xenografted tumours

Live bacterial therapeutics is gaining attention, especially for cancer therapy, because anaerobic bacteria selectively grow inside the solid tumours. However, the effect of tumour structure and bacterial characteristics on the pharmacokinetics of tumours is unclear; therefore, we aimed to elucidate the effects of tumour structure and types of bacteria on tumoral bacterial growth. Using six mouse xenograft models, including stroma-rich tumours similar to clinical tumours, and two models of live bacterial therapeutics, Salmonella typhimurium VNP20009 and Escherichia coli DH5α, we investigated bacterial growth and distribution in tumours after intravenous administration. Rapid growth of E. coli was observed in HCT116 and other tumours with few collagens, blood vessels not covered by mural cells, and a cancer cell area proliferated disorderly, whereas tumours with contrasting features, such as BxPC-3, showed lower bacterial growth and a limited intratumor distribution. Alternatively, Salmonella typhimurium VNP20009, when successfully proliferated (the probability was approximately 50%), grew to 10⁸ colony forming units/g tissue even in BxPC-3 tumours, and its intratumor distribution was extensive. This study suggests that the development of new methods to modify tumour structure will be essential for the development of anti-tumour clinical therapies based on live bacterial therapeutics.

64Cu-labeling of small extracellular vesicle surfaces via a cross-bridged macrocyclic chelator for pharmacokinetic study by positron emission tomography imaging

We developed a method of labeling the surfaces of small extracellular vesicles (sEVs) with ⁶⁴Cu using a cross-bridged, macrocyclic chelator (CB-TE1A1P) and applied to pharmacokinetics study with positron emission tomography (PET). After incubation in 20% plasma for 10 min, approximately a half of the ⁶⁴Cu was desorbed from ⁶⁴Cu-labeled sEVs purified by phosphate-buffered saline wash, suggesting partly weak interaction without coordinating to CB-TE1A1P. After subsequent purification with albumin, ⁶⁴Cu desorption was greatly reduced, resulting in a radiochemical stability of 95.7%. Notably, labeling did not alter the physicochemical and biological properties of sEVs. After intravenous injection, ⁶⁴Cu-labeled sEVs rapidly disappeared from the systemic blood circulation and accumulated mainly in the liver and spleen of macrophage-competent mice. In macrophage-depleted mice, ⁶⁴Cu-labeled sEVs remained in the blood circulation for a longer period and gradually accumulated in the liver and spleen, suggesting mechanisms of hepatic and splenic accumulation other than macrophage-dependent phagocytosis. The comparison of tissue uptake clearance between macrophage-competent and macrophage-depleted mice suggests that macrophages contributed to 67% and 76% of sEV uptake in the liver and spleen, respectively. The application of this method in pharmacokinetics PET studies can be useful in preclinical and clinical research and the development of sEV treatment modalities.