Phase I dose‐escalation trial to repurpose propagermanium, an oral CCL2 inhibitor, in patients with breast cancer

The formation of premetastatic niches creates a fertile environment for the seeding of disseminated cancer cells in selected secondary organs. This is crucial for the development of metastasis in various malignancies, including breast cancer (BC). We previously reported that the loss of FBXW7 in bone marrow‐derived stromal cells promoted cancer metastasis by increasing the production of the chemokine CCL2, which attracts myeloid‐derived suppressor cells and macrophages to the premetastatic niche. Furthermore, treatment with the CCL2 inhibitor propagermanium (PG), which has been used in Japan as a therapeutic agent against chronic hepatitis B, was shown to block the enhancement of metastasis in FBXW7‐deficient mice through inhibiting the formation of premetastatic niches. Here, we describe a phase I dose‐escalation study of PG used as an antimetastatic drug for perioperative patients with primary BC. The primary end‐point was the percentage of patients who experience dose‐limiting toxicity. Twelve patients were enrolled in the study. Dose‐limiting toxicity was not observed, and the maximum dose was determined to be 90 mg/body/day. The serum concentrations of PG were nearly within the normal range in all observation days. We observed an inverse correlation between FBXW7 mRNA levels in blood and the serum concentrations of CCL2 and interleukin (IL)‐6, in agreement with our previous mouse model. Also, IL‐6 was downregulated in a PG dose‐dependent manner, as observed in mice. Thus, PG was given safely and it is expected to have antimetastatic potential in BC. This trial is registered in the UMIN Clinical Trials Registry as UMIN000022494.