Pharmacological elimination of ther

Pharmacological elimination of therapy-induced senescent cells minimizes side effects of chemotherapy and prevents cancer recurrence in animals48. However, the feasibility of PCC1-mediated depletion of senescent cells from primary tumours to enhance the efficacy of anticancer treatments remains largely unknown. First, we chose to build tissue recombinants by admixing PSC27 cells with PC3 cells, which are a typical prostate cancer cell line of high malignancy, at a pre-optimized ratio (1:4)14. The cells were then subcutaneously implanted into the hind flank of mice with non-obese diabetes and severe combined immunodeficiency (NOD–SCID). Tumours of animals were measured at the end of an 8-week period, and tissues were acquired for pathological appraisal. Compared to tumours comprising PC3 cancer cells and naive PSC27 stromal cells, xenografts composed of PC3 cells and senescent PSC27 cells exhibited significantly increased volume, confirming the tumour growth-promoting effects of senescent cells (Extended Data Fig. 6a). To mimic clinical conditions, we experimentally designed a preclinical regimen incorporating genotoxic therapeutics and/or senolytics (Fig. 5a). Two weeks after subcutaneous implantation, when stable uptake of tumours in vivo was observed, a single dose of mitoxantrone (MIT, a chemotherapeutic drug) or placebo was delivered to animals on the 1st day of the 3rd, 5th and 7th weeks until the end of the 8-week regimen (Extended Data Fig. 6b). In contrast to the placebo-treated group, MIT administration remarkably delayed tumour growth, validating the efficacy of MIT as a chemotherapeutic agent (44.0% reduction in tumour size) (Fig. 5b). Notably, although administration of PCC1 itself did not cause tumour shrinkage, treatment with MIT followed by PCC1 delivery (at 20mg per kg via intraperitoneal (i.p.) injection 2 weeks after the first MIT dose and then delivered biweekly) remarkably enhanced tumour regression (55.2% reduction in tumour size compared with MIT alone; 74.9% reduction in tumour volume compared with the placebo treatment) (Fig. 5b). We next tested whether cellular senescence occurred in the tumour foci of these animals. Unsurprisingly, MIT administration induced the appearance of a large number of senescent cells in tumour tissue. However, delivery of PCC1 to these chemotherapytreated animals depleted the majority of senescent cells (Fig. 5c,d). Laser capture microdissection followed by transcript assays indicated significantly increased expression of SASP factors including IL6, CXCL8, SPINK1, WNT16B (also known as WNT16), GM-CSF (also known as CSF2), MMP3 and IL1A, a tendency accompanied by upregulation of the gene encoding the senescence marker p16INK4a in chemotherapy-treated animals (Fig. 5e and Extended Data Fig. 6c).