Platelets reprogram the breast tumor cell secretome. Angiogenesis arrays were used to identify factors secreted by breast tumor cells after exposure to APR. (A) To generate APR, platelets were exposed to 25 μM thrombin receptor activator peptide 6 (TRAP) or 3 × 10⁶/mL tumor cells, causing platelet activation and the release of stored factors into the supernatant. Tumor cells were then exposed to APR for 24 hours, and the resulting conditioned media was collected and compared with either APR alone or tumor cell-conditioned media alone. (A) Representative images from arrays are shown. Blue highlighted areas represent interleukin 8 (IL-8) signal. Three separate array experiments were performed: (B) MCF-7 tumor cells exposed to TRAP-induced APR (C) MCF-7 tumor cells exposed to MCF-7-induced APR and (D) MDA-MB-231 tumor cells exposed to MDA-MB-231-induced APR. Arrays were analyzed by densitometry, and factors that were increased at least 1.5-fold in the supernatant of releasate-treated tumor cells are depicted. (E) MDA-MB-231, BT-20, MCF-7, and SKBR-3 breast cancer cell lines were co-incubated with platelets for 24 hours and IL-8 within the supernatant measured by ELISA. For ELISAs, P values were determined by separate unpaired 2-tailed Student t tests. n = 5 to 7 independent replicates per treatment group. Angiogenesis array data represents a single experiment.