Synergistic interactions between F5, F7, F5-SM or F7-SM with niraparib on HTB75 cell viability at 48 h (a–d) and F5 or F7 with niraparib on HTB161 cell viability at 48 h (e,f) following combined treatments. Synergy of cytotoxic activity was calculated, based on the Bliss independence drug interaction model. Control was vehicle control (1.50% v/v methanol + 0.90% v/v DMSO for HTB75 and 1.38% v/v methanol + 2.50% v/v DMSO for HTB161). Synergy was apparent when the experimental (observed) value of cell survival inhibition was higher than the calculated (expected) value. Delta values of observed minus expected are shown on the Y axis. Supplementary Tables S4 and S5 present the significantly different synergistic delta values of F5, F7, F5-SM or F7-SM with niraparib from all pair combinations according to the Tukey–Kramer honest significant difference test (n = 3; HSD; p ≤ 0.05).