A careful design of La1−xSrxMnO3 (0.25 ≤ x ≤ 0.35) nanoparticles (NPs) was made to prepare a self-controlled heating agent for magnetic hyperthermia therapy (MHT). The results showed that the magnetic properties and heating efficacy of the tailored La1−xSrxMnO3 NPs are strongly dependent on the doping level of La/Sr cations, so that La0.73Sr0.27MnO3 NPs possessed the highest saturation magnetization and heating efficacy in response to safe alternating magnetic fields used in biomedical applications (H = 3.4–5.0 mT and f = 120 kHz). Furthermore, to improve the biocompatibility of the La0.73Sr0.27MnO3 NPs, the surface of the NPs was coated with a thin silica shell, and then the therapeutic efficacy of MHT using the silica-coated La0.73Sr0.27MnO3 NPs was investigated using a typical animal model of breast cancer. The results showed that in the control group, the mean tumor volume increased up to 300% over 6 days, while in the MHT group, the mean tumor volume decreased about 85% during the same period of time (Pvalue = 0.002). The outcomes of this study indicate that silica-coated La0.73Sr0.27MnO3 NPs are a promising tool for self-regulating MHT.
