Thesis title: FPR1 inhibition coupled with the restoration of Toll-like receptor 3 activity protects the heart from Doxorubicin-induced cardiomyopathy
Background.
Doxorubicin (DOX) is a highly effective chemotherapeutic agent but is limited by dose-dependent cardiotoxicity and immunosuppressive effects. Formyl peptide receptor 1 (FPR1) is essential for DOX-induced immunogenic cell death. A common loss-of-function FPR1 variant (rs867228) attenuates this signaling pathway and contributes to increased chemoresistance. In murine models, activation of Toll-like receptor 3 (TLR3) with the agonist polyinosinic:polycytidylic acid [poly(I:C)] can restore immune activation in this context.
Purpose.
This study aimed to determine whether pharmacological or genetic inhibition of FPR1, combined with TLR3 stimulation via poly(I:C), protects against DOX-induced cardiomyopathy (DCM) without diminishing DOX’s antitumor efficacy.
Methods.
Wild-type (WT) and FPR1-inhibited mice (knockout or treated with cyclosporin H, CsH) received weekly DOX (5 mg/kg; cumulative dose, 15 mg/kg). Additional groups were administered poly(I:C) and/or CsH three times per week for six weeks. Cardiac function was evaluated by echocardiography; histological, metabolomic, and proteomic analyses were performed to assess tissue remodeling and metabolic alterations. To evaluate the preservation of antitumor activity, EO771 tumor-bearing mice were treated with DOX ± poly(I:C) ± CsH for four weeks, with tumor growth and cardiac performance monitored throughout.
Results.
Six-week survival was higher in DOX-treated FPR1-KO mice compared with WT (96% vs. 70%, p ≤ 0.001, n = 10). DOX reduced fractional shortening in WT (43.1 ± 1.5% vs. 29.1 ± 2.1%, n = 7), whereas FPR1-KO mice were protected. Myocardial fibrosis increased in WT DOX-treated hearts (1.7 ± 1.1% vs. 0.5 ± 0.1%, n = 5) but not in FPR1-KO (0.3 ± 0.1%, n = 5). Apoptotic indices were elevated in WT DOX hearts—TUNEL-positive nuclei (0.4 ± 0.1% vs. 0.1 ± 0.05%, n = 8) and cleaved caspase-3 (3.5 ± 1.0 vs. 1.5 ± 0.5, n = 5)—but attenuated in FPR1-KO. Mitochondrial complex IV activity declined in WT DOX (0.2 ± 0.01 vs. 0.3 ± 0.03, n = 4) but was preserved in FPR1-KO (0.3 ± 0.01 vs. 0.2 ± 0.01, n = 4). Similarly, complex I integrity decreased in WT DOX (0.5 ± 0.1 vs. 1.0 ± 0.04, n = 6) but remained stable in FPR1-KO (1.0 ± 0.2, n = 6). Metabolomic analysis revealed enrichment of alternative energy and oxidative stress–adaptive pathways in FPR1-KO DOX hearts (p ≤ 0.05). Proteomics identified mitochondrial dysfunction, inflammation, and immune recruitment in WT DOX, which were absent in FPR1-KO (p ≤ 0.05).
In tumor-bearing mice, DOX and pIC + CsH + DOX similarly suppressed tumor growth (474 ± 61 mm³ and 554 ± 72 mm³, respectively, vs. 1412 ± 154 mm³ in controls, n = 8). Echocardiography demonstrated superior cardiac function in the DOX + pIC + CsH group compared with DOX alone, evidenced by improved global longitudinal strain (GLS, –16 ± 2 vs. –9.6 ± 3.5) and global circumferential strain (GCS, –19.5 ± 0.5 vs. –15.3 ± 3.5), as well as reduced end-diastolic (EDV, 24 ± 3 vs. 31.6 ± 3.9) and end-systolic volumes (ESV, 7.5 ± 0.5 vs. 14.3 ± 1.2), indicating enhanced systolic performance.
Conclusions.
Combined FPR1 inhibition and TLR3 activation mitigate DOX-induced cardiotoxicity by preserving cardiac function and mitochondrial integrity while preventing inflammation and immune cell recruitment. Importantly, this strategy maintains DOX’s antitumor efficacy, providing a promising approach to dissociate cardiotoxic effects from therapeutic benefit.