^99mTc-Duramycin imaging detects cancer therapy related cardiac dysfunction before onset of ventricular dysfunction.

Objectives: The remission rate of cancer has increased¹, however; chemotherapy-related cardiac dysfunction (CRCD) remains a major problem². Early detection of CRCD, prior to a decrease in ventricular function, is a major goal of patient management. An enzyme leak or decrease in LVEF is often associated with a permanent decrease in ventricular function^3-6. Although the mechanisms of CRCD are not fully elucidated, one of major mechanism is considered to be myocyte apoptosis ^7,8 Previous studies suggest that apoptotic injury is associated with increased expression of phosphatidylethanolamine (PE) on the outer leaflet of the cell membrane⁹ and ^99mTc-Duramycin binds with nanomolar affinity to extracellular expression of phophatidylethanolamine¹⁰. We evaluated ^99mTc labeled -Duramycin (TcD), as an early marker of cardiomyocyte damage initiated by doxorubicin (DOX) and Trastuzumab (Trz).

Methods: 54 male SD rats were divided into 9 groups. We tested duramycin in single (5-10 mg/kg DOX or vehicle) and multiple (2.5mg/kg Dox e.o.d for 2, 3 or 4 injections, or vehicle) injection models. Two groups received a single dose of 10mg/kg Trastuzumab (Trz) after 3 or 4 administration of Dox. Myocardial uptake of TcD was imaged with micro SPECT/CT imaging and scintillation well counting of the heart at the conclusion of the experiment. LVEF was determined by echocardiography. Plasma levels of Troponin I were measured. Following gamma counting, cardiac specimens were fixed overnight with 4% paraformaldehyde. H&E. and Tunel staining were performed. Electron microscopic (EM) analysis was also performed to identify cardiac damage. Measurement parameters were expressed as mean ± one standard deviation (SD). All parameters were assessed using the Shapiro-Wilk test, Levene’s test , one-way analysis of variance (ANOVA) with Tukey’s HSD post-hoc analysis or Welch’s test was used followed by Games-Howell post-hoc analysis and p < 0.05 was considered statistically significant.

Results: Single administration of DOX reduced LVEF compared with control (control = 75.2+2.3%; 5mg = 67.9±2.7%, p<0.05; 10mg = 60.6±2.5% p<0.05), and myocardial TcD uptake on counting (control = 0.047+0.006%ID/g; 5mg = 0.074±0.011 %ID/g, p<0.05 and 10 mg = 0.097±0.029 %ID/g, p<0.05). 2D ROI measurements of ex-vivo images showed a significantly higher concentration in the single Dox injection groups’ than the control groups (control= 28.4 ± 2.8 count/mm²; 5mg =55.7 ± 12.5 count/mm²; 10mg = 64.0 ± 17.0, p<0.05 count/mm²). In multiple DOX + Trz administration models, LVEF was substantially decreased compared to control (Control =74.3±1.7 %; 3 DOX+Trz = 65.9±1.3%, p<005; 4DOX+Trz = 60.9±2.9%, p<0.05) and was associated with increased TcD uptake on counting (Control = 0.048±0.009 %ID/g; 3 DOX+Trz = 0.084±0.010 %ID/g, p<0.05; 4DOX+Trz = 0.089±0.020 %ID/g p<0.05) and on ex-vivo images (Control = 28.3 ± 2.7 ount/mm²; 3 DOX+Trz = 54.4 ± 5.3 count/mm², p<0.05 ;4Dox+Trz = 55.8 ± 13.2 count/mm² , p<0.05). There was no significant reduction in LVEF between Dox 2, 3, or 4 administrations alone and control ( 2Dox =74.6±0.7%; 3Dox = 74.2±2.6 %; 4Dox = 72.9±5.4%), however;TcD myocardial uptake increased significantly with DOX on counting (2Dox = 0.081±0.015 %ID/g, p<0.05; 3Dox = 0.076±0.017 %ID/g, p<0.05; 4Dox = 0.076±0.015 %ID/g , p<0.05) and on ex-vivo images (2Dox = 49.8 ± 7.1 count/mm², p<0.05; 3Dox = 50.8 ± 5.8 count/mm², p<0.05; 4Dox = 50.6 ± 9.1 count/mm², p<0.05). There was no significant difference in LVEF at base line. EM showed mitochondrial damage, although Tunel staining was not increased. There was no increase in troponin.

Conclusion: ^99mTc-Duramycin imaging cardiac uptake increased while LVEF was unchanged and there was no increase troponin in animals receiving multiple doses of Dox. Research Support: SNMMI Wagner-Torizuka Fellowship and Uehara Memorial Foundation to TN. Japan Heart Foundation/ Bayer Yakuhin Research Grant abroad to TT. NHLBI grant 1R43HL127892-01 to JM.