Granzyme B PET Imaging Predicts Response to Immunotherapy in a Diet-Induced Obesity Model of Breast Cancer

Obesity induces changes in tumor microenvironment that influence survival. (A) Overall survival was significantly decreased for HFD-fed mice (median, 18 d) compared with LFD-fed mice (median, 28.5 d). (B) Quantification of flow cytometry data evaluating macrophage (CD86⁺ and CD206⁺) and T-cell (CD4⁺ and CD8⁺) populations in tumors of lean and obese mice. Macrophages are gated on live > CD45⁺ > CD11b⁺ > F4/80⁺, and T cells are gated on live > CD45⁺ > CD3⁺ (Supplemental Fig. 3). (C) ¹⁸F-FDG PET/CT imaging and quantification of SUV metrics show tumor glucose metabolism in lean and obese mice at baseline. Tumors are encircled with white dotted line. CON = control; TBR = tumor background ratio.

Fixed-dose immunotherapy significantly increased immune activation via GZB PET but was not sufficient to reduce tumor burden in obese mice. (A) Representative PET/CT images show coronal view of EO771 mice tumors imaged with ⁶⁸Ga-NOTA-GZP PET. (B) ⁶⁸Ga-NOTA-GZP SUV_mean in tumors treated with fixed-dose immunotherapy compared with controls for LFD and HFD groups. (C) Tumor volume reduction by fixed-dose immunotherapy observed in LFD-fed mice but not HFD-fed mice. CON = control; IMT = immunotherapy.

Weight-based immunotherapy significantly increased immune activation via ⁶⁸Ga-NOTA-GZP PET. (A) PET/CT images showing axial view of EO771 mice tumors imaged with ⁶⁸Ga-NOTA-GZP PET. (B) Frequency distribution for ⁶⁸Ga-NOTA-GZP expression. Percent GZP⁺ effector cell fraction calculated from SUV frequency distribution for [⁶⁸Ga]Ga-NOTA-GZP expression in lean and obese mice. (C) Tumor volumes were significantly decreased for mice receiving weight-based immunotherapy compared with controls. CON = control; IMT = immunotherapy; wt = weight.

⁶⁸Ga-NOTA-GZP PET was significantly associated with response to immunotherapy before significant changes in tumor volume. (A) Heat map displaying ¹⁸F-FDG SUV on days 0 and 6, ⁶⁸Ga-NOTA-GZP SUV on day 7, and relationship with iRECIST criteria for each mouse. (B) Comparison of responder and nonresponder tumors with day 6 ¹⁸F-FDG SUV_mean and day 7 ⁶⁸Ga-NOTA-GZP SUV_mean. (C) Receiver-operating-characteristic curve analysis shows sensitivity and specificity in predicting response of ¹⁸F-FDG SUV_mean (area under the curve, 0.6023; 95% CI, 0.5472–1.000; P = 0.31) and ⁶⁸Ga-NOTA-GZP SUV_mean (area under the curve, 0.8095; 95% CI, 0.4311–0.7344; P = 0.022). CR = complete response; NR = nonresponder; PD = progressive disease; PR = partial response; R = responder; SD = stable disease.