[⁸⁹Zr]ZrDFO-CR011 PET Correlates with Response to Glycoprotein Nonmetastatic Melanoma B–targeted Therapy in Triple-negative Breast Cancer

There is a need for prognostic markers to select patients most likely to benefit from antibody–drug conjugate (ADC) therapy. We quantified the relationship between pretreatment PET imaging of glycoprotein nonmetastatic melanoma B (gpNMB) with ⁸⁹Zr-labeled anti-gpNMB antibody ([⁸⁹Zr]ZrDFO-CR011) and response to ADC therapy (CDX-011) in triple-negative breast cancer. First, we compared different PET imaging metrics and found that standardized uptake values (SUV) and tumor-to-heart SUV ratios were sufficient to delineate differences in radiotracer uptake in the tumor of four different cell- and patient-derived tumor models and achieved high standardized effect sizes. These tumor models with varying levels of gpNMB expression were imaged with [⁸⁹Zr]ZrDFO-CR011 followed by treatment with a single bolus injection of CDX-011. The percent change in tumor volume relative to baseline (% CTV) was then correlated with SUV_mean of [⁸⁹Zr]ZrDFO-CR011 uptake in the tumor. All gpNMB-positive tumor models responded to CDX-011 over 6 weeks of treatment, except one patient-derived tumor regrew after 4 weeks of treatment. As expected, the gpNMB-negative tumor increased in volume by 130 59% at endpoint. The magnitude of pretreatment SUV had the strongest inverse correlation with the % CTV at 2–4 weeks after treatment with CDX-011 (Spearman r = -0.8). However, pretreatment PET imaging with [⁸⁹Zr]ZrDFO-CR011 did not inform on which tumor types will regrow over time. Other methods will be needed to predict resistance to treatment.