Abstract P5-01-06: Characterization of metastatic breast cancer lesions with ferumoxytol MRI and treatment response to MM-398, nanoliposomal irinotecan (nal-IRI)

Introduction Irinotecan has known activity in metastatic breast cancer (MBC). MM-398, nanoliposomal irinotecan (nal-IRI), is designed to exploit leaky tumor vasculature for enhanced drug delivery to tumors. Tumor deposition of nal-IRI and subsequent conversion to SN-38 in both neoplastic cells and tumor associated macrophages (TAM) may positively correlate with activity. Predictive biomarkers to measure tumor deposition could identify patients likely to benefit from nal-IRI. Ferumoxytol (FMX), an iron-oxide superparamagnetic nanoparticle with MRI contrast properties, is taken up by TAMs with similar distribution patterns to nal-IRI in preclinical models. Our previous work has shown the feasibility of quantitative FMX MRI (Fe-MRI) of tumor lesions, and we developed a quantitative mechanistic PK model of FMX deposition (AACR 2014, abstract #CT224). Here we report nal-IRI activity and FMX levels in MBC patients on the study. Patients and methods Patients (n=15) with refractory solid tumors and at least two metastatic lesions >2 cm accessible for percutaneous biopsy were enrolled in a Phase 1 study. Fe-MRI scans were performed using T2* iron sensitive sequences prior to and following FMX infusion (1 h, 24 h, 72 h). T2* signal was used to calculate FMX levels in total lesions by comparison to a standard curve. Comparison of quantified FMX lesion uptake with a mechanistic PK model previously indicated that tissue permeability to FMX contributed to early Fe-MRI signals at 1 h and 24 h, while FMX binding contributed at 72 h. Patients then received nal-IRI (80 mg/m2 q2w) until progression. Core biopsies were obtained 72 h after both FMX and nal-IRI infusions. RECIST evaluation was done by CT every 8 weeks. Results FMX was well tolerated, and adverse events to nal-IRI were consistent with previous studies. Three of the 13 patients receiving nal-IRI had ER/PR+ MBC (median # of prior Rx: 8 compared to 4 for all study patients). Thirteen liver lesions (4-5/pt) were evaluated by FMX-MRI and CT for these 3 patients. Average lesion size: 26.9±11.2 mm diameter and 8.1±11.3 cm3 (median 4.7 cm3). Time on treatment for the 3 patients was 57, 126 and 256 days (study median 57 days). Best overall response was 1 stable disease (SD) and 1 partial response (PR) in these 3 patients. The patient with a PR had an average lesion size reduction of 44.5%, while the patient with SD had an average lesion size increase of 12.5% at final evaluation. Lesions that shrank after nal-IRI showed higher early levels of FMX compared to the study median (median 39.6 vs. 32.6 mcg/mL at 1 h; median 37.7 vs. 34.5 mcg/mL at 24 h). This relationship between lesion response and FMX levels was consistent with the lesion behavior in the full data set (n=31 lesions/9 patients across 7 indications) of the study. Conclusions Clinical activity of nal-IRI was observed in a subset of heavily treated ER/PR+ MBC patients. The relationship between FMX levels in tumor lesions and nal-IRI activity suggests that lesion permeability to FMX may be a useful biomarker for nal-IRI deposition and tumor response in MBC and potentially other indications. A multi-institution expansion of this study in HER2-negative MBC is planned to confirm these findings. Citation Format: Jasgit C Sachdev, Ramesh K Ramanathan, Natarajan Raghunand, Jaeyeon Kim, Stephan G Klinz, Eliel Bayever, Jonathan B Fitzgerald, Ronald L Korn. Characterization of metastatic breast cancer lesions with ferumoxytol MRI and treatment response to MM-398, nanoliposomal irinotecan (nal-IRI) [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P5-01-06.