Combination of the mTOR inhibitor ridaforolimus and the anti-IGF1R monoclonal antibody dalotuzumab: preclinical characterization and phase I clinical trial

Abstract

Purpose: Mammalian target of rapamycin (mTOR) inhibition activates compensatory insulin-like growth factor receptor (IGFR) signaling. We evaluated the ridaforolimus (mTOR inhibitor) and dalotuzumab (anti-IGF1R antibody) combination.

Experimental design: In vitro and in vivo models, and a phase I study in which patients with advanced cancer received ridaforolimus (10-40 mg/day every day × 5/week) and dalotuzumab (10 mg/kg/week or 7.5 mg/kg/every other week) were explored.

Results: Preclinical studies demonstrated enhanced pathway inhibition with ridaforolimus and dalotuzumab. With 87 patients treated in the phase I study, main dose-limiting toxicities (DLT) of the combination were primarily mTOR-related stomatitis and asthenia at doses of ridaforolimus lower than expected, suggesting blockade of compensatory pathways in normal tissues. Six confirmed partial responses were reported (3 patients with breast cancer); 10 of 23 patients with breast cancer and 6 of 11 patients with ER(+)/high-proliferative breast cancer showed antitumor activity.

Conclusions: Our study provides proof-of-concept that inhibiting the IGF1R compensatory response to mTOR inhibition is feasible with promising clinical activity in heavily pretreated advanced cancer, particularly in ER(+)/high-proliferative breast cancer (ClinicalTrials.gov identifier: NCT00730379).

Figure 1

Combination therapy with mTOR and IGF1R inhibitors block feedback activation of AKT. A, diversity in feedback activation of AKT by ridaforolimus was observed in a panel of breast cancer cell lines. B, cell lines exhibiting feedback activation of AKT following ridaforolimus treatment showed sensitivity to anti-IGF1R therapy. C, knockdown of IGF1R and its signaling pathway components blocked feedback activation of AKT. A lentiviral shRNA screen identified mTOR as an enhancer of the activity of dalotuzumab in tumor cell lines, and AKT activation by mTOR was confirmed to be mediated via the IGF1R signaling pathway. D, representative results from a shRNA screen targeting various PI3K and MAPK kinases in HT-29 CRC cells. mTOR, mammalian target of rapamycin; IGF1R, insulin-like growth factor 1 receptor; shRNA, short hairpin RNA; PI3K, phosphatidylinositol 3-kinase; CRC, colorectal cancer; PTEN, phosphatase and tensin homolog.

Figure 2

Cotreatment with dalotuzumab and ridaforolimus enhances antitumor activity in IGF1R-expressing tumors. A, Western blot analysis of PI3K pathway components in cancer cells treated with dalotuzumab, ridaforolimus, or the combination. In IGF1R-expressing cancer cell lines (H2122), combination treatment suppresses the activation of AKT demonstrated by decreased phosphorylation of AKT and downstream targets FOXO3A and PRAS40. B, combination therapy with ridaforolimus and dalotuzumab results in increased cell death in anchorage-independent growth inhibition assays in IGF1R-expressing cells (H2122). No such combination benefit was observed in cancer cells expressing low levels of IGF1R (H1703). C, In vivo, combination therapy with ridaforolimus and dalotuzumab significantly inhibits growth over monotherapies. Tumor growth of primary human tumor–derived lung adenocarcinoma xenograft model LXFA629 in control (vehicle) or experimental agent–treated mice (n =10/group) were plotted. Combination therapy with ridaforolimus and dalotuzumab significantly enhanced tumor growth inhibition compared to vehicle-treated (P < 0.0001) or single-agent treated groups (P < 0.05).

Figure 3

RAS pathway activation and sensitivity to mTOR inhibition in ER⁺ breast cancer cell lines. A, RAS signature is associated with sensitivity to ridaforolimus in a panel of breast cancer cell lines. B, ER⁺ tumors have low levels of RAS pathway activation—unsupervised 2D clustering of the 5,000 most variable genes segregate breast tumors into ER⁺, HER2⁺, or triple negative (ER⁻, PR⁻, and HER2⁻) subtypes. RAS pathway activation is low in the ER⁺ tumors. C, IGF1R signaling pathway components are overexpressed in ER⁺ breast tumors. Differential expression of selected genes in the IGF1R receptor signaling pathway was compared between ER⁺(n =228) and ER⁻(n =87) breast tumors profiled by TCGA. The fold overexpression and P value for differential expression are indicated.

Figure 4

Effect of ridaforolimus and dalotuzumab treatment on tumor markers. A, ridaforolimus and dalotuzumab treatment results in a significant decrease in the GGI at day 19 compared with day 0 in patients who responded to the combination therapy. B, patients responding to treatment with ridaforolimus alone had less pronounced changes in GGI by day 5 compared with day 0. C, example of tumor response (PR; RECIST) in a breast cancer patient with liver metastases treated at dose level 4 (ridaforolimus 40 mg/day and dalotuzumab 10 mg/kg/week). D, PET-CT evaluation of a patient with breast cancer after one cycle of treatment at dose level 4: CT scans revealed a 28% decrease in the sum of the longer diameters of the target lesions, which corresponded to 48% decrease in ¹⁸FDG uptake. Arrows indicate target lesions of interest. p-S6RP, phosphorylated S6 ribosomal protein; NR, nonresponders; R, responders.