Cancer Therapy: Preclinical L-BLP25 Vaccine plus Letrozole Induces a TH1 Immune Response and Has Additive Antitumor Activity in MUC1-Expressing Mammary Tumors in Mice

Purpose: In this study, we examine the immunomodulatory effects and antitumor activity of tamoxifen and letrozole when combined with the human epithelial mucin (hMUC1)-specific vaccine, L-BLP25, in the hMUC1-expressing mammary tumor (MMT) mouse model. Experimental Design:Dose-finding studies were conducted for both tamoxifen and letrozole. Letrozole and L-BLP25 combination studies used 69 MMT female mice assigned to five groups: untreated, cyclophosphamideþ placebo, cyclophosphamideþ L-BLP25, letrozole 0.8 mg/kg, and cyclophosphamideþ LBLP25þ letrozole. Tamoxifen and L-BLP25 combination studies used 48MMT femalemice assigned to five treatment groups: untreated, cyclophosphamide þ placebo, cyclophosphamide þ L-BLP25, tamoxifen 50 mg/kg, and cyclophosphamideþ L-BLP25þ tamoxifen 50mg/kg group.Micewere injected subcutaneously with L-BLP25 (10 mg) weekly for 8 weeks. Serum cytokines were serially measured using a Luminex assay, whereas splenocytes at terminationwere analyzed by ELISpot to determine T-helper (TH)1/TH2 polarization of immune response. Results: Daily oral doses of 50 and 0.8 mg/kg of tamoxifen and letrozole, respectively, resulted in a significant survival advantage over controls (P < 0.05). A predominant TH1-polarized immune response in vaccinated mice was seen with or without tamoxifen or letrozole treatments. In the L-BLP25 plus letrozole treatment group, statistically significant (P < 0.05) additive antitumor activity was observed, whereas tamoxifen plus L-BLP25 was not significantly different (P > 0.05). Conclusion: The results of this study show that hormonal therapy does not interfere with L-BLP25– induced predominant TH1 response, and the combination of L-BLP25with letrozole has additive antitumor activity in the MMT mouse model. Clin Cancer Res; 18(10); 2861–71. 2012 AACR.