Subsequently the amount of bound GF120918 mouse albumin was determined by Western blot analysis using a primary p38 MAPK activation antibody recognizing denatured albumin. Untreated Lm-spa+ did not bind albumin, while Lm-spa+ coated with the albumin-specific antibody bound albumin (Figure 1D). Computer aided comparison of the band intensity of bacterially

bound albumin with the known protein amount of the positive control revealed a 7 times higher signal intensity. Thus 70 ng albumin were bound to 5 × 108 bacterial cells. With albumin having a protein mass of 69 kDa 70 ng correspond to 8,73*109 molecules. Divided by the number of bacteria employed for the coating (5*108 CFU) approximately 120 albumin molecules were bound per bacterial cell. Assuming two bound albumin molecules per antibody and one antibody per SPA molecule, this means that at least 60 SPA molecules are exposed in the correct orientation on the surface of each Lm-spa+ cell. Internalization of antibody coated Lm-spa+ into cancer cell lines expressing the respective antibody ligand After the successful demonstration of SPA binding to the bacterial surface, it was important to investigate whether

the binding of tumor receptor-specific antibodies to SPA on the surface of Lm-spa+ can mediate specific cell recognition and internalization of the bacteria into the tumor cells. The mouse mammary gland cell line 4T1 (HER1- and HER2 negative) and the isogenic cell line 4T1-HER2 (stably transfected with human-HER2 [26]) were used in these experiments as well as the monoclonal antibodies Cetuximab and Trastuzumab directed against HER1 and HER2, respectively. Both mAbs belong Fludarabine to the same IgG1 subclass of immunoglobulins, but Cetuximab is a mouse/human chimeric antibody whereas Trastuzumab is almost completely humanized. Cetuximab is therefore a control for unspecific antibody coating of Lm-spa+ when analyzing the interaction

of these bacteria with murine 4T1-HER2 cells. The Lm EGDe wild-type strain was able to efficiently enter both cell lines these 4T1 and 4T1-HER2 (data not shown). As expected, the Lm-spa- strain (which is InlAB-negative) was not internalized by 4T1 or 4T1-HER2 cells regardless of whether these bacteria were incubated with Cetuximab or Trastuzumab (Additional file 1a, c). Lm-spa+ was also unable to enter 4T1 and 4T1-HER2 cells without antibody coating or with Cetuximab coating. However, high internalization of Lm-spa+ into 4T1-HER2 cells was observed when these bacteria were coated with Trastuzumab (Figure 2A, Additional file 1e). Figure 2 Internalization of Cetuximab- or Trastuzumab- coated Lm-spa + relative to uncoated Lm-spa + (-mAb) into different cell lines. (a) Mouse mammary cancer cell line 4T1, the HER2 transduced isogenic 4T1-HER2 and (b) the human mammary/ovary cancer cell lines SK-BR-3 and SK-OV-3, respectively, were infected with Lm-spa+ after coating with different antibodies.