ErbB2-overexpressing human mammary carcinoma cells display an increased requirement for the phosphatidylinositol 3-kinase signaling pathway in anchorage-independent growth.

The proto-oncogene ErbB2 is known to be amplified and to play an important role in the development of about one-third of human breast cancers. Phosphatidylinositol 3-kinase (PI3K), which is often activated in ErbB2-overexpressing breast cancer cells, is known to regulate cell proliferation and cell survival. Selective inhibitors of the PI3K pathway were used to assess the relevance of PI3K signaling in the anchorage-independent growth of a series of human mammary carcinoma cell lines. Wortmannin, LY294002, and rapamycin at concentrations that did not affect MAPK phosphorylation but substantially inhibited PI3K, Akt, and p70(S6K) significantly suppressed the soft agar growth of tumor cell lines that overexpress ErbB2 but not the growth of tumor lines with low ErbB2 expression. A similar growth inhibition of ErbB2-overexpressing carcinoma lines was observed when a dominant negative p85(PI3K) mutant was introduced into these cells. Forced expression of ErbB2 in breast cancer lines originally expressing low ErbB2 levels augmented receptor expression and sensitized those lines to LY294002- and rapamycin-mediated inhibition of colony formation. Furthermore, treatment with LY294002 resulted in the selective increase of cyclin-dependent kinase inhibitors p21(Cip1) or p27(Kip1) and suppression of cyclin E-associated Cdk2 kinase activity in ErbB2-overexpressing lines, which may account for their hypersensitivity toward inhibitors of the PI3K pathway in anchorage-independent growth. Our results indicate that the PI3K/Akt/p70(S6K) pathway plays an enhanced role in the anchorage-independent growth of ErbB2-overexpressing breast cancer cells, therefore providing a molecular basis for the selective targeting of this signaling pathway in the treatment of ErbB2-related human breast malignancies.

Inhibition of mitogen-activated protein kinase kinase selectively inhibits cell proliferation in human breast cancer cells displaying enhanced insulin-like growth factor I-mediated mitogen-activated protein kinase activation.

Mitogen-activated protein (MAP) kinase mediates cell proliferation, cell differentiation, and cell survival by regulating signaling pathways activated by receptor protein tyrosine kinases (RPTKs), including the insulin-like growth factor 1 receptor (IGF-IR). We analyzed the upstream signaling components of the MAP kinase pathway, including RPTKs, in human breast cancer cell lines and found that some of those components were overexpressed. Importantly, signaling molecules such as IGF-IR, insulin receptor, and insulin receptor substrate 1, leading to the MAP kinase pathway, were found to be concomitantly overexpressed within certain tumor lines, i.e., MCF-7 and T-47D. When compared with the nonmalignant and other breast tumor lines examined, MCF-7 and T-47D cells displayed a more rapid, robust, and sustained MAP kinase activation in response to insulin-like growth factor I (IGF-I) stimulation. By contrast, IGF-I treatment led to a sustained down-regulation of MAP kinase in those lines overexpressing ErbB2-related RPTKs. Interestingly, blocking the MAP kinase pathway with PD098059 had the greatest antiproliferative effect on MCF-7 and T-47D among the normal and tumor lines tested. Furthermore, addition of an IGF-IR blocking antibody to growth medium attenuated the ability of PD098059 to suppress the growth of MCF-7 and T-47D cells. Thus, our study suggests that concomitant overexpression of multiple signaling components of the IGF-IR pathway leads to the amplification of IGF-I-mediated MAP kinase signaling and resultant sensitization to PD098059. The enhanced sensitivity to PD098059 implies an increased requirement for the MAP kinase pathway in those breast cancer cells, making this pathway a potential target in the treatment of selected breast malignancies.

Photoimmunotherapy and biodistribution with an OC125-chlorin immunoconjugate in an in vivo murine ovarian cancer model.

Photodynamic therapy (PDT) is an experimental approach to the treatment of neoplasms in which photosensitisers (PSs) accumulated in malignant tissues are photoactivated with appropriate wavelengths of light. The target specificity of PSs may be improved by linking them with carrier macromolecules such as monoclonal antibodies (MAbs). OC125 is a murine MAb that recognises the antigen CA 125, which is expressed on 80% of non-mucinous ovarian tumours. A chlorin derivative conjugated to OC125 was shown to be selectively phototoxic to ovarian cancer and other CA 125-positive cells in vitro and ex vivo. We now report in vivo studies using an ascitic Balb/c nude mouse ovarian cancer model. Ascites was induced by intraperitoneal injection of cells from the human ovarian cancer cell line NIH:OVCAR3. Six weeks after injection, when the animals had developed ascites, biodistribution studies were carried out by injecting the immunoconjugate (IC) or free PS intraperitoneally and sacrificing the animals at 3, 6, 12, 24, 48, 72 and 168 h later. The PS was quantitated by extraction and fluorescence spectroscopy. For both the IC and free PS, peak tumour concentrations were reached at 24 h; however, the absolute concentrations for the IC were always higher (2- to 3-fold) than the free PS. Tumour to non-tumour ratios at 24 h for the IC were 6.8 for blood, 6.5 for liver, 7.2 for kidney, 5.7 for skin and 3.5 for intestine. Evaluation of viable tumour cells in ascites following in vivo PDT with a single light exposure demonstrated a dose-dependent relationship with fluence and IC concentration. However, there was significant treatment-related toxicity at all fluences. With multiple low-dose treatments, the percentage of viable tumour cells was also significantly reduced and there were no treatment-related deaths. These data suggest that, while photoimmunotherapy remains promising as a new treatment modality for ovarian cancers, careful quantitative dosimetry of both IC and light may need to be combined with multiple treatments (as with radiation therapy and chemotherapy) to control malignant disease yet maintain acceptable toxicity in vivo.