Inhibition of CXCR4 by CTCE-9908 inhibits breast cancer metastasis to lung and bone.

Metastasis occurs, in part, due to tumor cell responses to chemokine secretion by ectopic organs or tissues. SDF-1 is constitutively expressed in tissues where metastases frequently develop while breast carcinoma cells express the receptor for SDF-1, CXCR4, which is correlated with increased bone metastasis and poor overall survival. We hypothesized that treatment with a CXCR4 antagonist, CTCE-9908, would decrease incidence of bone and lung metastasis. Treatment with CTCE-9908 (25 mg/kg) began the day prior to or the day of intravenous or intracardiac tumor cell inoculation of MDA-MB-231 human breast carcinoma cells expressing enhanced green fluorescent protein (GFP) into athymic mice. After 5 or 8 weeks (i.c. and i.v. injections, respectively), the presence of fluorescent foci at metastatic sites was assessed. Somewhat surprisingly, CTCE-9908 treatment did not decrease incidence of metastasis as hypothesized. However, CTCE-9908 did decrease metastatic burden (i.e., size of metastases) in all organs examined (lungs, bone, heart, liver, kidneys, pancreas and spleen). Based upon this and other studies, the use of CTCE-9908 is promising as an adjuvant therapy for metastatic disease.

Lactation failure in Src knockout mice is due to impaired secretory activation.

BACKGROUND: Mammary gland development culminates in lactation and is orchestrated by numerous stimuli and signaling pathways. The Src family of nonreceptor tyrosine kinases plays a pivotal role in cell signaling. In order to determine if Src plays a role in mammary gland development we have examined mammary gland development and function during pregnancy and lactation in mice in which expression of Src has been eliminated. RESULTS: We have characterized a lactation defect in the Src-/- mice which results in the death of over 80% of the litters nursed by Src-/- dams. Mammary gland development during pregnancy appears normal in these mice; however secretory activation does not seem to occur. Serum prolactin levels are normal in Src-/- mice compared to wildtype controls. Expression of the prolactin receptor at both the RNA and protein level was decreased in Src-/- mice following the transition from pregnancy to lactation, as was phosphorylation of STAT5 and expression of milk protein genes. These results suggest that secretory activation, which occurs following parturition, does not occur completely in Src-/- mice. Failed secretory activation results in precocious involution in the mammary glands of Src-/- even when pups were suckling. Involution was accelerated following pup withdrawal perhaps as a result of incomplete secretory activation. In vitro differentiation of mammary epithelial cells from Src-/- mice resulted in diminished production of milk proteins compared to the amount of milk proteins produced by Src+/+ cells, indicating a direct role for Src in regulating the transcription/translation of milk protein genes in mammary epithelial cells. CONCLUSION: Src is an essential signaling modulator in mammary gland development as Src-/- mice exhibit a block in secretory activation that results in lactation failure and precocious involution. Src appears to be required for increased expression of the prolactin receptor and successful downstream signaling, and alveolar cell organization.

Metastasis of hormone-independent breast cancer to lung and bone is decreased by alpha-difluoromethylornithine treatment.

INTRODUCTION: Polyamines affect proliferation, differentiation, migration and apoptosis of cells, indicating their potential as a target for cancer chemotherapy. Ornithine decarboxylase converts ornithine to putrescine and is the rate-limiting step in polyamine synthesis.alpha-Difluoromethylornithine (DFMO) irreversibly inhibits ornithine decarboxylase and MDA-MB-435 human breast cancer metastasis to the lung without blocking orthotopic tumor growth. This study tested the effects of DFMO on orthotopic tumor growth and lung colonization of another breast cancer cell line (MDA-MB-231) and the effects on bone metastasis of MDA-MB-435 cells. METHODS: MDA-MB-231 cells were injected into the mammary fat pad of athymic mice. DFMO treatment (2% per orally) began at the day of tumor cell injection or 21 days post injection. Tumor growth was measured weekly. MDA-MB-231 cells were injected into the tail vein of athymic mice. DFMO treatment began 7 days prior to injection, or 7 or 14 days post injection. The number and incidence of lung metastases were determined. Green fluorescent protein-tagged MDA-MB-435 cells were injected into the left cardiac ventricle in order to assess the incidence and extent of metastasis to the femur. DFMO treatment began 7 days prior to injection. RESULTS: DFMO treatment delayed MDA-MB-231 orthotopic tumor growth to a greater extent than growth of MDA-MB-435 tumors. The most substantial effect on lung colonization by MDA-MB-231 cells occurred when DFMO treatment began 7 days before intravenous injection of tumor cells (incidence decreased 28% and number of metastases per lung decreased 35-40%). When DFMO treatment began 7 days post injection, the incidence and number of metastases decreased less than 10%. Surprisingly, treatment initiated 14 days after tumor cell inoculation resulted in a nearly 50% reduction in the number of lung metastases without diminishing the incidence. After intracardiac injection, DFMO treatment decreased the incidence of bone metastases (55% vs 87%) and the area occupied by the tumor (1.66 mm2 vs 4.51 mm2, P < 0.05). CONCLUSION: Taken together, these data demonstrate that DFMO exerts an anti-metastatic effect in more than one hormone-independent breast cancer, for which no standard form of biologically-based treatment exists. Importantly, the data show that DFMO is effective against metastasis to multiple sites and that treatment is generally more effective when administered early.

Requirement for IGF-I in epidermal growth factor-mediated cell cycle progression of mammary epithelial cells.

Induction of cyclin proteins is required for progression of cells through the G(1)-S and G(2)-M cell cycle checkpoints and is a primary mechanism by which mitogens regulate cell cycle progression. IGF-I and the epidermal growth factor (EGF)-related ligands are mitogens for mammary epithelial cells in vitro and are essential for growth of the mammary epithelium during development. We report here that IGF-I in combination with EGF or TGFalpha is synergistic in promoting DNA synthesis in mammary epithelial cells in the intact mammary gland cultured in vitro. We further investigated the role of IGF-I and EGF in cyclin expression and cell cycle progression in the mammary gland and demonstrate that IGF-I and EGF induce expression of early G(1) cyclins. However, we show that IGF-I, but not EGF, induces late G(1) and G(2) cyclins and is required for mammary epithelial cells to overcome the G(1)-S checkpoint. These data demonstrate that IGF-I is essential for cell cycle progression in mammary epithelial cells and that it is required for EGF-mediated progression past the G(1)-S checkpoint in these cells.