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Increase in cell numbers is inhibited by adding mecillinam to vegetative cultures of Myxococcus xanthus. However, both cell length and volume continue to increase in the presence of the antibiotic. Different size classes of cells increase in proportion to their initial size. Incorporation of meso-diamino[C]pimelic acid into peptidoglycan and [H]uridine into RNA is not immediately affected by mecillinam. It is suggested that mecillinam inhibits the formation of new sites of wall synthesis, and these are necessary for cell division to occur. [ABSTRACT FROM AUTHOR]

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Introduction: Phosphoinositide 3-kinase (PI3K)-activated signalling has a critical role in the evolution of aggressive tumourigenesis and is therefore a prime target for anticancer therapy. Previously we have shown that the beta galactoside binding protein (betaGBP) cytokine, an antiproliferative molecule, induces functional inhibition of class 1A and class 1B PI3K. Here, we have investigated whether, by targeting PI3K, betaGBP has therapeutic efficacy in aggressive breast cancer cells where strong mitogenic input is fuelled by overexpression of the ErbB2 (also known as HER/neu, for human epidermal growth factor receptor 2) oncoprotein receptor and have used immortalised ductal cells and non-aggressive mammary cancer cells, which express ErbB2 at low levels, as controls., Methods: Aggressive BT474 and SKBR3 cancer cells where ErbB2 is overexpressed, MCF10A immortalised ductal cells and non-invasive MCF-7 cancer cells which express low levels of ErbB2, both in their naive state and when forced to mimic aggressive behaviour, were used. Class IA PI3K was immunoprecipitated and the conversion of phosphatidylinositol (4,5)-biphosphate (PIP2) to phosphatidylinositol (3,4,5)-trisphosphate (PIP3) assessed by ELISA. The consequences of PI3K inhibition by betaGBP were analysed at proliferation level, by extracellular signal-regulated kinase (ERK) activation, by akt gene expression and by apoptosis. Apoptosis was documented by changes in mitochondrial membrane potential, alteration of the plasma membrane, caspase 3 activation and DNA fragmentation. Phosphorylated and total ERK were measured by Western blot analysis and akt mRNA levels by Northern blot analysis. The results obtained with the BT474 and SKBR3 cells were validated in the MCF10A ductal cells and in non-invasive MCF-7 breast cancer cells forced into mimicking the in vitro behaviour of the BT474 and SKBR3 cells., Results: In aggressive breast cancer cells, where mitogenic signalling is enforced by the ErbB2 oncoprotein receptor, functional inhibition of the catalytic activity of PI3K by the betaGBP cytokine and loss of akt mRNA results in apoptotic death. A functional correlation between ERK and the kt gene was also found. The relationship between ERK, akt mRNA, PI3K and cell vulnerability to betaGBP challenge was sustained both in mammary ductal cells forced to mimic an aggressive behaviour and in non-aggressive breast cancer cells undergoing an enforced shift into an aggressive phenotype., Conclusions: betaGBP, a newly discovered physiological inhibitor of PI3K, is a selective and potent inducer of apoptosis in aggressive breast cancer cells. Due to its physiological nature, which carries no chemotherapeutic disadvantages, betaGBP has the potential to be safely tested in clinical trials.

This review highlights the discovery of beta-galactoside binding protein (betaGBP), an antiproliferative cytokine, as a potent and selective anticancer agent. Unlike drugs designed to block receptor tyrosine kinases or specific control points along signaling pathways, betaGBP does not harm normal cells. As a physiological effector molecule, betaGBP can selectively induce death in cancer cells by enforcing its regulatory functions to which normal and cancer cells respond differently, and thus exploit the genetic and molecular deviations developed by cancer cells.

We report here that beta-galactoside binding protein (betaGBP), an antiproliferative cytokine which can program cancer cells to undergo apoptosis, exhibits equal therapeutic efficacy against cancer cells that display diverse mechanisms of drug resistance and against their parental cells. The mechanisms of drug resistance in the cancer cells that we have examined include overexpression of P-glycoprotein, increased efficiency of DNA repair, and altered expression and mutation in the topoisomerase I and II enzymes. We also report that betaGBP exerted its effect by arresting the cells in S phase prior to the activation of programmed cell death. The uniquely similar profile of response to betaGBP by these drug-resistant cells and their parental cells extends the therapeutic potential of this cytokine in the treatment of cancers and offers a promising alternative to patients whose tumors are refractory to the currently available cadre of chemotherapeutic agents.

Cancer therapies based on drugs designed to interfere with specific targets within the molecular circuitry of cancer cells are currently under intense experimentation. Our strategy is based on the use of a naturally occurring immunomolecule which can selectively kill cancer cells, based on its ability to exploit genetic differences between normal and cancer cells. The betaGBP cytokine has previously been shown to negatively regulate the cell cycle by blocking cells in late S phase. In tumour cells, but not in normal cells, the S phase block has been shown to be followed by apoptosis. Mechanisms involved in S phase arrest have been pinpointed to downregulation of signalling and altered expression of cell cycle controller proteins, including E2F1, a transcription factor with ability to play a part in apoptosis. Here we discuss the use of betaGBP within the context of cancer surveillance and cancer therapeutics focussing on E2F1 as one mechanistic aspect relevant to betaGBP's selective induction of programmed cell death in cancer.