Changes in intracellular free Ca2+ concentration ([Ca2+]) are an important component in the control of cell division and, recent work suggests, mediate cellular oncogene activity. Control of intracellular [Ca2+] is a chemotherapeutic strategy that could lead to selective inhibition of growth of tumor cells, cell death and even reversal of oncogenesis. Current theories of action of intracellular [Ca2+] predict that the effect of a stimulus such as neoplastic transformation, that increases [Ca2+] and produces a undirectional response in a cell can be decreased by an agent that alters the level to which intracellular [Ca2+] rises or modifies the time course of intracellular Ca2+ above a threshold value. The first hypothesis we will examine is that tumor cells have a different Ca2+ homeostasis from normal cells. Aequorin and fura-2 will be used as indicators of intracellular [Ca2+] and 45Ca will be used to measure Ca2+ fluxes and intracellular Ca2+ pools in normal human lung and lung tumor cell lines. The effects of cell division on intracellular [Ca2+] will be separated from effects of transformation using growth arrested and synchronized cell populations. A second hypothesis we will examine is that some anticancer drugs produce their effect through a selective action on [Ca2+] homeostasis in tumor cells. We will study the effect of adriamycin, adriamycin analogues, and adriamycin covalently bound to microspheres on intracellular [Ca2+] and Ca2+ fluxes in normal human lung, lung tumor cell lines and murine neuroblastoma N1E-115. Intracellular microelectrode and on-cell patch clamp recording will be used to study cell membrane voltage dependent Ca2+ channels in normal and tumor cells. We have found that adriamycin is a potent antagonist of a cell membrane voltage dependent Ca2+ channel in murine neuroblastoma N1E-115. This is an important finding because it provides a possible mechanism linking an action of an anticancer drug at the cell surface to an effect on the nucleus and cell division. We will also study the effect of agents that modify Ca2+ movement on the growth inhibitory effect of the anticancer drugs in normal and tumor cells. The objective of our studies is to learn more of the role of intracellular [Ca2+] in the control of cell growth in normal and cancer cells and how drugs might be used to modulate cell growth through an effect on Ca2+ homeostasis.
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