Cell signaling in the tumor microenvironment is critical for the initiation, progression and metastasis of cancer. To better understand these communication pathways and therefore better design and develop therapies and diagnostics for cancers, experimental methods of probing cellular communication at a single to multi-cell level are needed. Here, we manipulate gold-coated liposomes encapsulating signaling molecules using an optical trap to initate cell signling cascades. The high polarizability of the liposome's unique gold shell allows stable optical trapping for subcellular manipulation in the presence of cells. Specifically, we encapsulated the cell signaling molecule inositol trisphosphate (IP3), a ubiquitous intracellular secondary messenger involved in GPCR and Akt signaling cascades, within 100 nm gold-coated liposomes and used an optical trapping laser to deliver liposomes into the cytosol of a single cell to initiate localized cell signaling. Upon optical injection of liposomal IP3 into a single ovarian carcinoma cell, we observed localized activation as reported by changes in Indo-1 fluorescence intensity. With established gap junctions between the injected cell and neighboring cells, we monitored propagation of this signaling to and through nearby cells. Subsequently, we investigated the ability to modulate cell signaling by, for example, varying the number of lP3-containing gold-coated liposomes injected into a single cell. By combining optical trapping with gold-coated liposomes encapsulating signaling molecules, we present a unique in vitro tool for studying cell signaling within the tumor microenvironment.