Fibroblast-like stromal cells modulate cancer cells through secreted factors and adhesion, but those factors are not fully understood. Here, we have identified critical stromal factors that modulate cancer growth positively and negatively. Using a cell co-culture system, we found that gastric stromal cells secreted IL-6 as a growth and survival factor for gastric cancer cells. Moreover, gastric cancer cells secreted PGE2 and TNFα that stimulated IL-6 secretion by the stromal cells. Furthermore, we found that stromal cells secreted glyceraldehyde 3-phosphate dehydrogenase (GAPDH). Extracellular GAPDH, or its N-terminal domain, inhibited gastric cancer cell growth, a finding confirmed in other cell systems. GAPDH bound to E-cadherin and downregulated the mTOR-p70S6 kinase pathway. These results demonstrate that stromal cells could regulate cancer cell growth through the balance of these secreted factors. We propose that negative regulation of cancer growth using GAPDH could be a new anti-cancer strategy.

The disruption of the tumor microenvironment (TME) is a promising anti-cancer strategy, but its effective targeting for solid tumors remains unknown. Here, we investigated the anti-cancer activity of the mitochondrial complex I inhibitor intervenolin (ITV), which modulates the TME independent of energy depletion. By modulating lactate metabolism, ITV induced the concomitant acidification of the intra-and extracellular environment, which synergistically suppressed S6K1 activity in cancer cells through protein phosphatase-2A-mediated dephosphorylation via G-protein-coupled receptor(s). Other complex I inhibitors including metformin and rotenone were also found to exert the same effect through an energy depletion-independent manner as ITV. In mouse and patient-derived xenograft models, ITV was found to suppress tumor growth and its mode of action was further confirmed. The TME is usually acidic owing to glycolytic cancer cell metabolism, and this condition is more susceptible to complex I inhibitors. Thus, we have demonstrated a potential treatment strategy for solid tumors.

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Fibroblast-like stromal cells modulate the growth of cancer cells, both positively and negatively. Growth modulation is achieved through the secretion of regulatory factors as well as by proteins within the extracellular matrix. Those cellular interactions present attractive targets for cancer chemotherapy. It was demonsrated a novel natural compound, intervenolin (ITV), inhibited the in vitro growth of human gastric cancer cells when co-cultured with stromal cells. Importantly, the inhibition was enhanced by the presence of stromal cells. The present study reported a mechanism of ITV action. Human gastric fibroblast-like stromal cells (Hs738) were treated with ITV. The resultant conditioned medium (ITV CM) inhibited the growth of human gastric cancer cells and suppressed the level of c-Myc protein. This result suggested that ITV negatively modulated cancer cell growth by upregulating the secretion of factors originating from stromal cells in the co-culture system. To better understand the mechanism, ITV CM was subjected to proteomic analysis. The data revealed that one of the candidate regulators was thrombospondin-1 (TSP-1). Recombinant human TSP-1 protein inhibited the growth of gastric cancer cells. Moreover, the growth-inhibitory activities of ITV CM as well as that of recombinant TSP-1 were blocked by neutralizing antibody targeting TSP-1. These results suggested that ITV inhibited the growth of gastric cancer cells through its modulation of stromal cell function.

The cancer tissue contains lots of stromal cells. Among them, fibroblast-like stromal cells regulate the growth of cancer cells positively and negatively through secreted factors and adhesion. We have been studying the interactions between cancer cells and stromal cells using small molecules that can modulate the interactions. We previously reported that gastric stromal cells enhance the growth of gastric cancer cells through secretion of IL-6, which is stimulated by gastric cancer cells through PGE2 and TNF-alpha reciprocally. Here we report that GAPDH, a house keeping protein, is a negative regulator of the interactions. By purifying the growth inhibitory activity against gastric cancer cells from secreted factors of gastric stromal cell we unexpectedly identified GAPDH as an active substance. While GAPDH is known to be secreted extracellularly, its growth inhibitory activity has not yet. As a result, GAPDH is found to be secreted from various organ-derived stromal cells and to inhibit the growth of various cancer cell lines. We have found that this growth inhibitory activity of GAPDH doesn't need its original enzymatic activity and GAPDH inhibits mTOR-p70S6 kinase pathway by binding to E-cadherin on cancer cell membranes. We propose that negative regulation of cancer growth using GAPDH could be a new anti-cancer strategy. Citation Format: Kawada Manabu, Junjiro Yoshida, Hiroyuki Inoue, Shun-ichi Ohba, Manabu Yamasaki, Ihomi Usami, Shuichi Sakamoto, Hikaru Abe, Takumi Watanabe, Akio Nomoto, Masakatsu Shibasaki. Stromal cells suppress cancer development by secreted GAPDH-E-cadherin interaction. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A196.