Differential regulation of cytokine expression determines the differential drug sensitivity between carcinomas and lymphomas towards mTOR inhibitor

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Purpose: The PI3K/Akt and mTORC1 pathways are among the critical signaling pathways in regulating proliferation and survival of normal and cancer cells. We examine the differential drug sensitivity of RAD001 between lymphoma and carcinomas and the underlying mechanisms.
 Experimental Design: The in vitro growth inhibitory effect of RAD001 was evaluated in 6 lymphoma cell lines (Raji, Pfeiffer, Ramos, SR786, H9, Jurkat) and 8 carcinoma cell lines (Hep3B, HepG2, SKhep1, PLC5, Huh7, TW01, HONE1, NCI-N87). Cell viability, signaling targets, and production of cytokines were determined by MTT assay, immunoblotting, and ELISA respectively.
 Results: The anti-proliferative effect of RAD001 in lymphoma cells was strikingly different from that in carcinoma cells. RAD001 induced a dose-dependent growth-inhibition in several lymphoma cell lines, with 50%-inhibitory concentrations (IC50s) at low- to sub-nM range. In contrast, a maximum of 30 to 50% of growth suppression was induced by RAD001 with the dose range up to μM range in all carcinoma cells tested. The treatment of RAD001 in carcinoma cell lines may lead to compensatory increase of secretion of cytokines (IL2, IL6, or IL10), leading to phosphorylation of Akt at thr473, and thereby, at least partly, providing a survival signaling. On the contrary, the treatment of RAD001 in lymphoma cell lines decreases cytokines (IL2, IL6, or IL10) production, resulting in no compensatory increase of phosphorylation of Akt. Inhibition of IL-10 or IL-6 by neutralizing antibody increased drug sensitivity toward RAD001 in carcinomas such as Huh7 and PLC5 cells. On the other hand, addition of exogenous IL-10 or IL-6 reversed the RAD001 growth arrest effect on Pfeiffer, a lymphoma cell line.
 Conclusions: Compared with lymphomas, carcinomas are in general more resistant to mTOR inhibitor. The underlying mechanisms may be associated with differential regulation of cytokines production of carcinoma and lymphoma.