Synergistic Interaction of Natural Human Tumor Necrosis Factor-α/Natural Human Interferon-α Mixture Alone and in Combination with Cisplatin Against Head and Neck Laryngeal Squamous Carcinoma Multicellular Tumor Spheroids

We evaluated the effects of each component, natural human tumor necrosis factor-a (nHuTNF-α) and natural human interferon-α (nHu-IFN-α), and the combined nHuTNF-α/nHuIFN-α preparation with or without cisplatin (DDP) at tumor mass level. Multicellular tumor spheroids (MTS) of approximately 500 μm in diameter were produced from HEp-2 laryngeal squamous carcinoma cell line by liquid overlay culture technique. Cell kill effects of 72 hr exposure to nHuTNF-α, nHuIFN-α, or nHuTNF-α/nHuIFN-α against cells in MTS were 2–3-fold less than those in monolayer. In MTS, dose response curves become progressively flat at high drug concentrations, indicative of poor drug penetration into the MTS core. Combination nHuTNF-α/nHuIFN-α produced synergistic cell kill for both MTS and monolayers. For monolayer cells exposure to nHuTNF-α/nHuIFN-α first (72 hr) followed by DDP (1 hr) after 1 hr rest period was synergistic with combination index (CI) of approximately 0.8 at LD₅₀. Simultaneous (72 hr in nHuTNF-α/nHuIFN-α with DDP in last 1 hr) or reverse order of exposure were antagonistic. In contrast, for MTS, DDP followed by nHuTNF-α/nHuIFN-α was most synergistic with CI of approximately 0.2. Simultaneous exposure or nHuTNF-α/nHuIFN-α followed by DDP showed synergism with CI of approximately 0.5 and 0.8, respectively. The improved efficacy of DDP followed by nHuTNF-α/nHuIFN-α sequence for MTS cells appears to be due to increased nHuTNF-α penetration into the MTS core aided dy DDP.