A lipophilic vasoactive intestinal peptide analog enhances the antiproliferative effect of chemotherapeutic agents on cancer cell lines

BACKGROUND. Vasoactive intestinal peptide (VIP) is one of several small neuropeptides that affect cancer growth. A lipophilic VIP analog, stearyl-Nle¹⁷-neurotensin_6-11 VIP_7-28 (SNH) that inhibited lung carcinoma growth has been described previously. The experiments performed were clonogenic assays in vitro and tumor xenografts in nude mice in vivo. These studies were now extended to colon carcinoma and to combination therapy with chemotherapeutic agents. METHODS. Assays were performed with cell lines, and tumor proliferation was assessed using the (3-[4,5-dimethylthiazol-2-yl-5]-[3-Carboxymethoxyphenyl]-2[4-sulfophenyl]-2H tetrazolium) (MTS) colorimetric assay for mitochondrial function of living cells. RESULTS. The lipophilic analog (SNH) enhanced the antiproliferative activity of diverse chemotherapeutic agents: doxorubicine (antibiotic); vinorelbine (vinca alkaloid, antimicrotubule formation); paclitaxel (antimicrotubule agent); gemcitabine (antimetabolite); irinotecan (topoisomerase I inhibitor); and cisplatin (platinum compound acting as an alkylating agent). In all,cases, the antiproliferative effect of SNH and the chemotheraputic agent was at least additive and for some combinations and concentrations even synergistic. For example, 2 μM of the antagonist that produced a 15-20% growth inhibition in the nonsmall cell lung carcinoma cell line reduced the IC₅₀ by 2-4-fold for most of the chemotherapeutic agents tested. Higher analog concentrations were even more efficacious. Similar results were obtained with colon carcinoma cell lines. CONCLUSIONS. Chemotherapeutic treatment of advanced solid tumors, such as nonsmall cell lung carcinoma, colon carcinoma, or prostate carcinoma, achieves a response rate of between 10% and 30% with significant toxicity. Combination therapy with the lipophilic VIP analog SNH and the preferred chemotherapeutic agent may greatly enhance the response rate, and by permitting a dose reduction, should significantly reduce side effects.