CAT3, a prodrug of 13a(S)-3-hydroxyl-6,7-dimethoxyphenanthro[9, 10-b]-indolizidine, circumvents temozolomide-resistant glioblastoma via the Hedgehog signaling pathway, independently of O6-methylguanine DNA methyltransferase expression

Purpose: Glioblastoma multiforme (GBM) is a malignant high-grade glioma with a poor clinical outcome. Temozolomide (TMZ) is the first-line GBM chemotherapy; however, patients commonly develop resistance to its effects. Materials and methods: We investigated the antitumor activity of CAT(3) in TMZ-resistant glioblastoma cell lines U251/TMZ and T98G. Orthotopic and subcutaneous mice tumor models were used to investigate the effects of various treatment regimes. Results: We found that PF403, the active metabolite of CAT(3), inhibited proliferation of both cell lines. PF403 repressed the Hedgehog signaling pathway in the U251/TMZ cell line, reduced O-6-methylguanine DNA methyltransferase (MGMT) expression, and abolished the effects of the Shh pathway. Moreover, PF403 blocked the Hedgehog signaling pathway in T98G MGMT-expressing cells and downregulated the expression of MGMT. CAT(3) suppressed growth in the U251/TMZ orthotopic and T98G subcutaneous xenograft tumor models in vivo. We also demonstrated that inhibition of the Hedgehog pathway by PF403 counteracted TMZ resistance and enhanced the antitumor activity of TMZ in vitro and in vivo. Conclusion: These results indicate that CAT(3) is a potential therapeutic agent for TMZ-resistant GBM.