Molecular-Targeted Antitumor Agents:  The Saururus cernuus Dineolignans Manassantin B and 4-O-Demethylmanassantin B Are Potent Inhibitors of Hypoxia-Activated HIF-1

Abstract

The transcription factor hypoxia-inducible factor-1 (HIF-1) is a key regulator of tumor cell adaptation and survival under hypoxic conditions. Selective HIF-1 inhibitors represent an important new class of potential molecular-targeted antitumor therapeutic agents. Extracts of plants and marine organisms were evaluated using a T47D human breast tumor cell-based reporter assay for HIF-1 inhibitors. Bioassay-guided fractionation of the lipid extract of Saururus cernuus resulted in the isolation of manassantin B (1) and a new compound, 4-O-demethylmanassantin B (2). The structure of 2 was determined spectroscopically. The absolute configurations of manassantin-type dineolignans have not been previously reported. Therefore, the absolute configurations of the chiral centers in each side chain were deduced from spectroscopic analysis of the Mosher MTPA ester derivatives of 1. Both 1 and 2 are among the most potent small molecule HIF-1 inhibitors discovered, to date, with IC(50) values of 3 and 30 nM, respectively. Compounds 1 and 2 selectively inhibited hypoxia-activated HIF-1 in contrast to iron chelator-activated HIF-1. Compounds 1 and 2 also inhibited hypoxic induction of the angiogenic factor VEGF. Further study revealed that 1 selectively blocked the induction of HIF-1alpha protein, the oxygen regulated HIF-1 subunit that determines HIF-1 activity.

Laurenditerpenol, a New Diterpene from the Tropical Marine Alga Laurencia intricata that Potently Inhibits HIF-1 Mediated Hypoxic Signaling in Breast Tumor Cells

“…The hypoxia-selective HIF-1 inhibitor manassantin B (0.1 μM) was used as a positive control. 21 Hypoxia (1% O 2 ) increased secreted VEGF protein level by 2.6-fold and 1 inhibited the induction by 55% at 1 μM (Figure 3). At the MIC (3 μM), an 80% inhibition of the induction was observed.…”

“…Recently, we reported the identification of dineolignans from Saururus cernuus as potent and physiological hypoxia selective HIF-1 inhibitors. 21 Few natural products share structural similarities with 1. Interestingly, the previously reported Laurencia pannosa sesquiterpene known as pannosane 10c and the Aplysia dactylomela diterpene dactylopyrinoid 30 also contain this unusual 7-oxabicyclo[2.2.1]heptane ring system.…”

Benzochromenones from the Marine Crinoid Comantheria rotula Inhibit Hypoxia-Inducible Factor-1 (HIF-1) in Cell-Based Reporter Assays and Differentially Suppress the Growth of Certain Tumor Cell Lines

“…18 Compounds 1-7 significantly inhibited both hypoxia-induced and iron chelator-induced HIF-1 activation (pHRE-TK-Luc) in T47D breast tumor cells (IC 50 values 1.7 -7.3 μM for hypoxia-induced and 0.6 -3.0 μM for 1,10-phenanthroline-induced, Table 3). Compounds 1-4 and 6 also inhibited hypoxia-induced HIF-1 activation (pHRE-TK-Luc) in PC-3 prostate tumor cells (IC 50 values 1.0 -10.0 μM, Table 3).…”

“…Transfection, compound treatment, exposure to hypoxic conditions and a hypoxia mimetic (10 μM 1,10-phenanthroline), and measurement of luciferase activity were performed as previously described. 18 The IC 50 values were determined using GraphPad Prism 4 software from experiments performed in triplicate. Compounds were tested at half-log concentrations and the standard deviation values for over 95% of the data points are less than 15%.…”

“…18,19 The only modification is that the cells were lysed with 250 μL M-PER mammalian protein extraction reagent (Pierce) after removal of the conditioned media, and protein concentrations in the cell lysates determined using the Micro BCA Protein Assay Kit (Pierce). The amount of secreted VEGF protein(s) was normalized to the amount of protein in the cellular lysates.…”