Synthesis and Biological Evaluation of Manassantin Analogues for Hypoxia-Inducible Factor 1α Inhibition

Abstract

To cope with hypoxia, tumor cells have developed a number of adaptive mechanisms mediated by hypoxia-inducible factor 1 (HIF-1) to promote angiogenesis and cell survival. Due to significant roles of HIF-1 in the initiation, progression, metastasis, and resistance to treatment of most solid tumors, a considerable amount of effort has been made to identify HIF-1 inhibitors for treatment of cancer. Isolated from Saururus cernuus, manassantins A (1) and B (2) are potent inhibitors of HIF-1 activity. To define the structural requirements of manassantins for HIF-1 inhibition, we prepared and evaluated a series of manassantin analogues. Our SAR studies examined key regions of manassantin’s structure in order to understand the impact of these regions on biological activity and to define modifications that can lead to improved performance and drug-like properties. Our efforts identified several manassantin analogues with reduced structural complexity as potential lead compounds for further development. Analogues MA04, MA07, and MA11 down-regulated hypoxia-induced expression of the HIF-1α protein and reduced the levels of HIF-1 target genes, including cyclin-dependent kinase 6 (Cdk6) and vascular endothelial growth factor (VEGF). These findings provide an important framework to design potent and selective HIF-1α inhibitors, which is necessary to aid translation of manassantin-derived natural products to the clinic as novel therapeutics for cancers.

Hypoxia‐inducible factor‐1 (HIF‐1) inhibitors from the last decade (2007 to 2016): A “structure–activity relationship” perspective

“…The ketone and hydroxy analogs of 43 without methoxy substituents at the distal phenyl ring also retained sub‐micromolar IC 50 values (IC 50 = 0.69 μM and 0.59 μM for 48h and 48i , respectively). Analog 47 regulated HIF‐1α but not HIF‐1β, and reduced Cdk6, VEGF, and mRNA levels markedly . Mechanistically, the hit protein of manassantin A related to HIF‐1 activity is filamin A, but more work is needed to understand the exact mechanism …”

“…18 The similar benzimidazole analog (4) of LW6 identified through an HRE-dependent cell-based assay was supposed to regulate HIF-1 through the Hsp90-Akt pathway. The benzimidazole analog (4) reduced tumor growth by 58.6% in a mouse model and exhibited an IC 50 (human colorectal carcinoma cells). 19 LW6 was further modified in search of a better analog by replacing ring B with nicotinic and isonicotinic acid, esters, or amides.…”

“…The biotin affinity probes 9a and 9b were bound non-specifically to the proteins because of the hydrophobic nature of LW6 under the experimental conditions. On the other hand, the click conjugation probe 10a and its negative control 10b, which has an acetylene moiety, exhibited good potency and complete loss of activity, respectively (IC 50 Figure 3.…”

Discovery of Manassantin A Protein Targets Using Large-Scale Protein Folding and Stability Measurements

“…1 In cell-based assays manassantin A has been shown to possess therapeutic potential for the treatment of diseases involving melanin production, 5,6 atherosclerosis, 7–9 and cancer. 1,10–12 Manassantin A exhibits cytotoxicity against a wide range of cancer cell lines including HT-29, HepG2, PC-3, and MDA-MB-231, but weak cytotoxicity against non-cancer cell lines. 1,10,11 This cytotoxic specificity makes manassantin A an attractive anti-cancer drug candidate.…”

“…19 Several manassantin A derivatives also inhibit HIF-1α in cell-based assays, some with lower IC 50 values than the parent compound. 12,16–18 One prominent HIF-1α target angiogenic gene, vascular endothelial growth factor (VEGF), is also inhibited by manassantin A. 12,17,18 While many cell-based studies have shown inhibition of HIF-1α by manassantin A, the molecular mechanism(s) by which this inhibition occurs are unknown.…”