Andrographolide derivatives inhibit guanine nucleotide exchange and abrogate oncogenic Ras function

Abstract

Aberrant signaling by oncogenic mutant rat sarcoma (Ras) proteins occurs in ∼15% of all human tumors, yet direct inhibition of Ras by small molecules has remained elusive. Recently, several smallmolecule ligands have been discovered that directly bind Ras and inhibit its function by interfering with exchange factor binding. However, it is unclear whether, or how, these ligands could lead to drugs that act against constitutively active oncogenic mutant Ras. Using a dynamics-based pocket identification scheme, ensemble docking, and innovative cell-based assays, here we show that andrographolide (AGP)-a bicyclic diterpenoid lactone isolated from Andrographis paniculata-and its benzylidene derivatives bind to transient pockets on Kirsten-Ras (K-Ras) and inhibit GDP-GTP exchange. As expected for inhibitors of exchange factor binding, AGP derivatives reduced GTP loading of wild-type K-Ras in response to acute EGF stimulation with a concomitant reduction in MAPK activation. Remarkably, however, prolonged treatment with AGP derivatives also reduced GTP loading of, and signal transmission by, oncogenic mutant K-RasG12V. In sum, the combined analysis of our computational and cell biology results show that AGP derivatives directly bind Ras, block GDP-GTP exchange, and inhibit both wild-type and oncogenic K-Ras signaling. Importantly, our findings not only show that nucleotide exchange factors are required for oncogenic Ras signaling but also demonstrate that inhibiting nucleotide exchange is a valid approach to abrogating the function of oncogenic mutant Ras.cancer | molecular dynamics | allosteric site | drug design

Combined Rational Design and a High Throughput Screening Platform for Identifying Chemical Inhibitors of a Ras-activating Enzyme

“…This suggests a potential new paradigm for dual targeting of catalytic pockets on enzymes with relatively large drug-accessible surfaces. In addition, recent studies have implicated SOS1 in oncogenic K-Ras tumorigenesis in pancreatic, colon, and breast cancer models by mediating H-Ras and N-Ras signaling through an autocrine loop (37,38,51), suggesting an interesting future utility of SOS1 inhibitors in K-Ras-mediated oncogenicity, which is supported here by the inhibition of MIA-PaCa-2 pancreatic cancer cell growth with both SOS1 inhibitors.…”

Approach for targeting Ras with small molecules that activate SOS-mediated nucleotide exchange

“…Although a number of small molecules have been reported to bind directly to Ras (7)(8)(9)(10)(11)(12), these compounds have relatively poor binding affinities, and none have advanced to the clinic to date.…”

“…Signaling from these WT isoforms of Ras can support the growth of cancer cells harboring oncogenic Ras mutations (17), and inhibiting nucleotide exchange is a valid approach to abrogate signaling arising from both mutant and WT Ras (11). As a key control point for the activation of multiple Ras isoforms and propagation of RTKRas signaling, SOS represents a promising point of intervention for Ras-driven cancers.…”

Fabrication and in vitro/in vivo evaluation of amorphous andrographolide nanosuspensions stabilized by D-α-tocopheryl polyethylene glycol 1000 succinate/sodium lauryl sulfate

“…cell lines, including breast, hepatic, cervical, colon and gastric cancers and glioblastoma in preclinical studies. 5,6 The potential use of ADG has attracted wide attention in recent years. Unfortunately, the clinical use of ADG remains challenging due to its extremely poor solubility (1.32×10 -7 M in water at 25°C) and efflux by P-glycoprotein (P-gp), [7][8][9] which results in low bioavailability after oral administration.…”