On April 21, 2015 SignalRx Pharmaceuticals Inc., focused on developing more effective oncology drugs though molecular design imparting selected multiple target inhibition, reported the presentation of scientific data on the Company’s proprietary dual inhibitor program in oncology (Press release, SignalRx, APR 21, 2015, http://www.ireachcontent.com/news-releases/signalrx-presents-at-10th-annual-drug-discovery-chemistry-conference-on-its-dual-kinase-epigenetic-inhibitors-for-treating-cancer-500857951.html [SID1234527330]). The presentation by Dr. Donald L. Durden, MD, PhD, co-founder and science advisor to SignalRx was made at the Tenth Annual Drug Discovery Chemistry meeting at the Hilton San Diego Resort & Spa in San Diego, California.
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The oral presentation entitled "Discovery of Dual PI3K/BRD4 (kinase/epigenetic) Inhibitors" was given during the Second Annual Epigenetic Inhibitor Discovery track of the meeting at the "Advances in BET Bromodomain Inhibitor Development" session. The presentation highlighted a novel thienopyranone molecular scaffold that selectively inhibits both PI3 kinase (PI3K) and the bromodomain protein BRD4. The presentation described how molecular modeling studies were used to identify and design SignalRx’s single small molecules that can bind and inhibit simultaneously PI3K and BRD4. While the small molecule SF2523 inhibits PI3K via ATP competitive binding at the catalytic site, BRD4 inhibition appears to take place by binding in the acetyl-lysine recognition moiety of BRD4 thus blocking BRD4’s ability to alter chromatin structure and induce transcription. Blocking the binding of BRD4 to acetylated histones within chromatin can then block the transcription of various genes that are promoting cancer cell survival and growth. Recent reports suggest that BRD4 inhibition may block cancer cell resistance arising from widespread epigenetic kinome adaptation following exposure to targeted kinase inhibitor drugs which in turn may lead to more durable anticancer effects.
The presentation also included a specific rationale for the dual PI3K/BRD4 inhibition approach in cancers driven by the key cancer promoting transcription factor MYC. MYC (both cMYC and MYCN) acts downstream of many cell receptor complexes and signal transduction pathways to activate genes that drive cancer cell growth and proliferation. To date, small molecule inhibitors of MYC have been elusive. Inhibition of PI3K enhances the degradation of the cancer promoting transcription factor MYC. Inhibition of BRD4 blocks the production of MYC; thus, a dual PI3K/BRD4 inhibitor can lead to maximal MYC extinction by inhibiting these two different mechanisms. Our approach enables us to go after cancers expected to be susceptible to maximal MYC extinction as a beneficial treatment, such as CLL, medulloblastoma, multiple myeloma, and certain ovarian cancers exhibiting elevated MYCN expression. In vivo data also showed that SF2523 (50 mg/kg 3X per week) exhibited potent antitumor efficacy and anti-metastatic effects without toxicity in renal cell carcinoma xenograft models, neuroblastoma mouse models, orthotopic pancreatic cancer model and Lewis lung cancer models. Lastly, pre-clinical in vivo proof-of-concept with SF2523 was presented showing the pharmacodynamic knockdown of both the PI3K pathway and MYC in mouse neuroblastoma tumor samples four hours after administration, confirming the dual PI3K/BRD4 inhibitory profile of lead compound SF2523. Further preclinical studies of several PI3K/BRD4 dual inhibitor thienopyranones are underway to identify and select a clinical candidate.