Discovery of a PFKFB3 inhibitor for phase I trial testing that synergizes with the B-Raf inhibitor vemurafenib

Abstract

In human cancers, loss of PTEN, stabilization of hypoxia inducible factor-1α, and activation of Ras and AKT converge to increase the activity of a regulator of glycolysis, 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (PFKFB3). This enzyme synthesizes fructose-2,6-bisphosphate, which is an activator of 6-phosphofructo-1-kinase, a key step of glycolysis that is tightly controlled by multiple metabolic feedback mechanisms. We recently identified the first competitive small molecule inhibitor of PFKFB3, 3-(3-pyridinyl)-1-(4-pyridinyl)-2-propen-1-one (3PO), and demonstrated that this agent is selectively cytotoxic to Ras-transformed epithelial cells and displays broad anti-tumor activity. We now report the discovery of a novel 3PO-derivative, PFK158, that is markedly more potent than 3PO, has excellent pharmacokinetic properties and causes ∼80% growth inhibition in several mouse models of human-derived tumors. Importantly, IND-enabling safety and toxicity studies have demonstrated that PFK158 is well tolerated in rats and dogs, providing support for a phase 1 trial in cancer patients planned for early 2014. Once the maximum tolerated dose is identified, we intend to conduct multiple phase 1/2 trials of PFK158 in combination with targeted agents given the ability of PFK158 to suppress glucose metabolism and multiple survival mechanisms. One such targeted agent, vemurafenib, is a mutant B-Raf inhibitor that was recently FDA-approved for BRAFV600E-positive melanoma patients. Unfortunately, a multitude of resistance mechanisms have resulted in disease progression in less than one year for the majority of melanoma patients treated with vemurafenib. We hypothesized that PFK158 would sensitize vemurafenib-resistant melanoma cells and found that the addition of PFK158 to vemurafenib caused a marked increase in the apoptotic death of several melanoma cell lines in vitro. These data provide rationale for the conduct of pre-clinical studies of PFK158 combined with vemurafenib in transgenic BRAFV600E melanoma mouse models which are in turn expected to justify a phase I/II trial of the combination in BRAFV600E-positive melanoma patients. In conclusion, PFK158 is the first PFKFB3 inhibitor to be examined in a phase I trial and may have significant clinical utility when combined with agents that target driver oncogenes.