Targeting the MAPK Signaling Pathway in Cancer: Promising Preclinical Activity with the Novel Selective ERK1/2 Inhibitor BVD-523 (Ulixertinib).

Aberrant activation of signaling through the RAS-RAF-MEK-ERK (MAPK) pathway is implicated in numerous cancers, making it an attractive therapeutic target. Although BRAF and MEK-targeted combination therapy has demonstrated significant benefit beyond single-agent options, the majority of patients develop resistance and disease progression after approximately 12 months. Reactivation of ERK signaling is a common driver of resistance in this setting. Here we report the discovery of BVD-523 (ulixertinib), a novel, reversible, ATP-competitive ERK1/2 inhibitor with high potency and ERK1/2 selectivity. In vitro BVD-523 treatment resulted in reduced proliferation and enhanced caspase activity in sensitive cells. Interestingly, BVD-523 inhibited phosphorylation of target substrates despite increased phosphorylation of ERK1/2. In in vivo xenograft studies, BVD-523 showed dose-dependent growth inhibition and tumor regression. BVD-523 yielded synergistic antiproliferative effects in a BRAFV600E-mutant melanoma cell line xenograft model when used in combination with BRAF inhibition. Antitumor activity was also demonstrated in in vitro and in vivo models of acquired resistance to single-agent and combination BRAF/MEK-targeted therapy. On the basis of these promising results, these studies demonstrate BVD-523 holds promise as a treatment for ERK-dependent cancers, including those whose tumors have acquired resistance to other treatments targeting upstream nodes of the MAPK pathway. Assessment of BVD-523 in clinical trials is underway (NCT01781429, NCT02296242, and NCT02608229). Mol Cancer Ther; 16(11); 2351-63. ©2017 AACR.

Evaluating the immortal strand hypothesis in cancer stem cells: symmetric/self-renewal as the relevant surrogate marker of tumorigenicity.

Stem cells subserve repair functions for the lifetime of the organism but, as a consequence of this responsibility, are candidate cells for accumulating numerous genetic and/or epigenetic aberrations leading to malignant transformation. However, given the importance of this guardian role, stem cells likely harbor some process for maintaining their precious genetic code such as non-random segregation of chromatid strands as predicted by the Immortal Strand Hypothesis (ISH). Discerning such non-random chromosomal segregation and asymmetric cell division in normal or cancer stem cells has been complicated by methodological shortcomings but also by differing division kinetics amongst tissues and the likelihood that both asymmetric and symmetric cell divisions, dictated by local extrinsic factors, are operant in these cells. Recent data suggest that cancer stem cells demonstrate a higher incidence of symmetric versus asymmetric cell division with both daughter cells retaining self-renewal characteristics, a profile which may underlie poorly differentiated morphology and marked clonal diversity in tumors. Pathways and targets are beginning to emerge which may provide opportunities for preventing such a predilection in cancer stem cells and that will hopefully translate into new classes of chemotherapeutics in oncology. Thus, although the existence of the ISH remains controversial, the shift of cell division dynamics to symmetric random chromosome segregation/self-renewal, which would negate any likelihood of template strand retention, appears to be a surrogate marker for the presence of highly malignant tumorigenic cell populations.

Cancer stem cells as the relevant biomass for drug discovery.

The poor success rate of discovering new, effective chemotherapeutics for oncology may reflect the failure of targeting treatments to the more aggressive, tumorigenic cells of the malignancy. Data have now emerged from several laboratories, examining both liquid and solid primary tumor tissues, that implicate cancer stem cells (CSCs) as the 'master-driver' cellular population for tumorigenicity. Moreover, these putative CSCs appear relatively resistant to existing chemotherapeutic and radiation therapy. Several different cellular pathways have been identified as likely mechanisms causal for the underlying insensitivity of the CSCs to conventional therapy. Progress has been made in the isolation and expansion of these CSCs for constructing conventional high-throughput phenotypic screening campaigns. However, challenges remain in designing optimal proof-of-concept trials for the clinical development of compounds targeting the elimination of CSCs.

Janus kinase 2 inhibitors. Synthesis and characterization of a novel polycyclic azaindole.

The synthesis and characterization of a novel polycyclic azaindole based derivative is disclosed, and its binding to JAK2 is described. The compound is further evaluated for its ability to block the EPO/JAK2 signaling cascade in vitro and in vivo.

Targeting cancer stem cells for more effective therapies: Taking out cancer's locomotive engine.

Novel therapies for the treatment of solid tumors have generally failed to improve patient overall survival. These therapeutic approaches are typically focused on targeting signaling pathways implicated in cell growth and/or survival in order to shrink the malignant mass and achieve an objective clinical response; however, too often these responses are followed by eventual regrowth of the tumor. This clinical conundrum could be explained by the existence of a tumorigenic cell population that is relatively resistant to these therapies and retains pluripotent status in order to repopulate the original tumor and/or contribute to distant metastasis following treatment. Compelling data from liquid tumors, and more recently from studies focused on solid tumors, now support the existence of such tumorigenic cells (i.e., cancer stem cells) as a distinct subpopulation within the total tumor cell mass. These cancer stem cells (CSCs), as compared to the non-CSC population, have the ability to reconstitute the primary tumor phenotype when transplanted into recipient animals. In addition, data are beginning to emerge demonstrating that many standard-of-care chemotherapeutics are less effective in promoting cell death or cytostasis in these putative cancer stem cells as compared to effects in the non-stem cell cancerous cells. Therefore, targeting these locomotive drivers of tumors, the cancer stem cell population, should be considered a high priority in the continued pursuit of more effective cancer therapies.