pik-75 and Neoplasm-Metastasis

Emerging data support the rationale of combined therapies in advanced melanoma. Specifically, the combined use of drugs with different mechanisms of action can reduce the probability of selecting resistant clones. To identify agents active against melanoma cells, we screened a library of 349 anti-cancer compounds, currently in clinical use or trials, and selected PIK-75, an inhibitor of the phosphatidylinositol 3-kinase/protein kinase B (PI3K/AKT) pathway, as the 'top active' drug. PIK-75 was then used alone or in combination with vemurafenib, the first BRAF inhibitor approved for patients with melanoma harboring BRAF mutations. We identified a combined dose of PIK-75 and vemurafenib that inhibited both the PI3K/AKT and mitogen-activated protein kinase pathways, thereby overcoming any compensatory activation. In view of the important tumor suppressor function induced by restoring expression of microRNA (miR)-126 in metastatic melanoma cells, we examined whether miR-126 has a synergistic role when included in a triple combination alongside PIK-75 and vemurafenib. We found that enforced expression of miR-126 (which alone can reduce tumorigenicity) significantly increased PIK-75 activity when used as either a single agent or in combination with vemurafenib. Interestingly, PIK-75 proved to be effective against early passage cell lines derived from patients' biopsies and on melanoma cell lines resistant to either vemurafenib or dabrafenib, thus suggesting that it potentially has the capability to overcome drug resistance. Finally, the synergistic role played by miR-126 in combination with vemurafenib and/or PIK-75 was demonstrated in vivo in mouse xenograft models, in which tumor growth inhibition was associated with increased apoptosis. These results not only show the efficacy of PIK-75 and vemurafenib co-treatment but also indicate that restoration of miR-126 expression in advanced melanoma can enhance their antitumor activity, which may possibly allow dose reduction to decrease adverse events without reducing the therapeutic benefits.

Topics: Animals; Antineoplastic Combined Chemotherapy Protocols; Cell Line, Tumor; Extracellular Signal-Regulated MAP Kinases; Female; Humans; Hydrazones; MAP Kinase Signaling System; Melanoma; Mice; Mice, Nude; MicroRNAs; Neoplasm Metastasis; Neoplasm Proteins; Phosphatidylinositol 3-Kinases; Phosphoinositide-3 Kinase Inhibitors; RNA, Neoplasm; Sulfonamides; Vemurafenib

Many malignancies show increased expression of the epidermal growth factor (EGF) receptor family member ErbB3 (HER3). ErbB3 binds heregulin β-1 (HRGβ1) and forms a heterodimer with other ErbB family members, such as ErbB2 (HER2) or EGF receptor (EGFR; HER1), enhancing phosphorylation of specific C-terminal tyrosine residues and activation of downstream signaling pathways. ErbB3 contains six YXXM motifs that bind the p85 subunit of phosphoinositide 3 (PI3)-kinase. Previous studies demonstrated that overexpression of ErbB3 in mammary tumor cells can significantly enhance chemotaxis to HRGβ1 and overall metastatic potential. We tested the hypothesis that ErbB3-mediated PI3-kinase signaling is critical for heregulin-induced motility, and therefore crucial for ErbB3-mediated invasion, intravasation and metastasis. The tyrosines in the six YXXM motifs on the ErbB3 C-terminus were replaced with phenylalanine. In contrast to overexpression of the wild-type ErbB3, overexpression of the mutant ErbB3 did not enhance chemotaxis towards HRGβ1 in vitro or in vivo. We also observed reduced tumor cell motility in the primary tumor by multiphoton microscopy, as well as a dramatically reduced ability of these cells to cross the endothelium and intravasate into the circulation. Moreover, whereas mutation of the ErbB3 C-terminus had no effect on tumor growth, it had a dramatic effect on spontaneous metastatic potential. Treatment with the PI3-kinase inhibitor PIK-75 similarly inhibited motility and invasion in vitro and in vivo. Our results indicate that stimulation of the early metastatic steps of motility and invasion by ErbB3 requires activation of the PI3-kinase pathway by the ErbB3 receptor.

Topics: Animals; Binding Sites; Breast Neoplasms; Cell Line, Tumor; Cell Movement; Female; Humans; Hydrazones; Immunoprecipitation; Mammary Neoplasms, Animal; Mice; Mice, SCID; Microscopy, Fluorescence, Multiphoton; Mutation; Neoplasm Invasiveness; Neoplasm Metastasis; Neuregulin-1; Phosphatidylinositol 3-Kinases; Phosphoinositide-3 Kinase Inhibitors; Phosphorylation; Protein Binding; Rats; Receptor, ErbB-3; Signal Transduction; Sulfonamides; Transplantation, Heterologous; Tyrosine