Vertical Targeting of the Phosphatidylinositol-3 Kinase Pathway as a Strategy for Treating Melanoma

Abstract

Purpose: Melanoma is relatively resistant to chemotherapy; improved targeting of molecules critical for cell proliferation and survival are needed. Phosphatidylinositol-3 kinase (PI3K) is an important target in melanoma; however, activity of PI3K inhibitors (PI3KI) is limited. Our purpose was to assess mTOR as a cotarget for PI3K.Methods: Using a method of quantitative immunofluorescence to measure mTOR expression in a large melanoma cohort, we studied associations with PI3K subunits, p85 and p110a. We assessed addition of the mTOR inhibitor rapamycin to 2 PI3KIs, NVP-BKM120 and LY294002. We studied in vitro activity of a novel dual PI3K/mTOR inhibitor NVP-BEZ235 and activity of the combination of NVP-BEZ235 and the MAP/ERK kinase (MEK) inhibitor AZD6244.Results: Strong coexpression of mTOR and p110a was observed (r ¼ 0.658; P < 0.0001). Less coexpression was seen with p85 (r ¼ 0.239; P < 0.0001). Strong synergism was shown between rapamycin and both PI3KIs. Activity of both PI3KIs was similarly enhanced with all rapamycin concentrations used. The dual PI3K/mTOR inhibitor effectively inhibited viability in 23 melanoma cell lines (IC 50 values in the nanomolar range), regardless of B-Raf mutation status, with resultant reduction in clonogenicity and downregulation of pAkt and pP70S6K. Synergism was seen when combining NVP-BEZ235 and AZD6244, with resultant increases in poly(ADP-ribose) polymerase and caspase-2 cleavage.Conclusions: mTOR and p110a are coexpressed in melanoma. Rapamycin concentrations as low as 1 nmol/L enhance activity of PI3KIs. The dual PI3K/mTOR inhibitor NVP-BEZ235 is highly active in melanoma cells in vitro, suggesting that concurrent PI3K and mTOR targeting in melanoma warrants further investigation, both alone and in combination with MEK inhibitors. Clin Cancer Res; 16(24); 6029-39.Ó2010 AACR.

Combined Application of Phosphoinositide 3-Kinase and Mammalian Target of Rapamycin Inhibitors Suppresses Cell Growth and Promotes Apoptosis in Human Lung Cancer Cell Lines

“…Aziz et al (24) has shown dual inhibitor of PI3K/mTOR has beneficial property for treating melanoma. In addition, they have found a synergism at a concentration of 5 µmol/L LY294002 with 1, 100 and 1000 nmol/L of rapamycin in patient-derived melanoma cell lines.…”

The Akt signaling pathway

“…40,41 Activation of PI3K is a key event for the initiation of Akt signaling in melanomas. 16,44 PI3K is activated by liganddependent activation of tyrosine kinase receptors, G-proteincoupled receptors, or integrins (Fig. 1).…”

“…[47][48][49] Therefore, targeting activated PI3K inhibits melanoma development. 44,50 For example, overexpression of a deleted subunit of PI3K (Deltap85) reduced PI3K signaling in the melanoma cell line G361. 51 Similarly, targeting PI3 kinase using siRNAs or pharmacological agent ZSTK474 inhibited melanoma tumor development.…”

“…NVP-BEZ235, an imidazoquinoline derivative inhibiting both PI3K and mTOR by binding to the ATP binding site, has been tested in preclinical models of melanoma. 44,130 In preclinical studies, blocking PI3K with ZSTK474 or blocking mTOR with rapamycin yielded promising results. 44,130 It is promising that NVP-BEZ235 was found to be more potent than the combination of ZSTK474 and rapamycin with respect to inhibition of melanoma cell proliferation.…”

“…44,130 In preclinical studies, blocking PI3K with ZSTK474 or blocking mTOR with rapamycin yielded promising results. 44,130 It is promising that NVP-BEZ235 was found to be more potent than the combination of ZSTK474 and rapamycin with respect to inhibition of melanoma cell proliferation. Currently this inhibitor is under Phase I/II clinical trial evaluation 198 Agents targeting upstream growth factor receptors in combination with expression of tumor suppressor proteins.…”