The applicability of mTOR inhibition in solid tumors.
The phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin-pathway (PI3K/AKT/mTOR-pathway) plays a role in the regulation of cell proliferation, cell survival, angiogenesis and resistance to anti-tumor treatments. In many tumor types the PI3K/AKT/mTOR-pathway is found activated through several different underlying mechanisms. Since this pathway is believed to largely drive the malignant behavior of several of these tumors, mTOR-inhibition is considered an attractive means to apply as anti-tumor treatment. Currently, four mTOR-inhibitors are explored for clinical use: rapamycin, temsirolimus (CCI-779), everolimus (RAD001) and deforolimus (AP23573). As monotherapy, mTOR-inhibitors yield interesting anti-tumor activity against various tumor types at the expense of relatively mild toxicities. This recently resulted in the registration of two mTOR-inhibitors for patients with metastatic renal cell carcinoma (RCC) while randomized studies in other tumors are currently in progress. Furthermore, mTOR-inhibitors are well-suited drugs to combine with other anti-tumor drugs as in preclinical models mTOR-inhibition overcomes chemoresistance. Consequently, mTOR-inhibitor-containing multidrug regimens are subject to clinical studies. As holds true for all anti-tumor therapies, identification of patients who are likely to respond to mTOR-inhibitor-containing therapies is of utmost importance to avoid over- or undertreatment. Preliminary results suggest that several factors reflecting activation of mTOR in tumors may be used for this purpose. This review addresses the mechanism of action and current clinical experience with mTOR-inhibitors as well as their role in overcoming resistance to conventional therapies. Additionally, potential predictors of outcome to mTOR-inhibition are discussed.
Department of Medical Oncology, Erasmus University Medical Center - Daniel den Hoed Cancer Center, Groene Hilledijk 301, 3075 EA Rotterdam, The Netherlands.
I R H M
IR
Konings
J
J
Verweij
E A C
EA
Wiemer
S
S
Sleijfer
D002455:Cell Division; D002470:Cell Survival; D002986:Clinical Trials as Topic; D019008:Drug Resistance, Neoplasm; D000068338:Everolimus; D005784:Gene Amplification; D006801:Humans; D009369:Neoplasms / Q000098:blood supply / Q000188:drug therapy / Q000235:genetics / Q000473:pathology*; D009389:Neovascularization, Pathologic / Q000503:physiopathology; D047428:Protein Kinase Inhibitors / Q000627:therapeutic use; D011494:Protein Kinases / Q000235:genetics / Q000502:physiology*; D020123:Sirolimus / Q000031:analogs & derivatives / Q000627:therapeutic use; D058570:TOR Serine-Threonine Kinases
D047428:Protein Kinase Inhibitors; C515074:ridaforolimus; C401859:temsirolimus; D000068338:Everolimus; D011494:Protein Kinases; C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus