Dual Inhibition of Akt/Mammalian Target of Rapamycin Pathway by Nanoparticle Albumin-Bound–Rapamycin and Perifosine Induces Antitumor Activity in Multiple Myeloma

Abstract

The PI3K/Akt/mTOR pathway mediates multiple myeloma (MM) cell proliferation, survival, and development of drug resistance, underscoring the role of mTOR inhibitors such as rapamycin with potential anti-MM activity. However, recent data demonstrate a positive feedback loop from mTOR/S6K1 to Akt, whereby Akt activation confers resistance to mTOR inhibitors. We confirmed that suppression of mTOR signaling in MM cells by rapamycin was associated with upregulation of Akt phosphorylation. We hypothesized that inhibiting this positive feedback by a potent Akt inhibitor perifosine would augment rapamycin-induced cytotoxicity in MM cells. Perifosine inhibited rapamycin-induced p-Akt, resulting in enhanced cytotoxicity in MM.1S cells even in the presence of IL-6, IGF-1 or bone marrow stromal cells. Moreover, rapamycin induced autophagy in MM.1S MM cells as evidenced by electron microscopy and immunocytochemistry, was augmented by perifosine. Combination therapy increased apoptosis detected by Annexin/PI analysis and caspase/PARP cleavage. Importantly, in vivo antitumor activity and prolongation of survival in a MM mouse xenograft model after treatment was enhanced with combination of nab-rapamycin and perifosine. Utilizing the in silico predictive analysis we confirmed our experimental findings of this drug combination on PI3K, Akt, mTOR kinases, and the caspases. Our data suggests that mutual suppression of the PI3K/Akt/mTOR pathway by rapamycin and perifosine combination induces synergistic MM cell cytotoxicity, providing the rationale for clinical trials in patients with relapsed / refractory MM.

Targeting the PI3K/AKT/mTOR Signaling Axis in Children with Hematologic Malignancies

“…Targeting multiple intermediates along the PI3K/AKT/mTOR axis may overcome this potential problem. [75][76][77] Most of the small molecule inhibitors that target mTORC1/2 also target other proteins in the PI3K/AKT/ mTOR signaling pathway, including PI3K, and are discussed in section 4.3. As with many kinase inhibitors, these agents can also affect other kinase pathways at higher concentrations, but the half maximal inhibitory concentration (IC50) values for mTOR kinase for many of these drugs, including PP242, are nearly 100-fold lower than their affinity for other kinases.…”

AC‐1001 H3 CDR peptide induces apoptosis and signs of autophagy in vitro and exhibits antimetastatic activity in a syngeneic melanoma model

“…Transmission electron microscopy analysis additionally revealed a massive cell vacuolization and organelles within some vesicles, seemingly autophagy suggesting images 41, 42, 43. Through autophagy, proteins and organelles are sequestered into double membrane vesicles (autophagosomes) and are subsequently delivered to the lysosomes for degradation 44.…”

Delineating the mTOR Kinase Pathway Using a Dual TORC1/2 Inhibitor, AZD8055, in Multiple Myeloma

“…DNA synthesis was measured by tritiated thymidine uptake (3H-TdR; Perkin-Elmer) as previously described (8). Briefly, MM.1S cells (2-3 Â 10 3 per well) were incubated in 96-well culture plates alone or in culture with BMSCs, IL6 (10 ng/mL), or IGF1 (50 ng/mL) in the presence of media or varying concentrations of AZD8055 or rapamycin for 48 hours at 37 C.…”

“…Multiple myeloma cells were cultured in media or with indicated concentrations of AZD8055 or rapamycin, harvested, and whole-cell lysates were subjected to SDS-PAGE, and transferred to nitrocellulose membrane (Bio-Rad Laboratories), as described previously (8).…”

“…Initial studies targeting mTOR in multiple myeloma have focused on the inhibition of mTORC1 with rapamycin (6)(7)(8). The observed mTORC2 activation of Akt following rapamycin treatment prompted the rapid development of mTOR kinase inhibitors (9).…”