Mechanisms of Activity of the TORC1 Inhibitor Everolimus in Waldenstrom Macroglobulinemia

Abstract

Purpose: The TORC1 inhibitor everolimus has previously shown significant activity as a single agent in hematologic malignancies, with reported responses of 30% to 70% in Waldenstrom macroglobulinemia. However, the specific mechanisms by which this class of mTOR inhibitors exerts antiWaldenstrom macroglobulinemia activity have not been fully investigated. We therefore sought to dissect the mechanisms of everolimus-dependent modulation of Waldenstrom macroglobulinemia cell survival.Experimental Design: We confirmed that everolimus targets mTOR in patients treated with everolimus and responding to therapy. We evaluated the effect of everolimus on proliferation and survival of primary Waldenstrom macroglobulinemia cells, as well as of other IgM-secreting lymphoma cell lines. Everolimus-dependent mechanisms of induced apoptosis and its effect on Waldenstrom macroglobulinemia cells in the context of bone marrow microenvironment have been also evaluated. miRNA-155 loss-of-function studies were conducted. Moreover, the combinatory effect of bortezomib and rituximab has been tested.Results: We showed that everolimus targeted mTOR downstream signaling pathways, ex vivo, in patients responding to everolimus treatment. Everolimus induced toxicity in primary Waldenstrom macroglobulinemia cells, as well as in other IgM-secreting lymphoma cells, supported by cell-cycle arrest and caspasedependent and -independent induction of apoptosis. Importantly, everolimus targeted Waldenstrom macroglobulinemia cells even in the context of bone marrow milieu, where it affected migration, adhesion, and angiogenesis. Everolimus-dependent anti-Waldenstrom macroglobulinemia activity was partially driven by miRNA-155. Moreover, everolimus synergized with bortezomib and rituximab in targeting Waldenstrom macroglobulinemia cells, as shown by synergistic inhibition of p65/ and p50/NF-kB activities.Conclusions: These findings provide a better understanding of the mechanisms that are responsible for everolimus-induced anti-Waldenstrom macroglobulinemia activity.

Chemical Inhibitors and microRNAs (miRNA) Targeting the Mammalian Target of Rapamycin (mTOR) Pathway: Potential for Novel Anticancer Therapeutics

“…Firstly, suppression of the mTOR pathway by mir-100 enhanced the chemotherapeutic effect of rapamycin analog RAD001 (everolimus) in clear cell ovarian cancer cells [154]. Furthermore, knocking down miRNA-155 expression in low-grade lymphoma, Waldenström macroglobulinemia cells was shown to partially inhibit everolimus-dependent induction of toxicity [170]. This finding indicates that miRNA-155 could be a target responsible for the everolimus-induced anti-Waldenström macroglobulinemia effect [170].…”

“…Furthermore, knocking down miRNA-155 expression in low-grade lymphoma, Waldenström macroglobulinemia cells was shown to partially inhibit everolimus-dependent induction of toxicity [170]. This finding indicates that miRNA-155 could be a target responsible for the everolimus-induced anti-Waldenström macroglobulinemia effect [170]. In addition, another rapamycin analogue, CCI-779 (temsirolimus), shows increased anti-proliferative effects in miR-101 negative anaplastic lymphoma kinase (ALK) + large-cell lymphoma (ALCL) cells compared to ALK − cells [155].…”

Long‐term results of the phase II trial of the oral mTOR inhibitor everolimus (RAD001) in relapsed or refractory Waldenstrom Macroglobulinemia

“…In addition, we, and others have shown that miR155 is upregulated in WM and can also lead to activation of the PI3K pathway . Therefore, this pathway is highly activated in patients with WM .…”

“…Significant advances have emerged in the understanding of the pathogenesis of WM in the last few years. Recent studies using whole genome sequencing as well as epigenetic studies have shown that the PI3K/mTOR pathway is highly activated in WM, possibly due to MYD88 mutation or miRNA‐155 activation . These results indicate that this rare lymphoplasmacytic lymphoma is dependent to the PI3K/mTOR pathway, despite the lack of specific mutations in the pathway itself.…”

“…TLR4‐mediated signaling pathways including NFkB and MAP kinases also lead to rapid activation of PI3K which is involved in regulation of cell growth, apoptosis, and motility . In addition, we, and others have shown that miR155 is upregulated in WM and can also lead to activation of the PI3K pathway . Therefore, this pathway is highly activated in patients with WM .…”