Neurofibromin level directs RAS pathway signaling and mediates sensitivity to targeted agents in malignant peripheral nerve sheath tumors

Abstract

Malignant peripheral nerve sheath tumor (MPNST) is a type of soft-tissue sarcoma strongly associated with dysfunction in neurofibromin; an inhibitor of the RAS pathway. We performed high-throughput screening of an array of FDA approved and promising agents in clinical development both alone and in combination at physiologically achievable concentrations against a panel of established MPNST cell line models. We found that drugs targeting a variety of factors in the RAS pathway can effectively lead to cell death in vitro with considerable drug combination synergy in regimens that target MEK or mTOR. We observed that the degree of relative sensitivity to chemotherapeutic agents was associated with the status of neurofibromin in these cell line models. Using a combination of agents that target MEK and mTORC1/2, we effectively silenced RAS/PI3K/MEK/mTOR signaling in vitro. Moreover, we employed RNAi against NF1 to establish that MPNST drug sensitivity is directly proportional to relative level of intracellular neurofibromin. Thus, two-drug combinations that target MEK and mTORC1/2 are most effective in halting the RAS signaling cascade, and the relative success of this and related small molecule interventions in MPNSTs may be predicated upon the molecular status of neurofibromin.

Integrative analysis identifies candidate tumor microenvironment and intracellular signaling pathways that define tumor heterogeneity in NF1

“…Specifically, we found two clusters of latent variables expressed in NF, pNF, and MPNST that had regulatory proteins enriched in targets of dovitinib and drug-like small molecules that inhibit receptor tyrosine kinases, as well as cyclin-dependent kinase (CDK) inhibitors such as abemaciclib or dinaciclib. These findings are consistent with previous studies that identify CDK inhibitors as useful in models of NF1 -deficient or RAS-dysregulated tumors [59][60][61][62] . Since latent variables that are correlated with HDACs were found to be expressed most highly in cNFs (Cluster 5, Figure 6C, Supplemental Figure 4C) and MPNSTs (cluster 1, Figure 6C, Supplemental Figure 4A), compounds like CUDC-101 and analogs could be potential candidates for treating cNF and MPNST.…”

“…Specifically, we found two clusters of latent variables expressed in NF, pNF, and MPNST that had regulatory proteins enriched in targets of dovitinib and drug-like small molecules that inhibit receptor tyrosine kinases, as well as cyclin-dependent kinase (CDK) inhibitors such as abemaciclib or dinaciclib. These findings are consistent with previous studies that identify CDK inhibitors as useful in models of NF1-deficient or RAS-dysregulated tumors [75][76][77][78].…”

“…Since latent variables that are correlated with HDACs were found to be expressed most highly in cNFs (Cluster 5, Figure 6C, Supplemental Figure 4C) and MPNSTs (cluster 1, Figure 6C, Supplemental Figure 4A), compounds like CUDC-101 and analogs could be potential candidates for treating cNF and MPNST. Indeed, HDAC inhibitors were previously found to be efficacious in in vitro and in vivo models of MPNSTs [59,61]. Thus our results further suggest that this therapeutic approach might be feasible in both MPNSTs and cNFs.…”

Malignant peripheral nerve sheath tumour (MPNST)

“…The use of the MEK inhibitor (PD0325901) resulted in the inhibition of the growth of both plexiform neurofibromas and MPNST in mice [19], and the activity of this inhibitor is potentiated by retinoids, including ATRA (all-trans retinoic acid) [20]. The efficacy of MEK inhibitors has been confirmed during in vitro studies also in combination with the mTOR1/2 INK128 double inhibitor [9]. This puts MEK inhibitors in the group of potential drugs in advanced forms of MPNST requiring systemic treatment.…”

“…Loss of neurofibromin function leads to activation of Ras kinase (Rat sarcoma) followed by its effector pathways associated with malignant transformation. The degree of activation of Ras and dependent signalling pathways, as well as the sensitivity of cells to their inhibitors, is inversely proportional to the level of neurofibromin expression [9]. Activation of Ras kinase leads to the activation of two types of effector pathways: MAPK pathways (Ras/Raf/MEK/Erk) and Akt/mTOR pathways that regulate cell function, among others in response to external stimuli such as growth factors or chemokines.…”