p53 Nongenotoxic Activation and mTORC1 Inhibition Lead to Effective Combination for Neuroblastoma Therapy

Abstract

Purpose mTORC1 inhibitors are promising agents for neuroblastoma therapy; however, they have shown limited clinical activity as monotherapy, thus rational drug combinations need to be explored to improve efficacy. Importantly, neuroblastoma maintains both an active p53 and an aberrant mTOR signaling. Experimental Design Using an orthotopic xenograft model and modulating p53 levels, we investigated the antitumor effects of the mTORC1 inhibitor temsirolimus in neuroblastoma expressing normal, decreased, or mutant p53, both as single agent and in combination with first- and second-generation MDM2 inhibitors to reactivate p53. Results Nongenotoxic p53 activation suppresses mTOR activity. Moreover, p53 reactivation via RG7388, a second-generation MDM2 inhibitor, strongly enhances the in vivo antitumor activity of temsirolimus. Single-agent temsirolimus does not elicit apoptosis, and tumors rapidly regrow after treatment suspension. In contrast, our combination therapy triggers a potent apoptotic response in wild-type p53 xenografts and efficiently blocks tumor regrowth after treatment completion. We also found that this combination uniquely led to p53-dependent suppression of survivin whose ectopic expression is sufficient to rescue the apoptosis induced by our combination. Conclusions Our study supports a novel highly effective strategy that combines RG7388 and temsirolimus in wild-type p53 neuroblastoma, which warrants testing in early-phase clinical trials.

Preclinical evaluation of the first intravenous small molecule MDM2 antagonist alone and in combination with temozolomide in neuroblastoma

“…However, a recent Phase II trial of irinotecan‐temozolomide with temsirolimus in children with refractory/relapsed neuroblastoma did not observe outcomes meriting further study . A recent study has reported potent preclinical efficacy combining the MTORC1 inhibitor temsirolimus with idasanutlin in neuroblastoma preclinical models . Temozolomide has previously been reported to be a substrate of MDR‐1, which is expressed at high levels in both SHSY5Y and NB1691 cells and we have previously reported that at very high concentrations idasanutlin is able to modulate MDR‐1 function .…”

“…36 A recent study has reported potent preclinical efficacy combining the MTORC1 inhibitor temsirolimus with idasanutlin in neuroblastoma preclinical models. 12 Temozolomide has previously been reported to be a substrate of MDR-1, which is expressed at high levels in both SHSY5Y and NB1691 cells and we have previously reported that at very high concentrations idasanutlin is able to modulate MDR-1 function. 21,37 Taken together, these provide potential mechanisms by which MDM2 antagonists enhance temozolomide mediated cytotoxicity, consistent with the observed efficacy of RO6839921 combined with temozolomide.…”

“…TP53 mutations are rare in neuroblastoma even at relapse, however upstream p53 pathway inactivation through MDM2 amplification (2.5–7%) and p14 ARF abnormalities (2–22% homozygous deletion; 7% methylation), have been reported particularly at relapse and support the use of MDM2 antagonists . We and others have demonstrated highly potent anti‐tumour effects of idasanutlin in preclinical neuroblastoma models, alone and in combination with chemotherapy currently used in the treatment of high‐risk neuroblastoma, namely cisplatin, doxorubicin, topotecan (induction), busulfan (consolidation) and temozolomide (relapse), and recently combinations with other targeted agents have been reported . In addition, another MDM2 antagonist in clinical trials, MI‐773 (SAR405838), has been shown to enhance doxorubicin mediated cytotoxicity in neuroblastoma cell lines .…”

“…[6][7][8][9] We and others have demonstrated highly potent anti-tumour effects of idasanutlin in preclinical neuroblastoma models, alone and in combination with chemotherapy currently used in the treatment of high-risk neuroblastoma, namely cisplatin, doxorubicin, topotecan (induction), busulfan (consolidation) and temozolomide (relapse), 10,11 and recently combinations with other targeted agents have been reported. 12,13 In addition, another MDM2 antagonist in clinical trials, MI-773 (SAR405838), has been shown to enhance doxorubicin mediated cytotoxicity in neuroblastoma cell lines. 14 To extend our original in vitro observations, 10 our study assessed RO6839921 the IV prodrug of idasanutlin, alone and in combination with temozolomide, equivalent to one cycle of treatment, in 2 orthotopic models of neuroblastoma.…”

The nucleolus, an ally, and an enemy of cancer cells

“…Temsirolimus, mTORC1 inhibitor, coupled with RG7388, an Mdm2 inhibitor, is effective therapy for p53-proficient neuroblastoma (Moreno-Smith et al 2017). Devlin et al (2016) evoked an interesting effect by application of the combined inhibition of rDNA transcription with CX-5461 and of PI3K-AKT-mTORC1-dependent ribosome and protein biosynthesis signaling with everolimus, mTORC1 inhibitor.…”