Abstract A015: Biochemical and preclinical anti-tumor activity of a bi-steric mTORC1-selective inhibitor in fusion positive rhabdomyosarcoma
Bibliographic record
Abstract
Abstract Rhabdomyosarcoma (RMS) is the most common soft tissue sarcoma in children. Although FOXO1 fusions portend a dismal prognosis for patients with both localized (5-year survival 65%) and metastatic (19%) disease, current therapy is largely agnostic to fusion status. The allosteric mTORC1 inhibitor temsirolimus delays disease progression in relapsed RMS but does not improve survival. We hypothesized that this incomplete response is due to inadequate suppression of critical downstream effectors of the mTORC1 complex. Recently described bi-steric mTORC1-selective inhibitors combine allosteric and catalytic modes of kinase inhibition, and have shown promise in diverse preclinical cancer models with early evidence of clinical activity. We therefore set out to compare the activity of the bi-steric mTORC1-selective inhibitor RMC-6272 to the allosteric mTOR inhibitor rapamycin in cell line and xenograft models of fusion positive RMS. Methods: We compared the in vitro anti-proliferative activity of RMC-6272 and rapamycin in FOXO1 fusion positive RMS cell lines at 72 and 144 hours. We assessed the ability of these inhibitors to suppress mTORC1 outputs, using immunoblot to quantify phosphorylation of p70S6K, RPS6, and 4EBP1, and m7-GTP pulldowns to assess repression of cap-dependent translation. In vivo studies were conducted in patient-derived xenograft (PDX) models subcutaneously implanted in NSG mice. We tested preclinical anti-tumor activity of RMC-6272 at two doses and used immunoblots and m7-GTP assays in tumors harvested from treated mice to assess target engagement. Results: We observed superior anti-proliferative effects of RMC-6272 when compared to rapamycin in vitro, with the latter having only modest effect. Biochemically, treatment of RMS cell lines with either RMC-6272 or rapamycin diminished phosphorylation of p70S6K and RPS6. However, RMC-6272 blocked 4EBP1 phosphorylation and cap-dependent translation much more potently than rapamycin. Based on these findings, we conducted in vivo studies using weekly intraperitoneal injections of RMC-6272 in PDX-harboring mice. Both doses were associated with tumor regressions in two fusion positive RMS PDX models: 2 CR and 1 PR at 8 mg/kg, and 3 CR, 1 PR, 1 SD, and 2 PD at 6 mg/kg. NSG mice treated at 8 mg/kg demonstrated more weight loss than those at 6 mg/kg, suggesting strain-specific determinants of tolerability. We confirmed in vivo suppression of p70S6K phosphorylation and cap-dependent translation in tumors. Conclusions: The mTORC1 inhibitor RMC-6272 exhibits greater anti-tumor activity than the allosteric inhibitor rapamycin in vitro, and is capable of inducing complete remissions as monotherapy in FOXO1 fusion positive RMS PDX. Increased anti-tumor activity was associated with suppression of cap-dependent translation as assessed by m7-GTP assays, nominating dephosphorylation of 4EBP1 as a potential response biomarker. Preclinical studies are ongoing to assess mechanism-informed combination therapeutic strategies incorporating this highly active agent in FOXO1 fusion positive RMS. Citation Format: Jacqueline Morales, Kristen Kwong, W. Clay Gustafson, Amit J. Sabnis. Biochemical and preclinical anti-tumor activity of a bi-steric mTORC1-selective inhibitor in fusion positive rhabdomyosarcoma [abstract]. In: Proceedings of the AACR Special Conference: Sarcomas; 2022 May 9-12; Montreal, QC, Canada. Philadelphia (PA): AACR; Clin Cancer Res 2022;28(18_Suppl):Abstract nr A015.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".