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Targeting protein homeostasis with nelfinavir/salinomycin dual therapy effectively induces death of mTORC1
Elaine A Dunlop1, Charlotte E Johnson1, Marie Wiltshire1
1Division of Cancer and Genetics, Cardiff University, Heath Park, Cardiff, CF14 4XN, UK.
Abstract:
Uncontrolled cell growth in Tuberous Sclerosis Complex occurs due to inappropriate activation of mechanistic (mammalian) target of rapamycin complex 1 (mTORC1). The current therapy, rapamycin, produced promising clinical trial results, but patient tumours regrow if treatment is discontinued, revealing rapamycin has cytostatic properties rather than a cytotoxic effect. Taking advantage of the enhanced levels of endoplasmic reticulum (ER) stress present in TSC2-null cells, we investigated drug combinations producing a cytotoxic response. We found a nelfinavir and salinomycin combination specifically killed TSC2-deficient, mTORC1 hyperactive cells. Cytotoxicity was rescued by reducing protein synthesis, either through mTORC1 inhibition or cycloheximide treatment. This indicates that the drug combination targets the cells by tipping the protein homeostasis balance of the already metabolically stressed TSC2-deficient cells in favour of cell death. Furthermore, this drug combination also inhibited tumour formation in TSC2-deficient cell models and caused tumour spheroid death in 3D culture. Importantly, the 3D assay could differentiate the cytostatic agent, rapamycin, from the cytotoxic nelfinavir/salinomycin combination. Sporadic cancer cell lines with hyperactive mTORC1 signalling were also susceptible to this nelfinavir/salinomycin drug combination. This work indicates that the protein homeostasis pathway is an attractive therapeutic target in both Tuberous Sclerosis Complex and mTORC1-driven sporadic cancers.
Insights
A novel drug combination of nelfinavir and salinomycin effectively kills Tuberous Sclerosis Complex cells by disrupting protein homeostasis. This targeted approach offers a cytotoxic alternative to rapamycin for TSC and mTORC1-driven cancers.
Area of Science:
- Oncology
- Cell Biology
- Pharmacology
Background:
- Tuberous Sclerosis Complex (TSC) involves uncontrolled cell growth driven by mechanistic (mammalian) target of rapamycin complex 1 (mTORC1) hyperactivation.
- Current therapy, rapamycin, exhibits cytostatic effects, leading to tumor regrowth upon discontinuation.
- TSC2-null cells exhibit elevated endoplasmic reticulum (ER) stress, presenting a therapeutic vulnerability.
Purpose of the Study:
- To identify drug combinations that induce cytotoxic effects in TSC2-deficient, mTORC1-hyperactive cells.
- To investigate the mechanism of action for novel cytotoxic drug combinations.
- To evaluate the efficacy of these combinations in preclinical models of TSC and sporadic cancers.
Main Methods:
- Screening of drug combinations in TSC2-deficient cell models.
- Assessment of cytotoxicity through protein synthesis inhibition rescue experiments.
- Evaluation of anti-tumorigenic effects in 3D culture models and tumor spheroid assays.
- Testing susceptibility of sporadic cancer cell lines with mTORC1 hyperactivation.
Main Results:
- A combination of nelfinavir and salinomycin demonstrated specific cytotoxicity against TSC2-deficient, mTORC1-hyperactive cells.
- Cytotoxicity was linked to the disruption of protein homeostasis, tipping the balance towards cell death.
- The drug combination inhibited tumor formation in TSC models and induced death in 3D tumor spheroids.
- This combination also proved effective against sporadic cancer cell lines with hyperactive mTORC1 signaling.
Conclusions:
- Nelfinavir and salinomycin offer a potent cytotoxic strategy for Tuberous Sclerosis Complex by targeting protein homeostasis.
- This drug combination represents a promising therapeutic avenue for both TSC and mTORC1-driven sporadic cancers.
- The protein homeostasis pathway is a viable target for novel anti-cancer therapies.