Tier 4 — mechanistic

Pharmacological activation of SIRT6 triggers lethal autophagy in human cancer cells

Sara Iachettini, Daniela Trisciuoglio, Dante Rotili, Alessia Lucidi, Erica Salvati, Pasquale Zizza, Luca Di Leo, Donatella Del Bufalo, Maria Rosa Ciriolo, Carlo Leonetti, Clemens Steegborn, Antonello Mai, Angela Rizzo, Annamaria Biroccio
Cell Death & Disease 2018 Volume 9, issue 10, article 996

Bibliography

PubMed
PMID 30250025
PubMed Central
PMC6155207
DOI
10.1038/s41419-018-1065-0
Funding
Italian Association for Cancer Research (AIRC #16910 to A.B., #17121 to E.S., #19162 to A.M., #18560 to D.D.B.); Italian PRIN 2016 (prot. 20152TE5PK to A.M.); Progetto Ateneo Sapienza 2016 (A.M.).
Competing interests
The authors declare no conflict of interest.

Study snapshot

DesignIn vitro treatment of human cancer cell lines with the SIRT6 activator UBCS039; western blot for LC3B lipidation, GFP-LC3 puncta imaging, ROS measurement, phosphorylation state of AMPK, ULK1, and mTOR, viability assays with and without the pan-caspase inhibitor zVAD-fmk and the autophagy inhibitor chloroquine (CQ). Catalytic-dead SIRT6 H133Y mutant used to confirm dependence on deacetylase activity.
ModelMultiple human tumour cell lines including non-small cell lung cancer, colorectal cancer, and osteosarcoma; wild-type and catalytic mutant SIRT6 H133Y overexpression systems.
SampleThree or more independent biological replicates per condition; multi-cell-line panel to confirm generality of the response.
InterventionUBCS039, the first-in-class synthetic SIRT6 deacetylase activator; comparator conditions included DMSO vehicle, SIRT6 catalytic-dead H133Y overexpression, N-acetylcysteine (NAC) antioxidant, zVAD-fmk pan-caspase inhibitor, and chloroquine autophagy inhibitor.
DurationTime-course experiments from short-term (hours) LC3B lipidation and ROS measurement through sustained (48 to 72 hour) viability endpoints.
EndpointsLC3B-II accumulation; autophagosomal puncta count by GFP-LC3 microscopy; intracellular ROS levels; AMPK, ULK1, and mTOR phosphorylation; cell viability under UBCS039 alone, with NAC, with zVAD-fmk, and with chloroquine; requirement for SIRT6 catalytic activity via H133Y mutant.

What the study showed, in plain terms

SIRT6 has been discussed as a potential anti-cancer target because in many tumour types it acts as a tumour suppressor. This paper tested that idea directly by treating several human cancer cell lines with UBCS039, at the time the first synthetic small molecule shown to activate SIRT6.

UBCS039 triggered autophagy — the cellular self-eating process — in every tumour cell line tested. The effect required functional SIRT6: a catalytically dead SIRT6 mutant (H133Y) failed to induce autophagy despite being present at normal levels, proving the response depends on SIRT6's deacetylase activity rather than an off-target effect of the drug.

Working out how activated SIRT6 caused autophagy, the authors found that the trigger was a burst of reactive oxygen species (ROS). The ROS activated the AMPK-ULK1 stress-response pathway and inhibited mTOR, the master regulator that normally holds autophagy back. Antioxidants blocked the entire cascade, confirming ROS as the upstream signal. When cells were exposed to UBCS039 for long enough, autophagy shifted from a protective response to a lethal one — the cells died. Blocking either apoptosis (with a caspase inhibitor) or autophagy (with chloroquine) rescued them, showing the two death programmes were linked.

The paper establishes UBCS039 as a working chemical tool for activating SIRT6 in cells and provides proof-of-principle that pharmacological SIRT6 activation can selectively kill cancer cells through autophagy-dependent cell death.

Key findings

  • UBCS039 triggered time-dependent autophagy in multiple human tumour cell lines, shown by increased LC3B lipidation on western blot and by GFP-LC3 puncta accumulation on microscopy.
  • Autophagy induction required SIRT6 catalytic activity: the deacetylase-dead SIRT6 H133Y mutant did not activate autophagy in response to UBCS039, ruling out off-target drug effects.
  • UBCS039 caused a rapid rise in intracellular reactive oxygen species (ROS) upstream of the autophagy response.
  • The ROS burst activated the AMPK-ULK1 pathway and inhibited mTOR, the canonical energy-stress signalling axis that drives autophagy initiation.
  • Co-treatment with the antioxidant N-acetylcysteine completely abolished UBCS039-induced autophagy, confirming ROS as the upstream trigger.
  • Sustained UBCS039 exposure caused autophagy-related cell death in tumour cells.
  • The pan-caspase inhibitor zVAD-fmk and the autophagy inhibitor chloroquine both attenuated UBCS039-induced cell death, indicating the death programme required both autophagic flux and caspase activity.
  • UBCS039 was validated as the first synthetic SIRT6 activator with confirmed on-target activity in intact cancer cells.

What this study can and cannot tell us

All experiments were performed in cancer cell lines in vitro. No xenograft, orthotopic, or genetically engineered mouse model was tested, so it is unknown whether UBCS039 doses achievable in vivo would replicate the ROS burst and lethal autophagy shown here.

UBCS039 has significant solubility and pharmacokinetic limitations that were not addressed in this study. Later work has produced improved second-generation SIRT6 activators (MDL-800, MDL-801) with better drug-like properties; the biological principle demonstrated here may or may not translate to those newer compounds.

The cell lines tested are cancer cells with baseline dysregulation of apoptosis, autophagy, and oxidative stress responses. Whether normal cells respond to SIRT6 activation with the same ROS burst and lethal autophagy — and if so, at what dose threshold — was not examined. This matters for any therapeutic use of SIRT6 activators because the therapeutic window depends on the difference between cancer-cell and normal-cell responses.

The paper does not identify the specific SIRT6 substrate whose deacetylation causes the ROS burst. The mechanism upstream of ROS therefore remains a black box.

Some tumour types (melanoma is the clearest example) depend on SIRT6 for growth and are inhibited when SIRT6 is knocked down. In those contexts, further SIRT6 activation may be counterproductive rather than helpful, and the death programme demonstrated here may not occur.

Related papers in the corpus

Tier 4
Mechanisms of the antiproliferative effects of SIRT6 inhibition in melanoma: a multi-omics analysis
Karla B. Anaya Aldrete et al. · Cancers · 2026

Editorial review

Reviewed by the Biohack Blueprint research team

Last verified

Dr. Khaled Mahmoud, MBBChCritical Care Medicine, Longevity Science & Editorial Direction Dr. Amr Yasser, PhDCardiometabolic, Musculoskeletal, Gut & Bioavailability Dr. Abdulla Mostafa, PhDCellular Senescence, Neurological, Mitochondrial & Brain-Ageing Biology