MCL-1 and Apoptosis: What Obatoclax Teaches Us About Cancer Cell Death

Cell-culture study · Mouse hybridoma cells · Peer-reviewedOctober 19, 2026 · 4 min read · Dr. Abdelmuhsen Abusneina

Key points

What was studied: how pro-survival proteins of the BCL-2 family protect Sp2/0-Ag14 mouse hybridoma cells, which undergo apoptosis within minutes of glutamine deprivation [1].
Main findings: MCL-1 was the dominant pro-survival BCL-2 family protein. Its level fell progressively as glutamine deprivation reduced survival, and obatoclax made the cells more sensitive to starvation-induced apoptosis [1].
Limits: one mouse cell line in culture. The abstract reports no numerical results, and nothing was tested in tumors [1].
The authors’ suggestion: combining inhibition of glutamine biosynthesis pathways with inhibition of BCL-2 family proteins may prove effective against some cancers [1].

Schematic of the study: cells with glutamine have high MCL-1; without glutamine MCL-1 falls and cells undergo apoptosis; obatoclax sensitizes the cells — Schematic prepared for this post (not a figure from the paper). With glutamine (Gln), the cells carry high levels of MCL-1. Without Gln, MCL-1 falls and the cells undergo apoptosis; obatoclax, which targets MCL-1, made starved cells more sensitive [1].

Why this matters

Some cancer cells die when glutamine is withheld, a dependence known as glutamine addiction [1]. For background, see the earlier explainer on glutamine addiction. Apoptosis, a form of programmed cell death, is held in check by pro-survival proteins of the BCL-2 family, and drugs called BH3 mimetics are designed to block them. The question in this study was which survival protein protects a glutamine-starved cell, and whether blocking it makes starvation more lethal [1].

The study

The work used Sp2/0-Ag14 (Sp2/0) mouse hybridoma cells, a cell line that undergoes apoptosis within minutes of glutamine deprivation [1]. Hybridoma cells are created by fusing an antibody-producing B cell with a myeloma cell.

The researchers measured the levels of anti-apoptotic BCL-2 family proteins by Western blot and followed MCL-1 during glutamine deprivation. They also compared two drugs: obatoclax, a broad BH3 mimetic that targets MCL-1, and ABT-737, a more selective drug that does not target MCL-1 [1].

What the researchers found

Question	Result
Which survival protein dominates?	MCL-1 was expressed at much higher levels than BCL-2, BCL-xL and BCL-2-like protein 2 [1].
What happens to MCL-1 during starvation?	Its protein level fell progressively, in step with the decline in cell survival [1].
Which drug works better?	The cells were much more sensitive to obatoclax, which targets MCL-1, than to ABT-737, which does not [1].
Does obatoclax add to starvation?	Yes. Obatoclax sensitized the cells to apoptosis after glutamine starvation [1].

The authors conclude that lowering MCL-1 is an important step in the sequence of events that starts apoptosis in glutamine-starved Sp2/0 cells [1].

For specialists

The anti-apoptotic proteins compared were BCL-2, BCL-xL (B-cell lymphoma extra-large) and BCL-2-like protein 2 (BCL2L2, also called BCL-w), measured by Western blot. The contrast between obatoclax and ABT-737 is the pharmacological argument: the drug that reaches MCL-1 had the stronger effect, and the selective drug that does not reach it had less [1].

What this does not show

One mouse cell line, in culture. Hybridoma cells are not human tumors, and the abstract reports no results in animals or patients [1].
A correlation plus a drug effect. MCL-1 fell as survival fell, and a drug that targets MCL-1 increased sensitivity. This supports a role for MCL-1 but does not show it is the only factor [1].
No numbers in the abstract. Effect sizes, drug doses and time points are in the full paper, which this summary did not use.
Obatoclax is a broad inhibitor. From the abstract alone, effects on other BCL-2 family proteins cannot be excluded [1].

What happens next

The authors suggest that combined inhibition of glutamine biosynthesis pathways and BCL-2 family proteins may prove effective against some cancers [1]. This study does not test that idea in tumors. The same group later reported that ammonium ions improved the survival of glutamine-starved hybridoma cells [2].

Original study

Paper: Harnett CC, Abusneina A, Clément J, Gauthier ER. Cell Biochemistry and Function 33(5):334–340, 2015. doi:10.1002/cbf.3121
PubMed: PMID 26178811
Basis: Abstract; full text not reviewed
Disclosure: The author of this post is a co-author of the paper.
Funding: Listed in the paper.

This post summarizes a published study for general information.

References

C. C. Harnett, A. Abusneina, J. Clément, and E. R. Gauthier, “Inhibition of MCL-1 by obatoclax sensitizes Sp2/0-Ag14 hybridoma cells to glutamine deprivation-induced apoptosis,” Cell Biochem. Funct., vol. 33, no. 5, pp. 334–340, Jul. 2015. doi: 10.1002/cbf.3121. PMID: 26178811.
A. Abusneina and E. R. Gauthier, “Ammonium ions improve the survival of glutamine-starved hybridoma cells,” Cell Biosci., vol. 6, art. 23, Apr. 2016. doi: 10.1186/s13578-016-0092-8. PMID: 27087916.

KeywordsApoptosis Cell death BCL-2 family Obatoclax Glutamine Hybridoma cells

Dr. Abdelmuhsen Abusneina, PhDAssociate Professor
Research focus: Molecular Oncology and Cancer Metabolism
Department of Molecular Diagnostics, Faculty of Biomedical Sciences, University of Benghazi, Libya

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