Loss of p53 expression in cancer cells alters cell cycle response after inhibition of exportin-1 but does not prevent cell death

ABSTRACT

The tumor suppressor protein p53 is central to the cellular stress response and may be a predictive biomarker for cancer treatments. Upon stress, wildtype p53 accumulates in the nucleus where it enforces cellular responses, including cell cycle arrest and cell death. p53 is so dominant in its effects, that p53 enforcement – or – restoration therapy is being studied for anti-cancer therapy. Two mechanistically distinct small molecules that act via p53 are the selective inhibitor of nuclear export, selinexor, and MDM2 inhibitor, nutlin-3a. Here, individual cells are studied to define cell cycle response signatures, which captures the variability of responses and includes the impact of loss of p53 expression on cell fates. The individual responses are then used to build the population level response. Matched cell lines with and without p53 expression indicate that while loss-of-function results in altered cell cycle signatures to selinexor treatment, it does not diminish overall cell loss. On the contrary, response to single-agent nutlin-3a shows a strong p53-dependence. Upon treatment with both selinexor and nutlin-3a there are combination effects in at least some cell lines – even when p53 is absent. Collectively, the findings indicate that p53 does act downstream of selinexor and nutlin-3a, and that p53 expression is dispensable for selinexor to cause cell death, but nutlin-3a response is more p53-dependent. Thus, TP53 disruption and lack of expression may not predict poor cell response to selinexor, and selinexor’s mechanism of action potentially provides for strong efficacy regardless of p53 function.

KEYWORDS:

• Exportin-1
• cell cycle
• p53
• selinexor
• nutlin-3a
• cell fate

Acknowledgments

We acknowledge Sakaue-Sawano et al. for the FUCCI reporters via MTA. We thank Karyopharm Therapeutics, Inc. (Newton, MA) for selinexor and for their generous gift to the University of Colorado Boulder for the study of cancer biology. We also acknowledge Dongjoo Park in the Orth laboratory for discussions, Xinyi Fu for help with immunoblotting, and the Light Microscopy Facility at the University of Colorado Boulder, Porter B047A, B, and B049.

Disclosure statement

No potential conflict of interest was reported by the authors.

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Funding

This work was supported by funding from the American Cancer Society, ACS-IRG #57-001-53, and University of Colorado Boulder (start-up funding) to James D. Orth. Russel T. Burke was partially supported by an NIH training grant, T32 GM0875.