The tumor suppressor p53 gene is mutated in approximately 50% of all human tumors. Many tumor-associated mutant p53 proteins misfold into a common, denatured conformation and accumulate to high levels in human tumors. In such tumors, these mutant forms of p53 provide a “gain of function” to promote tumor progression. Therefore, targeting mutant p53 has become an attractive approach for cancer therapy. In this issue, the study by Lu and colleagues supports the premise that certain forms of mutant p53 are temperature sensitive in conformation; these forms of p53 are mutant in conformation at physiologic temperature, but can refold into a normal, or “wild-type” conformation at lower temperature (32°C to 34°C). Notably, these temperature-sensitive mutants account for up to 7.5% of all human tumors that carry mutant p53, so this fraction of patients is estimated to be quite significant. Results from this study show that employing therapeutic hypothermia to reduce the core temperature of mice bearing tumors with these temperature-sensitive mutant forms of p53 (ts mutant p53) causes ts mutant p53 to switch to a wild-type conformation in tumors, inhibiting tumor growth. Moreover, combining hypothermia with chemotherapy leads to durable remission of such tumors, with no obvious toxicity to normal tissues.

See related article by Lu et al., p. 3905

The p53 tumor suppressor chiefly exerts its tumor-suppressive function via transcriptional regulation of its target genes (1). The p53 gene is mutated in close to half of all human tumors (2). The majority of p53 mutations in human tumors are missense mutations that result in single amino acid substitutions in the DNA-binding domain, leading to the expression of full-length mutant p53 protein (2). In addition to the loss of wild-type p53 function, many tumor-associated mutant p53 proteins promote tumor progression through the “gain-of-function” (GOF) mechanism (3). Many mutant p53 GOF activities have been reported, including enhanced cell proliferation, migration/invasion and metastasis, metabolic reprogramming, decreased cell differentiation, increased stemness, and enhanced resistance toward therapies (1, 3). Mutant p53 proteins typically accumulate to very high levels in tumors, which is crucial for them to exert their functions. Importantly, the presence of mutant p53 in human tumors is typically associated with poor clinical outcomes of patients with cancer. Accumulating evidence has shown that targeting mutant p53 directly or its crucial downstream signaling pathways can effectively suppress cancer progression, suggesting that cancer cells often become addicted to GOF mutant p53 (4, 5).

p53 missense mutations fall into two major categories: contact mutations and structural mutations. Contact mutants include those that mutate amino acids that directly contact DNA (such as R273H and R248Q). These mutant forms of p53 fail to bind to DNA in a sequence-specific manner, but these predominantly retain a wild-type p53 conformation. In contrast, structural mutations (such as R175H and R249S) substitute residues that are required for the proper folding of p53, and these mutants typically misfold into a denatured conformation. A subset of these p53 structural mutations are temperature sensitive (ts), wherein they regain wild-type p53 conformation and exhibit wild-type DNA-binding and transcriptional activity at temperatures between 32°C and 34°C. While the existence of ts p53 mutations has been known for some time and has been utilized as a tool to understand the function of p53, the potential of targeting ts mutant p53 in tumors by hypothermia as a targeted therapeutic strategy has not been tested previously.

The study by Lu and colleagues (6) estimated somatic p53 ts mutation frequency in human cancers by analyzing the Catalogue of Somatic Mutations in Cancer (COSMIC) database. The ts p53 mutations tested in this study include p53 ts mutations identified by a yeast transactivation assay at 30°C in a previous study (7) and several additional p53 ts mutations validated in human cells. Lu and colleagues found that approximately 15% of tumors carrying mutant p53 in the COSMIC database express ts mutant p53 proteins, which affect 62 amino acid residues in the DNA-binding domain (Fig. 1A). Two thirds of tumors carrying ts mutant p53 have p53 mutations at 10 hotspots. Given that approximately 50% of all human tumors contain p53 mutations, it is estimated that approximately 7.5% of human tumors may carry a ts p53 mutation. Therefore, a therapeutic that targets this subset of mutant p53 could impact a significant percentage of cancer patients.

Figure 1.

Hypothermia reactivates ts mutant p53 to inhibit tumor growth. A, The frequency of somatic ts p53 mutations in human tumors based on analysis of the COSMIC database. Numbers shown in each bar represent the case number. B, Hypothermia reactivates ts mutant p53 (left) to inhibit tumor growth (right).

Figure 1.

Hypothermia reactivates ts mutant p53 to inhibit tumor growth. A, The frequency of somatic ts p53 mutations in human tumors based on analysis of the COSMIC database. Numbers shown in each bar represent the case number. B, Hypothermia reactivates ts mutant p53 (left) to inhibit tumor growth (right).

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Lu and colleagues validated the ts feature of 17 most frequently observed ts p53 mutants found in the COSMIC database. These ts p53 mutations occur at 15 codons, including a hotspot mutation R282W. While the majority of these individual ts p53 mutants has <1% frequency in human tumors, altogether they have approximately 5% frequency in human tumors. Lu and colleagues showed that the refolding of ts mutant p53 at 32°C can be accomplished by exposing mice to therapeutic hypothermia. Therapeutic hypothermia has been used in the clinic for resuscitated cardiac arrest patients as well as newborn infants with hypoxic-ischemic encephalopathy for neuroprotection (8, 9). The A1 adenosine receptor (A1AR) agonist N6-cyclohexyladenoxine (CHA) and some antipsychotic drugs, such as chlorpromazine, can induce hypothermia in animals. By employing CHA to lower mouse core temperature, Lu and colleagues showed that B-cell lymphoma formed by GA10 cells, which contains a ts mutant p53 allele (p152L), significantly regressed after six rounds of treatment. In contrast, tumors formed by GA10 cells with CRISPR knockout of the ts mutant p53 were unaffected. The authors confirmed this observation using another pair of isogenic tumor cell lines, H1963 (a human lung cancer cell line containing a H214R ts mutant p53 allele) and H1963-p53KO with p53 knockout. Notably, they further showed that combined treatment of hypothermia and chemotherapy produced significantly more durable responses. Indeed, in response to the combined treatment of hypothermia and camptothecin, one-third of GA10 tumors showed durable remission with no relapse in the 50-day observation period after treatments (Fig. 1B).

Given the high frequency of p53 mutation in cancer, therapies targeting mutant p53 have attracted a great deal of interest, and some studies use small molecules that are designed to “refold” mutant p53 into the wild-type conformation (4). However, such compounds can have off-target toxicity issues; in contrast, hypothermia does not cause obvious damage to normal tissues. Currently, hypothermia is used in the clinic only under intensive care settings. Therefore, repurposing this procedure for cancer therapy could lead to significant therapeutic benefits. Further studies are needed to determine the antitumor effect of hypothermia in common cancer types, like lung, skin, brain, ovary, and breast cancers. Regarding clinical translation of the approach, it remains to be determined whether the current therapeutic hypothermia method used in the clinic is adequate for cancer treatment. New approaches are being developed to pharmacologically induce hypothermia, exclusively focusing on the treatment of stroke and brain injury (10). The findings from this study suggest advances in hypothermia induction will also create new opportunities for targeting cancers with ts mutant p53. In addition, methods of delivery can be further developed as well. If methods can be developed to reduce the temperature and maintain it at 32°C at the location of the tumor sites, this will help translate the findings from this study for the treatment of tumors containing ts mutant p53.

No disclosures were reported.

W. Hu is supported by the grants from NIH 1R01CA203965, and DoD W81XWH-18-10238. Z. Feng is supported by the grants from NIH 1R01CA227912 and 1R01CA214746.

1.
Pfister
NT
,
Prives
C
. 
Transcriptional regulation by wild-type and cancer-related mutant forms of p53
.
Cold Spring Harb Perspect Med
2017
;
7
:
a026054
.
2.
Donehower
LA
,
Soussi
T
,
Korkut
A
,
Liu
Y
,
Schultz
A
,
Cardenas
M
, et al
Integrated analysis of TP53 gene and pathway alterations in the cancer genome atlas
.
Cell Rep
2019
;
28
:
1370
84
.
3.
Zhang
C
,
Liu
J
,
Xu
D
,
Zhang
T
,
Hu
W
,
Feng
Z
. 
Gain-of-function mutant p53 in cancer progression and therapy
.
J Mol Cell Biol
2020
;
12
:
674
87
.
4.
Zhou
X
,
Hao
Q
,
Lu
H
. 
Mutant p53 in cancer therapy-the barrier or the path
.
J Mol Cell Biol
2019
;
11
:
293
305
.
5.
Gurpinar
E
,
Vousden
KH
. 
Hitting cancers' weak spots: vulnerabilities imposed by p53 mutation
.
Trends Cell Biol
2015
;
25
:
486
95
.
6.
Lu
J
,
Chen
L
,
Song
Z
,
Das
M
,
Chen
J
. 
Hypothermia effectively treats tumors with temperature-sensitive p53 mutations
.
Cancer Res
2021
;
81
:
3905
15
.
7.
Shiraishi
K
,
Kato
S
,
Han
SY
,
Liu
W
,
Otsuka
K
,
Sakayori
M
, et al
Isolation of temperature-sensitive p53 mutations from a comprehensive missense mutation library
.
J Biol Chem
2004
;
279
:
348
55
.
8.
Dietrich
WD
,
Bramlett
HM
. 
Therapeutic hypothermia and targeted temperature management for traumatic brain injury: Experimental and clinical experience
.
Brain Circ
2017
;
3
:
186
98
.
9.
Shipley
L
,
Gale
C
,
Sharkey
D
. 
Trends in the incidence and management of hypoxic-ischaemic encephalopathy in the therapeutic hypothermia era: a national population study
.
Arch Dis Child Fetal Neonatal Ed
2021
.
DOI: 10.1136/archdischild-2020-320902. Online ahead of print
.
10.
Liu
K
,
Khan
H
,
Geng
X
,
Zhang
J
,
Ding
Y
. 
Pharmacological hypothermia: a potential for future stroke therapy?
Neurol Res
2016
;
38
:
478
90
.