Clinical Overview of MDM2/X-Targeted Therapies

Abstract

MDM2 and MDMX are the primary negative regulators of p53, which under normal conditions, maintain low intracellular levels of p53 by targeting it to the proteasome for rapid degradation, and inhibiting its transcriptional activity. Both MDM2 and MDMX function as powerful oncogenes and are commonly over-expressed in some cancers, including sarcoma (~20%), and breast cancer (~15%). In contrast to tumours that are p53 mutant, whereby the current therapeutic strategy is restore the normal active conformation of p53, MDM2 and MDMX represent logical therapeutic targets in cancer for increasing wild type (WT) p53 expression and activities. Recent preclinical studies suggest that there may also be situations that MDM2/X inhibitors could be used in p53 mutant tumours. Since the discovery of nutlin-3a, the first in a class of small molecule MDM2 inhibitors that binds to the hydrophobic cleft in the N-terminus of MDM2, preventing its association with p53, there is now an extensive list of related compounds. In addition, a new class of stapled-peptides that can target both MDM2 and MDMX have also been developed. Importantly, preclinical modeling, which have demonstrated effective in vitro and in vivo killing of WT p53 cancer cells, have now been translated into early clinical trials allowing better assessment of their biological effects and toxicities in patients. In this overview, we will review the current MDM2 and MDMX targeted therapies in development, focusing particularly on compounds that have entered into early phase clinical trials. We will highlight the challenges pertaining to predictive biomarkers for and toxicities associated with these compounds, as well as identify potential combinatorial strategies to enhance its anti-cancer efficacy

Full text

January 2016 | Volume 6 | Article 71
MINI REVIEW
published: 27 January 2016
doi: 10.3389/fonc.2016.00007
Frontiers in Oncology | www.frontiersin.org
Edited by:
Haining Yang,
University of Hawaii Cancer Center,
USA
Reviewed by:
Takaomi Sanda,
National University of Singapore,
Singapore
Giovanni Gaudino,
University of Hawaii Cancer Center,
USA
*Correspondence:
Elgene Lim
e.lim@garvan.org.au
†Andrew Burgess and Kee Ming Chia
contributed equally to this work.
Specialty section:
This article was submitted to
Molecular and Cellular Oncology,
a section of the journal
Frontiers in Oncology
Received: 03December2015
Accepted: 11January2016
Published: 27January2016
Citation:
BurgessA, ChiaKM, HauptS,
ThomasD, HauptY and LimE (2016)
Clinical Overview of
MDM2/X-Targeted Therapies.
Front. Oncol. 6:7.
doi: 10.3389/fonc.2016.00007
Clinical Overview of
MDM2/X-Targeted Therapies
Andrew Burgess1,2† , Kee Ming Chia1† , Sue Haupt3 , David Thomas1,2 , Ygal Haupt3 and
Elgene Lim1,2*
1 The Kinghorn Cancer Centre, Garvan Institute of Medical Research, Sydney, NSW, Australia, 2 Faculty of Medicine,
St. Vincent’s Clinical School, UNSW Australia, Sydney, NSW, Australia, 3 The Sir Peter MacCallum Department of Oncology,
the University of Melbourne, Melbourne, VIC, Australia
MDM2 and MDMX are the primary negative regulators of p53, which under normal con-
ditions maintain low intracellular levels of p53 by targeting it to the proteasome for rapid
degradation and inhibiting its transcriptional activity. Both MDM2 and MDMX function
as powerful oncogenes and are commonly over-expressed in some cancers, including
sarcoma (~20%) and breast cancer (~15%). In contrast to tumors that are p53 mutant,
whereby the current therapeutic strategy restores the normal active conformation of p53,
MDM2 and MDMX represent logical therapeutic targets in cancer for increasing wild-
type (WT) p53 expression and activities. Recent preclinical studies suggest that there
may also be situations that MDM2/X inhibitors could be used in p53 mutant tumors.
Since the discovery of nutlin-3a, the rst in a class of small molecule MDM2 inhibitors
that binds to the hydrophobic cleft in the N-terminus of MDM2, preventing its association
with p53, there is now an extensive list of related compounds. In addition, a new class
of stapled peptides that can target both MDM2 and MDMX have also been developed.
Importantly, preclinical modeling, which has demonstrated effective invitro and invivo
killing of WT p53 cancer cells, has now been translated into early clinical trials allowing
better assessment of their biological effects and toxicities in patients. In this overview, we
will review the current MDM2- and MDMX-targeted therapies in development, focusing
particularly on compounds that have entered into early phase clinical trials. We will
highlight the challenges pertaining to predictive biomarkers for and toxicities associated
with these compounds, as well as identify potential combinatorial strategies to enhance
its anti-cancer efcacy.
Keywords: p53, MDM2, MDMX, cancer therapy, nutlin
INTRODUCTION: RATIONALE FOR TARGETING THE p53
PATHWAY
e tumor suppressor protein p53, nominated “the guardian of the genome,” is mutated in ~50%
of all human cancers. However, the incidence of p53 mutations diers signicantly between cancer
types, ranging from near universal mutation (~96%) in serous ovarian cancer to rare occurrence
(<10%) in thyroid cancer (Figure 1A). is disparity provides therapeutic opportunities for
targeting cancers with p53 wild-type (WT), in a distinct manner from those with p53 mutant can-
cers. Several preclinical studies have demonstrated that reconguration of mutant, to its normal,

FIGURE 1 | Rationale for targeting p53 in cancers. (A) Frequency of alterations are shown with mutation (green), deletion (blue), amplication (red), and
combination of alterations (gray) in p53, MDM2, and MDMX in cancers derived from cBioPortal (5) (http://www.cbioportal.org). Insert shows the mutual exclusivity
observed between MDM2 expression and p53 deletion in sarcomas. (B) Schematic representation of inhibitors in clinical trials (yellow box) or in preclinical studies
(blue box) targeting the p53–MDM2/X axis. Compounds are either small molecules (green circle) or peptide (blue circle).
January 2016 | Volume 6 | Article 72
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active WT p53 conformation, restores apoptosis and promotes
tumor regression (1–3). erapeutic targeting of mutant p53,
using small molecule drugs, is in the most advanced state for
PRIMA-1, and its derivative PRIMA-1MET, an approach which
restores the normal, active conformation of p53, which has been
previously explored in depth by Wiman and coworkers (4). In
the current review, we focus on therapies that target MDM2
and MDMX as a means of increase the stability of WT p53 and
the consequences for patients with either WT p53 or mutant
cancer cells.

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Regulation of p53 Stability by MDM2 and
MDMX
e primary response to a variety of cellular insults and stresses is
to concurrently activate and stabilize p53 within the cell. Activated
p53 then drives a vast transcriptional program that arrests the cell
cycle, promotes repair pathways, and in response to severe stress
initiates apoptosis. erefore, under normal conditions, it is criti-
cal that intracellular levels of p53 are kept low, which is achieved
by the rapid degradation of p53 by the proteasome. is degra-
dation occurs in both ubiquitin-dependent (6) and ubiquitin-
independent mechanisms (7) and can be modulated by various
signaling pathways including sumoylation, phosphorylation,
acetylation, methylation, and glycosylation (8). Of these, ubiqui-
tination is the most important (6, 9) and the E3 ligase MDM2 is
the primary negative regulator of p53 (10, 11), although several
other E3 and E4 ligases of p53 also exist (8, 9). Mechanistically,
engagement of the p53 N-terminal transactivation domain by the
N-terminal of MDM2, facilitates its C-terminal RING nger E3
ligase activity to transfer ubiquitin to multiple lysine residues of
p53, located in central DNA-binding and C-terminal regulatory
regions (8, 9). MDM2 ubiquitination of p53 (either mono- or
poly-ubiquitination) negatively regulates its transcriptional activ-
ity. Mono-ubiquitin triggers nuclear export, while poly-ubiquitin
targets nuclear p53 for degradation by the proteasome (12).
Notably, the C-terminal of MDM2 is also able to bind with the
C-terminal of the highly related protein MDMX (also known as
HDMX and MDM4). Although MDMX does not possess E3 ligase
activity, the MDM2–MDMX heterodimer ubiquitinates p53 with
higher eciency than MDM2 homodimers (13). MDMX, via its
N-terminus, is able to bind p53 and eciently inhibit its tran-
scriptional activity (14). Furthermore, MDM2 is transcriptionally
up regulated by p53 and this negative-feedback loop associated
with cyclical modulation of levels of both proteins, ensures that
p53 levels remain low under normal conditions (15).
Targeting MDM2 and MDMX
Given the importance of both MDM2 and MDMX in regulating
WT p53, it is unsurprising that they are commonly over-expressed
in some cancers, including sarcoma (~20%) and breast (~15%)
(Figure1A). In this context, they function as powerful oncogenes
and represent logical therapeutic targets for increasing WT p53
expression and activities. e concept of MDM2 targeting was
supported by the discovery of p14ARF (p19ARF in mice), an alternate
reading frame protein produced from the CDKN2A locus (16,
17). P14ARF binds to MDM2, sequestering it in the nucleolus and
preventing it from targeting p53 for degradation (18, 19). More
precisely, the capacity to bind and sequester MDM2 to the nucleus
was assigned to a 22 amino acid fragment from the N-terminus
of p14ARF, revealing a potential method for targeting MDM2 with
small peptide inhibitors (20). e rst successful realization of
this potential came in 2004, when nutlin-3a was discovered by
Vassilev etal. (21). Nutlin-3a potently binds to the hydrophobic
cle in the N-terminus of MDM2, preventing its association with
p53. Importantly, it is highly eective killing of WT p53 cancer
cells, both invit ro and i nvivo in preclinical models, provided vali-
dation for its use. However, its poor bioavailability, high toxicity
(discussed in greater detail below), and its limited eects on
MDMX overexpressing cells (22–24) has prevented its translation
to the clinic. Recent interest has switched to compounds that have
better bioavailability and can target both MDM2 and MDMX.
ese new compounds can be broadly segregated according to
their mode of action. e vast majority of preclinical and clinical
small molecule inhibitors work similarly to nutlin-3a, binding to
the N-terminal pocket of MDM2, inhibiting association with p53
(Figure1B). Despite the similarity in the N-terminal p53-binding
domain of MDM2 and MDMX, most of these small molecule
inhibitors bind with signicantly less avidity to MDMX and are
therefore primarily MDM2 specic (12). However, there are now
several new peptide-based inhibitors that are capable of binding
to the N-terminal of both MDM2 and MDMX (Tabl e 1). In addi-
tion, several small molecule inhibitors, which bind specically
to the N-terminus of MDMX, have recently been developed and
are currently undergoing preclinical testing (25, 26). In addition,
there are now a growing number of new MDM2/X inhibitors that
bind outside the N-terminus (Figure1B). ese include small
molecules that inhibit the ubiquitin ligase activity of MDM2
(27); disruptors of MDM2–MDMX heterodimerization (28);
transcriptional inhibitors of both MDM2 (29, 30) and MDMX
(31); MDM2 auto-ubiquitination activators (32, 33); inhibitors
of HSP90 to disrupt MDMX protein folding; and molecules that
directly engage p53 and prevent association with MDM2/X (34).
Cellular Responses to Increased p53
Increased cellular p53 protein levels, resulting from MDM2/X
inhibition, lead to a number of eects that can be simplied into
the broad categories of cell cycle arrest and apoptosis. e decision
between these two pathways is governed by the level and duration
of p53 induction. Lower and cyclical levels of p53 induce arrest,
while sustained levels of elevated p53 expression promotes death
(35). Cell cycle arrest is primarily achieved through transcrip-
tional activation of p53 target genes, primarily p21 and GADD45,
which block the activity of cyclin-dependent kinases (Cdk)
and cause arrest in G1/S (36) and G2 phases, respectively (37).
Interestingly, upregulation of p53 during mitosis does not delay
mitotic progression, but it is an important requirement for arrest-
ing and eliminating aberrant polyploid cells in the subsequent
G1 phase (38, 39). Continued p53 expression occurs when the
damage or stress incurred cannot be repaired or resolved. ese
stresses continue to generate a signaling cascade (e.g., ATM/
ATR, Chk1/2) that leads to the continued stabilization of p53,
and subsequently allows the accumulation of pro-apoptotic p53
targets, including PUMA, Noxa, and Bim within the cell (40, 41).
Once these proteins accumulate to sucient levels, they trigger
apoptosis (42, 43).
MDM2/X INHIBITORS IN CLINICAL
TRIALS
e majority of MDM2-targeted therapies currently in clinical
development are small molecule inhibitors (Tab l e 1 ). ese have
been crystallographically resolved and comprise derivatives
that bind to MDM2 by mimicking Phe19, Trp23, and Leu26,

TABLE 1 | MDM2 and MDMX inhibitors in clinical development.
MDM2 inhibitors in clinical development
Class and
specicity
Nature of
compound
Compound Status p53 NCT identier Company
Small molecule
MDM2 antagonists
Cis-imidazoline RG7112 Phase I in advanced solid and hematological
cancers, and liposarcoma (completed)
n/a NCT00559533
RG7112 with cytarabine Phase I in acute myelogenous leukemia
(completed)
n/a NCT01635296
RG7112 with doxorubicin Phase I in soft tissue sarcoma (completed) n/a NCT01605526 Roche
RO5503781 Phase I in advanced solid cancers (completed) n/a NCT01462175
RO5503781 with
cytarabine
Phase I in acute myelogenous leukemia (active
but not recruiting)
n/a NCT01773408
RO5503781 with
abiraierone
Phase I/II in advanced prostate cancer
(recruiting)
n/a CRUKE/12/032
Spiro-oxindole SAR405838 Phase I in advanced solid cancers (active but
not recruiting)
n/a NCT01636479 Sano-Aventis
SAR405838 with
pimasertib
Phase I in advanced solid cancers (recruiting) n/a NCT01985191
Imidazothiazole DS-3032b Phase I in advanced solid cancers (recruiting) n/a NCT01877382 Daiichi Sankyo
Dihydroisoquinolinone CGM-097 Phase I in advanced solid tumors (recruiting) wtp53 NCT01760525
n/a HDM201 Phase I in advanced solid and hematological
cancers (recruiting)
wtp53 NCT02143635 Novartis
HDM201 with ribociclib Phase Ib/II in liposarcoma (recruiting) wtp53 NCT02343172
Piperidines MK4828 with cytarabine Phase I in acute myelogenous leukemia
(terminated)
n/a NCT01451437 Merck
Piperidinone AMG232 Phase I in advanced solid cancers and multiple
myeloma (recruiting)
n/a NCT01723020 Amgen
AMG 232 with trametinib
and dabrafenib
Phase Ib/IIa in metastatic melanoma
(recruiting)
n/a NCT02110355
Pyrrolidine RG7388 Phase 1 in polycythemia vera and essential
ihrombocythemia (recruiting)
n/a NCT02407080 Pegasys
Stapled peptide
MDM2/X inhibitor
Peptide ALRN-6924 Phase I in advanced solid cancers (recruiting) wtp53 NCT02264613 Aileron
Data extracted from http://www.clinicaltrials.gov, accessed 1st December 2015.
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which are key residues engaged by p53. ALRN-6924 (Aileron
erapeutics) belongs to a dierent class of therapeutics, which
are stapled peptides designed to disrupt p53 interaction with
both MDM2 and MDMX. A number of these compounds are
also being evaluated clinically in combination with cytotoxics
(doxorubicin and cytarabine), and also molecular-targeted thera-
pies, including ribociclib (CDK4/6 inhibitor), dabrafenib (BRAF
inhibitor), trametinib, and pimasertinib (MEK1/2 inhibitors).
A number of these trials have excluded patients with p53 mutant
tumors; however, the majority have not dened a clear biomarker
for selection criteria, in keeping with the primary end points of
safety and tolerability. It is of interest that a number of these phase
1 trials have yet to be reported even though accrual was started
over 3years ago, which is unusually long in a phase 1 setting.
RG7112 is the most developed in this class of compounds,
and preclinical studies demonstrate strong binding to MDM2,
and eective apoptosis, particularly in MDM2-amplied tumors
(44). One of rst clinical trials reported was in patients with lipo-
sarcoma, a tumor characterized by a high proportion of MDM2
gene amplication and wild-type p53 (45). e primary end point
in this small neoadjuvant study of 20 patients was to assess tumor
biomarkers of p53 pathway activation and cell proliferation. e
results demonstrated an increase in intratumoral p53, p21, and
macrophage-inhibitory cytokine 1 (MIC1, a secreted protein
product of p53) concentrations, an increase in MDM2 mRNA
expression and a small decrease in Ki-67 positive cells in the
treated compared to the pretreated samples. Clinically, the results
were modest, with one partial response and stable disease in 70%
of the cohort. Importantly, there were serious adverse events
(grade 3 or 4) experienced by 40% of the patients, the majority of
which were hematological in nature.
RG7112 has also been evaluated in a phase 1 trial of patients
with relapsed/refractory leukemia, such as AML, ALL, CML, and
CLL (46). e most common toxicities were gastrointestinal and
hematological in nature, 22% of patients experiencing grade 3
and 4 febrile neutropenia. ere was clinical activity, particularly
in the AML cohort, whereby 5 out of 30 evaluable patients
achieved either a complete or partial response, and another 9
patients had stable disease. ese numbers suggest useful single
agent clinical activity, given the refractory nature of their disease
to other therapies. MDM2 inhibition resulted in p53 stabilization
and transcriptional activation of p53 target genes. Interestingly,
two patients who had p53 mutations (G266E and R181L) also
responded to RG7112 in this trial. e G266E is a gain-of-
function (GOF) p53 mutation that upregulates CXC-chemokine
expression and enhances cell migration (47), while R181L is
capable of inducing MDM2 and instigating a cell cycle arrest,
but not apoptosis (48). Consequently, these mutants (G266E and
R181L) may still be sensitive to MDM2/X inhibitors, and hence
patients with these mutations may benet from these inhibitors.

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Assessing the eects that MDM2/X inhibitors in the context of
the various GOF p53 mutants will be of signicant importance,
as MDM2/X inhibition has the potential to increase the levels
of GOF p53 mutants. Several GOF mutants have been shown
to increase cell proliferation, metabolism, invasion, and chem-
oresistance in cancer cells (49–53). Consequently, inhibition of
MDM2/X could place selective pressure on cancer cells with GOF
p53 mutations, driving the clonal evolution of more aggressive
cancer cells and exacerbating tumor growth and metastasis in
patients. Alternatively, a recent preclinical study demonstrated
that the novel small molecule NSC59984 activates p73, resulting
in an MDM2-dependent degradation of GOF p53 and subse-
quent inhibition of tumor growth (54). Other possible explana-
tions for the varied patient response include multiple clones
being present with the tumor (only some of which are mutant), a
retention of one wild-type allele, certain p53 mutations may still
have functional p53 activity (55). Taken together, it is clear that
much more work needs to be done to clearly identify biomark-
ers to improve patient selection for clinical trials of MDM2/X
inhibitors. Furthermore, understanding the heterogeneity of p53
expression and the specic mutations within a patient’s tumor
prior, during and post treatment will also be of considerable
importance for determining the suitability of treatment with
MDM2/X inhibitors.
e clinical eect of MDM2 inhibitors on p53 reactivation,
range from cytostasis to apoptosis, and a combination strategy
may be more ecacious in certain contexts. Preclincal mod-
eling with nutlin-3a has demonstrated improved anti-cancer
activity in combination with cytotoxic- and molecular-targeted
therapies, in dierent tumor types (45); however, the toxicity
prole of the combination partner is a critical determinant of
the success of such an approach clinically. e high incidence
of hematological toxicities in the clinical trials of RG7112
would suggest that therapies with an overlapping side eect
prole would not be suitable as combination partners (45, 46).
A number of clinical trials combining MDM2 inhibitors with
cytotoxics have completed accrual but have yet to be reported
(Table1).
TOXICITIES
A concern of p53 reactivating therapies is its eect on normal
cells. ese include the stabilization of p53 resulting in increased
apoptosis in these cells. is was reected in the clinical trial
of RG7112 in lipoma, whereby the most common toxicity
was hematological in nature, with a reported 30% of patients
experiencing grade 4 neutropenia, and 15% experiencing some-
times prolonged grade 4 thrombocytopenia (45, 46). Whether
hematologic toxicity correlates with prior exposure to genotoxic
therapies is not known. ere are also reports of an increased
incidence of p53 mutations following prolonged nutlin-3a
exposure (56), and concerns about this eect on the develop-
ment of new cancers (57). Other potential o-target eects on
MDM2 inhibitors include the loss of its ability to ubiquitinate
other proteins, such as the steroid hormone receptors [estrogen
receptor (ER) and androgen receptor (AR)] and Rb, as well as
interference with MDM2’s role in DNA repair and modifying
chromatin structure (58). e clinical relevance of these poten-
tial long-term toxicities have not been reported in the current
early phase trials.
CONCLUSION/PERSPECTIVE
Protein–protein interactions, once considered to be a major
hurdle to p53 therapeutic development, can now be targeted
with a growing number of small molecule inhibitors and stapled
peptides. e strategies to overcome this Achilles heel in many
cancers are increasingly varied, and build upon an understanding
of the crystallographic structure of p53 and its interactions with
its major inhibitors. Most of the major pharmaceutical companies
have one or more lead compounds targeting MDM2/X, and many
of these have only recently progressed from preclinical develop-
ment into early phase clinical trials.
e eect of MDM2/X-targeting therapies range from
cytostasis to apoptosis, and combinatory approaches with other
cytotoxic therapies or therapies that target other major onco-
genic pathways are logical approaches, and may allow for lower
and better tolerated doses of both drugs to be administered. For
example, in p53 mutant tumors, protection of normal cells can
be achieved by triggering p53-dependent cytostatic eects with
short, pulsed exposure to MDM2 inhibitors. is cyclotherapy
can reduce the toxic side eect of chemotherapy in these p53
mutant patients (59). Alternatively, recent preclinical evidence
has demonstrated that inhibition of MDM2 with nutlin-3a pre-
vents repair of DNA damage, providing synthetic lethality with
genotoxic agents, such as cisplatin (60). Importantly, this eect
was independent of p53 status and could provide a rational for
examining MDM2 combination therapy in p53 mutant patients.
Getting the therapeutic index right is critical in patients. It is
not surprising that hematological toxicities have been the most
commonly reported and dose-limiting toxicities in the trials
reported so far (45, 46). Long-term follow-up is also critical to
evaluate for the clinical relevance of the potential eects of an
increase in p53 mutations and other o-target eects of this class
of compounds.
e three major biomarkers that have been used to evaluate
therapeutic responses to MDM2/X inhibitors are p53 status,
MDM2, and MDMX levels. Interestingly, the over expression of
MDM2, MDMX, or mutation of p53 are oen mutually exclusive.
For example, liposarcoma, which is one of the rst tumors in
which MDM2 inhibitors have been evaluated (45), shows highly
signicant tendency toward mutual exclusivity (p-value <0.001)
between overexpression of MDM2 (19%) and p53 mutation
(12%) (Figure1A) (5). Other tumors with similar trends of exclu-
sivity include glioblastoma multiforme, melanoma, bladder, lung
andenocarcioma, prostate, and ER-positive breast cancers. ese
tumors present an obvious starting point for trialing MDM2/X
inhibitors in patients. e high rate of MDM2 overexpression
in prostate and ER-positive breast cancers, and the ability of
MDM2 inhibitors to ubiquitinate steroid hormone receptors, has
led to the evaluation of this class of drugs in combination with
endocrine therapies (CRUKE/12/032). It has also been shown
that estradiol modulates a subset of p53 and ER target genes that
can predict the relapse-free survival of patients with ER-positive

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breast cancer, and that p53 activation with nutlin in combination
with fulvestrant, a selective ER degrader, led to a greater degree
of apoptosis invitro (61).
Given the risk of mutations in p53 driving resistance
to MDM2/X inhibitors, additional biomarkers need to be
identied to maximize the chances of clinical success. is is
highlighted by evidence that p53 mutation status as currently
measured clinically, may not be an accurate representation of
functional p53 activity (46). In support, the recent discovery
that MDM2 inhibitor sensitivity could be predicted by a panel
of 13 p53 transcriptional target genes (62) was subsequently
shown to be based on a signicant number of miss-classied
p53 mutant cell lines (63). Removal of these lines unfortunately
abolished the predicative power of the gene signature. An
alternative approach would be to select for tumors with MDM2
amplication given the mutual exclusivity of p53 mutations and
MDM2 amplication (64). However, MDM2 and MDMX have
dierent and cooperative inhibitory eects on p53 activity, and
therefore inhibitors of one may not be as eective in the setting
of raised levels of the other protein (23). us, these biomark-
ers, while logical in their choice, unless further improved upon,
may potentially exclude patients who may benet from these
therapies.
AUTHOR CONTRIBUTIONS
All authors contributed to the preparation and writing of the
manuscript.
FUNDING
AB is a CINSW FRL fellow (10/FRL/3-02). KC is an NHMRC
Dora Lush Scholar. DT and YH are NHMRC principal research
fellows (APP1104364 and APP9628426, respectively). EL is an
NBCF/VCA practitioner fellow (PRAC14-002). is work was
supported by the Patricia Helen Guest fellowship and Love Your
Sister foundation. e funders had no role in analysis, decision to
publish, or preparation of the manuscript.
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