Therapeutic Approaches Target Cancers Mutant For P53 Protein Biology Essay

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About 7.6 million deaths of worldwide are related with cancers in 2007, according to the American Cancer Society. Currently, many scientists therefore are aware to develop the new drugs that target for the common alteration genes in most type of cancer e.g. p53. Approximately 50% of all human cancers (Hollatein et al., 1991) are associated with abnormal tumor suppressor p53 functions. Unlike other tumor suppressor genes mutations, most of p53 gene mutations are due to the point mutation (figure-4) (i.e., single nucleotide substitution) (Hainaut and Hollstein, 2000).These built the basic concept that restoration or regeneration of wild type functional p53 to defected or mutant p53 in cancer cells can be curative anticancer therapy. Normally, P53, an essential transcription factor, is also known as guardian of genome (Lane et al., 1992) because of its role in response to genotoxic and nongenotoxic stress signals to protect abnormal cell growth, prevent uncontrolled cell differentiation and proliferation by regulating cell cycle arrest, senescence and apoptosis (Oren et al., 1999). That is why nonfunctional p53 protein or deficient Wt p53 protein induce tumor evolution.

After undergoing a number of researches, their results revealed that targeting the either inactive wild type p53 protein or mutant p53 protein is a promising cancer therapeutic approach. By generally using two approaches: One is direct approach ,screening chemistry and structure based design to find out the suitable molecules that trigger the protein-protein interaction sites and protein folding pathways to be widen the range of drug target horizon. For example, Nutlin, PRIMA-1(Vassilev et al., 2004, Bykov et al., 2002b).The other approach is indirect approach, alteration in cellular pathways which associated with oncogenic mutation E.g. PARP inhibitors (inhibiting the DNA repair) (Dantzer et al., 2000). In contrast, whether new developed anti cancer drugs can promote prognosis of most cancer patient or not is a wonderful challenge.

In this dissertation, rather than the anticancer therapeutic approaches reactivated p53 functions in cancer with wild type p53, I will focus on the mutant p53 based anticancer therapeutic approaches such as p53 gene therapy, restoration of p53 function with various small molecules or peptides, mimicking the p53 function with p53 family members, cyclotherapy and so on.

Key concepts of Tp53 and Cancer

Since 1979, Lane and Crawford discovered 53kDa protein as SV 40 tumor antigen that present abundantly in cancers. On the late 1980s forward, 53kDa transcription factor p53 is a tetrameric tumor suppressor protecting against cancer evolution in response to cellular insults, DNA damage, hypoxia, genotoxic and non genotoxic stress (Figure-5).Then several specific signals are transmitted to downstream p53 target genes for their subsequent transcriptional activation or repression activities. Normally, wild type p53 protein levels in the cells are too low to detect because of MDM2 mediated p53 proteasomal degradation. Furthermore, gene expression of MDM2 is in p53 dependent manner leading to form the negative feedback loop between p53 and MDM2/HDM2 (murine/human double minute 2 and 4).

P53 discovery

Biomarker for therapeutic decision

Pharmacological control of

p53 in cancer therapy

Cloning of mouse p53 cDNA

Mutant p53 protein act as oncogen

Suppression of cell growth by wild-type p53

Mutated in many human cancers

Germline Tp53 mutations in

Li-Fraumeni Syndrome

Guardian of genome

Transcription factor

Adenovirus gene therapy

Lead compounds for pharmacological control

Prognostic and predictive value of mutations

Clinical trials for p53 smart drugs








Figure 1.p53 researches from discovery to clinical application

Critical steps in p53 research for p53 based anticancer therapy. Pink boxes show p53 discover and its functions (1979-1988). Green boxes indicate the p53 as body defense mechanism against cancer evolution (1988-1994). Blue boxes represent current p53 based therapeutic approaches and prognostic value (1995- present). Purple boxes illustrate about the ongoing and future projected applications of p53 for diagnosis and treatment of cancer. Adapted from (Hainaut and Wiman, 2009).

Figure-2. Regulation of p53 pathway molecules in response to cellular stress in healthy cell with normal p53 function. Adapted from (Bai and Zhu, 2006).

Mutations in p53 can produce the full length protein, especially in point mutation, but these mutated p53 protein cannot interact with MDM2 that remove p53 from nucleus to cytoplasm for proteasomal degradation. Then mutant p53 become more stable and accumulate in the tumor cells. Finally, over expressed mutant p53 protein levels exceed than normal wt p53 levels in non tumor cells leading to increase tumor progression (Rotter et al., 1983). Tumor without mutant p53 protein can also induce cancer progression by p53 inactivation. Wild type p53 knockout mice showed high risk to develop cancers spontaneously (Donehower et al., 1992). Li-Fraumeni syndrome patients can develop the early onset of cancers because of inherited germline mutation of one p53 allele inducing the subsequence loss of the remaining wild type p53 allele (Srivastava et al., 1990). This phenomenon is known as loss of heterozygosity (LOH) of p53.

The Tp53 (human p53 gene) encoded 393 amino acid is located at chromosome 17p13.1. From the structural point of view, this nuclear p53 protein composes of the four main functional domains such as N terminal transactivation domain (TAD) ,central core DNA binding domain (DBD) required for specific DNA binding to interact with many p53 target gene , oligomerization domain (OD), and C terminal regulatory domain (CRD)(Figure-3). Depending on the various p53 mutation types in cancers, mutant p53 structure and functions are varied. The conformational changes of normal and mutant p53 can be distinguished by monoclonal antibodies (mAb) pAb1620 and mAb pAb240 respectively. There are roughly categorizing the mutation of p53 into structural mutation (for example R248, R273) and DNA contact mutation (for example, R175, H179). Structural abnormality results in abnormal folding or unfolding protein, while DNA contact mutations defect the transactivation of p53 target genes (Cho et al., 1994).

Figure-3. Common mutation sites in Tp53 gene. Adapted from (Buganim and Rotter, 2009)

Less sensitive to various cells response for cancer protection

Oncogenic mutant p53



Cell cycle arrest

Sensitivity of radio/chemotherapy



Figure-4. Schematic of common cause of p53 mutations and mutant p53 gain of function in tumor development. Adapted from (Buganim and Rotter, 2009)

Oncogenic property of mutant p53 (Figure-4) is designated as mutant p53 gain of function in cancer. Principally, the three possible mutant p53 outcomes, such as loss of tumor suppressor function, dominate negative effects and gain of tumor induction function, are attractive issues for worldwide researchers to find out more about mutant p53, and then aim it for drugs target in human cancers (Michalovitz et al., 1991, Singal and Rotter, 2000, Weisz et al., 2007)




Figure -5. Showing Tp53 mutations in various human cancers and missense mutation is the most common Tp53 mutation types both in somatic mutations and germline mutations. Adapted from (Petitjean et al., 2007) IARC TP53 database from

Therapeutic approaches for mutant p53 associated cancers

Gene therapy based approaches

Restoration of wild type p53 function to mutant p53 become a target in therapeutic approach for various human cancers as bioactive p53 protein is an essential tumor suppressor to defense against tumor progression to maintain the genomic integrity and mutations of Tp53 gene are frequently associated with cancers. One of the approaches is p53 based gene therapy which is aimed to replace the exogenous functional wild type TP53 to either mutated Tp53 expressing cancer cells or inactive Tp53 containing tumor cells. For introducing the normal wild type p53 gene, the suitable effective delivery system such as physical, non-viral or viral vectors are primarily required to carry and transfect the target gene to designated cells. In viral mediated p53 gene therapy, replication-defective viruses such as retrovirus, adenovirus and herpes simplex virus VP22 are used in several recent pre-clinical and clinical trials (Table-1), (Figure-6).

Table 1. Vectors for gene delivery into cells

Vector, size





Requirement of cell division for transduction

Low transduction efficiency

Packaging cell line required

No targeting

Replication competence

Insert size ,9-12 kb

Requirement of cell division for transduction


High transduction efficiency

Infection of many cell types

Infection does not require cell division

No integration

Packaging cell line required

Safety toxicity immunogenicity

Replication competence

No targeting

Insert size, 4-5 kb

Adeno-associated virus

No viral genes

Infection does not require cell division

No targeting

Packaging cell line required


Insert size ,5 kb

Herpes simplex virus

Neuronal tropism

Large insert size, 40-50 kb

Latency expression

No targeting

Packaging cell line


Moreover, cationic liposome, non viral vectors, can deliver cDNA of Tp53 to the target cells by receptor-mediated endocytosis. In addition, mutated or defected p53 proteins containing cancer cells can be selectively eradicate by transfecting of genetically modified adenovirus without carrying normal Tp53 gene (Bouchet et al., 2006).

Figure-6. p53 gene therapy

When the p53 is mutated or deleted or truncated by genetic lesions, this viral based p53 gene therapy can be introduced the wild type p53 gene into the p53 defected tumor cells. Replication-defective adenoviral vector carrying the normal full length p53 cDNA (for e.g. Gendicine, Advexin, ScH-58500) is infected to the target tumor cells to replace functional p53 gene to mutant one. Modified adenovirus (ONXY-015) without wild type p53 gene is targeted to replicate in mutant or deficient p53 cancer cells and kill them. Adapted from (Buganim and Rotter, 2009).

Since late 1980s and early 1990s, wild type p53 gene was transfected into the human cancer cells leading to promote the apoptotic cells death and tumor cells growth arrest. An expected curative outcome was provided in murine model system as reactivation of p53 function occurred within the tumor cells. Subsequently, Ventura and colleagues pointed out that activation of normal p53 promoted cancer cells apoptosis in lymphoma models (Ventura et al., 2007). At the same time, Xue et al established that anti cancer effect of active p53 may be induction of liver tumor cells senescence (Xue et al., 2007).

In nu/nu mice with mutant Tp53 protein expression human lung cancer cells, the normal wild type Tp53 functions is restored via retroviral vector (LNp53B) resulting in suppressing the tumor growth locally (Fujiwara et al., 1994). In 1996, Roth and colleagues attempted the first p53 gene therapy in man to treat the non-small cell lung cancer by direct injection of retroviral vector carrying functional Tp53 gene linked with actin promoter (Roth et al., 1996). Afterward replication defected adenovirus vector was used to transfer the full length wild type Tp53.

Adenovirus vector carrying normal functional p53 gene (Ad5-p53) linked with cytomegalovirus promoter is directly injected into the prostate tumor of nude mice, and followed by conventional radiotherapy. For determination of the effectiveness of treatment, prostate-specific antigen (PSA) is measured before and after the treatment .There is a significantly fewer fall of PSA level in mice models treated with Ad5-p53 gene therapy followed by radiation than that of in control mice and adenoviral based p53 gene therapy alone mice. This study reveal that using of combination therapeutic approaches could be given more effective to inhibition of tumor growth by inducing the cancer cells radio-sensitivity than using of only p53 gene therapeutic approach (Cowen et al., 2000). In addition, Adenoviral mediated vector could suppress carcinogenesis that was proved by studies results from in vivo and in vitro experimental models with human cancer cells such as orthotopic lung, gliomas, colon, bladder, liver and head and neck cancers (Liu et al., 1994, Clayman et al., 1995, Yung et al., 1995, Badie et al., 1995, Drazen et al., 1994, Harris et al., 1996).

In viral mediated p53 gene therapeutic approach, however, there are still limitations and problems such as irretrievable stimulation of apoptosis, failure of viral vector to infect every cell of tumor, challenging in systemic effectiveness, duration of therapeutic effectiveness or repeated dosing because of host immune response reducing virus infectivity. Efficacy of gene therapy is one of the fundamental points to get approval from FDA for applying new treatment approach in different types of human cancers. Although many p53 genes based therapies are undergoing in cancers patients in USA and China with reasonable efficacy, Advexin has not got FDA approval yet (Senzer et al., 2007). On the other hand, since 2003, Gendicine, adenoviral mediated p53 gene-therapy- product, was approved in China to treat the head and neck cancer together with radiation. According to the recently data analysis, Gendicine, produced with international standard, was used in over 2000 patients (Shi and Zheng, 2009).

According to the several clinical trials, it can be assumed that replacement of biological active p53 gene in mutant p53 tumor cells can suppress the tumorgenesis by either inducing of tumor cells apoptosis or regressing of tumor growth or stabilizing of disease condition or promoting the effectiveness of conventional chemotherapy and radiotherapy (Xu et al., 2001). Many researches are tried to improve the vector transduction efficiency in tumor cells not only because vector are key for gene delivery and expression but also because current using vectors have some limitation for p53 gene delivery to the tumor region locally and systemically.

Reactivation of mutant p53 by small molecules

Figure- 7. Small molecules and peptides restore the wild type p53 activity in mutated p53 containing tumor cells. Adapted from (Buganim and Rotter, 2009).


Way of action

Clinical stage

Types of cancer in clinic


p53-Hdm2 complex inhibitor



p53-Hdm2 complex inhibitor




p53-Hdm2 complex inhibitor



p53-Hdm2 complex inhibitor



p53-Hdm2 complex inhibitor



Hdm2 E3 ligase inhibitor



Sir T deacetylase inhibitor



p53 encoding adenovirus

Approval in China

Head & Neck


p53 encoding adenovirus

Phase I-III

Mouth, Squamous cell carcinoma, Breast, Bladder, Liver and Head & Neck


p53 encoding adenovirus

Phase I-III

Brain, CNS, Fallopian tube, Ovarian and Peritoneal Cavity


Mutant p53 conversion and reactivation



Mutant p53 conversion and reactivation



Mutant p53 conversion and reactivation



Mutant p53 conversion and reactivation



Mutant p53 conversion and reactivation



Mutant p53 conversion and reactivation



Mutant p53 conversion and reactivation



E1B deficient adenovirus

Phase I-III

Sarcomas in combination with MAP Chemotherapy.

Table- 2 . List of some recent pharmaceutical products that can modulate p53 function by different mechanisms. Adapted from (Buganim and Rotter, 2009)

Small peptides (synthetic peptides p53C )

About 30 amino acids of C-terminal of p53 gene are essential negative regulatory domain for inhibition of activation of latent p53. By binding of monoclonal antibody (e.g., pAb241) in C-terminal residues can be activate the p53 protein function (Hupp et al., 1994). Selivanova and colleagues proved that small and short synthetic peptides of p53 C-terminus such as peptide 46 could restore the transcriptional transactivation function and could also induce particularly apoptotic cells death in several mutant p53 overexpressing cancer cells , but there was insignificant impede in cancer cells growth .In spite of being still unclear molecular mechanism , it was established that C-terminal derived peptide could restore DNA binding activity in vitro and stabilize native p53 folding .C-terminal peptide can enter the cells to activate mutant p53 of peritoneal cancer cells and lymphomas cells showing the curative effect ( i.e. disease-free) in animal models with prolong lifespan (Selivanova et al., 1997, Abarzua et al., 1996, Kim et al., 1999, Selivanova et al.,1999 ). However, there are still some obstacles to over including, the cost and complexity of synthesizing synthetic peptides and the limited stability of peptides in cells.


CDB3, a nine-residue peptide, is derived from ASPP/p53BP2 (a known p53- binding protein). CB3 could bind to core domain of both wild type and mutant p53 (R249S) to rise their melting temperature and stabilize native p53 conformation in vitro to rescue p53'sequence-specific DNA binding property. In addition, CDB3 was revealed as a molecular chaperone that prevented the p53 interaction with DNA by occupying at p53 DNA binding domain and was supposed to allow the proper folding of naïve p53 and even mutant p53. According to the studies, it could refold the contact mutation and structural mutation types of p53 genes (His273 and His175 mutations respectively) and then rescues p53 transactivational function leading to increase p53 target genes expression of MDM2, Gadd45 and p21.Although CDB3 was appeared to induce program cell death, administration of CDB3 alone could promote wt p53 expressing cells; instead could be increased their sensitivity to radiation mediated cells death (Friedler et al., 2002; 2003, Issaeva et al., 2003).CDB3, a fragment of ASPP that can stimulate the activation of other p53 family members p73 as p73 /p63 show 60% similar nucleotides of DBD. Therefore, CDB3 could also stabilize p73 and block the interaction between mutant p53 and functional p73 in cancer cells .It gives a hope for an anti-neoplastic therapeutic approach (Bergamaschi et al., 2004).


In 1999, Foster and colleagues revealed the concept that unfolded conformation of mutant p53 proteins can be restored to active p53 conformation by identifying several small synthetic non peptide molecules, such as CP 31398 from Pfizer on the basis of an in vitro assay of mutant p53 unfolding. CP 31398, having ability to restore active wild type p53 conformation in several mutant p53 cancers, could stabilize core DNA binding domain of p53 against time- and temperature - dependent degradation and then carry out the anti tumor activity both in cell-based and animals models. DBD conformation of mutant p53 proteins and wild type p53 proteins can be detected by distinct monoclonal antibody (mAb), mAb1620 and mAb240 respectively. Thus, CP31398 restore biologically active p53 folded conformation in cancer cells expressed Ala- 173 and His-273 mutant p53 proteins in vitro. Moreover, it could suppress of tumor growth by increasing the wild type p53 protein level and activity in various human cells lines, for instance ATM-null cells (Foster et al., 1999). On the other hand, recent studies cannot be able to establish the evidences of Cp31398 directly binding to either wild type or mutant p53. Instead it may be a DNA intercalator which interacts directly with DNA (Rippin et al., 2002). Although CP31398 may also not be inhibit the interaction between P53 and MDM2 in vivo, it could block the ubiquitous proteasomal degradation of p53 resulting in promoting active transcriptional level of p53 (Wong et al., 2003). What was more, CP31398 treated cells induced cell cycle arrest or apoptosis by inducing p53 target genes expressions such as p21WAF1 and BAX (Foster et al., 1999, Luu et al., 2002, Takimono et al., 2002). This drug was likely to be interacted with naïve p53 and then maintained its wild type conformation before completing its folding process or its function in anticancer cell growth may be in p53 independent manner (Woods et al., 2003). Further investigations established that the effect of CP31398 rescuing DBD activity has not seen in p53 family member p63 or p73 (Demma et al., 2004). In 2007, Tang and colleagues demonstrated that CP31398 could not only treat effectively in UV light induced non melanoma skin cancer in immunocompetent mice model but also be an attractive candidate for preventing of cancer development.


PRIMA1 is a small molecule that was identified from the result of cell-based screening assay using Tet-off regulated His-237 mutant p53 containing cell line, Saos-2. PRIMA-1 suppressed cancer cells growth and development (Bykov et al., 2002b), by inducing apoptotic program cells death and reactivating wt p53 transcriptional transactivation function to mutant one by restoring and enhancing the p53-Hsp90α interaction and translocation (Rehman et al., 2005). That's why it is designed as PRIMA1 (p53 reactivation and induction of massive apoptosis) .Biological function of p53 protein can be rescued by PRIMA-1 especially in DNA contact or universal structural p53 mutation types. According to the human cancer cells line researches, PRIMA-1 provided more therapeutic effectiveness in mutant p53 associated cancers compared to that in wt p53 expressed cancers (Bykov et al., 2002b), The anti neoplastic activity of PRIMA-1 can be established in human solid tumor xenografts (Bykov et al., 2002a) and also in myeloid leukemia treated together with anti leukemia drugs. Comparing with Cp31398, PRIMA-1 anticancer activity is seemed to affect on the earlier accumulated mutant p53 protein.

In addition, PRIMA-1 (MET) is the methylated version of PRIMA-1 and its anti tumor activity is more promising than PRIMA-1's as PRIMA-1(MET) can work synergistically with anti cancer agent, Cisplatin , resulting in significant increasing of cellular apoptosis to suppress the tumor growth in vivo (Bykov et al., 2005b). It is therefore assumed that treating with combination regime of PRIMA-1 with anticancer drugs provided more effectiveness than either of each alone regime. Even though the exact molecular mechanism of PRIMA-1 is still needed to expose more, the current knowledge from studies revealed that it may be associated with cJun NH2 Kinase pathway (Li et al., 2005) because PRIMA activity are block by inhibition of cJun NH2 Kinase. The advantage of PRIMA-1 is that its cytotoxic effect only showed in mutant p53 expression malignant cells and did not in wild type p53 expression cells. PRIMA-1 MET (commercially APR-246) is recently ongoing phase 1 clinical trial in refractory hematological cancer patients because of its selective anticancer effect in ex vivo studies and all together with appropriate pharmacokenitic properties showing nontoxic effect in animal models although there are limitation in knowledge of molecular mechanism of action of APR-246 (Nahi et al., 2004: 2006). From Lambert et al studies, their results established the fact that PRIMA-1 directly interacted with p53. Moreover, their work revealed that alkylation at cysteines residues of DNA binding domain of mutant p53 could restore p53 native folding .In addition , this cysteines alkylation have probably found in other small molecules such as MIRA-1 , STIMA-1 and Cp31398. (Lambert et al, 2009).


MIRA-1 is a new mutant p53 reactivated small molecule that structure is not similar to either PRIMA-1 or CP31398. In spite of having similar biological function like PRIMA-1, MIRA-1 showed a little more potent in promoting apoptosis than that of PRIMA-1. However, it is seemed in band shift assays that MIRA-1 can only rescue the native conformation of p53 from some types of p53 mutations, such as Gln248, Tyr-176/Trp248, His 175 and Tr282 p53 mutations. MIRA-1 and its analogs can also save normal p53 protein function by changing to biological active p53 conformation from mutant conformation, but the mechanism of this small molecule in cancer therapeutic approaches has not been certain yet. It is assumed to be because of MIRA-1 carrying a maleimide group that interact with thiol and amino group in protein and the alkylated modification in cysteine residues of mutant p53. Further studies are needed to expose the mechanism of action of MIRA-1in anticancer therapy (Bykov et al., 2005a).

PhiKan083/ PhiKan 059 (p53-Y220C-PhiKan083)

PhiKan083, a carbazole derivative, could rise the melting temperature of p.Y220C which a frequent mutation associated with p53 instability in many human cancers. According to the IARC (International Agency for Research of Cancer) Tp53 database, over 70,000 new annual cancer patients globally may related with p.Y220C mutant. Substitution of Tyrosine (Y) to Cysteine (C) at residue 220 may be widening the crevice that found in opposite site of DNA-binding surface. A small molecule, PhiKan083, can bind this crevice to rescue mutant p53 protein. Recently, some progression in the study of p.Y220C mutant was seemed to support a dream of p53-Y220C-PhiKan083 therapeutic approach (Bokeckler et al., 2008, Oliver et al., 2009).

p53R3 (quinazoline)

P53R3 was recently discovered as a new mutant p53 rescuer based on the result of biochemical screening of a chemical library. p53R3 could not only restore normal wild type p53 function and sequence-specific DNA-binding of mutant p53 (for example, R175H, R273H mutants overexpressing cancer cells in gel-shift assays) but also promote the regulation of inappropriate cells proliferation or growth arrest in the p53 dependent manner in p53 null glioma cell line with point mutations in p53 R175H , p53 R248W, p53 R273H . In spite of being unclear of its molecular mechanism, like PRIMA-1 ,p53R3 could increase the some p53 target genes expression that are responsible in cell cycle arrest such as p21 and Gadd45 and apoptosis such as PUMA,DR5 and CD95L (Weinmann et al., 2008).

WR2721,WR1065 (amifostine)

Amifostine (WR2721) is a known cytoprotector of radiation and chemotoxic agent in the clinic and it can not only activate normal p53 function in mammalian cell culture but also restore wild type p53 function totally or partly to mutant p53 in yeast functional assay (Maurici et al., 2001). Aminothiol WR1065 is an active metabolite of WR2721 and also a radio and chemoprotector. In addition, it can activate wt p53 in MCF7 cells line, restore bioactive conformation of p53 and induce cell cycle arrest at G1 in V272M mutant expressing esophageal malignant cells (North et al., 2002).

Ellipticine (9HE)

The plant (Ochrosia elliptica) derivative Ellipticine (EPC) is a natural compound which purified since 1959. It provided the well-known anticancer activity and cellular toxicity in a wide range of cancer types, but its toxic effect held back its therapeutic usage as anticancer agent. After systemically optimizing EPC structure, 9-hydroxy-ellipticine (9HE) exhibited its restoration of functional p53 to mutant p53 by stimulating cell cycle arrest and G1 phase-restricted program cell death in several cancers with mutant p53 (in His-175, Trp-248, Ser-249, and His-273). It is still unclear how 9HE could carry out its function (Sugikawa et al., 1999). However, in 2003, Peng et al provided the proof that EPC could rescue the transcriptional function of selectively p53 mutants in vitro and in nude mouse tumor xenografts by increasing p53 response genes expression including p21WAF1 and MDM2 and stimulating of p53 targeted luciferase reporter (SakamotoHojo et al., 1988, Garbett et al., 2004, Sugikawa et al., 1999, Peng et al., 2003).

Small molecules activate p53 family member (p73, p63) in a p53 mutant cancers

P53 protein family members, p63 and p73, are transcription factors having similar structure and biological tumor suppressor function like p53 protein. In addition, they can interact with each other to form heterodimer that cause more complex in the p53 signaling pathway. Unlike p53 genes, p63 and or p73 are critical in normal development and their mutations are not common in human cancers. As p73 expression levels could be upregulated by various chemotherapeutic agents in p53 independent manner and inhibition of p73 function could be associated with chemoresistance in tumor cells, it was assumed that p73 function may be related with cellular chemosensitivity (Irwin et al., 2003). On the other hand, it was pointed out that induction of tumor suppressor p63 and p73 proteins level could likely to defense tumor evolution by using small molecules (for example, NSC176327 , RETRA ) that promoted p73 levels in mutant p53 cancer cells (Vilgelm et al., 2008, Lu et al., 2009). NSC176327 is an ellipticine derivative compound that is identified through imaging-based cell assay (Wang et al., 2006). According to the studies, NSC176327 take part in stimulation of p73 expression via increasing DR5 and p21, p53 target genes, transactivation in cancers cells with defected p53 function (Lu et al., 2008).

In addition, some types of the mutant p53 protein with dominant negative activity can interact with wt p73 protein leading to reduce the transcriptional function of p73.So small molecular compounds blocking that kind of interaction may be rescue p53 function (Wang et al., 2008). RETRA (reactivation of transcriptional reporter activity) was recognized as a p53-reporter- activity enhancer depending on mutant p53. When human epidermal carcinoma cell line A431 containing R273H mutant p53 was treated with RETRA , it is showed that RETRA could promote p73 protein function specifically in Tp53 mutated cancers cells by inhibiting the mutant p53- p73 interaction which detail mechanism are currently blurred (Kravchenko et al., 2008).

Figure-9. Structural and functions relationship between p53 family members.

(A) p53 family has three members: p53, p63 and p73. All of them share high degree of similar conserved structural domains including N-terminal Transactivation domain (TA), Proline rich domain (PR), DNA binding domain (DBD) and Oligodimerization domain (OD). A sterile alpha motif (SAM), a putative protein-protein interaction domain, is found in p63 and p73 but not in p53.From the functional point of view, p53 protein is significantly involved in cell-cycle regulation and apoptosis but it is not associated with normal developmental process. P63 and p73 protein are essential for normal development and they are also involved in cell cycle arrest and apoptotic cells death (Adopted from Dotsch et al., 2010).


Cyclotherapy based on the basis concept that mutant p53 expression tumor cells are not killed or affected by treating with p53 reactivation drugs that can induce transient cell cycle arrest or promote apoptotic cell death in wild type p53 carrying cells to regulate the cancer growth and tumor development. The cycling mutant p53 containing tumor cells can continue to proliferate and so these rapidly divided cancer cells can be treat with anti mitotic inhibitor such as PLK1 inhibitor or taxane to selectively remove the tumor cells with mutant p53 protein. P53 mediated transient cell arrest keep the non tumor cells from cycling and then protect the unwanted normal health cells damage by antimitotic drugs used in chemotherapy. By using the combination of low dose nongenotoxic p53 activation drug such as nutlin, or actinomycin D (Carvajal et al., 2005, Choong et al., 2009) with antimitotic drugs, the common site effect of chemotherapy including hair loss, nausea, anemia, alimentary canal damage and lowering of white blood cell count can be reduced without affecting on the efficacy of antimitotic agents. Recently, Sur and colleagues supported the significant effectiveness of cyclotherapy in protecting WT p53 cells and selectively annihilating mutant p53 cells by using nutlin and polo-like kinase 1 (PLK1) inhibitor (Sur et al., 2009).

Others therapeutic approaches

Synthetic lethality

In the therapeutic approach that based on the genetic basis of synthetic lethality, genotype-selective anti tumor agents are specifically targeted to the tumor cells with preceding one mutation because the preexisting mutation in tumor cells due to either activation of oncogenes or loss of tumor suppressor gene can alter the normal gene function but can lead to cells death .In this condition, if the second mutation occur or induce in that same gene can lead cells death, for instance,PARP1 inhibitor and BRCA 1 or 2 absence breast cancer cells therapy .PARP1 is essential in base-excision DNA repair and so a blocking the PARP1 repair mechanism can induce cells death of mutated tumor cells .Therefore , synthetic lethality based therapeutic approach may be promising approach for cancer with mutant protein although further investigations are necessary to know more detail of drugs mechanism of action (Farmer et al., 2005).

Chimeric adaptor protein

Reactivation to some contact mutant p53 by a chimeric adaptor protein derived from DNA binding and oligomerization domains of p73 and the tetramerization domain of p53.Normaly, this one hybrid adaptor does not contain the transcriptional domain for carrying out transcriptional activity .However, Acting as a linker between mutant p53 and p53 specific target sequence, adaptor may be able to induce the p53 response genes expression in specific type of p53 mutation such as Arg273His and Arg248Trp and its effect may be seen in p53 null cells and wt p53 presenting cells. Adaptor can be transfer in the tumor cells by using adenoviral vector (Roth et al., 2003).

Second-site Suppressor mutation can restore functional p53 protein to mutant one

One of the therapeutic approaches for restoration of wild type p53 function to mutant p53 protein is based on the hypothesis that second site suppressor mutation can correct the carcinogenic effect of preceding original mutation by transferring of novel p53 -DNA contacts to save the p53 mutant losing its sequence specific DNA binding activity (Li et al., 2005).


In a word, although mutant p53 specifically based anticancer therapies are one of the promising new therapeutic approaches in many preclinical or clinical trials, there are still some obstacles to overcome to become successful approval approaches as a worldwide therapies for various human cancers. Furthermore, there are some technological challenges in developing the p53 mediated anticancer drugs or further modifications are still needed for p53 gene delivery system to avoid side effects.