APR-246/PRIMA-1MET inhibits thioredoxin reductase 1 and converts the enzyme to a dedicated NADPH oxidase

PARP-1 inhibitors sensitize HNSCC cells to APR-246 by inactivation of thioredoxin reductase 1 (TrxR1) and promotion of ROS accumulation

Head and neck squamous cell carcinoma (HNSCC) is the sixth most common cancer worldwide. Mutations of TP53 may reach 70% - 85% in HNSCC patients without human papillomavirus (HPV) infection. Recurrence rate remains particularly high for HNSCC patients with mutations in the TP53 gene although patients are responsive to surgery, irradiation, and chemotherapy early in the treatment. p53-Reactivation and Induction of Massive Apoptosis-1 (PRIMA-1) and its methylated analogue PRIMA-1Met (also known as APR-246) are quinuclidine compounds that rescue the DNA-binding activity of mutant p53 (mut-p53) and restore the potential of wild-type p53. In the current report, we demonstrated that inhibition of poly (ADP-ribose) polymerase-1 (PARP-1) with 6(5H)-phenanthridinone (PHEN) and N-(6-Oxo-5,6-dihydrophenanthridin-2-yl)-(N, N-dimethylamino) acetamide hydrochloride (PJ34) sensitizes UMSCC1, UMSCC14, and UMSCC17A, three HNSCC cell lines to the treatment of APR-246. PHEN enhances APR-246-induced apoptosis, but not programmed necrosis or autophagic cell death in HNSCC cells. The PARP-1 inhibition-induced sensitization of HNSCC cells to APR-246 is independent of TP53 mutation. Instead, PARP-1 inhibition promotes APR-246-facilitated inactivation of thioredoxin reductase 1 (TrxR1), leading to ROS accumulation and DNA damage. Overexpression of TrxR1 or application of antioxidant N-acetyl-L-cysteine (NAC) depletes the ROS increase, reduces DNA damage, and decreases cell death triggered by APR-246/PHEN in HNSCC cells. Thus, we have characterized a new function of PARP-1 inhibitor in HNSCC cells by inactivation of TrxR1 and elevation of ROS and provide a novel therapeutic strategy for HNSCC by the combination of PARP-1 inhibitors and APR-246.

PRIMA-1 induces p53-mediated apoptosis by upregulating Noxa in esophageal squamous cell carcinoma with TP53 missense mutation

TP53 is associated with the resistance of cytotoxic treatment and patient prognosis, and the mutation rate of TP53 in esophageal squamous cell carcinoma (ESCC) is extraordinarily high, at over 90%. PRIMA‐1 (p53 re‐activation and induction of massive apoptosis) has recently been reported to restore the function of mutant TP53; however, its antitumor effect and mechanism in ESCC remain unclear. After evaluating the TP53 mutation status of a panel of 11 ESCC cell lines by Sanger sequencing, we assessed the in vitro effect of PRIMA‐1 administration on cells with different TP53 status by conducting cell viability and apoptosis assays. The expression levels of proteins in p53‐related pathways were examined by Western blotting, while knockdown studies were conducted to investigate the mechanism underlying PRIMA‐1's function. An ESCC xenograft model was further used to evaluate the therapeutic effect of PRIMA‐1 in vivo. PRIMA‐1 markedly inhibited cell growth and induced apoptosis by upregulating Noxa expression in ESCC cell lines with TP53 missense mutations, whereas no apoptosis was induced in ESCC with wild‐type TP53 and TP53 with frameshift and nonsense mutations. Importantly, the knockdown of Noxa canceled the apoptosis induced by PRIMA treatment in ESCC cell lines with TP53 missense mutations. PRIMA‐1 administration, compared with placebo, showed a significant antitumor effect by inducing Noxa in the xenograft model of an ESCC cell line with a TP53 missense mutation. PRIMA‐1 exhibits a significant antitumor effect, inducing massive apoptosis through the upregulation of Noxa in ESCC with TP53 missense mutations.

PRIMA-1 and PRIMA-1Met (APR-246): From Mutant/Wild Type p53 Reactivation to Unexpected Mechanisms Underlying Their Potent Anti-Tumor Effect in Combinatorial Therapies

p53 protects cells from genetic assaults by triggering cell-cycle arrest and apoptosis. Inactivation of p53 pathway is found in the vast majority of human cancers often due to somatic missense mutations in TP53 or to an excessive degradation of the protein. Accordingly, reactivation of p53 appears as a quite promising pharmacological approach and, effectively, several attempts have been made in that sense. The most widely investigated compounds for this purpose are PRIMA-1 (p53 reactivation and induction of massive apoptosis )and PRIMA-1^Met (APR-246), that are at an advanced stage of development, with several clinical trials in progress. Based on publications referenced in PubMed since 2002, here we review the reported effects of these compounds on cancer cells, with a specific focus on their ability of p53 reactivation, an overview of their unexpected anti-cancer effects, and a presentation of the investigated drug combinations.

Targeting the Selenoprotein Thioredoxin Reductase 1 for Anticancer Therapy

The cytosolic selenoprotein thioredoxin reductase 1 (TrxR1, encoded in human by TXNRD1) is implied to have several different roles in relation to cancer. Its physiologic functions may protect normal cells from carcinogenesis, but may also promote cancer progression if carcinogenesis nonetheless occurs. With distinct links to Nrf2 signaling, ribonucleotide reductase-dependent production of deoxyribonucleotides and its support of several antioxidant systems counteracting oxidative stress, the metabolic pathways regulated, and affected by TrxR1, are altogether of crucial importance in cancer. These pathways and causal relationships are at the same time highly intricate. In spite of the complexity in the cellular redox networks, several observations discussed in this chapter suggest that specific targeting of TrxR1 may be promising as a mechanistic principle for anticancer therapy.

Mutant p53 as a target for cancer treatment

TP53 (p53) is the single most frequently altered gene in human cancers, with mutations being present in approximately 50% of all invasive tumours. However, in some of the most difficult-to-treat cancers such as high-grade serous ovarian cancers, triple-negative breast cancers, oesophageal cancers, small-cell lung cancers and squamous cell lung cancers, p53 is mutated in at least 80% of samples. Clearly, therefore, mutant p53 protein is an important candidate target against which new anticancer treatments could be developed. Although traditionally regarded as undruggable, several compounds such as p53 reactivation and induction of massive apoptosis-1 (PRIMA-1), a methylated derivative and structural analogue of PRIMA-1, i.e. APR-246, 2-sulfonylpyrimidines such as PK11007, pyrazoles such as PK7088, zinc metallochaperone-1 (ZMC1), a third generation thiosemicarbazone developed by Critical Outcome Techonologies Inc. (COTI-2) as well as specific peptides have recently been reported to reactive mutant p53 protein by converting it to a form exhibiting wild-type properties. Consistent with the reactivation of mutant p53, these compounds have been shown to exhibit anticancer activity in preclinical models expressing mutant p53. To date, two of these compounds, i.e. APR-246 and COTI-2 have progressed to clinical trials. A phase I/IIa clinical trial with APR-246 reported no major adverse effect. Currently, APR-246 is undergoing a phase Ib/II trial in patients with advanced serous ovarian cancer, while COTI-2 is being evaluated in a phase I trial in patients with advanced gynaecological cancers. It remains to be shown however, whether any mutant p53 reactivating compound has efficacy for the treatment of human cancer.

Understanding cell cycle and cell death regulation provides novel weapons against human diseases

Cell division, cell differentiation and cell death are the three principal physiological processes that regulate tissue homoeostasis in multicellular organisms. The growth and survival of cells as well as the integrity of the genome are regulated by a complex network of pathways, in which cell cycle checkpoints, DNA repair and programmed cell death have critical roles. Disruption of genomic integrity and impaired regulation of cell death may both lead to uncontrolled cell growth. Compromised cell death can also favour genomic instability. It is becoming increasingly clear that dysregulation of cell cycle and cell death processes plays an important role in the development of major disorders such as cancer, cardiovascular disease, infection, inflammation and neurodegenerative diseases. Research achievements in these fields have led to the development of novel approaches for treatment of various conditions associated with abnormalities in the regulation of cell cycle progression or cell death. A better understanding of how cellular life-and-death processes are regulated is essential for this development. To highlight these important advances, the Third Nobel Conference entitled 'The Cell Cycle and Cell Death in Disease' was organized at Karolinska Institutet in 2016. In this review we will summarize current understanding of cell cycle progression and cell death and discuss some of the recent advances in therapeutic applications in pathological conditions such as cancer, neurological disorders and inflammation.

Inhibiting the system xC-/glutathione axis selectively targets cancers with mutant-p53 accumulation

TP53, a critical tumour suppressor gene, is mutated in over half of all cancers resulting in mutant-p53 protein accumulation and poor patient survival. Therapeutic strategies to target mutant-p53 cancers are urgently needed. We show that accumulated mutant-p53 protein suppresses the expression of SLC7A11, a component of the cystine/glutamate antiporter, system x_C^-, through binding to the master antioxidant transcription factor NRF2. This diminishes glutathione synthesis, rendering mutant-p53 tumours susceptible to oxidative damage. System x_C^- inhibitors specifically exploit this vulnerability to preferentially kill cancer cells with stabilized mutant-p53 protein. Moreover, we demonstrate that SLC7A11 expression is a novel and robust predictive biomarker for APR-246, a first-in-class mutant-p53 reactivator that also binds and depletes glutathione in tumours, triggering lipid peroxidative cell death. Importantly, system x_C^- antagonism strongly synergizes with APR-246 to induce apoptosis in mutant-p53 tumours. We propose a new paradigm for targeting cancers that accumulate mutant-p53 protein by inhibiting the SLC7A11-glutathione axis.

Reviving the guardian of the genome: Small molecule activators of p53

The tumor suppressor p53 is one of the most important proteins for protection of genomic stability and cancer prevention. Cancers often inactivate it by either mutating its gene or disabling its function. Thus, activating p53 becomes an attractive approach for the development of molecule-based anti-cancer therapy. The past decade and half have witnessed tremendous progress in this area. This essay offers readers with a grand review on this progress with updated information about small molecule activators of p53 either still at bench work or in clinical trials.

Aging tumour cells to cure cancer: “pro-senescence” therapy for cancer

Robust scientific evidence demonstrates that senescence induction in cancer works as a potent weapon to eradicate tumorigenesis. Therapies that enhance senescence not only promote a stable cell growth arrest but also work as a strong stimulus for the activation of the antitumour immune response. However, recent advances suggest that if senescent tumour cells are not cleared from the tumours, they may promote tumour progression and metastasis. In this article, we focus on concepts that are relevant to a pro-senescence therapeutic approach, including caveats, and we propose therapeutic strategies that involve the combined use of pro-senescence therapies with immunotherapies to promote the clearance of senescent tumour cells. In our opinion, these approaches may avoid potential negative effects of pro-senescence therapies and may also enhance the efficacy of currently available immunotherapies.

Molecular Mechanisms of p53 Deregulation in Cancer: An Overview in Multiple Myeloma

The p53 pathway is inactivated in the majority of human cancers. Although this perturbation frequently occurs through the mutation or deletion of p53 itself, there are other mechanisms that can attenuate the pathway and contribute to tumorigenesis. For example, overexpression of important p53 negative regulators, such as murine double minute 2 (MDM2) or murine double minute 4 (MDM4), epigenetic deregulation, or even alterations in TP53 mRNA splicing. In this work, we will review the different mechanisms of p53 pathway inhibition in cancer with special focus on multiple myeloma (MM), the second most common hematological malignancy, with low incidence of p53 mutations/deletions but growing evidence of indirect p53 pathway deregulation. Translational implications for MM and cancer prognosis and treatment are also reviewed.

Hypoxic resistance of KRAS mutant tumor cells to 3-Bromopyruvate is counteracted by Prima-1 and reversed by N-acetylcysteine

Background

The metabolic inhibitor 3-bromopyruvate (3-BrPA) is a promising anti-cancer alkylating agent, shown to inhibit growth of some colorectal carcinoma with KRAS mutation. Recently, we demonstrated increased resistance to 3-BrPA in wt p53 tumor cells compared to those with p53 silencing or mutation. Since hypoxic microenvironments select for tumor cells with diminished therapeutic response, we investigated whether hypoxia unequally increases resistance to 3-BrPA in wt p53 MelJuso melanoma harbouring (Q61L)-mutant NRAS and wt BRAF, C8161 melanoma with (G12D)-mutant KRAS (G464E)-mutant BRAF, and A549 lung carcinoma with a KRAS (G12S)-mutation. Since hypoxia increases the toxicity of the p53 activator, Prima-1 against breast cancer cells irrespective of their p53 status, we also investigated whether Prima-1 reversed hypoxic resistance to 3-BrPA.

Results

In contrast to the high susceptibility of hypoxic mutant NRAS MelJuso cells to 3-BrPA or Prima-1, KRAS mutant C8161 and A549 cells revealed hypoxic resistance to 3-BrPA counteracted by Prima-1. In A549 cells, Prima-1 increased p21CDKN1mRNA, and reciprocally inhibited mRNA expression of the SLC2A1-GLUT1 glucose transporter-1 and ALDH1A1, gene linked to detoxification and stem cell properties. 3-BrPA lowered CAIX and VEGF mRNA expression. Death from joint Prima-1 and 3-BrPA treatment in KRAS mutant A549 and C8161 cells seemed mediated by potentiating oxidative stress, since it was antagonized by the anti-oxidant and glutathione precursor N-acetylcysteine.

Conclusions

This report is the first to show that Prima-1 kills hypoxic wt p53 KRAS-mutant cells resistant to 3-BrPA, partly by decreasing GLUT-1 expression and exacerbating pro-oxidant stress.

Mutant p53: a novel target for the treatment of patients with triple-negative breast cancer?

The identification and validation of a targeted therapy for patients with triple-negative breast cancer (TNBC) is currently one of the most urgent needs in breast cancer therapeutics. One of the key reasons for the failure to develop a new therapy for this subgroup of breast cancer patients has been the difficulty in identifying a highly prevalent, targetable molecular alteration in these tumors. Recently however, the p53 gene was found to be mutated in approximately 80% of basal/TNBC, raising the possibility that targeting the mutant p53 protein product might be a new approach for the treatment of this form of breast cancer. In this study, we investigated the anti-cancer activity of PRIMA-1 and PRIMA-1^MET (APR-246), two compounds which were previously reported to reactivate mutant p53 and convert it to a form with wild-type (WT) properties. Using a panel of 18 breast cancer cell lines and 2 immortalized breast cell lines, inhibition of proliferation by PRIMA-1 and PRIMA-1^MET was found to be cell-line dependent, but independent of cell line molecular subtype. Although response was independent of molecular subtype, p53 mutated cell lines were significantly more sensitive to PRIMA-1^MET than p53 WT cells (p = 0.029). Furthermore, response (measured as IC₅₀ value) correlated significantly with p53 protein level as measured by ELISA (p = 0.0089, r=-0.57, n = 19). In addition to inhibiting cell proliferation, PRIMA-1^MET induced apoptosis and inhibited migration in a p53 mutant-dependent manner. Based on our data, we conclude that targeting mutant p53 with PRIMA-1^MET is a potential new approach for treating p53-mutated breast cancer, including the subgroup with triple-negative (TN) disease.

2-Sulfonylpyrimidines: Mild alkylating agents with anticancer activity toward p53-compromised cells

The tumor suppressor p53 has the most frequently mutated gene in human cancers. Many of p53's oncogenic mutants are just destabilized and rapidly aggregate, and are targets for stabilization by drugs. We found certain 2-sulfonylpyrimidines, including one named PK11007, to be mild thiol alkylators with anticancer activity in several cell lines, especially those with mutationally compromised p53. PK11007 acted by two routes: p53 dependent and p53 independent. PK11007 stabilized p53 in vitro via selective alkylation of two surface-exposed cysteines without compromising its DNA binding activity. Unstable p53 was reactivated by PK11007 in some cancer cell lines, leading to up-regulation of p53 target genes such as p21 and PUMA. More generally, there was cell death that was independent of p53 but dependent on glutathione depletion and associated with highly elevated levels of reactive oxygen species and induction of endoplasmic reticulum (ER) stress, as also found for the anticancer agent PRIMA-1(MET)(APR-246). PK11007 may be a lead for anticancer drugs that target cells with nonfunctional p53 or impaired reactive oxygen species (ROS) detoxification in a wide variety of mutant p53 cells.

Strong synergy with APR-246 and DNA-damaging drugs in primary cancer cells from patients with TP53 mutant High-Grade Serous ovarian cancer

BACKGROUND

Mutation in the tumor suppressor gene TP53 is an early event in the development of high-grade serous (HGS) ovarian cancer and is identified in more than 96 % of HGS cancer patients. APR-246 (PRIMA-1(MET)) is the first clinical-stage compound that reactivates mutant p53 protein by refolding it to wild type conformation, thus inducing apoptosis. APR-246 has been tested as monotherapy in a Phase I/IIa clinical study in hematological malignancies and prostate cancer with promising results, and a Phase Ib/II study in combination with platinum-based therapy in ovarian cancer is ongoing. In the present study, we investigated the anticancer effects of APR-246 in combination with conventional chemotherapy in primary cancer cells isolated from ascitic fluid from 10 ovarian, fallopian tube, or peritoneal cancer patients, 8 of which had HGS cancer.

METHODS

Cell viability was assessed with fluorometric microculture cytotoxicity assay (FMCA) and Combination Index was calculated using the Additive model. p53 status was determined by Sanger sequencing and single strand conformation analysis, and p53 protein expression by western blotting.

RESULTS

We observed strong synergy with APR-246 and cisplatin in all tumor samples carrying a TP53 missense mutation, while synergistic or additive effects were found in cells with wild type or TP53 nonsense mutations. Strong synergy was also observed with carboplatin or doxorubicin. Moreover, APR-246 sensitized TP53 mutant primary ovarian cancer cells, isolated from a clinically platinum-resistant patient, to cisplatin; the IC50 value of cisplatin decreased 3.6 fold from 6.5 to 1.8 μM in the presence of clinically relevant concentration of APR-246.

CONCLUSION

These results suggest that combination treatment with APR-246 and DNA-damaging drugs could significantly improve the treatment of patients with TP53 mutant HGS cancer, and thus provide strong support for the ongoing clinical study with APR-246 in combination with carboplatin and pegylated liposomal doxorubicin in patients with recurrent HGS cancer.

Strong synergy with APR-246 and DNA-damaging drugs in primary cancer cells from patients with TP53 mutant High-Grade Serous ovarian cancer

BACKGROUND

Mutation in the tumor suppressor gene TP53 is an early event in the development of high-grade serous (HGS) ovarian cancer and is identified in more than 96 % of HGS cancer patients. APR-246 (PRIMA-1(MET)) is the first clinical-stage compound that reactivates mutant p53 protein by refolding it to wild type conformation, thus inducing apoptosis. APR-246 has been tested as monotherapy in a Phase I/IIa clinical study in hematological malignancies and prostate cancer with promising results, and a Phase Ib/II study in combination with platinum-based therapy in ovarian cancer is ongoing. In the present study, we investigated the anticancer effects of APR-246 in combination with conventional chemotherapy in primary cancer cells isolated from ascitic fluid from 10 ovarian, fallopian tube, or peritoneal cancer patients, 8 of which had HGS cancer.

METHODS

Cell viability was assessed with fluorometric microculture cytotoxicity assay (FMCA) and Combination Index was calculated using the Additive model. p53 status was determined by Sanger sequencing and single strand conformation analysis, and p53 protein expression by western blotting.

RESULTS

We observed strong synergy with APR-246 and cisplatin in all tumor samples carrying a TP53 missense mutation, while synergistic or additive effects were found in cells with wild type or TP53 nonsense mutations. Strong synergy was also observed with carboplatin or doxorubicin. Moreover, APR-246 sensitized TP53 mutant primary ovarian cancer cells, isolated from a clinically platinum-resistant patient, to cisplatin; the IC50 value of cisplatin decreased 3.6 fold from 6.5 to 1.8 μM in the presence of clinically relevant concentration of APR-246.

CONCLUSION

These results suggest that combination treatment with APR-246 and DNA-damaging drugs could significantly improve the treatment of patients with TP53 mutant HGS cancer, and thus provide strong support for the ongoing clinical study with APR-246 in combination with carboplatin and pegylated liposomal doxorubicin in patients with recurrent HGS cancer.

Strong synergy with APR-246 and DNA-damaging drugs in primary cancer cells from patients with TP53 mutant High-Grade Serous ovarian cancer

Background

Mutation in the tumor suppressor gene TP53 is an early event in the development of high-grade serous (HGS) ovarian cancer and is identified in more than 96 % of HGS cancer patients. APR-246 (PRIMA-1^MET) is the first clinical-stage compound that reactivates mutant p53 protein by refolding it to wild type conformation, thus inducing apoptosis. APR-246 has been tested as monotherapy in a Phase I/IIa clinical study in hematological malignancies and prostate cancer with promising results, and a Phase Ib/II study in combination with platinum-based therapy in ovarian cancer is ongoing. In the present study, we investigated the anticancer effects of APR-246 in combination with conventional chemotherapy in primary cancer cells isolated from ascitic fluid from 10 ovarian, fallopian tube, or peritoneal cancer patients, 8 of which had HGS cancer.

Methods

Cell viability was assessed with fluorometric microculture cytotoxicity assay (FMCA) and Combination Index was calculated using the Additive model. p53 status was determined by Sanger sequencing and single strand conformation analysis, and p53 protein expression by western blotting.

Results

We observed strong synergy with APR-246 and cisplatin in all tumor samples carrying a TP53 missense mutation, while synergistic or additive effects were found in cells with wild type or TP53 nonsense mutations. Strong synergy was also observed with carboplatin or doxorubicin. Moreover, APR-246 sensitized TP53 mutant primary ovarian cancer cells, isolated from a clinically platinum-resistant patient, to cisplatin; the IC₅₀ value of cisplatin decreased 3.6 fold from 6.5 to 1.8 μM in the presence of clinically relevant concentration of APR-246.

Conclusion

These results suggest that combination treatment with APR-246 and DNA-damaging drugs could significantly improve the treatment of patients with TP53 mutant HGS cancer, and thus provide strong support for the ongoing clinical study with APR-246 in combination with carboplatin and pegylated liposomal doxorubicin in patients with recurrent HGS cancer.

Details in the catalytic mechanism of mammalian thioredoxin reductase 1 revealed using point mutations and juglone-coupled enzyme activities

The mammalian selenoprotein thioredoxin reductase 1 (TrxR1) is a key enzyme in redox regulation, antioxidant defense, and cellular growth. TrxR1 can catalyze efficient reduction of juglone (5-hydroxy-1,4-naphthoquinone; walnut toxin) in a reaction which, in contrast to reduction of most other substrates of TrxR1, is not dependent upon an intact selenocysteine (Sec, U) residue of the enzyme. Using a number of TrxR1 mutant variants, we here found that a sole Cys residue at the C-terminal tail of TrxR1 is required for high-efficiency juglone-coupled NADPH oxidase activity of Sec-deficient enzyme, occurring with mixed one- and two-electron reactions producing superoxide. The activity also utilizes the FAD and the N-terminal redox active disulfide/dithiol motif of TrxR1. If a sole Cys residue at the C-terminal tail of TrxR1, in the absence of Sec, was moved further towards the C-terminal end of the protein compared to its natural position at residue 497, juglone reduction was, surprisingly, further increased. Ala substitutions of Trp407, Asn418 and Asn419 in a previously described "guiding bar", thought to mediate interactions of the C-terminal tail of TrxR1 with the FAD/dithiol site at the N-terminal domain of the other subunit in the dimeric enzyme, lowered turnover with juglone about 4.5-fold. Four residues of Sec-deficient TrxR1 were found to be easily arylated by juglone, including the Cys residue at position 497. Based upon our observations we suggest a model for involvement of the juglone-arylated C-terminal motif of TrxR1 to explain its high activity with juglone. This study thus provides novel insights into the catalytic mechanisms of TrxR1. One-electron juglone reduction by TrxR1 producing superoxide should furthermore contribute to the well-known prooxidant cytotoxicity of juglone.

PRIMA-1MET induces apoptosis through accumulation of intracellular reactive oxygen species irrespective of p53 status and chemo-sensitivity in epithelial ovarian cancer cells

There is an intensive need for the development of novel drugs for the treatment of epithelial ovarian cancer (EOC), the most lethal gynecologic malignancy due to the high recurrence rate. TP53 mutation is a common event in EOC, particularly in high-grade serous ovarian cancer, where it occurs in more than 90% of cases. Recently, PRIMA-1 and PRIMA‑1MET (p53 reactivation and induction of massive apoptosis and its methylated form) were shown to have an antitumor effect on several types of cancer. Despite that PRIMA-1MET is the first compound evaluated in clinical trials, the antitumor effects of PRIMA-1MET on EOC remain unclear. In this study, we investigated the therapeutic potential of PRIMA-1MET for the treatment of EOC cells. PRIMA-1MET treatment of EOC cell lines (n=13) resulted in rapid apoptosis at various concentrations (24 h IC50 2.6-20.1 µM). The apoptotic response was independent of the p53 status and chemo-sensitivity. PRIMA‑1MET treatment increased intracellular reactive oxygen species (ROS), and PRIMA-1MET-induced apoptosis was rescued by an ROS scavenger. Furthermore, RNA expression analysis revealed that the mechanism of action of PRIMA‑1MET may be due to inhibition of antioxidant enzymes, such as Prx3 and GPx-1. In conclusion, our results suggest that PRIMA-1MET represents a novel therapeutic strategy for the treatment of ovarian cancer irrespective of p53 status and chemo-sensitivity.

Redox effects and cytotoxic profiles of MJ25 and auranofin towards malignant melanoma cells

Malignant melanoma is the most dangerous type of skin cancer. Although recent progress in treatment has been achieved, lack of response, drug resistance and relapse remain major problems. The tumor suppressor p53 is rarely mutated in melanoma, yet it is inactive in the majority of cases due to dysregulation of upstream pathways. Thus, we screened for compounds that can activate p53 in melanoma cells. Here we describe effects of the small molecule MJ25 (2-{[2-(1,3-benzothiazol-2-ylsulfonyl)ethyl]thio}-1,3-benzoxazole), which increased the level of p53-dependent transactivation both as a single agent and in combination with nutlin-3. Furthermore, MJ25 showed potent cytotoxicity towards melanoma cell lines, whilst having weaker effects against human normal cells. MJ25 was also identified in an independent screen as an inhibitor of thioredoxin reductase 1 (TrxR1), an important selenoenzyme in the control of oxidative stress and redox regulation. The well-characterized TrxR inhibitor auranofin, which is FDA-approved and currently in clinical trials against leukemia and a number of solid cancers, displayed effects comparable with MJ25 on cells and led to eradication of cultured melanoma cells at low micromolar concentrations. In conclusion, auranofin, MJ25 or other inhibitors of TrxR1 should be evaluated as candidate compounds or leads for targeted therapy of malignant melanoma.

Anti-leukaemic effects induced by APR-246 are dependent on induction of oxidative stress and the NFE2L2/HMOX1 axis that can be targeted by PI3K and mTOR inhibitors in acute myeloid leukaemia cells

The small molecule APR-246 (PRIMA-1(MET) ) is a novel drug that restores the activity of mutated and unfolded TP53 protein. However, the mechanisms of action and potential off-target effects are not fully understood. Gene expression profiling in TP53 mutant KMB3 acute myeloid leukaemia (AML) cells showed that genes which protected cells from oxidative stress to be the most up-regulated. APR-246 exposure also induced reactive oxygen species (ROS) formation and depleted glutathione in AML cells. The genes most up-regulated by APR-246, confirmed by quantitative real time polymerase chain reaction, were heme oxygenase-1 (HMOX1, also termed HO-1), SLC7A11 and RIT1. Up-regulation of HMOX1, a key regulator of cellular response to ROS, was independent of TP53 mutational status. NFE2L2 (also termed Nrf2), a master regulator of HMOX1 expression, showed transcriptional up-regulation and nuclear translocation by APR-246. Down-regulation of NFE2L2 by siRNA in AML cells significantly increased the antitumoural effects of APR-246. The PI3K inhibitor wortmannin and the mTOR inhibitor rapamycin inhibited APR-246-induced nuclear translocation of NFE2L2 and counteracted the protective cellular responses to APR-246, resulting in synergistic cell killing together with APR-246. In conclusion, ROS induction is important for antileukaemic activities of APR-246 and inhibiting the protective response of the Nrf-2/HMOX1 axis using PI3K inhibitors, enhances the antileukaemic effects.

APR-246 (PRIMA-1(MET)) strongly synergizes with AZD2281 (olaparib) induced PARP inhibition to induce apoptosis in non-small cell lung cancer cell lines

APR-246 (PRIMA-1(Met)) is able to bind mutant p53 and restore its normal conformation and function. The compound has also been shown to increase intracellular ROS levels. Importantly, the poly-[ADP-ribose] polymerase-1 (PARP-1) enzyme plays an important role in the repair of ROS-induced DNA damage. We hypothesize that by blocking this repair with the PARP-inhibitor AZD2281 (olaparib), DNA damage would accumulate in the cell leading to massive apoptosis. We observed that APR-246 synergistically enhanced the cytotoxic response of olaparib in TP53 mutant non-small cell lung cancer cell lines, resulting in a strong apoptotic response. In the presence of wild type p53 a G2/M cell cycle block was predominantly observed. NOXA expression levels were significantly increased in a TP53 mutant background, and remained unchanged in the wild type cell line. The combined treatment of APR-246 and olaparib induced cell death that was associated with increased ROS production, accumulation of DNA damage and translocation of p53 to the mitochondria. Out data suggest a promising targeted combination strategy in which the response to olaparib is synergistically enhanced by the addition of APR-246, especially in a TP53 mutant background.

Inhibition of thioredoxin reductase by alantolactone prompts oxidative stress-mediated apoptosis of HeLa cells

The mammalian thioredoxin reductase (TrxR) isoenzymes, TrxR1 in cytosol or nucleus, TrxR2 in mitochondria, and TrxR3 in testis, are essential seleno-flavoenzymes with a conserved penultimate selenocysteine (Sec) residue at the C-terminus, and have attracted increasing interests as potential targets for development of cancer chemotherapeutic agents. The sesquiterpene lactone alantolactone (ATL), an active component from the traditional folk medicine Inula helenium, has been documented possessing multiple pharmacological functions, especially the anticancer activity. However, the underlying mechanism has not been well defined. We reported that ATL inhibits both the recombinant TrxR and the enzyme in the cellular environment. The alpha-methylene-gamma-lactone moiety in ATL and the Sec residue in TrxR are critical for targeting TrxR by ATL. By employing our newly developed pull down assay, we demonstrated the remarkable elevation of the oxidized thioredoxin in HeLa cells after ATL treatment. In addition, ATL elicits accumulation of reactive oxygen species, and eventually induces apoptosis of HeLa cells. Importantly, overexpression of the functional TrxR attenuates the cytotoxicity of ATL, while knockdown of the enzyme sensitizes the cells to ATL treatment. Targeting TrxR thus discloses a novel molecular mechanism underlying the cellular action of ATL, and sheds light in considering the usage of ATL as a potential cancer chemotherapeutic agent.

Targeting of Mutant p53 and the Cellular Redox Balance by APR-246 as a Strategy for Efficient Cancer Therapy

TP53 is the most frequently mutated gene in cancer. The p53 protein activates transcription of genes that promote cell cycle arrest or apoptosis, or regulate cell metabolism, and other processes. Missense mutations in TP53 abolish specific DNA binding of p53 and allow evasion of apoptosis and accelerated tumor progression. Mutant p53 often accumulates at high levels in tumor cells. Pharmacological reactivation of mutant p53 has emerged as a promising strategy for improved cancer therapy. Small molecules that restore wild type activity of mutant p53 have been identified using various approaches. One of these molecules, APR-246, is a prodrug that is converted to the Michael acceptor methylene quinuclidinone (MQ) that binds covalently to cysteines in p53, leading to refolding and restoration of wild type p53 function. MQ also targets the cellular redox balance by inhibiting thioredoxin reductase (TrxR1) and depleting glutathione. This dual mechanism of action may account for the striking synergy between APR-246 and platinum compounds. APR-246 is the only mutant p53-targeting compound in clinical development. A phase I/IIa clinical trial in hematological malignancies and prostate cancer showed good safety profile and clinical effects in some patients. APR-246 is currently tested in a phase Ib/II trial in patients with high-grade serous ovarian cancer.

Oxidation of structural cysteine residues in thioredoxin 1 by aromatic arsenicals enhances cancer cell cytotoxicity caused by the inhibition of thioredoxin reductase 1

Thioredoxin systems, composed of thioredoxin reductase (TrxR), thioredoxin (Trx) and NADPH, play important roles in maintaining cellular redox homeostasis and redox signaling. Recently the cytosolic Trx1 system has been shown to be a cellular target of arsenic containing compounds. To elucidate the relationship of the structure of arsenic compounds with their ability of inhibiting TrxR1 and Trx1, and cytotoxicity, we have investigated the reaction of Trx1 system with seven arsenic trithiolates: As(Cys)3, As(GS)3, As(Penicillamine)3, As(Mercaptoethanesulfonate)3, As(Mercaptopurine)3, As(2-mercaptopyridine)3 and As(2-mercaptopyridine N-oxide)3. The cytotoxicity of these arsenicals was consistent with their ability to inhibit TrxR1 in vitro and in cells. Unlike other arsenicals, As(Mercaptopurine)3 which did not show inhibitory effects on TrxR1 had very weak cytotoxicity, indicating that TrxR1 is a reliable drug target for arsenicals. Moreover, the two aromatic compounds As(2-mercaptopyridine)3 and As(2-mercaptopyridine N-oxide)3 showed stronger cytotoxicity than the others. As(2-mercaptopyridine)3 which selectively oxidized two structural cysteines (Cys62 and Cys69) in Trx1 showed mild improvement in cytotoxicity. As(2-mercaptopyridine N-oxide)3 oxidized all the Cys residues in Trx1, exhibiting the strongest cytotoxicity. Oxidation of Trx1 by As(2-mercaptopyridine)3 and As(2-mercaptopyridine N-oxide)3 affected electron transfer from NADPH and TrxR1 to peroxiredoxin 1 (Prx1), which could result in the reactive oxygen species elevation and trigger cell death process. These results suggest that oxidation of structural cysteine residues in Trx1 by aromatic group in TrxR1-targeting drugs may sensitize tumor cells to cell death, providing a novel approach to regulate cellular redox signaling and also a basis for rational design of new anticancer agents.

PRIMA-1(MET) induces death in soft-tissue sarcomas cell independent of p53

BACKGROUND

The aim of this study was to explore the efficacy and define mechanisms of action of PRIMA-1(MET) as a TP53 targeted therapy in soft-tissue sarcoma (STS) cells.

METHODS

We investigated effects of PRIMA-1(MET) on apoptosis, cell cycle, and induction of oxidative stress and autophagy in a panel of 6 STS cell lines with different TP53 status.

RESULTS

Cell viability reduction by PRIMA-1(MET) was significantly observed in 5 out of 6 STS cell lines. We found that PRIMA-1(MET) was capable to induce cell death not only in STS cells harboring mutated TP53 but also in TP53-null STS cells demonstrating that PRIMA-1(MET) can induce cell death independently of TP53 in STS cells. We identified an important role of reactive oxygen species (ROS), involved in PRIMA-1(MET) toxicity in STS cells leading to a caspase-independent cell death. ROS toxicity was associated with autophagy induction or JNK pathway activation which represented potential mechanisms of cell death induced by PRIMA-1(MET) in STS.

CONCLUSIONS

PRIMA-1(MET) anti-tumor activity in STS partly results from off-target effects involving ROS toxicity and do not deserve further development as a TP53-targeted therapy in this setting.

APR-246 potently inhibits tumour growth and overcomes chemoresistance in preclinical models of oesophageal adenocarcinoma

OBJECTIVES

p53 is a critical tumour suppressor and is mutated in 70% of oesophageal adenocarcinomas (OACs), resulting in chemoresistance and poor survival. APR-246 is a first-in-class reactivator of mutant p53 and is currently in clinical trials. In this study, we characterised the activity of APR-246 and its effect on p53 signalling in a large panel of cell line xenograft (CLX) and patient-derived xenograft (PDX) models of OAC.

DESIGN

In vitro response to APR-246 was assessed using clonogenic survival, cell cycle and apoptosis assays. Ectopic expression, gene knockdown and CRISPR/Cas9-mediated knockout studies of mutant p53 were performed to investigate p53-dependent drug effects. p53 signalling was examined using quantitative RT-PCR and western blot. Synergistic interactions between APR-246 and conventional chemotherapies were evaluated in vitro and in vivo using CLX and PDX models.

RESULTS

APR-246 upregulated p53 target genes, inhibited clonogenic survival and induced cell cycle arrest as well as apoptosis in OAC cells harbouring p53 mutations. Sensitivity to APR-246 correlated with cellular levels of mutant p53 protein. Ectopic expression of mutant p53 sensitised p53-null cells to APR-246, while p53 gene knockdown and knockout diminished drug activity. Importantly, APR-246 synergistically enhanced the inhibitory effects of cisplatin and 5-fluorouracil through p53 accumulation. Finally, APR-246 demonstrated potent antitumour activity in CLX and PDX models, and restored chemosensitivity to a cisplatin/5-fluorouracil-resistant xenograft model.

CONCLUSIONS

APR-246 has significant antitumour activity in OAC. Given that APR-246 is safe at therapeutic levels our study strongly suggests that APR-246 can be translated into improving the clinical outcomes for OAC patients.

APR-246 overcomes resistance to cisplatin and doxorubicin in ovarian cancer cells

Two main causes of platinum resistance are mutation in the tumor suppressor gene TP53 and drug-induced increase in intracellular glutathione concentration. Mutations in TP53 occur in about 50% of human tumors. APR-246 (PRIMA-1(MET)) is the first clinical-stage compound that reactivates mutant p53 and induces apoptosis. APR-246 is a prodrug that is converted to the active compound methylene quinuclidinone (MQ), a Michael acceptor that binds to cysteine residues in mutant p53 and restores its wild-type conformation. Here, we show that MQ also binds to cysteine in glutathione, thus decreasing intracellular free glutathione concentration. We also show that treatment with APR-246 completely restores the cisplatin and doxorubicin sensitivity to p53-mutant drug-resistant ovarian cancer cells. We propose that this unique ability of APR-246/MQ to bind to cysteines in both mutant p53 and glutathione has a key role in the resensitization as well as in the outstanding synergistic effects observed with APR-246 in combination with platinum compounds in ovarian cancer cell lines and primary cancer cells. However, MQ binding to cysteines in other targets, for example, thioredoxin reductase, may contribute as well. Strong synergy was also observed with the DNA-damaging drugs doxorubicin and gemcitabine, while additive effects were found with the taxane docetaxel. Our results provide a strong rationale for the ongoing clinical study with APR-246 in combination with platinum-based therapy in patients with p53-mutant recurrent high-grade serous (HGS) ovarian cancer. More than 96% of these patients carry TP53 mutations. Combined treatment with APR-246 and platinum or other DNA-damaging drugs could allow dramatically improved therapy of a wide range of therapy refractory p53 mutant tumors.

APR-246 overcomes resistance to cisplatin and doxorubicin in ovarian cancer cells

Two main causes of platinum resistance are mutation in the tumor suppressor gene TP53 and drug-induced increase in intracellular glutathione concentration. Mutations in TP53 occur in about 50% of human tumors. APR-246 (PRIMA-1(MET)) is the first clinical-stage compound that reactivates mutant p53 and induces apoptosis. APR-246 is a prodrug that is converted to the active compound methylene quinuclidinone (MQ), a Michael acceptor that binds to cysteine residues in mutant p53 and restores its wild-type conformation. Here, we show that MQ also binds to cysteine in glutathione, thus decreasing intracellular free glutathione concentration. We also show that treatment with APR-246 completely restores the cisplatin and doxorubicin sensitivity to p53-mutant drug-resistant ovarian cancer cells. We propose that this unique ability of APR-246/MQ to bind to cysteines in both mutant p53 and glutathione has a key role in the resensitization as well as in the outstanding synergistic effects observed with APR-246 in combination with platinum compounds in ovarian cancer cell lines and primary cancer cells. However, MQ binding to cysteines in other targets, for example, thioredoxin reductase, may contribute as well. Strong synergy was also observed with the DNA-damaging drugs doxorubicin and gemcitabine, while additive effects were found with the taxane docetaxel. Our results provide a strong rationale for the ongoing clinical study with APR-246 in combination with platinum-based therapy in patients with p53-mutant recurrent high-grade serous (HGS) ovarian cancer. More than 96% of these patients carry TP53 mutations. Combined treatment with APR-246 and platinum or other DNA-damaging drugs could allow dramatically improved therapy of a wide range of therapy refractory p53 mutant tumors.

APR-246 overcomes resistance to cisplatin and doxorubicin in ovarian cancer cells

Two main causes of platinum resistance are mutation in the tumor suppressor gene TP53 and drug-induced increase in intracellular glutathione concentration. Mutations in TP53 occur in about 50% of human tumors. APR-246 (PRIMA-1^MET) is the first clinical-stage compound that reactivates mutant p53 and induces apoptosis. APR-246 is a prodrug that is converted to the active compound methylene quinuclidinone (MQ), a Michael acceptor that binds to cysteine residues in mutant p53 and restores its wild-type conformation. Here, we show that MQ also binds to cysteine in glutathione, thus decreasing intracellular free glutathione concentration. We also show that treatment with APR-246 completely restores the cisplatin and doxorubicin sensitivity to p53-mutant drug-resistant ovarian cancer cells. We propose that this unique ability of APR-246/MQ to bind to cysteines in both mutant p53 and glutathione has a key role in the resensitization as well as in the outstanding synergistic effects observed with APR-246 in combination with platinum compounds in ovarian cancer cell lines and primary cancer cells. However, MQ binding to cysteines in other targets, for example, thioredoxin reductase, may contribute as well. Strong synergy was also observed with the DNA-damaging drugs doxorubicin and gemcitabine, while additive effects were found with the taxane docetaxel. Our results provide a strong rationale for the ongoing clinical study with APR-246 in combination with platinum-based therapy in patients with p53-mutant recurrent high-grade serous (HGS) ovarian cancer. More than 96% of these patients carry TP53 mutations. Combined treatment with APR-246 and platinum or other DNA-damaging drugs could allow dramatically improved therapy of a wide range of therapy refractory p53 mutant tumors.

TP53: an oncogene in disguise

The standard classification used to define the various cancer genes confines tumor protein p53 (TP53) to the role of a tumor suppressor gene. However, it is now an indisputable fact that many p53 mutants act as oncogenic proteins. This statement is based on multiple arguments including the mutation signature of the TP53 gene in human cancer, the various gains-of-function (GOFs) of the different p53 mutants and the heterogeneous phenotypes developed by knock-in mouse strains modeling several human TP53 mutations. In this review, we will shatter the classical and traditional image of tumor protein p53 (TP53) as a tumor suppressor gene by emphasizing its multiple oncogenic properties that make it a potential therapeutic target that should not be underestimated. Analysis of the data generated by the various cancer genome projects highlights the high frequency of TP53 mutations and reveals that several p53 hotspot mutants are the most common oncoprotein variants expressed in several types of tumors. The use of Muller's classical definition of mutations based on quantitative and qualitative consequences on the protein product, such as ‘amorph', ‘hypomorph', ‘hypermorph' ‘neomorph' or ‘antimorph', allows a more meaningful assessment of the consequences of cancer gene modifications, their potential clinical significance, and clearly demonstrates that the TP53 gene is an atypical cancer gene.

Novel and emerging targeted-based cancer therapy agents and methods

After several decades of uncovering the cancer features and following the improvement of therapeutic agents, however cancer remains as one of the major reasons of mortality. Chemotherapy is one of the main treatment options and has significantly improved the overall survival of cancer patients, but chemotherapeutic agents are highly toxic for normal cells. Therefore, there is a great unmet medical need to develop new therapeutic principles and agents. Targeted-based cancer therapy (TBCT) agents and methods have revolutionized the cancer treatment efficacy. Monoclonal antibodies (mAbs) and small molecule inhibitors (SMIs) are among the most effective agents of TBCT. These drugs have improved the prognosis and survival of cancer patients; however, the therapeutic resistance has subdued the effects. Several mechanisms lead to drug resistance such as mutations in the drug targets, activation of compensatory pathways, and intrinsic or acquired resistance of cancer stem cells. Therefore, new modalities, improving current generation of inhibitors and mAbs, and optimizing the combinational therapy regimens are necessary to decrease the current obstacles in front of TBCT. Moreover, the success of new TBCT agents such as mAbs, SMIs, and immunomodulatory agents has sparked further therapeutic modalities with novel targets to inhibit. Due to the lack of cumulative information describing different agents and methods of TBCT, this review focuses on the most important agents and methods of TBCT that are currently under investigation.

Battle against cancer: an everlasting saga of p53

Cancer is one of the most life-threatening diseases characterized by uncontrolled growth and spread of malignant cells. The tumor suppressor p53 is the master regulator of tumor cell growth and proliferation. In response to various stress signals, p53 can be activated and transcriptionally induces a myriad of target genes, including both protein-encoding and non-coding genes, controlling cell cycle progression, DNA repair, senescence, apoptosis, autophagy and metabolism of tumor cells. However, around 50% of human cancers harbor mutant p53 and, in the majority of the remaining cancers, p53 is inactivated through multiple mechanisms. Herein, we review the recent progress in understanding the molecular basis of p53 signaling, particularly the newly identified ribosomal stress—p53 pathway, and the development of chemotherapeutics via activating wild-type p53 or restoring mutant p53 functions in cancer. A full understanding of p53 regulation will aid the development of effective cancer treatments.

Anti-oxidative stress response genes: bioinformatic analysis of their expression and relevance in multiple cancers

Cells mount a transcriptional anti-oxidative stress (AOS) response program to scavenge reactive oxygen species (ROS) that arise from chemical, physical, and metabolic challenges. This protective program has been shown to reduce carcinogenesis triggered by chemical and physical insults. However, it is also hijacked by established cancers to thrive and proliferate within the hostile tumor microenvironment and to gain resistance against chemo- and radiotherapies. Therefore, targeting the AOS response proteins that are exploited by cancer cells is an attractive therapeutic strategy. In order to identify the AOS genes that are suspected to support cancer progression and resistance, we analyzed the expression patterns of 285 genes annotated for being involved in oxidative stress in 994 tumors and 353 normal tissues. Thereby we identified a signature of 116 genes that are highly overexpressed in multiple carcinomas while being only minimally expressed in normal tissues. To establish which of these genes are more likely to functionally drive cancer resistance and progression, we further identified those whose overexpression correlates with negative patient outcome in breast and lung carcinoma. Gene-set enrichment, GO, network, and pathway analyses revealed that members of the thioredoxin and glutathione pathways are prominent components of this oncogenic signature and that activation of these pathways is common feature of many cancer entities. Interestingly, a large fraction of these AOS genes are downstream targets of the transcription factors NRF2, NF-kappaB and FOXM1, and relay on NADPH for their enzymatic activities highlighting promising drug targets. We discuss these findings and propose therapeutic strategies that may be applied to overcome cancer resistance.

TAp73 promotes anti-senescence-anabolism not proliferation

TAp73, a member of the p53 family, has been traditionally considered a tumor suppressor gene, but a recent report has claimed that it can promote cellular proliferation. This assumption is based on biochemical evidence of activation of anabolic metabolism, with enhanced pentose phosphate shunt (PPP) and nucleotide biosynthesis. Here, while we confirm that TAp73 expression enhances anabolism, we also substantiate its role in inhibiting proliferation and promoting cell death. Hence, we would like to propose an alternative interpretation of the accumulating data linking p73 to cellular metabolism: we suggest that TAp73 promotes anabolism to counteract cellular senescence rather than to support proliferation.

PRIMA-1Met induces myeloma cell death independent of p53 by impairing the GSH/ROS balance

The aim of this study was to assess the efficiency of p53 reactivation and induction of massive apoptosis (PRIMA-1(Met)) in inducing myeloma cell death, using 27 human myeloma cell lines (HMCLs) and 23 primary samples. Measuring the lethal dose (LD50) of HMCLs revealed that HMCLs displayed heterogeneous sensitivity, with an LD50 ranging from 4 μM to more than 200 μM. The sensitivity of HMCLs did not correlate with myeloma genomic heterogeneity or TP53 status, and PRIMA-1(Met) did not induce or increase expression of the p53 target genes CDKN1A or TNFRSF10B/DR5. However, PRIMA-1(Met) increased expression of NOXA in a p53-independent manner, and NOXA silencing decreased PRIMA1(Met)-induced cell death. PRIMA-1(Met) depleted glutathione (GSH) content and induced reactive oxygen species production. The expression of GSH synthetase correlated with PRIMA-1(Met) LD50 values, and we showed that a GSH decrease mediated by GSH synthetase silencing or by and L-buthionine sulphoximine, an irreversible inhibitor of γ-glutamylcysteine synthetase, increased PRIMA-1(Met)-induced cell death and overcame PRIMA-1(Met) resistance. PRIMA-1(Met) (10 μM) induced cell death in 65% of primary cells independent of the presence of del17p; did not increase DR5 expression, arguing against an activation of p53 pathway; and synergized with L-buthionine sulphoximine in all samples. Finally, we showed in mouse TP53(neg) JJN3-xenograft model that PRIMA-1(Met) inhibited myeloma growth and synergized with L-buthionine sulphoximine in vivo.