mk-1775 and Lung-Neoplasms

Genomic profiling of tumours in patients in clinical trials enables rapid testing of multiple hypotheses to confirm which genomic events determine likely responder groups for targeted agents. A key challenge of this new capability is defining which specific genomic events should be classified as 'actionable' (that is, potentially responsive to a targeted therapy), especially when looking for early indications of patient subgroups likely to be responsive to new drugs. This Opinion article discusses some of the different approaches being taken in early clinical development to define actionable mutations, and describes our strategy to address this challenge in early-stage exploratory clinical trials.

Topics: Carcinoma, Non-Small-Cell Lung; Humans; Lung Neoplasms; Mutation; Pyrazoles; Pyrimidines; Pyrimidinones; Tumor Suppressor Protein p53

Adavosertib (AZD1775) is a first-in-class, selective, small-molecule inhibitor of Wee1.. The safety, tolerability, pharmacokinetics, and efficacy of adavosertib monotherapy were evaluated in patients with various solid-tumor types and molecular profiles.. Eligible patients had the following: confirmed diagnosis of ovarian cancer (OC), triple-negative breast cancer (TNBC), or small-cell lung cancer (SCLC); previous treatment for metastatic/recurrent disease; and measurable disease. Patients were grouped into six matched cohorts based on tumor type and presence/absence of biomarkers and received oral adavosertib 175 mg twice a day on days 1-3 and 8-10 of a 21-day treatment cycle.. Eighty patients received treatment in the expansion phase; median total treatment duration was 2.4 months. The most common treatment-related adverse events (AEs) were diarrhea (56.3%), nausea (42.5%), fatigue (36.3%), vomiting (18.8%), and decreased appetite (12.5%). Treatment-related grade ≥ 3 AEs and serious AEs were reported in 32.5% and 10.0% of patients, respectively. AEs led to dose interruptions in 22.5%, reductions in 11.3%, and discontinuations in 16.3% of patients. One patient died following serious AEs of deep vein thrombosis (treatment related) and respiratory failure (not treatment related). Objective response rate, disease control rate, and progression-free survival were as follows: 6.3%, 68.8%, 4.5 months (OC BRCA wild type); 3.3%, 76.7%, 3.9 months (OC BRCA mutation); 0%, 69.2%, 3.1 months (TNBC biomarker [CCNE1/MYC/MYCL1/MYCN] non-amplified [NA]); 0%, 50%, 2 months (TNBC biomarker amplified); 8.3%, 33.3%, 1.3 months (SCLC biomarker NA); and 0%, 33.3%, 1.2 months (SCLC biomarker amplified).. Adavosertib monotherapy was tolerated and demonstrated some antitumor activity in patients with advanced solid tumors.. ClinicalTrials.gov identifier NCT02482311; registered June 2015.

Topics: Female; Humans; Lung Neoplasms; Ovarian Neoplasms; Pyrazoles; Pyrimidinones; Small Cell Lung Carcinoma; Triple Negative Breast Neoplasms

Bromodomain and extraterminal domain (BET) inhibitors are broadly active against distinct types of cancer, including nonsmall cell lung cancer (NSCLC). Previous studies have addressed the effect of BET-inhibiting drugs on the expression of oncogenes such as c-Myc, but DNA damage repair pathways have also been reported to be involved in the efficacy of these drugs. AZD1775, an inhibitor of the G2-M cell cycle checkpoint kinase WEE1, induces DNA damage by promoting premature mitotic entry. Thus, we hypothesized that BET inhibition would increase AZD1775-induced cytotoxicity by impairing DNA damage repair. Here, we demonstrate that combined inhibition of BET and WEE1 synergistically suppresses NSCLC growth both in vitro and in vivo. Two BET inhibitors, JQ1 and AZD5153, increased and prolonged AZD1775-induced DNA double-strand breaks (DSBs) and concomitantly repressed genes related to nonhomologous end joining (NHEJ), including XRCC4 and SHLD1. Furthermore, pharmaceutical inhibition of BET or knockdown of the BET protein BRD4 markedly diminished NHEJ activity, and the BET-inhibitor treatment also repressed myelin transcription factor 1 (MYT1) expression and promoted mitotic entry with subsequent mitotic catastrophe when combined with WEE1 inhibition. Our findings reveal that BET proteins, predominantly BRD4, play an essential role in DSB repair through the NHEJ pathway, and further suggest that combined inhibition of BET and WEE1 could serve as a novel therapeutic strategy for NSCLC.

Topics: Animals; Antineoplastic Combined Chemotherapy Protocols; Azepines; Carcinoma, Non-Small-Cell Lung; Cell Cycle Proteins; Cell Line, Tumor; DNA Breaks, Double-Stranded; DNA End-Joining Repair; DNA-Binding Proteins; Drug Synergism; Female; Gene Knockdown Techniques; Heterocyclic Compounds, 2-Ring; Humans; Lung Neoplasms; Mice; Piperazines; Protein-Tyrosine Kinases; Pyrazoles; Pyridazines; Pyrimidinones; Transcription Factors; Triazoles; Xenograft Model Antitumor Assays

Topics: Animals; Carcinoma, Non-Small-Cell Lung; CCAAT-Enhancer-Binding Protein-beta; CDC2 Protein Kinase; Cell Cycle Proteins; Cell Division; Cell Line, Tumor; Cell Proliferation; Female; G2 Phase; Histone Deacetylase 2; Humans; Lung Neoplasms; Male; Mice, Nude; Middle Aged; Models, Biological; Nuclear Proteins; Phosphorylation; Protein Binding; Protein-Tyrosine Kinases; Pyrazoles; Pyrimidinones; Transcription, Genetic

KRAS mutations in non-small cell lung cancer (NSCLC) cause increased levels of DNA damage and replication stress, suggesting that inhibition of the DNA damage response (DDR) is a promising strategy for radiosensitization of NSCLC. This study investigates the ability of a WEE1 inhibitor (AZD1775) and a PARP inhibitor (olaparib) to radiosensitize KRAS-mutant NSCLC cells and tumors. In addition to inhibiting the DDR, these small-molecule inhibitors of WEE1 and PARP induce DNA replication stress via nucleotide exhaustion and PARP trapping, respectively. As monotherapy, AZD1775 or olaparib alone modestly radiosensitized a panel of KRAS-mutant NSCLC lines. The combination of agents, however, significantly increased radiosensitization. Furthermore, AZD1775-mediated radiosensitization was rescued by nucleotide repletion, suggesting a mechanism involving AZD1775-mediated replication stress. In contrast, radiosensitization by the combination of AZD1775 and olaparib was not rescued by nucleosides. Whereas both veliparib, a PARP inhibitor that does not efficiently trap PARP1 to chromatin, and PARP1 depletion radiosensitized NSCLC cells as effectively as olaparib, which does efficiently trap PARP, only olaparib potentiated AZD1775-mediated radiosensitization. Taken together, these mechanistic data demonstrate that although nucleotide depletion is sufficient for radiosensitization by WEE1 inhibition alone, and inhibition of PARP catalytic activity is sufficient for radiosensitization by olaparib alone, PARP1 trapping is required for enhanced radiosensitization by the combination of WEE1 and PARP inhibitors.

Topics: Animals; Carcinoma, Non-Small-Cell Lung; Cell Line, Tumor; Cell Proliferation; Cell Survival; DNA Replication; Drug Synergism; Humans; Lung Neoplasms; Mice; Mutation; Phthalazines; Piperazines; Poly (ADP-Ribose) Polymerase-1; Proto-Oncogene Proteins p21(ras); Pyrazoles; Pyrimidines; Pyrimidinones; Radiation-Sensitizing Agents; Xenograft Model Antitumor Assays

Non-Small-Cell Lung Cancer (NSCLC) is a poorly chemosensitive tumor and targeted therapies are only used for about 15% of patients where a specific driving and druggable lesion is observed (EGFR, ALK, ROS). KRAS is one of the most frequently mutated genes in NSCLC and patients harboring these mutations do not benefit from specific treatments. Sorafenib, a multi-target tyrosine kinase inhibitor, was proposed as a potentially active drug in KRAS-mutated NSCLC patients, but clinical trials results were not conclusive. Here we show that the NSCLC cells' response to sorafenib depends on the type of KRAS mutation. KRAS G12V cells respond less to sorafenib than the wild-type counterpart, in vitro and in vivo. To overcome this resistance, we used high-throughput screening with a siRNA library directed against 719 human kinases, and Wee1 was selected as a sorafenib response modulator. Inhibition of Wee1 by its specific inhibitor MK1775 in combination with sorafenib restored the KRAS mutated cells' response to the multi-target tyrosine kinase inhibitor. This combination of the Wee1 inhibitor with sorafenib, if confirmed in models with different genetic backgrounds, might be worth investigating further as a new strategy for KRAS mutated NSCLC.

Topics: Carcinoma, Non-Small-Cell Lung; Cell Cycle Proteins; Cell Line, Tumor; Humans; Lung Neoplasms; Mutation; Niacinamide; Nuclear Proteins; Phenylurea Compounds; Protein Kinase Inhibitors; Protein-Tyrosine Kinases; Proto-Oncogene Proteins p21(ras); Pyrazoles; Pyrimidines; Pyrimidinones; Sorafenib

Kinase inhibitors are important cancer therapeutics. Polypharmacology is commonly observed, requiring thorough target deconvolution to understand drug mechanism of action. Using chemical proteomics, we analyzed the target spectrum of 243 clinically evaluated kinase drugs. The data revealed previously unknown targets for established drugs, offered a perspective on the "druggable" kinome, highlighted (non)kinase off-targets, and suggested potential therapeutic applications. Integration of phosphoproteomic data refined drug-affected pathways, identified response markers, and strengthened rationale for combination treatments. We exemplify translational value by discovering SIK2 (salt-inducible kinase 2) inhibitors that modulate cytokine production in primary cells, by identifying drugs against the lung cancer survival marker MELK (maternal embryonic leucine zipper kinase), and by repurposing cabozantinib to treat FLT3-ITD-positive acute myeloid leukemia. This resource, available via the ProteomicsDB database, should facilitate basic, clinical, and drug discovery research and aid clinical decision-making.

Topics: Animals; Antineoplastic Agents; Cell Line, Tumor; Cytokines; Drug Discovery; fms-Like Tyrosine Kinase 3; Humans; Leukemia, Myeloid, Acute; Lung Neoplasms; Mice; Molecular Targeted Therapy; Protein Kinase Inhibitors; Protein Serine-Threonine Kinases; Proteomics; Xenograft Model Antitumor Assays

Inhibition of the WEE1 tyrosine kinase enhances anticancer chemotherapy efficacy. Accordingly, the WEE1 inhibitor AZD1775 (previously MK-1775) is currently under evaluation in clinical trials for cancer in combination with chemotherapy. AZD1775 has been reported to display high selectivity and is therefore used in many studies as a probe to interrogate WEE1 biology. However, AZD1775 also exhibits anticancer activity as a single agent although the underlying mechanism is not fully understood. Using a chemical proteomics approach, we here describe a proteome-wide survey of AZD1775 targets in lung cancer cells and identify several previously unknown targets in addition to WEE1. In particular, we observed polo-like kinase 1 (PLK1) as a new target of AZD1775. Importantly, in vitro kinase assays showed PLK1 and WEE1 to be inhibited by AZD1775 with similar potency. Subsequent loss-of-function experiments using RNAi for WEE1 and PLK1 suggested that targeting PLK1 enhances the pro-apoptotic and antiproliferative effects observed with WEE1 knockdown. Combination of RNAi with AZD1775 treatment suggested WEE1 and PLK1 to be the most relevant targets for mediating AZD1775's anticancer effects. Furthermore, disruption of WEE1 by CRISPR-Cas9 sensitized H322 lung cancer cells to AZD1775 to a similar extent as the potent PLK1 inhibitor BI-2536 suggesting a complex crosstalk between PLK1 and WEE1. In summary, we show that AZD1775 is a potent dual WEE1 and PLK1 inhibitor, which limits its use as a specific molecular probe for WEE1. However, PLK1 inhibition makes important contributions to the single agent mechanism of action of AZD1775 and enhances its anticancer effects.

Topics: Antineoplastic Agents; Apoptosis; Cell Cycle Proteins; Cell Line, Tumor; Cell Proliferation; Cell Survival; Dose-Response Relationship, Drug; Drug Delivery Systems; Enzyme Activation; Humans; Immunoblotting; Lung Neoplasms; Molecular Structure; Nuclear Proteins; Polo-Like Kinase 1; Protein Serine-Threonine Kinases; Protein-Tyrosine Kinases; Proto-Oncogene Proteins; Pyrazoles; Pyrimidines; Pyrimidinones

Lung cancer treatment remains a challenge for clinical practice and new therapeutic approaches are urgently needed. Loss of functional WEE1 kinase causes DNA replication stress, DNA damage and unscheduled mitotic entry due to elevated CDK activity. The selective WEE1 inhibitor MK-1775 synergize with DNA-damaging agent to inhibit cancer cell growth. Here we report that inhibition of Sirt1 deacetylase through small interfering RNA or selective inhibitor Ex527 greatly enhances MK-1775-induced growth inhibition and apoptosis in human lung cancer cells. We further demonstrate that Sirt1 interacts and deacetylates homologous recombination (HR) repair machinery proteins, including NBS1 and Rad51. Inhibition of Sirt1 impairs HR repair activity, which causes unrepairable damage when combining MK-1775 and Ex527. Meanwhile, combination of MK-1775 and Ex527 induces cooperative antitumor activity in lung cancer xenograft model in vivo. Thus, our study provides a novel therapeutic strategy to optimize MK-1775 treatment efficiency in lung cancers.

Topics: Animals; Apoptosis; Carbazoles; Cell Cycle Proteins; Cells, Cultured; DNA Damage; Female; Humans; Lung Neoplasms; Mice; Mice, Inbred BALB C; Nuclear Proteins; Protein-Tyrosine Kinases; Pyrazoles; Pyrimidines; Pyrimidinones; Sirtuin 1

The DNA damage response (DDR) involves a complex network of signaling events mediated by modular protein domains such as the BRCA1 C-terminal (BRCT) domain. Thus, proteins that interact with BRCT domains and are a part of the DDR constitute potential targets for sensitization to DNA-damaging chemotherapy agents. We performed a pharmacologic screen to evaluate 17 kinases, identified in a BRCT-mediated interaction network as targets to enhance platinum-based chemotherapy in lung cancer. Inhibition of mitotic kinase WEE1 was found to have the most effective response in combination with platinum compounds in lung cancer cell lines. In the BRCT-mediated interaction network, WEE1 was found in complex with PAXIP1, a protein containing six BRCT domains involved in transcription and in the cellular response to DNA damage. We show that PAXIP1 BRCT domains regulate WEE1-mediated phosphorylation of CDK1. Furthermore, ectopic expression of PAXIP1 promotes enhanced caspase-3-mediated apoptosis in cells treated with WEE1 inhibitor AZD1775 (formerly, MK-1775) and cisplatin compared with cells treated with AZD1775 alone. Cell lines and patient-derived xenograft models expressing both PAXIP1 and WEE1 exhibited synergistic effects of AZD1775 and cisplatin. In summary, PAXIP1 is involved in sensitizing lung cancer cells to the WEE1 inhibitor AZD1775 in combination with platinum-based treatment. We propose that WEE1 and PAXIP1 levels may be used as mechanism-based biomarkers of response when WEE1 inhibitor AZD1775 is combined with DNA-damaging agents. Mol Cancer Ther; 15(7); 1669-81. ©2016 AACR.

Topics: Antineoplastic Agents; Apoptosis; Carrier Proteins; CDC2 Protein Kinase; Cell Cycle; Cell Cycle Proteins; Cell Line, Tumor; Cluster Analysis; Cyclin-Dependent Kinases; DNA-Binding Proteins; Drug Discovery; Drug Resistance, Neoplasm; Drug Screening Assays, Antitumor; Humans; Lung Neoplasms; Mitosis; Nuclear Proteins; Phosphorylation; Platinum; Protein Binding; Protein Kinase Inhibitors; Protein-Tyrosine Kinases; Pyrazoles; Pyrimidines; Pyrimidinones

The potent inhibitor of the cell cycle checkpoint regulatory factor Wee-1, MK-1775, has been reported to enhance non-small cell lung cancer (NSCLC) cell sensitivity to photon radiation by abrogating radiation-induced G2 arrest. However, little is known about the effects of this sensitizer after exposure to carbon (C)-ion radiation. The purpose of this study was therefore to investigate the effects of C ions in combination with MK-1775 on the killing of NSCLC cells. Human NSCLC H1299 cells were exposed to X rays or C ions (290 MeV/n, 50 keV/μm at the center of a 6 cm spread-out Bragg peak) in the presence of MK-1775. The cell cycle was analyzed using flow cytometry and Western blotting. Radiosensitivity was determined using clonogenic survival assays. The mechanisms underlying MK-1775 radiosensitization were studied by observing H2AX phosphorylation and mitotic catastrophe. G2 checkpoint arrest was enhanced 2.3-fold by C-ion exposure compared with X-ray exposure. Radiation-induced G2 checkpoint arrest was abrogated by MK-1775. Exposure to radiation resulted in a significant reduction in the mitotic ratio and increased phosphorylation of cyclin-dependent kinase 1 (Cdk1), the primary downstream mediator of Wee-1-induced G2 arrest. The Wee-1 inhibitor, MK-1775 restored the mitotic ratio and suppressed Cdk1 phosphorylation. In addition, MK-1775 increased H1299 cell sensitivity to C ions and X rays independent of TP53 status. MK-1775 also significantly increased H2AX phosphorylation and mitotic catastrophe in irradiated cells. These results suggest that the G2 checkpoint inhibitor MK-1775 can enhance the sensitivity of human NSCLC cells to C ions as well as X rays.

Topics: Carbon; Cell Cycle Proteins; Cell Line, Tumor; Dose-Response Relationship, Drug; G2 Phase Cell Cycle Checkpoints; Heavy Ion Radiotherapy; Humans; Lung Neoplasms; Nuclear Proteins; Protein-Tyrosine Kinases; Pyrazoles; Pyrimidines; Pyrimidinones; Radiation-Sensitizing Agents; Treatment Outcome

Malignant mesothelioma (MM) is a very aggressive asbestos-related neoplasm of the serous membranes, whose incidence is increasing worldwide. Although the introduction of new drug combinations, such as cisplatin plus pemetrexed/gemcitabine, has determined an improvement in the patient quality of life, MM remains a universally fatal disease. The observation that key G 1/S checkpoint regulators are often functionally inactivated in MM prompted us to test whether the use of G 2/M checkpoint inhibitors, able to sensitize G 1/S checkpoint-defective cancer cells to DNA-damaging agents, could be successful in MM. We treated six MM cell lines, representative of different histotypes (epithelioid, biphasic, and sarcomatoid), with cisplatin in combination with MK-1775, an inhibitor of the G 2/M checkpoint kinase WEE1. We observed that MK-1775 enhanced the cisplatin cytotoxic effect in all MM cell lines, except the sarcomatoid cell line, which is representative of the most aggressive histotype. As expected, the enhancement in cisplatin toxicity was accompanied by a decrease in the inactive phosphorylated form of cyclin-dependent kinase 1 (CDK1), a key substrate of WEE1, which is indicative of G 2/M checkpoint inactivation. Consistently, we also observed a decrease in G 2/M accumulation and an increase in mitotic entry of DNA-damaged cells and apoptosis, probably due to the loss of the cell ability to arrest cell cycle in response to DNA damage, irrespectively of p53 mutational status. Notably, this treatment did not increase cisplatin cytotoxicity on normal cells, thus suggesting a possible use of MK-1775 in combination with cisplatin for a safe and efficient treatment of epithelioid and biphasic MM.

Topics: Antineoplastic Agents; Apoptosis; Cell Cycle Proteins; Cell Line, Tumor; Cisplatin; Drug Synergism; G2 Phase Cell Cycle Checkpoints; Humans; Lung Neoplasms; Mesothelioma; Mesothelioma, Malignant; Nuclear Proteins; Protein-Tyrosine Kinases; Pyrazoles; Pyrimidines; Pyrimidinones

It has been known for many years that manipulation of cell cycle checkpoint function represents one approach by which the toxicity of chemotherapy and of ionizing radiation can be increased in tumor cells. (1)(-) (3) In particular, abrogation of the G 2/M checkpoint has been shown to enhance the lethality of a wide range of toxic stresses. (1)(-) (3) Inhibition of the G 2/M checkpoint after chemotherapy/irradiation would result in tumor cells entering mitosis with damaged DNA, which would in turn result in loss of clonogenic survival (i.e., a lethal mitosis).

Topics: Antineoplastic Agents; Cell Cycle Proteins; Cisplatin; G2 Phase Cell Cycle Checkpoints; Humans; Lung Neoplasms; Mesothelioma; Mesothelioma, Malignant; Nuclear Proteins; Protein-Tyrosine Kinases; Pyrazoles; Pyrimidines; Pyrimidinones

The ATR-CHK1-WEE1 kinase cascade's functions in the DNA damage checkpoints are well established. Moreover, its roles in the unperturbed cell cycle are also increasingly being recognized. In this connection, a number of small-molecule inhibitors of ATR, CHK1, and WEE1 are being evaluated in clinical trials. Understanding precisely how cells respond to different concentrations of inhibitors is therefore of paramount importance and has broad clinical implications. Here we present evidence that in the absence of DNA damage, pharmacological inactivation of ATR was less effective in inducing mitotic catastrophe than inhibition of WEE1 and CHK1. Small-molecule inhibitors of CHK1 (AZD7762) or WEE1 (MK-1775) induced mitotic catastrophe, as characterized by dephosphorylation of CDK1(Tyr15), phosphorylation of histone H39(Ser10), and apoptosis. Unexpectedly, partial inhibition of WEE1 and CHK1 had the opposite effect of accelerating the cell cycle without inducing apoptosis, thereby increasing the overall cell proliferation. This was also corroborated by the finding that cell proliferation was enhanced by kinase-inactive versions of WEE1. We demonstrated that these potential limitations of the inhibitors could be overcome by targeting more than one components of the ATR-CHK1-WEE1 simultaneously. These observations reveal insights into the complex responses to pharmacological inactivation of the ATR-CHK1-WEE1 axis.

Topics: Apoptosis; Ataxia Telangiectasia Mutated Proteins; Blotting, Western; Carcinoma, Non-Small-Cell Lung; Cell Cycle; Cell Cycle Proteins; Cell Proliferation; Checkpoint Kinase 1; Flow Cytometry; Humans; Immunoenzyme Techniques; Lung Neoplasms; Mitosis; Nuclear Proteins; Protein Kinases; Protein-Tyrosine Kinases; Pyrazoles; Pyrimidines; Pyrimidinones; Thiophenes; Tumor Cells, Cultured; Urea

Radiotherapy is commonly used to treat a variety of solid tumors. However, improvements in the therapeutic ratio for several disease sites are sorely needed, leading us to assess molecularly targeted therapeutics as radiosensitizers. The aim of this study was to assess the wee1 kinase inhibitor, MK-1775, for its ability to radiosensitize human tumor cells.. Human tumor cells derived from lung, breast, and prostate cancers were tested for radiosensitization by MK-1775 using clonogenic survival assays. Both p53 wild-type and p53-defective lines were included. The ability of MK-1775 to abrogate the radiation-induced G₂ block, thereby allowing cells harboring DNA lesions to prematurely progress into mitosis, was determined using flow cytometry and detection of γ-H2AX foci. The in vivo efficacy of the combination of MK-1775 and radiation was assessed by tumor growth delay experiments using a human lung cancer cell line growing as a xenograft tumor in nude mice.. Clonogenic survival analyses indicated that nanomolar concentrations of MK-1775 radiosensitized p53-defective human lung, breast, and prostate cancer cells but not similar lines with wild-type p53. Consistent with its ability to radiosensitize, MK-1775 abrogated the radiation-induced G₂ block in p53-defective cells but not in p53 wild-type lines. MK-1775 also significantly enhanced the antitumor efficacy of radiation in vivo as shown in tumor growth delay studies, again for p53-defective tumors.. These results indicate that p53-defective human tumor cells are significantly radiosensitized by the potent and selective wee1 kinase inhibitor, MK-1775, in both the in vitro and in vivo settings. Taken together, our findings strongly support the clinical evaluation of MK-1775 in combination with radiation.

Topics: Animals; Antineoplastic Agents; Breast Neoplasms; Cell Cycle Proteins; Cell Line, Tumor; Combined Modality Therapy; Female; G2 Phase Cell Cycle Checkpoints; Humans; Lung Neoplasms; Male; Mice; Mice, Nude; Neoplasms; Nuclear Proteins; Prostatic Neoplasms; Protein Kinase Inhibitors; Protein-Tyrosine Kinases; Pyrazoles; Pyrimidines; Pyrimidinones; Radiation-Sensitizing Agents; Transplantation, Heterologous; Tumor Suppressor Protein p53; Xenograft Model Antitumor Assays