The causality dilemma between dysbiosis and cancer has given rise to numerous studies both exploring the mechanisms behind cancer progression and the associative shifts in the microbiota upon carcinogenesis. Aside from the hallmark study of Dr. Barry Marshall in establishing the true causal relationship between Helicobacter pylori and gastric adenocarcinoma, studies have only been successful in adding associative links of carcinogenesis mediated by bacteria to the literature. The current field is limited in its ability to establish causative relationships, and further work is needed to construct a reference community whose physiological responses reflect global community responses. In this thesis, the organism Lactobacillus acidophilus was selected as a pilot strain for the development of a novel framework to establish the fitness and physiological changes that occur when bacteria engage the human epithelial environment. The pilot strain was revived from the American Type Culture Collection (ATCC), verified through 16S rRNA Sanger sequencing, and grown in its conventional culture medium and human tissue culture medium to establish baseline growth rates and gauge its physiological responses to an in vitro tumor microenvironment. A set of standard conditions was proposed for growth under human tissue culture conditions. Finally, a metabolic study and spot plate assay were performed to elucidate the anabolic deficits and viability of this strain in human tissue culture medium, respectively. This research was performed to better understand the environmental and metabolic requirements for this pilot strain to inhabit the human epithelial environment, and to establish a workflow that will set the foundation for an appropriate clinical study to demonstrate the causative relationship between dysbiosis and carcinogenesis.

Cancer is the second most common cause of death in the world. One of the objectives of this thesis is to biologically evaluate a series of anti-cancer polymeric aromatic/heterocyclic bis-sulfonamides and pyridinium sulfonamides which were synthesized from three established aminosulfonamide carbonic anhydrase (CA, EC 4.2.1.1) inhibitor pharmacophores. Testing of these novel inhibitors and their precursors against a panel of membrane-bound CA isoforms, including tumor-overexpressed CA IX and XII and cytosolic isozymes, identified nanomolar-potent inhibitors against both classes and several compounds with medium isoform selectivity. In the case of pyridinium sulfonamides we used complexes of the inhibitors with cyclodextrins or sulfocalixarene to enhance aqueous solubility for biological testing. The ability of CA inhibitors to kill tumor cells overexpressing CA IX and XII was tested under normoxic and hypoxic conditions, using 2D and 3D in vitro cellular models. The study identified a nanomolar potent PEGylated bis-sulfonamide CA inhibitor (25), as well as cyclodextrin and sulfocalixarenes complexes, which were able to significantly reduce the viability of colon HT-29, breast MDA-MB231, and ovarian SKOV-3 cancer cell lines, thus revealing the potential of polymer conjugates in CA inhibition and cancer treatment. As a different disease state yet still a concern, cognitive dysfunction markedly impacts patients with a host of psychiatric conditions including attention deficit hyperactivity disorder, autism spectrum disorder, drug addiction, schizophrenia, depression, bipolar disorder, obsessive-compulsive disorder, and of course, Parkinson’s and Alzheimer’s diseases and other types of dementia. Another objective of this thesis was to profile several series of bis-imidazoles for physicochemical, in-vitro and in-vivo properties as potential memory and learning enhancers (nootropics). Biological testing on eight isozymes of carbonic anhydrase (CA) present in the human brain revealed compounds with nanomolar potency against at least one membrane bound, cytosolic or mitochondrial CA isozymes, combined with good physicochemical properties. We also identified lead compounds with the ability to rescue experimental animals from drug-induced memory deficits, using an optimized Novel Object Recognition Task (NORT) procedure. / Pharmaceutical Sciences

<p dir="ltr">Protein tyrosine phosphorylation is a key post-translational modification that drives numerous cell signaling pathways governing cell proliferation, differentiation, and transcriptional activation. Protein tyrosine kinases (PTKs) and protein tyrosine phosphatases (PTPs) coordinate the protein tyrosine phosphorylation levels while dysregulated PTKs or PTPs activity results in aberrant protein tyrosine phosphorylation levels and cause multiple human diseases including cancer, diabetes, and autoimmune diseases. Targeting PTKs using small molecule inhibitors or antibodies achieved many successes for various indications. For example, targeting epidermal growth factor receptor for cancer therapy and targeting Janus kinase 2 for autoimmune diseases. Meanwhile, targeting PTPs as therapeutic approaches remains underexplored due to the limited understanding of PTP biology and challenging inhibitor development.</p><p><br></p><p dir="ltr">So far, many substrates and pathological mechanisms of PTPs remain elusive. As an example, although it is well recognized that Phosphatases of Regenerating Liver (PRL) family members PRL1/2/3 are overexpressed in the majority of cancer types and are frequently associated with poor clinical outcomes, the pathological mechanism of PRLs is unclear due to the limited understanding of their substrates. In the presented study, I focused on understanding the oncogenic mechanisms of PRL2 phosphatase and the therapeutic potential of targeting PRL2. I developed the first breast-specific PRL2 deletion mouse model to understand the role of PRL2 in estrogen receptor-positive breast tumorigenesis driven by the aberrant PI3K/AKT signaling, which represents over 30% of the human breast cancer population. I found PRL2 deletion drastically extended the median tumor-free survival of mice harboring PI3K gain-of-function mutant from 377 days to 605 days while such extension was invalidated in the absence of PTEN, a major tumor suppressor and one of the substrates of PRL2.</p><p><br></p><p dir="ltr">PTPs are challenging targets for inhibitor development due to the highly conserved and positively charged active site. Most of the identified PTP inhibitors lack the selectivity as a chemical probe for interrogating the PTP biology and are negatively charged which limits their bioavailability as a therapeutic approach. To overcome these defects, we utilized the proteolysis targeting chimera (PROTACs) technique to generate bifunctional small molecules that recruit the protein of interest to an E3 ligase for protein ubiquitination and proteasome degradation. Compared with the traditional occupancy-based inhibitors, PROTACs have improved efficacy and selectivity due to the catalytic degradation turnover and the necessity of the formation of the target-PROTAC-E3 complex. We developed the first-in-class PTP1B/TC-PTP dual degrader named DU-14 and TC-PTP selective degrader named TP1L for cancer immunotherapy. Protein tyrosine phosphatase 1B (PTP1B) and T-cell protein tyrosine phosphatase (TC-PTP) play non-redundant negative regulatory roles in T-cell activation and tumor antigen presentation. Previous studies have shown that the deletion of these two PTPs elicits potent anti-tumor immunity in vivo. I have shown that DU-14 and TP1L efficiently degrade their corresponding target with outstanding selectivity and elevate the cytokine-mediated phosphorylation of their substrates. As a result, I have shown that DU-14 and TP1L elicit potent anti-tumor immunity using co-culture or in vivo tumor models.</p><p><br></p><p dir="ltr">I also discovered an unexpected but beneficial off-target effect of SHP2 allosteric inhibitors under clinical trial and investigated its therapeutic implications for aberrant RAS-driven cancers. Aberrant activation of RAS-MAPK signaling is common in cancer, and efforts to inhibit pathway components have yielded drugs with promising clinical activities. As a central node essential for receptor tyrosine kinase-mediated RAS activation, SHP2 has emerged as an attractive cancer target. Consequently, many SHP2 allosteric inhibitors are now in clinical testing. I discovered a previously unrecognized off-target effect associated with SHP2 allosteric inhibitors. I showed that off-target autophagy inhibition by SHP2 allosteric inhibitors contributes to their anti-tumor activity. Finally, I exemplified a new therapeutic framework that harnesses both the on- and off-target activities of SHP2 allosteric inhibitors for improved treatment of mutant RAS-driven and drug-resistant malignancies such as pancreatic and colorectal cancers.</p><p><br></p><p dir="ltr">In summary, these studies facilitate the understanding of PTP disease biology and provide examples of successful strategies in developing small molecule PTP inhibitors for cancer therapy.</p>

Proteasome inhibitors bortezomib and carfilzomib are FDA-approved anticancer agents that have contributed to significant improvements in treatment outcomes. However, the eventual onset of acquired resistance continues to limit their clinical utility, yet a clear consensus regarding the underlying mechanisms has not been reached. Bortezomib and carfilzomib are known to target both the constitutive proteasome and the immunoproteasome, two conventional proteasome subtypes comprising distinctive sets of catalytic subunits. While it has become increasingly evident that additional, ‘intermediate’ proteasome subtypes, which harbor non-standard mixtures of constitutive proteasome and immunoproteasome catalytic subunits, represent a considerable proportion of the proteasome population in many cell types, less is known regarding their contribution to cellular responses to proteasome inhibitors. Importantly, previous studies in murine models have shown that individual proteasome subtypes differ in sensitivity to specific proteasome inhibitors. Furthermore, research efforts in our laboratory and others have revealed that proteasome catalytic subunit expression levels and activity profiles are altered when human cancer cells acquire resistance to proteasome inhibitors. We therefore hypothesized that changes in the relative abundances of individual proteasome subtypes contribute to the acquired resistance of cancer cells to bortezomib and carfilzomib. A major obstacle in testing our hypothesis was a lack of chemical probes suitable for use in identifying distinct proteasome subtypes. We addressed this by developing a series of bifunctional proteasome probes capable of crosslinking specific pairs of catalytic subunits colocalized within individual proteasome complexes and compatible with immunoblotting-based detection of the crosslinked subunit pairs. We confirmed the utility of these probes in discerning the identities of individual proteasome subtypes in a multiple myeloma cell line that abundantly expresses catalytic subunits of both the constitutive proteasome and immunoproteasome. Our findings indicate that constitutive proteasomes, immunoproteasomes, and intermediate proteasomes co-exist within these cells and support conclusions drawn from previous studies in other cell types. We also established non-small cell lung cancer cell line models of acquired bortezomib and carfilzomib resistance in which to test our hypothesis. Using immunoblotting and proteasome activity assays, we discovered that changes in the expression levels and activities of individual catalytic proteasome subunits were associated with the emergence of acquired resistance to bortezomib or carfilzomib. These changes were inhibitor-dependent and persisted after the selective pressure of the inhibitor was removed. Finally, results obtained using our bifunctional proteasome probes suggest that the altered abundance of an intermediate proteasome subtype is associated with acquired proteasome inhibitor resistance. Collectively, our results provide evidence linking changes proteasome composition with acquired proteasome inhibitor resistance and support the hypothesis that such changes are involved in resistance mechanisms to these inhibitors.

Overexpression of tumor-derived mutant p53 is a common event in tumorigenesis, suggesting an advantageous selective pressure in cancer initiation and progression. Given that p53 is found to be mutated in 50% of all human cancers, restoration of mutant p53 to its wild type biological function has been a widely sought after avenue for cancer therapy. Most research efforts have largely focused on restoration of mutant p53 by artificial means given that p53 has some degree of conformational flexibility allowing for introduction of short peptides and artificial compounds. Recently, theoretical modeling and studies focused on restoration of mutant p53 by physiological means has raised the question of whether there are effective therapies worth exploring that focus on global physiological mechanisms of restoration of p53. Herein, we provide computational analysis of the thermodynamic stabilities of both wild-type and mutant p53 core domains by studying their respective minimum potential energies. Also, it is widely accepted that wild type p53 is modulated by various acetyl transferases as well as deactylases, but whether this mechanism of p53 modulation can be exploited for physiological restoration of mutant p53 remains under intense investigation. Using prostate cancer cell lines representative of varying stages of aggressiveness as a model, we show that ID4 dependent acetylation promotes mutant p53 DNA-binding capabilities to its wild type consensus sequence, thus regulating p53-dependent target genes leading to subsequent cell cycle arrest and apoptosis. Specifically, we identify that ID4 promotes acetylation of K373 and to a lesser extent K320, in turn regulating p53-dependent biological activities. Together, our data provides computational analysis of the core domain of certain mutant forms of p53 and a molecular understanding of ID4 dependent acetylation that suggests a strategy of enhancing p53 acetylation at sites K373 and K320, critical sites of post translational modification of p53, that may serve as a viable mechanism of physiological restoration of mutant p53 to its wild type biological function.

The expression of C-X-C Chemokine Receptor 4 (CXCR4) has been correlated with increased metastatic potential of cancer cells. CXCR4 increases tumor malignancy by encouraging tumors cells to migrate to distal organs expressing its cognate ligand, CXCL12, facilitating metastasis. Thus, targeting the CXCR4/CXCL12 signaling axis provides a good strategy to inhibit the metastatic spread of tumor cells and slow cancer progression. Various studies suggest that cannabis may have anti-proliferative as well as anti-metastatic properties, though a biochemical mechanism describing how this occurs has yet to be discovered. Our lab has confirmed that agonist-bound CXCR4 and agonist-bound Cannabinoid Receptor 2 (CB2) can form heterodimers that play a role in decreasing cancer cell migration. Simultaneous treatment of the breast cancer cell line, MDA-MB-231 and the prostate cancer cell line PC-3, with CXCL12 and AM1241, a synthetic ligand for CB2, desensitizes the intrinsic cellular response to migrate toward areas of high CXCL12 concentration. Furthermore, through co-immunoprecipitation and proximity ligation assays (PLA), we have determined that there is increased interaction between the two receptors with co-stimulation of respective agonists, providing evidence for the therapeutic notion that treating tumors that endogenously secrete CXCL12 with exogenous ligands for the cannabinoid can induce dimerization. Moreover, when CXCR4 and CB2 were activated simultaneously with various agonists, decreases in migration were observed, confirming that the regulatory activity was receptor-based, not agonist-based. Finally, to determine whether simultaneously–treated, dimerized receptors inhibited activity of respective receptors, calcium mobilization assays to determine G-protein coupled receptor activation were employed. Results showed that transiently activated calcium levels were significantly lower in response to simultaneous treated cells when compared to cells treated with their individual ligands. Phosphorylation of ERK and AKT were abrogated in response to simultaneous stimulation indicating loss in downstream signaling. Therefore, we believe that the interaction of CB2 with CXCR4 may play a role in inhibiting the cells response to CXCL12, leading to a loss in metastatic potential of cells expressing these receptors.

The inhibitor of DNA binding protein 4 (ID4) is a dominant negative regulator of basic helix loop helix (bHLH) family of transcription factors.1 Recently, Patel et al., demonstrated that inhibitor of differentiation 4 (ID4) acts as a tumor suppressor and its loss, frequently observed in prostate cancer, promotes castration-resistant prostate cancer (CRPC) through constitutive androgen receptor (AR) activation.2 However, the mechanism by which loss of ID4 promotes constitutively active AR signaling in the CRPC conditions is unknown. The rationale of the present study was to unravel the underlying molecular mechanisms through which loss of ID4 potentiates AR signaling in this setting. Initially, chromatin immunoprecipitation (ChIP) assay results demonstrated a significant increase in binding of AR to its respective response elements on PSA, FKBP51, TMPRSS2, and ETV1 promoters in L(-)ID4 cells, further implicating constitutive AR activity. Among the notable findings, proteomic profiling between prostate cancer cell line LNCaP (L+ns) and LNCaP lacking ID4 (L(-)ID4) revealed elevated protein levels of Heat shock protein 27 (Hsp27) and the 52-kDa FK506-binding protein (FKBP52), suggesting a role for these AR-associated co-chaperones in promoting constitutively active AR signaling in L(-)ID4 cells. Interestingly, protein interaction studies further confirmed a direct interaction between ID4 and FKBP52 in vitro but not with AR. Recent evidences suggest that FKBP52 is a positive regulator of AR signaling in cellular and whole animal models.3-6 Thus, we hypothesized that ID4 acts as a tumor suppressor by selectively regulating AR activity through interaction with FKBP52. To address the underlying mechanism, we blocked the FKBP52-AR signaling using a specific inhibitory compound known as MJC13.4, 6-7 The results demonstrated that MJC13 effectively inhibited AR-dependent expression and activity in a dose-dependent manner. In addition, xenograft studies further confirmed that inhibiting FKBP52-regulated AR activity via MJC13 significantly attenuated the growth of subcutaneous L(-)ID4 xenografts in vivo. Collectively, our results suggested that ID4 selectively regulates AR activity through direct interaction with FKBP52 in vitro, and, its loss promotes CRPC through FKBP52-mediated AR signaling. Increased AR signaling along with a subsequent decrease in ID4 expression levels in prostate cancer strongly supports this model.

Recent advances in understanding lung biology have shown evidence for the existence of resident lung stem cells. Independent studies in identifying and characterizing these somatic lung stem cells have shown the potential role of these cells in lung repair and regeneration. Understanding the functional characteristics of these tissue resident stem/progenitor cells has gained much importance with increasing evidence of cancer stem cells, cells in a tumor tissue with stem cell characteristics. Lung cancer is most commonly characterized by loss of p53 function which results in uncontrolled cell divisions. Incidence of p53 point mutations is highest in lung cancer, with a high percentage of missense mutations as a result of tobacco smoking. Certain point mutations in p53 gene results in its oncogenic gain of functions (GOF), with enhanced tumorigenic characteristics beyond the loss of p53 function. However, there are no available data on characterization of lung stem cells carrying GOF mutations and correlating them with those of normal stem cells, in this study, for the first time we show that percentage of Sca-1 expressing subpopulation is significantly higher in the lungs of mice carrying p53 GOF mutations than those in lungs isolated from p53+/+ wild type mice. Further, we successfully established lung cells differentially expressing two cell surface markers, Sca-1 and PDGFR-α, with results demonstrating existence of different subpopulations of cells in the lung. Results from our project demonstrate the importance of p53 GOF mutations as correlated with specific lung cell subpopulations.

Immunotherapy of cancer has been shown to be promising in prolonging patient survival. However, complete elimination of cancer and life-long relapse-free survival remain to be major challenge for anti-cancer therapeutics. We have previously reported that ex vivo reprogramming of tumor-sensitized immune cells by bryostatin 1/ionomycin (B/I) and the gamma-chain (γ-c) cytokines IL-2, IL-7, and IL-15 resulted in the generation of memory T cells as well as CD25+ NKT cells and CD25+ NK cells. Adoptive cellular therapy (ACT) utilizing these reprogrammed immune cells protected FVBN202 mice from tumor challenge, and overcame the suppressive functions of myeloid-derived suppressor cells (MDSCs). We then demonstrated that the presence of CD25+ NKT cells was required for anti-tumor efficacy of T cells as well as their resistance to MDSCs. Similar results were obtained by reprogramming of peripheral blood mononuclear cells (PBMC) from patients with early stage breast cancer, demonstrating that an increased frequency of CD25+ NKT cells in reprogrammed immune cells was associated with modulation of MDSCs to CD11b-HLA-DR+ immune stimulatory cells. Here, we tested the efficacy of immunotherapy in a therapeutic setting against established primary breast cancer (Chapter One), experimental metastatic breast cancer (Chapter Three) as well as against minimal residual disease (MRD) in patients with multiple myeloma (Chapter Two). We evaluated the ability of reprogrammed immune cells, including CD25+ NKT cells, to convert MDSCs to myeloid immune stimulatory cells, in vivo; this resulted in the identification and characterization of a novel antigen presenting cell (APC). These novel immune stimulatory cells differed from conventional APCs, including dendritic cells (DCs) and macrophages. We have also demonstrated that enhancing immunogenicity of mammary tumors by treatment with Decitabine (Dec) along with overcoming MDSCs by utilizing reprogrammed T cells and NKT cells in ACT prolongs survival of animals, but fails to eliminate the tumor. However, targeting cancer during a setting of MDR, when tumor cells are dormant, results in objective responses as evidenced in our multiple myeloma studies. This suggests that targeting breast cancer with immunotherapy following conventional therapies, in a setting of residual disease when tumor cells are dormant, may be effective in eliminating such residual cells or maintaining dormancy and extending time-to-relapse for breast cancer patients.

New drug discoveries and new approaches towards diagnosis and treatment have improved cancer therapeutics remarkably. One of the most influential and effective discoveries in the field of cancer therapeutics was antimetabolites, such as the antifolates. The interest in antifolates increased as some of the antifolates showed responses in cancers, such as mesothelioma, leukemia, and breast cancers. When pemetrexed (PTX) was discovered, our laboratory had established that the primary mechanism of action of pemetrexed is to inhibit thymidylate 22 synthase (TS) (E. Taylor et al., 1992). Preclinical studies have shown that PTX has a broad range of antitumor activity in human and murine models of cancer (Adjei, 2000; Adjei, 2004; S. Chattopadhyay, Moran, & Goldman, 2007; Miller et al., 2000). Accordingly, in February 2004, the FDA issued first-line treatment approval for pemetrexed in malignant pleural mesothelioma and in 2008 for first line treatment for locally advanced or metastatic NSCLC (reviewed in (Rollins & Lindley, 2005). As an antifolate this level of therapeutic activity of PTX against lung cancers was surprising and atypical (Hazarika, White, Johnson, & Pazdur, 2004). This led us to the question whether the effects of pemetrexed on other folate-dependent targets could explain the clinical activity of the drug. Our lab showed that, in addition to inhibiting thymidylate synthase, PTX also inhibits aminoimidazolecarboxamide ribonucleotide formyltransferase (AICART), the second folate-dependent enzyme of de novo purine synthesis. Inhibition of AICART leads to massive accumulation of its substrate 5-amino-4-imidazolecarboxamide ribonucleotide (ZMP), causing activation of AMP-dependent kinase (AMPK), which ultimately leads to suppression of mTORC1 signaling, a central regulator of cell growth and proliferation. This secondary mechanism could explain the unusual activity of PTX against mesothelioma and lung cancers. The large proportion of lung cancers are either null or mutant for p53 function. Therefore, this thesis focused on defining what the role of p53 is in the PTX-mediated AMPK activation and mTORC1 inhibition and how the loss of p53 affects mTORC1 signaling. These two questions proved to be interlinked. Chapter 2 investigates this relationship in detail. We found that, upon loss of p53, mTORC1 signaling is enhanced to a significant degree in colon carcinoma and lung cancer cell lines. Clearly, this observation required explanation. We found that the major factors responsible for these differences in mTORC1 activity upon loss of p53 23 were lower levels of two p53 target genes Tuberin (TSC2) and sestrin2. Immunoprecipitation studies of mTORC1 complexes from p53 wt and p53 null cells revealed quite interesting differences in the components of the mTORC1 complex. Immunoprecipitates from p53 null cells had higher levels of mTOR and lower levels of TSC2 and PRAS40 bound to raptor. This suggested that, in comparision to p53 competent cells, p53 null cells have more mTORC1 complex with enhanced activity due to decreased interaction of TSC2 and PRAS40, both of which are inhibitors of mTORC1. These observations explained the higher mTORC1 in p53 null cells and laid the foundation for determining the role of p53 in PTX-activated AMPK and mTORC1 inhibition. In the experiments described in Chapter 3, we found that PTX-mediated AMPK activation inhibited mTORC1 regardless of the p53 status in colon carcinoma cells. This suggested that mTORC1 inhibition by PTX was either independent of p53 mediated negative regulation of mTORC1 or was somewhere bypassing it. Therefore, we compared the effects of PTX with the classic AMPK activator aminoimidazolecarboxamide ribonucleoside (AICAR). In spite of a common mechanism of AMPK activation, namely, expansion of cellular ZMP levels, signaling from AMPK activated by PTX or AICAR were quite different. PTX-activated AMPK phosphorylated the mTORC1 component Raptor but not tuberin (TSC2), whereas AICARactivated AMPK phosphorylated both the targets. This differential behavior of two AMPK activators was due to differential behavior of p53 under these two treatments. Both, AICAR and PTX treatment led to increase in p53 levels but the p53 that accumulated after AICAR treatment was transcriptionally active while the p53 that accumulated after PTX treatment was not. Transcription of p53 targets, including TSC2 and sestrin2, was activated in AICAR- but not in PTX-treated cells. In the absence of p53 function, TSC2 was deficient and mTORC1 activity 24 enhanced, but Raptor phosphorylation by AMPK following PTX was robust and independent of both p53 and TSC2. Therefore we concluded that p53 deficiency suppresses TSC2 and upregulates mTORC1, but AMPK-phosphorylation of Raptor after pemetrexed treatment was sufficient to suppress mTORC1, even in TSC2 deficiency. This suggested pemetrexed as a drug for treatment of Tuberous Sclerosis, a genetic disease caused by functional inactivity of TSC1 or TSC2 due to point mutations in these genes. Mutation of p53 is one of the most common genetic alterations in human cancers and tumors. Cancers that express mutant p53 tend to be more aggressive, resistant to chemotherapy and show worse prognosis then p53-null tumors (Elledge et al., 1993; Olivier et al., 2006). This tumor-promoting activity of mutant p53 has been correlated with acquired and novel transcriptional activities of mutant p53. It has been shown that mutp53 can activate the transcription of cell growth promoting genes, such as, NFκB2, PCNA, MDR1, Axl, EGFR, hTERT, and HSP70, which are not usually transcriptional targets of wt p53. Interestingly, we found that whereas DNA damaging drugs enhance the acquired oncogenic transcriptional activities of mutp53, PTX interferes with this transcription activation. We also found in Chapter 4 that PTX can limit or block the DNA damaging drug-mediated increment of transcriptional activation of mutp53. This suggests that blockade of transcriptional activation of mutp53 by pemetrexed may provide an additional therapeutic benefit in mutp53 bearing cancers. As discussed in Chapter Three, although pemetrexed (with TdR) increases the levels of p53 and its binding to the promoter of its target gene, p21, this p53 is transcriptionally inactive. In order to understand the mechanism of the pemetrexed-mediated transcriptional defect of wt p53, we studied the PTX-mediated signaling towards ATM and ATR and their effects on their substrates Chk2 and Chk1, respectively. These studies suggested that the difference between 25 signaling under AICAR treatment and PTX treatment was that, unlike PTX, AICAR treatment was leading to DNA damage, followed by Chk2 phosphorylation at Thr68. We found there were three major differences between AICAR and pemetrexed (+ TdR) mediated signaling: AICAR caused DNA damage, followed by ATM mediated phosphorylation of Chk2 at Thr68 and phosphorylation of p53 at Ser15 all of which lead to activation of p53 transcriptional activity, events which do not take place under PTX treatment. Studies aimed at understanding the effects of PTX on wt and mutp53 transcriptional activities are discussed in detail in Chapters Three and Four of this dissertation. Overall, we concluded that PTX interferes with the transcription activity of wild type as well as gain-of-function mutant p53. The blockade of DNA damaging agent-mediated enhancement of mutp53 transcription activity by PTX, suggests the clinical relevance of PTX in carcinomas with mutp53. We suggest that this could be one of the contributing factors in the effects of PTX against human lung cancers.