Impact of DNA ligase inhibition on the nick sealing of polβ nucleotide insertion products at the downstream steps of base excision repair pathway

DNA ligase (LIG) I and IIIα finalize base excision repair (BER) by sealing a nick product after nucleotide insertion by DNA polymerase (pol) β at the downstream steps. We previously demonstrated that a functional interplay between polβ and BER ligases is critical for efficient repair, and polβ mismatch or oxidized nucleotide insertions confound final ligation step. Yet, how targeting downstream enzymes with small molecule inhibitors could affect this coordination remains unknown. Here, we report that DNA ligase inhibitors, L67 and L82-G17, slightly enhance hypersensitivity to oxidative stress-inducing agent, KBrO3, in polβ+/+ cells more than polβ-/- null cells. We showed less efficient ligation after polβ nucleotide insertions in the presence of the DNA ligase inhibitors. Furthermore, the mutations at the ligase inhibitor binding sites (G448, R451, A455) of LIG1 significantly affect nick DNA binding affinity and nick sealing efficiency. Finally, our results demonstrated that the BER ligases seal a gap repair intermediate by the effect of polβ inhibitor that diminishes gap filling activity. Overall, our results contribute to understand how the BER inhibitors against downstream enzymes, polβ, LIG1, and LIGIIIα, could impact the efficiency of gap filling and subsequent nick sealing at the final steps leading to the formation of deleterious repair intermediates.

Bacillus tequilensis influences metabolite production in tomato and restores soil microbial diversity during Fusarium oxysporum infection

This study evaluates cellular damage, metabolite profiling, and defence-related gene expression in tomato plants and soil microflora during Fusarium wilt disease after treatment with B. tequilensis PBE-1. Histochemical analysis showed that PBE-1 was the primary line of defence through lignin deposition and reduced cell damage. GC-MS revealed that PBE-1 treatment ameliorated stress caused by F. oxysporum infection. PBE-1 also improved transpiration, photosynthesis, and stomatal conductance in tomato. qRT-PCR suggested that the defence-related genes FLS2, SERK, NOS, WRKYT, NHO, SAUR, and MYC2, which spread infection, were highly upregulated during F. oxysporum infection, but either downregulated or expressed normally in PBE-1 + P treated plants. This indicates that the plant not only perceives the bio-control agent as a non-pathogen entity but its presence in normal metabolism and gene expression within the host plant is maintained. The study further corroborated findings that application of PBE-1 does not cause ecological disturbances in the rhizosphere. Activity of soil microflora across four treatments, measured by Average Well Colour Development (AWCD), showed continuous increases from weeks 1 to 4 post-pathogen infection, with distinct substrate usage patterns like tannic and fumaric acids impacting microbial energy source utilization and diversity. Principal Component Analysis (PCA) and diversity indices like McIntosh, Shannon, and Simpson further illustrated significant microbial community shifts over the study period. In conclusion, our findings demonstrate that B. tequilensis PBE-1 is an ideal bio-agent for field application during Fusarium wilt disease management in tomato.

Molecular editing of enabling discovery of benzodithiazinedioxide-guanidines as anticancer agents

DNA polymerase β (Polβ) is crucial for the base excision repair (BER) pathway of DNA damage repair and is an attractive target for suppressing tumorigenesis as well as chemotherapeutic intervention of cancer. In this study, a unique strategy of scaffold-hopping-based molecular editing of a bioactive agent NSC-666719 was investigated, which led to the development of new molecular motifs with Polβ inhibitory activity. NSC compound and its analogs (two series) were prepared, focusing on pharmacophore-based molecular diversity. Most compounds showed higher activities than the parent NSC-666719 and exhibited effects on apoptosis. The inhibitory activity of Polβ was evaluated in both in vitro reconstituted and in vivo intact cell systems. Compound 10e demonstrated significant Polβ interaction and inhibition characteristics, including direct, non-covalent, reversible, and comparable binding affinity. The investigated approach is useful, and the discovered novel analogs have a high potential for developing as anticancer therapeutics.

Altering phosphorylation in cancer through PP2A modifiers

Protein phosphatase 2A (PP2A) is a serine/threonine phosphatase integral to the regulation of many cellular processes. Due to the deregulation of PP2A in cancer, many of these processes are turned toward promoting tumor progression. Considerable research has been undertaken to discover molecules capable of modulating PP2A activity in cancer. Because PP2A is capable of immense substrate specificity across many cellular processes, the therapeutic targeting of PP2A in cancer can be completed through either enzyme inhibitors or activators. PP2A modulators likewise tend to be effective in drug-resistant cancers and work synergistically with other known cancer therapeutics. In this review, we will discuss the patterns of PP2A deregulation in cancer, and its known downstream signaling pathways important for cancer regulation, along with many activators and inhibitors of PP2A known to inhibit cancer progression.

Abstract 1655: Discovery of a novel PP2A activator as a potential therapeutic for FOLFOX resistant colon cancer

Protein phosphatase 2A (PP2A) is a diverse serine/threonine phosphatase that accounts for 50-70% of all serine/threonine phosphorylation in the cell. Due to the inactivation of PP2A in cancer, many of the cellular processes that PP2A regulates are aimed towards tumor progression. As such, the therapeutic targeting of PP2A in cancer is becoming a popular research avenue in the development of new chemotherapeutics. Currently, there have been a few PP2A activators observed to inhibit tumor progression in vitro and in vivo; however, these compounds have shown to have poor bioavailability, such as NSC49L, or uncertainty towards their ability to activate PP2A, as is the case with iHAP1. These hindrances demonstrate a need for further optimization of these molecules in order to produce a PP2A activator capable of inhibiting cancer without these limitations. As such, we have designed a series of compounds utilizing molecular modeling and fragment-based drug design based upon the known PP2A activators, NSC49L and iHAP1. These compounds were assessed for their ability to inhibit colon cancer (CRC) cells and FOLFOX-resistant CRC cells, where PPA24 was identified as the lead compound. The dose-response curves identified IC50 values in the range of 2.36-6.75µM for PPA24 across four CRC cell lines (HCT116, HT29, DLD1, and SW480) and two FOLFOX-resistant CRC cell lines (FOLFOX-HCT116 and FOLFOX-HT29), displaying more cytotoxicity than both the parent compounds and the other compounds in the series. Molecular docking recognized lower binding energies occurring during the association of PP2A with PPA24 than with either NSC49L or iHAP1. When examining the in vitro effect of PPA24 on stimulating PP2A activation, it was found that PPA24 significantly induced PP2A activity 2-3-fold higher than NSC49L or iHAP1. Likewise, PPA24 was able to induce apoptosis dose-dependently in both CRC and FOLFOX-resistant CRC cells. As PP2A is known for regulating the cell cycle progression, further exploration revealed PPA24 able to induce cell cycle arrest at the G2/M phase. And PP2A, being known as a regulator for many cellular processes, can be activated to assist in the degradation and inactivation of many signaling proteins such as c-myc, GSK3β, and ERK, which was observed in CRC cells treated with PPA24. Together, these results signify the potential of PPA24 to act as a novel PP2A activator in the treatment of CRC and FOLFOX-resistant CRC.

Citation Format: Hannah Johnson, Amandeep Singh, Asif Raza, Congzhou M. Sha, Nikolay V. Dokholyan, Satya Narayan, Arun K. Sharma. Discovery of a novel PP2A activator as a potential therapeutic for FOLFOX resistant colon cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1655.

All EGFR mutations are (not) created equal: focus on uncommon EGFR mutations

PURPOSE

Most common EGFR mutations in NSCLC include del19 and exon 21 L858R. Approximately 10% of patients have uncommon EGFR mutations (indels, missense mutations involving G719, L861 and S768 codons, and exon 20 insertions) that do not respond to TKIs.

METHODS

Of 490 EGFR mutated NSCLC samples, 60 cases harboring uncommon/compound EGFR mutations were reviewed retrospectively, and 44 were included for survival analysis.

RESULTS

Sixty (12.2%) patients with a median age of 63 years (25-84 years) had uncommon/compound EGFR mutations. Majority had no history of smoking (52; 86.7%). Most common major uncommon mutations (G719X in exon 18, L861Q in exon 21 and S768I in exon 20) were identified in 19 (31.7%) patients. 17 (28.3%) cases demonstrated exon 20 insertions. De novo T790M was observed in 7 (11.7%) cases and 9 cases exhibited compound/dual mutations. Among the 12 patients who received first-line EGFR TKI, 7 received afatinib. Median progression-free survival of patients following first-line afatinib was 8.13 months, irrespective of mutation type exhibited. Overall response rate to first-line afatinib therapy was 57.1%.

CONCLUSION

The current study highlighted that rare/dual EGFR mutations are heterogeneous with distinct clinical features in a large Indian cohort of EGFR mutated patients with NSCLC.

EEPD1 promotes repair of oxidatively-stressed replication forks

Unrepaired oxidatively-stressed replication forks can lead to chromosomal instability and neoplastic transformation or cell death. To meet these challenges cells have evolved a robust mechanism to repair oxidative genomic DNA damage through the base excision repair (BER) pathway, but less is known about repair of oxidative damage at replication forks. We found that depletion or genetic deletion of EEPD1 decreases clonogenic cell survival after oxidative DNA damage. We demonstrate that EEPD1 is recruited to replication forks stressed by oxidative damage induced by H2O2 and that EEPD1 promotes replication fork repair and restart and decreases chromosomal abnormalities after such damage. EEPD1 binds to abasic DNA structures and promotes resolution of genomic abasic sites after oxidative stress. We further observed that restoration of expression of EEPD1 via expression vector transfection restores cell survival and suppresses chromosomal abnormalities induced by oxidative stress in EEPD1-depleted cells. Consistent with this, we found that EEPD1 preserves replication fork integrity by preventing oxidatively-stressed unrepaired fork fusion, thereby decreasing chromosome instability and mitotic abnormalities. Our results indicate a novel role for EEPD1 in replication fork preservation and maintenance of chromosomal stability during oxidative stress.

Serpentine Supra-venous Hyperpigmentation "Badge of Courage" in Fight Against Cancer: An Brief Review

Persistent serpentine supra-venous hyperpigmentation (PSSH) describes a hyperpigmentation of the skin overlying peripheral veins with characteristic of underlying vessels that are patent. It has been described most commonly after injection of chemotherapeutic drugs. We describe a 44 year old man with diagnosed case of Ca stomach on FOLFOX based chemotherapy. After the 1st cycle of Chemotherapy he developed serpentine supra-venous hyperpigmentation. Introduction: Conventional chemotherapy agents commonly cause infusion-site lesions, such as chemical cellulitis due to drug extravasation and evanescent eruptions.(1) 5-Fluorouracil (5-FU) is a cytotoxic agent used mostly in combination to treat a variety of malignant disorders. Hyperpigmentation is a rare side effect occurring with 5-FU infusions; it has been reported in 2-5% of patients. Various types of pigmentary abnormalities have been reported with 5-FU use such as diffuse hyperpigmentation of the face and palms, macular pigmentary changes on the palms and soles, hyperpigmentation overlying the superficial venous network also called serpentine supravenous hyperpigmentation (SSH) and persistent supravenous erythematous eruptions (PSEE).(2) Keywords: Serpentine Supra-venous Hyperpigmentation, Dermatological toxicity, Fluorouracil.

Sensitization of FOLFOX-resistant colorectal cancer cells via the modulation of a novel pathway involving protein phosphatase 2A

The treatment of colorectal cancer (CRC) with FOLFOX shows some efficacy, but these tumors quickly develop resistance to this treatment. We have observed increased phosphorylation of AKT1/mTOR/4EBP1 and levels of p21 in FOLFOX-resistant CRC cells. We have identified a small molecule, NSC49L, that stimulates protein phosphatase 2A (PP2A) activity, downregulates the AKT1/mTOR/4EBP1-axis, and inhibits p21 translation. We have provided evidence that NSC49L- and TRAIL-mediated sensitization is synergistically induced in p21-knockdown CRC cells, which is reversed in p21-overexpressing cells. p21 binds with procaspase 3 and prevents the activation of caspase 3. We have shown that TRAIL induces apoptosis through the activation of caspase 3 by NSC49L-mediated downregulation of p21 translation, and thereby cleavage of procaspase 3 into caspase 3. NSC49L does not affect global protein synthesis. These studies provide a mechanistic understanding of NSC49L as a PP2A agonist, and how its combination with TRAIL sensitizes FOLFOX-resistant CRC cells.

Co-relation of SARS-CoV-2 related 30-d mortality with HRCT score and RT-PCR Ct value-based viral load in patients with solid malignancy

BACKGROUND

Coronavirus disease 2019 (COVID-19) patients with malignancy are published worldwide but are lacking in data from India.

AIM

To characterize COVID-19 related mortality outcomes within 30 d of diagnosis with HRCT score and RT-PCR Ct value-based viral load in various solid malignancies.

METHODS

Patients included in this study were with an active or previous malignancy and with confirmed severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection from the institute database. We collected data on demographic details, baseline clinical conditions, medications, cancer diagnosis, treatment and the COVID-19 disease course. The primary endpoint was the association between the mortality outcome and the potential prognostic variables, specially, HRCT score, RT-PCR Ct value-based viral load, etc. using logistic regression analyses treatment received in 30 d.

RESULTS

Out of 131 patients, 123 met inclusion criteria for our analysis. The median age was 57 years (interquartile range = 19-82) while 7 (5.7%) were aged 75 years or older. The most prevalent malignancies were of GUT origin 49 (39.8%), hepatopancreatobiliary (HPB) 40 (32.5%). 109 (88.6%) patients were on active anticancer treatment, 115 (93.5%) had active (measurable) cancer. At analysis on May 20, 2021, 26 (21.1%) patients had died. In logistic regression analysis, independent factors associated with an increased 30-d mortality were in patients with the symptomatic presentation. Chemotherapy in the last 4 wk, number of comorbidities (≥ 2 vs none: 3.43, 1.08-8.56). The univariate analysis showed that the risk of death was significantly associated with the HRCT score: for moderate (8-15) [odds ratio (OR): 3.44; 95% confidence interval (CI): 1.3-9.12; P = 0.0132], severe (> 15) (OR: 7.44; 95%CI: 1.58-35.1; P = 0.0112).

CONCLUSION

To the best of our knowledge, this is the first study from India reporting the association of HRCT score and RT-PCR Ct value-based 30-d mortality outcomes in SARS-CoV-2 infected cancer patients.

Machine-learned physiological signatures from the ECG predict sudden death in ischemic cardiomyopathy

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): National Institute of Health (NIH)

Background

Low left ventricular ejection fraction (LVEF) is an imperfect predictor of sudden cardiac death (SCD) in patients with ischemic cardiomyopathy. Novel features from the ECG might provide a readily available tool to better predict risk.

Purpose

We hypothesized that machine learning (ML) of the ECG can be used to predict SCD, and the ML-learned ECG features could be referenced to interpretable intracardiac signals (monophasic action potentials: MAP) to provide mechanistic insights.

Methods

We studied 5603 ECG Lead V1 beats in 41 patients (64±10 Y) with coronary disease and LVEF≤40% in steady-state pacing. Patients were randomly allocated to independent training and test cohorts in a 70:30 ratio, repeated K=10-fold. Support vector machines were trained to predict mortality at 3Y from the top 20 features derived from these beats. Patient-level predictions were made by computing an ECG score that indicates the proportion of test set beats in that patient computed by the beat-level model to predict death. Explainability analysis was performed using the arithmetic mean of MAP and ECG beats that predicted SCD versus those that predicted survival.

Results

Fig 1A. shows ECG lead V1 and MAP in a 79 Y man with LVEF 29%. Fig 1B shows the dataflow in the study. Predictive accuracies of ML models were 78 and 70% and optimal with 20 features for both ECG and MAP models respectively (Fig. 1C). Beat-level predictions in the validation (n=1678 Lead I beats) cohorts yielded c-statistics of 0.78 with the ECG (95% CI, 0.62–0.91) and 0.75 with MAPs (95% CI, 0.75-0.76) (data not shown). In multivariable patient-level models, c-statistic was 0.87 with ECGs (95% CI, 0.76-0.98) (Fig 1D) and 0.82 with MAPs. On explainability analysis, ECG beats that predicted SCD (Fig 2; red) had lower amplitude and more notched T-waves in lead V1 than beats that predicted no SCD (Fig 2; blue). MAP that predicted SCD had higher repolarization current at the same time points. Both QT duration (ECG) and action potential duration (MAP) did not differ (Fig 2).

Conclusions

Machine learning of the ECG reveals novel predictors of SCD risk in patients with ischemic cardiomyopathy analogous to those identified in intracardiac signals. This approach can be used as a point-of-care ECG risk tool to improve risk stratification and allocation for ICD therapy beyond LVEF alone and may shed insights into the pathophysiology of ventricular arrhythmias.

Hyper-Progressive Disease (HPD) during Immune Checkpoint Inhibitor (ICI) Therapy

Immune checkpoint inhibitor (ICI) restores an efficient antitumor T cell response against tumor cells fostering durable responses that can persist even after the treatment. However, these treatment effects can manifest as an unusual pattern of disease progression, pseudo-progression, or hyper-progression. Differentiating hyper progressive disease (HPD) from pseudo-progression has significant clinical implications and further decision-making for the patient on ICI. HPD is a dramatic acceleration of the rate of tumor progression with the advent of immunotherapeutic agents causing detrimental effects on the disease outcome.

Disruption of desmosome function leads to increased centrosome clustering in 14-3-3γ-knockout cells with supernumerary centrosomes

14-3-3 proteins are conserved, dimeric, acidic proteins that regulate multiple cellular pathways. Loss of either 14-3-3ε or 14-3-3γ leads to centrosome amplification. However, we find that while the knockout of 14-3-3ε leads to multipolar mitoses, the knockout of 14-3-3γ results in centrosome clustering and pseudo-bipolar mitoses. 14-3-3γ knockouts demonstrate compromised desmosome function and a decrease in keratin levels, leading to decreased cell stiffness and an increase in centrosome clustering. Restoration of desmosome function increased multipolar mitoses, whereas knockdown of either plakoglobin or keratin 5 led to decreased cell stiffness and increased pseudo-bipolar mitoses. These results suggest that the ability of the desmosome to anchor keratin filaments maintains cell stiffness, thus inhibiting centrosome clustering, and that phenotypes observed upon 14-3-3 loss reflect the dysregulation of multiple pathways.

Mucinous cystic neoplasm of the liver (MCN-L): a rare presentation and review of the literature

Mucinous cystic neoplasms of the liver (MCN-L, (previously referred to as cystadenomas or cystadenocarcinoma) are rare cystic tumors that occur within the liver parenchyma, or less frequently, in the extrahepatic bile ducts. They are reported to account for <5% of all liver cysts. The differential diagnosis of MCN-L includes intraductal papillary neoplasm of the bile duct (IPNB), intrahepatic cholangiocarcinoma with cystic change, echinococcal cyst, and a simple cyst. Invasive MCNs can only be differentiated from non-invasive MCNs by microscopic evaluation for the presence of ovarian-type stroma. Intraoperative biopsy and frozen section(s) are essential to differentiate MCNs from other cystic liver lesions. The treatment of choice is complete excision and can result in excellent survival with initial correct diagnosis. But its rare presentation and insufficient recognition frequently lead to an incorrect initial or delayed diagnosis or misdiagnosis.

Extent of atrium with 1:1 electrogram activation predicts response to ablation of atrial fibrillation

Funding Acknowledgements

Type of funding sources: Public grant(s) – National budget only. Main funding source(s): US National Institutes of Health

Background

Mechanisms associated with successful termination of persistent atrial fibrillation (AF) are still under debate. We sought to study the association between spatial extent of atrium with organized conduction and AF ablation success. We hypothesized that patients with large areas of atrium having 1:1 electrogram activation akin to ‘atrial tachycardia’ may have a higher likelihood of AF termination by ablation.

Methods

In n = 40 AF patients, n = 20 had termination by ablation ("Term"), and the remaining did not have AF termination by ablation ("Non-term"). Basket catheters (64 poles) were used to record unipolar electrograms (EGMs) in one or both atrium. Ablation targeted localized rotational/focal regions, after which pulmonary vein isolation was performed. Unipolar EGMs of 4sec duration at each 2x2 electrode neighborhood within 8x8 catheter grid were processed using a statistical correlation technique to identify the duration of 1:1 activations. Any EGM activation cycle that had a correlation above 80% was considered to be 1:1. Duration of contiguous 1:1 cycles was determined as percentage of total duration (4 sec).

Results

Spatial area of atrium (percentage of mapping field) and the corresponding 1:1 durations were assessed for patients in Term and Non-term groups. Fig A shows spatial 1:1 maps of a Term and a Non-term patient. Fig B shows examples of 1:1 and non-1:1 EGMs. Patients in Term group had higher average 1:1 atrial area than non-term group for any 1:1 duration (Fig C, 15 ± 22% vs 2 ± 4% with ≥70% 1:1 duration, p = 0.03). Positive and negative predictive values of duration≥70% for AF termination were 64.7%, and 75%, with specificity 60% and sensitivity 78.6%, exceeding clinical risk scores.

Conclusion

Persistent AF atrium shows areas of organized 1:1 conduction. Larger 1:1 atrial areas were identified in patients in whom AF terminated by ablation. Future studies should investigate mechanistic bases of organized conduction in AF. Abstract Figure.

Real-world data of osimertinib in the management of leptomeningeal metastases in EGFR mutant NSCLC: Light at the end of the tunnel?

e21197

Background: Presence of leptomeningeal metastases (LM) in NSCLC is indicative of aggressive disease and the incidence is as high as 9%-16% in the EGFR mutant subgroup. Traditionally, these patients had a dismal outcome with WBRT and intrathecal chemotherapy. Osimertinib crosses the blood brain barrier and is efficacious in the second line setting, as seen in BLOOM trial (LM ORR of 62%) and AURA program (LM ORR 55%). Osimertinib has also demonstrated CNS efficacy in the first line (FLAURA trial). This study is a retrospective review of cases with LM treated with osimertinib, and their response outcomes. Methods: 16 patients of EGFR mutant NSCLC developed LM at some point in their disease course and were treated with osimertinib. Clinical features and response outcomes were retrieved from medical record archives. Descriptive statistics were done using SPSS v23 software. LM PFS was defined as the time between 1st dose of osimertinib and date of progression in LM. LM OS was defined as the time between the first dose of osimertinib to the date of last follow up/death. ORR was defined as the percentage of cases showing CR/PR to osimertinib. Results: Median age was 61 years (range: 33-79) with 9 males and 7 females. Del19 mutations were seen in 9 patients and L858R in 7 patients. Only one patient was given WBRT prior to TKI. 6 patients with LM at diagnosis were given 1st line osimertinib. 3 (50%) progressed in LM and 3 (50%) showed partial response. Median LM PFS and median LM OS was not reached. ORR for osimertinib in the first line was 83.3%. 10 patients developed LM later in the course of the disease and median time to onset of LM was 12.47 months. Median LM PFS for osimertinib was 7.9 months (95% CI:3.2-8.3). Median LM OS was 8.2 months (95% CI: 2.6-19.8 months). ORR for osimertinib in the later line was 60%. Conclusions: This early experience reveals superior efficacy of osimertinib in LM with an excellent LM ORR in the first line setting and concordant results with second line BLOOM Study. Despite the small numbers in this study, this report becomes clinically relevant owing to the rarity of LM occurrence and paucity of available data. Efficacy of osimertinib in EGFR treatment-naive patients with LM requires further investigation and a larger prospective trial with a longer follow up may help confirm our preliminary findings.

Toxic Leukoencephalopathy: An unusual Presentation by 5-Fluorouracil Infusion

BACKGROUND

Toxic leukoencephalopathy predominantly affect white matter of the brain parenchyma. Patient presents either in acute, subacute or chronic phase. The clinical presentation may vary, ranging from mild cognitive impairment to severe neurological dysfunction. It can also mimic psychiatric illness.

CASE REPORT

A 50-year-old woman was diagnosed with locally advanced carcinoma buccal mucosa. She was planned for Neoadjuvant chemotherapy consisting of Docetaxel, Cisplatin, 5-FU (TPF). During 3rd day of 3rd cycle of 5-fluorouracil (5FU) infusion, patient developed hypoactive delirium and later became comatose state of drowsiness, with Glasgow Coma Scale (GCS) was 5. There was no previous history for the same. Hence, the infusion was stopped. Patient was evaluated with NCCT head. No abnormality was seen on CT scan. MRI brain was done and it showed diffusion restriction with T2 / FLAIR hyper intensities in bilateral centrum semiovale, white matter of bilateral parietal region and in corpus callosum. Patient received symptomatic care, nutrition by ryles tube during this period and she started to improve after 1st week of onset of symptoms. After 3 weeks, MRI was repeated and there was complete resolution of previous findings.

CONCLUSIONS

Development of neurological symptoms during 5FU infusion is a rare entity. Henceforth, occurrence of toxic leukoencephalopathy should be kept in mind. Diffusion weighted imaging play an important role in both acute episode of toxic encephalopathy and in follow up.

A Comparative Study of Uninterrupted Treatment by Radiotherapy versus Standard Gap Correction after Interruptions in Oropharyngeal Cancer

BACKGROUND

Radiation is an important modality in the treatment of cancer. The longer course of treatment, favors stem cells repopulation, increasing the bulk of stem cells that have to be obliterated. So overall treatment time increases, the chances of local cure by radiotherapy decreases. Primary aim of study is to test the efficacy of radiation treatment after standard correction in unplanned interruption.

MATERIAL AND METHOD

105 patients of head and neck cancer (Oropharynx) with ECOG performance score = 2, with squamous cell carcinoma histopathology and with stage III and IVa were enrolled and 95 patients have completed treatment. Patients were planned for Concurrent chemo-radiotherapy with Cisplatin 40mg/m2 with EBRT (66Gy/33#/2Gy/#) treatment completed in 6.5 weeks. During the treatment the patients were grouped into uninterrupted arm (48) and interrupted arm with standard correction (47).

RESULTS

The enrolled patients mean age: 50 years, males 76.8%, stage IVa disease 50.7%, ECOG performance status (0/1: 67.9%). The complete response (CR) in uninterrupted arm was 64.5% and CR in interrupted arm with standard correction was 61.7% at 6 months (X2= 1.883, p value=0.169). While considering alone Stage IV cases, had found that the locally advanced cases of uninterrupted arm have significant better response (X2= 5.90, p value=0.015). The quality of life was slightly poor, but was statistically insignificant in interrupted arm.

CONCLUSION

The study concludes that patients with advanced stage (i.e. IVa) have significantly poor treatment outcomes even the standard correction once treatment is interrupted. While the patient treated with gap correction also have similar outcomes in form of disease-free survival and overall survival at 3 years compared to uninterrupted arm.

Disseminated peritoneal leiomyomatosis: an unusual presentation of intra-abdominal lesion mimicking disseminated malignancy

Leiomyoma are commonly seen as benign smooth muscle tumors of the uterus. Smooth muscle tumors with unusual growth pattern are rare and include 3 primary neoplasms: intravenous leiomyomatosis (IVL), benign metastasizing leiomyoma (BML) and disseminated peritoneal leiomyomatosis (DPL). DPL is a rare benign disease, often giving the appearance of metastatic ovarian or peritoneal carcinoma. It is a disease that predominately affects women at their reproductive age. The risk of malignant transformation is 2–5%. There are no standard treatment guidelines for the management of the DPL. The unusual presentation of the disease delays the diagnosis or is often misdiagnosed and thus over treated, which may lead to increased morbidity and mortality. Therefore careful consideration and high index of suspicion is required for the proper management of such cases.

Clinical significance of a pvrl 4 encoded gene Nectin-4 in metastasis and angiogenesis for tumor relapse

PURPOSE

In the present study, we have systematically examined the clinical significance of Nectin-4 (encoded by the PVRL-4 gene), a marker for breast cancer stem cells (CSCs), in cancer metastasis and angiogenesis using a variety of human specimens, including invasive duct carcinoma (IDC) with multiple grades, several types of primary tumors to local and distant relapses, lymph node metastases and circulating tumor cells (CTCs).

METHODS

Nectin-4 was overexpressed in more than 92% of samples with 65.2% Nectin-4-positive cells. The level of expression was increased with increasing tumor grade (GI-III) and size (T1-4) of IDC specimens.

RESULTS

More induction of Nectin-4 was noted in relapsed samples from a variety of tumors (colon, tongue, liver, kidney, ovary, buccal mucosa) in comparison to primary tumors, while paired adjacent normal tissues do not express any Nectin-4. A high expression of Nectin-4 along with other representative markers in CTCs and lymph node metastasis was also observed in cancer specimens. An increased level of Nectin-4 along with representative metastatic (CD-44, Sca1, ALDH1, Nanog) and angiogenic (Ang-I, Ang-II, VEGF) markers were noted in metastatic tumors (local and distant) in comparison to primary tumors that were correlated with different grades of tumor progression. In addition, greater expression of Nectin-4 was observed in secondary tumors (distant metastasis, e.g., breast to liver or stomach to gall bladder) in comparison to primary tumors.

CONCLUSION

Our study demonstrated a significant correlation between Nectin-4 expression and tumor grade as well as stages (p < 0.001), suggesting its association with tumor progression. Nectin-4 was overexpressed at all stages of metastasis and angiogenesis, thus appearing to play a major role in tumor relapse through the PI3K-Akt-NFκβ pathway.

The splicing component ISY1 regulates APE1 in base excision repair

The integrity of cellular genome is continuously challenged by endogenous and exogenous DNA damaging agents. If DNA damage is not removed in a timely fashion the replisome may stall at DNA lesions, causing fork collapse and genetic instability. Base excision DNA repair (BER) is the most important pathway for the removal of oxidized or mono-alkylated DNA. While the main components of the BER pathway are well defined, its regulatory mechanism is not yet understood. We report here that the splicing factor ISY1 enhances apurinic/apyrimidinic endonuclease 1 (APE1) activity, the multifunctional enzyme in BER, by promoting its 5'-3' endonuclease activity. ISY1 expression is induced by oxidative damage, which would provide an immediate up-regulation of APE1 activity in vivo and enhance BER of oxidized bases. We further found that APE1 and ISY1 interact, and ISY1 enhances the ability of APE1 to recognize abasic sites in DNA. Using purified recombinant proteins, we reconstituted BER and demonstrated that ISY1 markedly promoted APE1 activity in both the short- and long-patch BER pathways. Our study identified ISY1 as a regulator of the BER pathway, which would be of physiological relevance where suboptimal levels of APE1 are present. The interaction of ISY1 and APE1 also establishes a connection between DNA damage repair and pre-mRNA splicing.

Abstract 1758: Splicing component ISY1 interacts with APE1 and regulates base excision repair

Cellular genome is continuously challenged by endogenous and exogenous DNA damaging agents. In the genome, base modifications are the most common form of DNA damage. Base excision DNA repair (BER) is the most important pathway for the removal of oxidized or alkylated DNA. If these base modifications continue to persist, the replisome may stall at DNA lesions, causing the replication fork to collapse, leading to genetic instability. While the main components of the BER pathway are well defined, its regulatory mechanism remains poorly understood. We report here that apurinic/apyrimidinic endonuclease 1 (APE1), a multifunctional protein interacts with the pre-mRNA splicing factor ISY1. However, this interaction is independent of DNA or RNA based upon our pull-down experimental results. ISY1 expression is induced by oxidative or DNA alkylation damage, which would then provide an immediate up-regulation of APE1 activity in vivo and enhanced BER of oxidized bases. This was supported from our results of in vitro reconstituted experiment suggesting that ISY1 can stimulate 5’-3’ endonuclease 1 activity of APE1 in both the short- and long-patch BER pathways and increase its binding to AP site DNA. The interaction between ISY1 and APE1 also establishes a connection between DNA damage repair and pre-mRNA splicing. Based upon these results, we propose that ISY1 is an important regulator of BER and enhances the ability of APE1 to efficiently recognize abasic sites in DNA. Role of ISY1 becomes important in aging tissues where decreased APE1 activity results in the accumulation of oxidative genomic damages. Therefore, ISY1 may work as an anti-aging factor. Induction of ISY1 in malignancies could constitute a mechanism to avoid apoptotic death after treatment with alkylating agents.

Citation Format: Aruna Jaiswal, Elizabeth Williamson, Bhavita Patel, Gayathri Srinivasan, Kimi Kong, Carrie Lomelino, Satya Narayan, Robert Hromas. Splicing component ISY1 interacts with APE1 and regulates base excision repair [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1758.

Nanoquinacrine sensitizes 5-FU-resistant cervical cancer stem-like cells by down-regulating Nectin-4 via ADAM-17 mediated NOTCH deregulation

PURPOSE

Cervical cancer is a major cause of cancer-related death in women world-wide. Although the anti-metabolite 5-FU is widely used for its treatment, its clinical utility is limited due to the frequent occurrence of drug resistance during metastasis. Cancer stem-like cells (CSCs), present in the heterogeneous population of CC cells, are thought to contribute to this resistance. Nectin-4, a CSC marker, is known to play an important role in the cellular aggressiveness associated with metastatic CC. This study was designed to assess the role of Nectin-4 in the acquisition of 5-FU resistance by metastatic CC cells, including its relation to the NOTCH signalling pathway.

METHODS

5FU-resistant CC cell lines were deduced from ME-180 and SiHA cells by continuous exposure to a single concentration of 5-FU. Thymidylate synthase (TS) positive cells were isolated from the 5-FU resistant cells, after which a metastatic model was developed. The role of Nectin-4 in the sensitization of 5-FU resistant metastatic CC cells upon incubation with Nano-formulated Quinacrine (NQC) was investigated using multiple bioassays including MTT, FACS, ELISA, immunoflurescence, Western blotting, comet and in vivo plasmid-based short patch and long patch base excision repair assays.

RESULTS

We found that the expression level of Nectin-4, as well as that of other CSC markers (Oct-4, β-catenin, SOX2) and representative NOTCH signalling components (NOTCH-1, Jagged-1, γ-secretase, ADAM-17) were elevated in the 5-FU resistant metastatic cells compared to those in control cells. Increased nuclear translocation of Nectin-4 and increased proliferation and invasion rates were observed after culturing the metastatic cells under hypoxic conditions. Treatment with NQC inhibited the nuclear translocation of Nectin-4 and decreased the proliferation and invasion rates of the cells by inhibiting the induction of base excision repair (BER) pathway components and ADAM-17 expression levels. After combination treatment of Nectin-4 overexpressing metastatic CC cells with a specific ADAM-17 inhibitor (GW280264) and NQC, a decreased Nectin-4 expression, without alterations in BER and/or other NOTCH pathway components, was noted.

CONCLUSION

Our data indicate that Nectin-4 may play a prominent role in 5-FU resistance of metastatic CC cells and that NQC sensitizes these cells by Nectin-4 deregulation through ADAM-17 inhibition, a major component of the NOTCH signalling pathway.

A novel proteotoxic combination therapy for EGFR+ and HER2+ cancers

While HER2 and EGFR are overexpressed in breast cancers and multiple other types of tumors, the use of EGFR and/or HER2 inhibitors have failed to cure many cancer patients, largely because cancers acquire resistance to HER2/EGFR-specific drugs. Cancers that overexpress the HER-family proteins EGFR, HER2, and HER3 are uniquely sensitive to agents that disrupt HER2 and EGFR protein folding. We previously showed that disruption of disulfide bond formation by Disulfide Disrupting Agents (DDAs) kills HER2/EGFR overexpressing cells through multiple mechanisms. Herein, we show that interference with proline isomerization in HER2/EGFR overexpressing cells also induces cancer cell death. The peptidyl-prolyl isomerase inhibitor Cyclosporine A (CsA) selectively kills EGFR+ or HER2+ breast cancer cells in vitro by activating caspase-dependent apoptotic pathways. Further, CsA synergizes with the DDA tcyDTDO to kill HER2/EGFR overexpressing cells in vitro and the two agents cooperate to kill HER2+ tumors in vivo. There is a critical need for novel strategies to target HER2+ and EGFR+ cancers that are resistant to currently available mechanism-based agents. Drugs that target HER2/EGFR protein folding, including DDAs and CsA, have the potential to kill cancers that overexpress EGFR or HER2 through the induction of proteostatic synthetic lethality.

ASR352, A potent anticancer agent: Synthesis, preliminary SAR, and biological activities against colorectal cancer bulk, 5-fluorouracil/oxaliplatin resistant and stem cells

Despite new agent development and short-term benefits in patients with colorectal cancer (CRC), metastatic CRC cure rates have not improved due to high rates of 5-fluorouracil (5-FU)/leucovorin/oxaliplatin (FOLFOX)-resistance and a clinical therapeutic plateau. At the same time, this treatment regime leads to significant toxicity, cost, and patient inconvenience. Drug-resistance is linked to CRC stem cells, which are associated with the epidermal-to-mesenchymal transition (EMT) pathway. Thus, to optimally treat CRC, a therapy that can target the cell survival and EMT pathways in both CRC bulk and stem cell populations is critical. We recently identified a novel small molecule NSC30049 (7a) that is effective alone, and in combination potentiates 5-FU-mediated growth inhibition of CRC bulk, FOLFOX-resistant, and CRC stem cells both in vitro and in vivo models. In the present study, we report the synthesis and anti-CRC evaluation of several stable and effective 7a analogs. ASR352 (7b) was identified as one of the equipotent 7a analogs that inhibited the growth of CRC bulk cells, sensitized FOLFOX-resistant cells, and reduced the sphere formation capacity of CRC stem cells. It appears that the complex mechanism of cytotoxicity for 7b includes abrogation of 5-FU-induced the S phase, reduction of the phosphorylation of Chk1 at S317P, S345P and S296P, increased γH2AX staining, activation of caspase 3/PARP1 cleavage, and enhancement of Bax/Bcl2 ratio. Further 7b-mediated reduced phosphorylation of Chk1 was an indirect effect, since it did not inhibit Chk1 activity in an in vitro kinase assay. Our findings suggest that 7b as a single agent, or in combination with 5-FU can be developed as a therapeutic agent in CRC bulk, FOLFOX-resistant, and CRC stem cell populations for unmanageable metastatic CRC conditions.

Visceral leishmaniasis: A novel nuclear envelope protein 'nucleoporins-93 (NUP-93)' from Leishmania donovani prompts macrophage signaling for T-cell activation towards host protective immune response

The shift of macrophage and T-cell repertoires towards proinflammatory cytokine signalling ensures the generation of host-protective machinery that is otherwise compromised in cases of the intracellular Leishmania parasite. Different groups have attempted to restore host protective immunity. These vaccine candidates showed good responses and protective effects in murine models, but they generally failed during human trials. In the present study, we evaluated the effect of 97 kDa recombinant nucleoporin-93 of Leishmania donovani (rLd-NUP93) on mononuclear cells in healthy and treated visceral leishmaniasis (VL) patients and on THP-1 cell lines. rLd-NUP93 stimulation increased the expression of the early lymphocyte activation marker CD69 on CD4⁺ and CD8⁺ T cells. The expression of the host protective pro-inflammatory cytokines IFN-γ, IL-12 and TNF-α was increased, with a corresponding down-regulation of IL-10 and TGF-β upon rLd-NUP93 stimulation. This immune polarization resulted in the up-regulation of NF-κB p50 with scant expression of SMAD-4. Augmenting lymphocyte proliferation upon priming with rLd-NUP93 ensured its potential for activation and generation of strong T-cell mediated immune responses. This stimulation extended the leishmanicidal activity of macrophages by releasing high amounts of reactive oxygen species (ROS). Further, the leishmanicidal activity of macrophages was intensified by the elevated production of nitric oxide (NO). The fact that this antigen was earlier reported in circulating immune complexes of VL patients highlights its antigenic importance. In addition, in silico analysis suggested the presence of MHC class I and II-restricted epitopes that proficiently trigger CD8⁺ and CD4⁺ T-cells, respectively. This study reported that rLd-NUP93 was an effective immunoprophylactic agent that can be explored in future vaccine design.

Abstract LB-266: Identification of novel checkpoint kinase inhibitor ASR352 with selective activity against 5-FU resistant colorectal cancer cells

Colorectal cancer (CRC) remains the third most common cancer in the United States, with a high mortality rate. More than 1.2 million new cases of CRC are diagnosed every year. Approximately 25% of these patients have metastatic lesions at diagnosis and almost 50% of these patients will eventually develop metastases. 5-Fluorouracil (5-FU) based cytotoxic chemotherapeutics such as FOLFOX and FOLFIRI have demonstrated improved response rates. 5-FU treatment induces DNA damage and stalling of DNA replication forks towards one sided double-strand breaks thus leading to apoptosis. However, these tumors quickly develop resistance to FOLFOX and FOLFIRI by stopping DNA damage process, and at the same time, this treatment regime leads to significant toxicity, cost, and patient inconvenience. To overcome the drug resistance developed in 5-FU based CRC chemotherapy, we looked for critical role of checkpoint kinase 1 (Chk1) that promotes DNA replication forks. Therefore, Chk1 kinase has been a target for developing mono or combination therapeutic agents. Recently, we demonstrated that an orphan azaadamantane molecule NSC30049 (NSC49L) is effective alone, and in combination potentiates 5-FU-mediated growth inhibition of CRC heterogeneous bulk and FOLFOX-resistant cell lines in culture with minimal effect on normal colonic epithelial cells. The pharmacokinetic analysis showed a higher bioavailability of this compound, however, with a short plasma half-life apparently due to reactive alkyl chloride group. To overcome this problem, we designed and synthesized several novel azaadamantane NSC49L analogs, and their cytotoxic efficacy against HCT116 and HT29 colorectal cancer cell lines was evaluated either alone or in combination with 5-FU with different concentrations for 48 h by MTT essay. ASR352 was identified as the best of all synthesized analogs. ASR352 was equally effective as NSC49L in (i) reducing the viability of 5-FU treated HCT116 and HT29 cell lines in a dose-dependent manner, (ii) inhibiting the FOLFOX-resistant HCT116 and HT29 cell lines, (iii) reducing the sphere formation capacity of CA2 cells, a CRC stem cell line, and (iv) causing the abrogation of 5-Fu induced G2/M and S phase arrests in HT29 cells. In addition,ASR352 inhibited the hydroxyurea (HU)-induced phosphorylation of Chk1 (P-Ser317), Chk1 (P-Ser345) and Chk1 (P-Ser296) in HT29 cell lines. In conclusion, a new clinical relevant drug-like molecule ASR352, that targets Chk1 pathway to reduce viability of particularly the 5-FU resistant CRC cells, has been identified.

Citation Format: Srinivasa Ramisetti, Sangyub Kim, Deepkamal Karelia, Junxuan Lu, Shantu Amin, Satya Narayan, Arun K. Sharma. Identification of novel checkpoint kinase inhibitor ASR352 with selective activity against 5-FU resistant colorectal cancer cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-266.

Alpha galactosidase A activity in Parkinson's disease

Glucocerebrosidase (GCase, deficient in Gaucher disease) enzymatic activity measured in dried blood spots of Parkinson's Disease (PD) cases is within healthy range but reduced compared to controls. It is not known whether activities of additional lysosomal enzymes are reduced in dried blood spots in PD. To test whether reduction in lysosomal enzymatic activity in PD is specific to GCase, we measured GCase, acid sphingomyelinase (deficient in Niemann-Pick disease types A and B), alpha galactosidase A (deficient in Fabry), acid alpha-glucosidase (deficient in Pompe) and galactosylceramidase (deficient in Krabbe) enzymatic activities in dried blood spots of PD patients (n = 648) and controls (n = 317) recruited from Columbia University. Full sequencing of glucocerebrosidase (GBA) and the LRRK2 G2019S mutation was performed. Enzymatic activities were compared between PD cases and controls using t-test and regression models adjusted for age, gender, and GBA and LRRK2 G2019S mutation status. Alpha galactosidase A activity was lower in PD cases compared to controls both when only non-carriers were included (excluding all GBA and LRRK2 G2019S carriers and PD cases with age-at-onset below 40) [2.85 μmol/l/h versus 3.12 μmol/l/h, p = 0.018; after controlling for batch effect, p = 0.006 (468 PD cases and 296 controls)], and when including the entire cohort (2.89 μmol/l/h versus 3.10 μmol/l/h, p = 0.040; after controlling for batch effect, p = 0.011). Because the alpha galactosidase A gene is X-linked, we stratified the analyses by sex. Among women who were non-carriers of GBA and LRRK2 G2019S mutations (PD, n = 155; control, n = 194), alpha galactosidase A activity was lower in PD compared to controls (2.77 μmol/l/h versus 3.10 μmol/l/h, p = 0.044; after controlling for a batch effect, p = 0.001). The enzymatic activity of acid sphingomyelinase, acid alpha-glucosidase and galactosylceramidase was not significantly different between PD and controls. In non-carriers, most lysosomal enzyme activities were correlated, with the strongest association in GCase, acid alpha-glucosidase, and alpha galactosidase A (Pearson correlation coefficient between 0.382 and 0.532). In a regression model with all five enzymes among non-carriers (adjusted for sex and age), higher alpha galactosidase A activity was associated with lower odds of PD status (OR = 0.54; 95% CI:0.31-0.95; p = 0.032). When LRRK2 G2019S PD carriers (n = 37) were compared to non-carriers with PD, carriers had higher GCase, acid sphingomyelinase and alpha galactosidase A activity. We conclude that alpha galactosidase A may have a potential independent role in PD, in addition to GCase.

Design and synthesis of novel thiobarbituric acid derivatives targeting both wild-type and BRAF-mutated melanoma cells

A series of novel thio- and seleno-barbituric acid derivatives were synthesized by varying the substituents at N1 and N3 (ethyl, methyl, allyl, and phenyl), and C5 tethered with dienyl and trienyl moieties attached to substituents such as phenyl, 2-furanyl, 2-thiophenyl, 1-naphthyl, and 3-pyridyl. The cytotoxic potential of these derivatives was evaluated by using MTT assay against melanoma cell lines expressing either wild-type (CHL-1) or mutant (UACC 903) BRAF gene. Among all, 2b and 8b were identified as the most potent compounds. Both 2b and 8b inhibited viability of various melanoma cells and induced cell death as evidenced by Live and Dead assay. Western blot analysis showed that they induce PARP cleavage and inhibit anti-apoptotic Bcl-2, Bcl-xL and Survivin in a dose-dependent manner within 24 h of the treatment. Novel thiobarbituric acid analogs also inhibited viability of various other solid tumor cell lines, such as pancreatic, breast, and colon. Overall, 2b, 2d, and 8b emerged as the most effective compounds and make good leads for the development of future therapeutic agents.

Site-Specific Fluorescence Dynamics To Probe Polar Arrest by Fob1 in Replication Fork Barrier Sequences

Fob1 protein plays an important role in aging and maintains genomic stability by avoiding clashes between the replication and transcription machinery. It facilitates polar arrest by binding to replication fork barrier (RFB) sites, present within the nontranscribed spacer region of the ribosomal DNA. Here, we investigate the mechanism of unidirectional arrest by creating multiple prosthetic forks within the RFB, with fluorescent adenine analogue 2-aminopurine incorporated site-specifically in both the "permissible" and "nonpermissible" directions. The motional dynamics of the RFB-Fob1 complexes analyzed by fluorescence lifetime and fluorescence anisotropy decay kinetics shows that Fob1 adopts a clamp-lock model of arrest and causes stronger perturbation with the bases in the double-stranded region of the nonpermissible-directed forks over those of the permissible directed ones, thereby creating a polar barrier. Corroborative thermal melting studies reveal a skewed distribution of GC content within the RFB sequence that potentially assists in Fob1-mediated arrest.

NSC30049 inhibits Chk1 pathway in 5-FU-resistant CRC bulk and stem cell populations

The 5-fluorouracil (5-FU) treatment induces DNA damage and stalling of DNA replication forks. These stalled replication forks then collapse to form one sided double-strand breaks, leading to apoptosis. However, colorectal cancer (CRC) stem cells rapidly repair the stalled/collapsed replication forks and overcome treatment effects. Recent evidence suggests a critical role of checkpoint kinase 1 (Chk1) in preventing the replicative stress. Therefore, Chk1 kinase has been a target for developing mono or combination therapeutic agents. In the present study, we have identified a novel orphan molecule NSC30049 (NSC49L) that is effective alone, and in combination potentiates 5-FU-mediated growth inhibition of CRC heterogeneous bulk and FOLFOX-resistant cell lines in culture with minimal effect on normal colonic epithelial cells. It also inhibits the sphere forming activity of CRC stem cells, and decreases the expression levels of mRNAs of CRC stem cell marker genes. Results showed that NSC49L induces 5-FU-mediated S-phase cell cycle arrest due to increased load of DNA damage and increased γ-H2AX staining as a mechanism of cytotoxicity. The pharmacokinetic analysis showed a higher bioavailability of this compound, however, with a short plasma half-life. The drug is highly tolerated by animals with no pathological aberrations. Furthermore, NSC49L showed very potent activity in a HDTX model of CRC stem cell tumors either alone or in combination with 5-FU. Thus, NSC49L as a single agent or combined with 5-FU can be developed as a therapeutic agent by targeting the Chk1 pathway in 5-FU-resistant CRC heterogeneous bulk and CRC stem cell populations.