Antifolate Agent Research Articles

Establishment and Characterization of Pemetrexed-resistant NCI-H460/PMT Cells.

Pemetrexed (PMT) is a multitargeted antifolate agent that is used for treating patients with Non-Small Cell Lung Cancer (NSCLC). However, patients have presented clinical responses of drug resistance to PMT. This study aimed to explore the underlying mechanisms of PMT resistance in NSCLC cells. PMT-resistant NCI-H460/PMT cells were established by treating with PMT in a concentrationescalation manner. MTT assay and colony formation were performed to detect cell proliferation. Immunofluorescence was used to detect the expression of Ki-67. Transwell assay was performed to measure cell migration ability. qPCR and Western blot were used to detect the mRNA and protein expression levels of indicated genes. Small interfering RNAs (siRNA) were used to knockdown ATP binding cassette subfamily B member 1 (ABCB1) and Thymidylate Synthase (TYMS). This study showed that compared with the parental cells, the NCI-H460/PMT cells displayed weakened proliferation and enhanced cell mobility. In addition, the NCI-H460/PMT cells demonstrated cellular senescence, which might result in PMT resistance. The NCI-H460/PMT cells exhibited cross-resistance to other chemotherapeutics, including fluorouracil, paclitaxel, doxorubicin, etoposide and gemcitabine, possibly because of the upregulated expression of ABCB1. However, the ABCB1 knockdown by siRNA failed to eradicate PMT resistance. Moreover, TYMS, a target of PMT, was obviously upregulated in the resistant cells. The genetic silence of TYMS partially abrogated PMT resistance, suggesting that the overexpression of TYMS was a key resistant mechanism of PMT. The overexpression of TYMS was an important resistance mechanism of PMT for KRAS-mutated NCI-H460 cells. Cross-resistance to other chemotherapeutics should be considered in addressing PMT resistance.

Abstract 385: MTAP gene deficiency creates vulnerability to anti-folate therapy in urothelial bladder carcinoma

Abstract Background: The methylthioadenosine phosphorylase (MTAP) gene encodes an essential enzyme for the salvage pathway of adenosine synthesis and is frequently lost in different types of cancer including urothelial bladder carcinoma. Therefore, MTAP-deficient tumors are theoretically very sensitive to anti-folate agents such as pemetrexed that can effectively block the de novo pathway of adenosine synthesis and as a result, create a state of synthetic lethality. We thus hypothesize that tumor MTAP gene deficiency is associated with response to pemetrexed therapy in bladder cancer. Methods: In this study, we investigated MTAP gene deficiency rates in the TCGA database and confirmed MTAP protein loss by immunohistochemistry using a tumor tissue microarray containing bladder tumor tissues from 151 patients. We then performed in vitro and in vivo studies using MTAP-proficient and MTAP-deficient human bladder cancer cell lines. Functional loss of MTAP was verified with mass spectrometry, which detects its substrate methylthioadenosine (MTA) levels. We also correlated these pre-clinical studies with clinical response data on patients with metastatic bladder cancer treated with pemetrexed. Results: We identified that 27.8% bladder cancer patients have MTAP protein deficiency, which is consistent with exome sequencing data from the TCGA database. In vitro data showed MTAP-deficient human bladder cancer cell lines were significantly more sensitive to pemetrexed, with IC50 at least 40 times lower than MTAP-proficient cell lines. Subsequent knockdown of the MTAP gene in MTAP-proficient cell lines increased sensitivities to pemetrexed treatment. Consistent with the in vitro data, pemetrexed significantly inhibited the growth of MTAP-deficient or knockdown xenograft tumors but not MTAP-proficient tumors. Furthermore, 4 of 4 (100%) patients with MTAP-deficient metastatic bladder cancer responded to pemetrexed treatment, whereas only 1 of 11 (9%) patients with MTAP-proficient metastatic bladder cancer responded to pemetrexed. Conclusion: Our data demonstrate that MTAP gene loss in urothelial bladder cancer leads to a metabolic state of synthetic lethality with pemetrexed therapy. Therefore, bladder tumor MTAP loss should be further investigated as a potential biomarker for selection of patients for anti-folate therapy. Citation Format: Jianfeng Chen, Omar Alhalabi, Guangchun Han, Wei-Lien Wang, Xin-Qiao Zhang, Jian H. Song, Lidia P. Lopez, Sumankalai Ramachandran, Anh G. Hoang, Tyrone Garnett, Matthew Campbell, Amishi Y. Shah, Jennifer Wang, Arlene O. Siefker-Radtke, Shi-Ming Tu, Mark Titus, Charles C. Guo, Gary E. Gallick, Eleni Efstathiou, William F. Benedict, Christopher J. Logothetis, Thai H. Ho, Linghua Wang, Jianjun Gao. MTAP gene deficiency creates vulnerability to anti-folate therapy in urothelial bladder carcinoma [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 385.

Correlation of methylthioadenosine phosphorylase (MTAP) loss with response to anti-folate therapy in urothelial bladder carcinoma (UBC).

4521 Background: The MTAP gene encodes an essential enzyme for the salvage pathway of nucleotide synthesis and is frequently deleted in UBC. Anti-folate agents such as pemetrexed can effectively inhibit the de novo pathway of nucleotide synthesis and as a result, create a synthetic lethality in MTAP deficient UBC. We hypothesize that MTAP gene loss correlates with enhanced response to pemetrexed in UBC. Methods: We investigated MTAP gene deletion rates in the TCGA database and determined MTAP protein loss rates by immunohistochemistry (IHC) using a UBC tissue microarray (TMA) from 151 patients (pts). We then performed in vitro and in vivo studies using MTAP proficient and MTAP deficient bladder cancer cell lines. At the clinical level, we performed a retrospective analysis based on MTAP status of pts treated with pemetrexed as 2nd line at our institution between 2014 and 2018. We are now enrolling pts in a single-arm, open-label, phase II clinical trial (NCT02693717) with pemetrexed in pts with MTAP deficient UBC. Results: Per our TCGA and TMA IHC analyses, MTAP deficiency rate was 25.9% and 27.8%, respectively. MTAP deficient UBC cell lines were at least 40 times more sensitive to pemetrexed than MTAP proficient lines. Knockdown of the MTAP gene increased apoptosis rate by pemetrexed from approximately 20% to 60%. Additionally, pemetrexed significantly inhibited the growth of MTAP deficient or knockdown xenograft tumors but not MTAP proficient tumors. Retrospective analysis of 12 pts using RECIST criteria indicated that all 4 MTAP deficient UBC pts responded to pemetrexed whereas only 1 of 8 (12.5%) MTAP proficient UBC pts responded. Of the 6 pts enrolled on the clinical trial, 3 (50%) had complete or partial response, 1 had stable disease, 1 was not evaluable and 1 had disease progression. Combined analysis of the entire experience demonstrates a higher response rate in MTAP deficient UBC (70%) as compared to MTAP proficient UBC (12.5%). Conclusions: Our preclinical and clinical data demonstrate that MTAP loss in UBC leads to a state of synthetic lethality when treated with pemetrexed and should be further investigated as a novel biomarker to predict response to anti-folate agents.

A retrospective analysis of elderly population with metastatic colorectal cancer treated with raltitrexed in the target therapy era.

e23022 Background: Raltitrexed is a antifolate chemotherapy agent with activity against metastatic colorectal cancer (mCRC). Most clinical trials with raltitrexed were performed before approval of anti-EGFR and anti-VEGF therapies. Its toxity profile suggests that might be a useful drug to treat elder patients, but there are no specific data in this population group. Methods: A retrospective review of elderly patients (70 years or older) with mCRC treated with raltitrexed monotherapy in our hospital between 2008 and 2017 was conducted. All of them had received previously oxaliplatin, irinotecan, fluoropyrimidines, and bevacizumab as standard therapy. All RAS native patients had received also anti-EGFR drugs. Results: Eighteen elder patients were reviewed, 11 (61%) male. Age ranged 70-85 years (median 78). All patients had ECOG PS 0 or 1. Locations were rectum (4), right colon (8), and left colon (6). Number of treatment lines ranged 2-5 (median 3). Three pts (16%) had received regorafenib previously. KRAS and BRAF were mutated in 61% and 5% respectively. Median number of cycles was 3 (1-13). Response rate was 11% (2 partial responses). Stable disease was achieved in 33%. Median progression-free and global survival were 2.8 (95% CI 1.2-10) and 5.9 (95% CI 1.6-18) months respectively. Grade 3-4 hematologic and non-hematologic toxicities were present in 22% and 5.5% respectively. Dose reduction was needed only in 11%. Sex, location, RAS status were not related to response or survival. Conclusions: Raltitrexed is a well tolerated option por elderly patients after standard treatment of mCRC.

A phase II trial to evaluate pemetrexed clinical responses in relation to tumor methylthioadenosine phosphorylase (MTAP) gene status in patients with previously treated metastatic urothelial carcinoma.

385 Background: According to The Cancer Genome Atlas, 26.8% of bladder tumors harbor homozygous deletion of the MTAP gene, which encodes for an essential enzyme for the salvage pathway of nucleotide synthesis. Pemetrexed is a well-known anti-folate agent that inhibits the de novo pathway of nucleotide synthesis. Therefore, we hypothesized that tumors with MTAP gene loss have a synthetic lethality to pemetrexed due to loss of both essential nucleotide synthesis pathways. We proposed a study to determine pemetrexed response rate in patients with MTAP-deficient metastatic urothelial carcinoma (mUC). Methods: We carried out a single-arm, open-label, phase II clinical trial with pemetrexed in patients with mUC and MTAP loss by immunohistochemistry. This is an interim analysis of results. Each patient receives pemetrexed (500 mg/m2) on day 1 of each 21-day cycle. Pemetrexed is continued until progression of disease (PD) and a repeat biopsy is obtained at that time. Pre- and post-treatment blood, urine and tumor samples are obtained for dynamic monitoring of immune and molecular correlates to clinical activity. Results: Six patients have been enrolled on this trial and all have received at least one previous treatment including a cisplatin-containing regimen in 5 (83%) patients and an immune checkpoint inhibitor in 4 (66%) patients. Of these 6 patients, 1 (17%) had complete response (CR); two (33%) had partial response (PR); 1 (17%) had stable disease; 1 (17%) was not evaluable; 1 (17%) had PD. Treatment was generally well tolerated with mostly grade 1 or 2 adverse events. Only 2 of 6 patients developed grade 3 anemia. Immunologic and molecular analyses are ongoing on all collected samples. Conclusions: Our study show that in heavily pretreated MTAP deficient mUC patients, pemetrexed is still an effective and well-tolerated therapy with an objective response rate (ORR=CR+PR) of 50%, which is higher than previously reported pemetrexed activity (ORR=8-28%) as first or second line treatment for mUC. Clinical trial information: NCT02693717.

Pemetrexed exerts anticancer effects by inducing G0/G1‑phase cell cycle arrest and activating the NOXA/Mcl‑1 axis in human esophageal squamous cell carcinoma cells

Esophageal squamous cell carcinoma (ESCC) is a dominant histological subtype of esophageal cancer with notably high incidence and mortality rates. Pemetrexed is a clinical antifolate therapeutic agent with anticancer properties. The present study aimed to understand whether pemetrexed is able to exert anticancer effects on ESCC cells, and to determine the underlying molecular mechanism. ESCC cells were treated with pemetrexed and cell survival was assessed with MTT assays. The cell cycle and apoptosis were evaluated using flow cytometry analysis, and proteins were detected using western blotting. It was demonstrated that pemetrexed inhibited cell survival and induced G0/G1 cell cycle arrest and apoptosis in human ESCC cells. Furthermore, the results demonstrated that the phorbol-12-myristate-13-acetate-induced protein 1/induced myeloid leukemia cell differentiation protein Mcl-1 axis is involved in intrinsic apoptosis induced by pemetrexed. The protein expression of endoplasmic reticulum stress markers inositol-requiring enzyme 1α, binding immunoglobulin protein and CCAAT-enhancer-binding protein homologous protein were upregulated following treatment with pemetrexed. These results suggest that pemetrexed may induce an endoplasmic reticulum stress response while activating intrinsic apoptosis. The present study provided important mechanistic insights into potential cancer treatments involving pemetrexed and enhanced the understanding of human ESCC.

New perspectives in the therapeutic approach of peripheral T-cell lymphoma.

Peripheral T-cell lymphoma (PTCL) is a heterogeneous group of mature T-cell and natural killer (NK)-cell neoplasms in the WHO 2016 classification. Patient prognosis is poor when treated with CHOP, and there is an unmet need for new drugs. Several agents have been developed for PTCL, and their use is the subject of this review. Phase 2 studies demonstrated the activity of new drugs in Relapsed/refractory PTCL. Only four compounds were approved by the food and drug administration: romidepsin and belinostat, which are epigenetic modifiers, the antifolate agent pralatrexate, the immuno-conjugate brentuximab vedotin. New combinations have been tested, but the results were disappointing. Given the latest progress in biology, targeted agents are evaluated in different subtypes of PTCL. Relapsed anaplastic large-cell lymphoma exhibits improved prognosis with the approved anti-CD30 drug conjugate brentuximab vedotin. Localized nasal NK/T is treated with radiotherapy and nonanthracycline chemotherapy with L-asparaginase. Recently, immune checkpoint inhibitors demonstrated activity in NK/T lymphoma and can be used in elderly patients. Treatment remains a challenge for PTCL, and several targeted drugs provide new approaches. Progress will be made incrementally in the different subtypes. One of the critical situations facing new drugs is the ability to run robust clinical trials in rare diseases.

Structure of 6-hydroxymethyl-7,8-dihydropterin pyrophosphokinase–dihydropteroate synthase from Plasmodium vivax sheds light on drug resistance

The genomes of the malaria-causing Plasmodium parasites encode a protein fused of 6-hydroxymethyl-7,8-dihydropterin pyrophosphokinase (HPPK) and dihydropteroate synthase (DHPS) domains that catalyze sequential reactions in the folate biosynthetic pathway. Whereas higher organisms derive folate from their diet and lack the enzymes for its synthesis, most eubacteria and a number of lower eukaryotes including malaria parasites synthesize tetrahydrofolate via DHPS. Plasmodium falciparum (Pf) and Plasmodium vivax (Pv) HPPK-DHPSs are currently targets of drugs like sulfadoxine (SDX). The SDX effectiveness as an antimalarial drug is increasingly diminished by the rise and spread of drug-resistant mutations. Here, we present the crystal structure of PvHPPK-DHPS in complex with four substrates/analogs, revealing the bifunctional PvHPPK-DHPS architecture in an unprecedented state of enzymatic activation. SDX's effect on HPPK-DHPS is due to 4-amino benzoic acid (pABA) mimicry, and the PvHPPK-DHPS structure sheds light on the SDX-binding cavity, as well as on mutations that effect SDX potency. We mapped five dominant drug resistance mutations in PvHPPK-DHPS: S382A, A383G, K512E/D, A553G, and V585A, most of which occur individually or in clusters proximal to the pABA-binding site. We found that these resistance mutations subtly alter the intricate enzyme/pABA/SDX interactions such that DHPS affinity for pABA is diminished only moderately, but its affinity for SDX is changed substantially. In conclusion, the PvHPPK-DHPS structure rationalizes and unravels the structural bases for SDX resistance mutations and highlights architectural features in HPPK-DHPSs from malaria parasites that can form the basis for developing next-generation anti-folate agents to combat malaria parasites.

A Phase II Study of Pemetrexed in Patients with Recurrent Thymoma and Thymic Carcinoma

IntroductionThymoma and thymic carcinoma (TC) are neoplastic diseases with reported chemosensitivity to a broad range of agents. However, because of the rarity of these diseases, few prospective trials have been conducted in patients with advanced thymic malignancies. We conducted a prospective phase II trial to evaluate the clinical activity of pemetrexed, a multitargeted antifolate agent, in previously treated patients with thymoma and TC. MethodsA total of 27 previously treated patients (16 with thymoma and 11 with TC) with advanced, unresectable disease were treated with pemetrexed, 500 mg/m2, intravenously every 3 weeks for a maximum of six cycles or until undue toxicity or progressive disease. All patients received folic acid, vitamin B12, and steroid prophylaxis. ResultsThe median number of cycles administered was 6 (range 1–6). Nine patients with a total of 14 events had grade 3 toxicities; no grade 4 toxicities were noted. In 26 fully evaluable patients, two complete and three partial responses (according to the Response Evaluation Criteria in Solid Tumors) were documented (all in patients with stage IVA thymoma, except for one partial response with stage IVA TC). A total of 14 patients completed the full six cycles of treatment, 7 patients progressed while undergoing therapy, 5 patients discontinued therapy because of intolerance, and 1 patient discontinued therapy because of progressive Morvan syndrome. The median progression-free survival time for all patients was 10.6 months (12.1 months for those with thymoma versus 2.9 months for those with TC). With 23 deaths at data cutoff, the median overall survival time was 28.7 months (46.4 months for those with thymoma versus 9.8 months for those with TC). ConclusionsPemetrexed is an active agent in this heavily pretreated population of patients with recurrent thymic malignancies, especially thymoma.

High UDG and BRCA1 expression is associated with adverse outcome in patients with pemetrexed treated non-small cell lung Cancer

ObjectiveThe antifolate chemotherapy agent pemetrexed has been widely used to treat non-small-cell-lung-cancer (NSCLC), but there is no clinically validated biomarker to select patients likely to respond. The aim of this study was to assess two proteins involved in DNA repair mechanisms, uracil DNA glycosylase (UDG) and BRCA1 as potential prognostic biomarkers in NSCLC patients treated with pemetrexed-based chemotherapy. Material and methodsFormalin-fixed-paraffin-embedded tumor specimens from 119 patients with advanced NSCLC treated with pemetrexed between 2004 and 2011 were retrospectively analyzed. Expression of UDG, BRCA1, and known prognostic factors ALK, TTF-1, thymidylate synthase and folylpolyglutamate synthase was assessed by immunohistochemistry using H-SCORE (product of percent stained cells and intensity of expression). Progression-free (PFS) and overall survival (OS) served as reference endpoint. ResultsMost NSCLC tumor samples had UDG positivity in at least 5% of tumor cells and 34% samples had more than 50% positive tumor cells. Using the median expression value as threshold, high UDG expression (H-SCORE≥75) was significantly associated with shorter median PFS (3-year PFS 7% vs. 37%, p = 0.045) and a trend for shorter OS (3-year OS 15% vs 42%, p = 0.066) compared to patients with low UDG. In multivariable Cox analysis, the association between high UDG and shorter PFS was close to statistically significant (p = 0.08) at a significance level of 0.05 after controlling for age, gender, ALK- and TTF1-status with hazard ratio of 2.1. Grouping patients according to combined UDG and BRCA1 expression, patients with a profile of UDGhigh/BRCA1high had the shortest PFS and OS compared to all other patient groups (p = 0.007 and 0.02, respectively). ConclusionOur results demonstrate an important prognostic role for high UDG expression in pemetrexed-treated NSCLC patients, in addition to its previously reported role in pemetrexed cytotoxicity. High UDG expression was predictive of shorter PFS and OS, and patients with a combined profile of UDGhigh/BRCA1high had the poorest outcome following pemetrexed treatment.

Abstract 2448: Chemotherapy drug-induced AXL activation and cell survival signaling via reactive oxygen species that can be inhibited to enhance drug efficacy in mesothelioma

Abstract Cellular oxidative stress is characterized by elevated reactive oxygen species (ROS), and is a frequent phenotype of cancer cells. The consequences of ROS are complex, where ROS can promote or inhibit tumorigenesis. In mesothelioma, asbestos exposure to serous membranes induces ROS through iron content and chronic inflammation, and ROS promote cell survival signaling in mesothelioma. On the other hand, a current chemotherapy regime for mesothelioma consisting of a platinum and antifolate agent combination also induce ROS. Mesothelioma is notoriously chemotherapy-resistant, and we propose that ROS induced by cisplatin and pemetrexed may promote cell survival signaling pathways, which ultimately may contribute to chemotherapy resistance. In The Cancer Genome Atlas datasets, we found AXL kinase expression is relatively high in mesothelioma compared to other cancer samples. We showed that ROS induce the phosphorylation of AXL, which was blocked by the selective inhibitor BGB324 in VMC40 and P31 mesothelioma cells. We also showed that cisplatin and pemetrexed induce the phosphorylation of AXL and Akt, which was also blocked by BGB324 as well as by N-acetylcysteine antioxidant. AXL knockdown in these cells enhances sensitivity to cisplatin and pemetrexed. Similarly, AXL inhibitor BGB324 also enhances sensitivity to cisplatin and pemetrexed. Finally, higher synergy was observed when cells were pretreated with BGB324 before adding chemotherapy. These results demonstrate cisplatin and pemetrexed induce ROS that activate AXL, and blocking AXL activation enhances the efficacy of cisplatin and pemetrexed. These results suggest AXL inhibition may represent an effective strategy to enhance the efficacy of chemotherapy in mesothelioma. We further hypothesize AXL signaling may be part of an adaptive response to chemotherapeutic agents, providing transient resistance to cisplatin and pemetrexed that may ultimately contribute to acquired chemotherapy resistance. Citation Format: Derek B. Oien, Tamás Garay, Sarah Eckstein, Jeremy Chien. Chemotherapy drug-induced AXL activation and cell survival signaling via reactive oxygen species that can be inhibited to enhance drug efficacy in mesothelioma [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 2448.

Lung cancer specific and reduction-responsive chimaeric polymersomes for highly efficient loading of pemetrexed and targeted suppression of lung tumor in vivo

Lung cancer is one of the worldwide leading and fast-growing malignancies. Pemetrexed disodium (PEM, Alimta®), a small hydrophilic drug, is currently used for treating lung cancer patients. However, PEM suffers from issues like fast elimination, low bioavailability, poor tumor cell selectivity and penetration. Here, we report on lung cancer specific CSNIDARAC (CC9) peptide-functionalized reduction-responsive chimaeric polymersomes (CC9-RCPs) for efficient encapsulation and targeted delivery of PEM to H460 human lung cancer cells in vitro and in vivo. PEM-loaded CC9-RCPs (PEM-CC9-RCPs) was obtained from co-self-assembly of poly(ethylene glycol)-b-poly(trimethylene carbonate-co-dithiolane trimethylene carbonate)-b-polyethylenimine (PEG-P(TMC-DTC)-PEI) and CC9-functionalized PEG-P(TMC-DTC) in the presence of PEM followed by self-crosslinking. PEM-CC9-RCPs displayed an optimal CC9 density of 9.0% in targeting H460 cells, a high PEM loading content of 14.2 wt%, a small hydrodynamic size of ca. 60 nm and glutathione-triggered PEM release. MTT assays showed that PEM-CC9-RCPs was 2.6- and 10- fold more potent to H460 cells than the non-targeting PEM-RCPs and free PEM controls, respectively. Interestingly, PEM-CC9-RCPs exhibited 22-fold longer circulation time and 9.1-fold higher accumulation in H460 tumor than clinical formulation Alimta®. Moreover, CC9-RCPs showed obviously better tumor penetration than RCPs. Remarkably, PEM-CC9-RCPs at 12.5 mg PEM equiv./kg effectively suppressed growth of H460 xenografts and significantly prolonged mouse survival time as compared to PEM-RCPs and Alimta® controls. These lung cancer specific and reduction-responsive chimaeric polymersomes provide a unique pemetrexed nanoformulation for targeted lung cancer therapy. Statement of SignificanceMultitargeted antifolate agent pemetrexed (PEM, Alimta®) is currently used for treating lung cancer patients and has low side-effects. However, PEM suffers from issues like fast elimination, low bioavailability, poor tumor cell selectivity and penetration. Scarce work on targeted delivery of PEM has been reported, partly because most conventional nanocarriers show a low and instable loading for hydrophilic, negatively charged drugs like PEM. Herewith, we report on lung cancer specific CSNIDARAC (CC9) peptide-functionalized reduction-responsive chimaeric polymersomes (CC9-RCPs) which showed efficient PEM encapsulation (14.2 wt%, 60 nm) and targeted delivery of PEM to H460 human lung cancer cells, leading to effective suppression of H460 tumor xenografts and significantly prolonged survival rates of mice than Alimta®. To the best of our knowledge, this represents a first report on targeted nanosystems that are capable of efficient loading and targeted delivery of PEM to lung tumors.

Cisplatin and Pemetrexed Activate AXL and AXL Inhibitor BGB324 Enhances Mesothelioma Cell Death from Chemotherapy.

Reactive oxygen species (ROS) can promote or inhibit tumorigenesis. In mesothelioma, asbestos exposure to serous membranes induces ROS through iron content and chronic inflammation, and ROS promote cell survival signaling in mesothelioma. Moreover, a current chemotherapy regimen for mesothelioma consisting of a platinum and antifolate agent combination also induce ROS. Mesothelioma is notoriously chemotherapy-resistant, and we propose that ROS induced by cisplatin and pemetrexed may promote cell survival signaling pathways, which ultimately may contribute to chemotherapy resistance. In The Cancer Genome Atlas datasets, we found AXL kinase expression is relatively high in mesothelioma compared to other cancer samples. We showed that ROS induce the phosphorylation of AXL, which was blocked by the selective inhibitor BGB324 in VMC40 and P31 mesothelioma cells. We also showed that cisplatin and pemetrexed induce the phosphorylation of AXL and Akt, which was also blocked by BGB324 as well as by N-acetylcysteine antioxidant. AXL knockdown in these cells enhances sensitivity to cisplatin and pemetrexed. Similarly, AXL inhibitor BGB324 also enhances sensitivity to cisplatin and pemetrexed. Finally, higher synergy was observed when cells were pretreated with BGB324 before adding chemotherapy. These results demonstrate cisplatin and pemetrexed induce ROS that activate AXL, and blocking AXL activation enhances the efficacy of cisplatin and pemetrexed. These results suggest AXL inhibition combined with the current chemotherapy regimen may represent an effective strategy to enhance the efficacy of chemotherapy in mesothelioma. This is the first study, to our knowledge, on chemotherapy-induced activation of AXL and cell survival pathways associated with ROS signaling.

In silico Identification of Novel Inhibitors against Plasmodium falciparum Triosephosphate Isomerase from Anti-Folate Agents

Malaria is a disease prevalent across majority of countries across the world—a reported 3.2 billion people are at risk of transmission according to World Health Organization (WHO) as of December 2015. There are reports of hundreds of thousands of deaths, with children and pregnant women succumbing to the disease at an alarmingly high rate. The disease occurs due the transmission of the Plasmodium species, which has evolved to become resistant to several drugs. Thus, finding new drug targets has become important. In this study, we have focused upon Triose phosphate isomerase (TIM) as a potential drug target for antifolate drugs. The structure of the protein was retrieved from PDB database, and the active site was identified. Nine antifolate compounds were tested against the protein, and the compounds Nolatrexed, Lometrexol and Pemetrexed were identified as the best inhibitors for the protein. Moreover, the results presented TIM as a good prospective drug target for antimalarial drugs.

Abstract A074: Killing late-stage cancer cells by coupling DNA damage induction with MAPK pathway activation

Abstract Acquired resistance of metastatic melanoma (MM) tumors to BRAF V600E inhibitors (BRAFis) is commonplace in the clinic. Habitual relapse of patients contributes to <20% 5-year survival rates in MM. We previously identified serine synthesis as a critical mechanism of late-stage cancer cell resistance to BRAFis. Pretreatment with DNA-damaging agent and nucleoside analog gemcitabine resensitized drug-resistant cancer cells to BRAFis dabrafenib (Tafinlar) and vemurafenib (Zelboraf). The combination treatments were effective against BRAF wild type cancer cells, potentially expanding the clinical reach of BRAFis. In this study, we identify two additional DNA-damaging agents that resensitized drug-resistant MM and pancreatic cancer cells to BRAFis dabrafenib and encorafenib. We identify the antifolate and DNA-damaging agent methotrexate (MTX), and the topoisomerase 1 inhibitor and DNA-damaging agent camptothecin (Camp) as sensitizers of late-stage, drug-resistant cancer cells to BRAFis dabrafenib and encorafenib (LGX818). Importantly, we show a novel positive correlation between DNA repair delay and and allosteric MAPK activation via BRAFi treatment in BRAF wild type cells. Cells arrest in G1/S following DNA-damaging agent + BRAFi combination treatments and ultimately, cell death is triggered via apoptosis, presumably due to DNA damage repair delays. Additionally, we have identified activating KRAS codon 12 mutations as critical to the efficacy of combination treatments. In summary, we have elucidated a novel method of cell death induction via DNA-damaging agent + BRAFi combination treatments that has the potential to significantly impact late-stage MM and pancreatic cancer therapy in the clinic. Citation Format: Vikram Bhattacharjee. Killing late-stage cancer cells by coupling DNA damage induction with MAPK pathway activation [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr A074.

Pemetrexed degradation by photocatalytic process: Kinetics, identification of transformation products and estimation of toxicity

This study employed a UV-A/visible/TiO2 system to investigate the degradation of pemetrexed, an antifolate agent used in chemotherapy. The laboratory-scale method employed a photostability chamber that could be used to study multiple samples. Reversed-phase HPLC coupled with high-resolution ESI-LTQ-Orbitrap mass spectrometry was used to determine the transformation products (TPs) of PEME. Based on the identified TPs and existing chemical knowledge, the mechanism of degradation of the target compound was proposed. Concentrations were monitored as a function of time, and the degradation kinetics were compared. The structures of seven TPs, four of which have not been described to date, were proposed. Most of the TPs stemmed from OH radical additions to the dihydropyrrole moiety and oxidative decarboxylation of the glutamate residue. Based on the elucidated structures, a computational toxicity assessment was performed, showing that the TPs with higher log D values than the parent compound are more toxic than the PEME itself. To support these findings, the toxicities of irradiated samples on Vibrio fischeri were monitored over time. The experimental results corresponded well with the results of previous computational studies.

The role of mitochondrial folate enzyme MTHFD1L in esophageal squamous cell carcinoma

Objective: The lack of novel therapeutic targets poses the major challenge to prolong survival and improve the quality of life for esophageal squamous cell carcinoma (ESCC). Methylenetetrahydrofolate dehydrogenase 1-like (MTHFD1L) plays critical roles in folate cycle maintenance. However, little information is available concerning the role of MTHFD1L in cancer cells, and no studies have addressed such issues in esophageal cancer.Materials and method: Surgical cancer and adjacent normal esophageal tissues were obtained from patients with esophagectomy and esophagogastrostomy for ESCC. Western blot, immunohistochemistry and Quantitative RT-PCR were performed to evaluate protein and RNA expression levels of MTHFD1L. Knockdown of MTHFD1L expression was achieved by using short hairpin RNA. The effects of MTHFD1L silencing on ESCC cell proliferation and apoptosis were assessed by the MTT assay, Celigo assays, Annexin V FACS assay and Caspase-3/7 array in vitro.Results: Twenty-three paired cancer and adjacent normal esophageal tissues from patients with ESCC were included in this study. MTHFD1L protein and RNA expression levels were significantly upregulated in ESCC tissue as compared with normal tissue. High expression of MTHFD1 was also detected in two esophageal cancer cell lines (TE-1 and EC109). Knockdown of MTHFD1L expression inhibited the proliferation of TE-1 cells, and the apoptosis was distinctly increased following shMTHFD1L infection.Conclusions: Our preliminary study highlighted for the first time that MTHFD1L might be involved in the development of ESCC, which may provide a new potential tumor-specific therapeutic targeting for anti-folate agents.

Renal failure during chemotherapy: renal biopsy for assessing subacute nephrotoxicity of pemetrexed

BackgroundPemetrexed, a multitargeted antifolate cytotoxic agent, is currently used primarily in combination with cisplatin for metastatic non-small cell lung cancer and for malignant mesothelioma. Acute renal toxicity of pemetrexed has been recently described with polychemotherapy, in which the individual responsibility of each drug is difficult to establish. Only one recent report documents renal involvement in long-term exposed patients.Case presentationWe report on a case of rapidly progressive nephropathy leading to the cessation of platinum salts and the secondary interruption of pemetrexed and bevacizumab. Acute tubular necrosis shown on the renal biopsy could potentially be due to pemetrexed. Persistent severe renal failure after the resumption of all drugs led to new treatment lines with gemcitabine (while the glomerular filtration rate was below 30 ml/min/1.73m2), then followed by Taxol.ConclusionsThe optimal strategy with regard to renal complications in cancer patients is not clear. Acute or chronic loss in renal function generally leads to a new treatment line, possibly impairing the overall success of the treatment. The use of chemotherapy in patients with a glomerular filtration rate below 30 ml/min/1.73m2 is usually associated with an increased risk of side effects when not contraindicated by renal elimination of the drug.

Investigating the Mechanisms of Methotrexate Neurotoxicity in Patients With Childhood Leukemia and Long-Term Survivors

Background/Objectives Adverse neurological events are common (4-20%) during treatment for pediatric acute lymphoblastic leukaemia (ALL) and include seizures, stroke like syndrome and leukoencephalopathy. In addition, chronic neurotoxicity is emerging as a worrying late effect of treatment with long-term survivors experiencing decreased executive function, processing speed and memory function. Survivors are also at increased risk of experiencing learning difficulties, social withdrawal issues and inattention hyperactivity disorders. Methotrexate, an anti-folate chemotherapy agent, is a mainstay of pediatric leukemia treatment regimens globally and is widely implicated as a cause of these neurological side effects. We hypothesise that methotrexate disrupts DNA methylation via effects on S-adenosyl methionine, a key metabolic component that has previously been described to regulate genes involved in myelination. Design/Methods Using both the oligodendrocytic-like cell line MO3.13 and glial cells derived from induced pluripotent stem cells (iPSC) treated with methotrexate, we assayed for changes in DNA methylation and effects on gene expression using whole-genome methylation arrays and RNAseq, respectively. Genes with corresponding methylation and expression changes were selected for further studies of expression by real-time qPCR and assessment of protein levels. Results We identified DNA methylation and corresponding expression changes in genes involved in neurodevelopmental pathways and neurological disorders. Of particular interest was dose-dependent demethylation and increased gene expression of IRS1, a vital component of insulin signalling pathways that is highly expressed in neural tissue and implicated in regulating cognitive performance. We also detected altered DNA methylation within the PLP1 gene, which encodes the most prevalent protein component of myelin. We found that methotrexate treatment in iPSC-derived oligodendrocytes resulted in increased PLP1 methylation associated with a reduction in PLP1 transcript levels as well as PLP1 protein levels. Conclusions Our work provides insight as to the biological mechanisms behind methotrexate-induced neurological side effects for the first time and implicates altered insulin signalling and myelination pathways as a potential causative factor in neurotoxicity. Further work including the use of animal models is warranted for advancing these results towards informing clinical practice.

Structural analyses of human thymidylate synthase reveal a site that may control conformational switching between active and inactive states

Thymidylate synthase (TS) is the sole enzyme responsible for de novo biosynthesis of thymidylate (TMP) and is essential for cell proliferation and survival. Inhibition of human TS (hTS) has been extensively investigated for cancer chemotherapy, but several aspects of its activity and regulation are still uncertain. In this study, we performed comprehensive structural and biophysical studies of hTS using crystallography and thermal shift assay and provided the first detailed structural information on the conformational changes induced by ligand binding to the hTS active site. We found that upon binding of the antifolate agents raltitrexed and nolatrexed, the two insert regions in hTS, the functions of which are unclear, undergo positional shifts toward the catalytic center. We investigated the inactive conformation of hTS and found that the two insert regions are also involved in the conformational transition between the active and inactive state of hTS. Moreover, we identified a ligand-binding site in the dimer interface, suggesting that the cavity in the dimer interface could serve as an allosteric site of hTS to regulate the conformational switching between the active and inactive states. On the basis of these findings, we propose a regulatory mechanism of hTS activity that involves allosteric regulation of interactions of hTS with its own mRNA depending on cellular demands for TMP.