Resistance to 5-fluorouracil: The molecular mechanisms of development in colon cancer cells.

Colon cancer is a significant health problem worldwide as it is one of the most common and deadliest cancers. The standard approach for the treatment of colon cancer is 5-fluorouracil (5-FU) based chemotherapy, which is limited by the development of resistance to this drug. Therefore, our study aimed to establish 5-FU resistance in SW-480 and HT-29 colon cancer cells and to precisely determine the molecular mechanisms and biomarkers that contribute to its development, both after short-term exposure and in cells with already developed resistance (SW-480-5FUR and HT-29-5FUR). The expression of various molecules involved in the different mechanisms of resistance development was monitored at the gene (qPCR) and protein (immunocytochemistry) levels. Based on the obtained results, alterations in the 5-FU anabolic pathway, biotransformation, drug efflux, mismatch repair, and apoptosis process together contributed to the development of 5-FU resistance in SW-480 and HT-29 colon cancer cells. In addition, UMPS, ABCC1, ABCC5, and MLH1, as well as the disturbed ratio of pro-apoptotic BAX and anti-apoptotic BCL2, should be taken into consideration as potential targets for the discovery of 5-FU resistance-related biomarkers in colon cancer cells. We suggest that future investigations focus on further validation of these findings by additional in vitro and in vivo testing, which is a limitation of our study.

Safety and antitumor activity of dostarlimab in patients with advanced or recurrent DNA mismatch repair deficient/microsatellite instability-high (dMMR/MSI-H) or proficient/stable (MMRp/MSS) endometrial cancer: interim results from GARNET-a phase I, single-arm study.

BACKGROUND: Dostarlimab is a humanized monoclonal antibody that binds with high affinity to PD-1, resulting in inhibition of binding to PD-L1 and PD-L2. We report interim data from patients with endometrial cancer (EC) participating in a phase I trial of single-agent dostarlimab. METHODS: GARNET, an ongoing, single-arm, open-label, phase I trial of intravenous dostarlimab in advanced solid tumors, is being undertaken at 123 sites. Two cohorts of patients with EC were recruited: those with dMMR/MSI-H disease (cohort A1) and those with proficient/stable (MMRp/MSS) disease (cohort A2). Patients received dostarlimab 500 mg every 3 weeks for 4 cycles, then dostarlimab 1000 mg every 6 weeks until disease progression. The primary endpoints were objective response rate (ORR) and duration of response (DOR) per RECIST V.1.1, as assessed by blinded independent central review. RESULTS: Screening began on April 10, 2017, and 129 and 161 patients with advanced EC were enrolled in cohorts A1 and A2, respectively. The median follow-up duration was 16.3 months (IQR 9.5-22.1) for cohort A1 and 11.5 months (IQR 11.0-25.1) for cohort A2. In cohort A1, ORR was 43.5% (95% CI 34.0% to 53.4%) with 11 complete responses and 36 partial responses. In cohort A2, ORR was 14.1% (95% CI 9.1% to 20.6%) with three complete responses and 19 partial responses. Median DOR was not reached in either cohort. In the combined cohorts, the majority of treatment-related adverse events (TRAEs) were grade 1-2 (75.5%), most commonly fatigue (17.6%), diarrhea (13.8%), and nausea (13.8%). Grade≥3 TRAEs occurred in 16.6% of patients, and 5.5% discontinued dostarlimab because of TRAEs. No deaths were attributable to dostarlimab. CONCLUSION: Dostarlimab demonstrated durable antitumor activity in both dMMR/MSI-H (ORR 43.5%) and MMRp/MSS EC (ORR 14.1%) with a manageable safety profile. TRIAL REGISTRATION NUMBER: NCT02715284.

Durable response after immune checkpoint inhibitor-related diabetes in mismatch repair-deficient pancreatic cancer.

Mismatch repair protein deficiency occurs in 0.8-2% of pancreatic ductal adenocarcinomas and confers susceptibility to immunotherapy. Herein, we report the case of a patient with Lynch syndrome-associated, locally advanced mismatch repair protein deficiency pancreatic ductal adenocarcinomas who demonstrated a sustained response to second-line treatment with pembrolizumab, but eventually developed immune-related diabetic ketoacidosis requiring discontinuation of treatment. He has since remained in remission, off treatment, over the following 3 years, with regular surveillance showing no clinical or radiographic evidence of disease progression. The patient's unusual disease course raises the question of whether this serious immune-related adverse event affecting the organ of malignant involvement may have predicted his remarkable and durable response.

Lay abstract A small subgroup of pancreatic cancers have mutations preventing effective repair of damaged DNA; a condition termed 'mismatch repair protein deficiency'. These tumors are often effectively treated with immunotherapy. Here we describe a patient whose mismatch repair protein deficiency pancreatic cancer responded well to pembrolizumab immunotherapy, but who later developed diabetes as an immunotherapy-related adverse effect. Treatment was stopped, but his tumor remained stable off treatment over the next 3 years. His unique clinical course raises the question of whether the development of diabetes, a pancreas-specific adverse effect, may have predicted the effective treatment of pancreatic cancer.

C. tropicalis promotes chemotherapy resistance in colon cancer through increasing lactate production to regulate the mismatch repair system.

Due to chemotherapeutic drug resistance, tumor recurrence is common in patients with colorectal cancer (CRC) and chemo-resistant patients are often accompanied by defects in the mismatch repair system (MMR). Our previous study has shown that Candida tropicalis (C. tropicalis) is closely related to the occurrence and development of colorectal cancer, but whether this conditional pathogenic fungus is involved in chemotherapy needs further investigation. Here we found that C. tropicalis promoted chemotherapy resistance of colon cancer to oxaliplatin. Compared with oxaliplatin-treated group, the expression of functional MMR proteins in tumors were decreased in C.tropicalis/oxaliplatin -treated group, while the glycolysis level of tumors was up-regulated and the production of lactate was significantly increased in C.tropicalis/oxaliplatin -treated group. Inhibiting lactate production significantly alleviated the chemoresistance and rescued the decreased expression of MMR caused by C. tropicalis. Furthermore, we found that lactate down-regulated the expression of MLH1 through the GPR81-cAMP-PKA-CREB axis. This study clarified that C. tropicalis promoted chemoresistance of colon cancer via producing lactate and inhibiting the expression of MLH1, which may provide novel ideas for improving CRC chemotherapy effect.

Inhibition of the DSB repair protein RAD51 potentiates the cytotoxic efficacy of doxorubicin via promoting apoptosis-related death pathways.

The anthracycline derivative doxorubicin (Doxo) induces DNA double-strand breaks (DSBs) by inhibition of DNA topoisomerase type II. Defective mismatch repair (MMR) contributes to Doxo resistance and has been reported for colon and mammary carcinomas. Here, we investigated the outcome of pharmacological inhibition of various DNA repair-related mechanisms on Doxo-induced cytotoxicity employing MMR-deficient HCT-116 colon carcinoma cells. Out of different inhibitors tested (i.e. HDACi, PARPi, MRE11i, RAD52i, RAD51i), we identified the RAD51-inhibitor B02 as the most powerful compound to synergistically increase Doxo-induced cytotoxicity. B02-mediated synergism rests on pleiotropic mechanisms, including pronounced G2/M arrest, damage to mitochondria and caspase-driven apoptosis. Of note, B02 also promotes the cytotoxicity of oxaliplatin and 5-fluoruracil (5-FU) in HCT-116 cells and, furthermore, also increases Doxo-induced cytotoxicity in MMR-proficient colon and mammary carcinoma cells. Summarizing, pharmacological inhibition of RAD51 is suggested to synergistically increase the cytotoxic efficacy of various types of conventional anticancer drugs in different tumor entities. Hence, pre-clinical in vivo studies are preferable to determine the therapeutic window of B02 in a clinically oriented therapeutic regimen.

Advances in immune therapies for the treatment of microsatellite instability­high/deficient mismatch repair metastatic colorectal cancer (Review).

Microsatellite instability­high/deficient mismatch repair colorectal cancer (MSI­H/dMMR CRC) is a molecular subtype characterized by high­frequency mutations within DNA mismatch repair genes. Defects in the DNA mismatch repair machinery lead to subsequent frame­shift mutations, resulting in the generation of frame­shift peptides that serve as neoantigens. This has translated into exquisite sensitivity to immune checkpoint inhibitors (ICIs) and a significant clinical benefit from immune therapies in this patient population. The present article provides a comprehensive review of the advances in the field of immune therapies for MSI­H/dMMR metastatic CRC, with a focus on the major randomized clinical trials that led to Food and Drug Administration approval of specific ICIs for this population, a detailed review of the molecular background responsible for tumor response, as well as the mechanisms of resistance to ICI therapy. Finally, ongoing investigations of other immunotherapeutic strategies to address and overcome the challenges that currently limit response and long­term response to ICIs were presented.

Saffron and Its Major Ingredients' Effect on Colon Cancer Cells with Mismatch Repair Deficiency and Microsatellite Instability.

BACKGROUND: Colorectal cancer (CRC) is one of the most common cancers worldwide. One of its subtypes is associated with defective mismatch repair (dMMR) genes. Saffron has many potentially protective roles against colon malignancy. However, these roles in the context of dMMR tumors have not been explored. In this study, we aimed to investigate the effects of saffron and its constituents in CRC cell lines with dMMR. METHODS: Saffron crude extracts and specific compounds (safranal and crocin) were used in the human colorectal cancer cell lines HCT116, HCT116+3 (inserted MLH1), HCT116+5 (inserted MSH3), and HCT116+3+5 (inserted MLH1 and MSH3). CDC25b, p-H2AX, TPDP1, and GAPDH were analyzed by Western blot. Proliferation and cytotoxicity were analyzed by MTT. The scratch wound assay was also performed. RESULTS: Saffron crude extracts restricted (up to 70%) the proliferation in colon cells with deficient MMR (HCT116) compared to proficient MMR. The wound healing assay indicates that deficient MMR cells are doing better (up to 90%) than proficient MMR cells when treated with saffron. CDC25b and TDP1 downregulated (up to 20-fold) in proficient MMR cells compared to deficient MMR cells, while p.H2AX was significantly upregulated in both cell types, particularly at >10 mg/mL saffron in a concentration-dependent manner. The reduction in cellular proliferation was accompanied with upregulation of caspase 3 and 7. The major active saffron compounds, safranal and crocin reproduced most of the saffron crude extracts' effects. CONCLUSIONS: Saffron's anti-proliferative effect is significant in cells with deficient MMR. This novel effect may have therapeutic implications and benefits for MSI CRC patients who are generally not recommended for the 5-fluorouracil-based treatment.

Subcutaneous envafolimab monotherapy in patients with advanced defective mismatch repair/microsatellite instability high solid tumors.

BACKGROUND: Monoclonal antibodies targeting programmed death ligand 1 (PD-L1) signaling currently approved for defective mismatch repair (dMMR)/microsatellite instability high (MSI-H) tumors must be delivered by intravenous infusion. Envafolimab, a humanized single-domain anti-PD-L1 antibody fused to an Fc fragment, represents a potential advance because it can be conveniently administered subcutaneously. METHODS: This open-label, single-arm, phase 2 study evaluated the efficacy and safety of envafolimab in patients with previously treated advanced dMMR/MSI-H tumors from 25 clinical sites across China. Adults with histologically confirmed locally advanced or metastatic malignant dMMR/MSI-H solid tumors received weekly 150 mg subcutaneous envafolimab injections in a 28-day treatment cycle. The primary efficacy endpoint was the objective response rate (assessed by a blinded independent review committee). Secondary efficacy outcomes were disease control rate, duration of response, progression-free survival, and overall survival. RESULTS: One hundred and three patients (65 with colorectal cancer, 18 with gastric cancer, and 20 with other solid tumors) were enrolled. Median follow-up was 11.5 months. The objective response rate was 42.7% (95% confidence interval [CI] 33.0-52.8), and the disease control rate was 66.0% (95% CI 56.0-75.1). Median duration of response was not reached; the duration of response rate at 12 months was 92.2% (95% CI 77.5-97.4). Median progression-free survival was 11.1 months (95% CI 5.5 to not evaluable). Overall survival at 12 months was 74.6% (95% CI 64.7-82.1). Sixteen patients (16%) had at least one grade 3 or 4 related treatment-emergent adverse event. No grade 5 treatment-emergent adverse events related to envafolimab were reported. Injection site reactions, all grade 1-2, were reported in nine patients (9%), but there were no infusion reactions. Eight patients (8%) had grade 3 or 4 immune-related adverse events. CONCLUSIONS: This is the first pivotal phase 2 study to examine the efficacy and safety of a single-domain immune checkpoint antibody in the treatment of cancer. Envafolimab was effective and had acceptable safety in the treatment of previously treated advanced dMMR/MSI-H solid tumors. As the first single-domain PD-L1-targeting antibody administered by rapid subcutaneous injection, envafolimab has the potential to be a significant advance in the treatment of cancer. Trial registration ClinicalTrials.gov, NCT03667170. Registered 10 September 2018-Retrospectively registered, https://clinicaltrials.gov/ct2/show/NCT03667170 .

Rhodium Complexes Targeting DNA Mismatches as a Basis for New Therapeutics in Cancers Deficient in Mismatch Repair.

Cancers with microsatellite instability (MSI), which include ≤20% of solid tumors, are characterized by resistance to chemotherapy due to deficiency in the DNA mismatch repair (MMR) pathway. Rhodium metalloinsertors make up a class of compounds that bind DNA mismatches with high specificity and show selective cytotoxicity in MSI cancer cells. We determined that rhodium complexes with an N∧O coordination showed significantly increased cell potency compared with that of N∧N-coordinated compounds, and we identified [Rh(chrysi)(phen)(PPO)]2+ (RhPPO) as the most potent, selective compound in this class. Using matched cell lines that are MMR-deficient (HCT116O) and MMR-proficient (HCT116N), we demonstrated that RhPPO preferentially activates the DNA damage response and inhibits DNA replication and cell proliferation in HCT116O cells, leading to cell death by necrosis. Using a fluorescent conjugate of RhPPO, we established that the metalloinsertor localizes to DNA mismatches in the cell nucleus and causes DNA double-strand breaks at or near the mismatch sites. Evaluation of RhPPO across MMR-deficient and MMR-proficient cell lines confirmed the broad potential for RhPPO to target MSI cancers, with cell potency significantly higher than that of platinum complexes used broadly as chemotherapeutics. Moreover, in a mouse xenograft model of MSI cancer, RhPPO shows promising antitumor activity and increased survival. Thus, our studies indicate that RhPPO is a novel DNA-targeted therapy with improved potency and selectivity over standard-of-care platinum-based chemotherapy and, importantly, that DNA mismatches offer a critical new target in the design of chemotherapeutics for MSI cancers.

A study of deregulated MMR pathways and anticancer potential of curcuma derivatives using computational approach.

Plant derived products have steadily gained momentum in treatment of cancer over the past decades. Curcuma and its derivatives, in particular, have diverse medicinal properties including anticancer potential with proven safety as supported by numerous in vivo and in vitro studies. A defective Mis-Match Repair (MMR) is implicated in solid tumors but its role in haematologic malignancies is not keenly studied and the current literature suggests that it is limited. Nonetheless, there are multiple pathways interjecting the mismatch repair proteins in haematologic cancers that may have a direct or indirect implication in progression of the disease. Here, through computational analysis, we target proteins that are involved in rewiring of multiple signaling cascades via altered expression in cancer using various curcuma derivatives (Curcuma longa L. and Curcuma caesia Roxb.) which in turn, profoundly controls MMR protein function. These biomolecules were screened to identify their efficacy on selected targets (in blood-related cancers); aberrations of which adversely impacted mismatch repair machinery. The study revealed that of the 536 compounds screened, six of them may have the potential to regulate the expression of identified targets and thus revive the MMR function preventing genomic instability. These results reveal that there may be potential plant derived biomolecules that may have anticancer properties against the tumors driven by deregulated MMR-pathways.

Mismatch repair deficiency predicts response to HER2 blockade in HER2-negative breast cancer.

Resistance to endocrine treatment occurs in ~30% of ER+ breast cancer patients resulting in ~40,000 deaths/year in the USA. Preclinical studies strongly implicate activation of growth factor receptor, HER2 in endocrine treatment resistance. However, clinical trials of pan-HER inhibitors in ER+/HER2- patients have disappointed, likely due to a lack of predictive biomarkers. Here we demonstrate that loss of mismatch repair activates HER2 after endocrine treatment in ER+/HER2- breast cancer cells by protecting HER2 from protein trafficking. Additionally, HER2 activation is indispensable for endocrine treatment resistance in MutL- cells. Consequently, inhibiting HER2 restores sensitivity to endocrine treatment. Patient data from multiple clinical datasets supports an association between MutL loss, HER2 upregulation, and sensitivity to HER inhibitors in ER+/HER2- patients. These results provide strong rationale for MutL loss as a first-in-class predictive marker of sensitivity to combinatorial treatment with endocrine intervention and HER inhibitors in endocrine treatment-resistant ER+/HER2- breast cancer patients.

Sulindac Modulates the Response of Proficient MMR Colorectal Cancer to Anti-PD-L1 Immunotherapy.

Immune-checkpoint inhibitor (ICI) therapy has been widely used to treat different human cancers, particularly advanced solid tumors. However, clinical studies have reported that ICI immunotherapy benefits only ∼15% of patients with colorectal cancer, specifically those with tumors characterized by microsatellite instability (MSI), a molecular marker of defective DNA mismatch repair (dMMR). For the majority of patients with colorectal cancer who carry proficient MMR (pMMR), ICIs have shown little clinical benefit. In this study, we examined the efficacy of sulindac to enhance the response of pMMR colorectal cancer to anti-PD-L1 immunotherapy. We utilized a CT26 syngeneic mouse tumor model to compare the inhibitory effects of PD-L1 antibody (Ab), sulindac, and their combination on pMMR colorectal cancer tumor growth. We found that mice treated with combination therapy showed a significant reduction in tumor volume, along with increased infiltration of CD8+ T lymphocytes in the tumor tissues. We also demonstrated that sulindac could downregulate PD-L1 by blocking NF-κB signaling, which in turn led to a decrease in exosomal PD-L1. Notably, PD-L1 Ab can be bound and consumed by exosomal PD-L1 in the blood circulation. Therefore, in combination therapy, sulindac downregulating PD-L1 leads to increased availability of PD-L1 Ab, which potentially improves the overall efficacy of anti-PD-L1 therapy. We also show that low-dose sulindac does not appear to have a systemic inhibitory effect on prostaglandin E2 (PGE2). In conclusion, our findings provide unique insights into the mechanism of action and efficacy for sulindac as an immunomodulatory agent in combination with anti-PD-L1 therapy for the treatment of pMMR colorectal cancer.

Olaparib-mediated enhancement of 5-fluorouracil cytotoxicity in mismatch repair deficient colorectal cancer cells.

BACKGROUND: The advances in colorectal cancer (CRC) treatment include the identification of deficiencies in Mismatch Repair (MMR) pathway to predict the benefit of adjuvant 5-fluorouracil (5-FU) and oxaliplatin for stage II CRC and immunotherapy. Defective MMR contributes to chemoresistance in CRC. A growing body of evidence supports the role of Poly-(ADP-ribose) polymerase (PARP) inhibitors, such as Olaparib, in the treatment of different subsets of cancer beyond the tumors with homologous recombination deficiencies. In this work we evaluated the effect of Olaparib on 5-FU cytotoxicity in MMR-deficient and proficient CRC cells and the mechanisms involved. METHODS: Human colon cancer cell lines, proficient (HT29) and deficient (HCT116) in MMR, were treated with 5-FU and Olaparib. Cytotoxicity was assessed by MTT and clonogenic assays, apoptosis induction and cell cycle progression by flow cytometry, DNA damage by comet assay. Adhesion and transwell migration assays were also performed. RESULTS: Our results showed enhancement of the 5-FU citotoxicity by Olaparib in MMR-deficient HCT116 colon cancer cells. Moreover, the combined treatment with Olaparib and 5-FU induced G2/M arrest, apoptosis and polyploidy in these cells. In MMR proficient HT29 cells, the Olaparib alone reduced clonogenic survival, induced DNA damage accumulation and decreased the adhesion and migration capacities. CONCLUSION: Our results suggest benefits of Olaparib inclusion in CRC treatment, as combination with 5-FU for MMR deficient CRC and as monotherapy for MMR proficient CRC. Thus, combined therapy with Olaparib could be a strategy to overcome 5-FU chemotherapeutic resistance in MMR-deficient CRC.

Patient-Derived Organoid Models of Human Neuroendocrine Carcinoma.

Gastroenteropancreatic neuroendocrine carcinoma (GEP-NEC) is a poorly understood disease with limited treatment options. A better understanding of this disease would greatly benefit from the availability of representative preclinical models. Here, we present the potential of tumor organoids, three-dimensional cultures of tumor cells, to model GEP-NEC. We established three GEP-NEC organoid lines, originating from the stomach and colon, and characterized them using DNA sequencing and immunohistochemistry. Organoids largely resembled the original tumor in expression of synaptophysin, chromogranin and Ki-67. Models derived from tumors containing both neuroendocrine and non-neuroendocrine components were at risk of overgrowth by non-neuroendocrine tumor cells. Organoids were derived from patients treated with cisplatin and everolimus and for the three patients studied, organoid chemosensitivity paralleled clinical response. We demonstrate the feasibility of establishing NEC organoid lines and their potential applications. Organoid culture has the potential to greatly extend the repertoire of preclinical models for GEP-NEC, supporting drug development for this difficult-to-treat tumor type.

Defining the current role of immune checkpoint inhibitors in the treatment of mismatch repair-deficient/microsatellite stability-high colorectal cancer and shedding light on future approaches.

Introduction: Mismatch repair deficient (MMR-D)/microsatellite instability-high (MSI-H) colorectal cancer (CRC) carries unique biologic features including high tumor mutation burden, increased amount of mutation-associated neoantigen generation, and the presence of marked tumor-infiltrating lymphocytes. Immune checkpoint inhibitor (ICI) therapy has rapidly changed the treatment algorithm of MMR-D/MSI-H CRC.Areas covered: In this review article, we discuss the recent data regarding the use of ICIs in metastatic MMR-D/MSI-H CRC patients. We also elaborated on potential biomarkers of ICI response and innovative therapeutic approaches that may prevail resistance mechanisms for the treatment of MMR-D/MSI-H colorectal cancer.Expert opinion: Pembrolizumab was recently granted approval by the FDA as first-line therapy for metastatic MMR-D/MSI-H CRC based on the results of the Keynote 177 study. The combination of nivolumab and ipilimumab will also likely be a choice for the initial therapy of MMR-D/MSI-H CRC in the near future. More therapeutic modalities with novel immunomodulatory agents as well as targeted therapy directed to immune resistance pathways are needed. The novel approaches discussed in this review article will define potential treatment options for the management of MMR-D/MSI-H CRC patients who progress on first-line ICI therapy.

Prognostic significance of BIRC7/Livin, Bcl-2, p53, Annexin V, PD-L1, DARC, MSH2 and PMS2 in colorectal cancer treated with FOLFOX chemotherapy with or without aspirin.

Evasion of apoptosis is associated with treatment resistance and metastasis in colorectal cancer (CRC). Various cellular processes are associated with evasion of apoptosis. These include overexpression of pro-apoptotic proteins (including p53 and PD-L1), anti-apoptotic proteins (BIRC7/Livin and Bcl-2), chemokine receptors (including DARC), and dysregulation of DNA mismatch repair proteins (including MSH2 and PMS2). The aim of this study was to determine the effect of folinic acid, 5-FU and oxaliplatin (FOLFOX) as a single agent and aspirin plus FOLFOX in various combinations on the aforementioned proteins in human CRC, SW480 cell line and rat models of N-Methyl-N-Nitrosourea (NMU)-induced CRC. In addition, effects of the NMU-induced CRC and chemotherapeutic regimens on haematological and biochemical parameters in the rat models were studied. Immunohistochemistry, immunofluorescence and immunoblot techniques were used to study the expression pattern of the related proteins in the human CRC cells pre- and post-treatment. Double contrast barium enema, post-mortem examination and histological analyses were used to confirm tumour growth and the effect of the treatment in vivo in rat models. Notably, we found in human mucinous CRC, a significant increase in expression of the BIRC7/Livin post-FOLFOX treatment compared with pre-treatment (p = 0.0001). This increase provides new insights into the prognostic role of BIRC7/Livin in evasion of apoptosis and facilitation of treatment resistance, local recurrence and metastasis particularly among mucinous CRCs post-FOLFOX chemotherapy. These poor prognostic features in the CRC may be further compounded by the significant suppression of DARC, PD-L1, PMS2 and overexpression of MSH2 and anti-apoptotic Bcl-2 and p53 proteins observed in our study (p < 0.05). Importantly, we found a significant reduction in expression of BIRC7/Livin and reactivation of DARC and PD-L1 with a surge in Annexin V expression in rat models of CRC cells post-treatment with a sequential dose of aspirin plus FOLFOX compared with other treatments in vivo (p <0.05). The mechanistic rational of these effects underscores the importance of expanded concept of possible aspirin combination therapy with FOLFOX sequentially in future CRC management. Validation of our findings through randomized clinical trials of aspirin plus FOLFOX sequentially in patients with CRC is therefore warranted.

Pathological Tumor Response Following Immune Checkpoint Blockade for Deficient Mismatch Repair Advanced Colorectal Cancer.

Immune checkpoint inhibition (CPI) for metastatic colorectal cancer (mCRC) with deficient mismatch repair (dMMR) demonstrates high clinical activity that appears durable, but the impact of CPI on pathological tumor response is unknown. In this retrospective analysis, our objective was to assess pathological response and clinical outcomes in dMMR mCRC patients treated with CPI prior to surgical resection of primary and/or metastatic tumor. Among 121 advanced dMMR mCRC patients treated with CPI at 2 institutions between November 2016 and December 2018, 14 underwent surgery. Pathologic complete response was noted in the resected specimens of 13 patients despite the presence of residual tumor on preoperative imaging in 12 of those patients. With median follow-up of 9 months, no patients have had disease relapse or progression. For this small retrospective study, the data suggest that residual radiographic tumor may not require systematic resection following response to anti-PD1-based therapy. However, larger prospective studies are warranted.

Drugging DNA Damage Repair Pathways for Trinucleotide Repeat Expansion Diseases.

DNA damage repair (DDR) mechanisms have been implicated in a number of neurodegenerative diseases (both genetically determined and sporadic). Consistent with this, recent genome-wide association studies in Huntington's disease (HD) and other trinucleotide repeat expansion diseases have highlighted genes involved in DDR mechanisms as modifiers for age of onset, rate of progression and somatic instability. At least some clinical genetic modifiers have been shown to have a role in modulating trinucleotide repeat expansion biology and could therefore provide new disease-modifying therapeutic targets. In this review, we focus on key considerations with respect to drug discovery and development using DDR mechanisms as a target for trinucleotide repeat expansion diseases. Six areas are covered with specific reference to DDR and HD: 1) Target identification and validation; 2) Candidate selection including therapeutic modality and delivery; 3) Target drug exposure with particular focus on blood-brain barrier penetration, engagement and expression of pharmacology; 4) Safety; 5) Preclinical models as predictors of therapeutic efficacy; 6) Clinical outcome measures including biomarkers.

RECIST and iRECIST criteria for the evaluation of nivolumab plus ipilimumab in patients with microsatellite instability-high/mismatch repair-deficient metastatic colorectal cancer: the GERCOR NIPICOL phase II study.

BACKGROUND: Immune checkpoint inhibitors (ICIs) are highly effective in patients with microsatellite instability/mismatch repair-deficient (MSI/dMMR) metastatic colorectal cancer (mCRC). Response Evaluation Criteria in Solid Tumors (RECIST) 1.1 criteria may underestimate response to ICIs due to the pseudoprogression phenomenon. The GERCOR NIPICOL phase II study aimed to evaluate the frequency of pseudoprogressions in patients with MSI/dMMR mCRC treated with nivolumab and ipilimumab. METHODS: Patients with MSI/dMMR mCRC previously treated with fluoropyrimidines, oxaliplatin, and irinotecan with/without targeted therapies received nivolumab 3 mg/kg plus ipilimumab 1 mg/kg every 3 weeks for four cycles then nivolumab 3 mg/kg every 2 weeks until progression or a maximum of 20 cycles. Computed tomography scan tumor assessments were done every 6 weeks for 24 weeks and then every 12 weeks. The primary endpoint was disease control rate at 12 weeks according to RECIST 1.1 and iRECIST by central review. RESULTS: Of 57 patients included between December 2017 and November 2018, 48.0% received ≥3 prior lines of chemotherapy, 18.0% had BRAFV600E mutation, and 56.0% had Lynch syndrome-related cancer. Seven patients (12.0%) discontinued treatment due to adverse events; one died due to a treatment-related adverse event. The disease control rate (DCR) at 12 weeks was 86.0% with RECIST 1.1% and 87.7% with iRECIST. Two pseudoprogressions (3.5%) were observed, at week 6 and at week 36, representing 18% of patients with disease progression per RECIST 1.1 criteria. With a median follow-up of 18.4 months, median progression-free survival (PFS) and overall survival (OS) were not reached. The 12-month PFS rate was 72.9% with RECIST 1.1% and 76.5% with iRECIST. The 12-month OS rate was 84%. Overall response rate was 59.7% with both criteria. RAS/BRAF status, sidedness, Lynch syndrome, and other baseline parameters were not associated with PFS. CONCLUSION: Pseudoprogression is rare in patients with MSI/dMMR mCRC treated with nivolumab and ipilimumab. This combined ICI therapy confirms impressive DCR and survival outcomes in these patients. TRIAL REGISTRATION NUMBER: NCT03350126.

Benzo[a]pyrene represses DNA repair through altered E2F1/E2F4 function marking an early event in DNA damage-induced cellular senescence.

Transcriptional regulation of DNA repair is of outmost importance for the restoration of DNA integrity upon genotoxic stress. Here we report that the potent environmental carcinogen benzo[a]pyrene (B[a]P) activates a cellular DNA damage response resulting in transcriptional repression of mismatch repair (MMR) genes (MSH2, MSH6, EXO1) and of RAD51, the central homologous recombination repair (HR) component, ultimately leading to downregulation of MMR and HR. B[a]P-induced gene repression is caused by abrogated E2F1 signalling. This occurs through proteasomal degradation of E2F1 in G2-arrested cells and downregulation of E2F1 mRNA expression in G1-arrested cells. Repression of E2F1-mediated transcription and silencing of repair genes is further mediated by the p21-dependent E2F4/DREAM complex. Notably, repression of DNA repair is also observed following exposure to the active B[a]P metabolite BPDE and upon ionizing radiation and occurs in response to a p53/p21-triggered, irreversible cell cycle arrest marking the onset of cellular senescence. Overall, our results suggest that repression of MMR and HR is an early event during genotoxic-stress induced senescence. We propose that persistent downregulation of DNA repair might play a role in the maintenance of the senescence phenotype, which is associated with an accumulation of unrepairable DNA lesions.