Identification of PARP-1 in cancer stem cells of gastrointestinal cancers: A preliminary study

Targeted Treatment against Cancer Stem Cells in Colorectal Cancer

The cancer stem cell (SC) theory proposes that a population of SCs serves as the driving force behind fundamental tumor processes, including metastasis, recurrence, and resistance to therapy. The standard of care for patients with stage III and high-risk stage II colorectal cancer (CRC) includes surgery and adjuvant chemotherapy. Fluoropyrimidines and their combination with oxaliplatin increased the cure rates, being able to eradicate the occult metastatic SC in a fraction of patients. The treatment for unresectable metastatic CRC is based on chemotherapy, antibodies to VEGF and EGFR, and tyrosine-kinase inhibitors. Immunotherapy is used in MSI-H tumors. Currently used drugs target dividing cells and, while often effective at debulking tumor mass, these agents have largely failed to cure metastatic disease. SCs are generated either due to genetic and epigenetic alterations in stem/progenitor cells or to the dedifferentiation of somatic cells where diverse signaling pathways such as Wnt/β-catenin, Hedgehog, Notch, TGF-β/SMAD, PI3K/Akt/mTOR, NF-κB, JAK/STAT, DNA damage response, and Hippo-YAP play a key role. Anti-neoplastic treatments could be improved by elimination of SCs, becoming an attractive target for the design of novel agents. Here, we present a review of clinical trials assessing the efficacy of targeted treatment focusing on these pathways in CRC.

DNA Repair and Therapeutic Strategies in Cancer Stem Cells

First-line cancer treatments successfully eradicate the differentiated tumour mass but are comparatively ineffective against cancer stem cells (CSCs), a self-renewing subpopulation thought to be responsible for tumour initiation, metastasis, heterogeneity, and recurrence. CSCs are thus presented as the principal target for elimination during cancer treatment. However, CSCs are challenging to drug target because of numerous intrinsic and extrinsic mechanisms of drug resistance. One such mechanism that remains relatively understudied is the DNA damage response (DDR). CSCs are presumed to possess properties that enable enhanced DNA repair efficiency relative to their highly proliferative bulk progeny, facilitating improved repair of double-strand breaks induced by radiotherapy and most chemotherapeutics. This can occur through multiple mechanisms, including increased expression and splicing fidelity of DNA repair genes, robust activation of cell cycle checkpoints, and elevated homologous recombination-mediated DNA repair. Herein, we summarise the current knowledge concerning improved genome integrity in non-transformed stem cells and CSCs, discuss therapeutic opportunities within the DDR for re-sensitising CSCs to genotoxic stressors, and consider the challenges posed regarding unbiased identification of novel DDR-directed strategies in CSCs. A better understanding of the DDR mediating chemo/radioresistance mechanisms in CSCs could lead to novel therapeutic approaches, thereby enhancing treatment efficacy in cancer patients.

Association of haplotype and linkage disequilibrium of PARP1 polymorphisms rs1136410, rs1805405 and rs3219088 with gallbladder cancer

BACKGROUND

Previously, we have reported that PARP1 rs1136410 is significantly associated with increased the risk of gallbladder cancer.

AIM

We aimed to investigate the association of PARP1 rs1805405 and rs3219088 polymorphisms with risk of GBC and also association of the haplotype and combined effect of PARP1 SNPs (rs1805405 G/A, rs3219088 G/T and rs1136410 A/G). We have also investigated the expression profile of PARP1 and its correlation with polymorphisms, clinical parameters and overall survival.

METHODS

PARP1 polymorphisms were genotyped by PCR-RFLP and the expression profile of PARP1 at mRNA level was analyzed by semi-quantitative PCR. Overall survival was analyzed using Kaplan-Meier plot and Cox-regression analysis.

RESULTS

Haplotype analysis of the PARP1 polymorphisms revealed that AGG, AAG and GGT haplotypes are significantly associated with decreased risk of GBC, while AAT, AGT, GGG and GAG haplotypes are significantly associated with increased risk of GBC. Patients with T1+T2 and treated with chemotherapy having risk genotypes of rs1805405 have decreased overall survival. Upregulation of PARP1 is significantly associated with longer overall survival in patients with GBC with different clinical parameters. SNPs rs1136410 and rs1805405 genotypes are significantly associated with PARP1 expression.

CONCLUSION

Haplotype analysis suggests that PARP1 may have a potential role in gallbladder carcinogenesis.

PARP1 inhibition by Olaparib reduces the lethality of pancreatic cancer cells and increases their sensitivity to Gemcitabine

Pancreatic cancer (PC) is one of the tumors with the lowest survival rates due to the poor efficacy of the treatments currently used. Gemcitabine (GMZ), one of the chemotherapeutic agents employed when the tumor is unresectable, frequently fails due to the development of drug resistance. PARP1 is a relevant protein in this phenomenon and appears to be related to cancer progression in several types of tumors, including PC. To determine the relevance of PARP1 in the development and treatment of PC, we used the Panc02 cell line to generate modified PC cells with stably inhibited PARP1 expression (Panc02-L) and used GMZ, Olaparib (OLA) and GMZ+OLA as therapeutic strategies. Viability, radiosensitization, angiogenesis, migration, colony formation, TUNEL, cell cycle, multicellular tumorsphere induction and in vivo assays were performed to test the influence of PARP1 inhibition on resistance phenomena and tumor progression. We demonstrated that stable inhibition or pharmacological blockade of PARP1 using OLA-sensitized Panc02 cells against GMZ significantly decreased their IC₅₀, reducing colony formation capacity, cell migration and vessel formation (angiogenesis) in vitro. Furthermore, in vivo analyses revealed that Panc02-L-derived (PARP1-inhibited) tumors showed less growth and lethality, and that GMZ+OLA treatment significantly reduced tumor growth. In conclusion, PARP1 inhibition, both alone and in combination with GMZ, enhances the effectiveness of this chemotherapeutic agent and represents a promising strategy for the treatment of PC.

Celastrol and Resveratrol Modulate SIRT Genes Expression and Exert Anticancer Activity in Colon Cancer Cells and Cancer Stem-like Cells

Simple Summary

The recovery rate in patients with metastatic colorectal cancer (CRC) remains low and declines with successive lines of treatment. This phenomenon is caused by the development of drug resistance and the presence of colorectal cancer stem cells (CSCs). Phytochemicals, like -celastrol and resveratrol, are very promising for colon cancer therapy, owing to their low or no toxicity and their pleiotropic activity, enabling them to interact with various biological targets. In the present study, the potential anticancer mechanisms of both compounds against metastatic colon cancer cells and the capacity to eradicate CSCs were investigated.

Abstract

Metastatic colorectal cancer (CRC) remains a hard-to-cure neoplasm worldwide. Its curability declines with successive lines of treatment due to the development of various cancer resistance mechanisms and the presence of colorectal cancer stem cells (CSCs). Celastrol and resveratrol are very promising phytochemicals for colon cancer therapy, owing to their pleiotropic activity that enables them to interact with various biological targets. In the present study, the anticancer activities of both compounds were investigated in metastatic colon cancer cells (LoVo cells) and cancer stem-like cells (LoVo/DX). We showed that celastrol is a very potent anti-tumor compound against metastatic colon cancer, capable of attenuating CSC-like cells at the molecular and cellular levels. In contrast, resveratrol has a much greater effect on colon cancer cells that are expressing standard sensitivity to anticancer drugs, than on CSC-like cells. In addition, both polyphenols have different influences on the expression of SIRT genes, which seems to be at least partly related to their anti-tumor activity.