Pharmacogenomics in chemotherapy for GI tract cancer

Molecular determinants of response to 5-fluorouracil-based chemotherapy in colorectal cancer: The undisputable role of micro-ribonucleic acids

5-flurouracil (5-FU)-based chemotherapy is the main pharmacological therapy for advanced colorectal cancer (CRC). Despite significant progress in the treatment of CRC during the last decades, 5-FU drug resistance remains the most important cause of failure in CRC therapy. Resistance to 5-FU is a complex and multistep process. Different mechanisms including microsatellite instability, increased expression level of key enzyme thymidylate synthase and its polymorphism, increased level of 5-FU-activating enzymes and mutation of TP53 are proposed as the main determinants of resistance to 5-FU in CRC cells. Recently, micro-ribonucleic acids (miRNA) and their alterations were found to have a crucial role in 5-FU resistance. In this regard, the miRNA-mediated mechanisms of 5-FU drug resistance reside among the new fields of pharmacogenetics of CRC drug response that has not been completely discovered. Identification of the biological markers that are related to response to 5-FU-based chemotherapy is an emerging field of precision medicine. This approach will have an important role in defining those patients who are most likely to benefit from 5-FU-based chemotherapy in the future. Thereby, the identification of 5-FU drug resistance mechanisms is an essential step to predict and eventually overcome resistance. In the present comprehensive review, we will summarize the latest knowledge regarding the molecular determinants of response to 5-FU-based chemotherapy in CRC by emphasizing the role of miRNAs.

Genetic predisposition resulting in sinusoidal obstruction syndrome in a patient with resected sigmoid cancer on adjuvant oxaliplatin

A Chinese man who had undergone a curative high anterior resection for sigmoid cancer was administrated XELOX (capecitabine and oxaliplatin) as postoperative adjuvant chemotherapy. He subsequently developed sinusoidal obstruction syndrome (SOS) that resolved on discontinuation of XELOX treatment. Genetic evaluation determined that he had the GSTT1-null and GSTM1-null genotype, known to be an independent risk factor for developing oxaliplatin-induced SOS.

Carcinoembryonic antigen expression level as a predictive factor for response to 5-fluorouracil in colorectal cancer

Carcinoembryonic antigen (CEA) expression has been shown to protect cancer cell lines from apoptosis and anoikis. The aim of this study was to further elucidate the role of CEA expression on resistance to anticancer drugs in human colorectal cancer (CRC). We transfected CEA negative CRC cell line SW742 as well as CHO cells to overexpress CEA and their chemoresistance were assessed by MTT assay. In comparison to the parental cell lines, transfected cells had significantly increased resistance to 5-fluorouracil (5-FU). The results also showed a direct correlation between the amount of cellular CEA protein and 5-FU resistance in CEA expressing cells. We found no significant difference in sensitivity to cisplatin and methotrexate between CEA-transfected cells and their counter parental cells. We also compared the association between CEA expression and chemoresistance of 4 CRC cell lines which differed in the levels of CEA production. The CEA expression levels in monolayer cultures of these cell lines did not correlate with the 5-FU resistance. However, 5-FU treatment resulted in the selection of sub-populations of resistant cells that displayed increased CEA expression levels by increasing drug concentration. We analyzed the effect of 5-FU in a 3D multicellular culture generated from the two CRC cell lines, LS180 and HT29/219. Compared with monolayer culture, CEA production and 5-FU resistance in both cell lines were stimulated by 3D growth. In comparison to the 3D spheroids of parental CHO, we observed a significantly elevated 5-FU resistance in 3D culture of the CEA-expressing CHO transfectants. Our findings suggest that the CEA level may be a suitable biomarker for predicting tumor response to 5-FU-based chemotherapy in CRC.

A rare case of primary choriocarcinoma in the sigmoid colon

Primary colorectal choriocarcinoma is an extremely rare neoplasm and is usually associated with a poor prognosis. Only 13 cases of colorectal choriocarcinoma have previously been reported. There is no standard chemotherapeutic regimen for this tumor type. A 68-year-old man presented with melena and was diagnosed with sigmoid colonic adenocarcinoma with multiple liver metastases. He underwent a laparoscopic sigmoidectomy. Pathology revealed choriocarcinoma with a focal component of moderately differentiated adenocarcinoma of colon origin. Based on the collagen gel droplet-embedded culture drug sensitivity test (CD-DST) results, mFOLFOX6 and bevacizumab were administered, which suppressed aggressive tumor growth for 4 mo. The patient died 9 mo after the initial diagnosis. Our study results suggest that the standard chemotherapy regimen for colorectal cancer might have suppressive effects against primary colorectal choriocarcinoma. Moreover, CD-DST may provide, at least in part, therapeutic insight for the selection of appropriate antitumor agents for such patients.

Glutathione S-transferase M1-null genotype as risk factor for SOS in oxaliplatin-treated patients with metastatic colorectal cancer

Background:

Oxaliplatin is used as a neo-adjuvant therapy in hepatic colorectal carcinoma metastasis. This treatment has significant side effects, as oxaliplatin is toxic to the sinusoidal endothelial cells and can induce sinusoidal obstruction syndrome (SOS), which is related to decreased overall survival. Glutathione has an important role in the defence system, catalysed by glutathione S-transferase (GST), including two non-enzyme producing polymorphisms (GSTM1-null and GSTT1-null). We hypothesise that patients with a non-enzyme producing polymorphism have a higher risk of developing toxic injury owing to oxaliplatin.

Methods:

In the nontumour-bearing liver, the presence of SOS was studied histopathologically. The genotype was determined by a semi-nested PCR.

Results:

Thirty-two of the 55 (58%) patients showed SOS lesions, consisting of 27% mild, 22% moderate and 9% severe lesions. The GSTM1-null genotype was present in 25 of the 55 (46%). Multivariate analysis showed that the GSTM1-null genotype significantly correlated with the presence of (moderate–severe) SOS (P=0.026).

Conclusion:

The GSTM1-null genotype is an independent risk factor for SOS. This finding allows us, in association with other risk factors, to conceive a potential risk profile predicting whether the patient is at risk of developing SOS, before starting oxaliplatin, and subsequently might result in adjustment of treatment.