Molecular markers in colorectal cancer: genetic bases for a customised treatment

Multidrug resistance protein 2 genetic polymorphism and colorectal cancer recurrence in patients receiving adjuvant FOLFOX-4 chemotherapy

Multidrug resistance protein 2 (MRP2), encoded by the ATP-binding cassette C2 (ABCC2) gene, is an efflux pump located on the apical membrane of many polarized cells, which transports conjugate compounds by an ATP-dependent mechanism. The correlation of G1249A ABCC2 polymorphism with the development of colorectal cancer (CRC) and poor prognosis was evaluated in patients who were treated with fluorouracil/-leucovorin (FL) plus oxaliplatin (FOLFOX-4). A total of 50 paraffin‑embedded tissue samples collected from CRC patients were analyzed to identify the polymorphism. Patients were in stage II/III and received postoperative FOLFOX-4 chemotherapy. As a control group, an equal number of unrelated healthy subjects were enrolled in the study. The polymorphism was genotyped by the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method, and results were compared with clinicopathological markers, early relapse and survival rates. During the 12 months of follow-up, local and distant recurrences were observed in 15 (30%) patients. No significant difference in the distribution of wild-type and polymorphic genotypes was observed between the patient and control groups and between the patients who experienced recurrence within 1 year and those who did not (all P>0.05). In conclusion, the G1249A polymorphism is not associated with CRC risk and early recurrence. However, significant correlation was observed between G1249A polymorphism and the overall survival and disease-free survival of the patients.

Lack of association between expression of MRP2 and early relapse of colorectal cancer in patients receiving FOLFOX-4 chemotherapy

Recurrence following failure of chemotherapy limits the application of high doses of anticancer drugs currently used for eliminating cancerous cells. It has been identified that ATP-binding cassette (ABC) multidrug transporters are associated with chemoresistance, which is a major obstacle in cancer therapy. The present study aimed to investigate the association of pretherapeutic multidrug resistance-associated protein 2 (MRP2) expression with response to chemotherapy in stage II/III colorectal cancer (CRC). Protein expression was determined by immunohistochemical analysis of 50 archival samples from patients who had not received preoperative chemotherapy and radiotherapy. All patients were treated with 5-fluorouracil/leucovorin (FL) plus oxaliplatin (FOLFOX-4) regimen for 6 months following curative resection. During the 12 months of follow-up, local and distant recurrences were observed in 15 (30%) cases, of which 5 occurred at the time of chemotherapy. MRP2 expression was observed in 24 (48%) and 7 (14%) cases in the tumor tissues and matched normal tissues, respectively. A significant difference was observed between the positive expression frequency in the tumor tissues compared to the surrounding normal mucosa (P=0.003). The incidence of recurrence and metastasis for patients in the MRP2-positive group was lower than that in the MRP2-negative group (P>0.05); however, all 5 cases who demonstrated recurrence during their treatment were MRP2-positive (P=0.022). MRP2 expression was not correlated with the clinicopathological markers in this group of patients. Kaplan-Meier analysis revealed that MRP2 expression was not associated with a shorter disease-free survival or overall survival of patients (P>0.05). The results of this study indicated that MRP2 is overexpressed in the course of CRC development and progression. However, expression of MRP2 was not associated with recurrence of patients treated with FL and oxaliplatin in the population studied.

The BRAFT1799A mutation confers sensitivity of thyroid cancer cells to the BRAFV600E inhibitor PLX4032 (RG7204)

Aberrant signaling of the Ras-Raf-MEK-ERK (MAP kinase) pathway driven by the mutant kinase BRAF(V600E), as a result of the BRAF(T1799A) mutation, plays a fundamental role in thyroid tumorigenesis. This study investigated the therapeutic potential of a BRAF(V600E)-selective inhibitor, PLX4032 (RG7204), for thyroid cancer by examining its effects on the MAP kinase signaling and proliferation of 10 thyroid cancer cell lines with wild-type BRAF or BRAF(T1799A) mutation. We found that PLX4032 could effectively inhibit the MAP kinase signaling, as reflected by the suppression of ERK phosphorylation, in cells harboring the BRAF(T1799A) mutation. PLX4032 also showed a potent and BRAF mutation-selective inhibition of cell proliferation in a concentration-dependent manner. PLX4032 displayed low IC(50) values (0.115-1.156μM) in BRAF(V600E) mutant cells, in contrast with wild-type BRAF cells that showed resistance to the inhibitor with high IC(50) values (56.674-1349.788μM). Interestingly, cells with Ras mutations were also sensitive to PLX4032, albeit moderately. Thus, this study has confirmed that the BRAF(T1799A) mutation confers cancer cells sensitivity to PLX4032 and demonstrated its specific potential as an effective and BRAF(T1799A) mutation-selective therapeutic agent for thyroid cancer.

DNA aptamers as molecular probes for colorectal cancer study

Background

Understanding the molecular features of specific tumors can increase our knowledge about the mechanism(s) underlying disease development and progression. This is particularly significant for colorectal cancer, which is a heterogeneous complex of diseases developed in a sequential manner through a multistep carcinogenic process. As such, it is likely that tumors with similar characteristics might originate in the same manner and have a similar molecular behavior. Therefore, specific mapping of the molecular features can be potentially useful for both tumor classification and the development of appropriate therapeutic regimens. However, this can only be accomplished by developing high-affinity molecular probes with the ability to recognize specific markers associated with different tumors. Aptamers can most easily meet this challenge based on their target diversity, flexible manipulation and ease of development.

Methodology and Results

Using a method known as cell-based Systematic Evolution of Ligands by Exponential enrichment (cell-SELEX) and colorectal cancer cultured cell lines DLD-1 and HCT 116, we selected a panel of target-specific aptamers. Binding studies by flow cytometry and confocal microscopy showed that these aptamers have high affinity and selectivity. Our data further show that these aptamers neither recognize normal colon cells (cultured and fresh), nor do they recognize most other cancer cell lines tested.

Conclusion/Significance

The selected aptamers can identify specific biomarkers associated with colorectal cancers. We believe that these probes could be further developed for early disease detection, as well as prognostic markers, of colorectal cancers.

Value of the identification of microsatellite instability in colorectal cancer

OBJECTIVE

Recent studies defend a possible prognostic and therapeutic value of the identification of microsatellite instability (MSI) in colorectal cancer. This work tries to assess the impact that the identification of MSI tumours can have in clinical practice.

MATERIAL AND METHODS

We recovered tumour samples from 92 of the 143 patients operated on for colorectal cancer in our institution between 1995 and 2000. Five MSI markers (BAT 25, BAT 26, D2S123, D5S346 and D17S250) were studied on them. The rate and clinicopathologic characteristics of MSI tumours were investigated along with their impact on the global and disease-free survival as compared with microsatellite stable (MSS) tumours.

RESULTS

All 5 microsatellite markers' status were established in 73 patients (79.3% of the samples). Among them, 7 tumours showed instability in just one marker (low microsatellite instability [MSI-L]) whereas 5 tumours had mutations in 2 or more markers (high microsatellite instability [MSI-H]), for a total 15.4% rate of MSI tumours. All MSI-H tumours were located in the right colon. We could not fi nd any impact from MSI detection on global or disease-free survival.

CONCLUSIONS

MSI determination did not identify groups of patients with a different prognosis. Moreover, with such low incidence its determination can only be justified in those cases that fulfill Bethesda's criteria to identify families with Lynch's syndrome.

Irinotecan as palliative chemotherapy for metastatic colorectal cancer: evolving tactics following initial treatment

BACKGROUND

Patients with metastatic colorectal cancer (mCRC) who progress despite treatment with fluoropyrimidine and irinotecan or oxaliplatin have diminished survival, but they may derive clinically meaningful benefit from second-line or later chemotherapy.

MATERIALS AND METHODS

Literature from 2000 through mid-2008 on the treatment of patients with unresectable mCRC was reviewed to identify options for chemotherapy-resistant patients with mCRC.

RESULTS AND CONCLUSIONS

A recurring finding is that overall survival increases when patients are exposed to all available active agents throughout their course of care, independent of the line of treatment in which medication is delivered. Sequential administration of agents, including irinotecan, oxaliplatin, bevacizumab, and cetuximab, or, alternatively, deferred administration of various medications in combination, have shown promising efficacy that is at least equivalent to established combination regimens with the same agents. Palliative chemotherapy clearly improves survival in patients with unresectable mCRC, with overall survival recently reaching 28 months.

Scaled-down purification protocol to access proteomic analysis of 20S proteasome from human tissue samples: comparison of normal and tumor colorectal cells

The proteasome is a proteolytic complex that constitutes the main pathway for degradation of intracellular proteins in eukaryotic cells. It regulates many physiological processes and its dysfunction can lead to several pathologies like cancer. To study the 20S proteasome structure/activity relationship in cells that derive from human biopsy samples, we optimized an immuno-purification protocol for the analysis of samples containing a small number of cells using magnetic beads. This scaled-down protocol was used to purify the cytoplasmic 20S proteasome of adjacent normal and tumor colorectal cells arising from tissue samples of several patients. Proteomic analyses based on two-dimensional gel electrophoresis (2DE) and mass spectrometry showed that the subunit composition of 20S proteasomes from these normal and tumor cells were not significantly different. The proteasome activity was also assessed in the cytoplasmic extracts and was similar or higher in tumor colorectal than in the corresponding normal cells. The scaled-down 20S proteasome purification protocol developed here can be applied to any human clinical tissue samples and is compatible with further proteomic analyses.