Digital detection of multiple minority mutants and expression levels of multiple colorectal cancer-related genes using digital-PCR coupled with bead-array

Detection of KRAS G12D in colorectal cancer stool by droplet digital PCR

AIM

To assess KRAS G12D mutation detection by droplet digital PCR (ddPCR) in stool-derived DNA from colorectal cancer (CRC) patients.

METHODS

In this study, tumor tissue and stool samples were collected from 70 patients with stage I-IV CRC diagnosed by preoperative biopsy. KRAS mutational status was determined by pyrosequencing analysis of DNA obtained from formalin-fixed paraffin-embedded (FFPE) tumor tissues. The KRAS G12D mutation was then analyzed by ddPCR in FFPE tumors and stool-derived DNA from patients with this point mutation. Wild-type (WT) tumors, as determined by pyrosequencing, were included as controls; analysis of FFPE tissue and stool-derived DNA by ddPCR was performed for these patients as well.

RESULTS

Among the total 70 patients included, KRAS mutations were detected by pyrosequencing in 32 (45.71%), whereas 38 (54.29%) had WT tumors. The frequency of KRAS mutations was higher in left-sided tumors (11 located in the right colon, 15 in the left, and 6 in the rectum). The predominant point mutation was KRAS G12D (14.29%, n = 10), which was more frequent in early-stage tumors (I-IIA, n = 7). In agreement with pyrosequencing results, the KRAS G12D mutation was detected by ddPCR in FFPE tumor-derived DNA, and only a residual number of mutated copies was found in WT controls. The KRAS G12D mutation was also detected in stool-derived DNA in 80% of all fecal samples from CRC patients with this point mutation.

CONCLUSION

ddPCR is a reliable and sensitive method to analyze KRAS G12D mutation in stool-derived DNA from CRC patients, especially at early stages. This non-invasive approach is potentially applicable to other relevant biomarkers for CRC management.

P15, MDM2, NF-κB, and Bcl-2 expression in primary bone tumor and correlation with tumor formation and metastasis

Primary bone tumor is one of the most common malignant tumors in skeletal system. It seriously affected bone movement and development with unclear pathogenesis. In this paper, rabbit VX-2 malignant bone tumor model was applied to explore apoptotic genes P15, MDM2, NF-κB and Bcl-2 correlation with primary bone tumor occurrence and metastasis. 0.3 ml rabbit VX-2 tumor cell suspension (1×10(6)/ml) was injected to the marrow cavity of the right tibia condyle to establish the rabbit malignant bone tumor model, while equal amount of the saline was injected to the left tibia as control. Real-time PCR was applied to determine P15, MDM2, NF-κB and Bcl-2 expression level. Immunohistochemistry was performed to detect the abovementioned genes expression in lung, stomach, kidney and bladder. Compared with control, P15 expression level in the inoculation site surrounding tissues decreased obviously following the inoculate time elongation (P<0.05), while Bcl-2, MDM2 and NF-κB expression significantly increased (P<0.05). Bcl-2 showed significant correlation with MDM2 and NF-κB (P<0.05). At the 2, 4, 6 weeks, Bcl-2, MDM2 and NF-κB in lung, Bcl-2 in kidney, and Bcl-2 and MDM2 in bladder positively expressed (P<0.05), whereas P15 gene exhibited no significant positive expression in these tissues (P>0.05). P15, MDM2, NF-κB, and Bcl-2 genes expression levels can effectively reflect malignant bone tumor growth of rabbit tibia. MDM2, NF-κB and Bcl-2 genes involved in primary bone tumors metastasis directly. It has important clinical significance for early diagnosis and treatment of primary bone tumor.