Percy C.K. Tsang

Differential DNA methylation profiles in gynecological cancers and correlation with clinico-pathological data

BackgroundEpigenetic gene silencing is one of the major causes of carcinogenesis. Its widespread occurrence in cancer genome could inactivate many cellular pathways including DNA repair, cell cycle control, apoptosis, cell adherence, and detoxification. The abnormal promoter methylation might be a potential molecular marker for cancer management.MethodsFor rapid identification of potential targets for aberrant methylation in gynecological cancers, methylation status of the CpG islands of 34 genes was determined using pooled DNA approach and methylation-specific PCR. Pooled DNA mixture from each cancer type (50 cervical cancers, 50 endometrial cancers and 50 ovarian cancers) was made to form three test samples. The corresponding normal DNA from the patients of each cancer type was also pooled to form the other three control samples. Methylated alleles detected in tumors, but not in normal controls, were indicative of aberrant methylation in tumors. Having identified potential markers, frequencies of methylation were further analyzed in individual samples. Markers identified are used to correlate with clinico-pathological data of tumors using χ2 or Fishers exact test.ResultsAPC and p16 were hypermethylated across the three cancers. MINT31 and PTEN were hypermethylated in cervical and ovarian cancers. Specific methylation was found in cervical cancer (including CDH1, DAPK, MGMT and MINT2), endometrial cancer (CASP8, CDH13, hMLH1 and p73), and ovarian cancer (BRCA1, p14, p15, RIZ1 and TMS1). The frequencies of occurrence of hypermethylation in 4 candidate genes in individual samples of each cancer type (DAPK, MGMT, p16 and PTEN in 127 cervical cancers; APC, CDH13, hMLH1 and p16 in 60 endometrial cancers; and BRCA1, p14, p16 and PTEN in 49 ovarian cancers) were examined for further confirmation. Incidence varied among different genes and in different cancer types ranging from the lowest 8.2% (PTEN in ovarian cancer) to the highest 56.7% (DAPK in cervical cancer). Aberrant methylation for some genes (BRCA1, DAPK, hMLH1, MGMT, p14, p16, and PTEN) was also associated with clinico-pathological data.ConclusionThus, differential methylation profiles occur in the three types of gynecologic cancer. Detection of methylation for critical loci is potentially useful as epigenetic markers in tumor classification. More studies using a much larger sample size are needed to define the potential role of DNA methylation as marker for cancer management.

High frequency of mitochondrial genome instability in human endometrial carcinomas

To investigate the occurrence of somatic mitochondrial DNA (mtDNA) mutations in human primary endometrial carcinomas, we sequenced the D-loop region, the 12S and 16S rRNA genes of mtDNA of cancer tissues and their matched normal controls. About 56% (28 out of 50) of cases carry one or more somatic changes in mtDNA including deletion, point mutation and mitochondrial microsatellite instability (mtMSI), namely the change in length of short base-repetitive sequences of mtDNA. In particular, mtMSI was frequently detected in 89% (25 out of 28) of all the cases carrying somatic changes followed by point mutations (25%; seven out of 28) and deletion (3.5%; one out of 28). The CCCCCTCCCC sequences located in the Hypervariable Regions I and II of the D-loop and 12S rRNA gene are instability hot spot regions in endometrial carcinomas. It is suggested that errors in replication may account for the high frequency of mtMSI in human endometrial carcinomas. The relatively high prevalence of mtMSI may be a potential new tool for detection of endometrial cancer.

Comparison of Human Papillomavirus DNA Levels in Gynecological Cancers: Implication for Cancer Development

We have previously demonstrated the presence of human papillomavirus (HPV) DNA in several gynecological cancers using conventional PCR. In the present study, to further understand the role of HPV in malignant transformation of these cancers, the infection rates and viral loads of HPV 16 and 18 in gynecological cancers were analyzed using real-time quantitative PCR (qPCR). HPV 16 DNA was detected in 61.0% (58/95), 15.2% (7/46) and 32.1% (18/56) of cases of cervical, endometrial and ovarian cancers, respectively. On the other hand, HPV 18 DNA was detected in 23.2% (22/95) of cervical cancers, 1.8% (1/56) of ovarian cancers, and in no cases of endometrial cancer. Thus, HPV 16 is much more prevalent than HPV 18 in malignancies of the female genital tract. We also found that both HPV 16 and 18 were significantly (p < 0.05) less frequently present in endometrial and ovarian cancers than in cervical cancer. The median copy numbers of HPV 16 DNA in endometrial and ovarian cancers were 3,500 and 7,590 copies/µg DNA, respectively. These amounts were also significantly (p < 0.05) lower than HPV 16 DNA in cervical cancer (492,800 copies/µg DNA). Thus, HPV 16 could be detected in all three types of gynecological cancer, whilst HPV 18 is extremely rare in endometrial and ovarian cancers. The lower HPV 16 infection rates and lower copy numbers when compared with cervical cancer tend to suggest that HPV plays a less essential role in the development of endometrial cancer and ovarian cancer.

Distribution of Six Oncogenic Types of Human Papillomavirus and Type 16 Integration Analysis in Chinese Women with Cervical Precancerous Lesions and Carcinomas

Objectives: The prevalent genotypes of human papillomavirus (HPV) infection and the significance of HPV16 integration in cervical precancerous lesions and cancer of Chinese women were investigated. Methods: HPV genotyping and HPV16 integration status were studied on 100 normal cervical cytology, 90 low-grade (LSIL) and 99 high-grade squamous intraepithelial lesions (HSIL), as well as 96 cervical cancer biopsies using DNA sequencing and quantitative real-time PCR. Results: HPV were detected in 12.0% of normal cytology, 93.3% of LSIL, 90.9% of HSIL and 89.6% of cervical cancer samples. High-risk HPV16, 18, 58, 52, 33 and 31 were the 6 major HPV types observed, composing 45.6, 82.8 and 85.4% of HPV infections in LSIL, HSIL and cervical cancers, respectively, with a significant rising trend in increasing disease severity (p = 0.002). While HPV16 and HPV18 were most commonly found in cervical cancer, HPV58 was prevalently observed in cervical precancerous lesions, and its frequency decreased with increased disease severity. Among HPV16-positive patients, 40.0% of LSIL, 88.9% of HSIL and 86.4% of cancer cases had HPV16 integration. The frequency of the integrated form of HPV16 significantly increased with the severity of the disease. Conclusions: Our results demonstrated that high-risk HPV infection and viral DNA integration were in progressive frequency from low-grade cervical precancerous lesions to cancer. HPV16 integration status had the potential to be a marker for cancer risk assessment of cervical precancerous lesions.

Potential Use of the Adenosine Triphosphate Cell Viability Assay in Endometrial Cancer

Objective: Adenosine triphosphate cell viability assay (ATP-CVA) was used prevously to evaluate chemotherapy in uterine cancer cell lines. In this study, we have performed the ATP-CVA on endometrial cancer patients to study the feasibility of using ATP-CVA in endometrial cancer to determine the intrinsic chemosensitivity of the cytotoxic drugs. Methods: Thirty-three patients with endometrial adenocarcinoma who presented for a staging operation were recruited. Endometrial cancer samples were obtained at the time of operation. In vitro ATP-CVA and chemosensitivity testing was performed using cisplatin, carboplatin, paclitaxel, etoposide, doxorubicin, 4-epidoxorubicin, and topotecan. Results: Thirty-two of the 33 endometrial cancer samples were evaluable for SF50 (survival fraction at 50% of the peak plasma concentration [PPC]) using ATP-CVA. The median SF50 of carboplatin (0.33) was significantly less than the median SF50 of cisplatin (0.71), topotecan (0.93), paclitaxel (0.68), doxorubicin (1.0), etoposide (0.70), or 4-epidoxorubicin (0.88) (Wilcoxon signed rank test, P <.001). Conclusion: This study showed the feasibility of using the ATP-CVA in endometrial cancer to determine the intrinsic chemosensitivity of cytotoxic drugs.