To elucidate the relationship between genomewide DNA hypomethylation and chromosome instability, 55 prostate carcinoma specimens were analyzed for extent of hypomethylation by Southern blot analysis of LINE-1 sequence methylation and for loss or gain of chromosomal material by comparative genomic hybridization. Seventeen (31%) tumors showed strong hypomethylation of DNA, whereas four (7%) displayed slight hypomethylation and the rest of the tumors normal-level methylation. Chromosomal aberrations were observed in 34 carcinomas. The most frequent chromosomal alterations were loss of 13q in 18 cases and aberrations in 8p (loss) or 8q (gain) in 16 cases. The presence of chromosomal loss or gain was significantly associated with the presence of strong hypomethylation. A striking correlation (P = 0.00001) was observed between aberrations on chromosome 8 and hypomethylation, whereas no association was seen between DNA hypomethylation and loss of 13q. The association between DNA hypomethylation and the presence of metastases was statistically significant (P = 0.044), and both chromosomal alterations and DNA hypomethylation tended to be more frequent in higher-stage tumors. In conclusion, the data indicate that hypomethylation is associated with chromosomal instability in prostate cancer. Specifically, a surprisingly strong association between alterations on chromosome 8 and genomewide hypomethylation was found. This association suggests that DNA hypomethylation and alterations in chromosome 8 may be mechanistically linked to each other in prostate carcinoma.

Androgens are necessary for the development of prostatic cancer. The mechanisms by which the originally androgen-dependent prostatic cancer cells are relieved of the requirement to use androgen for their growth are largely unknown. The human prostatic cancer cell line LNCaP has been shown to contain a point mutation in the human androgen receptor gene (hAR), suggesting that changes in the hAR may contribute to the abnormal hormone response of prostatic cells. To search for point mutations in the hAR, we used single strand conformation polymorphism analysis and a polymerase chain reaction direct sequencing method to screen 23 prostatic cancer specimens from untreated patients, 6 prostatic cancer specimens from treated patients, and 11 benign prostatic hyperplasia specimens. One mutation was identified in DNA isolated from prostatic cancer tissue, and the mutation was also detected in the leukocyte DNA of the patient and his offspring. The mutation changed codon 726 in exon E from arginine to leucine and was a germ line mutation. The mutation we found in exon E of the hAR gene does not alter the ligand binding specificity of the AR, but the mutated receptor was activated by estradiol to a significantly greater extent than the wild-type receptor. The AR gene mutation described in this study might be one explanation for the altered biological activity of prostatic cancer.

The molecular mechanisms underlying the development and progression of prostate cancer are poorly understood. Epidemiological studies have suggested that 5-10% of all prostate cancers are familial, and numerous chromosomal loci have been associated with prostate cancer in multicentre linkage studies. However, no putative susceptibility genes harboured in these chromosomal regions have thus far been identified. Several recurrent chromosomal alterations in prostate cancer have been detected in comparative genomic hybridization (CGH) and loss of heterozygosity (LOH) analysis. The target genes for many of these aberrations are still not known. It seems that the androgen receptor (AR) signalling pathway plays a crucial role in both early development as well as in late progression of the disease. Both germ-line and somatic genetic alterations in the AR gene have been demonstrated in prostate cancer patients. The intention of this review is to summarize the current knowledge of molecular mechanisms in the development of prostate cancer.

Prostate cancer is one of the most common cancers among men in many Western countries, including Finland. However, the molecular genetic events associated with the development and progression of the disease are poorly known. According to the multistep model of carcinogenesis, several genetic aberrations take place in prostate cancer, but only a few genes potentially involved in prostatic carcinogenesis have been identified.It has been suggested that genetic alterations take place in several chromosomal regions in prostate cancer and, in comparative genomic hybridization (CGH) studies, the long arm of chromosome 16 is among those showing the most frequent loss (Joos et al, 1995;Visakorpi et al, 1995;Cher et al, 1996). Losses at chromosome 16 have been reported to occur almost exclusively in the long arm (q) (Bergerheim et al, 1991;Visakorpi et al, 1995;Cher et al, 1996). Both primary and metastatic tumours have been found to show allelic loss at 16q, and the occurrence of loss of heterozygosity (LOH) has also been associated with clinicopathological variables such as aggressive and metastatic behaviour of the disease and poor differentiation of the tumour (Carter et al, 1990;Suzuki et al, 1996;Elo et al, 1997;Latil et al, 1997). The most common area of deletion has been suggested to be distal in 16q, but the most recent results have indicated evidence of loss of several independent regions in 16q (Suzuki et al, 1996;Elo et al, 1997;Latil et al, 1997).Particular interest in losses at 16q has been paid to the region 16q21.1, where a potential tumour-suppressor gene, that for Ecadherin, is located. Decreased E-cadherin expression has been associated with poor prognosis of prostate cancer (Umbas et al, 1994). Recently, the regions of loss at chromosome arm 16q have been narrowed down. It has been suggested in several reports that losses at 16q are concentrated in three independent regions (Suzuki et al, 1996;Latil et al, 1997). The proximal area of loss is suggested to be located somewhere at 16q21.1 and the distal area of loss has been suggested to lie at 16q24.3. The central region of loss has been reported to be at 16q23.2 (Latil et al, 1997), but it has also been reported to be located at 16q23.2-q24.1 (Suzuki et al, 1996). Our recent data indicate that a 7.6-cM central area of loss is located at 16q24.1-q24.2, between markers D16S504 and D16S422. In addition, LOH at 16q24.1-q24.2 (HSD17B2 and D16S422) was found to be the most frequent area of deletion, and it was significantly correlated with aggressive and metastatic behaviour of the disease and also with poorly differentiated tumours (Elo et al, 1997).There are several candidate genes putatively involved in prostatic carcinogenesis located distally at 16q. The 17HSD type 2 gene (HSD17B2), located at 16q24.1-q24.2, encodes the 17β-hydroxysteroid dehydrogenase (17HSD) type 2 isoenzyme, which Summary Loss of heterozygosity at chromosome arm 16q is a frequent event in human prostate cancer. In this study, loss of heterozygosity at 16q was studied in 44 prostate ca...

Clinical resistance to the HER-2 oncogene–targeting drug trastuzumab (Herceptin) exists, but studies of the resistance mechanisms are hampered by the lack of suitable experimental model systems. We established a carcinoma cell line (designated JIMT-1) from a pleural metastasis of a 62-year old patient with breast cancer who was clinically resistant to trastuzumab. JIMT-1 cells grow as an adherent monolayer and form xenograft tumors in nude mice. JIMT-1 cells have an amplified HER-2 oncogene, which showed no identifiable mutations in its coding sequence. JIMT-1 cells overexpress HER-2 mRNA and protein, and the levels of HER-1, HER-3, and HER-4 mRNA and protein were similar to the trastuzumab-sensitive cell line SKBR-3. The cell line lacks expression of hormone receptors (estrogen receptors and progesterone receptors) and is phenotypically of epithelial progenitor cell origin, as evidenced by immunohistochemical positivity for both cytokeratins 5/14 and 8/18. JIMT-1 cells were insensitive to trastuzumab and another HER-2-inhibiting drug, pertuzumab (2C4), in vitro and in xenograft tumors. Small molecule tyrosine kinase inhibitors Ci1033 and ZD1839 inhibited the JIMT-1 cell growth but to a lesser degree than in trastuzumab-sensitive BT-474 cells. The lack of growth inhibition was rationalized by the unaltered Akt phosphorylation in JIMT-1 cells. Erk1/2 phosphorylation was slightly reduced but still evident in JIMT-1 cells. We conclude that the JIMT-1 cell line provides a valuable experimental model for studies of new trastuzumab-resistance mechanisms.