Researchers Uncover Link Between microRNA Expression and Survival in Lung Cancer Patients
A group of researchers has published a study describing a link between the survival of patients with lung cancer and the expression profiles of two microRNAs, adding to the growing body of evidence that miRNAs play a significant role in disease — especially cancer — and may hold significant promise for prognostic, diagnostic, and therapeutic applications.
Using normal- and tumor-tissue samples from lung cancer patients who had undergone surgical treatment, the researchers found that either the over-expression of hsa-mir-155 or the under-expression of hsa-let-7a-2 correlated with poor survival in patients with adenocarcinoma of the lung. The study, which appears in the March 13 issue of Cancer Cell, also showed that a combination of both was even more closely associated with a negative patient outcome.
According to Curtis Harris, chief of the Laboratory of Human Carcinogenesis at the National Cancer Institute and co-lead author of the paper, the findings may help physicians identify which lung cancer patients treated with surgery would benefit from adjuvant therapy and which would not.
Surgery for lung cancer "is a potential cure," Harris told RNAi News this week. "But we also know that about half of [stage I patients] go on to develop metastatic disease," possibly due to the presence of micrometastases that have gone undetected by existing screening technologies or pathology. While these patients would benefit from additional therapies such as radiation or chemotherapy, these treatments carry "some side effects and untoward consequences, so if you don't need it, you don't want to have it.
"The goal is to have a number of biomarkers — and I think microRNAs are going to be one [type] — that allow you to predict with a high degree of specificity and sensitivity the prognosis and then have a therapeutic and screening regimen that are directed by those biomarkers."
"The goal is to have a number of biomarkers — and I think microRNAs are going to be one [type] — that allow you to predict with a high degree of specificity and sensitivity the prognosis and then have therapeutic and screening regimens that are directed by those biomarkers" so as not to unnecessarily administer potentially harmful treatments, Harris noted.
In the study — which was conducted by the NCI in collaboration with the Ohio State University Comprehensive Cancer Center, the Jikei University School of Medicine in Tokyo, and Japan's National Cancer Center Research Institute — researchers analyzed 104 pairs of primary lung cancers and corresponding non-cancerous lung tissues using an miRNA microchip developed by OSU professor Carlo Croce (see sidebar).
Microarray analysis comparing miRNA expression in cancerous and non-cancerous tissues revealed statistical differences in expression for 43 miRNAs. With further analysis, and by narrowing their analysis to the two most common forms of non-small cell lung cancer, adenocarcinoma and squamous cell carcinoma, the researchers were able to identify five miRNAs that expressed differently in cancerous tissues compared with controls.
Using Kaplan-Meier survival analysis, the researchers found that "lung adenocarcinoma patients with either high hsa-mir-155 or reduced hsa-let-7a-2 expression had a poorer survival than the patients with low hsa-mir-155 or high hsa-let-7a-2 expression, respectively," according to the Cancer Cell paper.
"There have been a variety of studies over the last year or two that have … suggested … that certain microRNAs can predict survival" in various malignancies, Harris said. Our work "adds to [this body of evidence] in a very rigorous way."
Using Ohio State University's miRNA Chip
To obtain the microRNA expression profiles used in their study, the researchers used an oligonucleotide microchip developed by Ohio State University's Carlo Croce and described in the June 29, 2004, issue of the Proceedings of the National Academy of Sciences.
According to the PNAS paper, the chip contains 368 gene-specific oligonucleotide probes generated from 248 human, mouse, and Arabidopsis miRNAs, and 15 human and mouse tRNAs. The sequences corresponded to human and mouse miRNAs found in the Wellcome Trust Sanger Institute's miRNA Registry and ones collected from published papers. For 76 of the miRNAs, two different oligo probes were designed, one containing the active sequence and the other specific for the precursor, which allow for the separate analysis of miRNA and pre-miRNA transcripts for the same gene, the PNAS paper states.
The miRNA microchip was used by Croce and colleagues from Thomas Jefferson University; Compugen; the University of Ferrara in Italy; the NCI; and Italy's Laboratorio di Analisi Cliniche, Ospedale Civile di la Spezia to obtain tissue-specific miRNA expression signatures in human and mouse tissues, which were confirmed by assessment of expression by Northern blots, real-time RT-PCR, and literature searches.
For instance, high expression of mir-155 has been found in certain non-lung cancers such as Burkitt's lymphoma and B cell lymphoma, while it has been reported that mir-143 and mir-145 are reduced in colon cancer, the researchers note in the paper. Additionally, it has been reported that that reduced expression of let-7 is possibly involved in lung cancers, as has increased expression of mir-17-92.
"Nevertheless, this is the beginning, and [the findings] need to be replicated by other laboratories in larger numbers," Harris added.
For his part, Harris said that he and his colleagues at the NCI are planning to follow up on their work in patients with different types of lung cancer and from different ethnic populations. "When you have multiple studies in different populations, you get a sense of whether this is going to be of utility in a much broader scale," he said. "I'm optimistic that will be the case but I want to see the data."
Additionally, he plans to look at "other kinds of cancer too — breast cancer and prostate cancer and colon cancer. I think within two years, maybe less, there will be a spate of reports that will evaluate microRNA profiles and specific microRNAs are a diagnostic and prognostic indicator," Harris said.
"Then, as you identify these different microRNAs as important in cancer, [the question is,] 'What are they doing?' That will hopefully lead to insights into the whole process of carcinogenesis and tumor metastases," and possibly provide new targets for therapeutic intervention.
— Doug Macron ([email protected])