An alternative fixative to formalin fixation for molecular applications: the RCL2(®)-CS100 approach

MGMT assessment in pituitary adenomas: comparison of different immunohistochemistry fixation chemicals

PURPOSE

Despite the established role of O6-methyl-guanine-DNA methyltransferase (MGMT) as a marker for temozolomide response, consensus of the most reliable method to assess MGMT expression in pituitary adenomas is still missing. Currently, immunohistochemistry (IHC) assessment of formaldehyde fixed tissue samples is most widely used in a semiquantitative description. As formaldehyde fails to completely preserve nucleic acids, RCL2, an alcohol-based formaldehyde-free fixative, has been proposed as a more reliable alternative in terms of cell stability. Furthermore, as the current method of IHC is semiquantitative and observer-dependent, pyrosequencing, an objective tool to evaluate the methylation status of the MGMT promoter, has emerged as a reliable and accurate alternative. The aim of this study was to validate the current IHC method for assessment of MGMT protein expression in pituitary adenomas.

METHODS

The tissue samples of 8 macroadenomas with positive IHC MGMT expression (> 50%) were investigated: first, we compared the time dependent stability of MGMT protein expression after pituitary adenoma removal between formaldehyde vs. RCL2. Then, we compared positive IHC MGMT expression with methylated promoter status using pyrosequencing.

RESULTS

In the first 12 h after adenoma removal, tissue samples remained MGMT positive in significantly more samples when fixated with formaldehyde than with RCL2, respectively (96 vs. 81%, p = 0.025).

CONCLUSION

Our data confirm that the current method using formaldehyde tissue fixation and IHC reveals stable and reliable results of MGMT assessment in pituitary adenomas.

Strategies for validation and testing of DNA methylation biomarkers

DNA methylation is a stable covalent epigenetic modification of primarily CpG dinucleotides that has recently gained considerable attention for its use as a biomarker in different clinical settings, including disease diagnosis, prognosis and therapeutic response prediction. Although the advent of genome-wide DNA methylation profiling in primary disease tissue has provided a manifold resource for biomarker development, only a tiny fraction of DNA methylation-based assays have reached clinical testing. Here, we provide a critical overview of different analytical methods that are suitable for biomarker validation, including general study design considerations, which might help to streamline epigenetic marker development. Furthermore, we highlight some of the recent marker validation studies and established markers that are currently commercially available for assisting in clinical management of different cancers.

The pre-analytical phase in surgical pathology

Several sequential passages are involved in the pre-analytical handling of surgical specimens from resection in the surgical theater to paraffin-embedding and storage. Each passage is highly critical and can significantly affect the preservation of morphology, antigens, and nucleic acids. Some key points in this process are still undefined and are subject to high variability among hospitals. High quality and standardization are demanded and pathologists should therefore work to comply with all novel clinical requests (such as genomic and antigenic testing for targeted molecular therapies). Under-vacuum sealing of surgical pieces can be a safe and reliable alternative to storage in large formalin-filled boxes; it prevents dehydration and favors cooling by removing air. Moreover, it implements tissue banking and preservation of nucleic acids. After transport of specimens to pathological anatomy laboratories, the next passage, fixation, has been the object of several attempt to find alternatives to formalin. However, none of the substitutes proved successful, and formalin fixation is still considered the gold standard for preservation of morphology and antigens. RNA has instead been found to be heavily affected by degradation and fragmentation in formalin-fixed tissues. Based on the hypothesis that RNA degradation would be inhibited by maintaining a low temperature, a protocol based on processing tissues with formalin at low temperature (cold fixation) was evaluated and proved useful in obtaining a reduction in RNA fragmentation. Finally, the problem of storage is discussed, in order to find ways to guarantee feasibility of molecular analyses even years after the original diagnosis.

A review of room temperature storage of biospecimen tissue and nucleic acids for anatomic pathology laboratories and biorepositories

Frozen biospecimens are crucial for translational research and contain well-preserved nucleic acids and protein. However, the risks of freezer failure as well as space, cost, and environmental concerns of frozen biospecimens are substantial.

OBJECTIVE

The purpose of the study was to review the current status of room temperature biospecimen storage.

METHODS

We searched Pubmed and vendor websites to identify relevant information.

RESULTS

Formalin-fixed paraffin embedded (FFPE) tissues have great value but their use is limited by cross-linking and fragmentation of nucleic acids, as well as loss of enzymatic activity. Stabilization solutions can now robustly preserve fresh tissue for up to 7days at room temperature. For longer term storage, commercial vendors of chemical matrices claim real time stability of nucleic acids of over 2 years and their accelerated aging studies to date suggest stability for 12years for RNA and 60years for DNA. However, anatomic pathology biorepositories store mostly frozen tissue rather than nucleic acids. Small quantities of tissue can be directly placed on some chemical matrices to stabilize DNA, however RNA and proteins are not preserved. Current lyophilization approaches can preserve histomorphology, DNA, RNA, and proteins though RNA shows moderate degradation after 1-2years. Formalin-free fixatives show improved but varying abilities to preserve nucleic acids and face validation as well as cost barriers in replacing FFPE specimens. The paraffin embedding process can degrade RNA.

CONCLUSION

Development of robust long-term room temperature biospecimen tissue storage technology can potentially reduce costs for the biomedical community in the face of growing targeted therapy needs and decreasing budgets.

Evaluation of two commercial and three home-made fixatives for the substitution of formalin: a formaldehyde-free laboratory is possible

BACKGROUND

Formaldehyde (HCHO) is a gas (available as a 37% concentrated solution, stabilized with methanol). The 10% dilution (approximately 4% formaldehyde) has been used as a fixative since the end of the 19th century. Alternative fixatives are also commercially available or may be prepared in-house in laboratories. Statements by the IARC, along with other USA agencies (CalEPA, RoC/NTP) on the carcinogenicity of formaldehyde for humans renders its substitution in Pathology Departments necessary since the annual use of formalin may exceed 3,500 liters for a medium-large laboratory. To achieve a "formalin-free laboratory" we tested straightforward-to-make fixatives along with registered reagents offered as formalin substitutes.

METHODS

More than two hundreds specimens were fixed in parallel with in-laboratory made fixatives PAGA (Polyethylenglycol, ethyl Alcohol, Glycerol, Acetic acid), two zinc-based fixatives (ZBF, Z7), and commercially-available alternatives (RCL2 and CellBlock). Tissue micro arrays were used for morphological and immunohistochemical comparison. Extraction of RNA was carried out to evaluate preservation of nucleic acids.

RESULTS

Differences compared to formalin fixation were evident in alcohol-based fixatives, mainly restricted to higher stain affinity and considerable tissue shrinkage. Conversely, nuclear detail was superior with these alcohol-based formulas compared to formalin or glyoxale-based recipes. RNA extraction was superior for Z7, PAGA and RCL2 with regard to concentration but relatively comparable regarding quality.

CONCLUSIONS

Abolition of the human carcinogen formaldehyde from pathology laboratories is possible even in contexts whereby commercial alternatives to formalin are unavailable or are too expensive for routine use, and aspiration devices are lacking or not adequately serviced. The use of known formulations, possibly with simple and not-noxious ("alimentary grade") constituents, comparable with registered proprietary products, may expand the search for the ideal fixative combining satisfactory morphology with improved preservation of nucleic acids and proteins as well as being easy and safe to dispose of.

RCL2, a potential formalin substitute for tissue fixation in routine pathological specimens

AIMS

To investigate RCL2 as a fixative for tissue fixation in routine histopathological examination and to assess tissue suitability for ancillary investigations.

METHODS AND RESULTS

  Forty-nine samples from 36 fresh specimens were cut into three equal pieces and fixed in RCL2 diluted in 100% ethanol, RCL2 in 95% ethanol, or neutral buffered formalin as control. Suitability for microtomy, quality of histomorphology, histochemistry, immunohistochemistry, fluorescent and silver in-situ hybridization analysis and extracted genomic DNA were assessed. Microtomy was straightforward in most tissue blocks, but there was difficulty in cutting in approximately a quarter of samples, which required careful handling by an experienced technician. There were no significant differences in tissue morphology between RCL2- and formalin-fixed tissues (P=0.08). Generally, the quality of histochemical staining, immunohistochemistry and in-situ hybridization were comparable to that of formalin-fixed tissues. Inconsistent immunoreactivity was noted, however, with antibodies against pan-cytokeratin and progesterone receptor. Genomic DNA concentration was higher in RCL2-fixed tissues. Using RCL2 diluted in 95% ethanol did not affect fixation quality.

CONCLUSION

RCL2 is a potential formalin substitute suitable as a fixative for use in routine histopathological examination; however, difficulty in microtomy and occasional discrepancies in immunohistochemical reactivity require further optimization of the methodology.