Adjuvant therapy for stages II and III colon cancer: risk stratification, treatment duration, and future directions

Background

To date, the role of adjuvant systemic therapy in stages ii and iii colon cancer remains a topic of interest and debate. The objective of the present review was to assess the most recent data, specifically addressing methods of risk stratification, duration of therapy, and future directions.

Methods

PubMed and medline were searched for literature pertinent to adjuvant chemotherapy in either stage ii or stage iii colorectal cancer.

Summary

Locoregional disease, histopathology, age, laterality, and a number of other biologic and molecular markers appear to have a role in disease risk stratification. The duration of adjuvant therapy for stage iii disease can vary based on risk factors, but use of adjuvant therapy and duration of therapy in stage ii disease remain controversial. Future directions should include genomic assays and improved study design to provide concrete evidence about the duration of adjuvant folfox or capox and about other types of chemotherapy and immunotherapy.

Efficacy and safety of conversion of mycophenolate mofetil to enteric-coated mycophenolate sodium in Mexican renal transplant children

The aim of the study was to evaluate the efficacy and safety of the conversion of MMF to EC-MPS in pediatric renal transplant recipients. We included 12 patients with stable graft function who were receiving MMF treatment. In the first visit, a complete medical examination was performed, which included a GSRS, a nine-point pharmacokinetic profile, samples for renal, liver and hematological tests and evaluation of IMPDH2 gene expression. The patients were transferred to an equimolar dose of EC-MPS. Two wk later, a clinical evaluation and blood collection, as in the first visit were performed. There was no change in serum creatinine, leukocyte count, serum albumin, or transaminase levels, but we found a statistically significant reduction of hemoglobin after conversion (13.2 +/- 1.6 g/dL with MMF vs. 12.5 +/- 1.3 g/dL when receiving EC-MPS). The GSRS total mean score was 16 +/- 12 with MMF vs. 8 +/- 5 with EC-MPA (p < 0.05). There was no statistically significant difference between formulations in the gene expression of IMPDH 2, in the AUC(0-12h) or in C(max). However, peak concentration occurred later with EC-MPS.

An intertypic herpes simplex virus helicase-primase complex associated with a defect in neurovirulence has reduced primase activity

R13-1 is an intertypic recombinant virus in which the left-hand 18% of the herpes simplex virus type 1 (HSV-1) genome is replaced by homologous sequences from HSV-2. R13-1 is nonneurovirulent and defective in DNA replication in neurons. The defect was localized to the UL5 open reading frame by using marker rescue analysis (D. C. Bloom and J. G. Stevens, J. Virol. 68:3761-3772, 1994). To provide conclusive evidence that UL5 is the only HSV-2 gene involved in the restricted replication phenotype of R13-1, we have characterized the phenotype of a recombinant virus (IB1) in which only the UL5 gene of HSV-1 was replaced by HSV-2 UL5. Data from 50% lethal dose determinations and the in vivo yields of virus suggested that IB1 has the same phenotypic characteristics as R13-1. UL5 is the helicase component of a complex with helicase and primase activities. All three subunits of this complex (UL5, UL8, and UL52) are required for viral DNA replication in all cell types. The intertypic complex HSV-2 UL5-HSV-1 UL8-HSV-1 UL52 was purified and biochemically characterized. The primase activity of the intertypic complex was 10-fold lower than that of HSV-1 UL5-HSV-1 UL8-HSV-1 UL52. The ATPase activity was comparable to that of the HSV-1 enzyme complex, and although the helicase activity was threefold lower, this did not interfere with the synthesis of leading strands by the HSV polymerase. One explanation for these findings is that the interactions between the subunits of the helicase-primase intertypic complex that are important for the full function of each subunit are inappropriate or weak.

Recognition of bacteriophage Qbeta plus strand RNA as a template by Qbeta replicase: role of RNA interactions mediated by ribosomal proteins S1 and host factor

RNA-protein interactions between bacteriophage Qbeta plus strand RNA and the components of the Qbeta replicase system were studied by deletion analysis. Internal, 5'-terminal and 3'-terminal deletions were assayed for template activity with replicase in vitro. Of the two internal binding sites previously described for replicase, we found that the S-site (map position 1247 to 1346) could be deleted without any significant effect on template activity, whereas deletion of the M-site (map position 2545 to 2867) resulted in a strong inactivation and a high salt sensitivity of the residual activity. Binding complexes of the deletion mutant RNAs with the different proteins involved in Qbeta RNA replication were analysed by electron microscopy. The formation of looped complex structures, previously reported and explained as simultaneous interactions with replicase at the S and the M-site, was abolished by deleting the S-site but, surprisingly, not by deleting the M-site. The same types of complexes observed with replicase were also formed with purified protein S1 (the alpha subunit of replicase), suggesting that these internal interactions with Qbeta RNA are mediated by the S1 protein. The Qbeta host factor, a protein required for the template activity of the Qbeta plus strand, was reported earlier to form similar complexes by binding to the S and M-sites (or adjacent sites) and in addition to the 3'-end, resulting in double-looped structures. The patterns of looped complexes observed with the deletion mutant RNAs suggest that the binding of host factor might not involve the S and M-sites themselves but adjacent downstream sites. An additional internal host factor interaction near map position 2300 was detected with several mutant RNAs. Qbeta RNA molecules with 3'-truncations formed 3'-terminal loops with similar efficiency as wild-type RNA, indicating that recognition of the 3'-end by host factor is not dependent on a specific 3'-terminal base sequence.

Identification of recognition elements on bacteriophage Q beta minus strand RNA that are essential for template activity with Q beta replicase

In order to identify the structural elements important for the activity of the Q beta minus strand RNA as a template for Q beta replicase, a series of minus strand RNAs with internal or external deletions were prepared by in vitro transcription from suitable expression plasmids. The template activities of the deletion mutants were determined by single-round replication assays using purified replicase holoenzyme or core enzyme (lacking subunit alpha) in vitro. Two elements of RNA structure and/or sequence important for template activity were found. The first is a segment in the 5'-terminal region (map segment 4078 to 4132) containing a potential stem-loop structure, whose sequence was previously recognized to be highly conserved in the small variant MDV-1 RNA and suggested to be involved in its template recognition. The second element is defined by two partially complementary sequence segments in the 3'-terminal region (map positions 557 to 576 and 24 to 35), that appear to be engaged in long-range base-pairing and may form the stem of a large secondary structure domain, whose branches are not necessary for template recognition. The results obtained with replicase holoenzyme and core enzyme were identical within the accuracy of the method. They confirm the absence of any role of S1 protein in the interaction of replicase with minus strand RNA and further emphasize the profound difference in the interactions of replicase with the plus and minus strand.

Different mechanisms of recognition of bacteriophage Q beta plus and minus strand RNAs by Q beta replicase

Our earlier work on the recognition of Q beta plus strand RNA by replicase had shown by RNase degradation and by electron microscopic techniques that specific binding interactions occurred at two internal sites, the S-site and the M-site, but not at the 3'-end, i.e. the site of initiation of synthesis. Using essentially similar methods, we have found now for binding complexes of replicase with the minus strand a completely different pattern, namely considerable terminal binding, whereas binding to internal sites was without detectable specificity. In the case of plus strand complexes, simultaneous binding at the two internal sites and at a terminal site could be demonstrated by electron microscopy after initiation of RNA synthesis in the presence of host factor, GTP and ATP. A variant plus strand RNA containing a 490 nucleotide duplication near the 5'-end resulted in similar double-looped complexes, however with an elongated free arm, showing that the protein-bound terminal site was the 3'-end of the RNA. Interestingly, the same two-looped structures were also found for complexes consisting of plus strand RNA and host factor without replicase. This suggests that the role of the host factor on the plus strand template is to bring the 3'-end into the proximity of the S-site/M-site domain, where replicase can initiate on it. In contrast, the 3'-end of the minus strand appears to be directly available to the enzyme.

Resistance to Pseudomonas toxin A: a sensitive marker to screen for mutagenic substances using V79 cells

The goal of this study was the development of a mutagenicity assay in V79 cells using Pseudomonas toxin A (PTA) as a selective agent and to compare it with the V79/hypoxanthineguaninephosphoribosyl transferase (HGPT) assay. PTA inhibits protein synthesis by covalently modifying elongation factor 2 (EF-2). Mutations in the EF-2 gene, in genes responsible for the modification of EF-2, and also in genes for the transport of the toxin into the cells, lead to PTA resistance. This involvement of several genes might explain the relatively high spontaneous mean mutation frequency of (122.7 +/- 38.8) x 10(-6) in growing cells (2 micrograms PTA/ml) as compared with (3.97 +/- 4.68) x 10(-6) in the HGPRT test (10 micrograms thioguanine/ml), where only mutations in the HGPRT gene lead to resistance. Methyl methanesulphonate, methyl nitroso urea and UV light were directly mutagenic in the V79/PTA assay. Aflatoxin B1 was mutagenic in the presence of an S9 mix. Benzidine, procarbazine, 2-acetylaminofluorene (2-AAF) and 4-acetylaminofluorene (4-AAF) were positive in the V79/PTA test when rat hepatocytes were used for metabolic activation. Using cells treated together with those used for the PTA assay, benzidine, 2-AAF and 4-AAF were negative in the V79/HGPRT test, while procarbazine was found to be positive under these test conditions. Hexamethyl phosphoramide (HMPA) was tested in the presence of rat hepatocytes and was negative in both test systems. Phorbol-12-myristate-13-acetate was highly cytotoxic, but did not induce mutations at the PTA resistance loci. In conclusion, it was demonstrated that the V79/PTA assay is an easy and sensitive method to screen for gene mutations in mammalian cells.