Early Initiation of Temozolomide Therapy May Improve Response in Aggressive Pituitary Adenomas

IntroductionAggressive pituitary adenomas (APAs) are, by definition, resistant to optimal multimodality therapy. The challenge lies in their early recognition and timely management. Temozolomide is increasingly being used in patients with APAs, but evidence supporting a favorable response with early initiation is lacking.MethodsThis was a single-center study of all patients with APAs who received at least 3 cycles of temozolomide (150–200 mg/m2). Their baseline clinico-biochemical and radiological profiles were recorded. Immunohistochemical evaluation for cell-cycle markers O6-methylguanine-DNA methyltransferase (MGMT), MutS homolog 2 (MSH2), MutS homolog 6 (MSH6), MutL homolog 1 (MLH1), and postmeiotic segregation increased 2 (PMS2) was performed, and h-scores (product of the number of positive cells and staining intensity) were calculated. Response was assessed in terms of radiological response using the RECIST criteria. Patients with controlled disease (≥30% reduction in tumor volume) were classified as responders.ResultsThe study comprised 35 patients (48.6% acromegaly, 37.1% prolactinomas, and 14.3% non-functioning pituitary adenomas). The median number of temozolomide (TMZ) cycles was 9 (IQR 6–14). Responders constituted 68.6% of the cohort and were more likely to have functional tumors, a lower percentage of MGMT-positive staining cells, and lower MGMT h-scores. There was a significantly longer lag period in the initiation of TMZ therapy in non-responders as compared with responders (median 36 vs. 15 months, p = 0.01). ROC-derived cutoffs of 31 months for the duration between diagnosis and TMZ initiation, low-to-intermediate MGMT positivity (40% tumor cells), and MGMT h-score of 80 all had a sensitivity exceeding 80% and a specificity exceeding 70% to predict response.ConclusionEarly initiation of TMZ therapy, functional tumors, and low MGMT h-score predict a favorable response to TMZ in APAs.

High-Frequency Homologous Recombination Occurred Preferentially in Populus

Homologous recombination (HR), the most significant event in meiosis, has important implications for genetic diversity and evolution in organisms. Heteroduplex DNA (hDNA), the product of HR, can be captured by artificially induced chromosome doubling during the development of the embryo sac to inhibit postmeiotic segregation, subsequently, and hDNAs are directly detected using codominant simple sequence repeat (SSR) markers. In the present study, two hybrid triploid populations derived from doubling the chromosomes of the embryo sac induced by high temperature in Populus tomentosa served as starting materials. Eighty-seven, 62, and 79 SSR markers on chromosomes 01, 04, and 19, respectively, that were heterozygous in the maternal parent and different from the paternal parent were screened to detect and characterize the hDNA in P. tomentosa. The results showed that the hDNA frequency patterns on chromosomes changed slightly when the number of SSR primers increased. The highest hDNA frequency occurred at the adjacent terminal on chromosomes, which was slightly higher than those at the terminals in the two genotypic individuals, and the hDNA frequency gradually decreased as the locus-centromere distance decreased. With the increase in the number of SSR markers employed for detection, the number of recombination events (REs) detected significantly increased. In regions with high methylation or long terminal repeat (LTR) retrotransposon enrichment, the frequency of hDNA was low, and high frequencies were observed in regions with low sequence complexity and high gene density. High-frequency recombination occurring at high gene density regions strongly affected the association between molecular markers and quantitative trait loci (QTLs), which was an important factor contributing to the difficulty encountered by MAS in achieving the expected breeding results.

PMS1 is a differentially expressed gene in brain metastatic human breast cancer.

Metastasis to the brain is a clinical problem in patients with breast cancer (1-3). We mined published microarray data (4, 5) to compare primary and metastatic tumor transcriptomes for the discovery of genes associated with brain metastasis in humans with metastatic breast cancer. We found that the homolog of postmeiotic segregation increased 1, encoded by PMS1, was among the genes whose expression was most different in the brain metastases of patients with metastatic breast cancer as compared to primary tumors of the breast. PMS1 mRNA was present at decreased quantities in brain metastatic tissues as compared to primary tumors of the breast. Expression of PMS1 in primary tumors was significantly correlated with patient overall survival. Modulation of PMS1 expression may be relevant to the biology by which tumor cells metastasize from the breast to the brain in humans with metastatic breast cancer.

Reconstitution of Saccharomyces cerevisiae DNA polymerase ε-dependent mismatch repair with purified proteins

Mammalian and Saccharomyces cerevisiae mismatch repair (MMR) proteins catalyze two MMR reactions in vitro. In one, mispair binding by either the MutS homolog 2 (Msh2)–MutS homolog 6 (Msh6) or the Msh2–MutS homolog 3 (Msh3) stimulates 5′ to 3′ excision by exonuclease 1 (Exo1) from a single-strand break 5′ to the mispair, excising the mispair. In the other, Msh2–Msh6 or Msh2–Msh3 activate the MutL homolog 1 (Mlh1)–postmeiotic segregation 1 (Pms1) endonuclease in the presence of a mispair and a nick 3′ to the mispair, to make nicks 5′ to the mispair, allowing Exo1 to excise the mispair. DNA polymerase δ (Pol δ) is thought to catalyze DNA synthesis to fill in the gaps resulting from mispair excision. However, colocalization of the S. cerevisiae mispair recognition proteins with the replicative DNA polymerases during DNA replication has suggested that DNA polymerase ε (Pol ε) may also play a role in MMR. Here we describe the reconstitution of Pol ε-dependent MMR using S. cerevisiae proteins. A mixture of Msh2–Msh6 (or Msh2–Msh3), Exo1, RPA, RFC-Δ1N, PCNA, and Pol ε was found to catalyze both short-patch and long-patch 5′ nick-directed MMR of a substrate containing a +1 (+T) mispair. When the substrate contained a nick 3′ to the mispair, a mixture of Msh2–Msh6 (or Msh2–Msh3), Exo1, RPA, RFC-Δ1N, PCNA, and Pol ε was found to catalyze an MMR reaction that required Mlh1–Pms1. These results demonstrate that Pol ε can act in eukaryotic MMR in vitro.

Possible association of postmeiotic segregation increased 2 (PMS 2) gene deletion and myelodysplastic syndrome.

e17021 Background: Postmeiotic segregation Increased 2 (PMS2) gene is one of the gene family members found in clusters on chromosome 7 involved in DNA mismatch repair. Mutations in this gene are associated with hereditary nonpolyposis colorectal cancer and Turcot syndrome. PMS-2 defects are not extensively studied and hence there is still considerable potential to detect new hemato-oncological associations with same. Chromosome 7 defects are the most commonly associated genetic abnormalities associated with myelodysplastic syndrome (MDS). Here, we describe a case of a patient with known PMS 2 gene deletion presenting with early onset MDS. Methods: A 52 year old caucasian female came in to our oncology clinic for evaluation after being diagnosed with DCIS of right breast. She underwent surgical resection followed by tamoxifen and surviellance mamograms. She developed gradual onset of fatigue, prompting follow-up laboratory tests which revealed WBC of 8,600, Hgb of 8.5, MCV of 101, and Plt 383,000. B12, folate, and iron studies were normal. Bone marrow biopsy revealed cellularity 80% and cytogenetics with trisomy 8.This lead to diagnosis of myelodysplastic syndrome, refractory cytopenia with multilineage dysplasia and ringed sideroblasts (RCMD-RS). Patient is currently treated with supportive transfusions after lack of benefit of darbopoietin (baseline epo level 67). Family history is pertinent for a son who died at age 21 from colon cancer and a daughter diagnosed at age 22 with colon cancer, who survives. Her daughter subsequently tested positive for G750 PMS-2 from her father and complete deletion of PMS2 from her mother (our patient). Results: PMS2 gene deletion might predispose patients to MDS. Conclusions: Given the common link with chromosome 7 abnormalities, it is therefore possible that there is an associated increased risk of MDS in PMS-2 patients. While our patient did not have any general abnormalities by karyotype, current assays and general karyotyping are of potentially limited value unless specific mutation points are identified. Therefore, additional evaluations may be necessary to better identify at-risk patients.