PD-1 blockade in subprimed CD8 cells induces dysfunctional PD-1+CD38hi cells and anti-PD-1 resistance

Understanding resistance to antibody to programmed cell death protein 1 (PD-1; anti-PD-1) is crucial for the development of reversal strategies. In anti-PD-1-resistant models, simultaneous anti-PD-1 and vaccine therapy reversed resistance, while PD-1 blockade before antigen priming abolished therapeutic outcomes. This was due to induction of dysfunctional PD-1⁺CD38^hi CD8⁺ cells by PD-1 blockade in suboptimally primed CD8 cell conditions induced by tumors. This results in erroneous T cell receptor signaling and unresponsiveness to antigenic restimulation. On the other hand, PD-1 blockade of optimally primed CD8 cells prevented the induction of dysfunctional CD8 cells, reversing resistance. Depleting PD-1⁺CD38^hi CD8⁺ cells enhanced therapeutic outcomes. Furthermore, non-responding patients showed more PD-1⁺CD38⁺CD8⁺ cells in tumor and blood than responders. In conclusion, the status of CD8⁺ T cell priming is a major contributor to anti-PD-1 therapeutic resistance. PD-1 blockade in unprimed or suboptimally primed CD8 cells induces resistance through the induction of PD-1⁺CD38^hi CD8⁺ cells that is reversed by optimal priming. PD-1⁺CD38^hi CD8⁺ cells serve as a predictive and therapeutic biomarker for anti-PD-1 treatment. Sequencing of anti-PD-1 and vaccine is crucial for successful therapy.

Continuous hyperfractionated accelerated radiotherapy using modern radiotherapy techniques for nonsmall cell lung cancer patients unsuitable for chemoradiation

INTRODUCTION

The continuous hyperfractionated and accelerated radiotherapy (CHART) regimen of radiotherapy (RT) for nonsmall cell lung cancer is underused outside the UK. We present the first Indian experience of using CHART for patients, who were not suitable for chemotherapy or concurrent chemo-RT.

METHODS

We retrospectively reviewed the data of patients treated using CHART at our institution between January 2014 and December 2015.

RESULTS

Thirty-seven patients were treated using CHART. Planning methods and dosimetry parameters are described. Three-dimensional conformal RT was used for treatment planning and delivery in 23 patients and volumetric modulated arc RT was necessary for 14 patients. Patients in our series had a median age of 70 years (interquartile range 65.50-74.00) and 86.5% had Stage III disease. Median follow-up was short at 13.0 months. Actuarial rates of 1-year progression-free survival, 1-year overall survival (OS), and 2-year OS were 31.9%, 59.5%, and 28.5%, respectively. This treatment was well tolerated with manageable and some reversible acute esophageal toxicity (91.9% CONCLUSION: Our results indicate that CHART is feasible, safe, and well tolerated in Indian patients who are clinically found to be not suitable for either sequential or concurrent chemo- RT.

Actual gains in dosimetry and treatment delivery efficiency from volumetric modulated arc radiotherapy for inoperable, locally advanced lung cancer over five-field forward-planned intensity-modulated radiotherapy

AIMS

Volumetric modulated arc radiotherapy (VMAT) is used for inoperable, locally advanced nonsmall cell lung cancer, where three-dimensional conformal radiotherapy (3D-CRT) cannot yield an acceptable plan.

METHODS

The planning and treatment data were prospectively collected on the first 18 patients treated using VMAT plans. We analyzed the actual dosimetric gain and impact on treatment, compared with complex multisegment 3D-CRT (five-field forward-planned intensity-modulated radiotherapy [IMRT]) that were generated for treatment. Proportion of planning target volume (PTV) receiving 95% dose (PTV-V95%) conformity index (CI), conformity number (CN), dose homogeneity index (DHI), monitor units (MUs), and treatment time were also analyzed.

RESULTS

The PTV coverage (PTV-V95%) was improved from a median of 91.41% for 5-F forward-IMRT to 98.25% for VMAT (P < 0.001). The CI improved with a mean of 1.12 for VMAT and 1.31 for 5-F forward-IMRT (P < 0.001). The mean DHI improved from 1.15 for forward-IMRT to 1.08 for VMAT (P < 0.001). The mean CN improved from 0.62 for forward-IMRT to 0.87 for VMAT (P < 0.001). No significant increase in the low-dose bath (V5, V10 and mean lung dose) to the lung was seen. Significantly higher number of MUs (P < 0.001) and shorter treatment delivery times (P = 0.03) were seen with VMAT.

CONCLUSION

VMAT resulted in improvement in target volume coverage, demonstrated by PTV-V95%, CI, CN, and DHI, without any increase in the low-dose bath to the lung. For conventional fractionation, VMAT requires more MUs (P < 0.001) but has a shorter treatment delivery time (P = 0.03) per fraction.

Concurrent PD-1 Blockade Negates the Effects of OX40 Agonist Antibody in Combination Immunotherapy through Inducing T-cell Apoptosis

Combination therapies that depend on checkpoint inhibitor antibodies (Abs) such as for PD-1 or its ligand (PD-L1) together with immune stimulatory agonist Abs like anti-OX40 are being tested in the clinic to achieve improved antitumor effects. Here, we studied the potential therapeutic and immune effects of one such combination: Ab to PD-1 with agonist Ab to OX40/vaccine. We tested the antitumor effects of different treatment sequencing of this combination. We report that simultaneous addition of anti-PD-1 to anti-OX40 negated the antitumor effects of OX40 Ab. Antigen-specific CD8⁺ T-cell infiltration into the tumor was diminished, the resultant antitumor response weakened, and survival reduced. Although we observed an increase in IFNγ-producing E7-specifc CD8⁺ T cells in the spleens of mice treated with the combination of PD-1 blockade with anti-OX40/vaccine, these cells underwent apoptosis both in the periphery and the tumor. These results indicate that anti-PD-1 added at the initiation of therapy exhibits a detrimental effect on the positive outcome of anti-OX40 agonist Ab. These findings have important implications on the design of combination immunotherapy for cancer, demonstrating the need to test treatment combination and sequencing before moving to the clinic. Cancer Immunol Res; 5(9); 755-66. ©2017 AACR.

High-dose Neural Stem Cell Radiation May Not Improve Survival in Glioblastoma

AIMS

To evaluate the effect of radiotherapy dose-volume parameters of neural stem cell (NSC) compartment on progression-free survival (PFS) and overall survival after post-resection chemoradiation in newly diagnosed glioblastoma.

MATERIALS AND METHODS

Sixty-one patients with unifocal glioblastoma were included. Ipsilateral (NSC_Ipsi), contralateral (NSC_Contra) and combined NSC (NSC_Combined) were contoured on radiotherapy planning computerised tomography datasets. NSC dose-volume parameters were correlated with PFS and overall survival. Serial magnetic resonance imaging scans were assessed to understand the frequency of pre- and post-treatment involvement of the NSC by contrast enhancing lesions (CELs).

RESULTS

Baseline involvement of NSC with CELs was seen in 67.2% and 95.9% had CELs and FLAIR abnormalities at progression. With a median follow-up of 14.1 months (interquartile range 9.4-20.6 months), median PFS and overall survival were 14.5 (95% confidence interval 11.6-17.5) and 16.2 (95% confidence interval 13.3-19.2) months, respectively. Poor Eastern Cooperative Oncology Group performance score, advanced recursive partitioning analysis class, unmethylated O6-methylguanine methyltransferase (MGMT) status, higher than median of mean NSC_Ipsi dose were associated with significantly inferior PFS and overall survival on univariate analysis. On multivariate analysis, unmethylated MGMT status, higher than median of mean doses to NSC_Ipsi and poor compliance to adjuvant temozolomide were independent predictors of inferior survival.

CONCLUSIONS

In this cohort, 67.2% of newly diagnosed glioblastoma patients had NSC involved with CELs at presentation and 95.9% at progression. This might be an imaging surrogate of the current notion of gliomagenesis and progression from NSC rests. A high radiation dose to NSC_Ipsi was significantly associated with inferior survival. This could be a function of larger tumours and planning target volumes in those with pre-treatment NSC involvement. Methylated MGMT and good compliance to adjuvant temozolomide were independent predictors of better survival. Until further evidence brings hope for glioblastoma, elective, partial NSC irradiation remains experimental.

Outcomes Following a Moderately Hypofractionated Adjuvant Radiation (START B Type) Schedule for Breast Cancer in an Unscreened Non-Caucasian Population

AIMS

Breast cancer is the most common cancer in women. Western data have confirmed hypofractionated radiation therapy to be safe and effective in the adjuvant radiation therapy of breast cancers. We report the disease-related outcomes in a non-Caucasian, unscreened population treated with hypofractionated radiation.

MATERIALS AND METHODS

Unselected case notes of patients presenting to a tertiary cancer centre between June 2011 and December 2013 were reviewed from the electronic hospital case records. Patients with a diagnosis of non-metastatic invasive non-sarcomatous breast cancer were identified. Demographic information, oestrogen receptor (ER), progesterone receptor (PR), HER2 status, pathological tumour, nodal stage at diagnosis and outcomes of treatment, including systemic therapies, surgery and hypofractionated radiation, were documented. Local recurrence rates, disease-free survival (DFS) and overall survival were calculated.

RESULTS

Overall 925 patents were identified, median age 53.0 years (interquartile range 45-61), 330 of whom had neoadjuvant chemotherapy. The median follow-up time was 22.6 months and 23.5 months for overall and neoadjuvant chemotherapy groups, respectively. ER, PR and HER2 status was available in 788 patients, 77.2% of whom were ER/PR positive, 14.7% had triple negative disease, while 9.5% were HER2 rich. Overall, 34.2% (113 patients) underwent breast conservation surgery; 744 (80.4%) patients were treated with systemic chemotherapy and 878 (94.9%) patients received adjuvant radiation therapy, of whom 407 (44.0%) received supraclavicular-fossa radiotherapy. Overall survival, DFS and locoregional recurrence-free survival (LRRFS) for the overall group were 93%, 86.9% and 97.1%, respectively. LRRFS in the breast conservation surgery versus mastectomy groups were 99% versus 95.5% (P=0.003), with more node-positive patients in the mastectomy group. Stage N0/1 had better LRRFS compared with N2/2 (99.1% versus 95.7%); 94.3% versus 82.3%; P=0.005, 0.000. Grade 3 (53.8%) tumours had worse overall survival compared with grade 1 or grade 2 disease (89.6% versus 100% and 96.4%; P<0.001) although the LRRFS was not significantly different between the groups (98.9% versus 97.8%; P=0.37). There was no difference in LRRFS based on molecular subtypes.

CONCLUSION

Local recurrence rates following hypofractionated radiation in our population were comparable with those reported by the START trialists and were found to be safe in the medium term for patients irrespective of breast conservation surgery/mastectomy or radiotherapy to the supraclavicular field. Molecular group frequencies were comparable with Western populations but did not affect LRRFS.

Pitfalls and Challenges to Consider before Setting up a Lung Cancer Intensity-modulated Radiotherapy Service: A Review of the Reported Clinical Experience

Intensity-modulated radiotherapy (IMRT) is being increasingly used for the treatment of non-small cell lung cancer (NSCLC), despite the absence of published randomised controlled trials. Planning studies and retrospective series have shown a decrease in known predictors of lung toxicity (V20 and mean lung dose) and the maximum spinal cord dose. Potential dosimetric advantages, accessibility of technology, a desire to escalate dose or a need to meet normal organ dose constraints are some of the factors recognised as supporting the use of IMRT. However, IMRT may not be appropriate for all patients being treated with radical radiotherapy. Unique problems with using IMRT for NSCLC include organ and tumour motion because of breathing and the potential toxicity from low doses of radiotherapy to larger amounts of lung tissue. Caution should be exercised as there is a paucity of prospective data regarding the efficacy and safety of IMRT in lung cancer when compared with three-dimensional conformal radiotherapy and IMRT data from other cancer sites should not be extrapolated. This review looks at the use of IMRT in NSCLC, addresses the challenges and highlights the potential benefits of using this complex radiotherapy technique.

Programmed death-1 & its ligands: promising targets for cancer immunotherapy

Novel strategies for cancer treatment involving blockade of immune inhibitors have shown significant progress toward understanding the molecular mechanism of tumor immune evasion. The preclinical findings and clinical responses associated with programmed death-1 (PD-1) and PD-ligand pathway blockade seem promising, making these targets highly sought for cancer immunotherapy. In fact, the anti-PD-1 antibodies, pembrolizumab and nivolumab, were recently approved by the US FDA for the treatment of unresectable and metastatic melanoma resistant to anticytotoxic T-lymphocyte antigen-4 antibody (ipilimumab) and BRAF inhibitor. Here, we discuss strategies of combining PD-1/PD-ligand interaction inhibitors with other immune checkpoint modulators and standard-of-care therapy to break immune tolerance and induce a potent antitumor activity, which is currently a research area of key scientific pursuit.

Abstract 5022: Peptide therapeutic inhibiting PD1 immune checkpoint ligands: Potential for greater anti-tumor immune response and better management of immune-related adverse events

Antibodies to immune checkpoint receptors have revolutionized the outlook of cancer therapy by achieving highly durable clinical responses. However, along with impressive clinical activity (response rate of ∼25% with either anti-CTLA4 or anti-PD1 as single agent, but &gt; 50% with a combination), severe immune-related adverse events (irAEs) due to the breaking of immune self- tolerance (25-30% with anti-CTLA4 and up to 15-17% with anti-PD1) are becoming increasingly evident. Sustained target inhibition as a result of a long half-life (&gt;15-20 days) and &gt;70% target occupancy for months are likely contributing to severe irAEs observed in the clinic with antibodies targeting immune checkpoint proteins. The antibodies targeting PD-1 signaling pathway are either based on receptor (PD-1) or its ligands (PD-L1 & PDL2). It has also been reported that PDL1 also interacts with B7-1(CD80) resulting in negative T-cell regulation. Our efforts are therefore focused on (a) developing a first in class peptide therapeutic inhibiting all three reported interaction of PD-1 pathway to improve the anti-tumor immune response (b) developing immune checkpoint blockers with potent anti-tumor activity but with a shorter pharmacokinetic profile as a strategy to better manage severe irAEs.

Peptide antagonist AUR-012, constructed with elements from human PD-1 receptor, displayed equipotent antagonism towards PD-L1 and PD-L2 with potent activity in rescue of lymphocyte proliferation and effector functions. Additionally crosslinking study to evaluate the effect of AUR-12 on B7.1 - PDL-1 interaction supports the finding that AUR-012 prevents the interaction of B7.1 with PD-L1. Rescue of proliferation of immune cells analyzed upon stimulation with anti-CD3/anti-CD-28 indicated a complete rescue of CD4+ and CD8+ T cells and a complete suppression of regulatory T cells. Sustained activation of circulatory immune cells and their ability to secrete IFN-γ up to 72 h indicate that pharmacodynamic effects persist even after the clearance of AUR-012 in animal models, thus supporting a dosing interval of up to 3 days. In models of melanoma, breast, kidney and colon cancers, AUR-012 showed efficacy in inhibition of both primary tumor growth and metastasis. Additionally, anti-tumor activity of AUR-012 in a pre-established CT26 model correlated well with pharmacodynamic effects as indicated by intratumoral recruitment of CD4+ and CD8+ T cells, and a reduction in PD1+ T cells (both CD4+ & CD8+) in tumor and blood. In 14-day repeated dose toxicity studies, AUR -012 was well tolerated at 100x of the efficacious doses.

These findings demonstrating inhibition of all PD-1/ PD-1 ligands mediated co-inhibitory signaling pathway and the observed correlation between anti-tumor activities with the modulation of specific T-cell populations support further development of AUR-012 in the clinic.

Citation Format: Murali Ramachandra, Pottayil G. Sasikumar, Rajeev K. Shrimali, Sreenivas Adurthi, Raghuvir Ramachandra, Leena K. Satyam, Amit A. Dhudashia, Samiulla Dhodheri, K B. Sunilkumar. Peptide therapeutic inhibiting PD1 immune checkpoint ligands: Potential for greater anti-tumor immune response and better management of immune-related adverse events. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 5022. doi:10.1158/1538-7445.AM2014-5022

Abstract B294: Antitumor efficacy of AUR-012, a peptide antagonist of the PD1 immune checkpoint pathway, correlates well with the modulation of specific T-cell populations

Recent breakthroughs in achieving highly durable clinical responses via immunotherapy to inhibit immune checkpoint proteins including CTLA4 and PD1 have revolutionized the outlook for cancer therapy. However, along with impressive clinical activity (response rate of ∼25% with either anti-CTLA4 or anti-PD1 as single agent, but more than 50% with a combination), immune-related toxicities due to the breaking of immune self-tolerance (25-30% with anti-CTLA4 and up to 15-17% with anti-PD1) are becoming increasingly visible. Sustained inhibition of the signaling as a result of a very long half-life (&gt;15-20 days) and &gt;70% target occupancy for months are likely contributing to severe adverse effects observed in clinical trials with antibodies targeting immune checkpoint proteins. Our efforts are therefore focused towards developing novel immune checkpoint blockers with potent antitumor activity but with a shorter pharmacokinetic profile as a strategy to better manage severe adverse effects. Herein we report our findings from the pharmacodynamic characterization of a novel peptide inhibitor of the PD1 signaling that displays desired pharmacokinetic and efficacy profile. Peptide antagonist AUR-012, constructed with elements from human PD-1 ectodomain, displayed equipotent antagonism towards PD-L1 and PD-L2 with potent activity in rescue of lymphocyte proliferation and effector functions. Rescue of proliferation of immune cell subset populations analyzed in vitro using anti-CD3/anti CD-28 stimulation indicated that the functional capacity of T-cells has been reinvigorated by AUR-012 resulting in a complete rescue of CD4+ and CD8+ T cell proliferation in the presence of PD-L1. Similar effect in the rescue of proliferation was also observed for B-cells and NK cells. Interestingly, the proliferation of CD4+, FOxP3+ T cells was completely abolished with AUR-012 treatment indicating a complete suppression of regulatory T cells. Sustained activation of circulatory immune cells and their ability to secrete IFN-γ up to 72 h indicate that pharmacodynamic effects persist even after the clearance of AUR-012 in animal models, thus supporting a dosing interval of up to 3 days irrespective of the short half-life of the peptide. In preclinical models of melanoma, breast, kidney and colon cancers, AUR-012 showed superior showed superior efficacy compared to therapeutic agents currently used in the clinic in inhibition of both primary tumor growth and metastasis. Additionally, antitumor activity of AUR-012 in a pre-established CT26 model correlated well with pharmacodynamic effects as indicated by intratumoral recruitment of CD4+ and CD8+ T cells, and a reduction in PD1+ T cells (both CD4+ & CD8+) in tumor and blood. In conclusion, the observed correlation between antitumor activities with the modulation of specific T-cell populations supports the use of immunophenotyping as a potential therapeutic biomarker strategy in the planned clinical studies with AUR-012.

Citation Information: Mol Cancer Ther 2013;12(11 Suppl):B294.

Citation Format: Murali Ramachandra, Pottayil G. Sasikumar, Rajeev K. Shrimali, Sreenivas Adurthi, Raghuveer Ramachandra, Leena K. Satyam, Amit A. Dhudashiya, Dodheri S. Samiulla, K B Sunilkumar. Antitumor efficacy of AUR-012, a peptide antagonist of the PD1 immune checkpoint pathway, correlates well with the modulation of specific T-cell populations. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2013 Oct 19-23; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(11 Suppl):Abstract nr B294.

Gene therapy using genetically modified lymphocytes targeting VEGFR-2 inhibits the growth of vascularized syngenic tumors in mice

Immunotherapies based on adoptive cell transfer are highly effective in the treatment of metastatic melanoma, but the use of this approach in other cancer histologies has been hampered by the identification of appropriate target molecules. Immunologic approaches targeting tumor vasculature provide a means for the therapy of multiple solid tumor types. We developed a method to target tumor vasculature, using genetically redirected syngeneic or autologous T cells. Mouse and human T cells were engineered to express a chimeric antigen receptor (CAR) targeted against VEGFR-2, which is overexpressed in tumor vasculature and is responsible for VEGF-mediated tumor progression and metastasis. Mouse and human T cells expressing the relevant VEGFR-2 CARs mediated specific immune responses against VEGFR-2 protein as well as VEGFR-2-expressing cells in vitro. A single dose of VEGFR-2 CAR-engineered mouse T cells plus exogenous IL-2 significantly inhibited the growth of 5 different types of established, vascularized syngeneic tumors in 2 different strains of mice and prolonged the survival of mice. T cells transduced with VEGFR-2 CAR showed durable and increased tumor infiltration, correlating with their antitumor effect. This approach provides a potential method for the gene therapy of a variety of human cancers.

Antiangiogenic agents can increase lymphocyte infiltration into tumor and enhance the effectiveness of adoptive immunotherapy of cancer

Adoptive cell transfer (ACT)-based immunotherapies can mediate objective cancer regression in animal models and in up to 70% of patients with metastatic melanoma; however, it remains unclear whether the tumor vasculature impedes the egress of tumor-specific T cells, thus hindering this immunotherapy. Disruption of the proangiogenic interaction of vascular endothelial growth factor (VEGF) with its receptor (VEGFR-2) has been reported to "normalize" tumor vasculature, enhancing the efficacy of chemotherapeutic agents by increasing their delivery to the tumor intersitium. We thus sought to determine whether disrupting VEGF/VEGFR-2 signaling could enhance the effectiveness of ACT in a murine cancer model. The administration of an antibody against mouse VEGF synergized with ACT to enhance inhibition of established, vascularized, B16 melanoma (P = 0.009) and improve survival (P = 0.003). Additive effects of an antibody against VEGFR-2 in conjunction with ACT were seen in this model (P = 0.013). Anti-VEGF, but not anti-VEGFR-2, antibody significantly increased infiltration of transferred cells into the tumor. Thus, normalization of tumor vasculature through disruption of the VEGF/VEGFR-2 axis can increase extravasation of adoptively transferred T cells into the tumor and improve ACT-based immunotherapy. These studies provide a rationale for the exploration of combining antiangiogenic agents with ACT for the treatment of patients with cancer.

Selenoproteins mediate T cell immunity through an antioxidant mechanism

Selenium is an essential dietary element with antioxidant roles in immune regulation, but there is little understanding of how this element acts at the molecular level in host defense and inflammatory disease. Selenium is incorporated into the amino acid selenocysteine (Sec), which in turn is inserted into selenoproteins in a manner dependent on Sec tRNA([Ser]Sec). To investigate the molecular mechanism that links selenium to T cell immunity, we generated mice with selenoprotein-less T cells by cell type-specific ablation of the Sec tRNA([Ser]Sec) gene (trsp). Herein, we show that these mutant mice exhibit decreased pools of mature T cells and a defect in T cell-dependent antibody responses. We also demonstrate that selenoprotein deficiency leads to oxidant hyperproduction in T cells and thereby suppresses T cell proliferation in response to T cell receptor stimulation. These findings offer novel insights into immune function of selenium and physiological antioxidants.

Low-dose palliative splenic irradiation in haematolymphoid malignancy

Patients are treated with palliative splenic irradiation (SI) to relieve pain, volume effects and the clinical consequences of hypersplenism. The case records of 19 patients treated with palliative SI at our centre, from April 2003 to November 2004, were reviewed. Twenty-two courses of SI were identified. The radiation doses delivered ranged from 150 to 800 cGy (median 450 cGy). The fraction sizes ranged from 25 to 100 cGy. Parallel-opposed anteroposterior-posteroanterior portals were the most common field arrangement. The target volume was reduced in 18 out of 22 courses. The percentage of field reduction ranged from 0 to 59.57% (mean 24.82%). Twelve of 14 courses were successful in achieving symptom palliation. Of the six patients who received SI for a combination of splenic symptoms and abnormal blood tests, five had symptomatic palliation but only one patient responded haematologically. Of two patients who were started on palliative SI for abnormal haematology alone, only one responded. In summary, 17 of 20 (85%) courses of SI initiated for symptom control resulted in effective palliation. Only two of eight (25%) courses of SI started for abnormal blood counts produced a desired response. To conclude, SI offers an effective and well-tolerated palliative treatment option.

Selenoprotein expression is essential in endothelial cell development and cardiac muscle function

LoxP-Cre technology was used to remove the selenocysteine tRNA gene, trsp, in either endothelial cells or myocytes of skeletal and heart muscle to elucidate the role of selenoproteins in cardiovascular disease. Loss of selenoprotein expression in endothelial cells was embryonic lethal. A 14.5-day-old embryo had numerous abnormalities including necrosis of the central nervous system, subcutaneous hemorrhage and erythrocyte immaturity. Loss of selenoprotein expression in myocytes manifested no apparent phenotype until about day 12 after birth. Affected mice had decreased mobility and an increased respiratory rate, which proceeded rapidly to death. Pathological analysis revealed that mice lacking trsp had moderate to severe myocarditis with inflammation extending into the mediastinitis. Thus, ablation of selenoprotein expression demonstrated an essential role of selenoproteins in endothelial cell development and in proper cardiac muscle function. The data suggest a direct connection between the loss of selenoprotein expression in these cell types and cardiovascular disease.

Selenocysteine tRNA identification in the model organisms Dictyostelium discoideum and Tetrahymena thermophila

Characterizing Sec tRNAs that decode UGA provides one of the most direct and easiest means of determining whether an organism possesses the ability to insert selenocysteine (Sec) into protein. Herein, we used a combination of two techniques, computational to identify Sec tRNA genes and RT-PCR to sequence the gene products, to unequivocally demonstrate that two widely studied, model protozoans, Dictyostelium discoideum and Tetrahymena thermophila, encode Sec tRNA in their genomes. The advantage of using both procedures is that computationally we could easily detect potential Sec tRNA genes and then confirm by sequencing that the Sec tRNA was present in the tRNA population, and thus the identified gene was not a pseudogene. Sec tRNAs from both organisms decode UGA. T. thermophila Sec tRNA, like all other sequenced Sec tRNAs, is 90 nucleotides in length, while that from D. discoideum is 91 nucleotides long making it the longest eukaryotic sequenced to date. Evolutionary analyses of known Sec tRNAs reveal the two forms identified herein are the most divergent eukaryotic Sec tRNAs thus far sequenced.

Integrins and disintegrins: the candidate molecular players in sperm-egg interaction

Fertilization includes sperm-egg recognition, adhesion, binding, fusion and egg activation. Integrin (ITG) receptors which are adhesion molecules are expressed on mouse, hamster and human gametes and their potential ligands also have been identified. Role of ITGs during fertilization is supported by inhibition of sperm-egg adhesion and/or fusion by means of anti-ITG mAbs, Arg-Gly-Asp (RGD) or disintegrin-like peptides. This review includes the current understanding of the molecular mechanism that regulates sperm-egg interaction and implications of this knowledge for assessing the fertility potential of men and immunocontraceptive method.