Octreotide LAR and Prednisone as Neoadjuvant Treatment in Patients with Primary or Locally Recurrent Unresectable Thymic Tumors: A Phase II Study

Therapeutic options to cure advanced, recurrent, and unresectable thymomas are limited. The most important factor for long-term survival of thymoma patients is complete resection (R0) of the tumor. We therefore evaluated the response to and the induction of resectability of primarily or locally recurrent unresectable thymomas and thymic carcinomas by octreotide Long-Acting Release (LAR) plus prednisone therapy in patients with positive octreotide scans. In this open label, single-arm phase II study, 17 patients with thymomas considered unresectable or locally recurrent thymoma (n = 15) and thymic carcinoma (n = 2) at Masaoka stage III were enrolled. Octreotide LAR (30 mg once every 2 weeks) was administered in combination with prednisone (0.6 mg/kg per day) for a maximum of 24 weeks (study design according to Fleming´s one sample multiple testing procedure for phase II clinical trials). Tumor size was evaluated by volumetric CT measurements, and a decrease in tumor volume of at least 20% at week 12 compared to baseline was considered as a response. We found that octreotide LAR plus prednisone elicited response in 15 of 17 patients (88%). Median reduction of tumor volume after 12 weeks of treatment was 51% (range 20%-86%). Subsequently, complete surgical resection was achieved in five (29%) and four patients (23%) after 12 and 24 weeks, respectively. Octreotide LAR plus prednisone treatment was discontinued in two patients before week 12 due to unsatisfactory therapeutic effects or adverse events. The most frequent adverse events were gastrointestinal (71%), infectious (65%), and hematological (41%) complications. In conclusion, octreotide LAR plus prednisone is efficacious in patients with primary or recurrent unresectable thymoma with respect to tumor regression. Octreotide LAR plus prednisone was well tolerated and adverse events were in line with the known safety profile of both agents.

Translation termination: new factors and insights

In eukaryotes, translation termination requires two eukaryotic release factors, eRF1 and eRF3. eRF1 is required for recognition of the stop codon and eRF3 supports the polypeptide chain release in a GTP dependent manner. Recently, several new players in translation termination have been identified. The DEAD-box RNA helicase Dbp5 has been shown to support eRF1 in stop codon recognition, possibly by proper placement of the release factor on the termination codon. Upon its dissociation from eRF1, Dbp5 allows the entry of the second termination factor eRF3 into the complex. Further, the Dbp5 interacting protein Gle1 and its co-factor inositol hexakisphosphate (IP 6) have been shown to participate in the termination process. Dbp5 and Gle1 are well known for their function in mRNA export from the nucleus to the cytoplasm. Most interestingly, also the ATP binding cassette (ABC) protein Rli1, which requires the mitochondrial and cytosolic Fe/S protein biogenesis machineries for its assembly, has recently been shown to function in translation termination and recycling of the ribosomes. Rli1 physically and genetically interacts with both, eRF1 and eRF3. Together, all of these novel termination factors modulate in association with the release factors more accurate stop codon recognition and these findings broaden our knowledge about the final steps in translation.

The iron-sulphur protein RNase L inhibitor functions in translation termination

The iron-sulphur (Fe-S)-containing RNase L inhibitor (Rli1) is involved in ribosomal subunit maturation, transport of both ribosomal subunits to the cytoplasm, and translation initiation through interaction with the eukaryotic initiation factor 3 (eIF3) complex. Here, we present a new function for Rli1 in translation termination. Through co-immunoprecipitation experiments, we show that Rli1 interacts physically with the translation termination factors eukaryotic release factor 1 (eRF1)/Sup45 and eRF3/Sup35 in Saccharomyces cerevisiae. Genetic interactions were uncovered between a strain depleted for Rli1 and sup35-21 or sup45-2. Furthermore, we show that downregulation of RLI1 expression leads to defects in the recognition of a stop codon, as seen in mutants of other termination factors. By contrast, RLI1 overexpression partly suppresses the read-through defects in sup45-2. Interestingly, we find that although the Fe-S cluster is not required for the interaction of Rli1 with eRF1 or its other interacting partner, Hcr1, from the initiation complex eIF3, it is required for its activity in translation termination; an Fe-S cluster mutant of RLI1 cannot suppress the read-through defects of sup45-2.