Liposomal daunorubicin: in vitro and in vivo efficacy in multiple myeloma.

Liposomal encapsulation of anthracyclines is a potential method of drug targeting, altering both the antitumour activity and side-effect profile of anthracyclines. Liposomal daunorubicin (daunoxome) shows both altered pharmacokinetics and a potential for reducing dose-limiting cardiotoxicity compared to conventional daunorubicin. Anthracyclines have a common role in the treatment of multiple myeloma, a prevalent and fatal haematological malignancy. Avoiding cumulative anthracycline toxicity in these patients is important. There is also a need for more effective relapse schedules given that many patients have chemosensitive disease at relapse. We have analysed daunoxome in vitro in myeloma cell lines using a thymidine-based cytotoxicity assay and show superior efficacy compared to a pegylated liposomal doxorubicin derivative. Subsequently we have treated seven relapsed myeloma patients with a regime consisting of oral CCNU 25-50 mg/m2 on day 1, 4 days of oral dexamethasone 10 mg/m2 and intravenous daunoxome (liposomal daunorubicin) given for 4 days (total 100 mg/m2). The main toxicity was myelosuppression but non-haematological toxicity was minimal and the regime was well tolerated. Four out of seven of these heavily pretreated patients responded. Together with the in vitro data on its cytotoxicity in myeloma and its favourable pharmacokinetic profile further studies of liposomal daunorubicin in myeloma would be warranted.

The MHC-encoded TAP1/LMP2 bidirectional promoter is down-regulated in highly oncogenic adenovirus type 12 transformed cells.

Cells transformed by human adenovirus 12 (Ad12) exhibit extremely low surface levels of MHC class I molecules and contain reduced levels of class I heavy chain mRNAs. We report that levels of MHC-encoded TAP1 and LMP2 mRNAs are also down-regulated in Ad12-transformed rat cells, and that transcription of rat TAP1 and LMP2 transcripts is directed from a 564 bp intergenic region which is significantly less active in Ad12-transformed cells compared to those transformed with Ad5. Our results suggest that, in common with MHC class I gene expression, TAP1 and LMP2 gene expression is reduced mainly at the level of transcription in Ad12-transformed cells.

A developmentally regulated gene encodes the dictyostelium homolog of yeast ribosomal protein S4 and mammalian LLRep3 proteins.

We report the sequence and expression of a single-copy gene from Dictyostelium discoideum which encodes the homolog of yeast ribosomal protein S4, a protein located on the small ribosomal subunit and known to play an important role in maintaining translational fidelity. Over a highly conserved central region, the Dictyostelium protein has 78% sequence similarity to the yeast protein and 83% sequence similarity to mammalian S4 protein homologs, the LLRep3 proteins. The Dictyostelium gene encodes a polypeptide 28,717 Da in size and hence this ribosomal protein has been named rp29. The N-terminal sequence of the Dictyostelium rp29 protein is extended by 61 amino acids and 14 amino acids compared to the mammalian and yeast proteins, respectively, and the C-terminus is correspondingly 15 amino acids or 2 amino acids shorter. Although the coding region of the rp29 gene is present on a single exon, a 157bp intron interrupts the 5' untranslated region and unusually contains four direct repeats of the sequence TCAATCT. The gene is expressed maximally during vegetative growth but a second peak of expression also occurs late in development which is restricted to prestalk cells; rp29 is the first Dictyostelium ribosomal protein gene reported which shows prestalk-specific developmental expression. During each round of expression, only a single 0.9kb transcript is produced which is similar in size to the yeast S4 ribosomal protein transcript (0.8kb) but markedly smaller than the mammalian LLRep3 mRNA (1.7kb) due to a much shorter 5' untranslated region.

Developmental expression and characterization of the gene encoding spore coat protein SP60 in Dictyostelium discoideum.

The complete coding sequence, upstream sequence and developmental expression of Dictyostelium discoideum AX2 spore coat protein gene SP60 is reported. The gene contains two exons, 154bp and 1121bp long, separated by a 119bp intron, and encodes a protein of 46,925 molecular weight plus a 23-amino-acid hydrophobic leader sequence. The N-terminus of the mature protein consists of four copies of a perfect hexapeptide repeat (GDWNNN). The central region is rich in cysteine residues, including four highly conserved cysteine-rich repeats with homology to 'EGF-like' repeats. The C-terminus is aspartate-rich and composed of multiple imperfect copies of a D(G/D)DYD repeat followed by several repeats of the tetrapeptide DNDW and derived sequences. A TATA box promoter motif juxtaposed to an oligo(dA) stretch lies 52bp upstream of the main transcriptional start site of the gene. Six AC-rich boxes occur in the region -327 to -556, all of which contain the consensus sequence CACAC. Two GC-rich boxes and a C-rich element (TTACCCCA) are also present upstream. Another open reading frame is positioned a short distance downstream of the SP60 gene in the opposite transcriptional orientation. Expression of the SP60 gene ceases upon disaggregation to single cells and cannot be restored by high levels of extracellular cAMP either alone or in combination with conditioned medium factors.