In general, most biopharmaceuticals are injected to avoid rapid degradation in the digestive tract. However, most injected proteins are also rapidly cleared from the blood.
Therefore, relatively high doses and/or frequent injections are typically needed to maintain therapeutic blood levels, resulting in potentially increased side effects and increased treatment costs as well as significant patient inconvenience and non-compliance. Many bioactive peptides long known for their potential beneficial pharmacological action have not also been further developed due to their very short serum half-life.
Albumin fusion technology recently developed allows scientists to create novel, next-generation protein drugs by fusing the gene that expresses human serum albumin(HSA) to the gene that expresses a therapeutically active protein or peptide.
Albumin fusion technology also exhibits a powerful demonstration of prolonging the half-life of small bioactive peptides and has been used successfully to produce long-acting versions of numerous peptides and proteins. Albumin fusion proteins may thus provide patients with long-acting treatment options that may offer a more convenient dosing regime, with similar or improved efficacy and safety.
A research team in the Institute of Genetic Medicine, Pyongyang Medical College,
Therapeutic proteins or peptides of albumin fusion protein the team developed are human growth hormone(hGH), human parathyroid hormone 1-34(hPTH 1-34), human parathyroid hormone 1-84(hPTH 1-84), human growth hormone releasing factor 1-44(hGHRF 1-44), human growth hormone releasing factor 1-29(hGHRF 1-29), human insulin-like growth factor-1(hIGF-1), human epidermal growth factor(hEGF), insulin, human glucagon-like peptide-1(hGLP-1), human interleukin–1 receptor antagonist(hIL-1ra) and human thymosin α-1(hTα-1).
Expression vectors of albumin fusion protein are pPIC9, pPIC9K and their expression hosts are GS115, SMD1168 and KM71 strains in Pichia pastoris.
Purification of albumin fusion proteins were followed from common protocol: Cell debris was removed by centrifugation and the interest proteins from supernatant was diafiltered, purified on Cu2+-chelating sepharose CL-6B, phenyl sepharose-4B, sulfopropyl sepharose FF and Sephadex G-25 columns.
Albumin fusion protein mostly contained flexible linkers(GGGGS or GGGGSGGGGS) between HSA and therapeutic peptides or proteins and also rarely existed without the flexible linker.
The results in clinical trials of albumin fusion protein showed that they were biologically active and well tolerated. There were no drug-related serious adverse events or discontinuations. Albumin fusion protein remained in the blood substantially longer than is reported for recombinant human therapeutic peptides or proteins.
Pharmacodynamic, immunogenicity, and biological activity also were evaluated. No patient developed an immune response against albumin fusion protein.
The band of purified HSA-hGH showed the single spot in the position of about 70kDa in SDS-PAGE.
A hundred and twenty short children with a height standard deviation score(SDS) <-2 SDS in the age range 8-15 years were given either single doses of recombinant long-acting human growth hormone(HSA-hGH)subcutaneously at 3.125 microg/kg, 6.25 microg/kg, or 12.5 microg/kg, or 2 doses of HSA-hGH subcutaneously at 6.25 microg/kg 7 days apart. Doses mostly depended on years of patients.
70% of patients (42 of 60) responded who received single doses of HSA-hGH at 12.5 microg/kg, and 80% of patients (48 of 60) responded who received 2 doses of HSA-hGH 7 days apart at 3.125 microg/kg.(P <0.05) The increased growth velocity in children with short stature was 7~12cm/year.
The band of purified HSA-hPTH 1-34 showed the single spot in the position of about 70.5kDa in SDS-PAGE.
A sixty patients with osteopenia(mean lumbar spine T score –1.0 ~ –2.5) or osteoporosis(mean lumbar spine T score <–2.5) in mean body weight 60kg were given single doses of recombinant long-acting human parathyroid hormone 1-34(HSA-hPTH 1-34)subcutaneously at 1.6 microg/kg 5 days apart for 12 months.
Lumbar spine density increased by 9.7%, compared with 1.1% in the placebo group, femoral neck density increased by 2.8% in the HSA-hPTH 1-34 group but decreased 0.7% in the placebo group.(P <0.01)
In all, 90% of patients (54 of 60) treated with single doses of HSA-hPTH 1-34 had an increase in bone mass.
Our investigation on the clinical validation of albumin fusion proteins continues.
