Stabilization of Octastatin, a somatostatin analogue: comparative accelerated stability studies of two formulations for freeze-dried products

Somatostatin and somatostatin receptors: implications for neoplastic growth and cancer biology

Somatostatin agonists (SM-As) are capable of achieving durable symptomatic relief and significant clinical responses in certain tumours. Herein, we review the diverse direct and indirect mechanisms of antineoplastic activity elicited by SM-As as well as the hurdles that complicate their use as monotherapies in a broader range of malignancies. Emphasis is placed on recent clinical attempts to neutralise the IGF-mediated survival factor effects in the bone metastasis microenvironment in advanced prostate cancer. The first clinical trials of this 'anti-survival factor manipulation' strategy utilised the ability of SM-As to suppress the growth hormone-dependent liver-derived IGF-I bioavailability in combination with other drugs, such as dexamethasone, zolendronate and oestrogens, acting systemically and at the bone metastasis microenvironment. These regimens restored androgen ablation responsiveness in stage D3 prostate cancer patients and successfully produced objective clinical responses while only mild toxicities were observed. Furthermore, we focus on the preclinical experimental data of a targeted SM-A coupled to the super-potent doxorubicin derivative AN-201. The resulting conjugate (AN-238) has shown increased antitumour potency with a favourable toxicity profile. The potential use of novel SM-As as anticancer drugs is discussed in relation to data suggesting other direct and indirect treatment approaches pertaining to the somatostatin system.

Impurity formation studies with peptide-loaded polymeric microspheres Part II. In vitro evaluation

Since acylated peptide impurities were isolated from octreotide microspheres following incubation in an in vivo environment, the present investigation was undertaken to determine the dosage form dynamics responsible for facilitating acylation. In particular, microsphere batches made with poly(L-lactide) (PLA) and poly(lactide-co-glycolide) (PLGA) 85:15 were studied for in vitro drug release, mass balance relationships, mass loss behavior, hydration uptake, and solid-state stability. Furthermore, native octreotide was incubated in a varying pH stability model (heat treated lactic acid solutions 42.5%, w/w) to determine the effects of acidity on impurity formation. From a review of the experimental results, the appearance of octreotide impurities or related substances occurred with the onset of polymeric mass loss. In fact, the significant formation of acylated peptide did not appear until >90% mass loss, which was observed at 14 days. It was surmised that because of water uptake, the hydrolytic cleavage of the polymeric backbone created an acidic microenvironment to facilitate the covalent coupling of peptide with polymer. The lactic acid solution stability model corroborated with greater evidence of acylation at pH 2.25 where the presence lactoyl (+72 m/z) derivatives of octreotide were confirmed by MALDI-TOF mass spectrometry.

Stability of Octastatin, a somatostatin analog cyclic octapeptide, in aqueous solution

In this study, the degradation of Octastatin, a cyclic octapeptide analog of somatostatin, was examined as a function of pH, temperature, buffer, and ionic strength by reversed-phase gradient high-performance liquid chromatography. Degradation of Octastatin followed a first-order kinetics. Various buffer species such as acetate, ammonium acetate, citrate, glutamate, phosphate, and borate showed differing effects on the degradation of the octapeptide. Good stability was found in glutamate and acetate buffer of pH 4.0. Degradation of Octastatin was greater in citrate- or phosphate-containing buffers than in glutamate or acetate buffers. With phosphate buffer, higher buffer concentration caused greater degradation, while in acetate buffer, the effect of buffer concentration and ionic strength was negligible. In addition, the degradation of Octastatin was markedly inhibited by increasing the concentration of glutamate buffer. This study allows the prediction of good stability in acetate buffer (0.01 M, pH 4.0) with a t90% of 84.1 days at 20 degrees C.