Arecor has been working on an in-house project involving the development of a heat stable formulation of Human Insulin which could be administered via a miniaturized pump. Insulin is a well characterized therapeutic peptide of approximately 6kDa. At concentrations found in commercial preparations Human Insulin exists in the hexameric form unless it has been genetically modified to reduce self-association as in the case Apidra® and other Insulin analogues such as Novo Rapid® or Lispro®.

The objective of this development program was to understand the stability of various formulations of Human Insulin at body temperature and develop a new formulation using Arestat™ technology having a stability profile which would allow it to be considered as a candidate for delivery at body temperature via a miniaturized pump.

Human Insulin is a relatively stable molecule at 2-8ºC in the presence of Zinc. All major degradation pathways of insulin, including deamidation, aggregation and fibril formation, are known to proceed more rapidly from the monomeric or dimeric forms than from the hexameric form. The onset of action (from the sight of injection) however, is considered to be much better with monomeric forms than hexameric insulin. The stability of all forms of insulin preparations is considered to be compromised at higher temperatures.

The objective of the program was to develop a heat stable form of Human Insulin. Several Arestat-T™ formulation of Human Insulin were developed using the following starting materials: two Insulin analogues (one monomeric [1] the other not [2]), and full sequence Human Insulin supplied by Sigma-Aldrich. None of the formulations developed were supplement with additional Zinc apart from what was already present at the time of purchase prior to dialysis. Zinc is known to remain tightly bound even after dialysis therefore none of the Arestat-T formulations were considered to be totally free of Zinc.

All the Arestat-T™ formulations of the various Insulin types had a better stability profile than the originator formulations. The stability (integrity) of Insulin in each formulation was measured using a qualified method for RP-HPLC:
• Zinc containing formulation of the full sequence of Human Insulin was unstable at 40ºC. Stability was restored when Human Insulin was re-formulated using Arestat-T™ buffers and excipients.
• Insulin analogue no. 1 in the originator’s formulation was the most robust demonstrating only a slight drop in the purity of the principal peak after 4 weeks. However, after 8 weeks the differential between the Arestat-T™ formulation (insulin analogue re-formulated using Arestat-T™ buffers and excipients) and the originator’s formulation became more apparent.
• Insulin analogue no. 2 in the originator’s formulation demonstrated loss of stability at 40ºC by 4 weeks. Again this instability was eliminated by re-formulating the insulin analogue in Arestat-T™ formulation.