The Second Battle, Opened From the Inside

Octreotide, acromegaly and the tight-junction trick that takes on the gut wall directly

Rybelsus proved a peptide could survive Battle One by avoiding Battle Two altogether. A different peptide, treating a different disease, took Battle Two on directly — prising open the wall between intestinal cells rather than finding a way around it. The technology works. The number it produces is smaller than the one it was built to beat.

By Ibumix · 6-minute read

The previous two articles in this series told the story of a peptide winning its battles indirectly. Semaglutide survives Battle Three, staying active in the blood, by resisting the enzyme that destroys it within minutes, engineered instead to circulate for roughly a week. Its oral version wins Battle One by borrowing a stomach-based microenvironment from an excipient called SNAC, absorbing in the stomach itself rather than fighting through the small intestine at all. Neither trick does anything for Battle Two — crossing the intestinal wall — because neither needed to.

A different peptide, treating a different disease, took Battle Two on directly. Octreotide is a synthetic analogue of somatostatin, a hormone that suppresses the release of growth hormone; injectable octreotide has been a standard treatment for acromegaly — a condition caused by chronic growth hormone excess, most often from a pituitary tumour — since the 1980s. On 26 June 2020, the FDA approved Mycapssa, an oral octreotide capsule, as the first and only oral somatostatin analogue, and the first medicine to reach market using a technology built specifically to open the intestinal wall itself ^[1].

A fence that can be persuaded to lean

Mycapssa’s route to the bloodstream runs through two separate pieces of engineering, tackling the two battles in order rather than sidestepping either. First, an enteric coating — Acryl-EZE, a methacrylate polymer — shields the capsule through Battle One, resisting stomach acid until it reaches the small intestine intact ^[2]. That part of the problem should look familiar by now: it is a coating solving Battle One in the way SNAC’s chemistry never had to.

What happens next is new. Once in the small intestine, the capsule releases its contents alongside sodium caprylate, a permeation enhancer known in the literature as C8. Chiasma’s own account of the mechanism is that C8 temporarily and reversibly reorganises the structural proteins — ZO-1 and claudin among them — that hold the tight junctions between intestinal cells closed ^[3]. For a short window, cell-to-cell space that is normally sealed against anything but the smallest molecules opens fractionally wider, wide enough for intact octreotide to pass through alongside it, before the junction reseals.

The tight junctions are not a locked door with a single key. They are closer to a fence that can be persuaded to lean, briefly, if pushed in the right way — and springs back the moment the pushing stops.

Winning the harder battle, losing more of the dose

This is, on its own terms, a genuine achievement: a formulation that crosses the intestinal wall by directly loosening its structure, rather than exploiting a gap in the digestive process the way SNAC does. It is also, on the numbers, a smaller win than the workaround it improves on. Mycapssa’s absolute bioavailability is below 1% at the 20 mg dose and below 0.2% at the 80 mg dose, measured against a 0.1 mg subcutaneous injection ^[4] — lower, at every dose studied, than Rybelsus’s 0.4–1% ^[5]. Confronting the harder of the three battles head-on did not produce a better result than routing around it. It produced a worse one, solved by a harder route.

The dosing instructions carry the same signature of a small, hard-won absorption window as Rybelsus’s do: taken on an empty stomach, at least one hour before food or two hours after, split into two 20 mg doses a day rather than one ^[6]. A therapy this precise about timing is, once again, a formulation working near the edge of what its chemistry can deliver — not a shortfall in the drug, but the price of the door it has to open.

Why the harder route still matters

The comparison invites an obvious question: if opening the tight junctions produces a lower bioavailability than simply avoiding the intestine altogether, why bother? The answer is that SNAC’s trick is, so far, largely specific to itself and to the drugs it has been formulated with — a local chemistry that creates a favourable stomach microenvironment for one class of molecule. Tight-junction modulation is a more general mechanism, one that does not depend on a drug being absorbable in the stomach at all. Octreotide’s disease has nothing to do with GLP-1, its target receptor is unrelated to glucose or appetite signalling, and it still needed the same underlying engineering problem solved: get a peptide through a wall built to keep peptides out. A mechanism that generalises across that wide a range of molecules and diseases is a more durable piece of pharmaceutical science than one number on one label, even when that number is smaller than a rival’s.

It is also, so far, proven only at a smaller scale than most of what oral peptide delivery is ultimately trying to solve. Octreotide is a compact eight-amino-acid cyclic peptide, a fraction of semaglutide’s thirty-one, and further still from insulin’s fifty-one amino acids across two linked chains. Tight-junction modulation has been proven commercially at octreotide’s scale; whether the same transient opening is wide enough for a molecule several times larger is a question this technology has not yet had to answer.

A third route, still to come

Two peptides, two diseases, two entirely different ways through the same three battles — and, so far, two formulations that each solve part of the problem well and leave the large majority of every dose behind. The next piece in this series turns to a third approach: not a local chemical trick and not a mechanical opening of the gut wall, but changing the physical form the drug travels in before it ever reaches either — the lipid-based delivery systems increasingly seen as the next serious attempt at getting a peptide through intact, in one piece, rather than negotiating passage for it one battle at a time.

Sources

• [1] Chiasma. FDA Approval of MYCAPSSA (Octreotide) Capsules, the First and Only Oral Somatostatin Analog. 26 June 2020. globenewswire.com
• [2] MYCAPSSA (octreotide) Full Prescribing Information — enteric coating and capsule formulation. FDA label. accessdata.fda.gov
• [3] Gastrointestinal Permeation Enhancers for the Development of Oral Peptide Pharmaceuticals — TPE technology, sodium caprylate (C8), tight-junction protein reorganisation (ZO-1, claudin). pmc.ncbi.nlm.nih.gov
• [4] MYCAPSSA Full Prescribing Information — absolute bioavailability below 1% (20 mg) and below 0.2% (80 mg) versus subcutaneous octreotide. accessdata.fda.gov
• [5] RYBELSUS Full Prescribing Information — estimated absolute bioavailability of 0.4–1%. accessdata.fda.gov
• [6] MYCAPSSA Full Prescribing Information — dosing instructions (40 mg/day as 20 mg twice daily, empty stomach, at least 1 hour before or 2 hours after food). accessdata.fda.gov

Ibumix is developing a series of new liquid drug delivery platforms built on glyceryl caprate (GCC) lipid chemistry, with a patent estate covering the underlying formulation and device.