PL-9643: a melanocortin eye drop for dry eye disease

The system's quieting signal, delivered by drop — the same peptide logic, asked only to calm an eye.

PL-9643 takes the melanocortin system somewhere unexpected: the eye. It is one of Palatin Technologies' investigational melanocortin agonists — this one an eye drop fordry eye disease, and like PL-8177 in the gut, it is built on the system's anti-inflammatory arm rather than its pigment or appetite roles.^[1]

Calming the surface, not just wetting it

Dry eye disease is not only a lubrication problem; a large part of it isinflammation of the ocular surface that becomes self-sustaining. PL-9643 activates melanocortin receptors on the eye to dampen that inflammation and push it toward resolution — the same broad biology that makes α-MSH a natural anti-inflammatory signal, applied topically.^[1]That mechanism is different both from artificial tears, which lubricate, and from broad immunosuppressants, which blunt immunity generally.

The Phase 3 result

PL-9643's pivotal trial, MELODY-1, enrolled 575 patients with moderate-to-severe dry eye. It met its co-primary symptom endpoint of ocular pain (P<0.025) along with several secondary symptom endpoints, with symptom relief emerging by week 2 and continuing to build through 12 weeks — and it did so withfewer treatment-related adverse events than the vehicle control. It did not, however, meet the other co-primary endpoint — asign of disease (conjunctival lissamine green staining), the objective, physician-graded measure that dry-eye drugs have long found hardest to move.^[1][2]Independent coverage framed it as a promising, potentially first-in-class approach.^[3]The program is not finished: two further trials, MELODY-2 andMELODY-3, are designed to evaluate both the signs and the symptoms of the disease — the fuller bar a dry-eye drug must clear.^[2]

The honest bottom line

PL-9643 is investigational, and a single positive symptom trial is a milestone, not an approval — the remaining MELODY studies still have to deliver. But it is a striking demonstration of the melanocortin system's reach: the same anti-inflammatory signalling behind pigment biology and gut disease, formulated as an eye drop. For the underlying biology, see α-MSH; for the wider landscape, see the melanocortin pipeline.

Common questions

What is PL-9643?+

PL-9643 is an investigational eye drop from Palatin Technologies — a melanocortin agonist being developed for dry eye disease. It applies the melanocortin system’s anti-inflammatory, tissue-calming biology directly to the surface of the eye.

How does PL-9643 work for dry eye?+

Dry eye disease is driven in large part by inflammation of the ocular surface. PL-9643 activates melanocortin receptors on the eye to dampen that inflammation and promote its resolution — a different approach from simply lubricating the eye or broadly suppressing the immune system.

What did the Phase 3 trial show?+

In the pivotal Phase 3 MELODY-1 trial (575 patients), PL-9643 met its co-primary symptom endpoint of ocular pain and several secondary symptom endpoints, with improvement emerging by week 2 and a favourable safety profile — fewer treatment-related side effects than the vehicle. It did not, however, meet its other co-primary endpoint, an objective sign of disease (conjunctival staining). Two further trials, MELODY-2 and MELODY-3, are evaluating both signs and symptoms.

References

1. 1.Palatin Technologies. Breakthrough symptom resolution in updated analyses from Phase 3 PL9643 MELODY-1 clinical trial in dry eye disease. Press release — MELODY-1 symptom endpoints and safety. 2025. link ↗
2. 2.Ophthalmology Times. Palatin reports positive interim analysis in Phase 3 pivotal study of a potential therapeutic for dry eye disease. Independent coverage of the PL9643 program. 2024. link ↗
3. 3.Applied Clinical Trials. Results of Phase III trial show promise of potential first-in-class treatment for dry eye disease. Independent coverage of MELODY-1 results. 2025. link ↗