Why Did PTC Therapeutics Stock Fall On Monday Despite Mid-Stage Study For Huntington's Hits Primary Goal?

PTC Therapeutics, Inc. PTCT on Monday announced results from the Phase 2 PIVOT-HD study of PTC518 (votoplam) in Stage 2 and Stage 3 Huntington’s disease (HD) patients.

Huntington’s disease is a progressive neurodegenerative disorder caused by mutation of the huntingtin (HTT) gene, leading to the breakdown of brain cells. It is characterized by uncontrolled movements (chorea), cognitive decline, and psychiatric disturbances.

The study met its primary endpoint of reduction in blood Huntingtin (HTT) protein levels (p<0.0001) at Week 12 and favorable safety and tolerability. In addition, the 12-month data from the Stage 2 patients are consistent with the previously reported dose-dependent lowering of HTT protein and dose-dependent trends across clinical scales.

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“We look forward to discussions on the next development and regulatory steps, including the potential for accelerated approval as we work to potentially bring the first disease-modifying therapy…,” said Matthew B. Klein, M.D., Chief Executive Officer, PTC Therapeutics.

Results from the full 12-month cohort demonstrate dose-dependent lowering in blood HTT levels, with 23% at the 5mg dose level for both Stage 2 and 3 patients and 39% and 36% at the 10mg dose level for Stage 2 and 3 patients, respectively. For Stage 2 patients, there were dose-dependent trends of benefit on clinical scales, including the Composite Unified Huntington’s Disease Rating Scale (cUHDRS) and Total Motor Score (TMS) subscale.

For Stage 3 patients, trends favored the 5mg dose group relative to placebo but not the 10mg dose group, suggesting that treatment effect may differ in Stage 3 patients relative to Stage 2 patients. It seems investors are reacting to this as the stock is trading almost 20% lower during the premarket session.

PTC518 showed a favorable safety and tolerability profile for all dose levels and disease stages with no treatment-related serious adverse events or neurofilament light chain protein (NfL) spikes.

In addition, 24-month treatment data from the patients on whom data were shared last year (N=21) demonstrate signals of dose-dependent trends on the cUHDRS, Total Function Capacity (TFC), and Symbol Digit Modalities Test (SDMT) subscales when compared to a propensity-matched natural history cohort from the ENROLL-HD Registry.

At Month 24, there was also a dose-dependent lowering of plasma NfL from a baseline of -8.9% (nominal p=0.12) for the 5mg dose level and -14% (nominal p=0.03) for the 10mg dose level.

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Price Action: PTCT stock fell 18.60% to $40.65 on Monday.

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