Blueprint Ayvakit shows response in long term data; elenestinib shows promise in phase 1

Blueprint Medicines (NASDAQ:BPMC) reported long term updated of Ayvakit from the PATHFINDER and EXPLORER trials in patients with advanced systemic mastocytosis (SM) and part of 1 of the HARBOR study of elenestinib.

Ayvakit is approved in the US. to treat advanced SM — a rare disorder which results in too many mast cells — type of white blood cells — building up in the body.

In the PATHFINDER trial, Ayvakit (avapritinib) showed broad clinical activity in treatment-naïve patients evaluable for response (n=25), including those with associated hematological neoplasm (SM-AHN) (n=19), as of a data cutoff date of April 20, 2021.

The company noted that he overall response rate (ORR) was defined as complete remission with full or partial recovery of peripheral blood counts (CR/CRh), partial remission or clinical improvement.

For treatment-naïve patients across advanced SM subtypes: ORR was 84% and CR/CRh rate was 32%, while median time to response was two months and median time to CR/CRh was six months, according to the company.

Blueprint said estimated two year overall survival (OS) rate was 88%.

For treatment-naïve patients with SM-AHN: ORR was 95% and CR/CRh rate was 37%, while estimated 24-month OS rate was 86%.

In addition, improvements were seen in several hematologic parameters, such as monocytes and eosinophils in the peripheral blood, the company added.

In the EXPLORER trial, 57 patients across lines of therapy were evaluable for response as of a data cutoff date of April 5, 2022.

The ORR was 77%, with median DOR and OS not reached in patients followed for up for six years.

Safety data from the PATHFINDER and EXPLORER trials were consistent with previously reported results, according to the company.

Part 1 of HARBOR trial in indolent SM:

HARBOR Part 1 was was undertaken to test concurrent dose groups of elenestinib plus best available therapy (elenestinib group) versus placebo plus best available therapy (placebo group) in patients with indolent SM.

The company said elenestinib led to rapid improvements in objective measures of mast cell burden, including serum tryptase and KIT D816V allele fraction, and total symptom score (TSS).

At 12 weeks, elenestinib showed similar reductions in TSS across dose groups, the company added.

In addition, consistent with previously reported data from the PIONEER trial of Ayvakit in indolent SM, change in serum tryptase was not correlated with change in TSS, according to the company.

Blueprint noted that elenestinib was generally well-tolerated, and there were no discontinuations due to AEs.