New data for Dynavax Technologies’ SD-101 suggest it could have an edge among new drugs that aim to stimulate immune responses in the tumour microenvironment.
Updated results from a trial of the toll-like receptor 9 (TLR9) agonist given alongside Merck & Co/MSD’s PD-1 inhibitor Keytruda (pembrolizumab) in melanoma and head-and-neck squamous cell carcinoma (HNSCC) suggest that delivering SD-101 by injection directly into tumours can cause them to regress, with additional benefits on other measures such as progression-free survival (PFS).
The results in PD-1 inhibitor-naïve melanoma patients, PD-1-resistant melanoma and PD-1-naïve HSNCC – were among the most eyecatching results reported at the ESMO conference in Munich over the weekend.
Analysts at William Blair say they show “consistent efficacy and safety data across three disease settings” and “may aid in the formation of partnership deals for SD-101 in the near future,” write the analysts in a research note.
The data are update on earlier results reported at this year’s ASCO in the US, and reveal that a 2mg dose of SD-101 plus Keytruda achieved a 70% overall response rate (ORR) while the median PFS has not yet been reached but looks likely to be at least 15 months.
The 2mg dose consistently outperformed a higher 8mg dose of the TLR9 agonist, which achieved an ORR of 48% and a PFS of a little over 10 months, and now looks set to be the dose taken forward into a phase 3 programme.
The consistent results, plus a side effect profile for SD-101 that seems fairly benign with the most common reactions mild, flu-like symptoms, means Dynavax is ready to advance the drug into phase 3 – but it will need a partner to help fund and progress those trials quickly, according to William Blair.
STING ‘has not stung’
Merck would be an obvious choice for that role, and the analysts also suggest that a deal for SD-101 could be more likely given a lacklustre showing for the big pharma company’s rival immune-boosting approach, which also made its clinical debut at ESMO.
Merck’s STING agonist MK-1454 – which like SD-101 is injected into the tumour in order to stimulate an innate immune response in the microenvironment – achieved a 0% ORR as a monotherapy and a 24% partial response rate when delivered to patients with advanced solid tumours or lymphomas, and was associated with dose-limiting toxicities in 8.7% and 14.3% of patients, respectively.
The William Blair analysts note that the STING agonist class has been viewed as competitive to TLR9 agonists as they share similar mechanisms of action and are also administered intratumorally, and also that the STING agonists were speculated to be more potent based on biology and some preclinical studies.
Now, they say “the apparent comparable potency between the two classes of agents, a potentially worse safety profile for STING, and the fact that STING agonists are about two years behind in development give Dynavax a stronger competitive edge for SD-101, in our view.”
It would be premature to write off STING just yet however. The data from Merck’s study are still maturing, and clinical results from another STING agonist from Novartis/Aduro is due for presentation at the SITC conference in Washington DC next month.