Idera Pharmaceuticals has revealed that the Phase III, pivotal ILLUMINATE-301 trial of tilsotolimod in combination with Bristol Myers Squibb’s Yervoy (ipilimumab) versus Yervoy alone in patients with anti-programmed death protein-1 (anti-PD-1)-refractory advanced melanoma did not meet its co-primary endpoint of objective response rate (ORR).

Idera had planned to apply for accelerated approval of this combination therapy, but will now have to wait for a potentially positive overall survival (OS) signal from the trial. These topline results will undermine confidence that tilsotolimod could be a sure bet for approval in this under-resourced line of therapy within melanoma.

Melanoma can be treated with immune checkpoint inhibitors (ICIs) such as anti-PD-1 or anti-cytotoxic T-lymphocyte-associated antigen-4 (CTLA-4) agents. Many patients respond well, but approximately 50% of patients will progress on ICIs, leaving them with few treatment alternatives after ICI therapy. Patients with anti-PD-1-resistant melanoma have a poor prognosis and their treatment remains an unmet clinical need. Previously, tilsotolimod looked set to meet this need.

Tilsotolimod is a therapeutic oligonucleotide that binds directly to the Toll-like receptor 9 (TLR9) in immune cells to stimulate an immune cascade. Tilsotolimod is designed to work with the ICI Yervoy to synergistically turn ‘cold’ tumors ‘hot’ by illuminating cancer cells to the immune system. While the ILLUMINATE-301 trial results only showed an ORR of 8.8%, this combination has previously achieved a 22.4% ORR in the ILLUMINATE-204 Phase I/II trial and received orphan drug and fast track designation from the FDA.

Idera is well placed to stay ahead of its competitors. There are no marketed agonist oligonucleotides for any cancer indication, but Checkmate Pharmaceuticals has remained Idera’s potential main competitor for years as its candidate, vidutolimod (CMP-001), also targets TLR9 and is in late-stage clinical trials for anti-PD-1-refractory melanoma.

While Idera believes that tilsotolimod has a competitive edge, because it avoids the increased manufacturing complexity that is brought by the virus-like particle encapsulation that vidutolimod requires, GlobalData’s recent patient-based forecast assigns a higher peak year revenue to vidutolimod. According to GlobalData’s consensus analyst forecasts, tilsotolimod’s sales are expected to reach $278M by 2027 if the tilsotolimod + Yervoy combination is approved for anti-PD-1-refractory melanoma. Idera’s plan is to open discussions with regulatory authorities and identify a path forward for this therapy in second-line patients if the ILLUMINATE-301 trial produces positive OS results.