SL-701 is an anti-cancer immunotherapy vaccine being developed by Stemline as a potential therapy for patients with glioblastoma multiforme (GBM), a type of malignant brain tumor.

How SL-701 works

SL-701 is composed of survivin; interleukin-13 receptor alpha-2 (IL-13Rα2); and ephrin A2 (EphA2) synthetic peptide antigens that have been modified to enhance the activity of the immune response. The three peptides are tumor-associated antigens (TAA) or proteins that are found in glioma tumors at much higher levels than normal.

Upon administration, SL-701 peptides are displayed on the surface of immune cells called dendritic cells and recognized as foreign by other specialized immune cells, called cytotoxic T-lymphocytes (CTLs). The CTLs initiate a potent immune response against tumor cells, eventually resulting in the elimination of the cancerous cells.

To amplify the activation of the immune system in patients, SL-701 can be combined with other immune system activators, including Leukine (sargramostim), and Aldara (imiquimod).

 SL-701 in clinical trials

An early version of SL-701, without the modification of the three TAA, was evaluated in an investigator-sponsored Phase 1/2 trial in adults and children with malignant glioma. Results of the study showed the vaccine was safe and well-tolerated, demonstrating tumor regression and durable complete responses (CRs) and partial responses (PRs) as well as prolonged disease stabilization.

The safety and efficacy of the new version of SL-701A, alone or together with Avastin (bevacizumab), is currently being tested in a Phase 1/2 clinical trial (NCT02078648) in patients with recurrent GBM.

Preliminary results from the 64 patients enrolled were presented at the annual meeting of the Society of Neuro-Oncology (SNO) in 2016. They showed that SL-701 was safe and well-tolerated, and demonstrated clinical activity, including major responses, when used alone or in combination with Avastin.

The study participants continue to be followed for response and survival, and additional clinical data are expected this year.

Other details

In 2015, SL-701 was granted orphan drug status by the U.S. Food and Drug Administration (FDA) for the treatment of glioma.

Orphan drug designation helps companies develop products for rare diseases (those that affect fewer than 200,000 people in the U.S.) by giving them incentives such as tax credits or exemption from FDA user fees, assistance in clinical trial design, and potential market exclusivity for up to seven years if the drug is approved.


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