Immuno-Oncology

Melanoma

    • New drugs, called “Checkpoint Inhibitors,” improve the immune system’s ability to fight cancer by helping maintain the presence and activity of immune cells that target cancer, cytotoxic T lymphocytes (CTLs).
    • Many patients fail to respond to Checkpoint Inhibitor therapy, which suggests that tumors utilize additional mechanisms to evade the immune system.
    • Research suggests that some tumors evade the immune system by recruiting myeloid-derived suppressor cells (MDSCs). MDSCs produce reactive nitrogen radicals (RNS) that alter the receptors on the surface of the tumor to “cloak” it from CTLs.
    • Omaveloxolone and other AIMs inhibit MDSC activity, suppress RNS, and restore anti-tumor immune responses in preclinical studies. They also have direct anticancer effects in vitro and in animals.
    • Reata is conducting a Phase 2 clinical study using omaveloxolone in combination with Checkpoint Inhibitors in patients with melanoma (REVEAL).

Combating Immunosuppression


New drugs such as Yervoy®, Opdivo®, and Keytruda®, called “Checkpoint Inhibitors,” have emerged as novel treatments of metastatic melanoma and non-small cell lung cancers. They improve the immune system’s ability to fight cancer by helping maintain the presence and activity of cytotoxic T lymphocytes (CTLs), immune cells that target cancer. While Checkpoint Inhibitors result in improved outcomes compared to previous therapies, patient response rates to treatment remain relatively low1.

A significant body of evidence has shown that certain immature white blood cells, known as myeloid derived suppressor cells (MDSCs), are present in tumors and play a critical role in suppressing the ability of CTLs to detect and destroy cancer cells. MDSCs have the ability to generate reactive nitrogen radicals (RNS) such as nitrotyrosine that bind to and change the conformation of marker proteins on the surface of cancer cells. This can create an RNS “cloak” around tumor cells that allows them to be unidentifiable to CTLs, even if CTL activity is facilitated by Checkpoint Inhibitors2. This hypothesis has been supported by several clinical studies associating poor survival with high MDSC activity, and higher MDSC levels in patients are correlated with lack of clinical response to Checkpoint Inhibitors.

Preclinical studies conducted by leading immuno-oncology researchers have shown that AIMs, including omaveloxolone, suppress the activity of MDSCs, reduce levels of RNS in tumors, and restore anti-tumor immunity3,4,5. AIM treatment improved immune cell infiltration of tumors and enhanced the anti-tumor effects of a cancer vaccine6. Omaveloxolone synergized with an anti-PD-1 (the target of Opdivo® and Keytruda®) antibody to promote immune rejection and regression of tumors7. Overexpression of RNS has been implicated as a potential contributing factor in MDSC-mediated immune evasion, and it is correlated with poor clinical outcomes in cancer patients8. In clinical studies, treatment with AIMs reduced levels of RNS in tumor biopsies from cancer patients5.

MDSCs are present and active in a broad range of tumor types. Accordingly, an agent that suppresses MDSC activity has the potential for wide use in combination with other cancer immunotherapies.

In addition to their inhibitory effects on MDSC, direct anti-cancer effects of AIMs have been extensively documented in non-clinical studies9,10.

    1. AIMs inhibit cancer cell proliferation in vitro and in vivo, and promote apoptosis of tumor cells by reducing the expression of Bcl-XL and other anti-apoptotic proteins.
    2. AIMs reduce the expression of proteins that promote tissue invasion and metastasis and are potent inhibitors of tumor-related angiogenesis.
    3. AIMs increase the effectiveness of other cancer therapies, including standard chemotherapy agents, targeted therapies, and radiation.
    4. AIMs prevent carcinogenesis and inhibit early tumor formation and growth. These effects have potential clinical relevance for the prevention of post-therapy recurrence and suppression of micrometastases.

Development Program


The initial development program for omaveloxolone in oncology is investigating whether the drug, when combined with other immunotherapies that act by different mechanisms (e.g., immune checkpoint inhibitors such as CTLA-4 inhibitors, PD-1 inhibitors, and other inhibitors of immuno-inhibitory ligands or receptors11), can restore or enhance CTL activity against tumors by suppressing the activity of MDSCs. Reata has initiated the REVEAL study, a Phase 1b/2 study of omaveloxolone in combination with immunotherapy in patients with melanoma.

References