Abstract 1595: Small molecule inhibition of the ubiquitin ligase CBL-B results in potent T and NK cell mediated anti-tumor response

Abstract

The E3 ubiquitin ligase Casitas B-lineage lymphoma b (CBL-B) is expressed in T cells where it functions as an important negative regulator of immune activation. CBL-B d attenuates T-cell activation initiated by TCR engagement in part by mediating the requirement for CD28 co-stimulation, thus setting the threshold for T cell activation. CD4+ and CD8+ T cells from mice deficient in cbl-b have 5 to 10-fold enhanced secretion of IL-2 and IFN-γ when stimulated ex vivo with anti-CD3. Cbl-b deficient mice also demonstrate enhanced NK cell function. Here we describe NX-1607, an investigational, orally bioavailable, small molecule inhibitor of CBL-B. NX-1607 demonstrates potent biochemical inhibition of CBL-B leading to stimulatory effects on human immune cells at low nanomolar concentrations. NX-1607 induction of IL-2 and IFN-γ secretion occurs in primary human T cells stimulated with anti-CD3 antibodies, in both the presence and absence of CD28 co-stimulation, although to a lesser degree in the absence of co-stimulation. In vivo, oral administration of NX-1607 in mice demonstrated significant tumor growth inhibition in two colon carcinoma tumor models, CT26 and MC38, as well as a triple negative breast tumor model, 4T1. The change in tumor microenvironment caused by NX-1607 treatment leads to rapid NK cell infiltration followed by infiltration of activated CD8+ T cells. Depletion of CD8+ T cells or NK cells completely abrogated NX-1607 antitumor activity. Importantly, the combination of NX-1607 and anti-PD-1 can substantially increase the median overall survival and the frequency of complete tumor rejections in all three tumor models. These studies provide significant insights into the antitumor activity of this novel, small molecule E3 ligase inhibitor and deliver experimental support for clinical development of NX-1607 given as monotherapy or in combination with PD-1 blockade. Citation Format: Ryan Rountree, Frederick Cohen, Austin Tenn-McClellan, Alexandra Borodovsky, Marilena Gallotta, Jennifer Stokes, Jose Gomez Romo, Chris Karim, Gwenn M. Hansen, Cristiana Guiducci, Arthur Sands, Jennifa Gosling. Small molecule inhibition of the ubiquitin ligase CBL-B results in potent T and NK cell mediated anti-tumor response [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1595.

Targeting Cbl-b in cancer immunotherapy

“…NX-1607 is an oral small molecule that significantly reduces tumor growth in colon and triple negative breast cancer murine models. 77 Cellular and molecular correlates of this inhibition demonstrate enhanced NK and CD8+ T cell activity in the TME; additionally, NX-1607 mediated tumor inhibition was reversed on NK or CD8 + T cell depletion in these models. 77 Given a reduction in TCR diversity and tumor reactive TIL following checkpoint blockade, Nurix has also developed an ex vivo Cbl-b inhibitor (NX-0255) to be used alongside adoptive T cell therapy.…”

“… 77 Cellular and molecular correlates of this inhibition demonstrate enhanced NK and CD8+ T cell activity in the TME; additionally, NX-1607 mediated tumor inhibition was reversed on NK or CD8 + T cell depletion in these models. 77 Given a reduction in TCR diversity and tumor reactive TIL following checkpoint blockade, Nurix has also developed an ex vivo Cbl-b inhibitor (NX-0255) to be used alongside adoptive T cell therapy. This platform, termed drug enhanced tumor infiltrating lymphocyte (DeTIL) therapy, cultures patient-derived tumor fragments with IL-2 and NX-0255 to further stimulate antigen-specific CD8+ T cells.…”

Small molecule inhibitors for cancer immunotherapy and associated biomarkers – the current status

“…Further x-ray crystallography studies of compound 23/C7683 elucidated that the molecule binds to the tyrosine kinase binding (TKB) and linker helix region (LHR) domains, while sparing the catalytic RING domain (Table 3A) (45). In T cell assays, the clinical candidate NX-1607 from Nurix increased IL2 and IFNg production (46). The structure of NX-1607 has not been formally disclosed, but it is very likely similar or identical to compound 23/ C7683.…”

“…Depleting either CD8 + T cells or NK cells impaired the efficacy of NX-1607, confirming the immuno-modulatory mechanism of action of the drug candidate. The combination of NX-1607 and an anti-PD-1 antibody increased tumor growth inhibition and median overall survival in all mouse efficacy models tested (46). Despite the compelling activity of the combination with the anti-PD-1 antibody, Nurix advanced NX-1607 into clinical phase 1 trials without CPIs as combinations partners (47).…”

777 Initial clinical characterization of novel proximal biomarkers for NX-1607, a first-in-class oral CBL-B inhibitor, in patients with advanced malignancies

“…NX-1607 is a first-in-class oral small molecule inhibitor of CBL-B that has demonstrated potent anti-tumor activity in animal models by reversing T cell dysfunction and overcoming suppressive signaling in the tumor microenvironment. 1 Nurix has identified and characterized novel proximal biomarkers of CBL-B inhibition that correlate with anti-tumor activity in syngeneic tumor models. Assays for these biomarkers characterize the activity of NX-1607 in a first-inhuman clinical trial (NCT05107674).…”