Abstract 3258: Discovery and characterization of SAR260301, a novel PI3Kβ-selective inhibitor in clinical development for the treatment of PTEN-deficient tumors

The PI3K/mTOR pathway is involved in promoting tumor cell proliferation, survival and metastasis. The development of new anticancer therapies targeting different components of this pathway has been motivated by the identification of somatic PIK3CA missense mutations as well as the high frequency of loss of negative regulatory proteins such as the tumor suppressor PTEN. In this last case, the abnormal activation of downstream effectors is mediated by PI3Kβ. PTEN deficiency has also been reported to be involved in the resistance to a variety of anticancer therapies. The preceding findings support investigation into selective modulators of the lipid kinase activity of p110β as agents for the treatment of PTEN-deficient tumors, with potentially reduced on-target adverse events described for pan-PI3K inhibitors currently undergoing clinical trials. SAR260301 is a selective PI3Kβ lipid kinase inhibitor that has demonstrated higher potency in vitro on p110β (IC50= 52 nM) than on p110δ and p110α isoforms and no or weak activity against p110γ, mTOR and a wide range of protein kinases (>400 enzymes). The potency and selectivity against the intended target was further confirmed in mechanistic cellular models (IC50 = 32 nM, p110β; 26- and 88-fold selective over p110δ and p110α, respectively). Moreover, SAR260301 also modulates pAkt levels exclusively in PTEN-deficient tumor cell lines with IC50 values ranging from 39 to 310 nM and from 20 to 209 nM for pAkt-S473 and pAkt-T308, respectively. When administered orally, the compound shows dose and time-dependent inhibition of the PI3K pathway in human PTEN-deficient tumor xenografts in mice. In these models, target engagement correlates with compound exposure and is associated with good tolerability. The MAPK pathway also plays an important role in cancer and is often constitutively and simultaneously activated with the PI3K pathway. Furthermore, PTEN loss has been shown to correlate with resistance to MAPK inhibitors. Preclinical data evidencing the ability of SAR260301 to modulate pAkt levels in genetic contexts where PTEN deficiency co-exists with MAPK pathway activation, as well as the effects of combining SAR260301 with MAPK inhibitors will also be presented. The foregoing studies support ongoing Phase I clinical investigation of SAR260301 in patients with PTEN-deficient malignancies. Citation Format: Angela Virone-Oddos, Hélène Bonnevaux, Olivier Lemaitre, Loic Vincent, Franck Halley, Brigitte Demers, Véronique C