PIK-75 overcomes venetoclax resistance via blocking PI3K-AKT signaling and MCL-1 expression in mantle cell lymphoma

Therapeutic resistance is the major challenge in clinic for patients with mantle cell lymphoma (MCL), an aggressive subtype of B-cell lymphoma. In addition to the FDA-approved Bruton's tyrosine kinase (BTK) inhibitors, multiple clinical trials have demonstrated clinical benefits in targeting BCL-2 by venetoclax and reported to greatly improve clinical outcome for refractory/relapsed patients with MCL alone or in combination with BTK inhibitors. However, resistance to venetoclax is no exception and marks as a new clinic challenge. To decode the underlying mechanisms driving venetoclax resistance, we established two MCL cell lines, Mino-Re and Rec1-Re, with acquired resistance to venetoclax from sensitive Mino and Rec-1. Using reverse phase protein assay (RPPA), an agnostic proteomic approach, we identified targetable signaling pathways that are associated with acquired venetoclax resistance in Mino-Re and Rec1-Re cells. A panel of pro-survival signals was identified to correlate well with venetoclax-resistance, including increased expression of MCL-1, BCL-xL and AKT phosphorylation, and decreased expression of BIM, BAX and PTEN. Based on a high throughput drug screening of over 320 FDA-approved/investigational drugs in the paired venetoclax-sensitive and -resistant cell lines Mino-Re and Rec1-Re, we identified the top candidates that are capable to overcome acquired venetoclax resistance in these cells. The best candidate is PIK-75, a dual inhibitor targeting both PI3K and CDK9. Its action to overcome venetoclax resistance was further confirmed in additional cell lines with primary venetoclax resistance (n=4) and primary patient samples (n=21). Mechanistically, PIK75 treatment potently diminished the elevated MCL-1 expression and AKT activation in cells with acquired or primary venetoclax resistance and resulted in potent anti-MCL activity to overcome these resistances. In addition, PIK75 is also potent in overcoming tumor microenvironment (TME)-associated venetoclax resistance. Furthermore, PIK-75 treatment is efficacious in overcoming primary and acquired venetoclax resistance in xenograft models and inhibited tumor cell dissemination to spleen in mice. Altogether, our data demonstrated that PIK-75 is highly potent in overcoming primary, acquired, or stromal cells-induced venetoclax resistances in MCL cells and revealed a new tumor vulnerability that can be exploited clinically in difficult to treat MCL cases, especially those with venetoclax resistance.

Extended treatment with selective phosphatidylinositol 3-kinase and mTOR inhibitors has effects on metabolism, growth, behaviour and bone strength

The class I phosphatidylinositol 3-kinases (PtdIns3Ks) mediate the effects of many hormones and growth factors on a wide range of cellular processes, and activating mutations or gene amplifications of class I PtdIns3K isoforms are known to contribute to oncogenic processes in a range of tumours. Consequently, a number of small-molecule PtdIns3K inhibitors are under development and in clinical trial. The central signalling role of PtdIns3K in many cellular processes suggests there will be on-target side effects associated with the use of these agents. To gain insights into what these might be we investigated the effect of extended daily dosing of eight small-molecule inhibitors of class Ia PtdIns3Ks. Animals were characterized in metabolic cages to analyse food intake, oxygen consumption and movement. Insulin tolerance and body composition were analysed at the end of the experiment, the latter using EchoMRI. Bone volume and strength was assessed by micro-CT and three-point bending, respectively. Surprisingly, after sustained dosing with pan-PtdIns3K inhibitors and selective inhibitors of the p110α isoform there was a resolution of the impairments in insulin tolerance observed in drug-naïve animals treated with the same drugs. However, pan-PtdIns3K inhibitors and selective inhibitors of the p110α have deleterious effects on animal growth, animal behaviour and bone volume and strength. Together, these findings identify a range of on target effects of PtdIns3K inhibitors and suggest use of these drugs in humans may have important adverse effects on metabolism, body composition, behaviour and skeletal health.