Comparative effect of two pan-class I PI3K inhibitors used as anticancer drugs on human T cell function

Recent Advances of PI3 Kinase Inhibitors: Structure Anticancer Activity Relationship Studies

Phosphatidyl-inositol-3-kinase (PI3K) has emerged as a potential therapeutic target for the development of novel anticancer drugs. The dysregulation of PI3K has been associated with many human malignancies such as breast, colon, endometrial, brain, and prostate cancers. The PI3K kinases in their different isoforms namely α, β, δ, and γ, encode PIK3CA, PIK3CB, PIK3CD, and PIK3CG genes. Specific gene mutation or overexpression of the protein is responsible for therapeutic failure of current therapeutics. Recently, various PI3K signaling pathway inhibitors have been identified which showed promising therapeutic results by acting on specific isoforms of the kinase too. Several inhibitors containing medicinally privileged scaffolds like oxadiazole, pyrrolotriazine, quinazoline, quinazolinone, quinazoline-chalcone hybrids, quinazoline-sulfonamide, pyrazolochalcone, quinolone hydroxamic acid, benzofuropyridinone, imidazopyridine, benzoxazines, dibenzoxanthene, indoloderivatives, benzimidazole, and benzothiazine derivatives have been developed to target PI3K pathway and/or a specific isoform. The PI3K inhibitors which are under clinical trial studies include GDC-0032, INK1117 for PI3K-α, and AZD8186 for PI3K-β. This review primarily focuses on the structural insights and structure anticancer activity relationship studies of recent PI3K inhibitors including their clinical stages of development and therapeutic values.

Research update on the anticancer effects of buparlisib

Buparlisib is a highly efficient and selective PI3K inhibitor and a member of the 2,6-dimorpholinopyrimidine-derived family of compounds. It selectively inhibits four isomers of PI3K, PI3Kα, PI3Kβ, PI3Kγ and PI3Kδ, by competitively binding the lipid kinase domain on adenosine 5'-triphosphate (ATP), and serves an important role in inhibiting proliferation, promoting apoptosis and blocking angiogenesis, predominantly by antagonizing the PI3K/AKT pathway. Buparlisib has been confirmed to have a clinical effect in patients with solid tumors and hematological malignancies. A global, phase II clinical trial with buparlisib and paclitaxel in head and neck squamous cell carcinoma has now been completed, with a manageable safety profile. Buparlisib currently has fast-track status with the United States Food and Drug Administration. The present review examined the biochemical structure, pharmacokinetic characteristics, preclinical data and ongoing clinical studies of buparlisib. The various mechanisms of influence of buparlisib in tumors, particularly in preclinical research, were summarized, providing a theoretical basis and direction for basic research on and clinical treatment with buparlisib.

The immunomodulatory effects of endocrine therapy in breast cancer

Endocrine therapies with SERMs (selective estrogen receptor modulators) or SERDs (selective estrogen receptor downregulators) are standard therapies for patients with estrogen receptor (ER)-positive breast cancer. Multiple small molecule inhibitors targeting the PI3K-AKT-mTOR pathway or CDK4/6 have been developed to be used in combination with anti-estrogen drugs to overcome endocrine resistance. In addition to their direct antitumor effects, accumulating evidence has revealed the tumor immune microenvironment (TIM)-modulating effects of these therapeutic strategies, which have not been properly acknowledged previously. The immune microenvironment of breast tumors plays a crucial role in tumor development, metastasis and treatment response to endocrine therapy and immunotherapy. Therefore, in our current work, we comprehensively review the immunomodulatory effect of endocrine therapy and discuss its potential applications in combination with immune checkpoint inhibitors in breast cancer treatment.

Healthy CD4+ T lymphocytes are not affected by targeted therapies against the PI3K/Akt/mTOR pathway in T-cell acute lymphoblastic leukemia

An attractive molecular target for novel anti-cancer therapies is the phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway which is commonly deregulated in many types of cancer. Nevertheless, the effects of PI3K/Akt/mTOR inhibitors on T lymphocytes, a key component of immune responses, have been seldom explored. In this study we investigated the effects on human CD4+ T-cells of a panel of PI3K/Akt/mTOR inhibitors: BGT226, Torin-2, MK-2206, and ZSTK474. We also assessed their efficacy against two acute leukemia T cell lines. T lymphocytes were stimulated with phytohemagglutinin. Inhibitor effects on cell cycle and apoptosis were analyzed by flow cytometry, while cytotoxicity was assessed by MTT assays. In addition, the activation status of the pathway as well as induction of autophagy were analyzed by Western blotting. Quiescent healthy T lymphocytes were unaffected by the drugs whereas mitogen-stimulated lymphocytes as well as leukemic cell lines displayed a cell cycle block, caspase-dependent apoptosis, and dephosphorylation of key components of the signaling pathway. Autophagy was also induced in proliferating lymphocytes and in JURKAT and MOLT-4 cell lines. When autophagy was inhibited by 3-methyladenine or Bafilomycin A1, drug cytotoxicity was increased, indicating that autophagy is a protective mechanism. Therefore, our findings suggest that PI3K/Akt/mTOR inhibitors preserve lymphocyte viability. This is a valuable result to be taken into account when selecting drugs for targeted cancer therapy in order to minimize detrimental effects on immune function.

Potential anti-cancer activity of 7-O-pentyl quercetin: Efficient, membrane-targeted kinase inhibition and pro-oxidant effect

Quercetin is a redox-active plant-derived flavonoid with potential anticancer effects, stemming largely from its interaction with a number of proteins, and in particular from inhibition of pro-life kinases. To improve efficacy, we reasoned that a local increase in concentration of the compound at the level of cell membranes would result in a more efficient interaction with membrane-associated signaling kinases. We report here the synthesis of all five isomeric quercetin derivatives in which an n-pentyl group was linked via an ether bond to each hydroxyl of the flavonoid kernel. This strategy proved effective in directing quercetin to cellular membranes, and revealed a remarkable dependence of the derivatives' bioactivity on the specific site of functionalization. The isomer bearing the pentyl group in position 7, Q-7P, turned out to be the most effective and promising derivative, selectively inducing apoptosis in tumoral and fast-growing cells, while sparing slow-growing, non-tumoral ones. Cytotoxicity for tumoral cells was strongly enhanced compared to quercetin itself. Q-7P induced massive ROS production, which however accounted only partially for cell death. Alterations in the levels of various signaling phospho-proteins were observed in a proteomics screen. An important contribution seems to come from inhibition of the PI3K/Akt pathway. This work opens new perspectives in developing membrane-associating, polyphenol-based anticancer agents.

MiR-21 is required for anti-tumor immune response in mice: an implication for its bi-directional roles

Here we show that miR-21, a microRNA known for its oncogenic activity, is also essential for mediating immune responses against tumor. Knockout of miR-21 in mice slowed the proliferation of both CD4⁺ and CD8⁺ cells, reduced their cytokine production and accelerated the grafted tumor growth. Further investigations indicated that miR-21 could activate CD4⁺ and CD8⁺ T cells via the PTEN/Akt pathway in response to stimulations. Taken together, these data suggest the key functions of miR-21 in mediating anti-tumor immune response and thereby uncover a bi-directional role of this traditionally known 'oncomiR' in tumorigenesis. Our study may provide new insights for the design of cancer therapies targeting microRNAs, with an emphasis on the dynamic and possibly unexpected role of these molecules.

Targeted Therapy and Immunosuppression in the Tumor Microenvironment

Small-molecule inhibitors offer great promise for targeting pathways that are specifically deregulated in different tumors. However, such 'targeted' therapies also elicit poorly understood effects on protective antitumor immunity. Given the emerging relevance of immunotherapies that boost pre-existing T cell responses, understanding how different immune cells are affected by small-molecule inhibitors could lead to more-effective interventions, alone or combined with immunotherapy. This review discusses the growing array of activities elicited by multiple 'targeted' inhibitors on antitumor immunity, underscoring the complex effects resulting from diverse activities on different immune cell types in vivo, and the need to conduct mechanistic research that identifies drugs performing well not only in immunocompromised mice but also in the presence of spontaneous or therapeutic antitumor immunity.

Targeting of PI3K/AKT/mTOR pathway to inhibit T cell activation and prevent graft-versus-host disease development

BACKGROUND

Graft-versus-host disease (GvHD) remains the major obstacle to successful allogeneic hematopoietic stem cell transplantation, despite of the immunosuppressive regimens administered to control T cell alloreactivity. PI3K/AKT/mTOR pathway is crucial in T cell activation and function and, therefore, represents an attractive therapeutic target to prevent GvHD development. Recently, numerous PI3K inhibitors have been developed for cancer therapy. However, few studies have explored their immunosuppressive effect.

METHODS

The effects of a selective PI3K inhibitor (BKM120) and a dual PI3K/mTOR inhibitor (BEZ235) on human T cell proliferation, expression of activation-related molecules, and phosphorylation of PI3K/AKT/mTOR pathway proteins were analyzed. Besides, the ability of BEZ235 to prevent GvHD development in mice was evaluated.

RESULTS

Simultaneous inhibition of PI3K and mTOR was efficient at lower concentrations than PI3K specific targeting. Importantly, BEZ235 prevented naïve T cell activation and induced tolerance of alloreactive T cells, while maintaining an adequate response against cytomegalovirus, more efficiently than BKM120. Finally, BEZ235 treatment significantly improved the survival and decreased the GvHD development in mice.

CONCLUSIONS

These results support the use of PI3K inhibitors to control T cell responses and show the potential utility of the dual PI3K/mTOR inhibitor BEZ235 in GvHD prophylaxis.

Anti-inflammatory effects of novel barbituric acid derivatives in T lymphocytes

We have used a high throughput small molecule screen, using a fission yeast-based assay, to identify novel phosphodiesterase 7 (PDE7) inhibitors. One of the most effective hit compounds was BC12, a barbituric acid-based molecule that exhibits unusually potent immunosuppressive and immunomodulatory actions on T lymphocyte function, including inhibition of T cell proliferation and IL-2 cytokine production. BC12 treatment confers a >95% inhibition of IL-2 secretion in phytohaemagglutinin (PHA) plus phorbol-12-myristate-13-acetate (PMA) stimulated Jurkat T cells. The effect of BC12 on IL-2 secretion is not due to decreased cell viability; rather, BC12 blocks up-regulation of IL-2 transcription in activated T cells. BC12 also inhibits IL-2 secretion in human peripheral T lymphocytes stimulated in response to CD3/CD28 co-ligation or the combination of PMA and ionomycin, as well as the proliferation of primary murine T cells stimulated with PMA and ionomycin. A BC12 analog that lacks PDE7 inhibitory activity (BC12-4) displays similar biological activity, suggesting that BC12 does not act via PDE7 inhibition. To investigate the mechanism of inhibition of IL-2 production by BC12, we performed microarray analyses using unstimulated and stimulated Jurkat T cells in the presence or absence of BC12 or BC12-4. Our studies show these compounds affect the transcriptional response to stimulation and act via one or more shared targets to produce both anti-inflammatory and pro-stress effects. These results demonstrate potent immunomodulatory activity for BC12 and BC12-4 in T lymphocytes and suggest a potential clinical use as an immunotherapeutic to treat T lymphocyte-mediated diseases.