Current perspectives on targeting PIM kinases to overcome mechanisms of drug resistance and immune evasion in cancer

PIM kinases are a class of serine/threonine kinases that play a role in several of the hallmarks of cancer including cell cycle progression, metabolism, inflammation and immune evasion. Their constitutively active nature and unique catalytic structure has led them to be an attractive anticancer target through the use of small molecule inhibitors. This review highlights the enhanced activity of PIM kinases in cancer that can be driven by hypoxia in the tumour microenvironment and the important role that aberrant PIM kinase activity plays in resistance mechanisms to chemotherapy, radiotherapy, anti-angiogenic therapies and targeted therapies. We highlight an interaction of PIM kinases with numerous major oncogenic players, including but not limited to, stabilisation of p53, synergism with c-Myc, and notable parallel signalling with PI3K/Akt. We provide a comprehensive overview of PIM kinase's role as an escape mechanism to targeted therapies including PI3K/mTOR inhibitors, MET inhibitors, anti-HER2/EGFR treatments and the immunosuppressant rapamycin, providing a rationale for co-targeting treatment strategies for a more durable patient response. The current status of PIM kinase inhibitors and their use as a combination therapy with other targeted agents, in addition to the development of novel multi-molecularly targeted single therapeutic agents containing a PIM kinase targeting moiety are discussed.

Trifluridine/tipiracil (FTD/TPI) in patients (pts) with metastatic gastroesophageal junction cancer (mGEJC): Subgroup analysis from TAGS

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Background: The incidence of GEJC is increasing in North America and Europe, especially among white men. Many pts present with metastatic disease or relapse locally or systemically after resection of early-stage disease. The global phase 3 study TAGS (NCT02500043) demonstrated the efficacy and safety of FTD/TPI in previously treated pts with metastatic gastric cancer (mGC)/mGEJC. Here we report results in the mGEJC subgroup from TAGS. Methods: Pts with mGC/mGEJC treated with ≥2 prior chemotherapy regimens were randomized (2:1) to receive FTD/TPI (35 mg/m2 BID on days 1–5 and 8–12 of each 28-day cycle) or placebo, plus best supportive care. A preplanned efficacy and safety analysis was performed in pts with mGEJC. Results: Of 507 randomized pts, 145 (29%) had GEJC as the sole primary disease site (FTD/TPI, 98/337; placebo, 47/170). Of pts with mGEJC, 85% were male and 83% were white (overall population, 73% and 70%). Baseline characteristics were generally balanced for pts with mGEJC across treatment groups, except for fewer pts having prior gastrectomy (40% vs 55%) and more pts having received ≥3 prior regimens (74% vs 66%) in the FTD/TPI group than in the placebo group. FTD/TPI had an efficacy benefit in pts with mGEJC, and the FTD/TPI safety profile was similar in this subgroup and the overall population (table). Conclusions: FTD/TPI showed a manageable safety profile and efficacy benefit in pts with mGEJC in the TAGS trial, despite heavier pretreatment of the FTD/TPI than the placebo group. Clinical trial information: NCT02500043. [Table: see text]

Updated Analysis of KEYNOTE-024: Pembrolizumab Versus Platinum-Based Chemotherapy for Advanced Non-Small-Cell Lung Cancer With PD-L1 Tumor Proportion Score of 50% or Greater

PURPOSE

In the randomized, open-label, phase III KEYNOTE-024 study, pembrolizumab significantly improved progression-free survival and overall survival (OS) compared with platinum-based chemotherapy in patients with previously untreated advanced non-small-cell lung cancer (NSCLC) with a programmed death ligand 1 tumor proportion score of 50% or greater and without EGFR/ALK aberrations. We report an updated OS and tolerability analysis, including analyses adjusting for potential bias introduced by crossover from chemotherapy to pembrolizumab.

PATIENTS AND METHODS

Patients were randomly assigned to pembrolizumab 200 mg every 3 weeks (for up to 2 years) or investigator's choice of platinum-based chemotherapy (four to six cycles). Patients assigned to chemotherapy could cross over to pembrolizumab upon meeting eligibility criteria. The primary end point was progression-free survival; OS was an important key secondary end point. Crossover adjustment analysis was done using the following three methods: simplified two-stage method, rank-preserving structural failure time, and inverse probability of censoring weighting.

RESULTS

Three hundred five patients were randomly assigned (pembrolizumab, n = 154; chemotherapy, n = 151). At data cutoff (July 10, 2017; median follow-up, 25.2 months), 73 patients in the pembrolizumab arm and 96 in the chemotherapy arm had died. Median OS was 30.0 months (95% CI, 18.3 months to not reached) with pembrolizumab and 14.2 months (95% CI, 9.8 to 19.0 months) with chemotherapy (hazard ratio, 0.63; 95% CI, 0.47 to 0.86). Eighty-two patients assigned to chemotherapy crossed over on study to receive pembrolizumab. When adjusted for crossover using the two-stage method, the hazard ratio for OS for pembrolizumab versus chemotherapy was 0.49 (95% CI, 0.34 to 0.69); results using rank-preserving structural failure time and inverse probability of censoring weighting were similar. Treatment-related grade 3 to 5 adverse events were less frequent with pembrolizumab compared with chemotherapy (31.2% v 53.3%, respectively).

CONCLUSION

With prolonged follow-up, first-line pembrolizumab monotherapy continues to demonstrate an OS benefit over chemotherapy in patients with previously untreated, advanced NSCLC without EGFR/ALK aberrations, despite crossover from the control arm to pembrolizumab as subsequent therapy.

When RON MET TAM in Mesothelioma: All Druggable for One, and One Drug for All?

Malignant pleural mesothelioma (MPM) is an aggressive inflammatory cancer with a poor survival rate. Treatment options are limited at best and drug resistance is common. Thus, there is an urgent need to identify novel therapeutic targets in this disease in order to improve patient outcomes and survival times. MST1R (RON) is a trans-membrane receptor tyrosine kinase (RTK), which is part of the c-MET proto-oncogene family. The only ligand recognized to bind MST1R (RON) is Macrophage Stimulating 1 (MST1), also known as Macrophage Stimulating Protein (MSP) or Hepatocyte Growth Factor-Like Protein (HGFL). In this study, we demonstrate that the MST1-MST1R (RON) signaling axis is active in MPM. Targeting this pathway with a small molecule inhibitor, LCRF-0004, resulted in decreased proliferation with a concomitant increase in apoptosis. Cell cycle progression was also affected. Recombinant MST1 treatment was unable to overcome the effect of LCRF-0004 in terms of either proliferation or apoptosis. Subsequently, the effect of an additional small molecular inhibitor, BMS-777607 (which targets MST1R (RON), MET, Tyro3, and Axl) also resulted in a decreased proliferative capacity of MPM cells. In a cohort of MPM patient samples, high positivity for total MST1R by IHC was an independent predictor of favorable prognosis. Additionally, elevated expression levels of MST1 also correlated with better survival. This study also determined the efficacy of LCRF-0004 and BMS-777607 in xenograft MPM models. Both LCRF-0004 and BMS-777607 demonstrated significant anti-tumor efficacy in vitro, however BMS-777607 was far superior to LCRF-0004. The in vivo and in vitro data generated by this study indicates that a multi-TKI, targeting the MST1R/MET/TAM signaling pathways, may provide a more effective therapeutic strategy for the treatment of MPM as opposed to targeting MST1R alone.

BBI608 inhibits cancer stemness and reverses cisplatin resistance in NSCLC

Non-small cell lung cancer (NSCLC) is the most common cause of cancer-related deaths worldwide. While partial or complete tumor regression can be achieved in patients, particularly with cisplatin-based strategies, these initial responses are frequently short-lived and are followed by tumor relapse and chemoresistance. Identifying the root of cisplatin resistance in NSCLC and elucidating the mechanism(s) of tumor relapse, is of critical importance in order to determine the point of therapeutic failure, which in turn, will aid the discovery of novel therapeutics, new combination strategies and a strategy to enhance the efficacy of current chemotherapeutics. It has been hypothesized that cancer stem cells (CSCs) may be the initiating factor of resistance. We have previously identified and characterized an aldehyde dehydrogenase 1 CSC subpopulation in cisplatin resistant NSCLC. BBI608 is a small molecule STAT3 inhibitor known to suppress cancer relapse, progression and metastasis. Here, we show that BBI608 can inhibit stemness gene expression, deplete CSCs and overcome cisplatin resistance in NSCLC.

Association of BRM promoter polymorphisms and esophageal adenocarcinoma outcome

Purpose

Brahma (BRM) is a critical catalytic subunit of the SWI/SNF chromatin remodeling complex; expression of BRM is commonly lost in various cancer types. BRM promoter polymorphisms (BRM-741; BRM-1321) are associated with loss of BRM expression, and with cancer risk/survival. We evaluated these two polymorphisms in the overall survival (OS) of esophageal adenocarcinoma (EAC) patients.

Results

Of 270 patients, 37% were stage IV. Minor allele frequencies were 47−49%; 15% were double-homozygotes. When compared to the wild-type genotype, the homozygous variant of BRM-741 carried an adjusted OS hazard ratio (aHR) of 1.64 (95% CI:1.1−2.4); for BRM-1321, the aHR was 2.09 (95% CI:1.4−3.0). Compared to the double wild-type, carrying homozygous variants of both promoter polymorphisms (double-homozygote) yielded an aHR of 2.21 (95% CI:1.4−3.6). Directions/magnitudes of associations were similar in subsets by age, gender, smoking status, use of platinum agents, and disease stage, and for progression-free survival.

Materials and Methods

In a cohort of EAC patients of all stages (84% male; median age of 64 years), two BRM polymorphisms were genotyped. Cox proportional hazards models, adjusted for known prognostic variables, estimated the association of polymorphisms with OS.

Conclusions

BRM polymorphisms were associated with OS in EAC in this study. Validation studies are warranted.

In pursuit of synergy: An investigation of the PI3K/mTOR/MEK co-targeted inhibition strategy in NSCLC

Clinical PI3K inhibition has been somewhat disappointing, due to both inadequate patient stratification and compensatory cell signalling through bypass mechanisms. As such, investigation of PI3K-MEK co-targeted inhibition has been recommended. With high mortality rates and a clear need for new therapeutic intervention strategies, non-small cell lung cancer (NSCLC) is an important setting to investigate the effectiveness of this approach.

Here, 174 NSCLC tumours were screened for 150 mutations by Fluidigm technology, with 15 patients being profiled for phosphoprotein expression. The effects of GDC-0941 (a pan PI3K inhibitor), GDC-0980 (a dual PI3K/mTOR inhibitor) and GDC-0973 (a MEK inhibitor) alone and in combination were assessed in 3 NSCLC cell lines.

PIK3CA was mutated in 5.17% of NSCLC patients. GDC-0941 and GDC-0980 treatment induced anti-proliferative and pro-apoptotic responses across all NSCLC cell lines, while GDC-0973 treatment induced only anti-proliferative responses. GDC-0980 and GDC-0973 combined treatment led to significant increases in apoptosis and synergistic reductions in proliferation across the panel of cell lines.

This study found that the PI3K/MEK co-targeted inhibition strategy is synergistic in all 3 molecular subtypes of NSCLC investigated. Consequently, we would advocate clinical trials for NSCLC patients combining GDC-0980 and GDC-0973, each of which are separately under clinical investigation currently.

Development and characterisation of a panel of phosphatidylinositide 3-kinase - mammalian target of rapamycin inhibitor resistant lung cancer cell lines

The PI3K-mTOR pathway is involved in regulating all hallmarks of cancer, and is often dysregulated in NSCLC, making it an attractive therapeutic target in this setting. Acquired resistance to PI3K-mTOR inhibition is a major hurdle to overcome in the success of PI3K-mTOR targeted agents. H460, A549, and H1975 resistant cells were generated by prolonged treatment in culture with Apitolisib (GDC-0980), a dual PI3K-mTOR inhibitor over a period of several months, from age-matched parent cells. Resistance was deemed to have developed when a log fold difference in IC50 had been achieved. Resistant cell lines also exhibited resistance to another widely investigated PI3K-mTOR dual inhibitor; Dactolisib (BEZ235). Cell lines were characterised at the level of mRNA (expression array profiling expression of >150 genes), miRNA (expression array profiling of 2100 miRNAs), protein (bottoms-up label-free mass spectrometry) and phosphoprotein (expression array profiling of 84 phospho/total proteins). Key alterations were validated by qPCR and Western blot. H1975 cells were initially most sensitive to Apitolisib (GDC-0980), but developed resistance more quickly than the other cell lines, perhaps due to increased selective pressure from the impressive initial effect. In-depth molecular profiling suggested epithelial-mesenchymal transition (EMT) may play a role in resistance to PI3K-mTOR dual inhibition in NSCLC.