Overview of the Development and Use of Akt Inhibitors in Prostate Cancer

Deregulation of the PI3K-Akt-mTOR pathway plays a critical role in the development and progression of many cancers. In prostate cancer, evidence suggests that it is mainly driven by PTEN loss of function. For many years, the development of selective Akt inhibitors has been challenging. In recent phase II and III clinical trials, Ipatasertib and Capivasertib associated with androgen deprivation therapies showed promising outcomes in patients with metastatic castration-resistant prostate cancer and PTEN-loss. Ongoing trials are currently assessing several Akt inhibitors in prostate cancer with different combinations, at different stages of the disease.

Endometrial Metaplastic/Reactive Changes Coexistent with Endometrial Hyperplasia and Carcinoma: A Morphological and Immunohistochemical Study

The aim of this study was to assess the relationship between endometrial metaplastic/reactive changes (EMRCs) and endometrial neoplastic lesions. Twenty cases of “simple” (without architecture complexity) EMRCs coexistent with endometrial malignant/premalignant lesions, twenty cases of neoplasia-unassociated EMRCs, and eight cases of complex metaplastic lesions were assessed by immunohistochemistry. EMRCs coexisted with endometrioid carcinoma (n = 12), atypical endometrial hyperplasia (n = 3), serous carcinoma (n = 2), and clear cell carcinoma (n = 3). Neoplasia-associated EMRCs showed a mean Ki67 labeling index of 12.6% (range 0–30%); with nuclear atypia in 16/20 (80%) cases; diffuse p16 expression in 15/20 (75%) cases; and heterogeneous ER, PR, and vimentin expression. Compared to the associated neoplasia, EMRCs showed a lower Ki67 expression (p < 0.001) and higher p16 expression (p < 0.001). No EMRC case showed mitotic activity, PTEN loss, MMR deficiency, nuclear β-catenin, p53-mutant pattern, Napsin A, or AMACR expression. No significant differences were found between neoplasia-associated and neoplasia-unassociated EMRCs. Complex metaplastic lesions showed a lower Ki67 expression than EMRCs (p = 0.044) and PTEN loss in 5/8 cases, even in the absence of nuclear atypia. In conclusion, neoplasia-associated simple EMRCs may show evident atypia and a worrisome immunophenotype, but no data support their involvement in endometrial carcinogenesis. Architectural complexity appears as a crucial factor to identify precancerous lesions.

LncRNA RP11-295G20.2 regulates hepatocellular carcinoma cell growth and autophagy by targeting PTEN to lysosomal degradation

PTEN is a crucial tumor suppressor and loss of PTEN protein is involved in various cancers. However, the detailed molecular mechanisms of PTEN loss in cancers remain elusive, especially the involvement of lncRNAs. Here, lncRNA RP11-295G20.2 is found to be significantly upregulated in hepatocellular carcinoma (HCC) and promotes the growth of liver cancer cells both in vitro and in vivo. Furthermore, RP11-295G20.2 inhibits autophagy in liver cancer cells. Interestingly, RP11-295G20.2 directly binds to the PTEN protein and leads to its degradation. RP11-295G20.2 expression is inversely correlated with PTEN protein expression in 82 TCGA/TCPA-LIHC samples. Surprisingly, RP11-295G20.2-induced PTEN degradation occurs through the lysosomal pathway instead of the proteasome pathway. RP11-295G20.2 binds to the N terminus of PTEN and facilitates the interaction of p62 with PTEN. Thus, PTEN is translocated into lysosomes and degraded. RP11-295G20.2 also influences AKT phosphorylation and forkhead box O 3a (FOXO3a) translocation into the nucleus, in turn regulating the transcription of autophagy-related genes. Collectively, RP11-295G20.2 directly binds to PTEN and enables its lysosomal degradation. This newly identified RP11-295G20.2/PTEN axis reveals an unexplored molecular mechanism regarding PTEN loss in liver cancer and might provide new therapeutic benefits for liver cancer patients.

CTNI-22. A PHASE 0/1 ‘TRIGGER’ TRIAL OF RIBOCICLIB PLUS EVEROLIMUS IN RECURRENT HIGH-GRADE GLIOMA

BACKGROUND mTOR activation is a mechanism of resistance in CDK4/6 targeting. We evaluated tumor pharmacokinetics (PK) and tumor pharmacodynamics (PD) of combined CDK4/6 and mTOR inhibition in recurrent high-grade glioma (HGG) patients. METHODS Recurrent HGG patients with (1) intact RB, (2) CDKN2A/B deletion or CDK4/6 amplification, and (3) PTEN loss or PIK3CA mutations receive five days of presurgical ribociclib plus everolimus prior to resection at 2, 8 or 24 hours after the final dose. Beginning at 400mg QD ribociclib plus 2.5mg QD everolimus, six dose-escalations summit at 600mg QD plus 60mg QW. Gadolinium [Gd]-enhancing and nonenhancing tumor regions, CSF, and plasma are collected. Total and unbound drug concentrations are determined using validated LC-MS/MS methods. RB and S6 phosphorylation are compared to matched archival tissue. To select patients for a therapeutic expansion phase of combined drug therapy, the protocol includes a PK ‘trigger’ (i.e., for each drug, unbound concentration in Gd-nonenhancing tumor &gt; 5-fold biochemical IC50) and a PD ‘trigger’ (i.e., for each tumor, &gt; 30% decrease in pRB and pS6). RESULTS 21 patients with WHO Grade III (n=2) and IV (n=19) gliomas were enrolled into the Phase 0 component of the study. No dose-limiting toxicities were observed. In Gd-nonenhancing tumor regions, the median unbound concentration of ribociclib was 719 nM, whereas unbound everolimus tumor concentrations were undetectable. Across all dose-levels, 62% (13/21) and 22% (5/21) of tumors demonstrated decreased tumor RB and S6 phosphorylation, respectively. Tumor proliferation (MIB-1) was decreased in 67% (14/21) of all patients. No patients qualified for the therapeutic expansion phase. CONCLUSION In adult HGG, ribociclib achieves pharmacologically-relevant concentrations in Gd-nonenhancing tumor whereas everolimus exhibits no meaningful tumor penetration. These findings support further clinical development of ribociclib, but not everolimus, for the treatment of high-grade glioma patients.

CSIG-11. KINASE-DIRECTED INHIBITION OF PYRIMIDINE BIOSYNTHESIS IN PTEN-DEFICIENT GLIOBLASTOMA

Targeting pyrimidine biosynthesis has been a mainstay of chemotherapy in oncology, including frontline treatment of pancreatic, breast, and colorectal carcinomas. In glioblastoma, the targeting pyrimidine biosynthesis is a promising emerging approach for counteracting the effects of PTEN-deficiency in glioblastoma. PTEN loss triggers the activation of mTORC1, which in turn phosphorylates and activates the ribosomal protein kinases S6K1 and S6K2. We have previously shown that combination treatment of inhibitors targeting S6K1 and the TYRO3-AXL-MERTK receptor tyrosine kinases (TAM-RTKs) triggers cytotoxic responses in PTEN-deficient glioblastoma cells. Here we show brain-penetrant inactivation of S6K1 and TAM-RTKs using the S6K1 inhibitor LY-2584702 and the TAM-RTK inhibitor BMS-777607, which reduced glioblastoma tumor growth. Pharmacogenetic analysis of signal transduction indicated a key role for S6K2 in sustaining survival signaling in PTEN-deficient glioblastoma cells. Steady-state metabolomics revealed that combined inactivation of S6K1 and TAM-RTKs resulted in decreased nucleotide biosynthesis, and flux analysis indicated reduced flux of glucose to pyrimidines. Altogether the results indicate a kinase-directed therapeutic strategy for targeting S6K1 and TAM-RTKs to reduce pyrimidine biosynthesis and glioblastoma tumor growth.

CTNI-13. MALIGNANT GLIOMA SUBSET FROM ACTUATE 1801 PHASE 1/2 STUDY OF 9-ING-41, A GLYCOGEN SYNTHASE KINASE 3 BETA (GSK-3β) INHIBITOR, AS A SINGLE AGENT AND COMBINED WITH CHEMOTHERAPY REFRACTORY

BACKGROUND GSK3β serine/threonine kinase regulates metabolism and glycogen biosynthesis. GSK3β overexpression promotes tumor progression and resistance through NF-κB and p53 apoptotic pathways. GSK3β inhibits immunomodulation by downregulating checkpoints, e.g. PD-L1 and LAG-3, and increasing NK and T-cell mediated tumor killing. 9-ING-41 is a small-molecule, potent, selective GSK3β inhibitor with preclinical activity. In chemoresistant PDX glioblastoma models, 9-ING-41 enhanced lomustine antitumor effect. METHODS Patients with refractory malignancies were treated with 9-ING-41 monotherapy (n=65) or combined with 8 cytotoxic regimens after prior exposure (n=162) in the first-in-human study (NCT03678883). The recurrent gliomas subset was treated with 9-ING-41 monotherapy IV TIW q21day cycles at 3.3, 5, 9.3, 15mg/kg, or combined with lomustine 30 mg/m² PO weekly q84day cycles. Primary objective was safety and tolerability. RESULTS An RP2D of 15mg/kg IV TIW was confirmed across all 9 regimens, no accentuation of chemotherapy toxicity noted. Of 18 glioma patients enrolled, 13 were glioblastoma, 2 anaplastic astrocytomas, 1 anaplastic oligodendroglioma, and 1 diffuse astrocytoma; 6 female, 12 male; median age 52 (30-69) years; median ECOG was 1 (0-2). All received initial radiation and temozolomide (18/18), prior salvage therapies included nitrosoureas (15/18), bevacizumab (8/18), TTFields (6/18), checkpoint inhibitor (4/18). Median recurrences 3 (1-6). NGS alterations included: IDH/wildtype (11), IDH/mutation(3); 1p19q/codeletion(10); MGMT/unmethylated(11), MGMT/methylated(1); EGFR/amplification(6), EGFR/v3mutation(3), TERT/mutation(6), PTEN/loss(3), NF1/rearrangement(2), ATRX/loss (2), TP53/mutation(4), CDKN2A/deletion(2), RB1/loss(1), PALB2/mutation(10). Four patients received 9-ING-41 monotherapy, 14 concurrently treated with lomustine. No SAEs or grade 3/4 AEs attributed to 9-ING-41 noted, only G1/2 vision changes (9/18, 50%), infusion reactions (4/18, 22%). Lomustine-related toxicities included G3/4 thrombocytopenia (3/14, 21%), and G1/2 fatigue (4/14, 28%). Median therapy duration was 55 (4-305); 1 partial response ( &gt;50%) noted with 9-ING-41/lomustine. Median PFS and OS were 1.9 (0.3-11.1) and 6.0 (1.6-16.6) months, respectively. CONCLUSIONS 9-ING-41 plus/minus lomustine is safe and warrants further study in glioma patients.

EXTH-03. COMBINED TOP1 AND PARP INHIBITION ENFORCES GENOMIC INSTABILITY AND CELL DEATH IN PTEN-DEFICIENT GLIOBLASTOMA

BACKGROUND Glioblastoma is an aggressive brain tumor with high mortality. The development of new therapies is critical for improving patient outcomes. LMP400, a novel topoisomerase I (TOP1) inhibitor, traps TOP1 cleavage complexes, thereby generating DNA damage. Poly(ADP-ribose) polymerase (PARP) is involved in DNA repair responses triggered by TOP1 inhibition. Niraparib is a potent PARP inhibitor that can cross the blood-brain barrier. Loss of phosphatase and tensin homolog (PTEN) occurs in 40% of GBM patients and is known to promote DNA damage repair deficiency. Here, we hypothesize that PTEN loss presents a vulnerability to a combined induction of DNA damage and inhibition of repair mechanisms. METHODS Human glioblastoma cells (U251, SNB-75, SF-295, LN18) and patient-derived glioblastoma stem cells (GSC923 and GSC827) were treated with LMP400 and/or Niraparib. Cell viability and apoptosis were examined using Celigo image cytometer and Annexin V/PI assay at 72h after treatment. Single clones after PTEN knockdown using shRNA were isolated after puromycin selection. For planned studies of PTEN knockout, sgRNA plasmids targeting PTEN will be transiently transfected and GFP-positive single KO clones will be isolated. PTEN will be restored in PTEN-null cells using lentiviral transduction. RESULTS CRISPR-Cas9 KO screening in GSC923 cells suggests that LMP400 is unlikely a substrate for ABC transporters. LMP400 and Niraparib synergistically induced cytotoxic effects in U251, SF-295, GSC923, GSC827 cells lacking PTEN expression. Combined LMP400/Niraparib led to increased expression of gamma-H2AX, cleaved caspase 3 and PARP, indicative of enhanced DNA damage and cell death. CONCLUSION LMP400 and Niraparib act synergistically to target PTEN-deficient glioblastoma by inducing DNA damage and cell death. These results will be further verified in isogenic cells in vitro as well as in vivo in a mouse model driven by PTEN deletion which would strongly support a novel therapeutic strategy in a subset of glioblastoma with PTEN loss.

Brain and Breast Cancer Cells with PTEN Loss of Function Reveal Enhanced Durotaxis and RHOB Dependent Amoeboid Migration Utilizing 3D Scaffolds and Aligned Microfiber Tracts

Background: Glioblastoma multiforme (GBM) and metastatic triple-negative breast cancer (TNBC) with PTEN mutations often lead to brain dissemination with poor patient outcome, thus new therapeutic targets are needed. To understand signaling, controlling the dynamics and mechanics of brain tumor cell migration, we implemented GBM and TNBC cell lines and designed 3D aligned microfibers and scaffolds mimicking brain structures. Methods: 3D microfibers and scaffolds were printed using melt electrowriting. GBM and TNBC cell lines with opposing PTEN genotypes were analyzed with RHO-ROCK-PTEN inhibitors and PTEN rescue using live-cell imaging. RNA-sequencing and qPCR of tumor cells in 3D with microfibers were performed, while scanning electron microscopy and confocal microscopy addressed cell morphology. Results: In contrast to the PTEN wildtype, GBM and TNBC cells with PTEN loss of function yielded enhanced durotaxis, topotaxis, adhesion, amoeboid migration on 3D microfibers and significant high RHOB expression. Functional studies concerning RHOB-ROCK-PTEN signaling confirmed the essential role for the above cellular processes. Conclusions: This study demonstrates a significant role of the PTEN genotype and RHOB expression for durotaxis, adhesion and migration dependent on 3D. GBM and TNBC cells with PTEN loss of function have an affinity for stiff brain structures promoting metastasis. 3D microfibers represent an important tool to model brain metastasizing tumor cells, where RHO-inhibitors could play an essential role for improved therapy.

Preliminary evidence of antitumour activity of Ipatasertib (Ipat) and Atezolizumab (ATZ) in glioblastoma patients (pts) with PTEN loss from the Phase 1 Ice-CAP trial (NCT03673787)

Aims Despite improved understanding of effector T-cell trafficking into the central nervous system, initial trials with anti-PD1/PD-L1 immune checkpoint inhibitors (ICIs) have failed to meet their primary endpoints. PTEN loss of function is frequent in GBM and has been correlated with not only poor overall prognosis, but also impaired antitumour responses, including reduced T cell infiltration into tumour and reduced efficacy of ICIs. Ipatasertib is a novel, potent, selective, small-molecule inhibitor of Akt. We have shown that Ipatasertib efficiently depletes FOXP3+ regulatory T cells from the tumour microenvironment (TME) resulting in increased infiltration of effector T cells in solid tumours (Lopez 2020, AACR). We hypothesize that the use of AKT inhibition in PTEN glioblastomas may deplete the TME of suppressive immune cells, and render malignant brain tumours more responsive to ICIs. We present updated data for the combination of Ipat+ATZ in patients with glioblastoma. Method Patients with relapsed WHO grade IV GBM with stable neurological symptoms ≥5 days prior to enrolment, requiring &lt;3mg Dexamethasone were recruited into two cohorts of this early phase, open-label, single-centre trial studying the combination of Ipatasertib (Ipat) and Atezolizumab (ATZ): a dose finding cohort (A2; n=9) and an expansion cohort (B3; n=7, recruitment ongoing). The Ice-CAP A2 cohort assessed safety, pharmacodynamic, and preliminary clinical activity of Ipat (200mg or 400mg OD) + ATZ (1200mg Q3W) in pts with potentially resectable relapsed WHO Grade IV GBM. Pts had a 14-21-day run-in phase of Ipat then surgical tumour resection. Combination Ipat+ATZ commenced post surgery. Patients who declined surgery or who were deemed high risk for surgery proceeded directly to combination. Patients in the expansion cohort B3 commenced directly on Ipat+ATZ at the RP2D of 400mg Ipat with ATZ. Results 16 evaluable recurrent GBM pts were enrolled across two cohorts. Median age 56 yrs (25-71 yrs). Median ECOG PS 1. Median lines of prior therapy 1 (range 1-4). 10 pts had PTEN loss by IHC (H&lt;30) and/or PTEN mutations on next generation sequencing. No DLTs, treatment-related (TR) serious adverse events (AEs), or immune-related AEs were observed. Most common TR AEs were G1 diarrhoea (44%), mucositis (17%), rash (28%). Clinical benefit rate (CR, PR and SD&gt; 6 cycles) at clinical cutoff date (23/02/21) in patients with PTEN aberration was 30% (3/10). A 58-year-old man with PTEN loss had MRI at Cycle 5 showing worsening enhancement suggestive of disease progression. Resection of the lesion showed intense lymphocyte infiltration and pathological CR. He is currently on Cycle 22 with no evidence of disease. Two other patients with PTEN loss with radiological stable disease per RANO criteria remain well on study for &gt;6 cycles. Conclusion Combination Ipat+ATZ appears safe and tolerable in GBM pts, with 400mg Ipatasertib OD + 1200mg ATZ Q3W declared as RP2D. Early efficacy signals were detected with PTEN loss being a promising predictive biomarker for response to combination. An expansion cohort enriched with pts with PTEN loss is ongoing.