Mediator Of Treatment Resistance Research Articles

Abstract P5-16-08: Phase Ib/II trial evaluating safety and efficacy of copanlisib (PI3K inhibitor) and trastuzumab in pre-treated advanced HER2-positive breast cancer: Results from the PantHER study

Abstract Background: De novo and acquired resistance to HER2 directed therapy is frequently encountered. Upregulation of the phosphatidylinositol-3-kinase (PI3K) pathway is an important mediator of treatment resistance. This can occur through an activating mutation of the PIK3CA gene or PTEN loss. PIK3CA mutations are present in approximately 20% of HER2 positive breast cancers and as such, the PI3K pathway has emerged as an attractive target for restoring sensitivity to HER2 directed therapy. Methods: We performed a single arm, multicentre, open label Phase Ib/II trial. Patients (pts) with advanced HER2-positive breast cancer whose disease had progressed on at least 1 line of Trastuzumab/T-DM1 based treatment in the metastatic setting were eligible if they met following criteria: ECOG PS ≤ 2 and adequate organ function. Pts with treated, controlled brain metastases were permitted to enrol. Exclusion criteria included uncontrolled hypertension or diabetes mellitus. Pts on Phase IB were treated according to a 6+6 study design with a dose escalation schedule of Copanlisib IV (level 1 = 45mg, level 2 = 60mg) on Day 1, 8 and 15 of a 28-day cycle along with a fixed dose of Trastuzumab 2mg/kg weekly. Phase II treatment was the MTD (maximum tolerated dose) of Copanlisib in combination with Trastuzumab. Archival tumour tissue, voluntary biopsies and serial plasma samples were collected for genomic sequencing. Primary endpoints were MTD (Phase I) and clinical benefit rate (CBR) which was defined as complete response (CR) or partial response (PR) at any time point; or stable disease (SD) lasting at least 24 weeks (Phase II). Secondary endpoints included safety and tolerability, tumor response rate, duration of response, time to treatment failure (TTF) and progression free (PFS) and overall survival (OS). Results: Twelve pts were enrolled in Phase IB. No dose limiting toxicity was observed. The MTD was established as Copanlisib 60mg and Trastuzumab 2mg/kg. Fourteen pts were enrolled in Phase II (6 pts treated at the MTD in Phase IB were included in the final Phase II analysis resulting in a total of 20 pts). The median number of lines of prior treatment in the metastatic setting was 3 (1-8). The most common grade 3-4 toxicities encountered in the Phase Ib/II cohorts included hypertension (n=7, 27%), hyperglycaemia (n=2, 8%) and vomiting (n=2, 8%). Three pts discontinued treatment due to toxicity. The median follow-up for the Phase II cohort was 7.5 months (95% CI 6.0-14.5). PR was observed in 4 pts (20%) and SD (at any time point) was seen in 8 pts (40%). The CBR was 30% (n=6). The duration of response was 15.0 weeks (95% CI 4.9 - 16.1). The median TTF was 11.9 weeks (95% CI 7.5 - 21.1). The median PFS was 3.0 mo (95% CI 0.2 - 5.8) and OS was 14.0 mo (95% CI 5.2-22.8). At the time of analysis, 9 of 20 patients were alive. PIK3CA mutations were detectable in the archival tissue of 11 of 26 pts (42%). PIK3CA hotspot mutations (H1047R, E542K and E545K) were detectable in the plasma of all 26 pts at various points throughout treatment. Pre and post treatment biopsies of 2 pts in the Phase IB trial revealed somatic mutations in DNAH3 and TRRAP, the latter of which encodes a PI3K-like protein kinase. Targeted next generation sequencing was performed on the circulating tumour DNA of 20 pts in the Phase II cohort taken before, during and after treatment to further validate these findings and to assess for other mechanisms of response or resistance. The final translational results will be presented at the meeting. Conclusions: The combination of Copanlisib and Trastuzumab is a safe and tolerable regimen and is associated with clinical efficacy in a heavily pre-treated metastatic HER2-positive breast cancer population. Translational studies may have identified novel resistance biomarkers in this pt cohort. Citation Format: Lisa Prior, Niamh M Keegan, Simon J Furney, Janice M Walshe, Giuseppe Gullo, John Crown, M John Kennedy, Diarmuid Smith, John McCaffrey, Catherine M Kelly, Keith Egan, Jennifer Kerr, Mark Given, Niall Sheehy, Peter O'Donovan, Andres Hernando, Ausra Teiserskiene, Imelda Parker, Elaine Kay, Ray McDermott, Maccon M Keane, Seamus O'Reilly, Liam Grogan, Oscar Breathnach, Patrick G Morris, Sinead Toomey, Bryan T Hennessy. Phase Ib/II trial evaluating safety and efficacy of copanlisib (PI3K inhibitor) and trastuzumab in pre-treated advanced HER2-positive breast cancer: Results from the PantHER study [abstract]. In: Proceedings of the 2021 San Antonio Breast Cancer Symposium; 2021 Dec 7-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2022;82(4 Suppl):Abstract nr P5-16-08.

V-ATPase as a mediator of treatment resistance in Glioblastoma Multiforme: an <em>in vitro</em> study to investigate new therapeutic strategies

Recent evidences suggest the involvement of the Vacuolar H+ ATPase (V-ATPase) in the development and/or progression of Glioblastoma Multiforme (GBM). This proton pump could be a valid therapeutic target but more in-depth studies are necessary. The aim of this study is to better define the in vitro effects on Glioma Stem Cell (GSC) primary cultures viability of single and combined treatment with Bafilomycin-A1 (Baf-A1), a V-ATPase inhibitor, and Temozolomide (TMZ), the chemotherapeutic agent currently used to treat GBM patients. We found out that GSC were resistant to TMZ and more sensitive to treatments with Baf-A1 and that the two drugs exerted a synergistic effect when administered together.

Fatty Acid Oxidation Is an Adaptive Survival Pathway Induced in Prostate Tumors by HSP90 Inhibition

HSP90 is a molecular chaperone required for stabilization and activation of hundreds of client proteins, including many known oncoproteins. AUY922 (luminespib), a new-generation HSP90 inhibitor, exhibits potent preclinical efficacy against several cancer types including prostate cancer. However, clinical use of HSP90 inhibitors for prostate cancer has been limited by toxicity and treatment resistance. Here, we aimed to design an effective combinatorial therapeutic regimen that utilizes subtoxic doses of AUY922, by identifying potential survival pathways induced by AUY922 in clinical prostate tumors. We conducted a proteomic analysis of 30 patient-derived explants (PDE) cultured in the absence and presence of AUY922, using quantitative mass spectrometry. AUY922 significantly increased the abundance of proteins involved in oxidative phosphorylation and fatty acid metabolism in the PDEs. Consistent with these findings, AUY922-treated prostate cancer cell lines exhibited increased mitochondrial mass and activated fatty acid metabolism processes. We hypothesized that activation of fatty acid oxidation is a potential adaptive response to AUY922 treatment and that cotargeting this process will sensitize prostate cancer cells to HSP90 inhibition. Combination treatment of AUY922 with a clinical inhibitor of fatty acid oxidation, perhexiline, synergistically decreased viability of several prostate cancer cell lines, and had significant efficacy in PDEs. The novel drug combination treatment induced cell-cycle arrest and apoptosis, and attenuated the heat shock response, a known mediator of HSP90 treatment resistance. This combination warrants further preclinical and clinical investigation as a novel strategy to overcome resistance to HSP90 inhibition. IMPLICATIONS: Metabolic pathways induced in tumor cells by therapeutic agents may be critical, but targetable, mediators of treatment resistance.

Vacuolar ATPase as a potential therapeutic target and mediator of treatment resistance in cancer.

Vacuolar ATPase (V‐ATPase) is an ATP‐dependent H+‐transporter that pumps protons across intracellular and plasma membranes. It consists of a large multi‐subunit protein complex and influences a wide range of cellular processes. This review focuses on emerging evidence for the roles for V‐ATPase in cancer. This includes how V‐ATPase dysregulation contributes to cancer growth, metastasis, invasion and proliferation, and the potential link between V‐ATPase and the development of drug resistance.

Highlights from Recent Cancer Literature

Highlights from Recent Cancer Literature

ACRIN 6684: Assessment of tumor hypoxia in newly diagnosed GBM using FMISO PET and MRI.

2024 Background: Tumor hypoxia is a potent mediator of treatment resistance because of the negative impact on the efficacy of radiation and associated poor tumor delivery of cytotoxic chemotherapy....

Relationship of STAT3-mediated treatment resistance on activated MAPK signaling in pancreatic cancer.

181 Background: Pancreatic ductal adenocarcinoma (PDAC) is one of the most difficult human malignancies to treat due to its intrinsic (de novo) and extrinsic (acquired) chemoresistance. We have previously identified constitutively activated STAT3 as a mediator of treatment resistance. Src or EGFR activate STAT3 and promote STAT3 mediated tumor progression and mediate communication within the tumor microenvironment (TME). The purpose of this study was to further understand the molecular mechanisms of stromal-mediated chemoresistance in PDAC to generate new and promising targeted therapies. Methods: We characterized the expression of total and activated STAT3 and MAPK proteins in human pancreatic tissues (n=106), PDAC cell lines (n=9) and in PanIn lesions, primary PDAC and liver metastasis cell lines generated from tumors established in genetically engineered mice. Effects of STAT3 and MAPK inhibition (drug or siRNA) were assessed for phosphorylation of STAT3, Src, MAPK, EGFR and GSK3β and expression of cyclin-D1, SPARC, VEGF, fibronectin, CD31 and tumorigenicity in vitro and in vivo. Results: STAT3 activation is necessary for the malignant phenotype and affects survival in PDAC. In both human and mouse PDAC cell lines and tissues, there is an inverse correlation between activation of STAT3 on MAPK and GSK3β signaling. Inhibition of STAT3 reciprocally activated MAPK, GSK3β, Src and EGFR which led to subsequent reactivation of STAT3. Targeting both STAT3 and MAPK inhibited activation of STAT3, MAPK, GSK3β, Src, EGFR and cyclin-D1. Combined inhibition of STAT3 and MAPK overcame STAT3 mediated resistance and resulted in synergistic inhibition of tumorigenicity as well as inhibition of the tumor stroma, angiogenesis and hypoxia within the TME. Conclusions: The mechanism of STAT3-mediated treatment resistance is dependent on activation of MAPK signaling which in turn leads to reactivation of multiple oncogenic signaling pathways. Combined inhibition of STAT3 and MAPK overcomes therapeutic resistance, targets the TME and reduces tumorigenicity in PDAC. Targeting STAT3 and MAPK is a potent treatment regimen and may be a novel approach to enhance drug delivery and improve therapeutic response in PDAC.

NF-ĸB and Bcl-3 Activation Are Prognostic in Metastatic Colorectal Cancer

Purpose: NF-ĸB is an antiapoptotic transcription factor that has been shown to be a mediator of treatment resistance. Bcl-3 is a regulator of NF-ĸB that may play a role in oncogenesis. The goal of this study was to correlate the activation status of NF-ĸB and Bcl-3 with clinical outcome in a group of patients with metastatic colorectal cancer (CRC). Methods: A retrospective study of 23 patients who underwent surgical resection of CRC at the University of North Carolina (UNC). Activation of NF-ĸB was defined by nuclear expression of select components of NF-ĸB (p50, p52, p65) and Bcl-3. Tissue microarrays were created from cores of normal mucosa, primary tumor, lymph node metastases and liver metastases in triplicate from disparate areas of the blocks, and an intensity score was generated by multiplying intensity (0–3+) by percent of positive tumor cells. Generalized estimating equations were used to note differences in intensity scores among normal mucosa and nonnormal tissues. Cox regression models were fit to see if scores were significantly associated with overall survival. Results: p65 NE was significantly higher in primary tumor and liver metastases than normal mucosa (both p < 0.01). p50 nuclear expression was significantly higher for all tumor sites than for normal mucosa (primary tumor and lymph node metastases p < 0.0001, liver metastases p < 0.01). Bcl-3 nuclear expression did not differ significantly between normal mucosa and tumor; however, nuclear expression in primary tumor for each of these components was strongly associated with survival: the increase in hazard for each 50-point increase in nuclear expression was 91% for Bcl-3, 66% for p65, and 52% for p50 (all p < 0.05). Conclusions: Activation of canonical NF-ĸB subunits p50 and p65 as measured by nuclear expression is strongly associated with survival suggesting NF-ĸB as a prognostic factor in this disease. Primary tumor nuclear expression appears to be as good as, or better than, metastatic sites at predicting prognosis. Bcl-3 nuclear expression is also negatively associated with survival and deserves further study in CRC.

A Hierarchy of Self-Renewing Tumor-Initiating Cell Types in Glioblastoma

The neural stem cell marker CD133 is reported to identify cells within glioblastoma (GBM) that can initiate neurosphere growth and tumor formation; however, instances of CD133(-) cells exhibiting similar properties have also been reported. Here, we show that some PTEN-deficient GBM tumors produce a series of CD133(+) and CD133(-) self-renewing tumor-initiating cell types and provide evidence that these cell types constitute a lineage hierarchy. Our results show that the capacities for self-renewal and tumor initiation in GBM need not be restricted to a uniform population of stemlike cells, but can be shared by a lineage of self-renewing cell types expressing a range of markers of forebrain lineage.

P3.68. Cancer stem cells as mediators of treatment resistance in squamous cell carcinoma of the head and neck

P3.68. Cancer stem cells as mediators of treatment resistance in squamous cell carcinoma of the head and neck

Cancer Stem Cells as Mediators of Treatment Resistance in Brain Tumors: Status and Controversies

Malignant primary brain tumors are characterized by a short median survival and an almost 100% tumorrelated mortality. Despite the addition of new chemotherapy regimes, the overall survival has improved marginally, and radiotherapy is only transiently effective, illustrating the profound impact of treatment resistance on prognosis. Recent studies suggest that a small subpopulation of cancer stem cells (CSCs) has the capacity to repopulate tumors and drive malignant progression and mediate radio- and chemoresistance. This implies that future therapies should turn from the elimination of the rapidly dividing, but differentiated tumor cells, to specifically targeting the minority of tumor cells that repopulate the tumor. Although there exists some support for the CSC hypothesis, there remain many uncertainties regarding theoretical, technical, and interpretational aspects of the data supporting it. If correct, the CSC hypothesis could have profound implications for the way tumors are classified and treated. In this review of the literature, we provide original data and hypotheses supporting alternative explanations and outline some of the therapeutic implications that can be derived.