Daniel W. Bowles

A Multicenter Phase I Trial of PX-866, an Oral Irreversible Phosphatidylinositol 3-Kinase Inhibitor, in Patients with Advanced Solid Tumors

Purpose: The objectives of the study were to evaluate the maximum tolerated dose (MTD), safety, pharmacodynamics, pharmacokinetics, and antitumor activity of PX-866 in patients with incurable cancers. Experimental Design: This was a phase I, open-label, dose-escalation study. Drug was administered orally once per day either on an intermittent (arm 1; days 1–5 and 8–12 of a 28-day cycle) or continuous (arm 2; days 1–28 of a 28-day cycle) schedule. Additional patients were treated at the arm 2 MTD in a food effects substudy. Results: Eighty-four patients were treated in the arm 1 (n = 51), arm 2 (n = 20), and food effects (n = 13) cohorts. The most frequent study drug–related adverse events were gastrointestinal disorders (69.0%), with diarrhea being the most common (48.8%). The MTD was 12 and 8 mg for arm 1 and 2, respectively. The dose-limiting toxicities (DLT) consisted of grade III diarrhea (n = 3) and grade III elevated aspartate aminotransferase (AST; n = 1). The pharmacokinetics profile was dose proportional, with no evidence of drug accumulation. PX-866–associated inhibition of platelet pAKTSER473 was observed at the arm 2 MTD. The best response per Response Evaluation Criteria in Solid Tumors (RECIST) was stable disease in 22% of evaluable patients in arm 1, 53% in arm 2, and 11% in the food effects cohort. Eight patients were on study for 4 or more months. Conclusions: This first-in-human study shows that PX-866, an irreversible small-molecule inhibitor of phosphatidylinositol 3-kinase (PI3K), was well tolerated and was associated with prolonged stable disease, particularly when using a continuous dosing schedule. Clin Cancer Res; 18(15); 4173–82. ©2012 AACR.

A patient tumor transplant model of squamous cell cancer identifies PI3K inhibitors as candidate therapeutics in defined molecular bins

Targeted therapy development in head and neck squamous cell carcinoma (HNSCC) is challenging given the rarity of activating mutations. Additionally, HNSCC incidence is increasing related to human papillomavirus (HPV). We sought to develop an in vivo model derived from patients reflecting the evolving HNSCC epidemiologic landscape, and use it to identify new therapies. Primary and relapsed tumors from HNSCC patients, both HPV+ and HPV−, were implanted on mice, giving rise to 25 strains. Resulting xenografts were characterized by detecting key mutations, measuring protein expression by IHC and gene expression/pathway analysis by mRNA‐sequencing. Drug efficacy studies were run with representative xenografts using the approved drug cetuximab as well as the new PI3K inhibitor PX‐866. Tumors maintained their original morphology, genetic profiles and drug susceptibilities through serial passaging. The genetic makeup of these tumors was consistent with known frequencies of TP53, PI3KCA, NOTCH1 and NOTCH2 mutations. Because the EGFR inhibitor cetuximab is a standard HNSCC therapy, we tested its efficacy and observed a wide spectrum of efficacy. Cetuximab‐resistant strains had higher PI3K/Akt pathway gene expression and protein activation than cetuximab‐sensitive strains. The PI3K inhibitor PX‐866 had anti‐tumor efficacy in HNSCC models with PIK3CA alterations. Finally, PI3K inhibition was effective in two cases with NOTCH1 inactivating mutations. In summary, we have developed an HNSCC model covering its clinical spectrum whose major genetic alterations and susceptibility to anticancer agents represent contemporary HNSCC. This model enables to prospectively test therapeutic‐oriented hypotheses leading to personalized medicine.

New phosphatidylinositol 3-kinase inhibitors for cancer

Introduction: Cancer treatment is moving away from conventional cytotoxic drugs and towards agents that target specific proteins important to cancer development or survival. The PI3K signaling axis is an important pathway involved in myriad human malignancies. Inhibition of this axis is a promising therapeutic approach for several cancers. Areas covered: This article reviews current literature and recent conference proceedings to analyze the rationale for targeting PI3K and its downstream effectors in cancer. Preclinical and clinical results of several PI3K and PI3K–mammalian target of rapamycin (mTOR) inhibitors in early clinical trials, as single agents and in combination with other drugs, are discussed. Thus far, clinical results have been mixed. Expert opinion: The clinical utility of PI3K and PI3K–mTOR inhibitors will depend on appropriate selection of patients. Mutations in the PI3K pathway may predict sensitivity to PI3K inhibition but they are not reliable biomarkers at this point. Efforts to define predictive biomarkers will probably be the key to finding therapeutic uses for this novel class of anticancer agents.

Hedgehog Signaling Alters Reliance on EGF Receptor Signaling and Mediates Anti-EGFR Therapeutic Resistance in Head and Neck Cancer

The EGF receptor (EGFR)-directed monoclonal antibody cetuximab is the only targeted therapy approved for the treatment of squamous cell carcinoma of the head and neck (HNSCC) but is only effective in a minority of patients. Epithelial-to-mesenchymal transition (EMT) has been implicated as a drug resistance mechanism in multiple cancers, and the EGFR and Hedgehog pathways (HhP) are relevant to this process, but the interplay between the two pathways has not been defined in HNSCC. Here, we show that HNSCC cells that were naturally sensitive to EGFR inhibition over time developed increased expression of the HhP transcription factor GLI1 as they became resistant after long-term EGFR inhibitor exposure. This robustly correlated with an increase in vimentin expression. Conversely, the HhP negatively regulated an EGFR-dependent, EMT-like state in HNSCC cells, and pharmacologic or genetic inhibition of HhP signaling pushed cells further into an EGFR-dependent phenotype, increasing expression of ZEB1 and VIM. In vivo treatment with cetuximab resulted in tumor shrinkage in four of six HNSCC patient-derived xenografts; however, they eventually regrew. Cetuximab in combination with the HhP inhibitor IPI-926 eliminated tumors in two cases and significantly delayed regrowth in the other two cases. Expression of EMT genes TWIST and ZEB2 was increased in sensitive xenografts, suggesting a possible resistant mesenchymal population. In summary, we report that EGFR-dependent HNSCC cells can undergo both EGFR-dependent and -independent EMT and HhP signaling is a regulator in both processes. Cetuximab plus IPI-926 forces tumor cells into an EGFR-dependent state, delaying or completely blocking tumor recurrence.

XactMice: humanizing mouse bone marrow enables microenvironment reconstitution in a patient-derived xenograft model of head and neck cancer

The limitations of cancer cell lines have led to the development of direct patient-derived xenograft models. However, the interplay between the implanted human cancer cells and recruited mouse stromal and immune cells alters the tumor microenvironment and limits the value of these models. To overcome these constraints, we have developed a technique to expand human hematopoietic stem and progenitor cells (HSPCs) and use them to reconstitute the radiation-depleted bone marrow of a NOD/SCID/IL2rg−/− (NSG) mouse on which a patient’s tumor is then transplanted (XactMice). The human HSPCs produce immune cells that home into the tumor and help replicate its natural microenvironment. Despite previous passage on nude mice, the expression of epithelial, stromal and immune genes in XactMice tumors aligns more closely to that of the patient tumor than to those grown in non-humanized mice—an effect partially facilitated by human cytokines expressed by both the HSPC progeny and the tumor cells. The human immune and stromal cells produced in the XactMice can help recapitulate the microenvironment of an implanted xenograft, reverse the initial genetic drift seen after passage on non-humanized mice and provide a more accurate tumor model to guide patient treatment.

Survival outcomes with concurrent chemoradiation for elderly patients with locally advanced head and neck cancer according to the National Cancer Data Base

The overall survival (OS) benefit of concurrent chemoradiotherapy (CRT) for head and neck squamous cell carcinoma patients older than 70 years is debated. This study examines the outcomes of elderly patients receiving CRT versus radiotherapy (RT) alone.

A randomized, phase 2 trial of docetaxel with or without PX-866, an irreversible oral phosphatidylinositol 3-kinase inhibitor, in patients with relapsed or metastatic head and neck squamous cell cancer

INTRODUCTION The phosphotidylinositol-3 kinase (PI3K)/serine-threonine kinase (AKT)/mammalian target of rapamycin (mTOR) signaling pathway is frequently altered in head and neck squamous cell cancer (HNSCC). PX-866 is an oral, irreversible, pan-isoform inhibitor of PI3K. Preclinical models revealed synergy with docetaxel and a phase 1 trial demonstrated tolerability of this combination. This randomized phase 2 study evaluated PX-866 combined with docetaxel in patients with advanced, refractory HNSCC. METHODS Patients with locally advanced, recurrent or metastatic HNSCC who had received at least one and no more than two prior systemic treatment regimens were randomized (1:1) to a combination of docetaxel (75mg/m(2) IV every 21days) with or without PX-866 (8mg PO daily; Arms A and B, respectively). The primary endpoint was progression free survival (PFS). Secondary endpoints included objective response rate (RR), overall survival (OS), toxicity, and correlation of biomarker analyses with efficacy outcomes. RESULTS 85 patients were enrolled. There was a non-significant improvement in response rate in the combination arm (14% vs. 5%; P=0.13). Median PFS was 92days in Arm A and 82days in Arm B (P=0.42). There was no difference in OS between the two arms (263 vs. 195days; P=0.62). Grade 3 or higher adverse events were infrequent, but more common in the combination arm with respect to diarrhea (17% vs. 2%), nausea (7% vs. 0%), and febrile neutropenia (21% vs. 5%); grade 3 or higher anemia was more frequent in arm B (7% vs. 27%). PIK3CA mutations or PTEN loss were infrequently observed. CONCLUSION The addition of PX-866 to docetaxel did not improve PFS, RR, or OS in patients with advanced, refractory HNSCC without molecular pre-selection.

Profiling of 149 Salivary Duct Carcinomas, Carcinoma Ex Pleomorphic Adenomas, and Adenocarcinomas, Not Otherwise Specified Reveals Actionable Genomic Alterations

Purpose: We sought to identify genomic alterations (GA) in salivary gland adenocarcinomas, not otherwise specified (NOS), salivary duct carcinomas (SDC), carcinoma ex pleomorphic adenoma (ca ex PA), and salivary carcinoma, NOS. Experimental Design: DNA was extracted from 149 tumors. Comprehensive genomic profiling (CGP) was performed on hybridization-captured adaptor ligation-based libraries of 182 or 315 cancer-related genes plus introns from 14 or 28 genes frequently rearranged for cancer and evaluated for all classes of GAs. Results: A total of 590 GAs were found in 157 unique genes (mean 3.9/tumor). GAs in the PI3K/AKT/mTOR pathway were more common in SDC (53.6%) than other histologies (P = 0.019) Cyclin-dependent kinase GAs varied among all histotypes: adenocarcinoma, NOS (34.6%); SDC (12.2%); ca ex PA (16.7%); carcinoma, NOS (31.2%; P = 0.043). RAS GAs were observed: adenocarcinoma, NOS (17.3%); SDC (26.8%); ca ex PA (4.2%); and carcinoma, NOS (9.4%; P = 0.054). ERBB2 GAs, including amplifications and mutations, were common: adenocarcinoma, NOS (13.5%); SDC (26.8%); ca ex PA (29.2%); carcinoma, NOS (18.8; P = 0.249). Other notable GAs include TP53 in >45% of each histotype; NOTCH1: adenocarcinoma, NOS (7.7%), ca ex PA (8.3%), carcinoma, NOS (21.6%); NF1: adenocarcinoma, NOS (9.6%), SDC (17.1%), carcinoma, NOS (18.8%). RET fusions were identified in one adenocarcinoma, NOS (CCDC6-RET) and two SDCs (NCOA4-RET). Clinical responses were observed in patients treated with anti-HER2 and anti-RET–targeted therapies. Conclusions: CGP of salivary adenocarcinoma, NOS, SDCs, ca ex PA, and carcinoma, NOS revealed diverse GAs that may lead to novel treatment options. Clin Cancer Res; 22(24); 6061–8. ©2016 AACR.

Predictors of overall survival in human papillomavirus-associated oropharyngeal cancer using the National Cancer Data Base

OBJECTIVES This study identifies clinical characteristics associated with HPV-positive oropharynx squamous cell carcinoma (OPSCC) and evaluates predictors of overall survival (OS) in HPV-positive patients undergoing definitive treatment within the National Cancer Data Base (NCDB). MATERIAL AND METHODS The NCDB was queried for patients ⩾18years old with OPSCC and known HPV status who underwent definitive treatment: surgery, radiation (RT), chemotherapy-RT (CRT), surgery+RT, surgery+CRT (S-CRT). Cox proportional hazards model was used for multivariate analysis (MVA) to evaluate predictors of OS by HPV status. RESULTS 3952 patients were included: 2454 (62%) were HPV-positive. Median follow up was 23.7months (range, 1.0-54.5). Unadjusted 2-year OS rates for HPV-positive vs. negative were 93.1% vs. 77.8% (p<0.001) with an adjusted hazard ratio of 0.44 (95% CI, 0.36-0.53; p<0.001). MVA identified multimodality treatment including CRT (HR, 0.42; p=0.024) and S-RT (HR, 0.30; p=0.024), but not S-CRT (HR, 0.51; p=0.086), as predictors for improved OS in HPV-positive stage III-IVB disease. Multimodality treatment including S-CRT was associated with longer OS in HPV-negative OPSCC. Nodal stage was poorly associated with OS in HPV-positive cancers. The presence of positive margins and/or extracapsular extension was associated with worse OS in HPV-negative (HR, 2.11; p=0.008) but not HPV positive OPSCC (HR, 1.61; p=0.154). CONCLUSION The established demographic and clinical features of HPV-positive OPSCC were corroborated in the NCDB. Population analysis suggests that AJCC staging is poorly associated with OS in HPV-positive cancer, and traditional high-risk features may be less impactful. Bimodality therapy appears beneficial in HPV-positive HNSCC.

Phase I study of oral rigosertib (ON 01910.Na), a dual inhibitor of the PI3K and Plk1 pathways, in adult patients with advanced solid malignancies.

Purpose: To determine the pharmacokinetics (PK), maximum tolerated dose (MTD), safety, and antitumor activity of an oral formulation of rigosertib, a dual phosphoinositide 3-kinase (PI3K) and polo-like kinase 1 (Plk1) pathway inhibitor, in patients with advanced solid malignancies. Experimental Design: Patients with advanced solid malignancies received rigosertib twice daily continuously in 21-day cycles. Doses were escalated until intolerable grade ≥2 toxicities, at which point the previous dose level was expanded to define the MTD. All patients were assessed for safety, PK, and response. Urinary PK were performed at the MTD. Archival tumors were assessed for potential molecular biomarkers with multiplex mutation testing. A subset of squamous cell carcinomas (SCC) underwent exome sequencing. Results: Forty-eight patients received a median of 2 cycles of therapy at 5 dose levels. Rigosertib exposure increased with escalating doses. Dose-limiting toxicities were hematuria and dysuria. The most common grade ≥2 drug-related toxicities involved urothelial irritation. The MTD is 560 mg twice daily. Activity was seen in head and neck SCCs (1 complete response, 1 partial response) and stable disease for ≥12 weeks was observed in 8 additional patients. Tumors experiencing ≥partial response had PI3K pathway activation, inactivated p53, and unique variants in ROBO3 and FAT1, two genes interacting with the Wnt/β-catenin pathway. Conclusions: The recommended phase II dose of oral rigosertib is 560 mg twice daily given continuously. Urinary toxicity is the dose-limiting and most common toxicity. Alterations in PI3K, p53, and Wnt/β-catenin pathway signaling should be investigated as potential biomarkers of response in future trials. Clin Cancer Res; 20(6); 1656–65. ©2014 AACR.