MET Inhibitor Capmatinib Radiosensitizes MET Exon 14-Mutated and MET-Amplified Non-Small Cell Lung Cancer

PURPOSE

The objective of this study was to investigate the effects of inhibiting the MET receptor with capmatinib, a potent and clinically relevant ATP-competitive tyrosine kinase inhibitor, in combination with radiation in MET exon 14-mutated and MET-amplified non-small cell lung (NSCLC) cancer models.

METHODS AND MATERIALS

In vitro effects of capmatinib and radiation on cell proliferation, colony formation, MET signaling, apoptosis, and DNA damage repair were evaluated. In vivo tumor responses were assessed in cell line xenograft and patient-derived xenograft models. Immunohistochemistry was used to confirm the in vitro results.

RESULTS

In vitro clonogenic survival assays demonstrated radiosensitization with capmatinib in both MET exon 14-mutated and MET-amplified NSCLC cell lines. No radiation-enhancing effect was observed in MET wild-type NSCLC and a human bronchial epithelial cell line. Minimal apoptosis was detected with the combination of capmatinib and radiation. Capmatinib plus radiation compared with radiation alone resulted in inhibition of DNA double-strand break repair, as measured by prolonged expression of γH2AX. In vivo, the combination of capmatinib and radiation significantly delayed tumor growth compared with vehicle control, capmatinib alone, or radiation alone. Immunohistochemistry indicated inhibition of phospho-MET and phospho-S6 and a decrease in Ki67 with inhibition of MET.

CONCLUSIONS

Inhibition of MET with capmatinib enhances the effect of radiation in both MET exon 14-mutated and MET-amplified NSCLC models.

Functionality of bone marrow mesenchymal stromal cells derived from head and neck cancer patients - A FDA-IND enabling study regarding MSC-based treatments for radiation-induced xerostomia

PURPOSE

Salivary dysfunction is a significant side effect of radiation therapy for head and neck cancer (HNC). Preliminary data suggests that mesenchymal stromal cells (MSCs) can improve salivary function. Whether MSCs from HNC patients who have completed chemoradiation are functionally similar to those from healthy patients is unknown. We performed a pilot clinical study to determine whether bone marrow-derived MSCs [MSC(M)] from HNC patients could be used for the treatment of RT-induced salivary dysfunction.

METHODS

An IRB-approved pilot clinical study was undertaken on HNC patients with xerostomia who had completed treatment two or more years prior. Patients underwent iliac crest bone marrow aspirate and MSC(M) were isolated and cultured. Culture-expanded MSC(M) were stimulated with IFNγ and cryopreserved prior to reanimation and profiling for functional markers by flow cytometry and ELISA. MSC(M) were additionally injected into mice with radiation-induced xerostomia and the changes in salivary gland histology and salivary production were examined.

RESULTS

A total of six subjects were enrolled. MSC(M) from all subjects were culture expanded to > 20 million cells in a median of 15.5 days (range 8-20 days). Flow cytometry confirmed that cultured cells from HNC patients were MSC(M). Functional flow cytometry demonstrated that these IFNγ-stimulated MSC(M) acquired an immunosuppressive phenotype. IFNγ-stimulated MSC(M) from HNC patients were found to express GDNF, WNT1, and R-spondin 1 as well as pro-angiogenesis and immunomodulatory cytokines. In mice, IFNγ-stimulated MSC(M) injection after radiation decreased the loss of acinar cells, decreased the formation of fibrosis, and increased salivary production.

CONCLUSIONS

MSC (M) from previously treated HNC patients can be expanded for auto-transplantation and are functionally active. Furthermore IFNγ-stimulated MSC(M) express proteins implicated in salivary gland regeneration. This study provides preliminary data supporting the feasibility of using autologous MSC(M) from HNC patients to treat RT-induced salivary dysfunction.

Marrow-Derived Autologous Stromal Cells for the Restoration of Salivary Hypofunction (MARSH): A pilot, first-in-human study of interferon gamma-stimulated marrow mesenchymal stromal cells for treatment of radiation-induced xerostomia

BACKGROUND AIMS

Xerostomia, or the feeling of dry mouth, is a significant side effect of radiation therapy for patients with head and neck cancer (HNC). Preliminary data suggest that mesenchymal stromal/stem cells (MSCs) can improve salivary function. We performed a first-in-human pilot study of interferon gamma (IFNγ)-stimulated autologous bone marrow-derived MSCs, or MSC(M), for the treatment of radiation-induced xerostomia (RIX). Here we present the primary safety and secondary efficacy endpoints.

METHODS

A single-center pilot clinical trial was conducted investigating the safety and tolerability of autologous IFNγ-stimulated MSC(M). The study was conducted under an approved Food and Drug Administration Investigational New Drug application using an institutional review board-approved protocol (NCT04489732). Patients underwent iliac crest bone marrow aspirate and MSC(M) were isolated, cultured, stimulated with IFNγ and cryopreserved for later use. Banked cells were thawed and allowed to recover in culture before patients received a single injection of 10 × 106 MSC(M) into the right submandibular gland under ultrasound guidance. The primary objective was determination of safety and tolerability by evaluating dose-limiting toxicity (DLT). A DLT was defined as submandibular pain >5 on a standard 10-point pain scale or any serious adverse event (SAE) within 1 month after injection. Secondary objectives included analysis of efficacy as measured by salivary quantification and using three validated quality of life instruments. Quantitative results are reported as mean and standard deviation.

RESULTS

Six patients with radiation-induced xerostomia who had completed radiation at least 2 years previously (average 7.8 years previously) were enrolled in the pilot study. The median age was 71 (61-74) years. Five (83%) patients were male. Five patients (83%) were treated with chemoradiation and one patient (17%) with radiation alone. Grade 1 pain was seen in 50% of patients after submandibular gland injection; all pain resolved within 4 days. No patients reported pain 1 month after injection, with no SAE or other DLTs reported 1 month after injection. The analysis of secondary endpoints demonstrated a trend of increased salivary production. Three patients (50%) had an increase in unstimulated saliva at 1 and 3 months after MSC(M) injection. Quality of life surveys also showed a trend toward improvement.

CONCLUSIONS

Injection of autologous IFNγ-stimulated MSC(M) into a singular submandibular gland of patients with RIX is safe and well tolerated in this pilot study. A trend toward an improvement in secondary endpoints of salivary quantity and quality of life was observed. This first-in-human study provides support for further investigation into IFNγ-stimulated MSC(M) injected in both submandibular glands as an innovative approach to treat RIX and improve quality of life for patients with HNC.

MET Inhibitor Capmatinib Radiosensitizes MET Exon 14-Mutated and MET-Amplified Non-Small Cell Lung Cancer

Purpose

The objective of this study was to investigate the effects of inhibiting the MET receptor with capmatinib, a potent and clinically relevant ATP-competitive tyrosine kinase inhibitor, in combination with radiation in MET exon 14-mutated and MET-amplified non-small cell lung (NSCLC) cancer models.

Methods and Materials

In vitro effects of capmatinib and radiation on cell proliferation, colony formation, MET signaling, apoptosis, and DNA damage repair were evaluated. In vivo tumor responses were assessed in cell line xenograft and patient-derived xenograft models. Immunohistochemistry (IHC) was used to confirm in vitro results.

Results

In vitro clonogenic survival assays demonstrated radiosensitization with capmatinib in both MET exon 14-mutated and MET-amplified NSCLC cell lines. No radiation-enhancing effect was observed in MET wild-type NSCLC and human bronchial epithelial cell line. Minimal apoptosis was detected with the combination of capmatinib and radiation. Capmatinib plus radiation compared to radiation alone resulted in inhibition of DNA double-strand break repair as measured by prolonged expression of γH2AX. In vivo, the combination of capmatinib and radiation significantly delayed tumor growth compared to vehicle control, capmatinib alone, or radiation alone. IHC indicated inhibition of phospho-MET and phospho-S6 and a decrease in Ki67 with inhibition of MET.

Conclusions

Inhibition of MET with capmatinib enhanced the effect of radiation in both MET exon 14-mutated and MET-amplified NSCLC models.

Targeted inhibition of BET proteins in HPV-16 associated head and neck squamous cell carcinoma reveals heterogeneous transcription response

Integrated human papillomavirus (HPV-16) associated head and neck squamous cell carcinoma (HNSCC) tumors have worse survival outcomes compared to episomal HPV-16 HNSCC tumors. Therefore, there is a need to differentiate treatment for HPV-16 integrated HNSCC from other viral forms. We analyzed TCGA data and found that HPV+ HNSCC expressed higher transcript levels of the bromodomain and extra terminal domain (BET) family of transcriptional coregulators. However, the mechanism of BET protein-mediated transcription of viral-cellular genes in the integrated viral-HNSCC genomes needs to be better understood. We show that BET inhibition downregulates E6 significantly independent of the viral transcription factor, E2, and there was overall heterogeneity in the downregulation of viral transcription in response to the effects of BET inhibition across HPV-associated cell lines. Chemical BET inhibition was phenocopied with the knockdown of BRD4 and mirrored downregulation of viral E6 and E7 expression. Strikingly, there was heterogeneity in the reactivation of p53 levels despite E6 downregulation, while E7 downregulation did not alter Rb levels significantly. We identified that BET inhibition directly downregulated c-Myc and E2F expression and induced CDKN1A expression. Overall, our studies show that BET inhibition provokes a G1-cell cycle arrest with apoptotic activity and suggests that BET inhibition regulates both viral and cellular gene expression in HPV-associated HNSCC.

A Pilot, First in Human Study of Autologous IFN-Gamma Stimulated Mesenchymal Stromal Cells for Treatment of Radiation-Induced Xerostomia

PURPOSE/OBJECTIVE(S)

There are no existing effective treatments for radiation-induced xerostomia (RIX), a common side effect of head and neck radiation. Mesenchymal stromal cells (MSCs) exhibit regenerative effects in multiple tissues and may represent an effective cell therapy for the treatment of RIX. Here we present the primary safety and secondary efficacy endpoints of a first-in-human pilot study of IFNγ-stimulated autologous bone marrow- derived MSCs [MSC(M)] for the treatment of RIX.

MATERIALS/METHODS

We conducted a single-center clinical trial investigating the safety and tolerability of autologous IFNγ-stimulated MSC(M). The study was conducted under an FDA-IND and approved by the local IRB. Patients underwent bone marrow aspiration, MSC(M) were then culture-expanded, stimulated with IFNγ, and cryopreserved. Banked IFNγ-stimulated MSC(M) were thawed, allowed to recover, and then 10 × 106 MSC(M) were injected transcutaneously via ultrasound guidance into one submandibular gland. The primary objective was safety and tolerability determined by dose-limiting toxicity (DLT) defined as submandibular pain > 5 on a standard 10-point pain scale or any serious adverse event (SAE) within one month after injection. Secondary objectives included analysis of efficacy as measured by salivary quantification and using 3 validated quality of life instruments. Quantitative results are reported as mean and standard deviation (SD).

RESULTS

Six radiation-induced xerostomia patients with head and neck cancer who had completed radiation at least 2 years earlier were enrolled. The median age was 71 (61-74) and 5 (83%) patients were male. Five patients (83%) were treated with chemoradiation and one patient (17%) with radiation alone. The average dose of radiation to the injected submandibular gland was 59.9 Gy. Three patients (50%) reported a pain score of 1 after submandibular gland injection, all pain resolved within 4 days. No patients reported pain 1 month after injection, with no SAEs or other DLTs reported 1 month after injection. The analysis of secondary endpoints demonstrated a trend of increased salivary production. The mean unstimulated saliva was 0.13 mL/min (SD 0.17) at baseline and increased to 0.14 mL/min (SD 0.12) at 1 month after injection and 0.19 mL/min (SD 0.21) at 3-months. Quality of life surveys also showed a trend towards improvement.

CONCLUSION

Injection of autologous IFNγ-stimulated MSC(M) into the submandibular gland of patients with RIX is safe and well tolerated. A trend towards an improvement in secondary endpoints of salivary quantity and quality of life was observed. This first-in-human pilot study provides support for further investigation into IFNγ-stimulated MSC(M) as an innovative, potentially curative, remedy to treat RIX. A phase I dose-escalation study injecting into bilateral submandibular glands is scheduled to begin accrual in the spring of 2023.

Biological Characterization of the Effects of Filtration on the Xoft Axxent® Electronic Brachytherapy Source for Cervical Cancer Applications

Low-energy X-ray sources that operate in the kilovoltage energy range have been shown to induce more cellular damage when compared to their megavoltage counterparts. However, low-energy X-ray sources are more susceptible to the effects of filtration on the beam spectrum. This work sought to characterize the biological effects of the Xoft Axxent® source, a low-energy therapeutic X-ray source, both with and without the titanium vaginal applicator in place. It was hypothesized that there would be an increase in relative biological effectiveness (RBE) of the Axxent® source compared to 60Co and that the source in the titanium vaginal applicator (SIA) would have decreased biological effects compared to the bare source (BS). This hypothesis was drawn from linear energy transfer (LET) simulations performed using the TOPAS Monte Carlo user code as well a reduction in dose rate of the SIA compared to the BS. A HeLa cell line was maintained and used to evaluate these effects. Clonogenic survival assays were performed to evaluate differences in the RBE between the BS and SIA using 60Co as the reference beam quality. Neutral comet assay was used to assess induction of DNA strand damage by each beam to estimate differences in RBE. Quantification of mitotic errors was used to evaluate differences in chromosomal instability (CIN) induced by the three beam qualities. The BS was responsible for the greatest quantity of cell death due to a greater number of DNA double strand breaks (DSB) and CIN observed in the cells. The differences observed in the BS and SIA surviving fractions and RBE values were consistent with the 13% difference in LET as well as the factor of 3.5 reduction in dose rate of the SIA. Results from the comet and CIN assays were consistent with these results as well. The use of the titanium applicator results in a reduction in the biological effects observed with these sources, but still provides an advantage over megavoltage beam qualities. © 2023 by Radiation Research Society.

Quantification of very late xerostomia in head and neck cancer patients after irradiation

Objective

Radiation therapy (RT) for head and neck cancer (HNC) can result in severe xerostomia, or the subjective feeling of dry mouth. Characterizing xerostomia is critical to designing future clinical trials investigating how to improve HNC patients' quality of life (QoL). Few studies have investigated the very late (>5 years post‐RT) effects of RT for HNC. We undertook preliminary studies quantifying very late xerostomia.

Methods

Six adults who underwent RT for HNC at least 5 years prior and reported xerostomia were enrolled. Five healthy adults without a self‐reported history of HNC or xerostomia were enrolled as controls. All participants completed three validated surveys to measure xerostomia‐related QoL. Salivary production rates were measured and compositional analysis of the saliva and oral microbiome was completed.

Results

The QoL survey scores for the HNC participants were significantly worse as compared to the control participants. The HNC participants produced less unstimulated saliva (p = .02) but not less stimulated saliva. The median salivary mucin significantly higher in HNC participants than in control participants (p = .02). There was no significant difference between the pH, amylase, or total protein. Microbiome analysis revealed alpha diversity to be significantly lower in the HNC participants.

Conclusion

In the survivors of HNC who suffer from late toxicities, multiple means of measuring toxicity may be useful. We found that in patients with radiation‐induced xerostomia over 5 years after therapy, not only were the QoL surveys significantly worse, as expected, but other measurements such as mucin and oral microbiome diversity were also significantly different.

Level of evidence

3.

Activation of the CREB Coactivator CRTC2 by Aberrant Mitogen Signaling promotes oncogenic functions in HPV16 positive head and neck cancer

Head and neck squamous cell carcinoma (HNSCC) is the 6th most common cancer worldwide and incidence rates are continuing to rise globally. Patients often present with locally advanced disease and a staggering 50% chance of relapse following treatment. Aberrant activation of adaptive response signaling pathways, such as the cAMP/PKA pathway, induce an array of genes associated with known cancer pathways that promote tumorigenesis and drug resistance. We identified the cAMP Regulated Transcription Coactivator 2 (CRTC2) to be overexpressed and constitutively activated in HNSCCs and this confers poor prognosis. CRTCs are regulated through their subcellular localization and we show that CRTC2 is exclusively nuclear in HPV(+) HNSCC, thus constitutively active, due to non-canonical Mitogen-Activated Kinase Kinase 1 (MEKK1)-mediated activation via a MEKK1-p38 signaling axis. Loss-of-function and pharmacologic inhibition experiments decreased CRTC2/CREB transcriptional activity by reducing nuclear CRTC2 via nuclear import inhibition and/or by eviction of CRTC2 from the nucleus. This shift in localization was associated with decreased proliferation, migration, and invasion. Our results suggest that small molecules that inhibit nuclear CRTC2 and p38 activity may provide therapeutic benefit to patients with HPV(+) HNSCC.

Abstract 207: MET inhibition enhances the effect of radiation in MET mutated non-small cell lung cancer brain metastasis patient derived xenografts

Objective: The MET receptor is mutated in 3-4% and amplified in 1-6% of patients with non-small cell lung cancer. The most common MET mutation is in exon 14, which results in deletion of the intracellular juxtamembrane domain of the receptor, leading to enhanced signaling. Mutation at Asp-1000 in the juxtamembrane region has also been reported and can lead to inhibition of apoptosis and cell proliferation. MET is involved in multiple pathways associated with radiation response. Therefore, we investigated the effects of inhibiting MET in combination with radiation in two preclinical non-small cell lung cancer (NSCLC) brain metastasis patient derived xenograft (PDX) models.

Methods: Surgically obtained tissue was implanted subcutaneously into immunodeficient mice. Histology and DNA loci were compared between original tumor and PDX. DNA sequencing was performed on tumors for mutation analysis. In vivo growth responses to the MET inhibitor capmatinib or savolitinib with and without radiation were assessed. Radiation was delivered in 10 daily fractions of 2 Gy. Drug was administered by oral gavage daily 1 hour prior to radiation at a dose of 2.5 mg/kg for savaolitnib or 20 mg/kg for capmatinib for 10 days. Immunohistochemistry (IHC) was performed to evaluate MET signaling and proliferation.

Results: PDXs were successfully established from two patients with MET mutated NSCLC brain metastases: a lung adenocarcinoma with a MET exon 14 skipping mutation and a lung sarcomatoid carcinoma with adenocarcinoma component with an Asp-1000 frameshift mutation. Morphologically, strong retention of cytoarchitectural features was observed between original patient tumors and PDXs. Short tandem repeat analysis confirmed 100% matching of alleles between patient tumors and PDXs. DNA sequencing confirmed METex14 and MET Asp-1000 frameshift mutation. In the METex14 PDX, savolitinib alone significantly inhibited tumor growth with a growth inhibition value of 46% (p<0.01). Combination of savolitinib and radiation significantly delayed growth compared to vehicle control, savolitinib alone or radiation alone (p<0.001). The absolute growth delay was 42.4 days for savolitinib plus radiation treatment compared to 9.3 days for savolitinib alone and 28.2 days for irradiation. In the MET Asp-1000 PDX, capmatinib and radiation significantly delayed growth compared the other treatment arms (p<0.01). IHC demonstrated inhibition of phospho-MET and pS6 and a decrease in Ki67 with MET inhibition.

Conclusion: Inhibition of MET enhanced the effect of radiation in our two preclinical in vivo MET mutated NSCLC brain metastasis models. Additional studies are currently underway evaluating the mechanisms of radiation sensitization and the efficacy of this combination in MET amplified PDX models.

Citation Format: Kwangok P. Nickel, Shrey Ramesh, Saahil Javeri, Nitin Somasundaram, Nan Sethakorn, Randall J. Kimple, Andrew M. Baschnagel. MET inhibition enhances the effect of radiation in MET mutated non-small cell lung cancer brain metastasis patient derived xenografts [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 207.

ATR Inhibitor M6620 (VX-970) Enhances the Effect of Radiation in Non-Small Cell Lung Cancer Brain Metastasis Patient-Derived Xenografts

M6620, a selective ATP-competitive inhibitor of the ATM and RAD3-related (ATR) kinase, is currently under investigation with radiation in patients with non-small cell lung cancer (NSCLC) brain metastases. We evaluated the DNA damage response (DDR) pathway profile of NSCLC and assessed the radiosensitizing effects of M6620 in a preclinical NSCLC brain metastasis model. Mutation analysis and transcriptome profiling of DDR genes and pathways was performed on NSCLC patient samples. NSCLC cell lines were assessed with proliferation, clonogenic survival, apoptosis, cell cycle, and DNA damage signaling and repair assays. NSCLC brain metastasis patient-derived xenograft models were used to assess intracranial response and overall survival. In vivo IHC was performed to confirm in vitro results. A significant portion of NSCLC patient tumors demonstrated enrichment of DDR pathways. DDR pathways correlated with lung squamous cell histology; and mutations in ATR, ATM, BRCA1, BRCA2, CHEK1, and CHEK2 correlated with enrichment of DDR pathways in lung adenocarcinomas. M6620 reduced colony formation after radiotherapy and resulted in inhibition of DNA DSB repair, abrogation of the radiation-induced G2 cell checkpoint, and formation of dysfunctional micronuclei, leading to enhanced radiation-induced mitotic death. The combination of M6620 and radiation resulted in improved overall survival in mice compared with radiation alone. In vivo IHC revealed inhibition of pChk1 in the radiation plus M6620 group. M6620 enhances the effect of radiation in our preclinical NSCLC brain metastasis models, supporting the ongoing clinical trial (NCT02589522) evaluating M6620 in combination with whole brain irradiation in patients with NSCLC brain metastases.

Dichotomic Potency of IFNγ Licensed Allogeneic Mesenchymal Stromal Cells in Animal Models of Acute Radiation Syndrome and Graft Versus Host Disease

Mesenchymal stromal cells (MSCs) are being tested as a cell therapy in clinical trials for dozens of inflammatory disorders, with varying levels of efficacy reported. Suitable and robust preclinical animal models for testing the safety and efficacy of different types of MSC products before use in clinical trials are rare. We here introduce two highly robust animal models of immune pathology: 1) acute radiation syndrome (ARS) and 2) graft versus host disease (GvHD), in conjunction with studying the immunomodulatory effect of well-characterized Interferon gamma (IFNγ) primed bone marrow derived MSCs. The animal model of ARS is based on clinical grade dosimetry precision and bioluminescence imaging. We found that allogeneic MSCs exhibit lower persistence in naïve compared to irradiated animals, and that intraperitoneal infusion of IFNγ prelicensed allogeneic MSCs protected animals from radiation induced lethality by day 30. In direct comparison, we also investigated the effect of IFNγ prelicensed allogeneic MSCs in modulating acute GvHD in an animal model of MHC major mismatched bone marrow transplantation. Infusion of IFNγ prelicensed allogeneic MSCs failed to mitigate acute GvHD. Altogether our results demonstrate that infused IFNγ prelicensed allogeneic MSCs protect against lethality from ARS, but not GvHD, thus providing important insights on the dichotomy of IFNγ prelicensed allogenic MSCs in well characterized and robust animal models of acute tissue injury.

AXL Mediates Cetuximab and Radiation Resistance Through Tyrosine 821 and the c-ABL Kinase Pathway in Head and Neck Cancer

PURPOSE

Radiation and cetuximab are therapeutics used in management of head and neck squamous cell carcinoma (HNSCC). Despite clinical success with these modalities, development of both intrinsic and acquired resistance is an emerging problem in the management of this disease. The purpose of this study was to investigate signaling of the receptor tyrosine kinase AXL in resistance to radiation and cetuximab treatment.

EXPERIMENTAL DESIGN

To study AXL signaling in the context of treatment-resistant HNSCC, we used patient-derived xenografts (PDXs) implanted into mice and evaluated the tumor response to AXL inhibition in combination with cetuximab or radiation treatment. To identify molecular mechanisms of how AXL signaling leads to resistance, three tyrosine residues of AXL (Y779, Y821, Y866) were mutated and examined for their sensitivity to cetuximab and/or radiation. Furthermore, reverse phase protein array (RPPA) was employed to analyze the proteomic architecture of signaling pathways in these genetically altered cell lines.

RESULTS

Treatment of cetuximab- and radiation-resistant PDXs with AXL inhibitor R428 was sufficient to overcome resistance. RPPA analysis revealed that such resistance emanates from signaling of tyrosine 821 of AXL via the tyrosine kinase c-ABL. In addition, inhibition of c-ABL signaling resensitized cells and tumors to cetuximab or radiotherapy even leading to complete tumor regression without recurrence in head and neck cancer models.

CONCLUSIONS

Collectively, the studies presented herein suggest that tyrosine 821 of AXL mediates resistance to cetuximab by activation of c-ABL kinase in HNSCC and that targeting of both EGFR and c-ABL leads to a robust antitumor response.

FGFR Inhibition Enhances Sensitivity to Radiation in Non-Small Cell Lung Cancer

FGFRs are commonly altered in non-small cell lung cancer (NSCLC). FGFRs activate multiple pathways including RAS/RAF/MAPK, PI3K/AKT, and STAT, which may play a role in the cellular response to radiation. We investigated the effects of combining the selective FGFR 1-3 tyrosine kinase inhibitor AZD4547 with radiation in cell line and xenograft models of NSCLC. NSCLC cell lines were assessed with proliferation, clonogenic survival, apoptosis, autophagy, cell cycle, and DNA damage signaling and repair assays. In vivo xenografts and IHC were used to confirm in vitro results. NSCLC cell lines demonstrated varying degrees of FGFR protein and mRNA expression. In vitro clonogenic survival assays showed radiosensitization with AZD4547 in two NSCLC cell lines. In these two cell lines, an increase in apoptosis and autophagy was observed with combined radiation and AZD4547. The addition of AZD4547 to radiation did not significantly affect γH2AX foci formation. Enhanced xenograft tumor growth delay was observed with the combination of radiation and AZD4547 compared with radiation or drug alone. IHC results revealed inhibition of pMAPK and pS6 and demonstrated an increase in apoptosis in the radiation plus AZD4547 group. This study demonstrates that FGFR inhibition by AZD4547 enhances the response of radiation in FGFR-expressing NSCLC in vitro and in vivo model systems. These results support further investigation of combining FGFR inhibition with radiation as a clinical therapeutic strategy.

Fibroblast Growth Factor Receptors as Targets for Radiosensitization in Head and Neck Squamous Cell Carcinomas

PURPOSE

We examined the capacity of the pan-fibroblast growth factor receptor (FGFR) inhibitor AZD4547 to augment radiation response across a panel of head and neck squamous cell carcinoma (HNSCC) cell lines and xenografts.

METHODS AND MATERIALS

FGFR1, FGFR2, and FGFR3 RNA in situ hybridization expression was assessed in a cohort of HNSCC patient samples, cell lines, and patient-derived xenografts (PDXs). In vitro effects of AZD4547 and radiation on cell survival, FGFR signaling, apoptosis, autophagy, cell cycle, and DNA damage repair were evaluated. Reverse phase protein array was used to identify differentially phosphorylated proteins in cells treated with AZD4547. In vivo tumor responses were evaluated in cell lines and PDX models.

RESULTS

FGFR1, FGFR2, and FGFR3 RNA in situ hybridization were expressed in 41%, 81%, and 89% of 107 oropharynx patient samples. Sensitivity to AZD4547 did not directly correlate with FGFR protein or RNA expression. In sensitive cell lines, AZD4547 inhibited p-MAPK in a time-dependent manner. Significant radiosensitization with AZD4547 was observed in cell lines that were sensitive to AZD4547. The mechanism underlying these effects appears to be multifactorial, involving inhibition of the MTOR pathway and subsequent enhancement of autophagy and activation of apoptotic pathways. Significant tumor growth delay was observed when AZD4547 was combined with radiation compared with radiation or drug alone in an FGFR-expressing HNSCC cell line xenograft and PDX.

CONCLUSIONS

These findings suggest that AZD4547 can augment the response of radiation in FGFR-expressing HNSCC in vivo model systems. FGFR1 and FGFR2 may prove worthy targets for radiosensitization in HNSCC clinical investigations.

Patient Derived Models to Study Head and Neck Cancer Radiation Response

Patient-derived model systems are important tools for studying novel anti-cancer therapies. Patient-derived xenografts (PDXs) have gained favor over the last 10 years as newer mouse strains have improved the success rate of establishing PDXs from patient biopsies. PDXs can be engrafted from head and neck cancer (HNC) samples across a wide range of cancer stages, retain the genetic features of their human source, and can be treated with both chemotherapy and radiation, allowing for clinically relevant studies. Not only do PDXs allow for the study of patient tissues in an in vivo model, they can also provide a renewable source of cancer cells for organoid cultures. Herein, we review the uses of HNC patient-derived models for radiation research, including approaches to establishing both orthotopic and heterotopic PDXs, approaches and potential pitfalls to delivering chemotherapy and radiation to these animal models, biological advantages and limitations, and alternatives to animal studies that still use patient-derived tissues.

Abstract 4273: Inhibition of autophagy increases HNSCC sensitivity to cancer therapies

Background: Radiation and EGFR-targeted therapies are commonly used in the treatment of head and neck squamous cell carcinoma (HNSCC). These treatments fail to control a significant number of cancers resulting in a 5-year survival rate that remains around 40-50%. We have shown that both cetuximab and radiation induce autophagy, a pro-survival cellular stress response, in head and neck cancer. In this study, we examine the consequence of autophagy inhibition and investigate the molecular mechanism underlying therapy-induced autophagy.

Methods: Autophagy was assessed using a nano-Luc LC3 reporter (Promega), immunofluorescence for LC3, p62, and acridine orange in HNSCC cell lines. RNAi knockdown of EGFR and LAPTM4B were used to test the involved signaling molecules. Radiation was delivered using a RS225 cabinet irradiator at a dose rate of approximately 3 Gy/min with dose validation by TLD using custom phantoms. Cetuximab was delivered via intraperitoneal injection. Vps34 inhibitor SAR405 and ULK1 inhibitor SBI-0206965 were used to determine whether inhibition of autophagy reduces cell survival or represses cancer cell growth in the clonogenic assay. A flank xenograft model using A253 cells was used to test the combination of autophagy inhibitors and current therapies in vivo.

Results: As previously shown, both cetuximab and radiation induced autophagy by two times. Knockdown of EGFR and LAPTM4B decreased autophagy (62.5% and 65%, respectively) when assessed using the nano-Luc reporter assay. Similar results were seen using IF. Using a clonogenic survival assay, the combination of SAR405 and radiation resulted in complete loss of cell survival suggesting a radiosensitizing effect. In vivo, SAR405 treatment improved tumor control when combined with radiation or cetuximab when compared to either treatment alone.

Conclusions: Therapy induced autophagy is dependent upon expression of both EGFR and LAPTM4B. Inhibition of autophagy resulted decreased cell survival in vitro and resulted in decreased in vivo tumor growth. These results suggest that inhibition of autophagy may be a viable approach to sensitize HNSCC to anti-cancer treatments.

Citation Format: Yong-Syu Lee, Justin Skiba, Jaimee Kubatzke, Kwangok P. Nickel, Randall Kimple. Inhibition of autophagy increases HNSCC sensitivity to cancer therapies [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4273.

Patient-Derived Cancer Organoid Cultures to Predict Sensitivity to Chemotherapy and Radiation

PURPOSE

Cancer treatment is limited by inaccurate predictors of patient-specific therapeutic response. Therefore, some patients are exposed to unnecessary side effects and delays in starting effective therapy. A clinical tool that predicts treatment sensitivity for individual patients is needed.

EXPERIMENTAL DESIGN

Patient-derived cancer organoids were derived across multiple histologies. The histologic characteristics, mutation profile, clonal structure, and response to chemotherapy and radiation were assessed using bright-field and optical metabolic imaging on spheroid and single-cell levels, respectively.

RESULTS

We demonstrate that patient-derived cancer organoids represent the cancers from which they were derived, including key histologic and molecular features. These cultures were generated from numerous cancers, various biopsy sample types, and in different clinical settings. Next-generation sequencing reveals the presence of subclonal populations within the organoid cultures. These cultures allow for the detection of clonal heterogeneity with a greater sensitivity than bulk tumor sequencing. Optical metabolic imaging of these organoids provides cell-level quantification of treatment response and tumor heterogeneity allowing for resolution of therapeutic differences between patient samples. Using this technology, we prospectively predict treatment response for a patient with metastatic colorectal cancer.

CONCLUSIONS

These studies add to the literature demonstrating feasibility to grow clinical patient-derived organotypic cultures for treatment effectiveness testing. Together, these culture methods and response assessment techniques hold great promise to predict treatment sensitivity for patients with cancer undergoing chemotherapy and/or radiation.

Abstract 856: Selection of radiosensitizers based on HRAS mutation in bladder cancer

Purpose/Objective(s): The ability of activated HRAS to promote radiation resistance and predict for sensitivity to potential radiosensitizers was tested in a bladder cancer model system.

Materials/Methods: Mutations in HRAS, KRAS, and NRAS were analyzed using cBioPortal in a bladder cancer cohort (TCGA). We employed a panel of urothelial carcinoma cell lines-T24 (HRASG12V), J82 and 5637 (RASWT). Cell growth and survival was tested with colony formation and proliferation assays. Radiation survival was assessed by clonogenic survival assay. Immunoblots were used to confirm mutant HRAS expression, and target activation/knockdown in overexpression and knockdown studies. Radiosensitization of mutant-HRAS bladder cancer was tested using a flank cell line xenograft model in nude mice.

Results: Approximately 10% of bladder cancers feature alterations in one of three RAS genes; mutations in HRAS comprise greater than 50% of these. An HRAS activating (G12V) mutation was detected in T24. Consistent with known roles for activated RAS, T24 is relatively insensitive to both cetuximab and radiation. Using both in vivo and in vitro studies, cetuximab exhibited no radiosensitization of T24. Treatment with cetuximab lowered AKT, but not ERK activation. Direct inhibition of the MEK/ERK or PI3K/MTOR pathway by selumetinib or BEZ235, respectively, decreased target protein activation and resulted in significant growth inhibition compared to control (p<0.05). Treatment with either selumetinib or BEZ235 radiosensitized HRASG12V expressing cells (SER 1.3-1.8), but had more modest effects on cells with wild-type HRAS. siRNA knockdown of HRAS radiosensitized T24, but not J82 or 5637 cells relative to non-targeting control. The combination of selumetinib and radiation therapy delayed the growth of T24 tumors in vivo.

Conclusions: Over 10% of bladder cancers feature alterations in the RAS family of genes. These mutations can lead to resistance to cetuximab, either as a single treatment or as a radiosensitizer. Inhibition of downstream MEK/ERK and PI3K/MTOR pathways can radiosensitize tumors with activating mutations in HRAS. Identification of additional mutation/drug combinations that result in radiosensitization may be valuable to advance the design of personalized radiation therapy.

Citation Format: Michael M. Fisher, Adam D. Swick, Kwangok P. Nickel, Randall J. Kimple. Selection of radiosensitizers based on HRAS mutation in bladder cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 856.

Anti-Trop2 blockade enhances the therapeutic efficacy of ErbB3 inhibition in head and neck squamous cell carcinoma

ErbB3 has been widely implicated in treatment resistance, but its role as a primary treatment target is less clear. Canonically ErbB3 requires EGFR or ErbB2 for activation, whereas these two established treatment targets are thought to signal independently of ErbB3. In this study, we show that ErbB3 is essential for tumor growth of treatment-naive HNSCC patient-derived xenografts. This ErbB3 dependency occurs via ErbB3-mediated control of EGFR activation and HIF1α stabilization, which require ErbB3 and its ligand neuregulin-1. Here, we show that ErbB3 antibody treatment selects for a population of ErbB3-persister cells that express high levels of the transmembrane protein Trop2 that we previously identified as an inhibitor of ErbB3. Co-treatment with anti-ErbB3 and anti-Trop2 antibodies is synergistic and produces a greater anti-tumor response than either antibody alone. Collectively, these data both compel a revision of ErbB-family signaling and delineate a strategy for its effective inhibition in HNSCC.

Abstract 51: Potential and challenges in co-targeting mTORC and EGFR signaling as a therapeutic strategy in HNSCC

Background: Head and neck squamous cell carcinomas (HNSCCs) have high rates of mutation and other alterations along the PI3K/AKT/mTORC signaling axis. This has led to interest in the use of therapeutics targeting this pathway; however, identifying reliable predictive biomarkers to guide patient selection remains challenging. Despite excellent preclinical data, the use of these compounds as monotherapy has been underwhelming in initial clinical trials. The EGFR monoclonal antibody cetuximab remains the only approved targeted agent for HNSCC and with reasonable toxicity profiles, has potential use in combination therapy.

Methods: Both catalytic mTORC (AZD8055) and PI3K/mTORC(NVP-BEZ-235) inhibitors were tested +/- cetuximab in several in vitro and in vivo pre-clinical models. A panel of HNSCC cell lines and patient derived xenografts (PDX) were evaluated for PI3K/AKT/mTORC pathway mutation by sequencing and potential protein biomarker by immunoblot and IHC. Cell lines were assayed for sensitivity to all three agents by growth inhibition and clonogenic survival assay. DNA replication (BrdU uptake) and apoptosis (Capase 3/7 activity) were investigated to assess the mechanism of inhibition. The specificity of the molecular targeted effects was confirmed by siRNA knockdown. Five unique PDX models that presented PIK3CA mutation or intrinsic cetuximab resistance were treated with a combination of cetuximab and the dual mTORC inhibitor AZD8055 in a nude mouse model. Matched PDX derived cell strains were generated to investigate differences in response observed in in vitro and in vivo settings.

Results: Assessment of the panel of HNSCC cell lines by mutational hotspot sequencing did not reveal any obvious sensitizing mutations, whereas putative protein biomarkers (e.g. PIK3CA, pAKT) were elevated in some cell lines. All cell lines showed modest response to both PI3K/mTORC and dual mTORC inhibition. The addition of cetuximab to either agent produced modest additive effect. Mechanistic studies revealed that growth inhibition rather than death induction was the major anticancer effect. SiRNA knockdown showed similar molecular signaling and functional effects to drug inhibition. Using the PDX models, in vivo single agent mTORC inhibition inhibited growth of a PIK3CA mutant cancer, but had no effect on any PIK3CAWT or a second PIK3CA mutant model. In all models the combination therapy showed greater growth delay than monotherapy. In matched PDX derived cell strains, in vitro responses were similar when grown in 3D culture but cells displayed greater sensitivity when grown in 2D culture, suggesting that tumor microenvironment contributes to response.

Conclusions: The uniform ability of PI3K/mTORC and mTORC inhibition to suppress the growth of HNSCC cells highlights the role of this signaling pathway to drive the proliferation. In vivo, despite some PDX models meeting likely selection criteria, the single agent therapy was largely ineffective. Conversely, the combination treatment produced growth delay and suggests the potential for adding a catalytic mTORC inhibitor to cetuximab therapy for HNSCC patients. Overall, these results add to a growing body of evidence suggesting approaches that attempt to match genetic alternation or other biomarker to the optimal therapy in HNSCC remain complex and challenging.

Citation Format: Adam D. Swick, Prashanth J. Prabakaran, Margot C. Miller, Amal M. Javaid, Michael M. Fisher, Emmanuel Sampene, Irene M. Ong, Mari Iida, Deric L. Wheeler, Kwangok P. Nickel, Justine Y. Bruce, Randall J. Kimple. Potential and challenges in co-targeting mTORC and EGFR signaling as a therapeutic strategy in HNSCC [abstract]. In: Proceedings of the AACR-AHNS Head and Neck Cancer Conference: Optimizing Survival and Quality of Life through Basic, Clinical, and Translational Research; April 23-25, 2017; San Diego, CA. Philadelphia (PA): AACR; Clin Cancer Res 2017;23(23_Suppl):Abstract nr 51.

Overcoming Resistance to Cetuximab with Honokiol, A Small-Molecule Polyphenol

Overexpression and activation of the EGFR have been linked to poor prognosis in several human cancers. Cetuximab is a mAb against EGFR that is used for the treatment in head and neck squamous cell carcinoma (HNSCC) and metastatic colorectal cancer. Unfortunately, most tumors have intrinsic or will acquire resistance to cetuximab during the course of therapy. Honokiol is a natural compound found in the bark and leaves of the Chinese Magnolia tree and is established to have several anticancer properties without appreciable toxicity. In this study, we hypothesized that combining cetuximab and honokiol treatments could overcome acquired resistance to cetuximab. We previously developed a model of acquired resistance to cetuximab in non-small cell lung cancer H226 cell line. Treatment of cetuximab-resistant clones with honokiol and cetuximab resulted in a robust antiproliferative response. Immunoblot analysis revealed the HER family and their signaling pathways were downregulated after combination treatment, most notably the proliferation (MAPK) and survival (AKT) pathways. In addition, we found a decrease in phosphorylation of DRP1 and reactive oxygen species after combination treatment in cetuximab-resistant clones, which may signify a change in mitochondrial function. Furthermore, we utilized cetuximab-resistant HNSCC patient-derived xenografts (PDX) to test the benefit of combinatorial treatment in vivo There was significant growth delay in PDX tumors after combination treatment with a subsequent downregulation of active MAPK, AKT, and DRP1 signaling as seen in vitro Collectively, these data suggest that honokiol is a promising natural compound in overcoming acquired resistance to cetuximab. Mol Cancer Ther; 17(1); 204-14. ©2017 AACR.

Abstract 5898: The consomic xenograft model identifies genetic changes in the tumor microenvironment that alter the growth and metastasis of head and neck cancers

Background: The tumor microenvironment (TME) is known to impact tumor growth, metastatic potential, and treatment response. Nearly all studies of head and neck cancer (HNC) have focused on somatic mutations in the malignant cells. We hypothesized that genetic determinants limited to the microenvironment would influence HNC growth and metastatic potential.

Approach: To demonstrate the impact of genetic differences in the TME on HNC cell line in vivo growth we utilized a novel tool, the consomic xenograft model (CXM). A consomic rat has an entire chromosome substituted into the isogenic background of another inbred strain by selective breeding. Use of immunodeficient (IL2Rγ-/-) consomic rats allows one to study the influence of stromal genetics on tumor biology without the confounding effect of differences in the immune system through the orthotopic implantation of cancer cells into different consomic rat strains. In this system, any differences in tumor growth or metastases are due to differences in the TME rather than cancer cells or immune response. We utilized SS and SS.BN3 consomic rat strains, previously shown to affect the growth of breast tumors, to study the effects of the TME on HNC tumor growth using two well-characterized HPV negative HNC cell lines, SCC-6 (base of tongue derived) and SCC-22b (derived from a hypopharyngeal cancer that had metastasized to lymph nodes). Both cell lines were modified to stably express luciferase. HNC cells were inoculated into the tongue of SS and SS.BN3 animals and tumor growth was monitored by biophotonic imaging after luciferin injection.

Results: A significant difference in the tumor growth was seen between rat strains for both cell lines, with the SS.BN3 rats exhibiting less tumor growth and metastasis. Median luciferase activity from baseline increased by 4.1-fold vs. 1.1 fold in SCC-6 tumors in SS vs SS.BN3 rats, respectively (p<0.03). SCC-22B tumors demonstrated a significant difference in tumor size as well, with median luciferase activity from baseline 12.7 vs 4.4 fold on day 26, for SS vs SS.BN3, respectively (p<0.05). A significant differences in lung metastases was also seen between strains. Lung metastases were seen in 88% of SS and 0% of SS.BN3 rats (n=6 per group) inoculated with SCC-6 (p<0.02) and in 75% of SS and 30% of SS.BN3 rats (n=10 per group) inoculated with SCC-22b (p<0.08). Despite a non-statistically significant difference in the number of SCC-22b inoculated animals with lung metastases, there was a significantly higher metastatic burden as measured by luciferase signal, with the median signal 6.8 fold higher in SS as compared to SS.BN3 (p<0.03).

Conclusions: The use of the CXM model demonstrates an important role for the TME in the growth and metastatic spread of HNC cell lines. This model allows for future congenic mapping to identify the causative genetic variants in the TME mediating the HNC changes in tumor growth and metastasis.

Citation Format: Michael W. Straza, Amy Rymaszewski, Kwangok P. Nickel, Anne Frei, Anirban Chatterjee, Rachel Schlaak, Amit Joshi, Michael Flister, Randy J. Kimple, Carmen Bergom. The consomic xenograft model identifies genetic changes in the tumor microenvironment that alter the growth and metastasis of head and neck cancers [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5898. doi:10.1158/1538-7445.AM2017-5898

Abstract 5187: Potent radiosensitization of adenoid cystic carcinoma in a patient derived xenograft model using the MDM2 inhibitor AMG 232

Purpose: Adenoid cystic carcinoma (ACC) is a relatively rare cancer that typically arises in major or minor salivary gland tissues of the head and neck. There are currently no approved systemic agents for ACC and no established data supporting the delivery of chemoradiation for ACC patients. The scarcity of validated preclinical model systems has hampered research efforts. We report the successful establishment and propagation of an ACC patient derived xenograft (PDX), genomic evaluation of cancer associated mutations, and in vivo response to MDM2 inhibition combined with radiotherapy. Because TP53 mutations are seen in <5% of ACCs, we investigated the role of a small molecule MDM2 inhibitor, AMG 232.

Methods: An ACC PDX was established and assessed for common cancer-associated mutations using the Illumina TruSeq Amplicon Cancer panel. Xenografts were treated with focal radiation with or without AMG 232. Focal radiation was delivered at 0, 2, 5, or 8 Gy x 8 fractions delivered twice weekly, with AMG 232 (50mg/kg) delivered daily by oral gavage. Tumor size was measured by caliper and comparisons between treatment groups made using a repeated measures ANOVA. A TCD50 was calculated by fitting log-transformed data to a dose-response curve and compared using the extra-sum-of-squares f test. Target inhibition and anti-cancer effect was confirmed via immuno-blotting of tumor lysates, and IHC staining or in situ hybridization of relevant targets within FFPE sections of tumors harvested 2 and 48 hrs post treatment.

Results: The histologic characteristics of the primary human tumor are maintained in subsequent murine passages of this ACC PDX. Mutational profiling determined that the PDX was wildtype for TP53. AMG 232 alone resulted in modest slowing of tumor growth. Radiation alone produced a tumor growth delay in a dose dependent manner but did not result in sustained local tumor control. Strikingly, the combination of AMG 232 with RT (including low dose radiation of 2 Gy) produced dramatic tumor shrinkage and potent tumor control three months after the end of treatment. Target inhibition of MDM2 was confirmed by western blot of tumor lysates and IHC of FFPE samples taken 2 hrs post treatment. Antiproliferative and apoptotic effects were confirmed by western blot of tumor lysates and IHC of FFPE samples taken at 48 hrs post treatment.

Conclusions: This study suggests that MDM2 inhibition may provide potent radiosensitization in TP53 WT ACC. While additional translational models are warranted, the powerful response profile observed suggests that phase I clinical trial evaluation of this combination is worthy for this challenging malignancy.

Citation Format: Amal Javaid, Adam D. Swick, Lauryn Werner, Prashanth Prabakaran, Rong Hu, Kwangok P. Nickel, Irene Ong, Emmanuel Sampene, Justine Bruce, Gregory Hartig, Aaron Wieland, Jude Canon, Paul Harari, Randall Kimple. Potent radiosensitization of adenoid cystic carcinoma in a patient derived xenograft model using the MDM2 inhibitor AMG 232 [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5187. doi:10.1158/1538-7445.AM2017-5187

Abstract 5192: Selection of radiosensitizers based on HRAS mutation in head and neck cancer

Purpose/Objective(s): The ability of activated HRAS to promote radiation resistance and predict for sensitivity to potential radiosensitizers was tested in a head and neck cancer model system.

Materials/Methods: Mutations in HRAS, KRAS, and NRAS were analyzed using cBioPortal in a head and neck cancer cohort. The Illumina TruSeq Amplicon Cancer panel was used to screen a panel of head and neck cancer cell lines for mutations in RAS-family genes. Cell growth and radiation survival was assessed by clonogenic survival assay. Immunoblots were used to confirm target activation/knockdown in overexpression and knockdown studies. A tumor control dose 50% (TCD50) assay was employed to investigate radiosensitization of a mutated-HRAS head and neck cancer cell line in a flank xenograft model in nude mice.

Results: Activating mutations in one of the three RAS genes are seen in 5-10% of head and neck cancer patients. Mutations in HRAS represent over 50% of these. Screening our panel of head and neck cancer cell lines identified a canonical activating mutation in HRAS (i.e. G12V) in SCC22B. Consistent with known roles for activated HRASG12V, SCC22B is relatively insensitive to both cetuximab and radiation. Using both in vitro and in vivo studies, cetuximab exhibited no ability to radiosensitize SCC22B. Cetuximab treatment decreased AKT, but not ERK activation. Direct inhibition pathways downstream of HRAS by selumetinib (MEK/ERK) or BEZ235 (PI3K/MTOR) decreased target protein activation and resulted in significant growth inhibition compared to control (p<0.05). Treatment with either selumetinib or BEZ235 radiosensitized HRASG12V expressing cells (SER 1.3-1.8) but had more modest effects on cells with wildtype HRAS. siRNA knockdown of HRAS radiosensitized SCC22B, but not SCC1 or SCC6 cells relative to non-targeting control. Overexpression of HRASG12V conferred relative radioresistance in wildtype cell lines. In vivo assessment of the radiosensitizing effects of these compounds (TCD50) is pending.

Conclusion: More than 5% of head and neck cancers harbor activating mutations in one of the RAS family of genes. These mutations lead to resistance to cetuximab, either as a single agent, or as a radiosensitizer. Inhibition of downstream targets such as the MEK/ERK and PI3K/MTOR pathways can radiosensitize tumors harboring activating mutations in HRAS. Identification of additional mutation/drug combinations that result in radiosensitization may be valuable to advance the design of personalized radiation therapy.

Citation Format: Michael M. Fisher, Adam D. Swick, Kwangok P. Nickel, Randall J. Kimple. Selection of radiosensitizers based on HRAS mutation in head and neck cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5192. doi:10.1158/1538-7445.AM2017-5192

Abstract 3307: Induction of autophagy as a mechanism of therapeutic resistance in head and neck cancer

Background: In the curative setting for head and neck cancer (HNC) a commonly used treatment is radiation combined with the anti-EGFR monoclonal antibody cetuximab (CTX). However, despite decades of research into improved treatments, therapeutic resistance remains a major challenge for this malignancy with roughly 40% of patients developing recurrent disease. We are studying the molecular mechanisms by which radiation and cetuximab induce autophagy and how this process can be modulated to improve the efficacy of therapy.

Methods: We evaluated a panel of both human papillomavirus (HPV) positive and negative HNC cell lines for autophagic response to both CTX treatment and ionizing radiation (XRT). Induction of autophagy was detected by immunoblot flux assays for LC3 and p62 and by immunofluorescent staining of autophagic vesicles. siRNA knockdown of EGFR, LAMPT4B, ULK1, Beclin1 and others was used to probe the involvement of different signaling molecules. The addition of specific autophagy inhibitors, such as the ULK1 inhibitor SBI-0206965, to CTX or XRT treatment was tested to determine whether the reduction of autophagic response reduced cell survival in a clonogenic survival assay. Induction of apoptosis was analyzed by immunoblot against cleaved Caspase and PARP and AnnexinV staining.

Results: Flux assays revealed that both CTX and XRT induced autophagy in a time and dose dependent manner. Immunofluorescent staining of LC3 to identify autophagic vesicles showed that a relatively small fraction of the total cell population is able to induce this response. Specific siRNA knockdown of EGFR and LAMPT4B was able to abrogate the induction of autophagy in response to both CTX and XRT. Involvement of alternative downstream pathways involving either ULK1 and Beclin1 or p53 in response to either treatment is under investigation. To determine whether blockade of cytoprotective autophagy can help overcome therapeutic resistance, we tested specific autophagy inhibitors in combination with either CTX or XRT treatment. The addition of the ULK1 inhibitor to CTX or XRT induced apoptosis as shown by caspase activity, AnnexinV staining, and reduced cell survival in clonogenic assays.

Conclusions: Autophagy may play a critical and protective role in how head and neck cancers respond to therapeutic stress. The addition of specific autophagy inhibitors to standard treatments may provide a way to overcome resistance to therapy.

Citation Format: Jaimee C. Eckers, Adam D. Swick, Tyler Fowler, Justin Skiba, Kwangok P. Nickel, Randall J. Kimple. Induction of autophagy as a mechanism of therapeutic resistance in head and neck cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3307. doi:10.1158/1538-7445.AM2017-3307

Radiosensitization of Adenoid Cystic Carcinoma with MDM2 Inhibition

Purpose: Adenoid cystic carcinoma (ACC) is a rare cancer arising from the major or minor salivary gland tissues of the head and neck. There are currently no approved systemic agents or known radiosensitizers for ACC. Unlike the more common head and neck squamous cell carcinomas that frequently harbor TP53 mutations, ACCs contain TP53 mutations at a rate of <5%, rendering them an attractive target for MDM2 inhibition.Experimental Design: We report the successful establishment and detailed characterization of a TP53-WT ACC patient-derived xenograft (PDX), which retained the histologic features of the original patient tumor. We evaluated this model for response to the MDM2 inhibitor AMG 232 as monotherapy and in combination with radiotherapy.Results: AMG 232 monotherapy induced modest tumor growth inhibition, and radiation monotherapy induced a transient tumor growth delay in a dose-dependent fashion. Strikingly, combination treatment of AMG 232 with radiotherapy (including low-dose radiotherapy of 2 Gy/fraction) induced dramatic tumor response and high local tumor control rates 3 months following treatment. Posttreatment analysis revealed that although both AMG 232 and radiotherapy alone induced TP53 tumor-suppressive activities, combination therapy amplified this response with potent induction of apoptosis after combination treatment.Conclusions: These data identify that MDM2 inhibition can provide potent radiosensitization in TP53-WT ACC. In light of the absence of effective systemic agents for ACC, the powerful response profile observed here suggests that clinical trial evaluation of this drug/radiotherapy combination may be warranted to improve local control in this challenging malignancy. Clin Cancer Res; 23(20); 6044-53. ©2017 AACR.

Cotargeting mTORC and EGFR Signaling as a Therapeutic Strategy in HNSCC

Head and neck squamous cell carcinomas (HNSCC) are frequently altered along the PI3K/AKT/mTORC signaling axis. Despite excellent preclinical data, the use of compounds targeting this pathway as monotherapy has been underwhelming in initial clinical trials, and identification of predictive biomarkers remains challenging. To investigate mTORC-specific inhibition, we tested catalytic mTORC (AZD8055) and PI3K/mTORC (NVP-BEZ-235) inhibitors ± cetuximab in a panel of HNSCC cell lines and patient-derived xenografts (PDX). Cell lines were assayed for response to all agents and siRNA knockdown of targets by multiple approaches. All cell lines showed similar response to both drug and siRNA inhibition of both PI3K and mTORC pathways, with anti-EGFR combination producing modest additive effect. Five PDX models that presented PIK3CA mutation or intrinsic cetuximab resistance were treated with a combination of cetuximab and AZD8055. In vivo single-agent mTORC inhibition inhibited growth of one PIK3CA-mutant cancer, but had little effect on any PIK3CA^WT or a second PIK3CA-mutant model. In all models, the combination therapy showed greater growth delay than monotherapy. The uniform ability of PI3K and mTORC inhibition to suppress the growth of HNSCC cells highlights the pathway's role in driving proliferation. Although single-agent therapy was largely ineffective in vivo, improved response of combination treatment in an array of PDXs suggests the potential for adding a catalytic mTORC inhibitor to cetuximab therapy. Overall, these results add to a growing body of evidence, suggesting that approaches that attempt to match biomarkers to the optimal therapy in HNSCC remain complex and challenging. Mol Cancer Ther; 16(7); 1257-68. ©2017 AACR.

Abstract 3044: Patient-derived adenoid cystic carcinoma xenografts to study molecular target modulation of tumor radiosensitivity

Background: Adenoid cystic carcinoma (ACC) is a relatively rare cancer that typically arises in salivary tissues of the head and neck region. Hallmark characteristics include slow growth rate, peri-neural tumor spread, and a high propensity for late distant metastasis. Surgery and radiation are the mainstays of treatment with no effective systemic agents to date. Due to infrequency, studies of novel therapeutics are not routinely feasible. In addition, whether these tumors can be sensitized to radiation by concurrent chemotherapy is not known. We report here the establishment and examination of ACC patient derived xenografts (PDX) to investigate the efficacy of novel chemotherapies and combinations of chemotherapy and radiation.

Methods: PDXs have been established and maintained in NOD-SCID gamma (NSG) mice from both research biopsies and surgical specimens. Common cancer-associated mutations in both the primary patient tumor and PDX were identified using the Illumina TruSeq Amplicon Cancer panel. Well described immunohistochemical markers of ACC were used to compare histological characteristics between the primary tumor and PDX. The ACC PDX was engrafted into the flanks of nude mice and treated with focal radiotherapy (5 Gy x 8 fractions delivered twice weekly), a panel of chemotherapeutic agents, or combination radiochemotherapy. Tumor size was measured over time and comparisons between treatment groups made by the extra-sum-of-squares f test.

Results: PDXs established from ACC maintain the histologic and physical characteristics of the primary tumor. Targeted mutational analysis of ACC identified expected alterations based on previously reported large scale sequencing of other human tumors including mutations in the receptor tyrosine kinases(RTKs) cKit and KDR/VEGFR2. Based on identified tumor mutations, several targeted therapies were selected including dovitinib, a multi-RTK inhibitor, BEZ235, a PI3K/mTORC inhibitor, and cetuximab, an EGFR mAB. Treatment with each of these compounds showed varying degrees of growth inhibition without evidence of frank tumor regression. However, combining these drugs with radiation demonstrated significantly improved tumor control in comparison to drug alone.

Conclusions: Studies using our PDX model suggest that several molecular targeting agents can significantly augment the impact of radiation on ACC tumor growth. These preliminary data identify the rationale to investigate selected molecular drug/radiation combinations for ACC, particularly when driven by tumor specific genetic biomarkers. Expansion of these ACC studies may be valuable to advance the design of new investigational treatment strategies for this challenging tumor.

Citation Format: Prashanth Prabakaran, Kwangok P. Nickel, David T. Yang, Lauryn R. Werner, Justine Y. Bruce, Aaron M. Wieland, Timothy M. McCulloch, Gregory K. Hartig, Paul M. Harari, Adam D. Swick, Randall J. Kimple. Patient-derived adenoid cystic carcinoma xenografts to study molecular target modulation of tumor radiosensitivity. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3044.

Abstract 3603: Molecular targeting of cetuximab resistant head and neck cancer

Despite promising preclinical data, the EGFR targeted monoclonal antibody, cetuximab, has limited use as single agent therapy in the treatment of head and neck cancer due to the development of therapeutic resistance. Improved approaches to treat these cancers will need to address the evolving molecular landscape of head and neck cancer. Recent reports describing mutations or copy number alterations in PI3K and PTEN as potential causes of cetuximab resistance have sparked interest in therapeutics that target these pathways as alternatives to or in combination with EGFR targeting drugs.

Using both in vitro and in vivo models of head and neck squamous cell carcinoma (HNSCC) we have recapitulated the diversity of responses to cetuximab observed in the patient population and are testing alternative therapies. Examining an array of HNSCC cell lines, including both human papillomavirus (HPV) positive and negative lines, we observed a wide range of sensitivities to this drug, with little to no growth inhibition in some lines even at micromolar concentrations. For lines that were sensitive to drug, effective growth inhibition, demonstrated in both proliferation and colony formation assays, was linked with suppressed phosphorylation of both Akt and ERK/MAPK signaling downstream of EGFR. Additionally, in the sensitive HPV+ HNSCC lines, cetuximab treatment induced apoptosis marked by caspase activity. Both sensitive and resistant HNSCC lines were then tested for response to both AZD8055, a dual mTORC1/2 inhibitor and BEZ235, a PI3K/mTORC1 inhibitor, resulting in both growth inhibition and successful suppression of phosphorylation of their Akt and S6 targets, suggesting that these drugs may be useful alternatives or adjuvants for cetuximab treatment.

In vivo models of HNSCC were also utilized to test the efficacy of cetuximab treatment and begin to evaluate alternative or combination therapies. Using immunocompromised mouse models, both cell line xenografts and novel patient derived xenografts presented a range of sensitivities to cetuximab. In an effort to identify potential biomarkers that would predict response to cetuximab, IHC staining of pre-treatment tumor samples was carried out and demonstrated that low phospho-Akt and phospho-ERK levels correlated with cetuximab sensitivity. Initial in vivo studies using the PI3K/mTORC inhibitors AZD8055 and BEZ235 to treat both cetuximab sensitive and resistant xenografts, have shown that these compounds may be effective at suppressing growth in both categories of tumors. These studies provide initial pre-clinical data to support the use of PI3K inhibition for the treatment of head and neck cancer.

Citation Format: Adam D. Swick, Dana Gunderson, Molly Smith, Grace Blitzer, Andrew Stein, Kwangok P. Nickel, Randall J. Kimple. Molecular targeting of cetuximab resistant head and neck cancer. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 3603. doi:10.1158/1538-7445.AM2015-3603

Abstract 1801: Biological validation of a novel high-throughput irradiator for predictive radiation sensitivity bioassays

Purpose: To improve our ability to study radiation response and screen for radiosensitizing compounds, we have developed a high-throughput variable dose rate microirradiator. We sought to use several assays of radiation induced cellular damage to validate the ability of this system to be used for high-throughput assays.

Methods: Immortalized human tonsillar epithelial cells were cultured in 96-well microtiter plates and irradiated in groups of eight wells to absorbed doses of 0, 1, 2, 4, and 8 Gy. Chloromethyl-H2DCFDA, a fluorescent reactive oxygen species (ROS) marker, was used to measure relative changes in ROS. Single cell gel electrophoresis (aka Comet assay, neutral) was used to detect physical DNA double-strand breaks. High-throughput immunofluorescent microscopy was used to detect γH2AX foci, a early marker of DNA double-strand breaks.

Results: Over the range of radiation doses tested, we confirmed increasing ROS generation as measured by CM-H2DCFDA fluorescence (R2 = 0.969). Over 1,450 comets were analyzed over a range of radiation doses and the Olive Tail Moment (OTM) calculated. A linear increase in OTM with radiation dose was seen (R2 = 0.991). A linear increase in γH2AX foci was seen with increasing radiation dose as measured by cell average γH2AX fluorescence (R2 = 0.999) Conclusions: We have developed a robust platform for high-throughput assays of radiation sensitivity allowing rapid assessment of effects over a range of radiation doses. This system provides a powerful tool for increasing the efficacy of genetic and pharmacologic modifiers of radiation response.

Citation Format: Alison Bailey, Tyler Fowler, Kwangok P. Nickel, Bryan Bednarz, Randall J. Kimple. Biological validation of a novel high-throughput irradiator for predictive radiation sensitivity bioassays. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1801. doi:10.1158/1538-7445.AM2015-1801

Human papillomavirus type 16 E7 oncoprotein causes a delay in repair of DNA damage

BACKGROUND AND PURPOSE

Patients with human papillomavirus related (HPV+) head and neck cancers (HNCs) demonstrate improved clinical outcomes compared to traditional HPV negative (HPV-) HNC patients. We have recently shown that HPV+ HNC cells are more sensitive to radiation than HPV- HNC cells. However, roles of HPV oncogenes in regulating the response of DNA damage repair remain unknown.

MATERIAL AND METHODS

Using immortalized normal oral epithelial cell lines, HPV+ HNC derived cell lines, and HPV16 E7-transgenic mice we assessed the repair of DNA damage using γ-H2AX foci, single and split dose clonogenic survival assays, and immunoblot. The ability of E7 to modulate expression of proteins associated with DNA repair pathways was assessed by immunoblot.

RESULTS

HPV16 E7 increased retention of γ-H2AX nuclear foci and significantly decreased sublethal DNA damage repair. While phospho-ATM, phospho-ATR, Ku70, and Ku80 expressions were not altered by E7, Rad51 was induced by E7. Correspondingly, HPV+ HNC cell lines showed retention of Rad51 after γ-radiation.

CONCLUSIONS

Our findings provide further understanding as to how HPV16 E7 manipulates cellular DNA damage responses that may underlie its oncogenic potential and influence the altered sensitivity to radiation seen in HPV+ HNC as compared to HPV- HNC.

Enhanced radiation sensitivity in HPV-positive head and neck cancer

Patients with human papillomavirus (HPV+)-associated head and neck cancer (HNC) show significantly improved survival outcome compared with those with HPV-negative (HPV-) tumors. Published data examining this difference offers conflicting results to date. We systematically investigated the radiation sensitivity of all available validated HPV+ HNC cell lines and a series of HPV- HNC cell lines using in vitro and in vivo techniques. HPV+ HNCs exhibited greater intrinsic radiation sensitivity (average SF2 HPV-: 0.59 vs. HPV+: 0.22; P < 0.0001), corresponding with a prolonged G2-M cell-cycle arrest and increased apoptosis following radiation exposure (percent change 0% vs. 85%; P = 0.002). A genome-wide microarray was used to compare gene expression 24 hours following radiation between HPV+ and HPV- cell lines. Multiple genes in TP53 pathway were upregulated in HPV+ cells (Z score 4.90), including a 4.6-fold increase in TP53 (P < 0.0001). Using immortalized human tonsillar epithelial (HTE) cells, increased radiation sensitivity was seen in cell expressing HPV-16 E6 despite the effect of E6 to degrade p53. This suggested that low levels of normally functioning p53 in HPV+ HNC cells could be activated by radiation, leading to cell death. Consistent with this, more complete knockdown of TP53 by siRNA resulted in radiation resistance. These results provide clear evidence, and a supporting mechanism, for increased radiation sensitivity in HPV+ HNC relative to HPV- HNC. This issue is under active investigation in a series of clinical trials attempting to de-escalate radiation (and chemotherapy) in selected patients with HPV+ HNC in light of their favorable overall survival outcome.

1,25-dihydroxyvitamin D inhibits vitamin E succinate-induced apoptosis in C3H10T1/2 cells but not Harvey ras-transfected cells

In this study, the effect of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] on regulation of apoptosis was compared in control C3H10T1/2 mouse fibroblast cells and those transfected with the Harvey ras oncogene. A known apoptotic stimulator, vitamin E succinate (VES), reduced cell number in a time- and dose-dependent manner in both cell types. In an assay for viable cells, there were significantly more C3H10T1/2 cells cotreated with VES and 1,25(OH)2D3 (-5.0 +/- 10.5% of vehicle-treated controls) compared to VES alone treated cells (-60.8 +/- 5.6%). In contrast, 1,25(OH)2D3 did not change the percentage of viable cells following treatment by VES in ras-transfected cells [-67.3 +/- 7.5%, VES alone compared to 57.3 +/-v 15.7% with VES and 1,25(OH)2D3 ]. Further studies confirmed that 1,25(OH)2D3 inhibited VES-mediated apoptosis (1.27 +/- 0.34-fold over vehicle control) compared to VES treatment alone (2.29 +/- 0.56-fold increase) in C3H10T1/2 cells, but not in ras-transfected cells [3.07 +/- 0.43-fold increase, VES treatment alone; 3.64 +/- 0.42-fold increase, VES and 1,25(OH)2D3]. Both C3H10T1/2 and ras-transfected cells treated with VES had increased concentrations of cellular VES with very little change in a-tocopherol, indicating that the cells took up VES intact. In addition, both cell lines contained similar levels of nuclear vitamin D receptor (VDR); however, the ras-transfected cells had reduced VDRE transcriptional activity. In conclusion, VES exerts its effect intact and 1,25(OH)2D3 preferentially protects C3H10T1/2 cells, whereas ras-transformed cells were not protected from VES-mediated apoptosis.

Activators of peroxisome proliferator-activated receptor-alpha partially inhibit mouse skin tumor promotion

Several recent reports have suggested that peroxisome proliferator-activated receptors (PPARs) may be involved in the development of neoplasias in different tissue types. The present study was undertaken to determine whether PPARs play a role in skin physiology and tumorigenesis. In an initiation-promotion study, SENCAR mice treated topically with the PPARalpha ligands conjugated linoleic acid and 4-chloro-6-(2,3-xylidino)-2-pyrimidinylthioacetic acid (Wy-14643) exhibited an approximately 30% lower skin tumor yield compared with mice treated with vehicle. The PPARgamma and PPARdelta activators troglitazone and bezafibrate, respectively, exerted little, if any, inhibitory activity. PPARalpha was detected in normal and hyperplastic skin and in papillomas and carcinomas by immunohistochemistry. In addition, PPARalpha, PPARdelta/PPARbeta, and PPARgamma protein levels were analyzed by immunoblotting in normal epidermis and papillomas. Surprisingly, the levels of all three isoforms were increased significantly in tumors as opposed to normal epidermis. In primary keratinocyte cultures, protein levels of PPARalpha and, to a lesser extent, PPARgamma were markedly increased when the cells were induced to differentiate with high-calcium (0.12 mM) conditions. In addition, we observed that Wy-14643 enhanced transcriptional activity of a peroxisome proliferator-response element-driven promoter in a mouse keratinocyte cell line. These results demonstrate that keratinocytes express functional PPARalpha, that PPARalpha may play a role in differentiation, and that ligands for PPARalpha are moderately protective against skin tumor promotion. We conclude that selective PPARalpha ligands may exert their protective role against skin tumor promotion by ligand activation of PPARalpha.

Activators of peroxisome proliferator-activated receptor-alpha partially inhibit mouse skin tumor promotion

Several recent reports have suggested that peroxisome proliferator-activated receptors (PPARs) may be involved in the development of neoplasias in different tissue types. The present study was undertaken to determine whether PPARs play a role in skin physiology and tumorigenesis. In an initiation-promotion study, SENCAR mice treated topically with the PPARalpha ligands conjugated linoleic acid and 4-chloro-6-(2,3-xylidino)-2-pyrimidinylthioacetic acid (Wy-14643) exhibited an approximately 30% lower skin tumor yield compared with mice treated with vehicle. The PPARgamma and PPARdelta activators troglitazone and bezafibrate, respectively, exerted little, if any, inhibitory activity. PPARalpha was detected in normal and hyperplastic skin and in papillomas and carcinomas by immunohistochemistry. In addition, PPARalpha, PPARdelta/PPARbeta, and PPARgamma protein levels were analyzed by immunoblotting in normal epidermis and papillomas. Surprisingly, the levels of all three isoforms were increased significantly in tumors as opposed to normal epidermis. In primary keratinocyte cultures, protein levels of PPARalpha and, to a lesser extent, PPARgamma were markedly increased when the cells were induced to differentiate with high-calcium (0.12 mM) conditions. In addition, we observed that Wy-14643 enhanced transcriptional activity of a peroxisome proliferator-response element-driven promoter in a mouse keratinocyte cell line. These results demonstrate that keratinocytes express functional PPARalpha, that PPARalpha may play a role in differentiation, and that ligands for PPARalpha are moderately protective against skin tumor promotion. We conclude that selective PPARalpha ligands may exert their protective role against skin tumor promotion by ligand activation of PPARalpha.

Characterization of 25-hydroxyvitamin D binding protein from intestinal cells

We have previously purified a cytosolic vitamin D metabolite binding protein (cDBP) from rat enterocytes, which has characteristics distinct from other vitamin D binding proteins. In these studies, we demonstrate that cDBP in a semi-purified fraction from human intestinal cells (Caco-2 cells) binds 25-hydroxyvitamin D (25OHD) with at least a 1000-fold greater affinity than 1, 25-dihydroxyvitamin D (1,25(OH)(2)D) or 24,25-dihydroxyvitamin D. Treatment of cells with 1,25(OH)(2)D reduced 25OHD binding to approximately one third that of the untreated cells (0.42 CPM/mg total protein vs 1.34 CPM/mg total protein, respectively). Finally, the cDBP is not immunoreactive to antibodies prepared against the C-terminus of the nuclear vitamin D receptor (VDR). In summary, cDBP bound 25OHD with greater affinity than either 1,25(OH)(2)D or 24,25 dihydroxyvitamin D, the cytosolic binding activity was down-regulated by 1,25(OH)(2)D and cBDP is distinct from the nuclear VDR.

Inositol hexaphosphate reduces 12-O-tetradecanoylphorbol-13-acetate-induced ornithine decarboxylase independent of protein kinase C isoform expression in keratinocytes

High-fiber diets have been shown to have beneficial effects on preventing tumorigenesis. Inositol hexaphosphate (InsP6 or phytic acid) which is a fiber-associated component of cereals and legumes has been demonstrated to inhibit cell proliferation and enhance cell differentiation, indicating its potential for chemopreventive roles. In this study, we investigated the effect of InsP6 on 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced ornithine decarboxylase (ODC) activity, an essential event in tumor promotion in HEL-30 cells, a murine keratinocyte cell line and SENCAR mouse skin. ODC activity was significantly reduced by 0.5 mM InsP6 in keratinocytes (P < 0.01). Furthermore, when mouse skin was treated with 10 mM InsP6, ODC induction was significantly inhibited (P < 0.05). In addition, the expression of TPA-induced c-myc mRNA was significantly inhibited by the same InsP6 treatments in HEL-30 cells and CD-1 mouse skin (P < 0.01). No changes in protein kinase C (PKC) isoform expression and phorbol dibutyrate binding due to InsP6 treatment were found in HEL-30 cells. These results indicate that InsP6 reduces TPA-induced ODC activity independent of PKC isoform expression.

Dietary conjugated linoleic acid normalizes impaired glucose tolerance in the Zucker diabetic fatty fa/fa rat

Conjugated linoleic acid (CLA) is a naturally occurring fatty acid which has anti-carcinogenic and anti-atherogenic properties. CLA activates PPAR alpha in liver, and shares functional similarities to ligands of PPAR gamma, the thiazolidinediones, which are potent insulin sensitizers. We provide the first evidence that CLA is able to normalize impaired glucose tolerance and improve hyperinsulinemia in the pre-diabetic ZDF rat. Additionally, dietary CLA increased steady state levels of aP2 mRNA in adipose tissue of fatty ZDF rats compared to controls, consistent with activation of PPAR gamma. The insulin sensitizing effects of CLA are due, at least in part, to activation of PPAR gamma since increasing levels of CLA induced a dose-dependent transactivation of PPAR gamma in CV-1 cells cotransfected with PPAR gamma and PPRE X 3-luciferase reporter construct. CLA effects on glucose tolerance and glucose homeostasis indicate that dietary CLA may prove to be an important therapy for the prevention and treatment of NIDDM.

Calcium bioavailability of vegetarian diets in rats: potential application in a bioregenerative life-support system

Calcium bioavailability of vegetarian diets containing various proportions of candidate crops for a controlled ecological life-support system (CELSS) was determined by femur 45Ca uptake. Three vegetarian diets and a control diet were labeled extrinsically with 45Ca and fed to 5-wk old male rats. A fifth group of rats fed an unlabeled control diet received an intraperitoneal (IP) injection of 45Ca. There was no significant difference in mean calcium absorption of vegetarian diets (90.80 +/- 5.23%) and control diet (87.85 +/- 5.25%) when calculated as the percent of an IP dose. The amounts of phytate, oxalate, and dietary fiber in the diets did not affect calcium absorption.

Calcium bioavailability from bovine milk and dairy products in premenopausal women using intrinsic and extrinsic labeling techniques

Stable isotopes were used to compare calcium fractional absorption from intrinsically and extrinsically labeled bovine milk as well as intrinsically labeled dairy product and cheese analogue. Healthy Caucasian women were fed a controlled diet for 4 d during the follicular phase of their menstrual cycle. With breakfast on the third day, participants ingested milk containing 44Ca (intrinsic) and 42CaCl2 (extrinsic) or dairy products containing 44Ca. Total feces were collected for 2 d prior to and 10 d after isotope ingestion. Polyethylene glycol was administered to monitor completeness of fecal collections. Total calcium was determined by atomic absorption spectrophotometry, and isotopic abundance was determined by high resolution fast atom bombardment mass spectrometry. Fractional absorption was determined as the difference between the administered isotopic dose and the quantity of 44Ca or 42Ca excreted in feces. The fractional absorption of calcium from milk was not affected by the method of labeling, lactose content, fermentation or the chemical form of calcium in dairy products or cheese analogue.

Dietary conjugated linoleic acid modulation of phorbol ester skin tumor promotion

The fatty acid derivative conjugated dienoic linoleate (CLA) has been shown to inhibit initiation and postinitiation stages of carcinogenesis in several experimental animal models. The goal of the present study was to determine the role of increasing levels of dietary CLA in mouse skin tumor promotion elicited by 12-O-tetradecanoylphorbol-13-acetate (TPA). Mice were fed control (no CLA) diet during initiation, then switched to diets containing 0.0%, 0.5%, 1.0%, or 1.5% (wt/wt) CLA during skin tumor promotion by TPA. Body weights of mice fed 0.5%, 1.0%, or 1.5% CLA were similar to each other but were significantly lower (p < 0.05) than weights of mice fed no CLA (0.0%) throughout promotion. A reduction in papilloma incidence was observed in mice fed 1.5% CLA from Weeks 8 to 24 compared with mice fed diets containing 0.0-1.0% CLA (p < 0.05). Twenty-four weeks after tumor promotion was begun, diets containing 1.0% and 1.5% CLA inhibited tumor yield (4.94 and 4.35 tumors/mouse, respectively) compared with diets without CLA (0.0% CLA, 6.65 tumors/mouse, p < 0.05) or 0.5% CLA (5.92 tumors/mouse, p < 0.05). These data indicate that CLA inhibits tumor promotion in a manner that is independent of its anti-initiator activity. Further studies are warranted in identifying cellular mechanisms that are likely to be involved with the antipromoter effects of CLA.