p16 Represses DNA Damage Repair via a Novel Ubiquitin-Dependent Signaling Cascade

Squamous cell carcinoma driven by human papillomavirus (HPV) is more sensitive to DNA-damaging therapies than its HPV-negative counterpart. Here, we show that p16, the clinically used surrogate for HPV positivity, renders cells more sensitive to radiotherapy via a ubiquitin-dependent signaling pathway, linking high levels of this protein to increased activity of the transcription factor SP1, increased HUWE1 transcription, and degradation of ubiquitin-specific protease 7 (USP7) and TRIP12. Activation of this pathway in HPV-positive disease led to decreased homologous recombination and improved response to radiotherapy, a phenomenon that can be recapitulated in HPV-negative disease using USP7 inhibitors in clinical development. This p16-driven axis induced sensitivity to PARP inhibition and potentially leads to "BRCAness" in head and neck squamous cell carcinoma (HNSCC) cells. Thus, these findings support a functional role for p16 in HPV-positive tumors in driving response to DNA damage, which can be exploited to improve outcomes in both patients with HPV-positive and HPV-negative HNSCC.

SIGNIFICANCE

In HPV-positive tumors, a previously undiscovered pathway directly links p16 to DNA damage repair and sensitivity to radiotherapy via a clinically relevant and pharmacologically targetable ubiquitin-mediated degradation pathway.

Indoleamine 2,3-dioxygenase 1 inhibition targets anti-PD1-resistant lung tumors by blocking myeloid-derived suppressor cells

Indoleamine 2,3-dioxygenase 1 (IDO1), involved in the catabolism of tryptophan (Trp) to kynurenine (Kyn) is an important regulator of tumor-mediated immunosuppression implicated in resistance to anti-PD1 immunotherapy. We investigated the role of IDO1 in an anti-PD1-resistant lung cancer model (344SQ_R) compared to the parental 344SQ tumors (344SQ_P). IDO1 was overexpressed in tumor-infiltrating leukocytes, and plasma Kyn levels were increased, in 344SQ_R vs. 344SQ_P. The IDO1 inhibitor INCB023843 retarded tumor growth and reduced lung metastases in 344SQ_R. IDO1 was expressed at higher levels in F4/80⁺Gr1^intCD11b⁺ myeloid-derived suppressor cells (MDSCs) that were prominent in 344SQ_R. The INCB023843 reduced IDO1 expression and percentages of these MDSCs while increasing CD8⁺ T cells infiltration, hence reactivating antitumor T-cell responses in 344SQ_R. Therefore, IDO1 inhibition holds promise for treating lung cancer that does not respond to anti-PD1 therapy.

Targeting anti-PD1-resistant tumors via indoleamine 2,3-dioxygenase 1 (IDO1) inhibition

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Background: Anti-PD1 inhibitors are effective in only a subset of lung cancers, and many that respond later develop resistance. We recently found in a mouse model of anti-PD1 resistance that tumor-infiltrating lymphocytes (TILs) overexpressed indoleamine 2,3-dioxygenase 1 (IDO1), a rate-limiting step in the catabolism of tryptophan (Trp) to kynurenine (Kyn) often implicated in immunosuppression. We tested whether inhibiting IDO would affect anti-PD1 mediated resistance. Methods: We used our anti-PD1-resistant lung cancer model (344SQ_R), which involved treating the parental 344SQ cells (344SQ_P) with anti-PD1 antibody followed by passage in 129SV/ev mice. We treated 344SQ_P and 344SQ_R mice with or without a selective IDO1 inhibitor (INCB023843) and measured tumor growth and lung metastasis. Plasma Trp and Kyn levels were tested by liquid chromatography–tandem mass spectrometry. TILs from blood and tumor-draining lymph nodes were isolated, analyzed by flow cytometry, and RNA was extracted for qPCR. Plasma C-C motif chemokine 22 (CCL22) levels were tested by ELISA. Data were analyzed with Prism 5.0 (GraphPad Software) and Flowjo V-10. Results: In untreated mice, IDO1 expression was 12 times higher in TILs from 344SQ_R mice than 344SQ_P mice, and mean plasma Kyn and Kyn/Trp levels were 3 times higher in 344SQ_R than in 344SQ_P. IDO inhibition was effective only in the PD1-resistant mice, reducing both tumor growth and lung metastasis. A subpopulation of myeloid-derived suppressor cells (Gr1int/lo CD11b+F4/80+) showed the greatest increase in IDO1 expression when comparing 344SQ_R to 344SQ_P and decreased after INCB023843 treatment only in 344SQ_R. INCB023843 also increased infiltrating CD8+ T cells, decreased CCL22 and regulatory T cells only in 344SQ_R tumors. Conclusions: Our results suggest that IDO1 is overexpressed in TILs from tumors resistant to anti-PD1 therapy; that a high plasma Kyn/Try ratio may be a marker of anti-PD1 resistance; and that IDO1 inhibition could be a promising approach for treating lung cancer that does not respond to anti-PD1 therapy.

Suppression of Type I IFN Signaling in Tumors Mediates Resistance to Anti-PD-1 Treatment That Can Be Overcome by Radiotherapy

Immune checkpoint therapies exhibit impressive efficacy in some patients with melanoma or lung cancer, but the lack of response in most cases presses the question of how general efficacy can be improved. In addressing this question, we generated a preclinical tumor model to study anti-PD-1 resistance by in vivo passaging of Kras-mutated, p53-deficient murine lung cancer cells (p53^R172HΔg/+K-ras^LA1/+ ) in a syngeneic host exposed to repetitive dosing with anti-mouse PD-1 antibodies. PD-L1 (CD274) expression did not differ between the resistant and parental tumor cells. However, the expression of important molecules in the antigen presentation pathway, including MHC class I and II, as well as β2-microglobulin, were significantly downregulated in the anti-PD-1-resistant tumors compared with parental tumors. Resistant tumors also contained fewer CD8⁺ (CD8α) and CD4⁺ tumor-infiltrating lymphocytes and reduced production of IFNγ. Localized radiotherapy induced IFNβ production, thereby elevating MHC class I expression on both parental and resistant tumor cells and restoring the responsiveness of resistant tumors to anti-PD-1 therapy. Conversely, blockade of type I IFN signaling abolished the effect of radiosensitization in this setting. Collectively, these results identify a mechanism of PD-1 resistance and demonstrate that adjuvant radiotherapy can overcome resistance. These findings have immediate clinical implications for extending the efficacy of anti-PD-1 immune checkpoint therapy in patients. Cancer Res; 77(4); 839-50. ©2016 AACR.

TRIP12 as a mediator of human papillomavirus/p16-related radiation enhancement effects

Patients with human papillomavirus (HPV)-positive head and neck squamous cell carcinoma (HNSCC) have better responses to radiotherapy and higher overall survival rates than do patients with HPV-negative HNSCC, but the mechanisms underlying this phenomenon are unknown. p16 is used as a surrogate marker for HPV infection. Our goal was to examine the role of p16 in HPV-related favorable treatment outcomes and to investigate the mechanisms by which p16 may regulate radiosensitivity. HNSCC cells and xenografts (HPV/p16-positive and -negative) were used. p16-overexpressing and small hairpin RNA-knockdown cells were generated, and the effect of p16 on radiosensitivity was determined by clonogenic cell survival and tumor growth delay assays. DNA double-strand breaks (DSBs) were assessed by immunofluorescence analysis of 53BP1 foci; DSB levels were determined by neutral comet assay; western blotting was used to evaluate protein changes; changes in protein half-life were tested with a cycloheximide assay; gene expression was examined by real-time polymerase chain reaction; and data from The Cancer Genome Atlas HNSCC project were analyzed. p16 overexpression led to downregulation of TRIP12, which in turn led to increased RNF168 levels, repressed DNA damage repair (DDR), increased 53BP1 foci and enhanced radioresponsiveness. Inhibition of TRIP12 expression further led to radiosensitization, and overexpression of TRIP12 was associated with poor survival in patients with HPV-positive HNSCC. These findings reveal that p16 participates in radiosensitization through influencing DDR and support the rationale of blocking TRIP12 to improve radiotherapy outcomes.

Inhibition of EGFR or IGF-1R signaling enhances radiation response in head and neck cancer models but concurrent inhibition has no added benefit

Interaction between the epidermal growth factor receptor (EGFR) and the insulin-like growth factor receptor (IGF-1R) has been well established in many cancer types. We investigated the effects of cetuximab (EGFR antibody) and IMC-A12 (IGF-1R antibody) on the response of head and neck squamous cell carcinoma (HNSCC) to radiation therapy (RT). The effects of cetuximab and IMC-A12 on cell viability and radiosensitivity were determined by clonogenic cell survival assay. Formation of nuclear γ-H2AX and 53BP1 foci was monitored by immunofluorescence. Alterations in target signaling were analyzed by Western blots. In vivo tumor growth delay assay was performed to determine the efficacy of triple therapy with IMC-A12, cetuximab, and RT. In vitro data showed that cetuximab differentially affected the survival and the radiosensitivity of HNSCC cells. Cetuximab suppressed DNA repair that was evident by the prolonged presence of nuclear γ-H2AX and 53BP1 foci. IMC-A12 did not have any effect on the cell survival. However, it increased the radiosensitivity of one of the cell lines. EGFR inhibition increased IGF-1R expression levels and also the association between EGFR and IGF-1R. Addition of IMC-A12 to cetuximab did not increase the radiosensitivity of these cells. Tumor xenografts exhibited enhanced response to RT in the presence of either cetuximab or IMC-A12. Concurrent treatment regimen failed to further enhance the tumor response to cetuximab and/or RT. Taken together our data suggest that concomitant inhibition of both EGFR and IGF-1R pathways did not yield additional therapeutic benefit in overcoming resistance to RT.

Abstract 4895: P16INK4A, a surrogate marker of HPV infection and prognosis for head and neck cancer, delays DNA damage repair and enhances radiation response

Human papillomavirus (HPV) type 16 is a major cause of oropharyngeal carcinoma (OPC). P16INK4A has been suggested to be a reliable surrogate marker of HPV-associated OPC with 100% sensitivity and about 80% specificity. Increasing data showed tumor HPV positivity or p16 expression was strongly associated with significantly better prognosis in patients with OPC. As a tumor suppressor gene, p16 has biological functions including regulation of cell cycle progression at the G1/S boundary, angiogenesis, cell senescence, tumor invasion, cell spreading, apoptosis and anoikis. The present study was undertaken to assess the role of p16 in regulating tumor radioresponse and the underlying mechanisms in OPC cell lines.

OPC cell lines HN-5 (HPV and p16 negative) and UMSCC-47 (HPV and p16 positive) were used. P16 overexpressing HN-5 cells and shRNA p16 knockdown UMSCC-47 cells were generated using lentivirus vectors. Treatment endpoint was clonogenic cell survival (CSA) determined 10-12 days (for HN5) or 17-20 days (for UMSCC-47) after exposing the cells to 2-10 Gy single doses of γ-radiation (IR). Compared with the control (scramble) cells, p16-overexpressing HN5 cells had significantly higher radiosensitivity (by a factor of 1.56 at 0.1 cell survival fraction); whereas, p16-knockingdown UMSCC-47 cells had less radiosensitivity (by a factor of 1.23 at 0.1 cell survival fraction). Overexpressing P16 in HN-5 cells significantly prolonged the presence of radiation-induced double-strand breaks detected on the basis of 53BP1 foci at 24h after 4 Gy IR. To directly gauge damaged DNA, an alkaline comet assay to detect both single- and double-strand DNA breaks was performed. P16 overexpressing HN-5 cells exhibited a 2.09-fold increase in the comet ‘tail moment’ 48 hours after IR. This finding was supported by increased expression of 53BP1 analyzed by Western blot.

In conclusion, other than being a robust surrogate marker for tumor control and survival outcome, our findings demonstrated that p16 also functions as a potent radiation sensitizer. The major underlying mechanism of p16 regulating radiosensitivity is by inhibition of DNA damage repair.

Citation Format: Li Wang, Peijing Zhang, David P Molkentine, Hailong Piao, Chunyan Chen, Jessica M Molkentine, Jinsong Zhang, David R Valdecanas, Heath Skinner, Thomas A Buchholz, Junjie Chen, Li Ma, Kathy A Mason, Kie-kian Ang, Raymond E Meyn. P16INK4A, a surrogate marker of HPV infection and prognosis for head and neck cancer, delays DNA damage repair and enhances radiation response. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4895. doi:10.1158/1538-7445.AM2014-4895

Abstract 857: Preclinical evaluation: efficacy of DI17E6, a therapeutic antibody against alpha v integrins, compared to cilengitide in sensitizing human cancers to radiation therapy

Purpose: Integrins are implicated in resistance of solid tumors to radiation therapy, suggesting that their inhibition would enhance therapeutic efficacy. We investigated the efficacy of DI17E6, a therapeutic antibody targeting alpha v (αv) integrins, in enhancing the radiosensitivity of non-small cell lung carcinoma (NSCLC) and head & neck cancer (HNSCC) cells using in vitro and in vivo models, and compared to the previously reported effects of the cyclic peptide cilengitide (inhibits αvβ3 and αvβ5 integrins).

Methods: NSCLC lines (A549 and H460) and HNSCC lines (FaDu and HN-5) were examined. Basal level of αv integrin was assessed by viable cell flow-cytometry and by Western blot. The effects of DI17E6 on cell viability were determined by MTS assay, and on cellular radiosensitivity by clonogenic cell survival assay after exposing the cells to γ-radiation with or without DI17E6. In vivo effect of DI17E6 on radioresponse of xenografts was evaluated by tumor growth delay assay. DI17E6 was given i.p.; as a single loading dose of 180 mg/kg followed by weekly doses of 10, 30 or 100 mg/kg given for 6 weeks; fractionated doses of local tumor irradiation was delivered using 137Cs γ-ray source (2 Gy daily for 7 days). When combined, the loading dose of DI17E6 was given either 4 h before or after the first radiation dose.

Results: DI17E6 (0.01-10 µg/ml, 24 h) had a minimal effect on the cell viability. However, DI17E6 reduced the plating efficiency of A549, H460 and FaDu with no effect on HN-5 cells. When combined with radiation, DI17E6 enhanced the radiosensitivity of NSCLC cells but not the HNSCC cells. These data are consistent with previously observed effects of cilengitide in vitro. In vivo experiments with A549 xenografts showed that DI17E6 as a single agent had no antitumor activity, but in combination with radiation it suppressed the tumor growth in a schedule- and dose-dependent manner. These data were compared to the previously reported effect of cilengitide, which did not enhance the response of A549 xenografts to radiation therapy. DI17E6 has an extended pharmacokinetics (with a half-life of >7 days) and blocks more αv integrins than cilengitide. The results imply that when αvβ3 and αvβ5 integrins were inhibited by cilengitide either the duration of blockade was insufficient, or that other αv integrins may have provided tumor growth advantage. In vivo studies on other tumor types are underway.

Conclusions: Inhibition of αv integrins by DI17E6 in combination with radiation enhanced radiosensitivity of NSCLC cell lines in vitro and in vivo enhanced A549 tumor xenograft response to radiation in mice. These results suggest that DI17E6 may improve the treatment outcome of patients with NSCLC when combined with radiotherapy in a clinical setting.

Supported by EMD Serono Merck KGaA, Germany

Citation Format: Amit A. Deorukhkar, David P. Molkentine, David R. Valdecanas, Kathryn A. Mason, Uma Raju. Preclinical evaluation: efficacy of DI17E6, a therapeutic antibody against alpha v integrins, compared to cilengitide in sensitizing human cancers to radiation therapy. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 857. doi:10.1158/1538-7445.AM2014-857

Noncovalent assembly of targeted carbon nanovectors enables synergistic drug and radiation cancer therapy in vivo

Current chemotherapeutics are characterized by efficient tumor cell-killing and severe side effects mostly derived from off-target toxicity. Hence targeted delivery of these drugs to tumor cells is actively sought. In an in vitro system, we previously demonstrated that targeted drug delivery to cancer cells overexpressing epidermal growth factor receptor (EGFR+) can be achieved by poly(ethylene glycol)-functionalized carbon nanovectors simply mixed with a drug, paclitaxel, and an antibody that binds to the epidermal growth factor receptor, cetuximab. This construct is unusual in that all three components are assembled through noncovalent interactions. Here we show that this same construct is effective in vivo, enhancing radiotherapy of EGFR+ tumors. This targeted nanovector system has the potential to be a new therapy for head and neck squamous cell carcinomas, deserving of further preclinical development.

Abstract A145: EGFR-targeting of carbon nanovectors loaded with paclitaxel improves their antitumor efficacy and radiosensitization of head and neck squamous cell carcinoma in vivo

Nanoparticels have been researched broadly as new generation of diagnostics, imaging agents, and drugs for detecting and treating cancer. We previously developed PEGylated small hydrophilic carbon clusters (PEG-HCCs) and reported that PEG-HCCs conjugated with paclitaxel (PTX/PEG-HCCs) is a stable effective drug delivery system with minimal toxicity. Here, we describe the establishment of targeted nanovectors by simply mixing PTX/PEG-HCCs with cetuximab (ImClone Systems), an anti-epidermal growth factor receptor (EGFR) monoclonal antibody. The specificity of this EGFR targeted method of delivery of PTX/PEG-HCCs was demonstrated in mice implanted subcutaneously on opposing flanks with EGFR expressing, OSC-19 (head and neck squamous cell carcinoma: HNSCC) cells and non-EGFR-expressing MCF-7 cells in a nude mouse. The targeted nanovector system, Cet/PTX/PEG-HCCs, showed greater efficacy superior than PTX/PEG-HCCs on OSC-19 tumor growth, but not on MCF-7 tumors. Cet/PTX/PEG-HCCs also showed greater growth inhibition prolonged survival compared to PTX or PTX/PEG-HCCs in an orthotopic nude mouse model of human HNSCC. These results suggested that Cet/PTX/PEG-HCCs can targeted to HNSCC overexpressing EGFR cells. In addition, Cet/PTX/PEG-HCCs were found to radiosensitize HNSCC cells both in vitro and in vivo. Cet/PTX/PEG-HCCs plus radiation inhibited tumor growth and prolonged survival in vivo. This work is highly significant as success would allow for targeted chemotherapy for HNSCC by simply mixing commercially available drugs and antibodies with a nanovector solution.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr A145.

Abstract 2509: Preclinical evaluation of the effects of cilengitide, an inhibitor of integrins, in sensitizing human solid cancer xenografts to radiation

Purpose: Integrins are implicated in resistance of solid tumors to therapies, including radiation therapy, suggesting that their inhibition would enhance efficacy of tumor therapy. Because cilengitide, a cyclic Arg-Gly-Asp (RGD)-derived peptide, inhibits αVβ3 and αVβ5 integrins, we investigated the efficacy of cilengitide in enhancing in vitro cancer cell radiosensitivity and in vivo radioresponse of cancer xenografts.

Methods: Three non-small cell lung carcinoma lines (NSCLCs) (H460, A549 and H1299) and five head and neck squamous cell carcinoma lines (HNSCCs) (FaDu, SCC-15, SCC-25, HN-5 and UMSCC-1) cell lines were used for in vitro experiments. Of these, H460 and FaDu were used for in vivo testing when grown as xenografts in nude mice. The effects of cilengitide (1 – 50 µg/ml, 24 h) on in vitro cell viability was determined by MTS assay and on cellular radiosensitivity by clonogenic cell survival assay after exposing the cells to graded single doses of γ-radiation with or without cilengitide (given 1 h before and continued for 23 h after irradiation). In vivo effect of cilengitide on radioresponse of xenografts was assessed by tumor growth delay. When tumor xenografts reached 7 mm in diameter cilengitide treatment (30 or 60 mg/d/5days) was initiated followed by a single dose of 15 Gy local radiation (using 137Cs γ-ray source), when the tumors reached 8 mm.

Results: Cilengitide (5µg/ml, 24 h) reduced in vitro viability of 7 out of 8 cell lines tested, which ranged between 71.4 ± 2.2% (SCC-15) and 27.8 ± 4.2% (H1299). In general, NSCLCs were more sensitive to cilengitide than HNSCCs. When combined with radiation, cilengitide significantly enhanced the radiosensitivity of all 3 NSCLC, by enhancement factors of 1.35 for H460, 1.56 for A549 and 1.3 for H1299. In contrast, cilengitide exerted only an additive effect on radiosensitivity of HNSCC lines. In vivo experiments showed that cilengitide as a single agent had no antitumor activity, but in combination with radiation it significantly enhanced response of both H460 (NSCLC) and FaDu (HNSCC) tumor xenografts. The enhancement factors were 1.7 for H460 and 2.0 for FaDu.

Conclusion: The results showed that cilengitide reduced in vitro cell viability of lung and head and neck cancer cells but had no effect on tumor growth in vivo. When combined with radiation, the drug enhanced radiosensitivity of lung but not head and neck carcinoma cells. In contrast, cilengitide was highly effective in enhancing radiation response of both lung (H460) and head and neck (FaDu) tumor xenografts. These results suggest that cilengitide has potential to improve the treatment outcome of patients with NSCLC and HNSCC when combined with radiotherapy. Mechanistic studies addressing cilengitide-radiation interactions both in vitro and in vivo are underway.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2509. doi:10.1158/1538-7445.AM2011-2509

Vandetanib restores head and neck squamous cell carcinoma cells' sensitivity to cisplatin and radiation in vivo and in vitro

PURPOSE

We investigated whether vandetanib, an inhibitor of the tyrosine kinase activities of vascular endothelial growth factor receptor-2 (VEGFR-2), epidermal growth factor receptor (EGFR), and rearranged during transfection (RET), could augment the antitumor activity of radiation with or without cisplatin in preclinical in vitro and in vivo models of human head and neck squamous cell carcinoma (HNSCC).

EXPERIMENTAL DESIGN

OSC-19 and HN5 HNSCC cells that were cisplatin and radioresistant were treated with vandetanib, cisplatin, and radiation alone or in combination in vitro and in vivo using an orthotopic nude mouse model. Treatment effects were assessed using clonogenic survival assay, tumor volume, bioluminescence imaging, tumor growth delay, survival, microvessel density, tumor and endothelial cell apoptosis, and EGFR and Akt phosphorylation data.

RESULTS

Vandetanib plus cisplatin radiosensitized HNSCC cells in vitro and in vivo. The combination treatment with vandetanib, cisplatin, and radiation was superior to the rest of treatments (including the double combinations) in antitumoral effects, prolonging survival, decreasing cervical lymph node metastases in vivo. It also increased both tumor and tumor-associated endothelial cell apoptosis and decreased microvessel density in vivo. An analysis of tumor growth delay data revealed that vandetanib plus cisplatin enhanced radioresponse in vivo. All vandetanib-containing treatments inhibited EGFR and Akt phosphorylation in vitro and in vivo.

CONCLUSION

The addition of vandetanib to combination therapy with cisplatin and radiation was able to effectively overcome cisplatin and radioresistance in in vitro and in vivo models of HNSCC. Further study of this regimen in clinical trials may be warranted.

Abstract 369: Treatment with vandetanib can overcome resistance of head and neck squamous cell carcinoma cells to cisplatin and radiation in an orthotopic animal model

Objective

Despite advances in treatment, the survival of patients with Head and neck squamous cell carcinoma (HNSCC) has not significantly improved over the past several decades. While concurrent chemotherapy with cisplatin and radiation has become a standard of care for many patients with HNSCC, some HNSCCs are resistant and persist/recur after this type of treatment. To determine whether we could overcome this resistance, we evaluated whether vandetanib, an inhibitor of tyrosine kinase activities of vascular endothelial growth factor receptor-2 (VEGFR-2) and epidermal growth factor receptor (EGFR) could augment the anti-tumor activity of concurrent chemotherapy with cisplatin and radiation in pre-clinical in vitro and in vivo models of human HNSCC

Method

To determine the effects of cisplatin and irradiation on HNSCC cell proliferation in vitro, we first performed MTT assays with cisplatin and clonogenic survival assay with radiation using 18 HNSCC cell lines. We chose HN5 as a relatively cisplatin & irradiation-resistant cell line. Clonogenic survival assays with irradiaton + cisplatin on HN5 were also performed to see the interaction between cisplatin and irradiation. We used an orthotopic nude mouse model of HNSCC by injecting human HN5 lines into the tongue of the mouse. Nine days after cell inoculation, the animals were randomly divided into 8 groups to receive vehicle, cisplatin (1 mg/kg, intravenously, once a week for 2 weeks), vandetanib (20 mg/kg, daily oral gavage, for 2 weeks), vandetanib plus cisplatin, irradiation (5 Gy at day 10), cisplatin plus irradiation, vandetanib plus irradiation, or vandetanib plus cisplatin plus irradiation. We assessed in vivo effects of the treatment by tumor size.

Results

Cisplatin GI50 values spanned a 10-fold range from 1.031 to 10.58 μM and the surviving fraction at 2 Gy (SF2) values ranged from 0.22 to 0.8 with 18 HNSCC cell lines. The GI50 value of vandetanib was 9.084 μM and the SF2 value was 0.75 for HN5 which indicated this line was a relatively cisplatin and irradiation-resistant cell line. In the clonogenic survival assay with iradiation and cisplatin on HN5, cisplatin did not improve radiosensitivity. At day 35 after cell inoculation, the treatment with cisplatin alone, vandetanib alone, vandetanib plus cisplatin, irradiation alone, cisplatin plus irradiation, vandetanib plus irradiation, and vandetanib plus cisplatin plus irradiation reduced tumor size by 5.0% (P=0.6843), 41.9% (P=0.0370), 49.2% (P <0.0001), 8.28% (P =0.3190), 30% (P =0.0926), 52.1% (P =0.0001) and 63.9% (P <0.0001), respectively, compared with control mice.

Conclusion

These data indicate that the addition of vandetanib to combination therapy with cisplatin and radiation may be effective in overcoming cisplatin-radiation resistance HNSCC and has the potential as a novel therapeutic startegy for patients with advanced HNSCC.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 369.