Broad-spectrum Receptor Tyrosine Kinase Research Articles

Sunitinib Combined with Th1 Cytokines Potentiates Apoptosis in Human Breast Cancer Cells and Suppresses Tumor Growth in a Murine Model of HER-2pos Breast Cancer.

Although immune-based therapies have made remarkable inroads in cancer treatment, they usually must be combined with standard treatment modalities, including cytotoxic drugs, to achieve maximal clinical benefits. As immunotherapies are further advanced and refined, considerable efforts will be required to identify combination therapies that will maximize clinical responses while simultaneously decreasing the unpleasant and sometimes life-threatening side effects of standard therapy. Over the last two decades, evidence has emerged that Th1 cytokines can play a central role in protective antitumor immunity and that combinations of Th1 cytokines can induce senescence and apoptosis in cancer cells. To explore the possibility of combining targeted drugs with Th1-polarizing vaccines, we undertook a study to examine the impact of combining Th1 cytokines with the relatively broad-spectrum receptor tyrosine kinase antagonist, sunitinib. We found that when a panel of five phenotypically diverse human breast cancer cell lines was subjected to treatment with sunitinib plus recombinant Th1 cytokines IFN-γ and TNF-α, synergistic effects were observed across a number of parameters including different aspects of apoptotic cell death. Interestingly, sunitinib was found to have a profoundly suppressive effect of T cell's capacity to secrete IFN-γ, indicating that in vivo use of this drug may hinder robust Th1 responses. Nonetheless, this suppression was circumvented in a mouse model of HER-2pos breast disease by supplying recombinant interferon-gamma to achieve a combination therapy significantly more potent than either agent.

Abstract 3812: Overcoming de novo and acquired modes of cetuximab resistance by broad-spectrum receptor tyrosine kinase inhibitors

Abstract MEK inhibition has been shown to delay emergence of cetuximab resistance in colorectal cancer (CRC) (Nat Commun 22;6:8305, 2015). By exploiting a novel 3D culture system, we herein show that three broad-spectrum tyrosine kinase inhibitors overcome de novo and acquired resistance to cetuximab. By culturing a CRC cell line, HCA-7 in 3D in type I collagen, we previously identified two novel modes of cetuximab resistance. In 3D culture, HCA-7-derived CC are sensitive to cetuximab, while SC exhibit de novo cetuximab resistance (PNAS 114:E2852-E2861, 2017). Continuous exposure of CC to cetuximab resulted in colonies that acquired resistance to cetuximab, designated CC-CR, which was dependent in part on increased levels of lncRNA MIR100HG that leads to increased WNT signaling (Nat Med 23:1331-1341, 2017). We previously showed increased MET and RON tyrosine phosphorylation in SC cells and that MET/RON inhibitor, crizotinib overcomes SC cetuximab resistance. We now show that crizotinib also overcomes acquired cetuximab resistance in CC-CR. A phospho-RTK array showed increased phosphorylation of several RTKs, including MET and RON, in SC and CC-CR cells compared to cetuximab-sensitive CC counterparts. Furthermore, other multi-RTK inhibitors cabozantinib and BMS-777607 helped overcome cetuximab resistance, as measured by 3D colony growth and activation state of key signaling molecules. Conversely, addition of RTK ligands HGF and NRG1 induced cetuximab resistance in CC cells, which could be blocked by addition of crizotinib and this was associated with disorganized spindle positioning during cell division, leading to multi-layering of CC cultures. By FACS analysis, we observed increased cell cycle arrest in G1 phase in SC and CC-CR cultures treated with cetuximab and crizotinib. Furthermore, we show that crizotinib overcomes cetuximab resistance in vivo in SC nude mice xenografts. Finally, in a direct comparison between vertical suppression (EGFR/MEK inhibition) and parallel inhibition (EGFR/multi-RTK inhibition), we observed a higher degree of synergy with the latter strategy. The non-overlapping toxicities of cetuximab and crizotinib warrants consideration for its clinical deployment. Note: This abstract was not presented at the meeting. Citation Format: Bhuminder Singh, Ramona Graves-Deal, Galina Bogatcheva, Robert J. Coffey. Overcoming de novo and acquired modes of cetuximab resistance by broad-spectrum receptor tyrosine kinase inhibitors [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 3812.

Broad-spectrum receptor tyrosine kinase inhibitors overcome de novo and acquired modes of resistance to EGFR-targeted therapies in colorectal cancer.

It is increasingly appreciated that 3D cultures are more predictive of in vivo therapeutic efficacy than 2D cultures. Using in vitro 3D type I collagen cultures of human colorectal cancer (CRC) cell line HCA-7 derivatives CC, SC, and CC-CR, we previously identified that activation of receptor tyrosine kinases (RTKs) MET and RON contributed to resistance to the EGF receptor (EGFR)-directed therapeutic antibody cetuximab. The de novo mode of cetuximab resistance in SC cells could be overcome by crizotinib, a multi-RTK inhibitor that also targets MET and RON. We now show that crizotinib also overcomes acquired cetuximab resistance in CC-CR cells. Phospho-RTK array analysis showed increased phosphorylation of several RTKs, including MET and RON, in SC and CC-CR cells compared to cetuximab-sensitive CC counterparts. Furthermore, other multi-RTK inhibitors cabozantinib and BMS-777607 helped overcome cetuximab resistance, as measured by 3D colony growth and activation state of key signaling molecules. Conversely, addition of RTK ligands HGF and NRG1 induced cetuximab resistance in CC cells, which could be blocked by addition of crizotinib. We further determined the mechanism of the cooperative effect of cetuximab and crizotinib by FACS analysis and observed increased cell cycle arrest in G1 phase in cetuximab-resistant CRC 3D cultures. Finally, we show that crizotinib overcomes cetuximab resistance in vivo in SC nude mice xenografts. Thus, our work shows that multi-RTK inhibition strategy is a potent, broadly applicable strategy to overcome resistance to EGFR-targeted therapeutics in CRC and highlights the relevance of 3D cultures in these studies.Statement of implication: Using in vitro 3D CRC cultures and in vivo CRC xenografts, we show that parallel inhibition of multiple RTKs with small molecule inhibitors overcomes de novo and acquired resistance to EGFR-directed therapies in CRC.

Abstract 5036: Elucidating an oncogenic role of an extracellular matrix protein, Agrin, in hepatocellular carcinoma

Abstract Hepatocellular carcinoma (HCC) is one of the most fatal cancers worldwide. Despite offering poor survival advantage, broad spectrum receptor tyrosine kinase inhibitors are the sole chemotherapeutic treatments for advanced stages of HCC. Hence, there is a pressing clinical need to broaden the scope of HCC treatments through the systematic identification of suitable candidate(s) overexpressed in liver cancer. Therefore, we performed a SILAC based quantitative proteomics of cell surface proteins in HCC lines and identified proteoglycan Agrin to be overexpressed and secreted in HCC. Our systematic cell biological analysis indicated a role of Agrin in maintaining focal adhesion integrity through stimulation of focal adhesion kinase (FAK). We showed that Agrin functions in cellular migration, invasion and tumor growth. However, the exact mechanisms by which Agrin's mediates liver tumorigenesis remain unknown. The present study dissects how Agrin mediated signals from the extracellular matrix are sensed by tumor cells. Our evidences reveal that Agrin binds to its co-receptor(s) Lrp4 and subsequently activates MuSK to mediate oncogenic effects through activating focal adhesions. Additionally, integrins and focal adhesions collaborate closely with Agrin in communicating ECM signals to intracellular components in multiple HCC cell lines, thereby stimulating their invasive, migratory and growth capabilities. More importantly, Lrp4-MuSK as well as integrin-FAK pathways are crucial downstream signaling axes of Agrin's functions in liver tumorigenesis. The signal transduction network initiated by Agrin activates the oncogenic program in liver by negatively regulating tumor suppressor pathways. These novel insights will have profound impact on the possibility of targeting Agrin mediated oncogenesis in HCC. Citation Format: Sayan Chakraborty, Wanjin Hong. Elucidating an oncogenic role of an extracellular matrix protein, Agrin, in hepatocellular carcinoma. [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 5036.

Pediatric Medullary Thyroid Carcinoma.

Medullary thyroid carcinoma (MTC), which originates from thyroid parafollicular C cells, accounts for 3 to 5% of thyroid malignancies. MTC occurs either sporadically or in an inherited autosomal dominant manner. Hereditary MTC occurs as a familial MTC or as a part of multiple endocrine neoplasia (MEN) type 2A and B syndromes. A strong genotype-phenotype correlation has been observed between hereditary MTC and germ-line “gain of function” mutations of the RET proto-oncogene. Most cases of pediatric MTC are hereditary whereas sporadic MTC is rare in children and is usually diagnosed in adults. Therefore, MTC in children is most often diagnosed in the course of a familial genetic investigation. The standard treatment of MTC mainly requires surgery involving total thyroidectomy and central neck node dissection before extrathyroidal extension occurs. To prevent MTC development in hereditary syndromes, prophylactic thyroidectomy is performed in presymptomatic patients. An appropriate age at which the surgery should take place is determined based upon the data from genotyping, serum calcitonin measurements, and ultrasonography. For the treatment of advanced MTC cases, the broad spectrum receptor tyrosine kinase inhibitors vandetanib and cabozantinib, which also inhibit RET, are used although they are not always effective.

Identification of Novel Therapeutic Strategies for NUP98-NSD1-Positive AML By Drug Sensitivity Profiling

BackgroundThe t(5;11)(q35;p15.5) translocation resulting in fusion of the nucleoporin NUP98 and methyltransferase NSD1 (NUP98-NSD1) genes is a recurrent aberration observed in pediatric and adult AML. The NUP98-NSD1 fusion often co-occurs with the FLT3-ITD mutation and characterizes a group of cytogenetically normal AML patients with very poor prognosis. Despite advances in the understanding of the biology of NUP98-NSD1-positive AML, its therapeutic success rate has remained low. We aimed to identify novel candidate drugs for NUP98-NSD1-positive AML by testing primary patient cells and in vitro cell models with a high-throughput drug sensitivity platform.MethodsLeukemic blasts were Ficoll separated from bone marrow (BM) aspirates of an AML patient positive for t(5;11)(q35;p15.5) and FLT3-ITD. RNA extracted from primary cells was used for RNA sequencing and gene expression analysis. NUP98-NSD1 cDNA was amplified from primary cell RNA and expressed from a lentiviral vector (LeGO-iCer2) also encoding the cerulean fluorescent marker. The NUP98-NSD1/LeGo-iCer2 and empty LeGo-iCer2 viruses were used to establish stably expressing Ba/F3 cell lines. Primary murine (BALB/c) BM cells were transduced with NUP98-NSD1 and FLT3-ITD retroviruses alone or in combination (NNF) in vitro (“preleukemic”) or passaged in vivo (“leukemic”) as previously described (Thanasopoulou et al, 2014). For screening, 309 small molecule inhibitors including FDA/EMA-approved and investigational oncology drugs were plated on 384-well plates in a 10,000-fold concentration range. Cells were dispensed on the pre-drugged plates and incubated at 37°C for 72h, and then cell viability measured using the CellTiter-Glo® luminescent assay. Drug response curves were generated and a drug sensitivity score determined (Yadav et al, 2014). Select drug sensitivity was calculated for each drug by comparing results between primary leukemic and healthy donor BM cells or between the cell constructs and empty vector transduced controls cells.ResultsPrimary patient cells and murine BM cells expressing FLT3-ITD alone or in combination with NUP98-NSD1 were selectively sensitive to specific FLT3 inhibitors (e.g. quizartinib, sorafenib and lestaurtinib), and broad-spectrum receptor tyrosine kinase inhibitors targeting FLT3-ITD (e.g. cabozantinib, crenolanib, foretinib, midostaurin, MGCD-265 and ponatinib). Furthermore, these cells were highly sensitive to checkpoint kinase 1/2- inhibitor AZD7762. The primary murine cells expressing both NUP98-NSD1 and FLT3-ITD showed higher sensitivity to all of the above-mentioned drugs compared to cells expressing either of the events alone indicating functional synergy. A very distinct drug response pattern was observed in the leukemic NNF cells cultured in vivo compared to the same cells cultured in vitro suggesting that microenvironment may also affect the observed drug responses. Interestingly, the preleukemic murine cells expressing NUP98-NSD1 with or without FLT3-ITD as well as the primary patient cells showed extreme vulnerability to BCL2/BCL-xL inhibitor navitoclax. Furthermore, primary murine cells expressing NUP98-NSD1 alone showed high select sensitivity to JAK-inhibitors ruxolitinib, BMS-911543, AZD1480 and tofacitinib indicating the fusion may stimulate JAK/STAT-signaling. Similar sensitivity was also observed in the Ba/F3-cells expressing NUP98-NSD1. In support of these findings, gene expression analyses showed high expression of anti-apoptotic factors BCL2, BCL-xL and MCL1 in the patient cells. MCL1 is regulated by STAT3 while BCL-xL is regulated by STAT5, which were also highly expressed.ConclusionsIn summary, we have observed an enhanced response to specific and non-specific FLT3 inhibitors in cells expressing NUP98-NSD1 and FLT3-ITD together compared to cells expressing either of the two alone. This coincides with previous findings that functional co-operation between NUP98-NSD1 and FLT3-ITD is important in AML (Thanasopoulou et al, 2014). We have seen high in-vitro-in-vivo correlation between primary patient cells and murine cells expressing NUP98-NSD1 and FLT3-ITD. Moreover, we have identified potential candidate compounds targeting oncogenic signaling activated by these two events. These data form a basis for clinical evaluation of candidate compounds for NUP98-NSD1-positive AML. DisclosuresPorkka:Bristol-Myers Squibb: Honoraria, Research Funding; Novartis: Honoraria, Research Funding. Heckman:Celgene: Research Funding.

Pro-MMP-9 upregulation in HT1080 cells expressing CD9 is regulated by epidermal growth factor receptor

Degradation of the surrounding extracellular matrix (ECM) by matrix metalloproteinases (MMPs) drives invasion and metastasis of cancer cells. We previously demonstrated that tetraspanin CD9 expression upregulates pro-MMP-9 expression and release and promotes cellular invasion in a human fibrosarcoma cell line (HT1080). These events were dependent upon the highly functional second extracellular loop of CD9. We report here that the epidermal growth factor receptor (EGFR) tyrosine kinase expression and activity are involved in the CD9-mediated increase in pro-MMP-9 release and cellular invasion. Pro-MMP-9 expression was significantly decreased in a dose-dependent manner using first a broad spectrum receptor tyrosine kinase inhibitor and multiple specific EGFR inhibitors in CD9-HT1080 cells. Furthermore, gefitinib treatment of CD9-HT1080 cells reduced invasion through matrigel. EGFR knockdown using short interfering RNA resulted in decreased pro-MMP-9 expression and release into the media and subsequent cellular invasion without affecting CD9 expression or localization. Conclusively, this study points to EGFR as a key mediator between CD9-mediated pro-MMP-9 release and cellular invasion of HT1080 cells.

Identification Of AML Subtype-Selective Drugs By Functional Ex Vivo Drug Sensitivity and Resistance Testing and Genomic Profiling

Introduction Adult acute myeloid leukemia (AML) exemplifies the challenges of modern cancer drug discovery and development in that molecularly targeted therapies are yet to be translated into clinical use. No effective second-line therapy exists once standard chemotherapy fails. While many genetic events have been linked with the onset and progression of AML, the fundamental disease mechanisms remain poorly understood. There is significant genomic and molecular heterogeneity among patients. Several targeted therapies have been investigated for improved second-line AML therapy but none has been approved for clinical use to date. It would be critically important to identify patient subgroups that would benefit from such therapies and to identify combinations of drugs that are likely to be effective. Methods To identify and optimize novel therapies for AML, we studied 28 samples from 18 AML patients with an individualized systems medicine (ISM) approach. The ISM platform includes functional profiling of AML patient cells ex vivo with drug sensitivity and resistance testing (DSRT), comprehensive molecular profiling as well as clinical background information. Data integration was done to identify disease- and patient-specific molecular vulnerabilities for translation in the clinic. The DSRT platform comprises 306 anti-cancer agents, each tested in a dose response series. We calculated differential drug sensitivity scores by comparing AML responses to those of control cells in order to distinguish cancer-specific drug effects. Next generation RNA- and exome-sequencing was used to identify fusion transcripts and mutations that link to drug sensitivities. Results Individual AML patient samples had a distinct drug sensitivity pattern, but unsupervised hierarchical clustering of the drug sensitivity profiles of the 28 AML patient samples identified 5 functional AML drug response subtypes. Each subtype was characterized by distinct combinations of sensitivities: Bcl-2 inhibitors (e.g. navitoclax; Group 1), JAK inhibitors (e.g. ruxolitinib) (Group 2) and MEK inhibitors (e.g. trametinib) (Groups 2 and 4), PI3K/mTOR inhibitors (e.g. temsirolimus; Groups 4 and 5), broad spectrum receptor tyrosine kinase inhibitors (e.g. dasatinib) (Groups 3, 4 and 5) and FLT3 inhibitors (e.g. quizartinib, sunitinib) (Group 5). Correlation of overall drug responses with genomic profiles revealed that RAS and FLT3 mutations were significantly linked with the drug response subgroups 4 and 5, respectively. Activating FLT3 mutations contributed to sensitivity to FLT3 inhibitors, as expected, but also to tyrosine kinase inhibitors not targeting FLT3, such as dasatinib. Hence, these data point to the potential synergistic combinatorial effects of FLT3 inhibitors with dasatinib for improved therapy outcome (Figure). Early clinical translational results based on compassionate use support this hypothesis. Therefore, by combinations of drugs we expect to see synergistic drug responses that can be translated into efficacious and safe therapies for relapsed AML cases in the clinic. Clinical application of DSRT results in the treatment of eight recurrent chemorefractory patients led to objective responses in three cases according to ELN criteria, whereas four of the remaining five patients had meaningful responses not meeting ELN criteria. After disease progression, AML patient cells showed ex vivo resistance to the drugs administered to the patients, as well as significant changes in clonal architecture during treatment response. Furthermore, we saw genomic alterations potentially explaining drug resistance, such as appearance of novel fusion genes. Summary The ISM approach represents an opportunity for improving therapies for cancer patients, one patient at the time. We show that the platform can be used to identify functional groups of AML linking to vulnerabilities to single targeted drugs and, importantly, unexpected drug combinations. This information can in turn be used for personalized medicine strategies and for creating hypotheses to be explored in systematic clinical trials, both for approved and investigational drugs. Disclosures: Off Label Use: Many of the compounds included in our DSRT platform are not indicated for AML therapy. Mustjoki:BMS: Honoraria, Research Funding; Novartis: Honoraria. Porkka:Novartis: Honoraria, Research Funding; BMS: Honoraria, Research Funding. Kallioniemi:Medisapiens: Membership on an entity’s Board of Directors or advisory committees; Roche: Research Funding.

Therapeutic efficacy of Sunitinib and other broad spectrum receptor tyrosine kinase inhibitors (RTKI) in bleomycin-induced pulmonary fibrosis

Platelet-derived growth factor (PDGF) has ample evidence to support its importance in pulmonary fibrosis. Expression of PDGF in the lungs of IPF patients as well as in BAL samples from animal models of lung fibrosis support its involvement during disease development. Vascular endothelial growth factor (VEGF) being a key regulator of angiogenesis and its receptors have been shown to be involved in the pathogenesis of pulmonary sarcoidosis and fibrosis. The hypothesis under investigation is that receptor tyrosine kinase inhibitors (e.g. Sutent) will slow both the fibrotic processes associated with PDGF signaling and the angiogenic processes regulated by VEGF. We tested two RTKi compounds from Pfizer’s internal portfolio (SU-11248 (Sutent), SU-14813) in the bleomycin-induced pulmonary fibrosis mouse model. Prophylactic as well as therapeutic dosing protocols were conducted. Endpoints included histology, body weights, wet lung weights, lung HO-Pro levels and tissue and serum samples for biomarker and lung exposure analyses. Statistically significant reductions in histological changes were demonstrated in lungs treated with both RTK inhibitors in both percentage of total collagen and inflammatory collagen present. RTK inhibitors demonstrated a statistically significant reduction in both wet lung weight and lung HO-Pro content when dosed prophylactically and therapeutically compared to controls. We have demonstrated that broad-spectrum RTK inhibition is efficacious in inhibiting established pulmonary fibrosis in the bleomycin-induced mouse model. Sutent and other broad spectrum RTKis may provide therapeutic benefit to IPF patients by slowing both the fibrotic and angiogenic processes regulated by tyrosine kinases.

Abrogation of the G2 Checkpoint by Inhibition of Wee-1 Kinase Results in Sensitization of p53-Deficient Tumor Cells to DNA-Damaging Agents

Inducing DNA damage is a well known strategy for attacking cancer, already being used for many years by the application of a variety of anti cancer drugs. Tumor cells and other rapidly dividing cells are more sensitive to DNA damage caused by DNA damaging agents compared to normal cells. While normal cells can rely on various mechanisms for DNA repair in order to protect the integrity of the genome and to promote cell survival, most tumor cells, due to genetic changes, are more challenged when it comes to repair of DNA damage. Wee 1 is a tyrosine kinase that phosphorylates CDC2 at Tyr 15 and as such plays a pivotal role in the G2 DNA damage checkpoint. The strategy of inhibition of Wee 1 by a tyrosine kinase inhibitor is exploiting the impaired options for DNA damage repair especially in cells with deregulated p53, which results in malfunction of the G1 checkpoint. Tumor cells that are unable to rely on the G1 checkpoint are more sensitive to G2 checkpoint abrogation. Administration of DNA damaging chemotherapy in combination with a Wee 1 inhibitor may therefore selectively sensitize p53 deficient cells, while normal cells are spared from toxicity. PD-166285 has been described as a novel G2 abrogator and Wee 1 inhibitor, but has also been characterized as a broad-spectrum receptor tyrosine kinase inhibitor. MK-1775 is a specific and potent inhibitor of Wee-1 and is currently under investigation in a multi-center phase I study in combination with either gemcitabine, carboplatin or cisplatin in patients with advanced solid tumors. Preliminary results show good tolerability and promising anti-cancer activity.

Broad spectrum receptor tyrosine kinase inhibitor, SU6668, sensitizes radiation via targeting survival pathway of vascular endothelium

PurposeRecent studies have demonstrated radiosensitization by inhibiting receptor tyrosine kinases (RTKs). Irradiation activates RTKs and their downstream prosurvival molecule, Akt. In this study, we investigated the mechanism by which SU6668, an inhibitor of RTKs involved in angiogenic pathways, enhances effects of irradiation. Methods and materialsWestern blots were used to determine Akt phosphorylation. Clonogenic assays were performed to determine endothelial survival after combination of SU6668 and irradiation. This combination therapy was also tested in mouse models with Lewis lung carcinoma or glioblastoma multiforme (GL261) for inhibition of tumor growth and tumor vasculature by examining tumor volume, tumor vascular window, and blood flow. ResultsWe found that SU6668 inhibited the Akt activation inducible by irradiation. Clonogenic survival of endothelial cells was decreased after the combined therapy compared with radiotherapy alone. In vivo studies demonstrated reduction of tumor vasculature and blood flow. In addition, 21 Gy in 7 fractions given concurrently with SU6668 resulted in tumor growth delay compared to either treatment alone. ConclusionThese data suggest that the combination therapy was more effective in destroying tumor vasculature than either treatment alone. SU6668 augments tumor-suppressive effects of radiotherapy in Lewis lung carcinoma and GL261 xenographs, possibly through reducing the survival of tumor endothelium.

Anti-angiogenic activity of selected receptor tyrosine kinase inhibitors, PD166285 and PD173074: implications for combination treatment with photodynamic therapy.

Angiogenesis, the formation of new blood vessels from an existing vasculature, is requisite for tumor growth. It entails intercellular coordination of endothelial and tumor cells through angiogenic growth factor signaling. Interruption of these events has implications in the suppression of tumor growth. PD166285, a broad-spectrum receptor tyrosine kinase (RTK) inhibitor, and PD173074, a selective FGFR1TK inhibitor, were evaluated for their anti-angiogenic activity and anti-tumor efficacy in combination with photodynamic therapy (PDT). To evaluate the anti-angiogenic and anti-tumor activities of these compounds, RTK assays, in vitro tumor cell growth and microcapillary formation assays, in vivo murine angiogenesis and anti-tumor efficacy studies utilizing RTK inhibitors in combination with photodynamic therapy were performed. PD166285 inhibited PDGFR-beta-, EGFR-, and FGFR1TKs and c-src TK by 50% (IC50) at concentrations between 7-85 nM. PD173074 displayed selective inhibitory activity towards FGFR1TK at 26 nM. PD173074 demonstrated (>100 fold) selective growth inhibitory action towards human umbilical vein endothelial cells compared with a panel of tumor cell lines. Both PD166285 and PD173074 (at 10 nM) inhibited the formation of microcapillaries on Matrigel-coated plastic. In vivo anti-angiogenesis studies in mice revealed that oral administration (p.o.) of either PD166285 (1-25 mg/kg) or PD173074 (25-100 mg/kg) generated dose dependent inhibition of angiogenesis. Against a murine mammary 16c tumor, significantly prolonged tumor regressions were achieved with daily p.o. doses of PD166285 (5-10 mg/kg) or PD173074 (30-60 mg/kg) following PDT compared with PDT alone (p<0.001). Many long-term survivors were also noted in combination treatment groups. PD166285 and PD173074 displayed potent anti-angiogenic and anti-tumor activity and prolonged the duration of anti-tumor response to PDT. Interference in membrane signal transduction by inhibitors of specific RTKs (e.g. FGFR1TK) should result in new chemotherapeutic agents having the ability to limit tumor angiogenesis and regrowth following cytoreductive treatments such as PDT.