Receptor Tyrosine Kinases and Their Signaling Pathways as Therapeutic Targets of Curcumin in Cancer

Receptor tyrosine kinases (RTKs) are transmembrane cell-surface proteins that act as signal transducers. They regulate essential cellular processes like proliferation, apoptosis, differentiation and metabolism. RTK alteration occurs in a broad spectrum of cancers, emphasising its crucial role in cancer progression and as a suitable therapeutic target. The use of small molecule RTK inhibitors however, has been crippled by the emergence of resistance, highlighting the need for a pleiotropic anti-cancer agent that can replace or be used in combination with existing pharmacological agents to enhance treatment efficacy. Curcumin is an attractive therapeutic agent mainly due to its potent anti-cancer effects, extensive range of targets and minimal toxicity. Out of the numerous documented targets of curcumin, RTKs appear to be one of the main nodes of curcumin-mediated inhibition. Many studies have found that curcumin influences RTK activation and their downstream signaling pathways resulting in increased apoptosis, decreased proliferation and decreased migration in cancer both in vitro and in vivo. This review focused on how curcumin exhibits anti-cancer effects through inhibition of RTKs and downstream signaling pathways like the MAPK, PI3K/Akt, JAK/STAT, and NF-κB pathways. Combination studies of curcumin and RTK inhibitors were also analysed with emphasis on their common molecular targets.

RTK Inhibitors in Melanoma: From Bench to Bedside

MAPK (mitogen activated protein kinase) and PI3K/AKT (Phosphatidylinositol-3-Kinase and Protein Kinase B) pathways play a key role in melanoma progression and metastasis that are regulated by receptor tyrosine kinases (RTKs). Although RTKs are mutated in a small percentage of melanomas, several receptors were found up regulated/altered in various stages of melanoma initiation, progression, or metastasis. Targeting RTKs remains a significant challenge in melanoma, due to their variable expression across different melanoma stages of progression and among melanoma subtypes that consequently affect response to treatment and disease progression. In this review, we discuss in details the activation mechanism of several key RTKs: type III: c-KIT (mast/stem cell growth factor receptor); type I: EGFR (Epidermal growth factor receptor); type VIII: HGFR (hepatocyte growth factor receptor); type V: VEGFR (Vascular endothelial growth factor), structure variants, the function of their structural domains, and their alteration and its association with melanoma initiation and progression. Furthermore, several RTK inhibitors targeting the same receptor were tested alone or in combination with other therapies, yielding variable responses among different melanoma groups. Here, we classified RTK inhibitors by families and summarized all tested drugs in melanoma indicating the rationale behind the use of these drugs in each melanoma subgroups from preclinical studies to clinical trials with a specific focus on their purpose of treatment, resulted effect, and outcomes.

Identification of Wee1 as Target in Combination with Avapritinib for the Treatment of Gastrointestinal Stromal Tumor

Management of gastrointestinal stromal tumor (GIST) has been revolutionized by the identification of activating mutations in KIT and PDGFRA, and the clinical application of receptor tyrosine kinase (RTK) inhibitors in the advanced disease setting. Stratification of GIST into molecularly defined subsets provides insight into clinical behavior and response to approved targeted therapies. Although these RTK inhibitors are effective in the majority of GIST, resistance to these agents remains a significant clinical problem. Development of effective treatment strategies for refractory GIST subtypes requires identification of novel targets to provide additional therapeutic options. Global kinome profiling has the potential to identify critical signaling networks and reveal protein kinases that are essential in GIST. Using Multiplexed Inhibitor Beads and Mass Spectrometry, we explored the majority of the kinome in GIST specimens from the three most common molecular subtypes to identify novel kinase targets. Kinome profiling revealed distinct signatures in GIST subtypes and identified kinases that are universally activated in all GIST, as well as kinases that are unique to each subtype. Kinome profiling in combination with loss-of-function assays identified a significant role for the G2-M tyrosine kinase, Wee1, in GIST cell survival. In vitro and in vivo studies revealed significant efficacy of MK-1775 (Wee1 inhibitor) in combination with avapritinib in KIT and PDGFRA-mutant GIST cell lines, and notable efficacy of MK-1775 as a single agent in the PDGFRA-mutant line. These studies provide strong preclinical justification for the use of MK-1775 in GIST.

Activation and function of receptor tyrosine kinases in human clear cell renal cell carcinomas

Background The receptor tyrosine kinases (RTKs) play critical roles in the development of cancers. Clear cell renal cell carcinoma (ccRCC) accounts for 75% of the RCC. The previous studies on the RTKs in ccRCCs mainly focused on their gene expressions. The activation and function of the RTKs in ccRCC have not been fully investigated. Methods In the present study, we analyzed the phosphorylation patterns of RTKs in human ccRCC patient samples, human ccRCC and papillary RCC cell lines, and other kidney tumor samples using human phospho-RTK arrays. We further established ccRCC patient-derived xenograft models in nude mice and assessed the effects of RTKIs (RTK Inhibitors) on the growth of these cancer cells. Immunofluorescence staining was used to detect the localization of keratin, vimentin and PDGFRβ in ccRCCs. Results We found that the RTK phosphorylation patterns of the ccRCC samples were all very similar, but different from that of the cell lines, other kidney tumor samples, as well as the adjacent normal tissues. 9 RTKs, EGFR1–3, Insulin R, PDGFRβ, VEGFR1, VEGFR2, HGFR and M-CSFR were found to be phosphorylated in the ccRCC samples. The adjacent normal tissues, on the other hand, had predominantly only two of the 4 EGFR family members, EGFR and ErbB4, phosphorylated. What’s more, the RTK phosphorylation pattern of the xenograft, however, was different from that of the primary tissue samples. Treatment of the xenograft nude mice with corresponding RTK inhibitors effectively inhibited the Erk1/2 signaling pathway as well as the growth of the tumors. In addition, histological staining of the cancer samples revealed that most of the PDGFRβ expressing cells were localized in the vimentin-positive periepithelial stroma. Conclusions Overall, we have identified a set of RTKs that are characteristically phosphorylated in ccRCCs. The phosphorylation of RTKs in ccRCCs were determined by the growing environments. These phosphorylated/activated RTKs will guide targeting drugs development of more effective therapies in ccRCCs. The synergistical inhibition of RTKIs combination on the ccRCC suggest a novel strategy to use a combination of RTKIs to treat ccRCCs.

Phase 2 trial of the novel multi-receptor tyrosine kinase inhibitor sitravatinib in well-differentiated/dedifferentiated liposarcoma.

TPS11082 Background: Well-differentiated/dedifferentiated liposarcoma (WD/DD LPS) is a sarcoma subtype of adipocytic origin characterized by amplification of cyclin dependent kinase 4 (CDK4) and MDM2. WD/DD LPS is resistant to chemotherapy and success with CDK4 inhibitors is limited. We recently characterized the landscape of activated receptor tyrosine kinases (RTKs) and intracellular signaling pathways finding marked heterogeneity by sarcoma subtype [Patwardhan et al. Oncotarget 2016;7(4)]. In WD/DD LPS cell lines, phosphorylated (p) IGF1-R, MET and PDGFRb are strongly expressed. Selective siRNA knockdown of expression of 1 or more of these RTKs inhibited growth of WD/DD LPS cell lines. Sitravatinib (S) is a novel inhibitor of a broad panel of related RTKs. We showed that S abrogates expression of p-RTKs, including IGF1-R, MET and PDGFRb, at low nanomolar concentrations and potently inhibits proliferation of WD/DD LPS cell lines, where anti-proliferative effects of S were superior to other RTK inhibitors including imatinib, crizotinib and pazopanib. S suppressed tumor growth in vivo in WD/DD LPS . A phase 1 trial of S in solid tumors showed clinical activity in WD/DD LPS. Recommended phase 2 dose was 150 mg/day. As there are no approved RTK inhibitors for adipocytic sarcomas, and based on these findings, we initiated a phase 2 trial of S in WD/DD LPS. Methods: This is a single-arm open-label multi-center Simon 2 stage phase II trial of S in 29 patients (pts) with advanced WD/DD LPS who failed 1 prior therapy and show disease progression before enrollment. Pts receive S 150 mg orally daily continuously. Primary endpoint is the progression free rate at 12 weeks (PFR12) versus historical controls. The design has power of 85% to show improvement in PFR12 from 20% (inactive) to 40% (active) with α = 0.10. Secondary endpoints are ORR, PFS and safety. A subset of pts undergo baseline and on-treatment biopsies and reverse phase protein array used to measure changes in expression of p-RTKs and signaling pathway proteins with confirmation by immunoblot. Genomic landscape of these tumors will be analyzed by next generation sequencing. The study opened in 1/2017. Clinical trial information: NCT02978859.