Pazopanib: A Review of Its Use in the Management of Advanced Renal Cell Carcinoma

From standard therapies to monoclonal antibodies and immune checkpoint inhibitors - an update for reconstructive surgeons on common oncological cases

Malignancies represent a persisting worldwide health burden. Tumor treatment is commonly based on surgical and/or non-surgical therapies. In the recent decade, novel non-surgical treatment strategies involving monoclonal antibodies (mAB) and immune checkpoint inhibitors (ICI) have been successfully incorporated into standard treatment algorithms. Such emerging therapy concepts have demonstrated improved complete remission rates and prolonged progression-free survival compared to conventional chemotherapies. However, the in-toto surgical tumor resection followed by reconstructive surgery oftentimes remains the only curative therapy. Breast cancer (BC), skin cancer (SC), head and neck cancer (HNC), and sarcoma amongst other cancer entities commonly require reconstructive surgery to restore form, aesthetics, and functionality. Understanding the basic principles, strengths, and limitations of mAB and ICI as (neo-) adjuvant therapies and treatment alternatives for resectable or unresectable tumors is paramount for optimized surgical therapy planning. Yet, there is a scarcity of studies that condense the current body of literature on mAB and ICI for BC, SC, HNC, and sarcoma. This knowledge gap may result in suboptimal treatment planning, ultimately impairing patient outcomes. Herein, we aim to summarize the current translational endeavors focusing on mAB and ICI. This line of research may serve as an evidence-based fundament to guide targeted therapy and optimize interdisciplinary anti-cancer strategies.

Six-Membered Aromatic Nitrogen Heterocyclic Anti-Tumor Agents: Synthesis and Applications

Cancer stands as a serious malady, posing substantial risks to human well-being and survival. This underscores the paramount necessity to explore and investigate novel antitumor medications. Nitrogen-containing compounds, especially those derived from natural sources, form a highly significant category of antitumor agents. Among these, antitumor agents with six-membered aromatic nitrogen heterocycles have consistently attracted the attention of chemists and pharmacologists. Accordingly, we present a comprehensive summary of synthetic strategies and clinical implications of these compounds in this review. This entails an in-depth analysis of synthesis pathways for pyridine, quinoline, pyrimidine, and quinazoline. Additionally, we explore the historical progression, targets, mechanisms of action, and clinical effectiveness of small molecule inhibitors possessing these structural features.

Platelets and tyrosine kinase inhibitors: clinical features, mechanisms of action, and effects on physiology

Tyrosine kinase inhibitors (TKIs) have emerged as a promising class of target-directed, small molecule inhibitors used to treat hematologic malignancies, inflammatory diseases, and autoimmune disorders. Recently, TKIs have also gained interest as potential antiplatelet-directed therapeutics that could be leveraged to reduce pathologic thrombus formation and atherothrombotic complications, while minimally affecting platelet hemostatic function. This review provides a mechanistic overview and summarizes the known effects of tyrosine kinase inhibitors on platelet signaling and function, detailing prominent platelet signaling pathways downstream of the glycoprotein VI (GPVI) receptor, integrin αIIbβ3, and G protein-coupled receptors (GPCRs). This review focuses on mechanistic as well as clinically relevant and emerging TKIs targeting major families of tyrosine kinases including but not limited to Bruton's tyrosine kinase (BTK), spleen tyrosine kinase (Syk), Src family kinases (SFKs), Janus kinases (JAK), and signal transducers and activators of transcription (STAT) and evaluates their effects on platelet aggregation and adhesion, granule secretion, receptor expression and activation, and protein phosphorylation events. In summation, this review highlights current advances and knowledge on the effects of select TKIs on platelet biology and furthers insight on signaling pathways that may represent novel druggable targets coupled to specific platelet functional responses.

Successful first-line treatment of simultaneous multiple primary malignancies of lung adenocarcinoma and renal clear cell carcinoma: A case report

Background

Multiple Primary Malignancies (MPMs) refer to the occurrence of two or more primary malignancies in the same organ or multiple organs and tissues of the same patient simultaneously or sequentially, with an incidence rate ranging from 2-17%. According to the difference in the time of occurrence of each primary tumor, MPMs can be classified as simultaneous malignancies and heterochronic malignancies. The former refers to the occurrence of two or more malignancies one after another within 6 months, while the latter refers to the occurrence of two malignancies at an interval of more than 6 months. Currently, there is a lack of effective treatment options for MPMs both nationally and internationally.

Case presentation

The patient was a 65-year-old male smoker with a definite diagnosis of advanced lung adenocarcinoma with kirsten rat sarcoma viral oncogene (KRAS) mutation, concomitant with primary renal clear cell carcinoma (RCCC), who had a progression-free survival (PFS) for 7 months after first-line treatment with albumin-bound paclitaxel and cisplatin in combination with sintilimab.

Conclusion

In this paper, we report a case of advanced lung adenocarcinoma combined with RCCC as a concurrent double primary malignancy, which achieved a satisfactory outcome after first-line chemotherapy combined with immunotherapy, with the aim of exploring effective treatment modalities for this type of MPMs, in order to improve the survival and prognosis of the patient.

The VHL/HIF Axis in the Development and Treatment of Pheochromocytoma/Paraganglioma

Pheochromocytomas and paragangliomas (PPGLs) are rare neuroendocrine tumors originating from chromaffin cells in the adrenal medulla (PCCs) or extra-adrenal sympathetic or parasympathetic paraganglia (PGLs). About 40% of PPGLs result from germline mutations and therefore they are highly inheritable. Although dysfunction of any one of a panel of more than 20 genes can lead to PPGLs, mutations in genes involved in the VHL/HIF axis including PHD, VHL, HIF-2A (EPAS1), and SDHx are more frequently found in PPGLs. Multiple lines of evidence indicate that pseudohypoxia plays a crucial role in the tumorigenesis of PPGLs, and therefore PPGLs are also known as metabolic diseases. However, the interplay between VHL/HIF-mediated pseudohypoxia and metabolic disorder in PPGLs cells is not well-defined. In this review, we will first discuss the VHL/HIF axis and genetic alterations in this axis. Then, we will dissect the underlying mechanisms in VHL/HIF axis-driven PPGL pathogenesis, with special attention paid to the interplay between the VHL/HIF axis and cancer cell metabolism. Finally, we will summarize the currently available compounds/drugs targeting this axis which could be potentially used as PPGLs treatment, as well as their underlying pharmacological mechanisms. The overall goal of this review is to better understand the role of VHL/HIF axis in PPGLs development, to establish more accurate tools in PPGLs diagnosis, and to pave the road toward efficacious therapeutics against metastatic PPGLs.

Long-term cardiovascular effects of vandetanib and pazopanib in normotensive rats

Vandetanib and pazopanib are clinically available, multi-targeted inhibitors of vascular endothelial growth factor (VEGF) and platelet-derived growth factor (PDGF) receptor tyrosine kinases. Short-term VEGF receptor inhibition is associated with hypertension in 15%-60% of patients, which may limit the use of these anticancer therapies over the longer term. To evaluate the longer-term cardiovascular implications of treatment, we investigated the "on"-treatment (21 days) and "off"-treatment (10 days) effects following daily administration of vandetanib, pazopanib, or vehicle, in conscious rats. Cardiovascular variables were monitored in unrestrained Sprague-Dawley rats instrumented with radiotelemetric devices. In Study 1, rats were randomly assigned to receive either daily intraperitoneal injections of vehicle (volume 0.5 mL; n = 5) or vandetanib 25 mg/kg/day (volume 0.5 mL; n = 6). In Study 2, rats received either vehicle (volume 0.5 mL; n = 4) or pazopanib 30 mg/kg/day (volume 0.5 mL; n = 7), dosed once every 24 hours for 21 days. All solutions were in 2% Tween, 5% propylene glycol in 0.9% saline solution. Vandetanib caused sustained increases in mean arterial pressure (MAP), systolic blood pressure (SBP), and diastolic blood pressure (DBP) compared to baseline and vehicle. Vandetanib also significantly altered the circadian cycling of MAP, SBP, and DBP. Elevations in SBP were detectable 162 hours after the last dose of vandetanib. Pazopanib also caused increases in MAP, SBP, and DBP. However, compared to vandetanib, these increases were of slower onset and a smaller magnitude. These data suggest that the cardiovascular consequences of vandetanib and pazopanib treatment are sustained, even after prolonged cessation of drug treatment.

Pazopanib: Evidence review and clinical practice in the management of advanced renal cell carcinoma

Background

Pazopanib is indicated in the first-line treatment of metastatic renal cell cancer (mRCC). The aim of this study was to review the efficacy, safety, and pharmacokinetics of pazopanib and see how these aspects are linked to clinical practice.

Methods

A non-exhaustive systematic review was conducted according to the three topics. No publication restrictions were imposed and the selected languages were Spanish and English. After that, a summary of the main results and findings of the review was presented and discussed during three meetings (one for each topic) with 13 medical oncologists that usually treat mRCC. At these meetings, a questionnaire on the first-line use of pazopanib in clinical practice was also drawn up. After the meetings, the questionnaire was completed by 60 specialist medical oncologists in renal cancer.

Results

The efficacy and safety of pazopanib have been demonstrated in several clinical trials, and subsequently confirmed in studies in real-world clinical practice. In addition to its clinical benefit and good safety profile, quality of life results for pazopanib, which compare favorably to sunitinib, make it a good option in the first-line treatment of patients. Special populations have been included in studies conducted with pazopanib, and it is safe for use in elderly patients, poor functional status, kidney failure, and mild or moderate hepatic impairment, and in patients with concomitant cardiovascular disease. The results of the questionnaire have shown that pazopanib is perceived as an effective drug, in which quality of life (QoL) outcomes are valued above all.

Conclusions

This paper offers a comprehensive and critical summary of efficacy, tolerability, and pharmacokinetics of pazopanib in the treatment of mRCC. Pazopanib is an effective treatment with an acceptable safety profile. Its QoL and tolerability results offer certain advantages when compared with other therapeutic alternatives, and its use appears to be safe in different patient profiles.

Tyrosine Kinase Inhibitor Pazopanib Inhibits Platelet Procoagulant Activity in Renal Cell Carcinoma Patients

Pazopanib is an angiostatic tyrosine kinase inhibitor (TKI) presently used for cancer treatment, particularly in patients with renal cell carcinoma (RCC). This treatment can be accompanied by mild bleeding as an adverse effect. Given the role of protein tyrosine kinases in platelet activation processes, we investigated whether and how pazopanib can affect platelet functions in purified systems and during treatment of advanced RCC patients. In isolated platelets from healthy volunteers, pazopanib dose-dependently reduced collagen-induced integrin activation and secretion, as well as platelet aggregation. Pazopanib addition diminished glycoprotein (GP) VI-dependent tyrosine phosphorylation of multiple platelet proteins, including the tyrosine kinase Syk. Furthermore, pazopanib inhibited GPVI-induced Ca²⁺ elevation, resulting in reduced exposure of the procoagulant phospholipid phosphatidylserine (PS). Upon perfusion of control blood over a collagen surface, pazopanib inhibited thrombus size as well as PS exposure. Blood samples from 10 RCC patients were also analyzed before and after 14 days of pazopanib treatment as monotherapy. This treatment caused an overall lowering in platelet count, with 3 out of 10 patients experiencing mild bleeding. Platelets isolated from pazopanib-treated patients showed a significant lowering of PS exposure upon activation. In addition, platelet procoagulant activity was inhibited in thrombi formed under flow conditions. Control experiments indicated that higher pazopanib concentrations were required to inhibit GPVI-mediated PS exposure in the presence of plasma. Together, these results indicated that pazopanib suppresses GPVI-induced platelet activation responses in a way partly antagonized by the presence of plasma. In treated cancer patients, pazopanib effects were confined to a reduction in GPVI-dependent PS exposure. Together with the reduced platelet count, this may explain the mild bleeding tendency observed in pazopanib-treated patients.

Recent advances in the management of malignant pheochromocytoma and paraganglioma: focus on tyrosine kinase and hypoxia-inducible factor inhibitors

Inactivating mutations of the succinate dehydrogenase subunit B ( SDHB) gene and the subsequent stabilization and activation of the hypoxia-inducible factor 2-alpha (HIF2α) unit are recognized hallmarks associated with the development of metastatic pheochromocytomas and paragangliomas (MPPG). Despite this discovery, the development of systemic therapies for patients with MPPG has been very slow. The rarity of the disease, the lack of preclinical animal models, and the impracticable development of large clinical trials has hindered the therapeutic progress for MPPG. Chemotherapy and low-specific activity ¹³¹meta-iodo-benzyl-guanidine (MIBG) (manufactured by simple isotope exchange methodology) led to positive clinical responses in about a third of patients. Molecular targeted therapies were introduced into oncological clinical practice at the beginning of the 21st century. These therapies have been demonstrated to be effective for patients with cancers that previously exhibited limited responses to systemic chemotherapy, such as kidney and thyroid carcinomas and pancreatic neuroendocrine tumors. The pathogenesis of MPPG overlaps in some way with the pathogenesis of kidney, medullary thyroid, and pancreatic neuroendocrine carcinomas, providing scientific support to explore molecular targeted therapies such as tyrosine kinase and HIF inhibitors.

Arterial Thrombosis in Patients with Cancer

PURPOSE OF REVIEW

Cancer is a common cause of morbidity and mortality in the USA. While the association between venous thrombosis and malignancy is well established, arterial thrombosis has more recently been recognized as a serious complication of cancer and certain chemotherapeutic agents. This review aims to summarize the most recent literature regarding the incidence and risk factors for cancer-related arterial thrombosis, understand the pathophysiologic mechanisms of thrombosis, and highlight the specific diagnostic and treatment considerations relevant to cancer patients.

RECENT FINDINGS

Based on a recent study looking at the Surveillance, Epidemiology, and End Results (SEER) database, the incidence of arterial thromboembolic events (ATEs) in patients with cancer at 6 months is 4.7%; the presence of an ATE is predictive of worse outcomes. Certain drugs such as platinum-based agents, vascular endothelial growth factor inhibitors, tyrosine kinase inhibitors, and taxanes have been associated with high rates of ATEs. Increased platelet reactivity appears crucial to development of arterial thrombosis in cancer patients. Cancer patients have an increased risk of arterial thrombosis that is likely due to both a cancer-associated procoagulant state as well as the adverse effects of certain chemotherapeutic agents. Treatment of arterial thromboembolism in cancer patients typically requires a multidisciplinary approach in part due to high rates of thrombocytopenia and stent thrombosis in the setting of percutaneous interventions. More studies are needed to investigate optimal prophylaxis, surveillance strategies, and treatments of cancer-related arterial thromboembolic disease.

Efficacy and safety of regorafenib in the treatment of metastatic colorectal cancer: A systematic review

PURPOSE

Despite advances in the treatment of colorectal cancer, third-line treatment options are still limited. Regorafenib was approved in 2012 for the treatment of patients with metastatic colorectal cancer previously treated with approved standard therapy. The purpose of this review is to present existing clinical data on regorafenib.

METHOD

We systematically searched the PubMed and Embase databases, as well as ASCO and ESMO conference abstracts, for studies in English including ≥30 patients, evaluating the efficacy and safety of regorafenib in patients with metastatic colorectal cancer. A meta-analysis was conducted on the published, randomized phase III trials.

RESULTS

24 eligible studies were included. In two phase III trials, regorafenib significantly increased overall survival (OS), progression free survival (PFS), and disease control rate when compared to placebo. Survival benefits of 1.4 and 2.5 months were presented. The meta-analysis indicated a significant greater treatment effect on OS (hazard ratio 0.67) and PFS (hazard ratio 0.40), compared to placebo. The non-randomized studies mostly supported these results. The most frequently reported adverse events were hand-foot-skin reaction (25%-86%), hypertension (11%-47%) and fatigue (2%-73%).

CONCLUSION

Large phase III randomized trials indicate that regorafenib provides a benefit in OS and PFS when compared to placebo. Adverse events were common, but manageable and typical of multi-target tyrosine kinase inhibitors. Further research is needed to investigate alternative approaches to the dosing of regorafenib and to explore clinical and molecular biomarkers that can guide patient selection.

High quality, small molecule-activity datasets for kinase research

Kinases regulate cell growth, movement, and death. Deregulated kinase activity is a frequent cause of disease. The therapeutic potential of kinase inhibitors has led to large amounts of published structure activity relationship (SAR) data. Bioactivity databases such as the Kinase Knowledgebase (KKB), WOMBAT, GOSTAR, and ChEMBL provide researchers with quantitative data characterizing the activity of compounds across many biological assays. The KKB, for example, contains over 1.8M kinase structure-activity data points reported in peer-reviewed journals and patents. In the spirit of fostering methods development and validation worldwide, we have extracted and have made available from the KKB 258K structure activity data points and 76K associated unique chemical structures across eight kinase targets. These data are freely available for download within this data note.

Classical and non-classical proangiogenic factors as a target of antiangiogenic therapy in tumor microenvironment

Angiogenesis is sustained by classical and non-classical proangiogenic factors (PFs) acting in tumor microenvironment and these factors are also potential targets of antiangiogenic therapies. All PFs induce the overexpression of several signaling pathways that lead to migration and proliferation of endothelial cells contributing to tumor angiogenesis and survival of cancer cells. In this review, we have analyzed each PF with its specific receptor/s and we have summarized the available antiangiogenic drugs (e.g. monoclonal antibodies) targeting these PFs, some of these agents have already been approved, others are currently in development for the treatment of several human malignancies.

First-line sunitinib versus pazopanib in metastatic renal cell carcinoma: Results from the International Metastatic Renal Cell Carcinoma Database Consortium

BACKGROUND

Sunitinib (SU) and pazopanib (PZ) are standards of care for first-line treatment of metastatic renal cell carcinoma (mRCC). However, how the efficacy of these drugs translates into effectiveness on a population-based level is unknown.

PATIENTS AND METHODS

We used the International mRCC Database Consortium (IMDC) to assess overall survival (OS), progression-free survival (PFS), response rate (RR) and performed proportional hazard regression adjusting for IMDC prognostic groups. Second-line OS (OS2) and second-line PFS (PFS2) were also evaluated.

RESULTS

We obtained data from 7438 patients with mRCC treated with either first-line SU (n = 6519) or PZ (n = 919) with an overall median follow-up of 40.4 months (95% confidence interval [CI] 39.2-42.1). There were no significant differences in IMDC prognostic groups (p = 0.36). There was no OS difference between SU and PZ (22.3 versus 22.6 months, respectively, p = 0.65). When adjusted for IMDC criteria, the hazard ratio (HR) of death for PZ versus SU was 1.03 (95% CI 0.92-1.17, p = 0.58). There was no PFS difference between SU and PZ (8.4 versus 8.3 months, respectively, p = 0.17). When adjusted for IMDC criteria, the HR for PFS for PZ versus SU was 1.08 (95% CI 0.981-1.19, p = 0.12). There was no difference in RR between SU and PZ (30% versus 28%, respectively, p = 0.15). We also found no difference in any second-line treatment between either post-SU or post-PZ groups for OS2 (13.1 versus 11 months, p = 0.27) and PFS2 (3.7 versus 5.0 months, p = 0.07).

CONCLUSIONS

We confirmed in real-world practice that SU and PZ have similar efficacy in the first-line setting for mRCC and do not affect outcomes with subsequent second-line treatment.

Shared mechanism of teratogenicity of anti-angiogenic drugs identified in the chicken embryo model

Angiogenesis, the formation of new blood vessels, is essential for tumor growth, stabilization and progression. Angiogenesis inhibitors are now widely used in the clinic; however, there are relatively few published studies on the mechanism of their presumed teratogenic effects. To address this issue, we screened a variety of angiogenesis inhibitors in developing zebrafish and chicken embryo models to assess for developmental defects and potential teratogenic effects. We confirmed previous reports that sunitinib, sorafenib and TNP-470 are teratogenic and demonstrate that axitinib, pazopanib, vandetanib, and everolimus are also teratogens in these models. A dose response study identified the drugs inhibit HUVEC cell proliferation in vitro, and also target the developing blood vessels of embryos in vivo. This provides further evidence for the potential risk of fetal toxicity when using these drugs in a clinical setting, and emphasizes the importance of the development and maintenance of the vasculature in the embryo. We conclude that angiogenesis inhibitors, regardless of the molecular target, are teratogenic when exposed to chicken embryos.

High quality, small molecule-activity datasets for kinase research

Kinases regulate cell growth, movement, and death. Deregulated kinase activity is a frequent cause of disease. The therapeutic potential of kinase inhibitors has led to large amounts of published structure activity relationship (SAR) data. Bioactivity databases such as the Kinase Knowledgebase (KKB), WOMBAT, GOSTAR, and ChEMBL provide researchers with quantitative data characterizing the activity of compounds across many biological assays. The KKB, for example, contains over 1.8M kinase structure-activity data points reported in peer-reviewed journals and patents. In the spirit of fostering methods development and validation worldwide, we have extracted and have made available from the KKB 258K structure activity data points and 76K associated unique chemical structures across eight kinase targets. These data are freely available for download within this data note.

High quality, small molecule-activity datasets for kinase research

Kinases regulate cell growth, movement, and death. Deregulated kinase activity is a frequent cause of disease. The therapeutic potential of kinase inhibitors has led to large amounts of published structure activity relationship (SAR) data. Bioactivity databases such as the Kinase Knowledgebase (KKB), WOMBAT, GOSTAR, and ChEMBL provide researchers with quantitative data characterizing the activity of compounds across many biological assays. The KKB, for example, contains over 1.8M kinase structure-activity data points reported in peer-reviewed journals and patents. In the spirit of fostering methods development and validation worldwide, we have extracted and have made available from the KKB 258K structure activity data points and 76K associated unique chemical structures across eight kinase targets. These data are freely available for download within this data note.

Inhibition of Tumor Growth and Metastasis in Pancreatic Cancer Models by Interference With CD44v6 Signaling

BACKGROUND & AIMS

Cancer cells with high metastatic potential and stem cell-like characteristics express the cell surface marker CD44. CD44 isoforms that include the v6 exon are co-receptors for the receptor tyrosine kinases MET and Vascular Endothelial Growth factor Receptor-2 (VEGFR-2). We studied CD44v6 signaling in several pancreatic cancer cell lines, and its role in tumor growth and metastasis in several models of pancreatic cancer.

METHODS

We analyzed the effects of v6 peptides that interfere with the co-receptor functions of CD44v6 for MET and VEGFR-2 in tumors and metastases grown from cells that express different CD44 isoforms, including CD44v6. The peptides were injected into rats with syngeneic tumors and mice with orthotopic or xenograft tumors. We also tested the effects of the peptides in mice with xenograft tumors grown from patient tumor samples and mice that express an oncogenic form of RAS and develop spontaneous pancreatic cancer (KPC mice). We measured levels of CD44v6 messenger RNA (mRNA) in pancreatic cancer tissues from 136 patients.

RESULTS

Xenograft tumors grown from human cancer cells injected with v6 peptides were smaller and formed fewer metastases in mice. The v6 peptide was more efficient than the MET inhibitor crizotinib and/or the VEGFR-2 inhibitor pazopanib in reducing xenograft tumor growth and metastasis. Injection of KPC mice with the v6 peptide increased their survival time. Injection of mice and rats bearing metastases with the v6 peptide induced regression of metastases. Higher levels of CD44v6 mRNA in human pancreatic tumor tissues were associated with increased expression of MET, tumor metastasis, and shorter patient survival times.

CONCLUSIONS

Peptide inhibitors of CD44v6 isoforms block tumor growth and metastasis in several independent models of pancreatic cancer. The v6 peptides induced regression of metastases. Levels of CD44v6 mRNA are increased, along with those of MET mRNA, in patients with metastatic pancreatic tumors, compared with nonmetastatic tumors; the increased levels correlated with shorter patient survival time.

A combination of sorafenib and nilotinib reduces the growth of castrate-resistant prostate cancer

Castrate-resistant prostate cancer (CRPC) remains incurable due to the lack of effective therapies. Several tyrosine kinases have been implicated in the development and growth of CRPC, as such targeting these kinases may offer an alternative therapeutic strategy. We established the combination of two tyrosine kinase inhibitors (TKIs), sorafenib and nilotinib, as the most cytotoxic. In addtion, to improve their bioavailability and reduce their metabolism, we encapsulated sorafenib and nilotinib into styrene-co-maleic acid micelles. The micelles' charge, size, and release rate were characterized. We assessed the effect of the combination on the cytotoxicity, cell cycle, apoptosis, protein expression, tumor spheroid integrity, migration, and invasion. The micelles exhibited a mean diameter of 100 nm, a neutral charge, and appeared highly stable. The micellar TKIs promoted greater cytotoxicity, decreased cell proliferation, and increased apoptosis relative to the free TKIs. In addition, the combination reduced the expression and activity of several tyrosine kinases and reduced tumor spheroid integrity and metastatic potential of CRPC cell lines more efficiently than the single treatments. The combination increased the therapeutic potential and demonstrated the relevance of a targeted combination therapy for the treatment of CRPC. In addition, the efficacy of the encapsulated drugs provides the basis for an in vivo preclinical testing.

Anti-proliferative but not anti-angiogenic tyrosine kinase inhibitors enrich for cancer stem cells in soft tissue sarcoma

BACKGROUND

Increasing studies implicate cancer stem cells (CSCs) as the source of resistance and relapse following conventional cytotoxic therapies. Few studies have examined the response of CSCs to targeted therapies, such as tyrosine kinase inhibitors (TKIs). We hypothesized that TKIs would have differential effects on CSC populations depending on their mechanism of action (anti-proliferative vs. anti-angiogenic).

METHODS

We exposed human sarcoma cell lines to sorafenib, regorafenib, and pazopanib and assessed cell viability and expression of CSC markers (ALDH, CD24, CD44, and CD133). We evaluated survival and CSC phenotype in mice harboring sarcoma metastases after TKI therapy. We exposed dissociated primary sarcoma tumors to sorafenib, regorafenib, and pazopanib, and we used tissue microarray (TMA) and primary sarcoma samples to evaluate the frequency and intensity of CSC markers after neoadjuvant therapy with sorafenib and pazopanib. Parametric and non-parametric statistical analyses were performed as appropriate.

RESULTS

After functionally validating the CSC phenotype of ALDHbright sarcoma cells, we observed that sorafenib and regorafenib were cytotoxic to sarcoma cell lines (P < 0.05), with a corresponding 1.4 - 2.8 fold increase in ALDHbright cells from baseline (P < 0.05). In contrast, we observed negligible effects on viability and CSC sub-populations with pazopanib. At low doses, there was progressive CSC enrichment in vitro after longer term exposure to sorafenib although the anti-proliferative effects were attenuated. In vivo, sorafenib improved median survival by 11 days (P < 0.05), but enriched ALDHbright cells 2.5 - 2.8 fold (P < 0.05). Analysis of primary human sarcoma samples revealed direct cytotoxicity following exposure to sorafenib and regorafenib with a corresponding increase in ALDHbright cells (P < 0.05). Again, negligible effects from pazopanib were observed. TMA analysis of archived specimens from sarcoma patients treated with sorafenib demonstrated significant enrichment for ALDHbright cells in the post-treatment resection specimen (P < 0.05), whereas clinical specimens obtained longitudinally from a patient treated with pazopanib showed no enrichment for ALDHbright cells (P > 0.05).

CONCLUSIONS

Anti-proliferative TKIs appear to enrich for sarcoma CSCs while anti-angiogenic TKIs do not. The rational selection of targeted therapies for sarcoma patients may benefit from an awareness of the differential impact of TKIs on CSC populations.