Signaling Pathways and Therapeutic Strategies in Advanced Basal Cell Carcinoma

Non-melanoma skin cancers (NMSCs) are the most common human neoplasms world-wide. In detail, basal cell carcinoma (BCC) is the most frequent malignancy in the fair-skinned population. The incidence of BCC remains difficult to assess due to the poor registration practice; however, it has been increasing in the last few years. Approximately, 85% of sporadic BCCs carry mutations in Hedgehog pathway genes, especially in PTCH, SUFU and SMO genes, which lead to the aberrant activation of GLI transcriptional factors, typically silent in cells of adult individuals. The management of advanced BCC (aBCC), both metastatic (mBCC) and locally advanced BCC (laBCC), not candidates for surgical excision or radiotherapy, remains challenging. The discovery of mutations in the Hh signaling pathway has paved the way for the development of Hh pathway inhibiting agents, such as vismodegib and sonidegib, which have represented a breakthrough in the aBCC management. However, the use of these agents is limited by the frequent occurrence of adverse events or the development of drug resistance. In this review, we thoroughly describe the current knowledge regarding the available options for the pharmacological management of aBCCs and provide a forward-looking update on novel therapeutic strategies that could enrich the therapeutic armamentarium of BCC in the near future.

Repurposing the Hedgehog pathway inhibitor, BMS-833923, as a phosphatidylglycerol-selective membrane-disruptive colistin adjuvant against ESKAPE pathogens

The rapid emergence and spread of multi-drug- or pan-drug-resistant bacterial pathogens, such as ESKAPE, pose a serious threat to global health. However, the development of novel antibiotics is hindered by difficulties in identifying new antibiotic targets and the rapid development of drug resistance. Drug repurposing is an effective alternative strategy for combating antibiotic resistance that both saves resources and extends the life of existing antibiotics in combination treatment regimens. Screening of a chemical compound library identified BMS-833923 (BMS), a smoothened antagonist that kills Gram-positive bacteria directly, and potentiates colistin to destroy various Gram-negative bacteria. BMS did not induce detectable antibiotic resistance in vitro, and showed effective activity against drug-resistant bacteria in vivo. Mechanistic studies revealed that BMS caused membrane disruption by targeting the membrane phospholipids phosphatidylglycerol and cardiolipin, promoting membrane dysfunction, metabolic disturbance, leakage of cellular components, and, ultimately, cell death. This study describes a potential strategy to enhance the efficacy of colistin and combat multi-drug-resistant ESKAPE pathogens.

Advances in the drug management of basal cell carcinoma

INTRODUCTION

Basal cell carcinoma (BCC) is the most common skin cancer in humans. Recently, BCCs were suggested to be classified into 'easy to treat' and 'difficult to treat,' and different therapeutic options are suggested for their management.

AREAS COVERED

In this review, the authors discuss treatment options that are approved, recommended for, or are still in development for treatment of BCC. The review covers approved local therapies, such as imiquimod and 5-fluorouracil, and systemic therapies, such as hedgehog inhibitors. New medical agents, investigated in clinical trials, are reviewed. These include: targeted therapies, such as GLI antagonists or anti-VEGFR agents, immunotherapies, such as checkpoint inhibitors, recombinant cytokines or silencing RNA, as well as intralesional virotherapies with modified adeno- or herpes viruses.

EXPERT OPINION

The progress made in recent years has improved the management of patients with advanced BCC; however, neither tumor targeting nor immune system engaging agents provide a cure. New treatment approaches directed not only to known targets but also the tumor microenvironment are in development and are anticipated to improve the management of difficult to treat BCC.

Recent Advances in Signaling Pathways Comprehension as Carcinogenesis Triggers in Basal Cell Carcinoma

Basal cell carcinoma (BCC) is the most common malignant skin tumor. BCC displays a different behavior compared with other neoplasms, has a slow evolution, and metastasizes very rarely, but sometimes it causes an important local destruction. Chronic ultraviolet exposure along with genetic factors are the most important risk factors involved in BCC development. Mutations in the PTCH1 gene are associated with Gorlin syndrome, an autosomal dominant disorder characterized by the occurrence of multiple BCCs, but are also the most frequent mutations observed in sporadic BCCs. PTCH1 encodes for PTCH1 protein, the most important negative regulator of the Hedgehog (Hh) pathway. There are numerous studies confirming Hh pathway involvement in BCC pathogenesis. Although Hh pathway has been intensively investigated, it remains incompletely elucidated. Recent studies on BCC tumorigenesis have shown that in addition to Hh pathway, there are other signaling pathways involved in BCC development. In this review, we present recent advances in BCC carcinogenesis.

Hedgehog Signaling Inhibition by Smoothened Antagonist BMS-833923 Reduces Osteoblast Differentiation and Ectopic Bone Formation of Human Skeletal (Mesenchymal) Stem Cells

Background

Hedgehog (Hh) signaling is essential for osteoblast differentiation of mesenchymal progenitors during endochondral bone formation. However, the critical role of Hh signaling during adult bone remodeling remains to be elucidated.

Methods

A Smoothened (SMO) antagonist/Hedgehog inhibitor, BMS-833923, identified during a functional screening of a stem cell signaling small molecule library, was investigated for its effects on the osteoblast differentiation of human skeletal (mesenchymal) stem cells (hMSC). Alkaline phosphatase (ALP) activity and Alizarin red staining were employed as markers for osteoblast differentiation and in vitro mineralization capacity, respectively. Global gene expression profiling was performed using the Agilent® microarray platform. Effects on in vivo ectopic bone formation were assessed by implanting hMSC mixed with hydroxyapatite-tricalcium phosphate granules subcutaneously in 8-week-old female nude mice, and the amount of bone formed was assessed using quantitative histology.

Results

BMS-833923, a SMO antagonist/Hedgehog inhibitor, exhibited significant inhibitory effects on osteoblast differentiation of hMSCs reflected by decreased ALP activity, in vitro mineralization, and downregulation of osteoblast-related gene expression. Similarly, we observed decreased in vivo ectopic bone formation. Global gene expression profiling of BMS-833923-treated compared to vehicle-treated control cells, identified 348 upregulated and 540 downregulated genes with significant effects on multiple signaling pathways, including GPCR, endochondral ossification, RANK-RANKL, insulin, TNF alpha, IL6, and inflammatory response. Further bioinformatic analysis employing Ingenuity Pathway Analysis revealed significant enrichment in BMS-833923-treated cells for a number of functional categories and networks involved in connective and skeletal tissue development and disorders, e.g., NFκB and STAT signaling.

Conclusions

We identified SMO/Hedgehog antagonist (BMS-833923) as a powerful inhibitor of osteoblastic differentiation of hMSC that may be useful as a therapeutic option for treating conditions associated with high heterotopic bone formation and mineralization.

Small Molecule Inhibitors of the Hedgehog Pathway in the Treatment of Basal Cell Carcinoma of the Skin

Basal cell carcinoma (BCC) is the most common type of skin cancer, with rising incidence rates primarily attributed to an aging population and ultraviolet radiation exposure. While the majority of BCCs are localized and respond to standard therapies, a very small minority of these tumors become locally destructive or metastasize. These advanced BCCs may not be amenable to localized treatment with surgery and/or radiation therapy. Most BCCs result from mutations in key receptors in the Hedgehog (HH) signaling pathway. As a result, identification of drugs that inhibit the receptor Smoothened (SMO) in the HH pathway has resulted in novel therapeutic approaches to treating patients with advanced BCC. These HH-pathway inhibiting medications have shown efficacy in clinical trials, and two medications, vismodegib and sonidegib, have received FDA approval. However, several limitations of these drugs have been identified, including treatment-limiting adverse events, drug resistance, and the formation of additional malignancies. This paper aims to summarize the clinical trials leading to the approval of SMO inhibitors, as well as reviewing potential mechanisms driving tumor resistance and the formation of cutaneous squamous cell carcinomas. Strategies to overcome some of these challenges, including the development of drugs that inhibit other downstream targets in the HH pathway, are the subject of ongoing clinical trials.

Long-term efficacy and safety of sonidegib in patients with locally advanced and metastatic basal cell carcinoma: 30-month analysis of the randomized phase 2 BOLT study

BACKGROUND

Patients with locally advanced basal cell carcinoma (laBCC) or metastatic BCC (mBCC), two difficult-to-treat populations, have had limited treatment options. Sonidegib, a hedgehog pathway inhibitor (HPI), was approved in laBCC based on results from the BOLT trial.

OBJECTIVE

To evaluate long-term efficacy and safety of sonidegib in laBCC and mBCC in the BOLT 18- and 30-month analyses.

METHODS

BOLT (NCT01327053, ClinicalTrials.gov), a double-blind phase 2 study, enrolled patients from July 2011 until January 2013. Eligible HPI-treatment-naïve patients with laBCC not amenable to curative surgery/radiotherapy or mBCC were randomized 1 : 2 to sonidegib 200 mg (laBCC, n = 66; mBCC, n = 13) or 800 mg (laBCC, n = 128; mBCC, n = 23). Tumour response was assessed per central and investigator review.

RESULTS

With 30 months of follow-up, among patients treated with sonidegib 200 mg (approved dose), objective response rates were 56.1% (central) and 71.2% (investigator) in laBCC and 7.7% (central) and 23.1% (investigator) in mBCC. Tumour responses were durable as follows: median duration of response was 26.1 months (central) and 15.7 months (investigator) in laBCC and 24.0 months (central) and 18.1 months (investigator) in mBCC. Five patients with laBCC and three with mBCC in the 200-mg arm died. Median overall survival was not reached in either population; 2-year overall survival rates were 93.2% (laBCC) and 69.3% (mBCC). In laBCC, efficacy was similar regardless of aggressive or non-aggressive histology. Sonidegib 200 mg continued to have a better safety profile than 800 mg, with lower rates of grade 3/4 adverse events (43.0% vs. 64.0%) and adverse events leading to discontinuation (30.4% vs. 40.0%).

CONCLUSION

Sonidegib continued to demonstrate long-term efficacy and safety in these populations. These data support the use of sonidegib 200 mg per local treatment guidelines.

Sonidegib: A Review in Locally Advanced Basal Cell Carcinoma

Sonidegib (Odomzo®), an oral smoothened (SMO) antagonist, is indicated for the treatment of adults with locally advanced basal cell carcinoma (laBCC) who are not candidates for surgery or radiation therapy, or adults with recurrent laBCC following surgery or radiation therapy. In the multicentre BOLT trial, the primary endpoint (i.e., an objective tumour response rate point estimate of ≥30 % and a 95 % confidence interval lower bound of >20 % in patients with fully assessable laBCC and all patients with metastatic BCC) was met at the primary analysis cut-off date (median follow-up 13.9 months) in the sonidegib 200 mg (36 % [95 % CI 24-50]) and 800 mg (34 % [95 % CI 25-43]) once-daily groups. Sonidegib 200 mg once daily (recommended dosage) had a better benefit-risk profile than the 800 mg dosage. Central review of the patients with laBCC in this population showed that 43 % achieved an objective response with sonidegib 200 mg once daily at the primary analysis date. Clinically meaningful responses were sustained in the sonidegib 200 mg group, based on an 18-month analysis. The majority of treatment-emergent adverse events were of mild to moderate severity and manageable with dosage adjustments, concomitant medications and/or non-drug therapies (e.g., adequate hydration). The acceptable benefit-risk profile of sonidegib, along with a paucity of treatment options and the seriousness of the condition, makes sonidegib an emerging option for the treatment of adults with laBCC that has recurred following surgery or radiation therapy, or in those who are not candidates for surgery or radiation therapy.

Novel small molecules targeting ciliary transport of Smoothened and oncogenic Hedgehog pathway activation

Trafficking of the G protein-coupled receptor (GPCR) Smoothened (Smo) to the primary cilium (PC) is a potential target to inhibit oncogenic Hh pathway activation in a large number of tumors. One drawback is the appearance of Smo mutations that resist drug treatment, which is a common reason for cancer treatment failure. Here, we undertook a high content screen with compounds in preclinical or clinical development and identified ten small molecules that prevent constitutive active mutant SmoM2 transport into PC for subsequent Hh pathway activation. Eight of the ten small molecules act through direct interference with the G protein-coupled receptor associated sorting protein 2 (Gprasp2)-SmoM2 ciliary targeting complex, whereas one antagonist of ionotropic receptors prevents intracellular trafficking of Smo to the PC. Together, these findings identify several compounds with the potential to treat drug-resistant SmoM2-driven cancer forms, but also reveal off-target effects of established drugs in the clinics.

Efficacy of Hedgehog pathway inhibitors in Basal cell carcinoma

Basal cell carcinoma (BCC) is the most commonly diagnosed cancer. While most BCCs are amenable to surgery, some tumors can reach a more advanced stage or metastasize, and become ineligible for surgical resection or radiotherapy. Abnormal activation of the Hedgehog (Hh) pathway is a key driver in BCC pathophysiology. Consequently, inhibitors of the Hh pathway have been developed. Molecules that inhibit the receptor protein Smoothened (SMO) are the most advanced in clinical development. Vismodegib is the first-in-class SMO inhibitor and has been approved in a number of countries for the treatment of metastatic or locally advanced BCC. Several molecules have demonstrated antitumoral activity, but treatment may be limited in duration by a number of side effects, and it is not yet established whether these agents are truly curative or whether continued treatment will be required. Resistance to SMO inhibition has been reported in the clinic for which incidence and mechanisms must be elucidated to inform future therapeutic strategies. Intermittent dosing regimens to improve tolerability, as well as neoadjuvant use of Hh pathway inhibitors, are currently under investigation. Here, we review the most recent outcomes obtained with Hh inhibitors under clinical investigation in BCC.

Emerging drugs and combination strategies for basal cell carcinoma

INTRODUCTION

Basal cell carcinoma (BCC) is a malignancy that is driven by an activated Hedgehog (Hh) pathway. Smoothened inhibitors are a new promising treatment option for patients with locally advanced or metastatic BCC or basal cell nevus syndrome. But long-term data are still limited, the optimal treatment duration is not yet defined and there are already documented cases with acquired resistance.

AREAS COVERED

Treatment modalities with Hh inhibitors, side effects and potential pharmacological combination options are discussed. The current literature, including PubMed, Cochrane database and registered trials on ClinicalTrials.gov, was searched.

EXPERT OPINION

BCCs typically regress during therapy with Hh inhibitors. Muscle toxicity, dysgeusia and hair loss can be considered as on target adverse reactions. Muscle toxicity is the dose-limiting toxicity of sonidegib. It was not seen with vismodegib because of its high binding to plasma protein α-1-acid glycoprotein. Sonidegib is different and shows a clear dose-toxicity relationship, which allows to address the question of whether there is a dose dependency of regression rate, cure rate and progression-free survival. In addition, basic research has offered strategies to enhance efficacy by the combination with other molecules, such as EGFR inhibitors, MEK inhibitors or immunotherapy.

A phase I, multicenter, open-label, first-in-human, dose-escalation study of the oral smoothened inhibitor Sonidegib (LDE225) in patients with advanced solid tumors

PURPOSE

This phase I trial was undertaken to determine the maximum tolerated dose (MTD), dose-limiting toxicities (DLT), safety, tolerability, pharmacokinetics, pharmacodynamics, and preliminary antitumor activity of the novel smoothened inhibitor sonidegib (LDE225), a potent inhibitor of hedgehog signaling, in patients with advanced solid tumors.

EXPERIMENTAL DESIGN

Oral sonidegib was administered to 103 patients with advanced solid tumors, including medulloblastoma and basal cell carcinoma (BCC), at doses ranging from 100 to 3,000 mg daily and 250 to 750 mg twice daily, continuously, with a single-dose pharmacokinetics run-in period. Dose escalations were guided by a Bayesian logistic regression model. Safety, tolerability, efficacy, pharmacokinetics, and biomarkers in skin and tumor biopsies were assessed.

RESULTS

The MTDs of sonidegib were 800 mg daily and 250 mg twice daily. The main DLT of reversible grade 3/4 elevated serum creatine kinase (18% of patients) was observed at doses ≥ the MTD in an exposure-dependent manner. Common grade 1/2 adverse events included muscle spasm, myalgia, gastrointestinal toxicities, increased liver enzymes, fatigue, dysgeusia, and alopecia. Sonidegib exposure increased dose proportionally up to 400 mg daily, and displayed nonlinear pharmacokinetics at higher doses. Sonidegib exhibited exposure-dependent reduction in GLI1 mRNA expression. Tumor responses observed in patients with medulloblastoma and BCC were associated with evidence of hedgehog pathway activation.

CONCLUSIONS

Sonidegib has an acceptable safety profile in patients with advanced solid tumors and exhibits antitumor activity in advanced BCC and relapsed medulloblastoma, both of which are strongly associated with activated hedgehog pathway, as determined by gene expression.

Unraveling the therapeutic potential of the Hedgehog pathway in cancer

Major progress has been made in recent years in the development of Hedgehog (Hh) pathway inhibitors for the treatment of patients with cancer. Promising clinical trial results have been obtained in cancers that harbor activating mutations of the Hh pathway, such as basal cell carcinoma and medulloblastoma. However, for many cancers, in which Hh ligand overexpression is thought to drive tumor growth, results have been disappointing. Here we review the preclinical data that continue to shape our understanding of the Hh pathway in tumorigenesis and the emerging clinical experience with smoothened inhibitors.

Targeted therapy for advanced Basal-cell carcinoma: vismodegib and beyond

Basal-cell carcinoma is a commonly occurring skin malignancy that has the potential to progress into locally invasive or resistant disease, as well as spread distantly. Due to advances in the molecular understanding of the disease over the last two decades, it has been discovered that the Hedgehog pathway plays an important role in the pathogenesis of this disease and can be exploited as a treatment target. Several agents that inhibit the Hedgehog pathway have reached clinical studies and one drug, vismodegib, has recently been US Food and Drug Administration (FDA) approved based on clinical activity and tolerability in patients with advanced basal-cell carcinoma. This review will describe the clinical development of vismodegib, as well as the proper application of the drug in clinical practice. Other important clinical questions, such as mechanisms of resistance to vismodegib and the role of other Hedgehog pathway inhibitors currently in development will also be discussed.

Overlapping activities of TGF-β and Hedgehog signaling in cancer: therapeutic targets for cancer treatment

Recent advances in the field of cancer therapeutics come from the development of drugs that specifically recognize validated oncogenic or pro-metastatic targets. The latter may be mutated proteins with altered function, such as kinases that become constitutively active, or critical components of growth factor signaling pathways, whose deregulation leads to aberrant malignant cell proliferation and dissemination to metastatic sites. We herein focus on the description of the overlapping activities of two important developmental pathways often exacerbated in cancer, namely Transforming Growth Factor-β (TGF-β) and Hedgehog (HH) signaling, with a special emphasis on the unifying oncogenic role played by GLI1/2 transcription factors. The latter are the main effectors of the canonical HH pathway, yet are direct target genes of TGF-β/SMAD signal transduction. While tumor-suppressor in healthy and pre-malignant tissues, TGF-β is often expressed at high levels in tumors and contributes to tumor growth, escape from immune surveillance, invasion and metastasis. HH signaling regulates cell proliferation, differentiation and apoptosis, and aberrant HH signaling is found in a variety of cancers. We discuss the current knowledge on HH and TGF-β implication in cancer including cancer stem cell biology, as well as the current state, both successes and failures, of targeted therapeutics aimed at blocking either of these pathways in the pre-clinical and clinical settings.

Small molecule inhibitors of the hedgehog signaling pathway for the treatment of cancer

Over the past decade, the Hedgehog signaling pathway has attracted considerable interest because the pathway plays important roles in the tumorigenesis of several types of cancer as well as developmental processes. It has also been observed that Hedgehog signaling regulates the proliferation and self-renewal of cancer stem cells. A great number of Hedgehog pathway inhibitors have been discovered through small molecule screens and subsequent medicinal chemistry efforts. Among the inhibitors, several Smo antagonists have reached the clinical trial phase. It has been proved that the inhibition of Hedgehog signaling with Smo antagonists is beneficial to cancer patients with basal cell carcinoma and medulloblastoma. In this review, we provide an overview of Hedgehog pathway inhibitors with focusing on the preclinical and/or clinical efficacy and molecular mechanisms of these inhibitors.

Advances in the treatment of Basal cell carcinoma: Hedgehog inhibitors

Basal cell carcinoma (BCC) is the most common tumor of the skin and can result in significant morbidity as well as costs. The discovery of aberrant Hedgehog (HH) signaling in patients with genetic propensity to develop BCCs has resulted in a better understanding of the genetic abnormalities leading to the development of BCC. The current state of knowledge with regard to the genetics of BCC is discussed. Existing therapies are reviewed, in particular new targeted therapies to the HH signaling pathway that have resulted in a landmark breakthrough for patients with refractory BCC. Data from recent and ongoing trials are presented.

Vismodegib

Vismodegib (GDC-0449), an orally bioavailable small-molecule inhibitor of Hedgehog signaling, was recently approved by the U.S. Food and Drug Administration for the treatment of basal cell carcinoma that is either metastatic or locally advanced in patients who are not candidates for surgical resection or radiation. Given the absence of previously defined effective drug therapy for this disease, approval was granted primarily on the basis of outcome of a nonrandomized parallel cohort phase II study of 99 patients with advanced basal cell carcinoma, with a primary endpoint of objective response rate. Response rates of 30.3% and 42.9% were observed in metastatic and locally advanced cohorts in this study, respectively, associated with median progression-free survival in both cohorts of 9.5 months. Ongoing clinical investigations include evaluation of the potential efficacy of vismodegib in a variety of diseases and in combination with other agents. The mechanism of action, preclinical and clinical data, and potential utility in other disease contexts are reviewed here.

The controversial role of the Hedgehog pathway in normal and malignant hematopoiesis

Hedgehog (Hh) is a developmental signaling pathway in which Hh ligands bind Patched (Ptch), which relieves its inhibition of Smoothened (Smo), allowing the Gli family of transcription factors to translocate to the nucleus and activate Hh target genes. The role of Hh signaling in hematopoiesis is controversial and ill defined. Although some groups observed self-renewal defects with decreased replating and reduced efficiency of secondary murine transplants, other groups reported no hematopoietic phenotypes, which may be related to the timing of Hh abrogation. In malignant hematopoiesis, most attention has been focused on the role of Hh signaling in chronic myeloid leukemia (CML), considered by many to be a stem cell disorder that bears the constitutively active BCR-ABL tyrosine kinase. Despite the elimination of most leukemia cells through BCR-ABL inhibition, most patients remain PCR positive, suggesting that the putative CML stem cell may be resistant to kinase antagonism. Groups are now exploring the Hh pathway as an alternate pathway supporting CML stem cell survival. Knockdown or inhibition of Smo abrogates or delays the appearance of CML in several in vitro and in vivo models. These data have lead to clinical trials using BCR-ABL kinase and novel Smo inhibitors in combination.

Targeting the Hedgehog pathway in cancer: can the spines be smoothened?

Aberrant Hedgehog (Hh) pathway signaling has been suggested to play a role in the development of multiple solid tumors and hematologic malignancies. GDC-0449 is a novel first-in-human, first-in-class smoothened (SMO) inhibitor, which has completed its phase I evaluation and achieved proof of concept in tumors with Hh pathway mutations.