Basal cell carcinoma: a paradigm for targeted therapies

Update in the treatment of non-melanoma skin cancers: the use of PD-1 inhibitors in basal cell carcinoma and cutaneous squamous-cell carcinoma

Non-melanoma skin cancer (NMSC) includes a wide range of cutaneous tumors, the most frequent of which are basal cell carcinoma (BCC) and cutaneous squamous cell carcinoma (CSCC). Although NMSC is usually cured by surgical resection, in rare cases it can progress to locally advanced and metastatic disease. Risk factors for advanced disease include comorbidities, neglect, and immunosuppression. Advanced NMSC may require systemic treatment if surgery and radiation are not feasible. Chemotherapy, epidermal growth factor receptor (EGFR) inhibitors in CSCC, and hedgehog inhibitors in BCC have been used but are generally of limited benefit, with responses often short-lived and toxicity issues. Given the high mutational burden of NMSC, the use of immunotherapy has been investigated and two anti-PD-1 antibodies, cemiplimab and pembrolizumab, are approved for the treatment of advanced CSCC not curable by surgery or radiation. Both have shown durable responses with good tolerability in patients in phase II trials and anti-PD-1 therapy is now the standard of care for locally advanced and metastatic CSCC. PD-1 blockade is also approved as second-line therapy in advanced BCC, with frequent and durable responses after failure on hedgehog inhibitor therapy. PD-1 checkpoint inhibition is being assessed for NMSC in combination with other modalities, including oncolytic viruses and EGFR inhibitors. Adjuvant and neoadjuvant use of cemiplimab and pembrolizumab is also being investigated with several ongoing trials. Further clinical trials of immunotherapy must be prioritized in NMSC for further improvement in outcomes.

PKAc-directed interaction and phosphorylation of Ptc is required for Hh signaling inhibition in Drosophila

Ptc is a gatekeeper to avoid abnormal Hh signaling activation, but the key regulators involved in Ptc-mediated inhibition remain largely unknown. Here, we identify PKAc as a key regulator required for Ptc inhibitory function. In the absence of Hh, PKAc physically interacts with Ptc and phosphorylates Ptc at Ser-1150 and -1183 residues. The presence of Hh unleashes PKAc from Ptc and activates Hh signaling. By combining both in vitro and in vivo functional assays, we demonstrate that such Ptc–PKAc interaction and Ptc phosphorylation are both important for Ptc inhibitory function. Interestingly, we further demonstrate that PKAc is subjected to palmitoylation, contributing to its kinase activity on plasma membrane. Based on those novel findings, we establish a working model on Ptc inhibitory function: In the absence of Hh, PKAc interacts with and phosphorylates Ptc to ensure its inhibitory function; and Hh presence releases PKAc from Ptc, resulting in Hh signaling activation.

Hedgehog- and mTOR-targeted therapies for advanced basal cell carcinomas

Basal cell carcinomas (BCCs) are the most frequent human cancer. Over 90% of all BCCs have a mutation in PTCH1 or smoothened, two conducting proteins of the Hedgehog pathway. They rarely progress deeply and metastasize; however, if they do, these advanced basal cell carcinoma become amenable to treatment by inhibiting the Hedgehog and the P13K-mTOR pathways. Such innovative drugs include vismodegib, cyclopamine, itraconazole, everolimus and a few other agents that are in early clinical development.

Molecular and genetic aspects of odontogenic lesions

In this article we outline the molecular findings of select odontogenic tumors. In each section, we briefly review selected the clinicoradiographic, histologic, immunologic features, focusing on the molecular findings and their applications in practice. The understanding of molecular pathobiology at various other organ sites has developed quite rapidly in recent years, however much remains unknown about the genetic profile of odontogenic tumors. Improved understanding of mutations in odontogenic tumors may clarify classification schema and elucidate targets for novel therapies. Molecular testing will no doubt improve our understanding of odontogenic tumor pathogenesis and will likely be, someday, an important component of routine clinical practice and its role will only increase in the coming years.

ErbB2 signaling activates the Hedgehog pathway via PI3K-Akt in human esophageal adenocarcinoma: identification of novel targets for concerted therapy concepts

The Hedgehog pathway plays an important role in the pathogenesis of several tumor types, including esophageal cancer. In our study, we show an expression of the ligand Indian hedgehog (Ihh) and its downstream mediator Gli-1 in primary resected adenocarcinoma tissue by immunohistochemistry and quantitative PCR in fifty percent of the cases, while matching healthy esophagus mucosa was negative for both proteins. Moreover, a functionally important regulation of Gli-1 by ErbB2-PI3K-mTORC signaling as well as a Gli-1-dependent regulation of Ihh in the ErbB2 amplified esophageal adenocarcinoma cell line OE19 was observed. Treatment of OE19 cells with the Her2 antibody trastuzumab, the PI3K-mTORC1 inhibitor NVP BEZ235 (BEZ235) or the knockdown of Akt1 resulted in a downregulation of Gli-1 and Ihh as well as in a reduction of viable OE19 cells in vitro. Interestingly, the Hedgehog receptor Smo, which acts upstream of Gli-1, was not expressed in OE19 cells and in the majority of primary human esophageal adenocarcinoma, suggesting a non-canonical upregulation of Gli-1 expression by the ErbB2-PI3K axis. To translate our findings into a therapeutic concept, we targeted ErbB2-PI3K-mTORC1 by trastuzumab and BEZ235, combining both compounds with the Gli-1/2 inhibitor GANT61. The triple combination led to significantly stronger reduction of tumor cell viability than cisplatinum or each biological alone. Therefore, concomitant blockage of the ErbB2-PI3K pathway and the Hedgehog downstream mediator Gli-1 may provide a new therapeutic strategy for esophageal cancer.

[Genodermatoses with malignant skin tumors]

Cutaneous malignancies can manifest as isolated and sporadic tumors as well as multiple and disseminated tumors. In the latter case they often point to a genetic disease, which either can be restricted to the skin exclusively or also involve extracutaneous organs in the context of a hereditary tumor syndrome. Such hereditary tumor syndromes are clinically and genetically very heterogeneous. Therefore, the prevailing specific skin tumors play an important diagnostic role in the case of complex symptom constellations. Elucidation of the genetic basis of rare monogenetically inherited disorders and syndromes can contribute to a better understanding of the pathogenesis of frequently occurring cutaneous malignancies because the mutated genes often encode proteins, which have a key position in metabolic signaling pathways that are of high significance for the development of targeted therapies. Here we provide an overview of genodermatoses, which are associated with basal cell carcinomas, sebaceous carcinomas, keratoacanthomas, squamous cell carcinomas and malignant melanomas.

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.

Mesoscopic fluorescence tomography of a photosensitizer (HPPH) 3D biodistribution in skin cancer

RATIONALE AND OBJECTIVES

Photodynamic therapy (PDT) is a promising strategy for treating cancer. PDT involves three components: a photosensitizer (PS) drug, a specific wavelength of drug-activating light, and oxygen. A challenge in PDT is the unknown biodistribution of the PS in the target tissue. In this preliminary study, we report the development of a new approach to image in three dimensions the PS biodistribution in a noninvasive and fast manner.

MATERIALS AND METHODS

A mesoscopic fluorescence tomography imaging platform was used to image noninvasively the biodistribution of 2-[1-hexyloxyethyl]-2 devinyl pyropheophorbide-a (HPPH) in preclinical skin cancer models. Seven tumors were imaged and optical reconstructions were compared to nonconcurrent ultrasound data.

RESULTS

Successful imaging of the HPPH biodistribution was achieved on seven skin cancer tumors in preclinical models with a typical acquisition time of 1 minute. Two-dimensional fluorescence signals and estimated three-dimensional PS distributions were located within the lesions. However, HPPH distribution was highly heterogeneous with the tumors. Moreover, HPPH distribution volume and tumor volume as estimated by ultrasound did not match.

CONCLUSIONS

The results of this proof-of-concept study demonstrate the potential of MFMT to image rapidly the HPPH three-dimensional biodistribution in skin cancers. In addition, these preliminary data indicate that the PS biodistribution in skin cancer tumors is heterogeneous and does not match anatomical data. Mesoscopic fluorescence molecular tomography, by imaging fluorescence signals over large areas with high spatial sampling and at fast acquisition speeds, may be a new imaging modality of choice for planning and optimizing of PDT treatment.