Rocky Lowenthal,a Megan Taylor,a Jennifer A. Gidden,b Billie Heflin,a Jackson O. Lay, Jr,b,c Nathan Avaritt,a Alan J. Tackett,a,* and Alicja Urbaniaka,*
Keywords: Melanoma, Trametes versicolor, Coriolus versicolor, Mushroom, Turkey tail
Abstract
Melanoma is one of the most aggressive forms of skin cancer and is characterized by high metastatic potential. Despite improvements in early diagnosis and treatment, the mortality rate among metastatic melanoma patients continues to represent a significant clinical challenge. Therefore, it is imperative that we search for new forms of treatment. Trametes versicolor is a mushroom commonly used in Chinese traditional medicine due to its numerous beneficial properties. In the present work, we demonstrate T. versicolor fruiting body and mycelium ethanol extracts exhibit potent cytotoxic activity towards A375 (IC50 = 663.3 and 114.5 μg/mL respectively) and SK- MEL-5 (IC50 = 358.4 and 88.6 μg/mL respectively) human melanoma cell lines. Further studies revealed that T. versicolor mycelium extract induced apoptotic cell death and poly (ADP-ribose) polymerase cleavage, upregulated the expression of autophagy-associated marker LC3-II, increased the presentation of major histocompatibility complex II and expression of programmed death-ligand receptor, and inhibited cell migration in SK- MEL-5 cells. Therefore, our present findings highlight the therapeutic potential of T. versicolor mycelium extract for the treatment of melanoma and merit further study.
Introduction
Melanoma arises from genetic mutations in melanocytes—pigmented cells found largely in the skin [1]. Its incidence has increased dramatically over the last 30 years [2]. Although melanoma accounts for approximately 1% of skin cancers [2], it is responsible for nearly 80% of all deaths from dermatological malignancies [3]. Current therapeutic approaches vary depending on tumor progression and patients’ health and include tumor removal, chemotherapy, metastasectomy, immunotherapy, radiotherapy, photodynamic therapy, and forms of targeted therapy [4]. Major limitations in treating melanoma are related to the adverse side effects of treatments as well as reduced drug efficiency [4]. New forms of therapy that overcome these limitations while combating the increased incidence of melanoma are highly desirable.
Chemotherapy is one of the main forms of cancer treatment, with multiple examples of approved drugs that have natural origin [5]. Many of these drugs include compounds from fungal sources such as doxorubicin, daunomycin, mitomycin C, and bleomycin [5].
Medicinal mushrooms, in addition to their nutritional value, have emerged in recent years as adjuvants to conventional chemo- and radiotherapies to both increase their effectiveness and reduce side effects [6]. Trametes versicolor (Synn. Coriolus versicolor), also known as Turkey Tail mushroom, is one of the best investigated medicinal mushrooms [5]. It is a common fungus found in all regions of temperate Asia, North America, and Europe [5]. T. versicolor has been used in Chinese traditional medicine for at least 2000 years, where it is known to have general health-promoting effects [5]. Numerous studies and clinical trials also point to its anti-cancer activity [5,7–9]. The antitumor properties of T. versicolor are mediated not only through the direct cytotoxic effect of its bioactive compounds but also by immunomodulating regulation [10–12]. In particular, bioactive compounds from T. versicolor were shown to increase the activity of monocytes and natural killer cells, elevate the production of reactive oxygen species, upregulate the level of cytokines such as tumor necrosis factor (TNF) α, interferon (IFN) ɣ, and interleukin (IL)− 6 [11,13–16]. While individual studies support the use of T. versicolor due to putative immunity benefits [12], characterization of direct interactions between T. versicolor extract and tumor cells and the utility of its combination with other anti-cancer drugs, have not been thoroughly studied.
The clinical benefits of the fruiting body of the organism T. versicolor are thought to be derived from polysaccharopeptides (PSP), proteoglycans, and polysaccharide-K (Krestin, PSK) produced during growth and development [5,17,18]. T. versicolor also has a highly bioactive mycelium [19], the branching, thread-like hyphae may contain a broader profile of bioactive compounds than the fruiting body, including up to 40% more protein-coding genes [20]. Prior studies have shown that these macromolecules of T. versicolor can induce direct cell cycle inhibition and apoptosis in cancer cells [5] and can activate immune cells and pro-inflammatory cytokine signaling [20]. Additionally, T. versicolor extract was shown to be well tolerated clinically without adverse side effects [9,21], though additional research is needed to determine the exact mechanisms by which it elicits these reponses.
Due to T. versicolor’s history of use in Asia, potential to work directly against invading cancers, and immunostimulatory properties, the mushroom has been selected for additional studies to determine its efficacy as a monotherapy against melanoma tumor cells as well as in combination with other drugs as a novel therapeutic strategy. In particular, the present study aims to evaluate the cytotoxic effect of T. versicolor’s fruiting body and mycelium ethanol extracts on the A375 and SK-MEL-5 human melanoma cell lines. We further investigated the ability of T. versicolor’s mycelium extract to induce apoptosis, reduce cell migration, increase major histocompatibility complex (MHC) II presentation, and increase the cleavage of poly (ADP-ribose) polymerase (PARP) and autophagy-associated marker LC3-II in the SK-MEL-5 cell line. Additionally, we performed a combination assay to determine whether T. versicolor’s mycelium extract would enhance the activity of paclitaxel, ABT-263, or palbociclib—drugs commonly used to treat melanoma in clinics.