Withaferin A, a Cytotoxic Steroid from Vassobia breviflora, Induces Apoptosis in Human Head and Neck Squamous Cell Carcinoma

Abstract

As part of a program to discover drug leads from plant biodiversity, the present investigation was undertaken to explore the anticancer potential of compounds derived from selected Latin American plants. Bioassay-guided fractionation of a crude extract of the aerial parts of Vassobia breviflora led to the isolation of the withanolide-type steroidal lactone, withaferin A (1). This compound was tested for antiproliferative activity against the head and neck squamous cell carcinoma (HNSCC) cell lines, MDA1986, JMAR, UM-SCC-2, and JHU011. The inhibitory concentrations to reduce cell viability to 50% (IC 50 ) were determined by the MTS cytotoxicity assay and 1 reduced cell viability with IC 50 values in the range 0.5-2.2 μM. A mechanistic study showed that 1 induces apoptosis and cell death in HNSCC cells as well as a cell-cycle shift from G 0 /G 1 to G 2 /M. Cells treated with 1 exhibited inactivation of Akt and the reduction in total Akt concentration. This investigation constitutes the first report of the antiproliferative activity of withaferin A (1) against head and neck squamous carcinoma.Head and neck squamous cell carcinoma (HNSCC) is the fifth most common cancer in humans and accounts for 90% of all head and neck malignancies, with over 780,000 new cases diagnosed yearly worldwide.

Cytotoxic withanolide constituents of Physalis longifolia

“…a For cell lines used, see text. Withanolides 6,[9][10][11][12][13][14]17,18,20,and 21 were inactive for all cell lines used (IC 50 > 10 μM). …”

“…2,3,6 It has been reported that those withanolides displaying the most promising antitumor characteristics contain an α,β-unsaturated ketone in ring A, a 5β,6β-epoxy group in ring B, and a nine-carbon side chain with an α,β-unsaturated δ-lactone group. 10 The typical withanolide withaferin A (16) (Figure 1) contains these three moieties and has been shown in vitro and in vivo to suppress the growth of an array of tumor cells, including breast, pancreatic, prostate, lung, leukemia, and head and neck squamous cell carcinoma (HNSCC), by inducing apoptosis, 11 thus possessing potential application as an antiproliferative agent. As part of an ongoing study of withanolides from plant sources, 11,12 a library of 224 native plant extracts from the U.S. Great Plains was evaluated for cytotoxic activities against HNSCC and melanoma cell lines using the MTS viability assay.…”

Antiproliferative withanolides from the solanaceae: A structure-activity study

“…From the biogenetic origin, it is likely that type I compounds are precursors to the more advanced structural types II−XXII. Type I withanolides that display the most promising antiproliferative characteristics also contain Δ 2 -1-oxo-functionality in ring A, a 5β,6β-epoxy-group in ring B, and a nine-carbon side chain incorporating the δ-lactone functionality found in withaferin A 1 [17], withacnistin 59 [18,19], withanolide D 48 [20][21][22][23], withanolide E 36 [8,[24][25][26][27], and 4β-hydroxywithanolide E 37 (Fig. 4) [8,[24][25][26][27].…”

“…Withaferin A 1 (Fig. 1) was shown to induce apoptosis in vitro and in vivo by suppressing the growth of an array of tumor cells, including breast, pancreatic, prostate, lung, leukemia, as well as various head and neck squamous cell carcinomas (HNSCCs) [17]. This compound has the potential for development as an antiproliferative agent.…”

“…Of these, 29 withanolides (1, 3-6, 9, 12-18, and 20-35) were isolated from the three taxa investigated whereas the remaining six analogues (2, 7, 8, 10, 11, and 19) were prepared from the naturally occurring compounds (1, 6, and 9). In this report, we provide a summary of the withanolide chemistry and anti proliferative results obtained during our studies [17,28,29] and attempt to provide a structure-activity relationship analysis (SARA) in comparison with published data in the literature for other withanolides with antiproliferative activity.…”