Evaluation of natural products derived from Physalis peruviana (poha) as anticancer agents

Abstract

Cancer continues to be a leading cause of death in the United States and worldwide. Natural products obtained from plants have been the source of many approved anticancer drugs. This study is part of an ongoing collaboration to discover plant-derived anticancer agents. A tropical plant of the family Solanaceae (Physalis peruviana L.), collected on the island of Hawai‘i, was investigated as a possible source of anticancer lead compounds. Our initial study showed that extracts of the fruits and aerial parts of P. peruviana decreased the activities of Nuclear Factor-kappa B (NF-B) and Signal Transducer and Activator of Transcription 3 (STAT3), two key redox-regulated transcription factors that control cellular and disease processes. Constitutive STAT3 activation is a molecular abnormality that is causally linked to cancer aggressiveness. This dissertation describes the isolation, structure elucidation, and biological evaluation of withanolides isolated from P. peruviana (aerial parts and fruits). In addition, acetylated analogues and their biological evaluation have been determined. Bioactivity-guided fractionation of the extracts of P. peruviana yielded five new withanolides, physaperuvin G (1), physaperuvin I (2), physaperuvin J (3), physaperuvin M (4), and physaperuvin N (5) along with twelve known analogs (6  17). Six withanolides acetylated derivatives (1a, 4a, 8a, 10a, 13a, and 14a) were subsequently semi-synthesized via acetylation. The structures of 1 ‒ 5 were determined by spectroscopic methods, including UV, IR, [α]25D, CD, HRMS, 1D (1H-, 13C-, and DEPT-NMR) and 2D (COSY-, HSQC-, HMBC-, NOESY-NMR) NMR. The absolute configuration of compounds 1 and 4 were confirmed using X-ray diffraction analysis. In order to identify biological activities of anti-inflammatory and inhibition of cell viability activity against cancer cells line, all compounds were evaluated for: a) inhibition of nitric oxide (NO) production in lipopolysaccharide (LPS)-activated murine macrophage RAW 264.7 cells; b) tumor necrosis factor alpha (TNF-α)-induced NF-B activity using stable transfected human embryonic kidney cells, 293; and c) inhibitory effects against U251MG glioblastoma and MDA-MB-231 breast cancer cells. Of these, compounds 4, 5, 6, 13 and acetyl derivatives 1a, 4a, 8a, 13a, showed the highest inhibitory activity against TNF α-induced NF-B activity with IC50 values in the range of 0.01  0.8 μM. The remaining withanolides were either moderately active (IC50 1.1  24.6 μM) or inactive. Compound 13 showed the highest inhibitory activity (IC50 0.2 μM) against LPS-induced NO release at non-cytotoxic levels (IC50 50 M). Compounds 5, 8, and 10 inhibited NO production at IC50 values in the range of 2.3  3.3 μM without apparent cytotoxicity to host cells. The acetylated derivatives 8a, 10a, and 13a were similarly active at IC50 values in the range of 0.24  1.8 μM. However, these compounds with the exception of compound 10a, exhibited cytotoxicity to host cells. Compound 13 and four of its acetylated derivatives (4a, 8a, 10a, and 13a) exhibited potent inhibitory effects against the viability of U251MG glioblastoma and MDA-MB-231 breast cancer cells that harbor aberrantly-active STAT3, compared to normal NIH-3T3 mouse fibroblast cells that show no evidence of activated STAT3. Compounds 13 and 8a inhibited constitutively active STAT3 at IC50 values in the range of 1.3  2.4 µM. In addition, treatment of U251MG and MDA-MB-231 cells with compounds 13 and 8a inhibited the formation of intracellular phospho-tyrosine STAT3 (pY705STAT3). In brief, our investigation of P. peruviana collected in Pepeekeo, Hawai‘i, provided new and active lead compounds for possible development in the fight against cancer.