Dennis Ma

Chemoenzymatic Synthesis of Amaryllidaceae Constituents and Biological Evaluation of their C-1 Analogues. The Next Generation Synthesis of 7-Deoxypancratistatin and trans-Dihydrolycoricidine†

An efficient synthesis of C-1 derivatives of 7-deoxypancratistatin is reported. The key steps include the following: selective opening of an epoxide with aluminum acetylide in the presence of an aziridine; solid-state silica-gel-catalyzed opening of an aziridine; and oxidative cleavage of a phenanthrene core and its recyclization to phenanthridone to provide the key C-1 aldehyde 22. The conversion of this aldehyde to C-1 acetoxymethyl and C-1 hydroxymethyl derivatives is described along with the evaluation of their biological activity against several cancer cell lines and in an apoptosis study. The C-1 acetoxymethyl derivative has shown promising activity comparable to that of the natural product. In addition, a total synthesis of trans-dihydrolycoricidine and a formal total synthesis of 7-deoxypancratistatin are reported from aldehyde 22. Detailed experimental and spectral data are provided for all new compounds.

Selective cytotoxicity against human osteosarcoma cells by a novel synthetic C-1 analogue of 7-deoxypancratistatin is potentiated by curcumin.

The natural compound pancratistatin (PST) is a non-genotoxic inducer of apoptosis in a variety of cancers. It exhibits cancer selectivity as non-cancerous cells are markedly less sensitive to PST. Nonetheless, PST is not readily synthesized and is present in very low quantities in its natural source to be applied clinically. We have previously synthesized and evaluated several synthetic analogues of 7-deoxypancratistatin, and found that JC-TH-acetate-4 (JCTH-4), a C-1 acetoxymethyl analogue, possessed similar apoptosis inducing activity compared to PST. In this study, notoriously chemoresistant osteosarcoma (OS) cells (Saos-2, U-2 OS) were substantially susceptible to JCTH-4-induced apoptosis through mitochondrial targeting; JCTH-4 induced collapse of mitochondrial membrane potential (MMP), increased reactive oxygen species (ROS) production in isolated mitochondria, and caused release of apoptosis inducing factor (AIF) and endonuclease G (EndoG) from isolated mitochondria. Furthermore, JCTH-4 selectively induced autophagy in OS cells. Additionally, we investigated the combinatory effect of JCTH-4 with the natural compound curcumin (CC), a compound found in turmeric spice, previously shown to possess antiproliferative properties. CC alone had no observable effect on Saos-2 and U-2 OS cells. However, when present with JCTH-4, CC was able to enhance the cytotoxicity of JCTH-4 selectively in OS cells. Such cytotoxicity by JCTH-4 alone and in combination with CC was not observed in normal human osteoblasts (HOb) and normal human fetal fibroblasts (NFF). Therefore, this report illustrates a new window in combination therapy, utilizing a novel synthetic analogue of PST with the natural compound CC, for the treatment of OS.

A novel synthetic C-1 analogue of 7-deoxypancratistatin induces apoptosis in p53 positive and negative human colorectal cancer cells by targeting the mitochondria: enhancement of activity by tamoxifen

SummaryThe natural compound pancratistatin (PST), isolated from the Hymenocallis littoralis plant, specifically induces apoptosis in many cancer cell lines. Unlike many other chemotherapeutics, PST is not genotoxic and has minimal adverse effects on non-cancerous cells. However, its availability for preclinical and clinical work is limited due to its low availability in its natural source and difficulties in its chemical synthesis. Several synthetic analogues of 7-deoxypancratistatin with different modifications at C-1 were synthesized and screened for apoptosis inducing activity in human colorectal cancer (CRC) cells. We found that a C-1 acetoxymethyl derivative of 7-deoxypancratistatin, JC-TH-acetate-4 (JCTH-4), was effective in inducing apoptosis in both p53 positive (HCT 116) and p53 negative (HT-29) human CRC cell lines, demonstrating similar efficacy to that of natural PST. JCTH-4 was able to decrease mitochondrial membrane potential (MMP), increase levels of reactive oxygen species in isolated mitochondria, cause release of the apoptogenic factor cytochrome c (Cyto c) from isolated mitochondria, and induce autophagy in HCT 116 and HT-29 cells. Interestingly, when JCTH-4 was administered with tamoxifen (TAM), there was an enhanced effect in apoptosis induction, reactive oxygen species (ROS) production and Cyto c release by isolated mitochondria, and autophagic induction by CRC cells. Minimal toxicity was exhibited by a normal human fetal fibroblast (NFF) and a normal colon fibroblast (CCD-18Co) cell line. Hence, JCTH-4 is a novel compound capable of selectively inducing apoptosis and autophagy in CRC cells alone and in combination with TAM and may serve as a safer and more effective alternative to current cancer therapies.

Inhibition of stress induced premature senescence in presenilin-1 mutated cells with water soluble Coenzyme Q10

A water-soluble formulation of CoQ10 (WS-CoQ10) was shown to stabilize mitochondria and prevent oxidative stress-induced neuronal death. Presenilin-1 (PS-1)-mutated Alzheimers Disease (AD) fibroblasts (PSAF) were used for studying the effects of PS-1 mutation. PS-1 mutation correlated to increased reactive oxygen species (ROS) production and stress induced premature senescence (SIPS) in PSAF; WS-CoQ10 treatment decreased ROS generation, increased population doublings, and postponed SIPS. Treated PSAF had higher PCNA expression, and lower levels of MnSOD, p21, p16Ink4A, and Rb. WS-CoQ10 caused the resumption of autophagy in PSAF. Thus, WS-CoQ10 as inhibitor of SIPS and ameliorator of autophagy could be an effective prophylactic/therapeutic agent for AD.

Cancer Cell Mitochondria Targeting by Pancratistatin Analogs is Dependent on Functional Complex II and III

Enhanced mitochondrial stability and decreased dependence on oxidative phosphorylation confer an acquired resistance to apoptosis in cancer cells, but may present opportunities for therapeutic intervention. The compound pancratistatin (PST) has been shown to selectively induce apoptosis in cancer cells. However, its low availability in nature has hindered its clinical advancement. We synthesized PST analogs and a medium-throughput screen was completed. Analogs SVTH-7, -6, and -5 demonstrated potent anti-cancer activity greater than PST and several standard chemotherapeutics. They disrupted mitochondrial function, activated the intrinsic apoptotic pathway, and reduced growth of tumor xenografts in vivo. Interestingly, the pro-apoptotic effects of SVTH-7 on cancer cells and mitochondria were abrogated with the inhibition of mitochondrial complex II and III, suggesting mitochondrial or metabolic vulnerabilities may be exploited by this analog. This work provides a scaffold for characterizing distinct mitochondrial and metabolic features of cancer cells and reveals several lead compounds with high therapeutic potential.

Evaluation of the efficacy & biochemical mechanism of cell death induction by Piper longum extract selectively in in-vitro and in-vivo models of human cancer cells.

Background Currently chemotherapy is limited mostly to genotoxic drugs that are associated with severe side effects due to non-selective targeting of normal tissue. Natural products play a significant role in the development of most chemotherapeutic agents, with 74.8% of all available chemotherapy being derived from natural products. Objective To scientifically assess and validate the anticancer potential of an ethanolic extract of the fruit of the Long pepper (PLX), a plant of the piperaceae family that has been used in traditional medicine, especially Ayurveda and investigate the anticancer mechanism of action of PLX against cancer cells. Materials & Methods Following treatment with ethanolic long pepper extract, cell viability was assessed using a water-soluble tetrazolium salt; apoptosis induction was observed following nuclear staining by Hoechst, binding of annexin V to the externalized phosphatidyl serine and phase contrast microscopy. Image-based cytometry was used to detect the effect of long pepper extract on the production of reactive oxygen species and the dissipation of the mitochondrial membrane potential following Tetramethylrhodamine or 5,5,6,6′-tetrachloro-1,1′,3,3′-tetraethylbenzimidazolylcarbocyanine chloride staining (JC-1). Assessment of PLX in-vivo was carried out using Balb/C mice (toxicity) and CD-1 nu/nu immunocompromised mice (efficacy). HPLC analysis enabled detection of some primary compounds present within our long pepper extract. Results Our results indicated that an ethanolic long pepper extract selectively induces caspase-independent apoptosis in cancer cells, without affecting non-cancerous cells, by targeting the mitochondria, leading to dissipation of the mitochondrial membrane potential and increase in ROS production. Release of the AIF and endonuclease G from isolated mitochondria confirms the mitochondria as a potential target of long pepper. The efficacy of PLX in in-vivo studies indicates that oral administration is able to halt the growth of colon cancer tumors in immunocompromised mice, with no associated toxicity. These results demonstrate the potentially safe and non-toxic alternative that is long pepper extract for cancer therapy.

Selective Targeting of Cancer Cells by Oxidative Vulnerabilities with Novel Curcumin Analogs

Recently, research has focused on targeting the oxidative and metabolic vulnerabilities in cancer cells. Natural compounds like curcumin that target such susceptibilities have failed further clinical advancements due to the poor stability and bioavailability as well as the need of high effective doses. We have synthesized and evaluated the anti-cancer activity of several monocarbonyl analogs of curcumin. Interestingly, two novel analogs (Compound A and I) in comparison to curcumin, have increased chemical stability and have greater anti-cancer activity in a variety of human cancer cells, including triple-negative, inflammatory breast cancer cells. In particular, the generation of reactive oxygen species was selective to cancer cells and occurred upstream of mitochondrial collapse and execution of apoptosis. Furthermore, Compound A in combination with another cancer-selective/pro-oxidant, piperlongumine, caused an enhanced anti-cancer effect. Most importantly, Compound A was well tolerated by mice and was effective in inhibiting the growth of human triple-negative breast cancer and leukemia xenografts in vivo when administered intraperitoneally. Thus, exploiting oxidative vulnerabilities in cancer cells could be a selective and efficacious means to eradicate malignant cells as demonstrated by the curcumin analogs presented in this report with high therapeutic potential.

Structurally simplified biphenyl combretastatin A4 derivatives retain in vitro anti-cancer activity dependent on mitotic arrest

The cis-stilbene, combretastatin A4 (CA4), is a potent microtubule targeting and vascular damaging agent. Despite promising results at the pre-clinical level and extensive clinical evaluation, CA4 has yet to be approved for therapeutic use. One impediment to the development of CA4 is an inherent conformational instability about the ethylene linker, which joins two aromatic rings. We have previously published preliminary data regarding structurally simplified biphenyl derivatives of CA4, lacking an ethylene linker, which retain anti-proliferative and pro-apoptotic activity, albeit at higher doses. Our current study provides a more comprehensive evaluation regarding the anti-proliferative and pro-apoptotic properties of biphenyl CA4 derivatives in both 2D and 3D cancerous and non-cancerous cell models. Computational analysis has revealed that cytotoxicity of CA4 and biphenyl analogues correlates with predicted tubulin affinity. Additional mechanistic evaluation of the biphenyl derivatives found that their anti-cancer activity is dependent on prolonged mitotic arrest, in a similar manner to CA4. Lastly, we have shown that cancer cells deficient in the extrinsic pathway of apoptosis experience delayed cell death following treatment with CA4 or analogues. Biphenyl derivatives of CA4 represent structurally simplified analogues of CA4, which retain a similar mechanism of action. The biphenyl analogues warrant in vivo examination to evaluate their potential as vascular damaging agents.

Enhancement of apoptotic and autophagic induction by a novel synthetic C-1 analogue of 7-deoxypancratistatin in human breast adenocarcinoma and neuroblastoma cells with tamoxifen.

Breast cancer is one of the most common cancers amongst women in North America. Many current anti-cancer treatments, including ionizing radiation, induce apoptosis via DNA damage. Unfortunately, such treatments are non-selective to cancer cells and produce similar toxicity in normal cells. We have reported selective induction of apoptosis in cancer cells by the natural compound pancratistatin (PST). Recently, a novel PST analogue, a C-1 acetoxymethyl derivative of 7-deoxypancratistatin (JCTH-4), was produced by de novo synthesis and it exhibits comparable selective apoptosis inducing activity in several cancer cell lines. Recently, autophagy has been implicated in malignancies as both pro-survival and pro-death mechanisms in response to chemotherapy. Tamoxifen (TAM) has invariably demonstrated induction of pro-survival autophagy in numerous cancers. In this study, the efficacy of JCTH-4 alone and in combination with TAM to induce cell death in human breast cancer (MCF7) and neuroblastoma (SH-SY5Y) cells was evaluated. TAM alone induced autophagy, but insignificant cell death whereas JCTH-4 alone caused significant induction of apoptosis with some induction of autophagy. Interestingly, the combinatory treatment yielded a drastic increase in apoptotic and autophagic induction. We monitored time-dependent morphological changes in MCF7 cells undergoing TAM-induced autophagy, JCTH-4-induced apoptosis and autophagy, and accelerated cell death with combinatorial treatment using time-lapse microscopy. We have demonstrated these compounds to induce apoptosis/autophagy by mitochondrial targeting in these cancer cells. Importantly, these treatments did not affect the survival of noncancerous human fibroblasts. Thus, these results indicate that JCTH-4 in combination with TAM could be used as a safe and very potent anti-cancer therapy against breast cancer and neuroblastoma cells.

Corrigendum: Cancer Cell Mitochondria Targeting by Pancratistatin Analogs is Dependent on Functional Complex II and III

This corrects the article DOI: 10.1038/srep42957.