Immune Checkpoint Inhibitors: Recent Clinical Advances and Future Prospects.

Immune checkpoints are vital molecules and pathways of the immune system with defined roles of controlling immune responses from being destructive to the healthy cells in the body. They include inhibitory receptors and ligands, which check the recognition of most cancers by the immune system. This happens when proteins on the surface of T cells called immune checkpoint proteins identify partner proteins on the cancer cells and bind to them, sending brake signals to the T cells to evade immune attack. However, drugs called immune checkpoint inhibitors block checkpoint proteins from binding to their partner proteins, thereby inhibiting the brake signals from being sent to T cells. This eventually allows the T cells to destroy cancer cells and arbitrate robust tumor regression. Many such inhibitors have already been approved and are in various developmental stages. The well-illustrated inhibitory checkpoints include the cytotoxic T lymphocyte-associated molecule-4 (CTLA-4), programmed cell death receptor-1 (PD-1), and programmed cell death ligand-1 (PD-L1). Though many molecules blocking these checkpoints have shown promise in treating many malignancies, such treatment options have limited success in terms of the immune response in most patients. Against this backdrop, exploring new pathways and next-generation inhibitors becomes imperative for developing more responsive and effective immune checkpoint therapy. Owing to the complex biology and unexplored ambiguities in the mechanistic aspects of immune checkpoint pathways, analysis of the activity profile of new drugs is the subject of strenuous investigation. We herein report the recent progress in developing new inhibitory pathways and potential therapeutics and delineate the developments based on their merit. Further, the ensuing challenges towards developing efficacious checkpoint therapies and the impending opportunities are also discussed.

Synthesis, Aromatase Inhibitory, Antiproliferative and Molecular Modeling Studies of Functionally Diverse D-Ring Pregnenolone Pyrazoles.

BACKGROUND: Aromatase, a cytochrome P450 hemoprotein that is responsible for estrogen biosynthesis by conversion of androgens into estrogens, has been an attractive target in the treatment of hormonedependent breast cancer. Design of new steroidal aromatase inhibitors becomes imperative. OBJECTIVE: Synthesis and biological evaluation of two classes of structurally and functionally diverse D-ring pregnenolone pyrazoles as type I aromatase inhibitors and antiproliferative agents. METHODS: Pregnenolone (1) was converted to 3ß-hydroxy-21-hydroxymethylidenepregn-5-en-20-one (2), which upon cyclization with phenylhydrazine generated regioisomeric pairs of pyrazoles 4 and 5. Further, Knoevenagel condensation of pregnenolone (1) with 3-oxo-3-phenylpropanenitrile (6) produced 2-benzoyl-3-(3b-hydroxyandrostan- 5-ene-20-ylidene)-but-2-enenitrile (7), which upon cyclization with hydrazine or phenylhydrazine generated the pyrazoles 8 and 9. All new steroidal derivatives were tested for their aromatase inhibition activity using Dibenzylfluorescein (DBF) based fluorescence assay developed by Stresser et al. Antiproliferative activities were measured using Sulforhodamine B assay. The activities were promising and there was a coherence between aromatase inhibitory and antiproliferative activities. RESULTS: The study reveals the immense potential of pregnenolone pyrazoles as aromatase inhibitors for the treatment of breast cancer. Molecular docking studies proved efficient binding of the new steroidal analogs on human placental aromatase. CONCLUSION: In the overall study, most of the compounds exhibited potential activity for the treatment of hormone dependent breast cancer. Compounds 4c and 4d were found to be the most promising pharmacons. Furthermore, compounds 4c and 4d were applied for their molecular docking study on human placental aromatase to predict their possible binding modes with the enzyme. These studies revealed that such molecules have high scope and potential for further investigation towards the treatment of estrogen dependent breast cancer.

Potential Repurposed Therapeutics and New Vaccines against COVID-19 and Their Clinical Status.

SARS-CoV-2, the virus that causes coronavirus disease 2019 (COVID-19), was first reported in Wuhan, China, in December 2019. Since then, the virus has stretched its grip to almost all the countries in the world, affecting millions of people and causing enormous casualties. The World Health Organization (WHO) declared COVID-19 a pandemic on March 11, 2019. As of June 12, 2020, almost 7.30 million people have already been infected globally, with 413,000 reported casualties. In the United States alone, 2.06 million people have been infected and 115,000 have succumbed to this pandemic. A multipronged approach has been launched toward combating this pandemic, with the main focus on exhaustive screening, developing efficacious therapies, and vaccines for long-term immunity. Several pharmaceutical companies in collaboration with various academic institutions and governmental organizations have started investigating new therapeutics and repurposing approved drugs so as to find fast and affordable treatments against this disease. The present communication is aimed at highlighting the efforts that are currently underway to treat or prevent SARS-CoV-2 infection, with details on the science, clinical status, and timeline for selected investigational drugs and vaccines. This article is going to be of immense help to the scientific community and researchers as it brings forth all the necessary clinical information of the most-talked-about therapeutics against SARS-CoV-2. All the details pertaining to the clinical status of each therapeutic candidate have been updated as of June 12, 2020.

Development of N-Acetylated Dipalmitoyl-S-Glyceryl Cysteine Analogs as Efficient TLR2/TLR6 Agonists.

Cancer vaccine is a promising immunotherapeutic approach to train the immune system with vaccines to recognize and eliminate tumors. Adjuvants are compounds that are necessary in cancer vaccines to mimic an infection process and amplify immune responses. The Toll-like receptor 2 and 6 (TLR2/TLR6) agonist dipalmitoyl-S-glyceryl cysteine (Pam2Cys) was demonstrated as an ideal candidate for synthetic vaccine adjuvants. However, the synthesis of Pam2Cys requires expensive N-protected cysteine as a key reactant, which greatly limits its application as a synthetic vaccine adjuvant in large-scaled studies. Here, we report the development of N-acetylated Pam2Cys analogs as TLR2/TLR6 agonists. Instead of N-protected cysteine, the synthesis utilizes N-acetylcysteine to bring down the synthetic costs. The N-acetylated Pam2Cys analogs were demonstrated to activate TLR2/TLR6 in vitro. Moreover, molecular docking studies were performed to provide insights into the molecular mechanism of how N-acetylated Pam2Cys analogs bind to TLR2/TLR6. Together, these results suggest N-acetylated Pam2Cys analogs as inexpensive and promising synthetic vaccine adjuvants to accelerate the development of cancer vaccines in the future.

Synthesis, 17α-hydroxylase-C17,20-lyase Inhibitory and 5AR Reductase Activity of Novel Pregnenolone Derivatives.

BACKGROUND: The potential of steroids for development into lead pharmacological molecules lies in the regulation of a variety of biological processes by these molecules and also because of these being a fundamental class of signaling molecules. Steroid based scaffolds have been extensively used as active pharmaceutical agents for the treatment of various diseases including the deadly disease of cancer which despite the recent advances in the early diagnosis, prevention and therapy, remains a clinical challenge affecting millions of people world over and is one of the leading causes of death. It thus warrants the development of new drugs against this dreadful disease through exploitation of emerging molecularly defined targets. METHODS: The present study explores the effect of novel steroidal pyrazolines as presumed inhibitors of 5α- reductase (5AR) and 17α-hydroxylase-C17,20-lyase as a target for treatment of prostate cancer. A series of 1,5- diaryl pyrazoline pregnenolones were synthesized and screened for 5α-reductase inhibitory activities. Synthesis of the analogs is multistep and proceeds in good overall yields. The key step in the synthesis of 1,5- disubstituted pyrazolinyl pregnenolones is the heterocyclization of bezylidine derivatives (3) in presence of phenylhydrazines (4) through the initial formation of the phenylhydrazones, which undergo concomitant cyclization to generate the stable pyrazoline derivatives. RESULTS: All the synthesised D-ring 1,5-disubstituted pyrazolinyl pregnenolone derivatives (5a-l) were screened for prostate cancer cell inhibitory, 5α-reductase and 17α-hydroxylase-C17,20-lyase inhibitory activity. Amongst all the compounds screened for their 5α-reductase inhibitory activities, compound 5c, 5e, 5g and 5l were found to be the most active. Further, compounds 5g and 5h were found to have moderate 17α-hydroxylase-C17,20-lyase inhibitory activities. CONCLUSION: A series of D-ring 1,5-disubstituted pyrazolinyl pregnenolone derivatives (5a-l) were synthesized and screened for their prostate cancer cell inhibitory, 5a-reductase and 17α-hydroxylase-C17,20-lyase inhibitory activity. Amongst all the compounds screened for their 5α-reductase inhibitory activities, compound 5c, 5e, 5g and 5l were found to be the most active whereas compounds 5g and 5h were found to have moderate 17α- hydroxylase-C17,20-lyase inhibitory activities.

Cancer vaccine adjuvants--recent clinical progress and future perspectives.

Despite recent breakthroughs in the prognosis, prevention and treatment, cancer still remains the leading cause of death and affects millions of people worldwide. With the US FDA approval of various preventive cancer vaccines such as Gardasil (Merck), Cervarix (Glaxosmithkline) and the therapeutic vaccine Sipulencel-T (Provenge), cancer vaccine development is gaining huge ground. Approval of these vaccines has encouraged the concept of cancer treatment through cellular immunotherapy. The FDA approval of the above vaccines has provided support for renewed interest and attention which the development of new therapeutic cancer vaccines deserves. However, most of the new generation vaccines including that for cancer are poorly immunogenic sub-unit vaccines and thus essentially need adjuvants in their formulations to compensate for the immune suppression. Adjuvants are the essential components of a potent vaccine which increases the efficacy by enhancing the antigen-specific immune response. However, the design of a successful adjuvant is not easy because of the complexity and the difficulty in designing adjuvants that are safe, potent and economically viable. The present communication takes a short review of the advancements in adjuvant technology, current clinical scenario of new adjuvants and application of their molecularly defined formulations to new generation cancer vaccines which are currently under development.

Steroidal pyrazolines and pyrazoles as potential 5α-reductase inhibitors: synthesis and biological evaluation.

Taking pregnenolone as the starting material, two series of pyrazolinyl and pyrazolyl pregnenolones were synthesized through different routes. The synthesis of the analogs of both series is multistep and proceeds in good overall yields. While the key step in the synthesis of pyrazolinyl pregnenolones is the heterocyclization of benzylidine derivatives (3) in presence of hydrazine hydrate, it is the condensation of 3ß-hydroxy-21-hydroxymethylidenepregn-5-en-3ß-ol-20-one (5) with phenylhydrazine in the synthesis of pyrazolyl derivatives. Compounds of both the series were tested for their 5α-reductase inhibitory activities. Amongst all the compounds screened for their 5α-reductase inhibitory activities, compound 4b, 4c and 6b were found to be the most active.

Design and synthesis of D-ring steroidal isoxazolines and oxazolines as potential antiproliferative agents against LNCaP, PC-3 and DU-145 cells.

Two series of novel steroidal isoxazolines and oxazolines were synthesized through different routes from dehydroepiandrosterone acetate and pregnenolone acetate, respectively. The synthesis of the analogs of both series is multistep and proceeds in good overall yields. While the key step in the synthesis of former is the cycloaddition of aromatic nitrile oxides across α,ß-unsaturated olefins, it is the condensation of α,ß-azidoalcohols with aromatic aldehydes in the later. Compounds of both the series were tested for their cytotoxic activities against LNCaP, PC-3 and DU-145 prostate cancer cell lines. Amongst all the compounds of both the series screened for their prostate cancer activity, compound 6a, 6e and 12a are the most active especially against LNCaP and DU-145 cancer cell lines.

Benzylidine pregnenolones and their oximes as potential anticancer agents: synthesis and biological evaluation.

The present study reveals the anticancer activity of benzylidine pregnenolones and their oxime derivatives. The synthesis of the analogs of both series is very simple and involves aldol condensation in the first step followed by nucleophillic addition of hydroxylamine across carbonyl in the second step. Quantitative yields of more than 80% are obtained in both the steps. All the compounds were tested for their cytotoxic activities against a panel of six human cancer cell lines. Amongst all the compounds of both the series screened for their cytotoxic activity, compound 3e, 3f and 4e are very potent especially against HCT-15 and MCF-7 cancer cell lines.

Antimicrobial studies of unsymmetrical bis-1,2,3-triazoles.

Aryl azides were treated with allenylmagnesium bromide to generate 1,5-disubstituted butynyl 1,2,3-triazoles in a domino fashion, which upon Cu(I) catalyzed 1,3-dipolar cycloaddition with aryl azides afforded novel bis-1,2,3-triazoles in quantitative yields. The final products were analyzed for their antimicrobial activities against a panel of bacterial and fungal strains which revealed the products to be potent antimicrobials.

Synthesis and antimicrobial studies of chalconyl pregnenolones.

An efficient and facile synthesis of 17-chalconyl derivatives of pregnenolone and their evaluation as antimicrobial agents against various microbial strains is reported. The scheme involves the transformation of the starting pregnenolone acetate into pregnenolone, conversion of pregnenolone to the corresponding chalcone derivatives. The compounds 3a-3j showed significant antimicrobial activity against all microbial strains used for testing.

D-ring substituted 1,2,3-triazolyl 20-keto pregnenanes as potential anticancer agents: Synthesis and biological evaluation.

A facile synthesis of 21-triazolyl derivatives of pregnenolone and their potential antitumour activity is reported. The scheme involves the transformation of the starting pregnenolone acetate into pregnenolone, conversion of pregnenolone to 21-bromo pregnenolone and finally the one-pot, two-step in situ conversion of the bromo derivative to the 21-triazolyl pregnenolone using the 'click chemistry' approach. These derivatives were screened for their anticancer activity against seven human cancer cell lines. The compounds especially 5a, 5b, 5c, 5e, 5g and 5h exhibited significant anticancer activity with compound 5e as the most active in this study.

Studies on novel D-ring substituted steroidal pyrazolines as potential anticancer agents.

An efficient and facile synthesis of 17-pyrazolinyl derivatives of pregnenolone and their evaluation as potential anticancer agents against various human cancer cell lines are reported. The scheme involves the transformation of the starting pregnenolone acetate into pregnenolone, conversion of pregnenolone to the corresponding benzylidine derivatives and finally the conversion of this derivative to the stable steroidal 17-pyrazoline. Various compounds 4b, 4c, 4e, 4f, 4h and 4j showed significant cytotoxic activity especially against HT-29, HCT-15, 502713 cell lines.

Synthesis of novel steroidal D-ring substituted isoxazoline derivatives of 17-oxoandrostanes.

A facile synthesis of isoxazoline derivatives of 17-oxoandrostane at the side chain of D-ring is reported. The scheme involves the transformation of the starting dehydroepiandrosterone acetate (ketone) to the Knoevenegel product, reduction to the nitrile, and elimination to the carboxaldehyde. Cycloaddition of nitrileoxides across olefinic aldehyde intermediate led to the synthesis of novel side chain isoxazoline derivatives.