Oxygen- and Sulphur-Containing Heterocyclic Compounds as Potential Anticancer Agents

Oxygen- and sulphur-based heterocycles form the core structure of many biologically active molecules as well as U.S. FDA-approved drugs. Moreover, they possess broad range of biological activities, viz. anticancer, antiinflammatory, antioxidant, antitumour, antibacterial, antiviral, antidiabetic, anticonvulsant, anti-tubercular, analgesic, anti-leishmanial, antimalarial, antifungal, and anti-histaminic, Hence, O- and S-based heterocycles are gaining more attention in recent years on the road to the discovery of innovative anticancer drugs after the extensive investigation of nitrogen-based heterocycles as anticancer agents. Several attempts have been made to synthesize fused oxygen- and sulphur-based heterocyclic derivatives as joining one heterocyclic moiety with another may lead to improvement in the biological profile of a molecule. Humans have been cursed with cancer since long time. Despite the development of several heterocyclic anticancer medications such as 5-fluorouracil, doxorubicin, methotrexate, and daunorubicin, cure of cancer is difficult. Hence, researchers are trying to synthesize new fused/spiro heterocyclic molecules to discover novel anticancer drugs which may show promising anticancer effects with fewer side effects. Furthermore, fused heterocycles behave as DNA intercalating agents which have the ability to interact with DNA, leading to cell death thereby exerting anticancer effect. This review article highlights the synthesis and anticancer potentiality of oxygen- and sulphur-containing heterocyclic compounds covering the period from 2011 to 2021.

Re-Expression of Poly/Oligo-Sialylated Adhesion Molecules on the Surface of Tumor Cells Disrupts Their Interaction with Immune-Effector Cells and Contributes to Pathophysiological Immune Escape

Glycans linked to surface proteins are the most complex biological macromolecules that play an active role in various cellular mechanisms. This diversity is the basis of cell-cell interaction and communication, cell growth, cell migration, as well as co-stimulatory or inhibitory signaling. Our review describes the importance of neuraminic acid and its derivatives as recognition elements, which are located at the outermost positions of carbohydrate chains linked to specific glycoproteins or glycolipids. Tumor cells, especially from solid tumors, mask themselves by re-expression of hypersialylated neural cell adhesion molecule (NCAM), neuropilin-2 (NRP-2), or synaptic cell adhesion molecule 1 (SynCAM 1) in order to protect themselves against the cytotoxic attack of the also highly sialylated immune effector cells. More particularly, we focus on α-2,8-linked polysialic acid chains, which characterize carrier glycoproteins such as NCAM, NRP-2, or SynCam-1. This characteristic property correlates with an aggressive clinical phenotype and endows them with multiple roles in biological processes that underlie all steps of cancer progression, including regulation of cell-cell and/or cell-extracellular matrix interactions, as well as increased proliferation, migration, reduced apoptosis rate of tumor cells, angiogenesis, and metastasis. Specifically, re-expression of poly/oligo-sialylated adhesion molecules on the surface of tumor cells disrupts their interaction with immune-effector cells and contributes to pathophysiological immune escape. Further, sialylated glycoproteins induce immunoregulatory cytokines and growth factors through interactions with sialic acid-binding immunoglobulin-like lectins. We describe the processes, which modulate the interaction between sialylated carrier glycoproteins and their ligands, and illustrate that sialic acids could be targets of novel therapeutic strategies for treatment of cancer and immune diseases.

Protein based therapeutic delivery agents: Contemporary developments and challenges

As unique biopolymers, proteins can be employed for therapeutic delivery. They bear important features such as bioavailability, biocompatibility, and biodegradability with low toxicity serving as a platform for delivery of various small molecule therapeutics, gene therapies, protein biologics and cells. Depending on size and characteristic of the therapeutic, a variety of natural and engineered proteins or peptides have been developed. This, coupled to recent advances in synthetic and chemical biology, has led to the creation of tailor-made protein materials for delivery. This review highlights strategies employing proteins to facilitate the delivery of therapeutic matter, addressing the challenges for small molecule, gene, protein and cell transport.

Phase I study of IMGN901, a CD56-targeting antibody-drug conjugate, in patients with CD56-positive solid tumors

Background IMGN901 is a CD56-targeting antibody-drug conjugate designed for tumor-selective delivery of the cytotoxic maytansinoid DM1. This phase 1 study investigated the safety, tolerability, pharmacokinetics, and preliminary activity of IMGN901 in patients with CD56-expressing solid tumors. Methods Patients were enrolled in cohorts of escalating IMGN901 doses, administered intravenously, on 3 consecutive days every 21 days. A dose-expansion phase accrued patients with small cell lung cancer (SCLC), Merkel cell carcinoma (MCC), or ovarian cancer. Results Fifty-two patients were treated at doses escalating from 4 to 94 mg/m(2)/day. The maximum tolerated dose (MTD) was determined to be 75 mg/m(2). Dose-limiting toxicities included fatigue, neuropathy, headache or meningitis-like symptoms, chest pain, dyspnea, and myalgias. In the dose-expansion phase (n = 45), seven patients received 75 mg/m(2) and 38 received 60 mg/m(2) for up to 21 cycles. The recommended phase 2 dose (RP2D) was established at 60 mg/m(2) during dose expansion. Overall, treatment-emergent adverse events (TEAEs) were experienced by 96.9 % of all patients, the majority of which were Grade 1 or 2. The most commonly reported Grade 3 or 4 TEAEs were hyponatremia and dyspnea (each 8.2 %). Responses included 1 complete response (CR), 1 clinical CR, and 1 unconfirmed partial response (PR) in MCC; and 1 unconfirmed PR in SCLC. Stable disease was seen for 25 % of all evaluable patients who received doses ≥60 mg/m(2). Conclusions The RP2D for IMGN901 of 60 mg/m(2) administered for 3 consecutive days every 3 weeks was associated with an acceptable tolerability profile. Objective responses were observed in patients with advanced CD56+ cancers.

Engineering THIOMABs for site-specific conjugation of thiol-reactive linkers

Antibody conjugates are used in many therapeutic and research applications and are generated by chemically linking a cysteine or lysine residue to potent chemotherapeutic drugs or other functional groups through a flexible linker. Recently, we have engineered THIOMABs (antibodies with engineered reactive cysteine residues) for site-specific conjugation and showed that these antibody conjugates display homogeneous labeling with optimal in vitro and in vivo characteristics. Here, we describe protocols for engineering, selection, and site-specific conjugation of THIOMABs with thiol-reactive linkers.

Antibody delivery of drugs and radionuclides: factors influencing clinical pharmacology

The therapeutic rationale of antibody conjugates is the selective delivery of a cytotoxin to tumor cells via binding and internalization of the monoclonal antibodies to a specific cell-surface antigen, thereby enhancing the therapeutic index of the cytotoxin. The key structural and functional components of an antibody conjugate are the antibody, the linker and the cytotoxin (chemical or radionuclide) with each component being critical for the successful development of the conjugate. Considerable efforts have been made in understanding the pharmacokinetics, pharmacodynamics, tissue distribution, metabolism and pharmacologic effects of these complex macromolecular entities. The purpose of this article is to discuss the properties and various structural components of antibody conjugates that influence their clinical pharmacology.

Antibody-DM1 conjugates as cancer therapeutics

Synthetic derivatives of the microtubule-targeted agent maytansine, commonly known as drug maytansinoids or DMs, are emerging as potential cancer therapeutics. DM1 is an antibody-conjugatable maytansinoid that was developed to overcome systemic toxicity associated with maytansine and to enhance tumor-specific delivery. Antibody-DM1 conjugates showed promising results in preclinical and clinical evaluations. However, the molecular mechanism of the drug component DM1 was largely unknown. Recently, researchers have examined the mechanism of DM1 at molecular and cellular levels. According to their findings, DM1 binds at the tips of microtubules and suppresses the dynamicity of microtubules. The antibody-DM1 conjugate cleaves inside cells and releases the active drug in a time-dependent manner. The suppression of microtubule dynamics by DM1 induces mitotic arrest and cell death.

Treatment options for small cell lung cancer - do we have more choice?

Small cell lung cancer (SCLC) is a significant health problem worldwide because of its high propensity for relapse. This review discusses existing and future therapies for the treatment of SCLC.

Current status of second-line treatment and novel therapies for small cell lung cancer

Despite high response rates to first-line standard treatment, the great majority of patients with small cell lung cancer (SCLC) will relapse and succumb to their disease rather quickly. In the context of salvage therapy, symptom palliation and quality-of-life improvements, besides survival prolongation, are primary treatment endpoints. A variety of single-agent and multi-agent chemotherapy regimens have been tested with limited success in patients with recurrent SCLC. A number of combination regimens have demonstrated high response rates in second-line settings, but these can be considered only for patients with good performance status. Treatment outcome depends on many factors, including type of response to first-line therapy, treatment-free interval, and performance status. Currently, topotecan represents an effective, tolerable therapeutic option and is the only agent approved for this indication. The management of patients with recurrent disease remains an area of active research. This review provides an update of clinical research on second-line chemotherapy of SCLC and of recent results obtained with novel molecular targeted approaches in both first- and second-line therapy.

Targeted therapies in small-cell lung cancer

Small-cell lung cancer is an aggressive form of lung cancer that, overall, remains the most common cause of cancer death in the US. Some advances have been made in the treatment of small-cell lung cancer using cytotoxic chemotherapeutic agents but no truly targeted therapies are available as of yet. At present, research is focused on finding therapies that can target the specific molecular mechanisms responsible for the survival, growth and metastasis of the tumor thereby improving responses to chemotherapy and minimizing toxicity. Several new agents, such as angiogenesis inhibitors and regulators of apoptosis, have reached clinical testing and multiple others are in preclinical trials. Some of these will be discussed in this review.

Fast, hungry and unstable: finding the Achilles' heel of small-cell lung cancer

Over 95% of patients with small-cell lung cancer (SCLC) die within five years of diagnosis. The standard of care and the dismal prognosis for this disease have not changed significantly over the past 25 years. Some of the characteristics of SCLC that have defined it as a particularly virulent form of cancer -- rapid proliferation, excessive metabolic and angiogenic dependence, apoptotic imbalance and genetic instability -- are now being pursued as tumor-specific targets for intervention both in preclinical and early phase clinical studies. Here, we summarize areas of ongoing anti-cancer drug development, including classes of agents that target essential pathways regulating proliferation, angiogenesis, apoptotic resistance, chromosomal and protein stability, and cell-cell and cell-matrix interaction.

Multiple myeloma: monoclonal antibodies-based immunotherapeutic strategies and targeted radiotherapy

Multiple myeloma (MM) is an incurable B-cell malignancy of terminally differentiated plasma cells. Besides conventional treatments, several targeted therapies are emerging for MM. We review recent developments in monoclonal antibodies (MoAbs) and (radio)immunoconjugates-based targeted immunotherapeutic (serotherapies) strategies, as well as skeletal targeted radiotherapy (STR) in MM. MoAbs-based strategies include the targeting of cytokines and their receptors as well as toxins, drugs or radionuclide delivery to MM cells. Both targeted radioimmunotherapy (RIT) and STR have proved efficient in the treatment of radiosensitive tumours. We conclude that there is a need for more mechanistic investigations of drug action to identify novel therapeutic targets in myeloma cells, as well as in the bone marrow microenvironment.

In vivobehaviour of antibody–drug conjugates for the targeted treatment of cancer

It is a commonly held belief that most treatments for disseminated cancers are only moderately effective because the agents lack cell-killing mechanisms that act specifically on cancer cells. In antibody-drug conjugates, such nonspecific cytotoxic agents are combined with exquisitely specific monoclonal antibodies that bind to tumour-associated antigens and, thus, get endowed with new pharmacological characteristics. Not only is their activity newly targeted towards tumours and tumour cells, which hopefully renders them more tumour-specific, but they also acquire much of the pharmacokinetic behaviour of the monoclonal antibody component. With the structural composition of a macromolecular protein (the antibody), a small chemical cytotoxic agent and a linker to chemically connect these two molecules, antibody-drug conjugates are some of the most complex pharmacological agents ever developed. Their development over the last 20 years or so owes much to sophisticated in vitro and in vivo preclinical testing. This review attempts to summarise and exemplify many of the factors that had to be considered during the development, with special emphasis on the in vivo pharmacology of these agents.

Management of small cell lung cancer

Small cell lung cancer (SCLC) is an aggressive type of lung cancer characterized by rapid growth and early metastasis. It is chemosensitive and radiosensitive, yet decades of research investigating multimodality treatments have failed to control or cure this disease in most patients. First-line treatment of limited-stage disease consists of chemotherapy (often etoposide/cisplatin or etoposide/carboplatin) combined with thoracic radiation therapy (TRT), followed by prophylactic cranial irradiation to decrease brain metastases as a site of disease progression for those who experience complete remission or a very good partial response to multimodality treatment. In a Japanese trial, the combination of irinotecan and cisplatin had initially shown promise in treating patients with extensive-stage SCLC, but a confirmatory trial in the United States did not find a difference in overall survival with irinotecan/cisplatin versus etoposide/cisplatin. Adding a third drug to the etoposide/cisplatin combination, as well as other triplet therapies, has mostly been ineffective in improving outcomes. Variables in chemotherapy administration, including maintenance therapy, alternating non-cross-resistance regimens, and dose intensification, have not been shown to increase survival at large. In terms of radiation therapy, early administration of TRT concurrent with chemotherapy, and hyperfractionation, have been beneficial in treatment of limited-stage disease. In patients who relapse, second-line therapy options consist of reinduction of previous chemotherapy or administration of a single agent. Targeted biological therapies for SCLC are now being investigated, and although a great deal of research remains to be done, these agents and their derivatives may provide the most hope for future treatment of SCLC.

Arming antibodies: prospects and challenges for immunoconjugates

Immunoconjugates--monoclonal antibodies (mAbs) coupled to highly toxic agents, including radioisotopes and toxic drugs (ineffective when administered systemically alone)--are becoming a significant component of anticancer treatments. By combining the exquisite targeting specificity of mAbs with the enhanced tumor-killing power of toxic effector molecules, immunoconjugates permit sensitive discrimination between target and normal tissue, resulting in fewer toxic side effects than most conventional chemotherapeutic drugs. Two radioimmunoconjugates, ibritumomab tiuxetan (Zevalin) and tositumomab-131I (Bexxar), and one drug conjugate, gemtuzumab ozogamicin (Mylotarg), are now on the market. For the next generation of immunoconjugates, advances in protein engineering will permit greater control of mAb targeting, clearance and pharmacokinetics, resulting in significantly improved delivery to tumors of radioisotopes and potent anticancer drugs. Pre-targeting strategies, which separate the two functions of antibody-based localization and delivery or generation of the toxic agent into two steps, also promise to afford superior tumor targeting and therapeutic efficacy. Several challenges in optimizing immunoconjugates remain, however, including poor intratumoral mAb uptake, normal tissue conjugate exposure and issues surrounding drug potency and conditional release from mAb carriers. Nonetheless, highly promising results from preclinical models will continue to drive the clinical development of this therapeutic class.