Recent advances and future directions on small molecule VEGFR inhibitors in oncological conditions.

"A journey of mixed emotions" is a quote that best describes the progress chart of vascular endothelial growth factor receptor (VEGFR) inhibitors as cancer therapeutics in the last decade. Exhilarated with the Food and Drug Administration (FDA) approvals of numerous VEGFR inhibitors coupled with the annoyance of encountering the complications associated with their use, drug discovery enthusiasts are on their toes with an unswerving determination to enhance the rate of translation of VEGFR inhibitors from preclinical to clinical stage. The recently crafted armory of VEGFR inhibitors is a testament to their growing dominance over other antiangiogenic therapies for cancer treatment. This review perspicuously underscores the earnest attempts of the researchers to extract the antiproliferative potential of VEGFR inhibitors through the design of mechanistically diverse structural assemblages. Moreover, this review encompasses sections on structural/molecular properties and physiological functions of VEGFR, FDA-approved VEGFR inhibitors, and hurdles restricting the activity range/clinical applicability of VEGFR targeting antitumor agents. In addition, tactics to overcome the limitations of VEGFR inhibitors are discussed. A clear-cut viewpoint transmitted through this compilation can provide practical directions to push the cart of VEGFR inhibitors to advanced-stage clinical investigations in diverse malignancies.

DNA polymerase ß of Leishmania donovani is important for infectivity and it protects the parasite against oxidative damage.

The visceral leishmaniasis is caused by L. donovani, a neglected tropical disease with an estimated number of 500,000 cases worldwide. Apart from the absence of effective vaccine, the available drugs have limitations like toxic side effects and emergence of drug resistance. The genome of Leishmania is remarkably challenged by the oxidative stress present inside the human macrophage. To maintain genomic integrity, a number of specialized DNA repair pathways assist in the recognition and repair of damaged DNA. In general, Base Excision Repair (BER) plays an essential role in the maintenance of genomic stability. We demonstrate here that the treatment of L. donovani with oxidative agents causes DNA damage and upregulation of Polß. On the other hand, parasite overexpressing Polß shows more resistance against Amp B, H2O2 and menadione as compared to wild type cells. We also observed a higher infectivity in the parasites that overexpress Polß. The upregulation of Polß was also found in stationary phase and axenic amastigote of L. donovani. Overall, we propose that Polß is crucial for infectivity and survival of the parasite. Discovery of specific inhibitors against Polß could offer an attractive strategy against leishmaniasis.

Oxidative Stress-Mediated Overexpression of Uracil DNA Glycosylase in Leishmania donovani Confers Tolerance against Antileishmanial Drugs.

Leishmania donovani is an intracellular protozoan parasite that causes endemic tropical disease visceral leishmaniasis (VL). Present drugs used against this fatal disease are facing resistance and toxicity issues. Survival of leishmania inside the host cells depends on the parasite's capacity to cope up with highly oxidative environment. Base excision repair (BER) pathway in L. donovani remains unexplored. We studied uracil DNA glycosylase (UNG), the key enzyme involved in BER pathway, and found that the glycosylase activity of recombinant LdUNG (Leishmania donovani UNG) expressed in E. coli is in sync with the activity of the parasite lysate under different reaction conditions. Overexpression of UNG in the parasite enhances its tolerance towards various agents which produce reactive oxygen species (ROS) and shows a higher infectivity in macrophages. Surprisingly, exposure of parasite to amphotericin B and sodium antimony gluconate upregulates the expression of UNG. Further, we found that the drug resistant parasites isolated from VL patients show higher expression of UNG. Mechanisms of action of some currently used drugs include accumulation of ROS. Our findings strongly suggest that targeting LdUNG would be an attractive therapeutic strategy as well as potential measure to tackle the problem of drug resistance in the treatment of leishmaniasis.

HAT2 mediates histone H4K4 acetylation and affects micrococcal nuclease sensitivity of chromatin in Leishmania donovani.

Histone post-translational modifications (PTMs) such as acetylation and methylation are known to affect chromatin higher order structures. Primary targets of these modifications include basic residues present at N-terminus tail region of core histones. Four histone acetyltransferase (HAT) genes have been identified in trypanosomatids. HAT1, HAT3 and HAT4 of Leishmania donovani have been partially characterized. However, there is no report about HAT2 of Leishmania donovani. Lysine residues present on the N-terminal tail of Leishmania donovani histone H4 are conserved in other trypanosomatids and humans. PTMs of lysines modulate various functions at chromatin level. The four histone acetyltransferases encoded in Leishmania genome were over-expressed to analyse their functional activity. All four HATs were found actively acetylating core histones H3/H4. Similar to L. donovani HAT3 and HAT4, HAT2 was found to be a member of MYST family protein and have SAS2 type domain. Over-expression of HAT2 significantly increases acetylation of H4K4. To analyse the effect of HAT2 over-expression on chromatin accessibility, micrococcal nuclease digestion assay was performed. MNase digestion resulted in a higher proportion of the mononucleosomes and dinucleosomes in HAT2 over-expressing cells as compared to WT L. donovani cells. Acetylation of lysine-4 neutralizes the amino terminal region of histone H4. This weakens its interaction with neighbouring nucleosomes and the linker DNA. HAT2 over-expression in L. donovani resulted in highly accessible chromatin suggesting chromatin decondensation. HAT2 may have an important role to play in global regulation of transcription in L. donovani. Better understanding of these epigenetic determinants of parasite would help in designing novel therapeutic strategies.

Adenosine generated by ectonucleotidases modulates the host immune system during visceral leishmaniasis.

Adenosine, an endogenous purine nucleoside is one such extracellular signaling molecule whose role in the regulation of anti-inflammatory cytokines and immune pathogenicity in visceral leishmaniasis is indeterminate. Here, we have evaluated the adenosine in the plasma of 20 visceral leishmaniasis (VL) patients during active disease and after successful treatment. We observed the elevated plasma adenosine during active VL disease (26.73±1.95µM) and the level subsides as the treatment progresses and falls to the normal level after successful treatment (4.32±0.45µM). We demonstrated a direct correlation between changes in the plasma adenosine level and the Th1/Th2 balance in VL patients and it was corroborated with in vitro experiment. Further, we delineated the molecular mechanism involved in the elevation of plasma adenosine during visceral leishmaniasis. Our results reveal that the elevated plasma adenosine level associated with pathogenicity and plays a critical role in skewing immune response from Th1 to Th2 type to influence the outcome of the disease.

Plasma Gelsolin Level in HIV-1-Infected Patients: An Indicator of Disease Severity.

Plasma gelsolin (pGSN) is a multifunctional protein involved mainly in severing and clearing of actin filaments. Its level correlates with inflammation and several diseases making it a potential biomarker of diagnostic and prognostic values. The pGSN level in groups of treated and untreated HIV-1-infected Indian patients is investigated in this study. This study aims at investigating the levels of pGSN in HIV-1-infected patients across different age, sex, severity of disease, and treatment status. Blood samples of 213 patients were analyzed for CD4 counts by flow cytometry and pGSN was quantified by enzyme-linked immunosorbent assay (ELISA). The level of pGSN is significantly increased in HIV-1 infected patients (227.2 ± 54.3 µg/ml) compared to healthy volunteers (167.9 ± 61.8 µg/ml). The level correlates with CD4 cell counts as patients with lower CD4 counts showed higher pGSN levels and vice versa. Gender does not affect pGSN level; however, antiretroviral (ARV) treatment reduces pGSN toward normal. Within low CD4 cell count group, the untreated patients have 52% higher pGSN than healthy volunteers, whereas with treatment, the difference reduces to 24%. Similarly, high CD4 cell count (>350 cells/mm3) group of patients showed 44% increase in pGSN in untreated patients compared to 21% increase in treated patients. There is an upregulation of pGSN in HIV-1 infection and it is inversely correlated with CD4 cell counts. Treatment with ARV drugs decreases pGSN levels toward normal. The monitoring of pGSN level in HIV-1-infected patients could be an important indicator of severity of disease and recovery during treatment.

The Effect of Small Oligomeric Protein Aggregates on the Immunogenicity of Intravenous and Subcutaneous Administered Antibodies.

The role of aggregates in the immunogenicity of biologics is a major concern. A recent US FDA guidance on the issue suggests that a gap in knowledge exists regarding the type and size of aggregates involved in the immunogenicity of biologics. Furthermore, the guidance suggests that current techniques cannot capture the crucial stages of protein aggregation. Using a protein unfolding model developed earlier, we generated and classified aggregates of two therapeutic antibodies based on size and conformation. The immunogenic potential of these aggregates were then tested in a murine model. Our findings show that small native-like oligomeric aggregates (<100 nm) are more immunogenic toward the native protein than monomer and large non-native aggregates in the micron-size range, irrespective of route of administration [intravenous (i.v.) vs. subcutaneous (s.c.)]. Those smaller oligomeric aggregates represented 5%-20% of the total protein concentration in the test formulations. Furthermore, in vitro data suggest that TNF-α production by bone marrow-derived dendritic cells could serve as a predictive marker for increased immunogenic risk of aggregates after s.c. administration. The use of orthogonal techniques such as fluorescence anisotropy and quasielastic light scattering may be useful to detect these oligomeric aggregates.