Viralkumar Patel
@dsvv.ac.in
Coordinator & Scientist, Yagyavalkya Center for Yagya Research
Dev Sanskriti Vishwavidyalaya
RESEARCH INTERESTS
* Experienced in ancient therapeutic model research, Yagya Research, Herbal Inhalation Therapy,
* Oncology therapeutics research with emphasis on translational medicine
Scopus Publications
Scholar Citations
Scholar h-index
Scholar i10-index
Scopus Publications
V K Patel, B Lamothe, M L Ayres, J Gay, J P Cheung, K Balakrishnan, C Ivan, J Morse, M Nelson, M J Keating,et al.
Springer Science and Business Media LLC
V M Patel, K Balakrishnan, M Douglas, T Tibbitts, E Y Xu, J L Kutok, M Ayers, A Sarkar, R Guerrieri, W G Wierda,et al.
Springer Science and Business Media LLC
Viralkumar Patel, Kumudha Balakrishnan, Elena Bibikova, Mary Ayres, Michael J. Keating, William G. Wierda, and Varsha Gandhi
American Association for Cancer Research (AACR)
Abstract Purpose: Ibrutinib inhibits Bruton tyrosine kinase (BTK) by irreversibly binding to the Cys-481 residue in the enzyme. However, ibrutinib also inhibits several other enzymes that contain cysteine residues homologous to Cys-481 in BTK. Patients with relapsed/refractory or previously untreated chronic lymphocytic leukemia (CLL) demonstrate a high overall response rate to ibrutinib with prolonged survival. Acalabrutinib, a selective BTK inhibitor developed to minimize off-target activity, has shown promising overall response rates in patients with relapsed/refractory CLL. A head-to-head comparison of ibrutinib and acalabrutinib in CLL cell cultures and healthy T cells is needed to understand preclinical biologic and molecular effects. Experimental Design: Using samples from patients with CLL, we compared the effects of both BTK inhibitors on biologic activity, chemokine production, cell migration, BTK phosphorylation, and downstream signaling in primary CLL lymphocytes and on normal T-cell signaling to determine the effects on other kinases. Results: Both BTK inhibitors induced modest cell death accompanied by cleavage of PARP and caspase-3. Production of CCL3 and CCL4 chemokines and pseudoemperipolesis were inhibited by both drugs to a similar degree. These drugs also showed similar inhibitory effects on the phosphorylation of BTK and downstream S6 and ERK kinases. In contrast, off-target effects on SRC-family kinases were more pronounced with ibrutinib than acalabrutinib in healthy T lymphocytes. Conclusions: Both BTK inhibitors show similar biological and molecular profile in primary CLL cells but appear different on their effect on normal T cells. Clin Cancer Res; 23(14); 3734–43. ©2016 AACR.
Viralkumar Patel, Michael J. Keating, William G. Wierda, and Varsha Gandhi
Informa UK Limited
Chronic lymphocytic leukemia (CLL) is a B-cell malignancy in which apoptotic-resistant mature lymphocytes relentlessly accumulate in bone-marrow, lymph nodes and peripheral blood. In these body compartments, CLL B cells get survival signals mainly through the B-cell antigen receptor (BCR) pathway. The critical role of BCR signaling in CLL pathogenesis, i.e. proliferation, survival, adhesion, migration, and differentiation, is very well established. Bruton’s tyrosine kinase (BTK) is a key component of the BCR pathway and is required for CLL maintenance and development. BCR pathway inhibition through irreversible inhibition of BTK at Cys481 residue in its ATP-binding domain by ibrutinib has significantly improved the treatment outcome in CLL via disrupting the interactions with microenvironment. Phase 1 clinical trial of ibrutinib (PCI-32765) in relapsed or refractory CLL malignancy patients resulted in 70% overall response rate [1]. Phase 1b and 2 ibrutinib clinical testing in patients with relapsed and refractory disease also showed similar (70%) response rate which lead to breakthrough status for ibrutinib [2]. Outstanding outcome during clinical trials without untoward toxicity resulted in FDA approval of ibrutinib for patients with CLL who have received at least one prior therapy. Long-term follow-up suggested a revolutionary role of ibrutinib for CLL patients. Single-agent ibrutinib induced durable responses in the majority of CLL patients; however, these were mostly partial remissions, less than 10% achieved complete remission and, importantly, patients are not cured. A major part of the reason for partial remission is lymphocytosis after ibrutinib treatment which was due to the egress of CLL lymphocytes from lymph node niches. A key feature of ibrutinib therapy was early and dramatic reduction in lymph nodes with a parallel increase in CLL cells in blood circulation [2]. Ibrutinibmediated BTK inhibition does not induce cell death directly but impairs BCR-associated integrin-mediated adhesion and migration, which leads to CLL cells efflux from lymphoid tissues (lymph node microenvironment) to peripheral blood. In peripheral blood due to lack of sustained survival factors which are in lymphoid tissues, these lymphocytosed CLL cells slowly undergo cell death. However, this slow process might allow the opportunity of selection or outgrowth of resistant clones of CLL cells. In fact, during therapy, in many individuals, peripheral blood lymphocytosis was prolonged. Furthermore, some of the patients on continuous therapy with ibrutinib developed resistance to ibrutinib therapy [3]. Among these patients, mutation at the ibrutinib-binding site on BTK, mutation in additional molecules in the BTK axis such as PLCg2, and non BCR pathway modulations were identified [3]. Moreover driver mutation SF3B1 which is associated with poor prognosis also contributed to ibrutinib-acquired resistance [4]. Finally, increased Bcl-2 protein with a decline in Mcl-1 and Bcl-XL has also been observed and suggested as a survival mechanism for ibrutinib-treated CLL cells [5]. These data underscore a need to identify pharmacological agents that can synergistically partner with ibrutinib. Continuous and prolonged use of ibrutinib incurs a high cost of therapy. Finding optimal drug combinations would not only help achieve deeper responses but may also taper the high cost of chronic ibrutinib intake. TP-0903 is a selective inhibitor of Axl receptor tyrosine kinase. Axl receptor, a member of TAM (Tyro3, Axl and Mertk) family of receptor tyrosine kinases, is overexpressed in CLL and plays an oncogenic survival role [6]. Previously Sinha and colleagues [7] demonstrated
Aloke Sarkar, Kumudha Balakrishnan, Jefferson Chen, Viralkumar Patel, Sattva S. Neelapu, John S. McMurray, and Varsha Gandhi
Impact Journals, LLC
The resistance of apoptosis in cancer cells is pivotal for their survival and is typically ruled by mutations or dysregulation of core apoptotic cascade. Mantle cell lymphoma (MCL) is a non-Hodgkin's B-cell malignancy expressing higher anti-apoptotic proteins providing survival advantage. B-PAC-1, a procaspase activating compound, induces apoptosis by sequestering Zn bound to procaspase-3, but the amino acids holding Zn in Caspase-3 is not known. Here we show that reintroduction of WT caspase-3 or 7 in Caspase3–7 double knock-out (DKO) mouse embryonic fibroblasts (MEF) promoted B-PAC-1 to induce apoptosis (27–43%), but not in DKO MEFs or MEFs expressing respective Casp3–7 catalytic mutants (12–13%). Using caspase-6 and -9 exosite analysis, we identified and mutated predicted Zn-ligands in caspase-3 (H108A, C148S and E272A) and overexpressed into DKO MEFs. Mutants carrying E272A abrogated Zn-reversal of apoptosis induced by B-PAC-1 via higher XIAP and smac expressions but not in H108A or C148S mutants. Co-immunoprecipitation analysis revealed stronger XIAP-caspase-3 interaction suggesting a novel mechanism of impulsive apoptosis resistance by disrupting predicted Zn-ligands in caspase-3. B-PAC-1 sponsored apoptosis in MCL cell lines (30–73%) via caspase-3 and PARP cleavages accompanied by loss of Mcl-1 and IAPs including XIAP while Zn substantially abrogated B-PAC-1-driven apoptosis (18–36%). In contrary, Zn is dispensable to inhibit staurosporin, bendamustine, ABT199 or MK206-induced apoptosis. Consistent to cell lines, B-PAC-1 stimulated cell death in primary B-lymphoma cells via caspase-3 cleavage with decline in both Mcl-1 and XIAP. This study underscores the first genetic evidence that B-PAC-1 driven apoptosis is mediated via Zn chelation.
Viralkumar Patel, Kumudha Balakrishnan, Michael J. Keating, William G. Wierda, and Varsha Gandhi
American Society of Hematology
Key Points Pharmacologic activation of executioner procaspases by B-PAC-1 in CLL bypasses antiapoptotic mechanisms and induces apoptosis. B-PAC-1 activates apoptosis by abrogating the zinc ion-dependent inhibition of executioner procaspase activation.
Viralkumar Patel, Lisa S. Chen, William G. Wierda, Kumudha Balakrishnan, and Varsha Gandhi
Informa UK Limited
Abstract Chronic lymphocytic leukemia (CLL) is the most common form of adult leukemia in the Western world. High levels of Bcl-2 family anti-apoptotic proteins are responsible for apoptosis resistance. Besides anti-apoptotic proteins, the microenvironment provides substantial survival signals to CLL leukemic cells. However, in-depth knowledge on the role of individual Bcl-2 family members in the context of the microenvironment is still limited. We performed a comprehensive analysis of transcripts and proteins of 18 Bcl-2 family members using an “apoptosis array microfluidic card” in primary cells before and after stromal co-cultures. Our data showed that five of six anti-apoptotic members (excluding Bcl-b), two of three pro-apoptotic members (excluding Bok) and six of nine BH3-only members were present at detectable mRNA levels in CLL cells. Importantly, stromal-mediated extended survival of CLL cells was strongly associated with elevated global transcription. Upon co-culturing with stromal cells, there was an early response of an increase in anti- (2/5) and pro-apoptotic protein (3/8) transcripts on day 1, while an increase in anti-apoptotic proteins was observed on day 3, with no significant change in pro-apoptotic proteins. Our study revealed a differential pattern of expression of both transcripts and proteins following stromal co-cultures, proposing a significance of Bcl-2 family members in the stromal microenvironment.