Update on the role of venetoclax and rituximab in the treatment of relapsed or refractory CLL

MiRNA-16-1 Suppresses Mcl-1 and Bcl-2 and Sensitizes Chronic Lymphocytic Leukemia Cells to BH3 Mimetic ABT-199

<strong>Objective</strong>: Chronic lymphoid leukemia (CLL) is the most common type of leukemia among adults. Increased levels of Mcl-1 and Bcl-xL is linked to resistance to Bcl-2 inhibitors including ABT-199. In this study, we investigated the effect of miRNA-16-1 on apoptosis and sensitivity of the CLL cells to ABT-199.<br /><strong>Materials and Methods:</strong> In this experimental study, the Mcl-1 and Bcl-2 expression were measured using qualitative reverse transcription-polymerase chain reaction (qRT-PCR) and western blotting. The effect of treatments on cell survival and growth were explored with MTT assay and Trypan blue assay, respectively. The drug interaction was evaluated using combination index analysis. Apoptosis was assessed by ELISA cell death and caspase-3 activity assays.<br /><strong>Results:</strong> MiRNA-16-1 markedly inhibited the expression of Mcl-1 and Bcl-2 in a time dependent manner (P<0.05, relative<br />to blank control). Pretreatment with miRNA-16-1 synergistically suppressed the cell growth and survival and reduced the half-maximal inhibitory concentration (IC50) value of ABT-199. Moreover, miRNA-16-1 markedly augmented the apoptotic effect of ABT-199 in CLL cells (P<0.05).<br /><strong>Conclusion: </strong>Our findings propose that miRNA-16-1 act in concert with ABT-199 to exert synergistic anticancer efficacy against CLL, which is attributed to the inhibition of Bcl-2 and Mcl-1. This may propose a promising strategy for CLL resistant patients.

Discovery of Small Molecule Bak Activator for Lung Cancer Therapy

Rationale: Bak is a major proapoptotic Bcl2 family member and a required molecule for apoptotic cell death. High levels of endogenous Bak were observed in both small cell lung cancer (SCLC) and non-small cell lung cancer (NSCLC) cell lines. Increased Bak expression was correlated with poor prognosis of NSCLC patients, suggesting that Bak protein is an attractive target for lung cancer therapy. The BH3 domain functions as death domain and is required for Bak to initiate apoptotic cell death. Thus, the BH3 domain is attractive target for discovery of Bak agonist.

Methods: The BH3 death domain binding pocket (aa75-88) of Bak was chosen as a docking site for screening of small molecule Bak activators using the UCSF DOCK 6.1 program suite and the NCI chemical library (300,000 small molecules) database. The top 500 compounds determined to have the highest affinity for the BH3 domain were obtained from the NCI and tested for cytotoxicity for further screening. We identified a small molecule Bak activator BKA-073 as the lead compound. The binding affinity of BKA-073 with Bak protein was analyzed by isothermal titration calorimetry (ITC) assay. BKA-073-mediated Bak activation via oligomerization was analyzed by a cross-linking with Bis (maleimido) hexane (BMH). Sensitivity of BKA-073 to lung cancer cells in vitro was evaluated by dynamic BH3 profiling (DBP) and apoptotic cell death assay. The potency of BKA-073 alone or in combination with radiotherapy or Bcl2 inhibitor was evaluated in animal models.

Results: We found that BKA-073 binds Bak at BH3 domain with high affinity and selectivity. BKA-073/Bak binding promotes Bak oligomerization and mitochondrial priming that activates its proapoptotic function. BKA-073 potently suppresses tumor growth without significant normal tissue toxicity in small cell lung cancer (SCLC) and NSCLC xenografts, patient-derived xenografts, and genetically engineered mouse models of mutant KRAS-driven cancer. Bak accumulates in radioresistant lung cancer cells and BKA-073 reverses radioresistance. Combination of BKA-073 with Bcl-2 inhibitor venetoclax exhibits strong synergy against lung cancer in vivo.

Conclusions: Development of small molecule Bak activator may provide a new class of anticancer agents to treat lung cancer.

Identification of a novel resistance mechanism in venetoclax treatment and its prediction in chronic lymphocytic leukemia

BACKGROUND

The Bcl-2 inhibitor venetoclax has been recently introduced into the treatment of chronic lymphocytic leukemia. Venetoclax is a highly effective drug, however acquired resistance may make long-term treatment challenging. In our study, we present potential novel resistance mechanisms and prognostic markers that are potentially able to predict the early appearance of the resistance.

MATERIAL AND METHODS

Repeated complete blood counts, flow cytometric measurements, and physical examinations were performed during the patient follow-up. Clinical and laboratory parameters showed that the patient developed clinical resistance to venetoclax on day 450 of therapy. Resistance mutation analysis (D103Y) and apoptosis arrays from samples at the time of resistance were done.

RESULTS

We were able to identify the resistance mutations just a very low variant allele frequency level from the resistant samples. Furthermore we detected increased Bcl-2 expression in peripheral blood (PB), and XIAP overexpression in bone marrow (BM) that could lead to venetoclax resistance. We examined the immunophenotype of CLL cells and recognized that while the expression of CD86 did not change until day 270 of the treatment, since then its expression steadily increased. Moreover, we compared the expression of CD86 in the resistant PB and BM samples and did not find a notable difference between the compartments.

CONCLUSION

Our results imply that CLL cells may try to avoid the apoptotic effect of venetoclax through increased CD86 expression by activating antiapoptotic mechanisms. Confirmatory experiments are still required to unequivocally prove that CD86 is a prognostic marker, however, its predictive property during the venetoclax treatment is promising.

[Orbital mantle cell lymphoma succesfully treated by Bcl-2 inhibitor: Report of a case]

Lymphoma is the most common orbital malignancy in adults. Among the types of lymphoma, mantle cell lymphoma is a particularly aggressive form, often discovered through systemic involvement, with a dismal prognosis due to frequent recurrences. It is secondary to a t (11 ; 14) (q13; q32) chromosomal translocation resulting in an anti-apoptotic signal via overexpression of Bcl-2. Treatment is based on R-CHOP poly-chemotherapy. We describe the case of a patient with an orbital recurrence of mantle cell lymphoma successfully treated with oral Bcl-2 inhibitor monotherapy. A 58-year-old man who was treated with R-CHOP 8 years ago for mantle cell lymphoma, in remission for 5 years, presented with progressive decreased visual acuity in the left eye, along with binocular diplopia. Clinical examination revealed a decrease in visual acuity in the left eye to 1/20 Parinaud 20 and a relative afferent pupillary defect on the left. External examination revealed a left cranial nerve VI palsy, 2mm of painless proptosis, and hypesthesia of the left V1 territory, leading to a diagnosis of left orbital apex syndrome. The disc and macular OCT were normal. The visual field showed enlargement of the left blind spot. An emergency CT scan and MRI revealed an apical extraconal tissue mass infiltrating the medial rectus muscle, extending to the superior orbital fissure, optic canal and left cavernous sinus, hyperintense on T2 weighted images and isointense on T1. The morphological appearance was strongly suggestive of an infiltrative lymphomatous process. An 18 FDG PET-scan identified the orbital lesion as well as enhancing lesions in the axilla and colon; given the clinical features and test results, the diagnosis of recurrent mantle cell lymphoma was made without biopsy. Treatment with Venetoclax (Bcl-2 inhibitor) was initiated. At one month of treatment, the orbital apex syndrome had entirely resolved, with visual acuity increased to 8/10 Parinaud 4 and a metabolic return to normal on PET scan. The PET scanner and clinical examination at 3 months were entirely normal. At the one-year follow-up visit, the patient was still on Venetoclax, the clinical examination was unchanged, and the PET-scan still showed a complete metabolic response.