Targeting of saporin to Hodgkin's lymphoma cells by anti-CD30 and anti-CD25 bispecific antibodies

CD30 as a therapeutic target for lymphoma

Hodgkin's lymphoma (HL) and ALK(+) anaplastic large-cell lymphoma (ALCL) have become highly curable due to the success of modern regimens of chemotherapy and radiotherapy. However, up to one-third of the patients experience relapse or do not respond to first-line therapy, and half of them relapse again after secondary therapy with limited options for further treatment. In the last 15 years, monoclonal antibodies (mAbs) directed to surface receptors became a new and valuable therapeutic option in many hematologic malignancies. Due to its restricted expression on normal activated lymphocytes and its high expression on malignant cells, CD30 represents an attractive target molecule for HL and ALCL therapy. However, unconjugated CD30 mAbs have demonstrated a lack of objective clinical responses in patients with recurrent HL. CD30 exhibits complex signaling pathways, and binding of its natural ligand or anti-CD30 mAbs can induce apoptosis but may also promote proliferation and activation depending on the cellular context. Moreover, CD30 rapidly internalizes after crosslinking, which counteracts efficient recruitment of immunologic effectors but also provides the opportunity to transfer cytotoxic payloads coupled to CD30-specific mAbs into the tumor cells. Several tumor targeting approaches have been studied, including radio-immunoconjugates, immunotoxins, immunoRNases, immunokinases, and antibody drug conjugates (ADCs). In 2011, the ADC brentuximab-vedotin, consisting of the CD30-specific chimeric mAb cAC10 and the potent tubulin toxin monomethyl auristatin E, gained regulatory approval as a well tolerated and highly active drug in patients with refractory and relapsed HL and ALCL. SGN-35 is on the way to being incorporated in the standard management of CD30(+) lymphoma with significant therapeutic impact. This review gives a critical overview about anti-CD30 therapies with unconjugated, engineered, and conjugated mAbs and the therapeutic challenges of treatment of CD30(+) lymphoma.

Methods for Evaluating Cell-Specific, Cell-Internalizing RNA Aptamers

Recent clinical trials of small interfering RNAs (siRNAs) highlight the need for robust delivery technologies that will facilitate the successful application of these therapeutics to humans. Arguably, cell targeting by conjugation to cell-specific ligands provides a viable solution to this problem. Synthetic RNA ligands (aptamers) represent an emerging class of pharmaceuticals with great potential for targeted therapeutic applications. For targeted delivery of siRNAs with aptamers, the aptamer-siRNA conjugate must be taken up by cells and reach the cytoplasm. To this end, we have developed cell-based selection approaches to isolate aptamers that internalize upon binding to their cognate receptor on the cell surface. Here we describe methods to monitor for cellular uptake of aptamers. These include: (1) antibody amplification microscopy, (2) microplate-based fluorescence assay, (3) a quantitative and ultrasensitive internalization method (“QUSIM”) and (4) a way to monitor for cytoplasmic delivery using the ribosome inactivating protein-based (RNA-RIP) assay. Collectively, these methods provide a toolset that can expedite the development of aptamer ligands to target and deliver therapeutic siRNAs in vivo.

Effect of basic fibroblast growth factor-saporin (bFGF-SAP) conjugate on bovine choriocapillary endothelial cells

We evaluated the effect of a basic fibroblast growth factor (bFGF) and saporin conjugate (bFGF-SAP) on proliferation, migration and tubule formation in bovine choriocapillary endothelial cells (BCECs). Cell proliferation and MTS assays were done with 0.01, 0.1, 1, 10, and 100 nM bFGF-SAP, and an equimolar concentration of bFGF and saporin. TUNEL assay was performed to confirm apoptosis. Cells were treated with 1, 10, and 100 nM bFGF-SAP and migration assay and tubule formation assay were done. Results were evaluated with image analysis. All experiments were performed in triplicate and repeated three times. Viable cells (ID50 = 0.62) and cell proliferation by MTS assay (ID50 = 0.75 nM) were inhibited. Saporin caused cytotoxicity and inhibition of proliferation at high concentration. DNA fragmentation was identified by TUNEL assay. Migration and tubule formation were also inhibited. All mechanisms responsible for neovascularization were inhibited, and this could be applied in the management of subretinal choroidal neovascularization (SRN).

Affinity purification of novel bispecific antibodies recognising carcinoembryonic antigen and doxorubicin

We have developed a method which combines Protein A affinity chromatography and HPLC analytical and semipreparative hydroxyapatite affinity chromatography to purify bispecific antibodies (BsMabs) from hybrid-hybridomas secreting antibodies recognising carcinoembryonic antigen (CEA) and the chemotherapeutic drug doxorubicin (Dox). Elution of the HPLC hydroxyapatite columns with a 60-360 mM phosphate buffer gradient was found to give better separation than elution with a 60-180 mM phosphate buffer gradient. Careful monitoring of HPLC fractions by enzyme linked immunosorbent assays for anti-CEA, anti-Dox and dual anti-CEA/anti-Dox activity, and pooling of fractions on the basis of these results, enabled the purification of novel BsMabs for use in in vitro and preclinical in vivo experiments.

Bispecific antibody targeting of doxorubicin to carcinoembryonic antigen-expressing colon cancer cell linesin vitro andin vivo

A bispecific monoclonal antibody (BsMAb) recognising carcinoembryonic antigen (CEA) and doxorubicin (Dox) was used in colorimetric microcytotoxicity assays with 3 human colon cancer cell lines (COLO320DM, SKCO1 and LS174T) showing no, high or medium CEA expression, respectively. The IC50 values for Dox with COLO320DM, SKCO1 and LS174T were 1,163, 28.5 and 324 ng/ml, respectively. BsMAb caused statistically significant reductions in Dox IC50 values at 1, 0.1 and 0.01 microg/ml with the CEA-expressing cell lines SKCO1 and LS174T but not with COLO320DM. BsMAb or control antibody alone had no significant effect on the cell viability of any of the cell lines and did not reduce Dox IC50 values. In vivo, there was a statistically significant inhibition of the growth of CEA-expressing LS174T cells growing as xenografts in nude mice treated with BsMAb and Dox compared to control mice. This effect was not seen with COLO320DM xenografts. Our results demonstrate that a BsMAb that recognises CEA and Dox can reduce the IC50 for Dox in vitro and inhibit growth in vivo in a CEA-specific manner.

Anti-CD30 antibody-based therapy

The increased expression of CD30 on some neoplasms versus its limited expression on normal tissue makes it an excellent target for antibody-based therapy. Recent studies have shown that anti-CD30 antibodies may serve as signaling molecules as well as mediators of interactions with the immune system. Unmodified anti-CD30 antibodies as well as anti-CD30-based bispecific antibodies, immunotoxins, and radioimmunoconjugates have been examined in preclinical and clinical studies. The data show that anti-CD30-based therapies are promising new treatment modalities for CD30+ neoplasms.