Design, synthesis and development of a dual inhibitor of Topoisomerase 1 and poly (ADP-ribose) polymerase 1 for efficient killing of cancer cells

Phase 1 studies of the indenoisoquinolines LMP776 and LMP744 in patients with solid tumors and lymphomas

PURPOSE

Indenoisoquinolines are a class of topoisomerase I (TOP1) inhibitors designed to overcome clinical limitations of camptothecins. Three indenoisoquinolines (LMP400, LMP776, and LMP744) demonstrated activity in murine models and a comparative canine lymphoma study. Clinical data for LMP400 were previously reported (NCT01051635). The maximum tolerated dose (MTD), safety, and clinical data from phase 1 studies of LMP776 (NCT01051635) and LMP744 (NCT03030417) are reported herein.

METHODS

Patients ≥ 18 years of age with advanced, refractory solid tumors or lymphomas received either LMP776 (n = 34) or LMP744 (n = 35) intravenously following a Simon accelerated titration design. Both LMP776 and LMP744 were administered daily for 5 days (QDx5) in 28-day cycles. Adverse events and clinical responses were evaluated according to CTCAE and RECIST v1.1 criteria, respectively. Pharmacokinetic and pharmacodynamic changes were evaluated.

RESULTS

The MTD of LMP776 was 12 mg/m2/day and that of LMP744 was 190 mg/m2/day. Dose-limiting toxicities (DLTs) for LMP776 included hypercalcemia, anemia, and hyponatremia; DLTs for LMP744 included hypokalemia, anemia, and weight loss. There was 1 confirmed partial response (cPR) among 35 patients receiving LMP744 (overall response rate 3%) and no objective responses in patients receiving LMP776. Tumor biopsies from the patient with cPR demonstrated high baseline expression of SLFN11 and a unique pattern of pharmacodynamic responses, including increased RAD51, phosphorylated KAP1 (pKAP1), γH2AX, and cleaved caspase-3 (cCasp3).

CONCLUSION

MTDs and safety profiles are reported for LMP776 and LMP744. Target engagement by an indenoisoquinoline was measured for the first time in human samples.

Targeting Replication Fork Processing Synergizes with PARP Inhibition to Potentiate Lethality in Homologous Recombination Proficient Ovarian Cancers

Synthetic lethality in homologous recombination (HR)-deficient cancers caused by Poly (ADP-ribose) polymerase inhibitors (PARPi) has been classically attributed to its role in DNA repair. The mode of action of PARPi and resistance thereof are now believed to be predominantly replication associated. Therefore, effective combinatorial approaches of targeting replication fork processing along with HR-downregulation to target HR-proficient and possibly PARPi-resistant tumors are warranted. Stilbenes are a privileged class of molecules, which include resveratrol, pterostilbene, piceatannol, etc, that modulate both replication processes and RAD51-expression. In this investigation, by screening a small library of stilbenes, including in-house synthesized molecules, trans-4,4'-dihydroxystilbene (DHS) was discovered as a potent natural agent, which downregulates RAD51 expression and HR repair (GFP-reporter assay). DHS induces extensive synergistic cell death in ovarian cancers when combined with talazoparib (PARPi). Mechanistically, DHS elicits replication-stress through severely impeding replication fork progress, speed, and inducing fork-asymmetry. This leads to robust induction of single stranded DNA (ssDNA) gaps and poly-ADP-ribosylation (PARylation) in S-phase cells, signifying issues related to lagging (Okazaki) strand synthesis. PARPi, which abrogates PARylation, potentiates DHS induced ssDNA gaps, and their conversion into lethal double strand breaks through MRE11 action. Furthermore, the combination is highly effective in mitigating ovarian tumor xenograft growth in SCID mice and exhibited a good therapeutic-index with no/minimal tissue-toxicity.

The recent advance and prospect of poly(ADP-ribose) polymerase inhibitors for the treatment of cancer

Chemotherapies are commonly used in cancer therapy, their applications are limited to low specificity, severe adverse reactions, and long-term medication-induced drug resistance. Poly(ADP-ribose) polymerase (PARP) inhibitors are a novel class of antitumor drugs developed to solve these intractable problems based on the mechanism of DNA damage repair, which have been widely applied in the treatment of ovarian cancer, breast cancer, and other cancers through inducing synthetic lethal effect and trapping PARP-DNA complex in BRCA gene mutated cancer cells. In recent years, PARP inhibitors have been widely used in combination with various first-line chemotherapy drugs, targeted drugs and immune checkpoint inhibitors to expand the scope of clinical application. However, the intricate mechanisms underlying the drug resistance to PARP inhibitors, including the restoration of homologous recombination, stabilization of DNA replication forks, overexpression of drug efflux protein, and epigenetic modifications pose great challenges and desirability in the development of novel PARP inhibitors. In this review, we will focus on the mechanism, structure-activity relationship, and multidrug resistance associated with the representative PARP inhibitors. Furthermore, we aim to provide insights into the development prospects and emerging trends to offer guidance for the clinical application and inspiration for the development of novel PARP inhibitors and degraders.

A BODIPY-Naphtholimine-BF2 Dyad for Precision Photodynamic Therapy, Targeting, and Dual Imaging of Endoplasmic Reticulum and Lipid Droplets in Cancer

Currently, effective therapeutic modalities for pancreatic ductal adenocarcinoma (PDAC) are quite limited, leading to gloomy prognosis and ∼6-months median patient survival. Recent advances showed the promise of photodynamic therapy (PDT) for PDAC patients. Next generation photosensitizers (PS) are based on "organelle-targeted-PDT" and provide new paradigm in the field of precision medicines to address the current challenge for treating PDAC. In this investigation, we have constructed a novel PS, named as N b B, for precise and simultaneous targeting of endoplasmic reticulum (ER) and lipid droplets (LDs) in PDAC, based on the fact that malignant PDAC cells are heavily relying on ER for hormone synthesis. Our live cell imaging and fluorescence recovery after photobleaching (FRAP) experiments revealed that N b B is quickly targeted to ER and subsequently to LDs and shows simultaneous dual fluorescence color due to polar and nonpolar milieu of ER and LDs. Interestingly, the same molecule generates triplet state and singlet oxygen efficiently and causes robust ER stress and cellular lipid peroxidation, leading to apoptosis in two different PDAC cells in the presence of light. Together, we present, for the first time, a potential next generation precision medicine for ER-LD organelle specific imaging and PDT of pancreatic cancer.

Prospects of Topoisomerase Inhibitors as Promising Anti-Cancer Agents

Topoisomerases are very important enzymes that regulate DNA topology and are vital for biological actions like DNA replication, transcription, and repair. The emergence and spread of cancer has been intimately associated with topoisomerase dysregulation. Topoisomerase inhibitors have consequently become potential anti-cancer medications because of their ability to obstruct the normal function of these enzymes, which leads to DNA damage and subsequently causes cell death. This review emphasizes the importance of topoisomerase inhibitors as marketed, clinical and preclinical anti-cancer medications. In the present review, various types of topoisomerase inhibitors and their mechanisms of action have been discussed. Topoisomerase I inhibitors, which include irinotecan and topotecan, are agents that interact with the DNA-topoisomerase I complex and avert resealing of the DNA. The accretion of DNA breaks leads to the inhibition of DNA replication and cell death. On the other hand, topoisomerase II inhibitors like etoposide and teniposide, function by cleaving the DNA-topoisomerase II complex thereby effectively impeding the release of double-strand DNA breaks. Moreover, the recent advances in exploring the therapeutic efficacy, toxicity, and MDR (multidrug resistance) issues of new topoisomerase inhibitors have been reviewed in the present review.