👤 José Jimeno

PURPOSE: R,R-1,2 cyclohexanediamine-pyrophosphato-platinum(II) (PT-112) is a novel immunogenic cell death-inducing small molecule under phase II development in several cancer types. It inhibits ribosome biogenesis and causes organelle stresses, leading to selective immunogenic cell death in cancer cells. The possibility of PT-112's pyrophosphate moiety driving high drug concentrations to bone sites of disease has led to an interest in PT-112's use in multiple myeloma. In this study, we present findings from phase I and in vivo studies for PT-112 in relapsed or refractory multiple myeloma. EXPERIMENTAL DESIGN: PT-112 biodistribution was analyzed in mice via laser ablation inductively coupled plasma mass spectrometry. The activity of PT-112 was assessed in de novo and transplantable Tg(Igkv3-5*-MYC)#Plbe (Vk*MYC) multiple myeloma mouse models as monotherapy or combination therapies. M-spike levels and survival were measured. A phase I dose escalation study of PT-112 monotherapy was conducted using a 3 + 3 design in patients with heavily pretreated relapsed or refractory multiple myeloma with exhausted available therapies. RESULTS: In vivo biodistribution imaging revealed high concentrations in the bone, kidney, lung, skin, and liver. PT-112 was active in Vk*MYC multiple myeloma mouse models, both alone and in combination. Phase I data showed that PT-112 monotherapy was safe and well-tolerated, establishing a recommended phase II dose of 360 mg/m2 on days 1, 8, and 15 of a 28-day cycle. Confirmed responses and other signals of activity were observed. CONCLUSIONS: These results suggest a lack of cross-resistance with the standard of care and support the translational value of the Vk*MYC model system. Further clinical investigation of PT-112 is warranted in multiple myeloma. Show less

PT-112 is a novel immunogenic cell death (ICD)-inducing small molecule currently under Phase 2 clinical development, including in metastatic castration-resistant prostate cancer (mCRPC), an immunologically cold and heterogeneous disease state in need of novel therapeutic approaches. PT-112 has been shown to cause ribosome biogenesis inhibition and organelle stress followed by ICD in cancer cells, culminating in anticancer immunity. In addition, clinical evidence of PT-112-driven immune effects has been observed in patient immunoprofiling. Given the unmet need for immune-based therapies in prostate cancer, along with a Phase I study (NCT#02266745) showing PT-112 activity in mCRPC patients, we investigated PT-112 effects in a panel of human prostate cancer cell lines. PT-112 demonstrated cancer cell selectivity, inhibiting cell growth and leading to cell death in prostate cancer cells without affecting the non-tumorigenic epithelial prostate cell line RWPE-1 at the concentrations tested. PT-112 also caused caspase-3 activation, as well as stress features in mitochondria including ROS generation, compromised membrane integrity, altered respiration, and morphological changes. Moreover, PT-112 induced damage-associated molecular pattern (DAMP) release, the first demonstration of ICD in human cancer cell lines, in addition to autophagy initiation across the panel. Taken together, PT-112 caused selective stress, growth inhibition and death in human prostate cancer cell lines. Our data provide additional insight into mitochondrial stress and ICD in response to PT-112. PT-112 anticancer immunogenicity could have clinical applications and is currently under investigation in a Phase 2 mCRPC study. Show less

PT-112 is a novel pyrophosphate-platinum conjugate, with clinical activity reported in advanced pretreated solid tumors. While PT-112 has been shown to induce robust immunogenic cell death (ICD) in vivo but only minimally bind DNA, the molecular mechanism underlying PT-112 target disruption in cancer cells is still under elucidation. The murine L929 in vitro system was used to test whether differential metabolic status alters PT-112's effects, including cell cytotoxicity. The results showed that tumor cells presenting mutations in mitochondrial DNA (mtDNA) (L929dt and L929dt cybrid cells) and reliant on glycolysis for survival were more sensitive to cell death induced by PT-112 compared to the parental and cybrid cells with an intact oxidative phosphorylation (OXPHOS) pathway (L929 and dtL929 cybrid cells). The type of cell death induced by PT-112 did not follow the classical apoptotic pathway: the general caspase inhibitor Z-VAD-fmk did not inhibit PT-112-induced cell death, alone or in combination with the necroptosis inhibitor necrostatin-1. Interestingly, PT-112 initiated autophagy in all cell lines, though this process was not complete. Autophagy is known to be associated with an integrated stress response in cancer cells and with subsequent ICD. PT-112 also induced a massive accumulation of mitochondrial reactive oxygen species, as well as changes in mitochondrial polarization-only in the sensitive cells harboring mitochondrial dysfunction-along with calreticulin cell-surface exposure consistent with ICD. PT-112 substantially reduced the amount of mitochondrial CoQ10 in L929 cells, while the basal CoQ10 levels were below our detection limits in L929dt cells, suggesting a potential relationship between a low basal level of CoQ10 and PT-112 sensitivity. Finally, the expression of HIF-1α was much higher in cells sensitive to PT-112 compared to cells with an intact OXPHOS pathway, suggesting potential clinical applications. Show less